556172

TIP 0404-63

ISSUED 2003 REVISED - 2006

2006 TAPPI

The information and data contained in this document were prepared by a technical committee of the Association. The committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published.

TIP Category: Automatically Periodically Reviewed (Five-year review)

TAPPI

Paper machine energy conservation Scope The paper mill area is a major energy consumer in most pulp and paper mills. The rising cost of energy makes it important to implement energy management and conservation measures. Paper machine energy consumption represents 50-70% of purchased energy for an otherwise efficient integrated mill. If the paper machine is uncompetitive on energy, the mill will be as well. Efforts to reduce energy consumption can reduce operating costs and increase profitability. Reducing paper machine energy consumption requires attention to details in design, operation, maintenance, and control of nearly all aspects of the papermaking process. This TIP discusses guidelines for monitoring, benchmarking, and optimizing energy-intensive unit operations to reduce paper machine energy consumption. Safety precautions Follow normal safety precautions when working around paper machinery, including use of personal protective equipment. Do not allow loose clothing or equipment to contact rotating machinery or ropes. Beware of overhead cranes and thermal and slip hazards around the dryer section. Avoid direct contact with hot surfaces. Use hearing protection in noisy areas. Eye protection should be worn in all production areas. Safety shoes and safety helmets should also be worn where required. Energy reduction strategy Efforts to improve paper machine energy efficiency center around five basic principles: Minimize the amount of water to evaporate in the dryers (and pressure of steam used to evaporate it). Minimize the amount of steam condensed outside the dryers. Maximize condensate return flow and pressure to the powerhouse. Minimize electrical consumption for key users. Monitor and manage energy consumption and cost. Mill-wide energy savings require a multi-faceted approach, including purchasing smarter, using less, integrating processes from different parts of the mill, and generating more and cheaper electricity. Human factors such as training, publicity, visibility, accountability, benchmarking, and targets can aid in achieving energy conservation goals. System monitoring Scottish mathematician and physicist Lord William Thomson Kelvin (1824-1907) said, If you cant measure it, you cant improve it. A key first step in energy conservation activities is monitoring energy consumption and making sure flowmeters and cost information are accurate. Some mills have developed mill-wide system balances that can be used to check accuracy of individual flowmeters. Assigning a person to be responsible for energy conservation in the mill and/or paper machine area can help increase visibility and accountability of conservation efforts. Steps for an effective monitoring program include: Meter energy flows to each machine.

TIP 0404-63 Paper machine energy conservation / 2

Establish key energy parameters. Highlight variables that affect energy consumption. Include energy parameters in operator rounds and centerlining efforts. Provide information to operators, engineers, and managers to encourage continuous improvement. Discuss energy cost and conservation efforts in production meetings. Conduct periodic check-ups of key systems. Benchmark machine operation with best in class and best achievable for the equipment installed. Utilities to be monitored include: Pressure (kPa or psig), temperature (C or F), and flow (kg/hr or lb/hr) for each steam header supplying the

machine. Electrical consumption for each machine (MW). Natural gas (m3/hr or scfm) Water flows and temperatures mill water, warm or hot water from other areas of the mill, and sewer (l/min or

gpm, C or F). Compressed air pressure (kPa or psig) and flow (m3/hr or scfm). Condensate return flow (l/min or gpm, kg/hr or lb/hr) and temperature (C or F). Based on these measurements and paper machine production rates, specific energy indices can be calculated and tracked: Steam consumption (kg/tonne or lb steam/ton paper) Electrical consumption (kWh/ton) Natural gas consumption (m3/tonne or kscf/ton) Total energy consumption (kWh/tonne or MMBtu/ton) Water consumption (m3/tonne or gal/ton) Compressed air consumption (m3/tonne or kscf/ton) Condensate return (%) Total energy cost ($/ton) Determination of energy unit costs typically requires assistance from mill accounting and powerhouse personnel. Understanding the relative cost of different energy sources can help papermakers minimize total energy costs. Note that the cost of various energy sources will change based on relative cost of corresponding raw materials. Cost components that should be included in evaluation of total costs include: Net cost of steam to each paper mill supply header ($/kg or $/klb). One method is to determine fuel cost for

high-pressure steam minus the value of electricity generated by turbines. Marginal cost of steam (cost of the last steam generated) should be used to measure the value of steam savings. Marginal cost is usually higher than average cost since powerhouses use more expensive fuel to top off demand. Note that this method of calculation may be an over-simplification if pressure and flow in a low-pressure steam header are maintained by high-pressure make-up steam supplied from a pressure-reducing valve in the powerhouse.

Natural gas cost (typically expressed in $/kcal, $/therm or $/MMBtu) Electrical cost ($/MWh). Calculating $/kW/yr or $/hp/yr can assist in calculating electrical energy savings. Water and sewer costs ($/M liter or $/MMgal). Both supply and sewer water treatment costs should be included

to determine true value of water conservation projects. The value of condensate returned to the powerhouse. This should include associated energy, water treatment

costs, wastewater treatment costs, and raw water pumping costs to get it to the water treatment plant. Cost should be adjusted downward for condensate polishing costs.

The combination of production rates, energy consumption, and cost information can be used to determine energy cost per ton of product. It is also important to understand energy contracts. Generally managing energy savings downward is the correct move; however, with some peak energy contracts unless you are able to save off of peak there are no apparent savings and conversely if you can save off of peak there is an immediate benefit.

3 / Paper machine energy conservation TIP 0404-63

Performance indices Performance indices can be used to benchmark energy consumption and identify opportunities for improvement. TAPPI TIP 0404-47 Paper machine performance guidelines (1) provides a broad range of indices for different grades of paper. Target values for key indices applicable to energy consumption are shown in Table 1 for various grades. Table 1. Energy performance indices Grade Bleached Corrugating Market Fluff Index Units Fine Board Liner Medium Pulp Pulp Uptime % 93 93 94 94 95 95 First quality % 93 90 97 97 99 97 Overall machine efficiency % 87 84 91 91 94 92 Total steam consumption lb/ton 4,000 4,000 2,800 2,750 2,000 2,500 kg/tonne 2,000 2,000 1,400 1,400 1,000 1,250 Electrical consumption kWh/ton 350 350 300 300 150 150 kWh/tonne 385 385 330 330 165 165 Total energy cons. MMBtu/ton 6.0 7.0 5.0 5.0 4.0 4.5 kWh/tonne 1,935 2,260 1,615 1,615 1,290 1,450 Water consumption gal/ton 2,000 2,000 1,500 1,500 1,000 1,000 m3/ton 7.6 7.6 5.7 5.7 3.8 3.8 Couch solids % 22 25 27 27 28 28 Press solids % 42/45 42 42/50 42/50 50 45 Size press moisture % 3.0 3.0 NA NA NA NA Reel moisture % 5.0 5.0 7.5 9.0 7.5 7.5 Drying steam lb steam / lb water evap 1.2 1.2 1.2 1.2 1.2 1.2 PV supply temperature F 180 180 180 180 NA NA C 80 80 80 80 NA NA Condensate return % 75-80 75-80 75-80 75-80 75-80 75-80 Key factors Each machine typically has several key factors that influence energy consumption on the machine. Green/yellow/red indicators can be used for key process conditions that affect energy consumption to show whether values are in desired ranges. DCS and/or data historian trending can be used to track trends of key parameters. Sheet consistency out of the press section is often the primary variable affecting paper machine energy consumption. Regular grab samples (TAPPI TIP 0404-01 Determination of water removal by wet presses discusses the proper procedure) or the use of portable or fixed sheet moisture gauges specifically designed for use in the press section are recommended to track solids. Press solids can also be calculated based on press section and/or dryer section water balances. Typical additional key factors include: Venting from dryer section thermocompressor or cascade sections Condenser water valve output/condensate flow Differential pressure (especially for lead dryers) Wire pit steam valve position Basis weight versus standard Press section weir flows


Moisture to the size press Size press starch solids Pocket ventilation temperature Temperatures through hood exhaust heat recovery systems Warm water flow from pulp mill Winter/summer operating strategy for machine room ventilation Any additional steam venting Energy surveys Energy audits can provide useful first steps to identify and prioritize opportunities to reduce paper machine energy consumption. Data can be collected from direct observation; data historians; discussions with mill operating; maintenance, and engineering personnel; and previous reports conducted on subsystems of the paper machine. A computer simulation of the papermaking process can help validate data and determine potential benefits from process changes. Keys to successful implementation of recommendation from an energy audit include: Obtaining buy-in from all parties involved Focusing on optimal measures, but not forgetting incremental gains Understanding the costs, risks, and benefits of potential projects Considering life cycle costs in project evaluation Thoroughly planning implementation Training Documenting results Optimizing the system after the project Additional surveys A detailed review of various paper machine systems can ensure that systems and equipment are operating efficiently. Some of these recommended surveys and suggested frequency are shown below. Steam trap surveys (annual) Compressed air system surveys (annual) Refining optimization (on-going) and mechanical surveys (annual) Saveall audit to check capacity and filtrate quality (annual) Showering surveys (every 2 years) Press section optimization (on-going) Press section nip surveys (every 2-3 years) Vacuum pump boroscopes or orifice plate testing (annual) Vacuum system surveys/optimization (every 3 years) Thermography to check for leaks and hot spots (annual) Steambox surveys (annual) Dryer steam and condensate system surveys (annual) Hood air system surveys (annual) Machine room ventilation studies (every 5 years) Pulp dryer maintenance/capacity reviews (annual) Tissue machine hood balances/inspections (annual) System optimization Key process areas to consider when in a program to reduce paper machine energy consumption are discussed below.


Reducing the amount of water to evaporate Drying steam represents the majority of energy consumption on a paper machine. A step in minimizing energy consumption is reducing the amount of water to evaporate in the dryers. Opportunities to do this include: Increase press dryness (high-load, shoe presses) Optimize press fabrics and roll cover designs (venting and hardness, nip dewatering vs. Uhle box dewatering) Reduce basis weight (while meeting the product specifications) Trim the sheet at the wet end rather than at the dry end Improve moisture profiles Reduce amount of over-drying before the size press Increase starch solids used in size press (metering size press) Increase moisture content of the sheet at the reel (when sheet properties and profiles allow). Machine efficiency Increasing overall machine efficiency has a direct effect on specific energy consumption since it takes as much or more energy to produce a ton of broke as it does to make a ton of first-quality paper. Some steps that can be taken to increase machine efficiency include: Reduce sheet break and grade change times. Shorten open press-to-dryer draws, provide direct sheet support. Minimize trim losses with good edge control and coordination with business logistics. Full machine threading - including features that minimize break recovery and thread times. Optimize performance of trim squirts. Utilize camera systems to identify and characterize breaks. Optimize quality control system (QCS) performance to ensure good machine-direction (MD) and cross-machine

direction (CD) profiles. Control sheet in open draws in the dryer section. Utilize capability of distributive control systems (DCS) and data historians to impact efficiency and

troubleshooting. Optimize process chemistry for runnability and maximizing ash content - closed loop control of retention,

charge, etc. Manage broke to maintain stability. Optimize whitewater saveall to maximize overall retention, to stabilize wet end during break conditions, and to

increase clear filtrate quality and quantity for replacement of mill water in showers. Agitation Chest agitation is a significant contributor to paper machine electrical consumption. Opportunities to reduce energy consumption with design and operation of agitation include: Do not overestimate consistency when designing systems Design chests for the optimum dimensional ratios (cube is best) Do not underestimate temperature Allow for a larger manhole to install a larger impeller at low speed Keep flow impediments [ladders, etc] out of chest design Only operate the number of pulper agitators necessary Consider variable-speed or two-speed agitator motors Utilize zone agitation where complete mixing is not required. Consider top-entry instead of side-entry agitators Do not put pump suction behind the impeller


Slow down an agitator and reduce horsepower if operating consistency has dropped substantially from design. Make sure there is not excessive motion when you look in a chest. Work with a supplier that understands the mixing process intimately Pump and motor systems U.S. Department of Energy (DOE) information indicates that average motor energy cost/mill/year is $1.7 MM for pulp mills, $4.6 MM for paper mills, and $3.0 MM for board mills. Average available motor savings opportunities per year are estimated to be $483,000 for pulp mills, $679,000 for paper mills, and $492,000 for board mills. The U.S. DOE Office of Industrial Technologies web site (3) includes information on pump and motor systems, compressed air systems, steam, and other opportunities to conserve energy. Approximately 30% of paper mill electrical energy consumption is by pumps, 20% by fans, 5% by compressors, and 45% by other equipment. Potential electrical energy savings opportunities are available through pumps and fans (53%), motor efficiency upgrades (23%), air compressors (6%), rewind improvements (6%), motor downsizing (6%), and other systems (6%). Pump-based systems represent the largest single group of energy-consuming equipment and offer greatest potential savings. DOE indicates that 80% of electrical consumption is by 10% of the motor population (motors greater than 50 hp). 200-500 hp motors typically have the largest percentage of savings opportunities. The primary reasons pumps waste energy are over-design, change in process conditions, or degradation. Over-design can be the result of overestimating design conditions, contingencies, safety factors, catch-up capability, room to grow, or design for a wide range of process conditions. Energy is wasted when a pump system is changed; resulting in a lower flow rate or lower head pressure requirements, but the pump, motor, and/or piping are not downsized to meet the change. Energy is also wasted when a larger pump than required is used for the purpose of commonality of spares. This also highlights the need to build to what will be required instead of building to some future incremental capacity. Pumps that operate in caustic or solids applications tend to experience impeller and wear ring degradation, causing a loss in pump efficiency. Routine inspection of pumps in these applications is recommended. Parts should be maintained and/or replaced as necessary. DOE promotes identifying motors with the greatest saving potential for further investigation. The greatest savings potential is typically centrifugal loads with a high duty cycle. These motors are referred to as the vital few. The following steps can identify them: 1. Categorize motors by size times operating time. Establish a threshold for more detailed consideration. (Should

be a one-day effort in most plants a plant-wide motor inventory is not necessary). 2. Segregate by load type (focus on centrifugal loads) 3. Look for symptoms in pumping systems that indicate potential opportunity:

Systems controlled by throttling valves Recirculation line normally open Systems with multiple parallel pumps with the same number of pumps always operating Constant pump operation in a batch environment or frequent cycle batch operation in a continuous process. Cavitation noise (at pump or elsewhere in the system) High system maintenance Systems that have undergone a change in function.

4. Establish policies to replace seldom-used, small-load, and large, non-centrifugal systems with high-efficiency motors. PSAT is downloadable at http://www.oit.doe.gov/bestpractices (3). The Pumping System Assessment Tool (PSAT) can be used to quantify energy consumption and cost savings potential from a pump. The assessment requires flow rate, pressure, and motor current or power data.


Note that cost to buy a pumping system is usually much less than its operating cost. Life cycle cost should be used for evaluating pumps. Opportunities to reduce energy consumption by pumps and motor systems include: Replace throttling valves with speed controls where appropriate Reduce speed for fixed-load pumps Install parallel system for highly variable loads Equalize flows using surge vessels Replace motors and/or pumps with more efficient models Avoid recirculation control Avoid incompatible duties on common pumps Do not operate in startup configurations permanently Design systems with proper line sizes Avoid tanks where feasible Optimize process configuration, consistency and pressure setpoints Determine what can be shut off or bypassed during slow backs. Refining Refiners must be in good mechanical condition to minimize energy consumption and optimize fiber development. Effective life of refiners between rebuilds is typically 10-15 years. Mechanical condition can be estimated by checking no-load horsepower by backing off refiners while stock is running through them. Higher than normal no-load power indicates mechanical problems such as bad bearings, sticking quill, improperly greased slide coupling, etc. Lower than normal no-load horsepower indicates worn refiner plates. Poor mechanical condition can increase no-load horsepower by over 10%. Refiners should be inspected annually to check mechanical condition. Some questions to ask when evaluating a refining system include: Is the Net Specific Energy applied within normal guidelines for the grade/pulp? Is the refiner operating properly alignment and no sticking (e.g., splined shaft conversions can prevent

sticking and alignment problems)? Is plate design matched properly to the fiber and refiner to achieve effective compression index and number of

fiber treatments (optimize strength lift per unit of freeness loss)? Is the impact of refining on water retention value (WRV) and dewatering understood, i.e., run just enough

refining? Is the hardware run within proper flow limits? Opportunities to optimize refining energy include: Select refiner type, size, speed, and plates to minimize pumping and no-load energy losses. Operate refiners within design hydraulic flow range. Stocks flow above and below design capacity will reduce

refining efficiency. Refine at 3.5-5.0% stock consistency for best fiber development, depending on fiber type. Select refiner plate patterns to provide desired fiber property development with the lowest net energy applied. Operate with recommended refiner rpm. No-load horsepower increases exponentially with higher refiner rpm. Operate with lowest plate diameter consistent with stock flow and refining intensity requirements. No-load

horsepower increases exponentially with refiner plate diameter. Bypass and shut down unnecessary and underused refiners. Check freeness drop per hpd/t regularly to monitor refining efficiency and determine whether refiners are

working correctly. Typical Canadian Standard Freeness (CSF) drops per net hpd/t are 25-60 for Southern bleached softwood kraft and 50-60 CSF/net hpd/t for bleached hardwood.


Approach systems Opportunities to reduce energy consumption in the stock approach system include: Determine whether cleaners are needed. Size system properly for machine wet end. Utilize cleaners designed for low pressure drops (less than 207 kPa or 30 psi pressure drop). Conduct flow balances and verify operating conditions (consistency, pressure drop, efficiency, and debris

removal) of cleaners. Reduce flows to fiber recovery stages based on balancing the system properly. Shut down cleaners where product quality permits. Determine whether deaeration is needed. Monitor pressure screen differential pressure and reject flows. Minimize stuff box flow and recirculation. Install variable-speed drives for machine chest pump (to eliminate stuff box), fan pumps, and other variable-

flow requirements. Design for low friction losses in piping. Consider installing compact stock approach systems offered by several suppliers. Some systems have reported

energy savings as much as 25% from elimination of tanks and pumps. Recycled fiber systems Opportunities to minimize energy consumption in recycled fiber systems include: Ensure that pumps are not oversized. Install frequency control on motors to reduce energy waste. Reduce pulp and water volume. Increase consistency as much as possible to reduce hydraulic volume for pumping and agitating. Simplify process configuration. Run equipment at optimum operation point. Make process stable and homogeneous. Increase process temperature to gain additional production, being careful not to exceed the stickies activation

temperature. Close water loops. Refine and disperse pulp as little as necessary. Use latest development of machinery equipment to increase overall efficiency. Water heating Substantial savings in water consumption can be accomplished with limitations in retention, quality, and energy dissipation. The reduction in water-usage will also lead to an equivalent saving in energy consumption. Basic rules for water conservation include reduce, reuse, and recycle. Reduce simply means reducing water fresh water usage. A systematic approach is recommended with clear identification of every stream. Paper mill water usage varies between 0 and 60 ton of water per ton of paper produced. Approximately 4-6 tons per ton represent a practical minimum. Zero consumption is possible, but only with serious quality drawbacks and only achievable with products such as recycled fiber grades. Simple water reduction possibilities are often overlooked, so it is sometimes possible to achieve reduction of water and wet end energy consumption by up to 50%. Wet end water consumption can represent 20-45% of overall paper machine energy consumption. Reuse can require a systematic study of possibilities of substitution. New process equipment, such as filters, will be required to allow whitewater streams to be reused. Recycling can result in significant water and energy reduction, but extra equipment such as filters and/or evaporators may be required. Heat dissipation and chemical concentration can become issues as water systems are closed.


Opportunities to minimize steam required for water heating include: Maximize stock temperature from the pulp mill. Utilize waste heat from the pulp mill or hood exhaust heat recovery instead of steam to heat whitewater and

warm water. Return only warm/hot water streams to the warm/hot water systems. Minimize mill water infiltration into whitewater and warm water systems. Minimize flow and maximize temperature of water from condenser systems. Maximize strained/polished whitewater reuse in paper machine showers. Ensure proper saveall design, maintenance, and operation. Utilize strainers and polishing filters after saveall clear legs to allow reuse in showers. Utilize circulation cooling towers for vacuum pump seal water. Keep whitewater temperature set point at 140oF (60oC). Higher temperatures do not significantly increase

drainage rate. Savealls Effective saveall design and operation are essential for minimizing material losses and reducing water consumption on the machine. Increasing capacity, improving maintenance, and/or installing post-saveall strainers and filters can improve filtrate water quality to allow saveall filtrate to be reused in place of fresh water. Key saveall parameters to evaluate include: Installation and equipment, including size (number of installed discs and available blanked-off discs), droplegs

(diameter and layout), and sector type (cover type and condition). Operation, including proper sweetener type and quantity, well-tuned vat level control, dilution of recovered

stock with rich white water bypass, and cloudy filtrate recycle. Maintenance including sector cover condition, sector-to-rotor seals, and knock-off and oscillating cleaning

showers. Showering Showering is a major source of fresh water consumption on many machines. Any shower water used on the former that is below whitewater temperature requires steam to return the silo to desired temperature. Cool showers in the press section can lead to deposits and reduced press solids. From an energy and water conservation perspective, showers should utilize filtered/polished whitewater wherever feasible. One approach to optimize shower performance is to assign a whitewater reuse risk factor for each shower based on: Water filtered with current technology Likelihood nozzles will plug Potential felt plugging from fines Negative effect on paper making process Typical low-risk showers include: Breast roll showers Knock-off showers Medium-risk showers typically include: Lubrication showers Wetting showers High-risk showers include: High-pressure wire cleaning High-pressure felt cleaning Steps for optimizing shower performance include: Determine optimum shower flows, shower and nozzle design, and water quality requirements. Calculate potential energy and fiber savings from utilizing whitewater instead of fresh/warm water.


Improve saveall and filtering to achieve water quality requirements. Chemistry Chemistry can impact paper machine energy consumption by affecting sheet properties and improving drainage. Make-down and introduction of chemicals into the system can also affect energy consumption. Opportunities to reduce energy consumption through chemical systems include: Utilize polyamine products to increase strength. This can provide savings through reduced refining, reduced

basis weight, increased couch and press solids, and /or reduced starch usage. Utilize enzymes for fiber modification to reduce refining needs. Utilize silica and microparticles to improve drainage. Utilize whitewater instead of mill water for chemical injection. Maximize ash content in the sheet. Headboxes Basis weight profiles ultimately impact pressing, runnability, and dryer operation. Pressure drop through headboxes have increased with headbox design evolution. Turbulence level and nozzle convergence impact MD/CD ratio capability. Consistency profiled designs require lower flow from the cleaner system. Some areas where headboxes affect paper machine energy consumption include: Minimize MD and CD basis weight variability to improve runnability and maximize dewatering and drying

efficiency Improve moisture profile to allow maximum possible moisture content at the reel Optimize turbulence level and nozzle convergence. The impact on MD/CD ratio capability can help optimize

required strength characteristics to allow for reduced basis weight or reduced refining levels Impact MD/CD ratio capability Optimize headbox contribution to formation and sheet uniformity to aid forming, pressing, and drying rates,

improve runnability, and to improve strength allowing the use of higher freeness furnishes. Operate headbox within designed flow range. Over-designed flow capability generally has very poor results Maintain cleanliness for efficiency. Formers Formers consume energy directly through drive load and vacuum systems. Formation and drainage affect performance of downstream processes. Areas where the former affects energy consumption include: Utilize former type and headbox that provide optimum formation results at higher consistency Match hardware to drainage needs Avoid sealing the sheet early in the forming process. Graduate vacuum down the table to reduce drag load and provide proper sheet consolidation. Utilize multi-compartment high-vacuum boxes. Evaluate drainage element materials for impact on drag load Avoid couch re-wet (suction box orientation, double doctors, air doctors) Optimize headbox and forming temperatures for impact on drainage and solids Monitor former solids frequently, maintain high level of solids Paper machine clothing Properly designed clothing can have an impact on energy consumption that far exceeds the cost of the fabrics. Forming fabrics affect energy efficiency in much the same way as formers: Consistency off the couch, with ~10% of solids improvement transferring to the dryers Improved formation resulting in better pressing uniformity Flatbox vacuum requirements


Reduced drive loads Press fabrics are an important part of press section optimization. Opportunities include: Pressure uniformity through micropressing Increasing consistency into dryers Minimizing sheet rewet Nip dewatering Opportunities to reduce Uhle box vacuum Dryer fabrics can affect capacity and energy efficiency through: Fabric tension Surface contact heat transfer Pocket ventilation mass transfer Resistance to contamination Vacuum systems The vacuum system is often the second largest process in the paper mill for electrical energy consumption (after paper machine drives), and is frequently one of the least understood parts of the papermaking process. Vacuum systems can have from 1,000 to 10,000 installed horsepower. Some of the most common vacuum system problems that can increase energy consumption and/or reduce system efficiency include: Hot seal water. High backpressure on vacuum pumps. High seal water pressure. Use of synchronous versus induction motors can affect power factor for the entire paper mill. High seal water flow from recirculated system without cooling or a poorly operated cooling tower. High pressure. Worn or missing orifices and nozzles. Scale build-up in pumps and piping. Worn pump rotor, casing, or lobes. Older, less efficient vacuum pumps. High piping losses and incorrect system design. Additional guidelines to minimize vacuum system energy consumption include: Use fans or exhausters instead of vacuum pumps for low-vacuum applications such as vacuum foils. Control vacuum level by bleeding air into the system instead of by throttling liquid ring pumps. Graduate flatbox vacuum to maximize dryness and minimize drag load. Eliminate unnecessary vacuum boxes (remove or drop out of contact with the fabrics). In addition to requiring

additional vacuum pumps, sucking excessive air through the sheet can cool the sheet and cause press solids to drop more than the small amount of water that comes out with the air, especially on lightweight, open webs. Extra flatboxes also add drag load to the table. Proper flatbox setup can remove more water while reducing table drive load by as much as 10%.

Ensure proper Uhle box slot size to provide required flow capacity and dwell time. Ensure proper vacuum pump application (high-vacuum vs. low-vacuum pump design). Prevent carryover of process fluids from suction point. Provide water/air separation ahead of the pump to prevent two-phase flow at the pump. Use proper separator removal pump design. Take unnecessary vacuum pumps out of service. Check vacuum pump internal clearances and/or capacity annually. Rebuild pumps operating at less than 80% of

design capacity.


Conduct routine maintenance of vacuum pumps and auxiliary equipment, including belt and gear drives and motors.

Replace and calibrate gauges and process instrumentation (vacuum gauges, seal water pressure gauges, level transmitters in vacuum pump sumps, amp meters for motors)

Remove old, inefficient vacuum pumps from service. Do not rebuild obsolete pumps with inefficient designs. System audits can be used to help reduce wasted energy. Replacing or calibrating gauges can ensure proper indication of vacuum levels. Key operating data should be monitored, reviewed and recorded. Sheet and fabric moisture should be checked regularly to ensure effective use of vacuum. As with many areas, one of the most effective ways to manage vacuum system energy is through EMBWA (Energy Management By Wandering Around). Additional information on vacuum system optimization is included in TAPPI TIP 0404-55 Performance evaluation techniques for paper machine vacuum systems (4). Press section On a typical paper machine with 0.5% headbox consistency, 20% couch solids, 40% press solids, and 5% reel moisture, 195 kg water is removed per kg fiber in the forming section, 2.5 kg water per kg fiber in the press section, and 1.45 kg water per kg fiber in the dryer section. However, the cost of water removal is significantly lower in the forming and pressing sections than in the dryer section. Removal of the water content after the press section represents more than 50% of the energy consumption in the paper machine system. Each one percentage-point improvement in solids out of the press section results in 3-5% less water that needs to be evaporated in the dryer section. Maximizing press performance is thus one of the most important aspects of paper machine energy conservation. Primary conservation opportunities in the press section are increased water removal, steam savings, increased production, more efficient water removal, and fiber savings on bulk sensitive and strength grades. Factors influencing press water removal are furnish, time, temperature, and pressure. Press performance can be improved by increasing nip load and by increasing the time during which the press load is applied. Press impulse (press nip load / nip residence time) has been shown to be a good performance indicator for press water removal. Development of shoe presses has significantly increased time available in the nip. Press performance can also be improved by increasing temperature of the web during pressing. Experience indicates that solids content of the pressed web can be increased by one percentage point for each 10C (18F) increase in web temperature. Methods to increase temperature in the press section include increased stock temperature, steam shower applications on the sheet or on the fabric, heated press rolls, or hot water flooded nip showers. Energy efficiency of heating the sheet in the press section should be compared with that in the dryer section (typically 1.3 kg steam per kg water evaporated). Operating felt showers with cool water (such as fresh water) further cools the fabric. High-pressure and low-pressure shower water should be at least equal to the temperature of stock at the headbox. Shower water temperature of 54C (130F) or above is beneficial in maintaining fabric temperatures. Shower water heating is an excellent application for heat recovery. Uniformity of pressure applied to the sheet in the press is important, especially with modern shoe press technology, because of increased nip dwell times and lower peak nip pressures. Modern press fabric designs provide improved pressure uniformity and higher sheet solids content. Multi-axial laminated fabrics provide superior pressure uniformity, excellent bridging on vented/drilled rolls, and more steady-state pressing compared to conventional fabrics. Flat batt fibers can offer contact area equal to round fine denier batt without sacrificing wear volume. TAPPI TIP 0404-52 Press Section Optimization (5) provides guidelines for evaluating and improving press section performance. The TAPPI Paper Machine Wet Press Manual (6) provides more complete coverage of press section optimization. Opportunities to optimize pressing include:


Shoe pressing increases dryness potential, and for bulk-sensitive grades, adds degree of freedom (bulk vs. dryness).

Single versus double felting impact on press solids. Double felting improves dewatering on heavyweight grades. Steam boxes increase sheet temperature and increase exiting dryness; can also be used for profile improvement. Felt heating will help clean the fabric as well as help maintain or increase sheet temperature. Optimizing roll cover hardness and use of blind drilled or other cover designs where required can improve press

dewatering. Balance between nip and Uhle box dewatering over fabric life. Nip dewatering efficiency, press geometry, fabric selection, and operations can result in improved profiles,

solids, and in vacuum for uhle boxes. Felt and belt design optimization - press fabric design greatly impacts press efficiency, solids level. Minimize rewet (fabric runs / sheet runs; sleeve doctors, double doctors, air doctors, use of catch pans on high

dewatering nips that generate water spray). Minimize draw to maximize CD strength on grades requiring high CD strength properties. Check nip profiles and optimize crowns, dubs, and fabric cleaning to improve moisture profiles. Monitoring of pressing performanceon-line monitoring of press water flows, frequent CD and MD

monitoring of fabric permeability, moisture, and temperature. Check press solids frequently. Steam showers Steam shower efficiency depends on the product being made, where the steambox is installed and how it is operated. TAPPI TIP 0404-58 discusses steam shower applications in the forming section. Steam showers are most energy efficient with low steam ratios on relatively cool systems with vacuum assist beneath the steambox. Best steam utilization efficiency occurs when steam showers are located ahead of the last press nip since there is less water to heat. For most applications, efficient steam flow ratios are 0.10 lb steam/lb paper for fourdrinier applications and 0.075 lb/lb for press section applications. Mills should determine the value of steamboxes for specific applications and operate accordingly. Opportunities to optimize steam shower performance include: Utilize low pressure waste or vented steam. Turn off/reduce steam flow when grades that are not drying limited are being produced. Apply only as much steam as can be condensed in or on the sheet. Lower steam supply to reduce excess fog in the machine room. Use profiling capability to apply steam only where needed. Reduce vacuum to reduce sheet cooling and air infiltration under the steam shower. Increase vacuum to improve steam penetration into sheet. Control steam temperature to improve condensation rates. Provide proper mist elimination when utilizing flash steam. In many cases, some high-pressure make-up steam

is required to introduce a small amount of superheat. Cut off non-profiling preheat section of profiling steam shower. Extend and contain steam in wedges and tunnels. Maintain pressure and temperature gauges. Eliminate pulp splatter from trim squirts. Utilize Teflon and/or polished surfaces to minimize build-up and allow operation at design clearances. Dryer section The dryer section represents the largest thermal energy consumer on the paper machine. Information on monitoring dryer section performance is included in TAPPI TIP 0404-33 Dryer section performance monitoring (7). The 10 Commandments of energy efficient drying are: 1. Dont dry any more than you must 2. Dont vent steam anywhere 3. Match the air flow to drying 4. Use steam from lowest header pressure possible


5. Keep the machine running 6. Improve the moisture profile 7. Increase the heat transfer rate 8. Measure what you must control 9. Keep the steam system calibrated 10. Dont use motive when you can use make-up Five rules for dryer energy efficiency are: 1. Keep the system tight 2. Efficiently utilize flash steam from high temperature condensate 3. Maximize use of low pressure steam 4. Minimize heat used for hood supply air heating 5. Manage the system Energy efficient drying requires a combination of steam system design, equipment, operation, maintenance, and control. Dryer arrangement Dryer section arrangement primarily affects energy consumption by increasing machine efficiency. Examples include: Single tier arrangements increase dryer wrap and reduce unsupported length. Threading efficiency also

improves. Increased sheet restraint improves contact with dryers and reduces CD shrinkage. Draw reduction increases CD strength vacuum assisted blow boxes, placement and quantity of draw points Windage control impacts runnability Optimize felt tension for best drying heat transfer. Felt design to optimize uniformity of sheet contact with dryer surface and heat transfer. Cleanliness impacts

performance. Blow box systems to improve high speed runnability and efficiency. Thermocompressor systems Thermocompressor systems utilize high-pressure motive steam to recompress blowthrough steam and reuse it in the same dryer section. Good separators, proper piping design, and adequate motive steam pressure are critical for efficient operation. Opportunities to minimize energy consumption using thermocompressor systems include: Ensure no steam venting during normal operation. Utilize blow-through control and/or automatic pressure letdown to minimize venting during sheet breaks. Optimize differential pressures for condensate evacuation and blow-through flows. Utilize properly sized thermocompressors. Optimize motive steam pressure to minimize amount of motive steam flow required and net thermal energy

cost. Utilize non-condensable bleed steam in low-pressure dryers or other low-pressure steam user such as air pre-

heat coils. Cascade systems Cascade systems reuse flash and blowthrough steam in a different dryer section that operates at lower steam pressure. Opportunities to reduce energy consumption with cascade systems include: Arrange dryers to minimize steam venting Minimize number of dryers draining to a condenser and amount of blowthrough steam from these dryers. Ensure proper section splits to prevent venting during normal operation. Utilize blow-through control and/or automatic pressure letdown to minimize venting during sheet breaks. Provide make-up steam from the lowest available steam pressure header that will support section pressure

requirements.


Steam system design There is no one and only correct solution for steam and condensate system design. The proper application depends on the mill steam supply and condensate return systems. Proper sizing of piping and equipment are critical. Detailed piping design should be done and reviewed by a qualified party to ensure proper system operation. Considerations for energy-efficient steam system designs include: Ensure no steam venting during normal operation. Utilize low-pressure instead of high-pressure steam where appropriate. Utilize blow-through control and/or automatic pressure letdown to minimize venting during sheet breaks. Separator efficiency is important, especially with blow through control. Measure condenser water temperature at outlet. Recover flash steam from separator tanks. Return condensate to the boiler house at 230F. Do not shut down dryers to control drying capacity. Improve flexibility of the steam and condensate system

instead. Steam system hardware Proper syphon design is a key component in making the steam system energy efficient. Stationary syphons tend to reduce blow through steam (as low as 10% of condensing load with stationary vs. 15-30% with rotary) and differential pressure (15-35 kPa or 2-5 psi with stationary vs. 40-95 kPa or 6-14 psi with rotary). In dryers draining directly to a condenser or heat exchanger, reduced blowthrough steam directly results in energy savings. In sections that cascade to lower pressure groups or in sections with thermocompressors, evaluation of energy savings is more complicated. In a thermocompressor section, energy savings will be achieved with stationary syphons if the section is venting with rotary syphons and lower differential pressures and blowthrough flows prevent the venting. In a section that is not venting, savings opportunities depend on relative cost of motive and make-up steam. Reduced blowthrough and differential pressure will result in less motive steam and more make-up steam but the total amount of steam will remain the same. If both motive and make-up steam are supplied from the same header, there will be no energy savings resulting from converting to stationary syphons. However, if the powerhouse is able to generate significantly more electricity from the lower-pressure make-up steam extraction than from the higher-pressure motive steam, energy savings can be significant. Turbines typically make the most electricity when most of the high-pressure steam goes through all of the stages. Likewise, in a cascade system, there is no net energy savings from simply converting to stationary syphons if the lower-pressure section condenses all of the blowthrough steam sent to it (with the exception of wet end sections). Dryer bars are recommended for all dryers operating above rimming speed to provide optimum profile, heat transfer, and drying rate. Rimming speed depends on dryer diameter and condensate layer thickness, but is typically around 300 meters/minute (1000 fpm). A dryer section will evaporate more water with dryer bars installed. However, it takes additional steam to evaporate this water, so the kg steam used per kg of water evaporated remains nearly the same. This same principle also applies to felting unfelted dryers or increasing dryer fabric tension. Drying rates will improve, but energy efficiency (as measured by kg of steam used per kg of water evaporated) will see little change. Additional information on dryer bars is included in TAPPI TIP 0404-35 Application of dryer bars (8). Minor reductions in energy consumption are possible with dryer bars related to operation at lower steam pressures with improved heat transfer. Guidelines for steam system hardware include: Utilize stationary syphons where advantages can be realized from lower differential pressures and blow-through

flows. Install modern steam joints. Install dryer bars (increase drying rates in most cases). Size thermocompressors for the current steam system operation.


Optimize thermocompressor design and operation. Check sizing of rotary syphons. Use appropriate steam trap designs for heaters. Utilize pilot-operated safety relief valves for applications that operate close to maximum allowable working

pressure. Improve mechanical reliability of equipment to prevent leaks. Steam system operation A properly designed steam and condensate with good equipment will still waste energy if not operated properly. Considerations for energy-efficient steam system operation include: Operate dryer differential pressures at the proper setpoint for condensate evacuation and blow-through flows. Ramp warm-up dryers to maximize runnability Maximize drying in sections that use low-pressure whenever possible Minimize dryer can surface contamination Minimize steam venting to condensers Utilize proper dryer warm-up procedures to minimize steam joint leaks. Close separator tank drains Check separator tank level controls Check vacuum tank level control Avoid over drying minimize number of cans in the falling rate zone Conduct regular roof rounds to check for venting and leaking safety relief valves. Regularly check vacuum systems for air leaks. Steam system maintenance Dryer section maintenance items that can affect energy consumption include: Ensure tight shut-off of steam vent, bypass, and blow-down valves Calibrate pressure and differential-pressure transmitters Disconnect steam to bottom unorun dryers, felt dryers, and Feeney dryers that do not contact the sheet Check that steam traps are functioning properly Check steam valves and thermocompressor actuators Fix leaks. A small pinhole, a leaking gasket, a trap thats stuck open, or a leaky steam joint can easily waste

150-250 lb/hr steam. The cost of maintenance is typically small compared to potential energy savings. Steam system control Opportunities to utilize steam system control to minimize energy consumption include: Control vacuum condenser to match differential pressure requirement. Automate dryer warm-up and shutdown sequencing. Automate dryer sheet break recovery response. Automate grade change response. Automate dryer steam system pressure and differential control. Install thermocompressor cut-off control to prevent venting. Install smart control valves to support preventive maintenance. Trend major process variables. Provide troubleshooting help. Flash steam utilization High temperature condensate will generate flash steam as it is collected in a lower pressure tank. This flash steam is often wasted or poorly used. Often it is vented either at the machine or at the boiler house. Low pressure flash steam can be reused as make-up steam to wet end dryers, steam showers, water heating, or flash coils in the pocket ventilation system. If flash steam is used for steam showers, condensate carryover must be avoided through good separation, steam traps, and proper piping design. In some cases, small amounts of higher-pressure steam are


required to provide a small amount of superheat to the line. Note that care should be taken in reusing flash steam. It is possible to distill pH-controlling amines from flash steam and end up with corrosive carbonic acid that will quickly eat through steam coils. In some cases it may be easier and more cost effective to pump hot condensate through air heating coils rather than utilizing a low-pressure flash tank. It is important to keep the condensate pressurized to prevent flashing and hammering before the coil, so level control valves must be positioned downstream of the coils. Pocket ventilation and hood supply systems Supply air temperatures of 82-93C (180F to 200F) are generally optimal for pocket ventilation system performance. Dryer air systems operated at elevated temperatures increase energy consumption, but offer little or no improvement in drying capacity. There is typically no need for pocket ventilation temperature to be higher than sheet temperature. As an example, a machine with 3400 m3/min (120,000 cfm) of pocket ventilation air supplied to the dryers will utilize 8,220 kg/hr (18,100 lb/hr) of steam at 116C (240F), and only 6,040 kg/hr (13,300 lb/hr) steam at 93 C (200F). Operation at the lower temperature results in $230,000/yr energy savings at steam costs of $13.20/1000 kg steam ($6.00/1000 lb steam). Additional information on hood air systems is included in TAPPI TIP 0404-24 Recommended operation of dryer section hood air systems (9). Opportunities to reduce energy consumption with dryer section hoods and air systems include: Operate pocket ventilation system at 180 -200F. Optimize hood exhaust humidity. Adjust air exhaust to match drying load and hood capability. Recover heat from hood exhaust streams. Use inside air rather than outside air for pocket ventilation. Insulate dryer hoods and ductwork. Replace damaged hood panels and panel seals. Monitor condition and cleanliness of air system filters and coils. Change ventilation system filters when necessary. Check heater tubes for leaks Check air heater uniformity from top to bottom Pocket humidity control impacts drying rate and profiles. Monitor supply ventilation air temperature rise Monitor ventilation air exhaust temperature drop Replace existing hoods with high-performance hood designs. Size press The size press offers opportunities to reduce energy consumption by reducing the amount of water evaporated, increasing machine efficiency, and optimizing sheet strength. Opportunities include: Evaluate product need to dictate application technique surface application or heavy penetration. Film-type designs can minimize water load applied. Maximizing solids content of material applied. Maximize ingoing moisture content. Threading and spreading (efficiency). Early after dryer surfaces to improve runnability and minimize picking (air turns, alternative drying methods). Optimize strength with size press application - to minimize fiber, optimize filler content. Reel Improvements to reel operation contribute to increased machine efficiency. Sheet defects near the spool and edges negatively increase slab losses and impact process efficiency. Spool deflection can contribute to defects. Opportunities include:


Rubber covered reel spools to minimize turn-up losses Nip relieving and/or controlled primary/secondary arm transfers can reduce defects Control winding parameters (torque, nip, tension) Maximize turn-up efficiency (# sets) Utilize turn-up systems and reel brakes to minimize slab losses Monitor and display slab losses, report results - control to maintain world class levels Miscellaneous steam systems The energy lost in steam lines from the powerhouse to the paper machine room and in condensate lines back to the powerhouse can be reduced by eliminating steam leaks, avoiding unnecessary pressure drops, ensuring proper operation of steam traps, and maximizing the amount of condensate that is returned. Opportunities to reduce energy consumption in the overall steam and condensate system include: Repair steam leaks. Insulate steam system piping and separators. Utilize the lowest feasible steam pressure for miscellaneous steam users such as steam showers, water heating,

and air heating. Conduct regular steam trap surveys and repair leaking or plugged traps. Check for excessive pressure drops through flowmeters, lines, etc. Ensure that proper pressure and temperature compensation factors are used in steam flowmeter calculations. Utilize pilot-operated safety relief valves for applications that operate close to maximum allowable working

pressure. Conduct regular roof rounds to check for venting and leaking safety relief valves. Utilize degrees of superheat control for desuperheaters, where temperature setpoints are established based on

a given superheat level above saturated steam pressure. Determine standard operating procedures for steam trap and drain line valving during warm-up and normal

operating conditions. Clean heat exchanger and monitor U-factors. Maximize condensate return to the powerhouse. Compressed air systems Compressed air is one of the most inefficient sources of energy in the mill. It takes 5-6 kW (7-8 hp) of electricity to generate sufficient compressed air to drive a 0.75 kW (1-hp) air motor. A typical 56 kW (75 hp) compressor with 5-day/week, 2-shift operation will typically have $20,000 equipment cost, $20,000 maintenance cost, and $130,000 electrical cost over a 10-year life. Replacement of the air-driven motor with an efficient electric motor has the potential for significant savings over the life of the unit. Opportunities to minimize compressed air cost include: Instrument air dew point should be 10C (18F) below the lowest temperature the system would see. Utilize ultrasonic leak detectors to identify system leaks. Conduct annual air system audits. Utilize dedicated compressor instead of mill air for headbox air pads Reclaim water from compressors where appropriate. Air system audits can typically identify energy savings of approximately 30% of compressor energy consumption. For a large mill, this can result in $250,000 - $1,000,000/yr in energy savings. Compressed air surveys typically involve: Developing a block diagram of the system. Measuring baseline conditions. Implementing an appropriate control strategy. Re-measuring after controls are adjusted.


Walking through the system to find preventive maintenance and additional opportunities. Identifying and fixing leaks and correcting inappropriate use. Implementing awareness and continuing improvement plans and reporting results to management. Air-padded headboxes require relatively high volumes of compressed air (4.25 to 7 m3/min or 150 to 250 scfm) at low pressures (less than 100 kPa or 15 psig). These should utilize dedicated headbox compressors instead of bleeding off of mill air headers. Reclaiming water from air compressors can also provide energy and water savings. Additional information and references on compressed air systems are included in reference 3. Machine room ventilation Effective maintenance, proper temperature setpoints, and winter/summer operating strategies can be used to improve energy efficiency of machine room ventilation systems. Machine room ventilation is discussed more completely in TAPPI TIP 0404-50 Machine room ventilation guidelines (10). Opportunities to reduce energy consumption associated with machine room ventilation include: Establish winter and summer operating conditions for machine room supply and exhaust fans. Operate air make-up units at 21C (70F) setpoints and roof supply systems at 49C (120F). Utilize water or glycol systems (with heat recovery) to heat make-up air. Utilize inside air instead of outside air for motor cooling, roof supply, and pocket ventilation. Shut off steam coil or glycol systems to air make-up units when fans are shut off. Ensure that there is proper

freeze protection. Heat recovery An energy balance around the paper machine room shows that all thermal energy provided to the machine room exits with the sheet (very small amount), exhaust air streams, and water streams. Opportunities for dryer hood heat recovery are typically limited to supply air preheating. Air-to-air economizers have limited potential to recapture energy from exhaust streams. The amount of energy recoverable in the drying section is limited due to the ratio of latent heat in the exhaust and the sensible heating of the dryer air. Overall energy content in the exhaust air is about 6-10 times greater than the potential heating of incoming air. Air-to-liquid economizers used for heating fresh water, whitewater, or circulating water or glycol systems provide greater opportunity to improve the amount of recovered heat. More elaborate heat recovery systems could substantially improve the degree of energy saving, but these systems typically have increased complexity. High humidity closed hoods require much less hood exhaust and offer much greater heat recovery potential. Areas with opportunity for heat recovery include: Dryer section hood exhaust Yankee hood exhaust Pulp machine air dryer hood exhaust. TMP steam Vacuum blower exhaust Waste heat from pulp mill and evaporators. Sewer streams Tissue machines Tissue and towel machines offer additional opportunities to optimize energy consumption. Most machines with conventional Yankee dryers utilize steam showers, suction pressure rolls, steam-heated Yankee dryers, and gas-fired hoods to remove water from the sheet. Energy conservation requires maximizing use of low-cost energy sources


(typically low-pressure steam used in steam showers) and minimizing consumption of high-cost sources (typically natural gas used for hood burners). Increasing recirculation air and reducing make-up air and exhaust from the Yankee hood system will reduce energy consumption at the cost of drying rate. Good performance for tissue machine drying steam and gas usage is 5.2 GJ/tonne (6.0 MMBtu/ton). Low energy users utilize 3.4-4.3 GJ/tonne (4-5 MMBtu/ton), below average users are 4.3-5.2 GJ/tonne (5-6 MMBtu/ton), high-energy users are 5.2-6.0 GJ/tonne (6-7 MMBtu/ton), and very high-energy users are 6.0-6.9 GJ/tonne (7-8 MMBtu/ton). Through-air dried (TAD) machines typically use significantly more energy per kg of product than conventional Yankee machines. This is because more water is dried and none is mechanically pressed from the sheet. Additional information on TAD is included in TAPPI TIP 0404-25 Through drying (11). Opportunities to optimize energy consumption on tissue machine hood and air systems include: Operate in cascade mode instead of parallel mode. Optimize air system burner efficiency and stabilize static pressure to nozzles. Set up air supply and exhaust dampers (or fan speeds) to optimize energy efficiency. Utilize hood humidity

sensors (0.40 0.45 lb/lb typically optimal). Adjust air system fuel/air ratio. Optimize hood impingement temperature vs. impingement velocity. Optimize air cap gap (3/4) to increase heat transfer from the nozzles. Balance hood to minimize infiltration and exfiltration. Maximize heat recovery from hood exhaust. Preheat air make-up and combustion air streams to minimize natural gas usage. Ensure no leaks from hood, bypass dampers, or duct flange connections. Conduct regular system surveys. Additional opportunities to minimize energy consumption on tissue and towel machines include: Monitor and benchmark energy flows. Optimize pressing to maximize sheet solids. Take regular sheet moisture samples after suction pressure rolls. Optimize use of press section steam showers. Maximize Yankee operating steam pressure (within limits of dryer code), sheet quality, Yankee coating, and

thermocompressor venting issues) to minimize use of natural gas in heating hood air. Maximize proportion of drying done by after-dryers on wet-crepe machines. Utilize infrared cameras to check ductwork insulation for hot spots. Optimize thermocompressor system operation to eliminate venting. Increase reel moisture when quality considerations allow. Conversions GJ/t X 0.8606 = MMBtu/ton KWh/t X 0.9072 = kWh/ton Keywords Energy, Paper Machines Literature cited 1. TAPPI TIP 0404-47 Paper Machine Performance Guidelines 2. Energy Cost Reduction in the Pulp and Paper Industry, First Edition, PAPRICAN, November 1999 3. U.S. Department of Energy Office of Industrial Technologies web site: http://www.oit.doe.gov/bestpractices 4. TAPPI TIP 0404-55 Performance Evaluation Techniques for Paper Machine Vacuum Systems 5. TAPPI TIP 0404-52 Press Section Optimization 6. Paper Machine Wet Press Manual, Fourth Edition, TAPPI PRESS, 1999.


7. TAPPI TIP 0404-33 Dryer Section Performance Monitoring 8. TAPPI TIP 0404-35 Application of Dryer Bars 9. TAPPI TIP 0404-24 Recommended Operation of Dryer Section Hood Air Systems 10. TAPPI TIP 0404-50 Machine Room Ventilation Guidelines 11. TAPPI TIP 0404-25 Through Drying Note that this TIP was originally developed from a panel discussion on Paper Machine Energy Conservation at the 2001 TAPPI Engineering Conference. The 2006 revision utilized material and discussions from the Energy Conservation Track at the 2006 TAPPI Papermakers Conference. Additional information Effective date of issue: August 29, 2006. Working Group: Jeff Reese Chairman, International Paper Marc Foulger GL&V Helmuth Gabl Andritz Ken Hill , Kadant Johnson Systems Jon Kerr Andritz Pekka Kormano Deublin Steam Systems Jack Milliken GL&V John Neun Albany International Dick Reese Dick Reese and Associates Doug Sweet Doug Sweet and Associates Rick Wasson Irving Tissue Greg Wedel Kadant Johnson Philip Wells Wells Enterprises Inc.

g

Paper Machine Energy Update

Dick Reese

Dick Reese and Associates, Inc.

5121 Edgerton Dr

Norcross, GA 30092

(770) 448-8002

[email protected]

2006 TAPPI Papermakers Energy Track Summary

Energy costs are not likely to go down soon. The rising cost of energy makes the case for

implementation of energy management and conservation measures.

Paper machine energy consumption is 50-70% of purchased energy for an efficient integrated mill.

If the paper machines are uncompetitive on energy, the mill will be as well.

Reducing paper machine energy consumption requires attention to details in design, operation, maintenance, monitoring, and control of nearly all aspects of the papermaking process.

Whats New?

Energy prices are down-Will they stay down?

Some mills have reduced energy expenses by focusing on reducing consumption.

DOE is now supporting paper machine energy surveys.

TIP 0404-63, paper machine energy conservation updated.

Energy 37%

Labor 32%

Fiber 24%

Chemicals

Low-Cost Producer

Energy Cost

Energy cost is typically one of the highest components of manufacturing cost and as much as 40% of total cost.

Some fuel costs have more than doubled in the past 3 years.

Mills that do not focus on reducing energy cost and consumption will not be competitive.

Energy management will become a life or death issue in many mills.

Typical U.S. Energy Costs

$2 to 10$5.00$/klb65-psig Steam

$2.50 to 11$6.00$/klb165-psig Steam

$4 to 12$7.00$/klb400-psig Steam

$35 to 110$40.00$/MWhElectricity (MW)

$225 to 700$260$/hp/yrElectricity (hp)

RangeAverageUnits

Energy Opportunities

Energy consumption on the averagepaper machine is ~20% higher than good performance targets.

Based on 2005 TAPPI PM Energy Survey

TIP 0404-63 Whats New?

Updated to include information presented at 2006 TAPPI Papermakers.

Very comprehensive energy bible. Twice as long as 2003 version, now 21 pages.

Includes energy performance indices for fine paper, liner, medium, market and fluff pulp, and bleached board.

TAPPI TIP 0404-63 Paper Machine Energy Conservation

Five Basic Principles

1. Minimize amount of water evaporated in the dryers.

2. Minimize amount of steam condensed outside the dryers.

3. Maximize condensate return flow and pressure.

4. Minimize electrical consumption for key users.

5. Monitor and manage energy consumption and cost.

Energy Observations

There are opportunities to improve condenser operation on many machines.

There are opportunities to improve press section dewatering at low cost on many machines.

Whitewater system design and operation is often not energy efficient.

There are opportunities to recover heat from hood exhausts and effluent in several mills.

Energy Observations Wet End Dryer Control

One machine did not have a differential pressure valve after wet end separator. Flash steam was vented to atmosphere.

One machine was sending flash steam from nearly half of the dryers to condensers.

Three machines in one mill were trying to control condenser operation by monitoring condensate temperature.

Energy Observation Specialty Fine Paper Mill

50% of dryers flash steam to condensers.

Comments

Opportunity to reduce dryer steam consumption by 10% by rebuilding steam and condensate system.

Potential annual savings $400,000.

Energy Observations Dryer Condensers

Control vacuum and/or cooling water exit temperature (not condensate temperature).

Check system for vacuum leaks on every shutdown.

Energy Observations Wet End Dryer Control

Control differential pressure for dryers draining to condensers to minimize blowthrough steam flow.

Use stationary syphons and steam joints to minimize differential pressure.

Shut off and disconnect steam to bottom unorun dryers.

Use flash steam for steam showers, etc.

T

AlternativelySteam Can BeFlashed Into ALow Pressure Header

1

Make-up SteamFrom Low PressureHeader

High Temperature CondensateFrom Individual Separator Stations

Atmos.

PT

PT FTTT

To Wet End SteamShower

MoistureEliminator

LTLT

Flash Steam To

Wet End Steam

Shower

Flash SteamSteam Utilization

Flash Steam Uses

BestSend pressurized condensate to boiler

UnacceptableDischarge to atmosphere (machine or boiler)

PoorMachine silo

Fair?Machine shower water heating

Fair?Former or wet end steam shower

GoodPocket ventilation preheat air

GoodIn low pressure dryers

RankingFlash Steam Use

Energy Observation Corrugating Medium Paper Mill

Run steam in bottom unorun dryers to improve runnability? Running 9 lb dp with stationary syphons and flash steam going to a condenser.

Comments Most machines shut off steam to bottom unorun dryers since

the sheet does not contact these dryers.

Many medium and liner machines run high steam pressures in early dryers and do not need a condenser.

Reducing dp to 4 lb would reduce blowthrough steam flow by a factor of 2+.

Syphon Blowthrough Versus Differential Pressure

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

0 100 200 300 400 500 600 700 800 900 1000

Blowthrough Flow (pph)

Differential Pressure (psi)

Rotary Syphon Stationary Syphon

Rotary SyphonOperating Point

Stationary SyphonOperating Point

Energy Observation Specialty Wallboard Mill

Discharges 200,000 gallons per day of 150oF effluent. Average fresh water temperature is 55oF.

Comments Opportunity to recover 75 MM Btu per day by installing a spiral heat recovery unit to preheat fresh water.

Potential annual energy savings are $260,000.

Energy Observation Recycled Paperboard Mill

Discharges 400,000 gallons per day of 80oF effluent. Average fresh water temperature is 55oF.

Comments Opportunity to recover 67 MM Btu per day by installing a spiral heat recovery unit to preheat fresh water.

Potential annual energy savings are $240,000.

Spiral Heat ExchangerSpiral Heat Exchanger--Single Single Channel with CounterChannel with Counter--current Flowcurrent Flow

Liquids Flow Counter-currently in Individual Spiral Channels

Spiral Heat Exchanger

Energy Observation Specialty Wallboard Mill

Has gas-fired kiln dryer with no heat recovery. Exhaust temperatures are 320 to 350oF.

Comment

Opportunity to recover heat to preheat burner combustion air, kiln edge seal air, and building supply air.

Energy Observation Recycled Paperboard

Have six-high stacked dryers (midwestern U S State).

Comment

Opportunity to recover heat to preheat vapor absorption system make-up air, incoming mill water, and machine room supply air.

Typical Multi-Stage Heat Recovery System

3 Stages For Maximum Heat Recovery

Stage 1- Air to Air (24/7)

Stage 2- Air to Glycol (seasonal)

Stage 3- Air to Process Water (24/7)

Typical 3 Stage Heat Recovery System

Air/Air

1st Stage

Air/Liquid

2nd Stage

Air/Liquid

3rd Stage

Exhaust


Trim loss at winder is 10% of reel deckle on major grade that is 55% of grade mix.

Comments

Opportunity to reduce dryer steam consumption by 10% on this grade. Potential annual steam savings $400,000.

Will require wet trim capability and small pulping unit (cylinder wet end with no broke pit).

Narrow Deckle Considerations

Machines that produce grades with narrow deckles can reduce dryer steam consumption by moving trim squirts.

Potential problems include press fabric filling, broke handling, threading issues, changes in blow through steam, roll wear issues, and winder operating issues.

Lateral Corrugator Technology Description

Conventional corrugating does not utilize the strength advantage of machine direction fiber alignment. Compression strength enhancement by orienting the linerboard transversely can as much as 30%.

Project Goal: Develop a commercially viable lateral corrugating process including designing and building a pilot lateral corrugator, testing and evaluating the pilot machine, and developing a strategy for commercialization.

Lateral Corrugator Benefits

Lateral corrugating is a cut-to-width operation resulting in considerable benefits at the box plant (bp) and paper mill (pm):

Waste reduction (bp)

Trim optimization (bp & pm)

Ability to utilize paper machine trim rolls (pm)

May permit basis weight reduction (pm)

Reduced inventory (bp)

Shipping optimization (pm to bp)

Lateral Corrugator Project Partners

Financial Support:

Temple-Inland Paperboard and Packaging

Smurfit-Stone Container Corp.

U. S. Department of Energy

IPST at Georgia Tech

Equipment and Expertise:

Corrugated Gear MarquipWardUnited

Hardy Instrumentation

Albany International Corn Products

Container Graphics Corp. CUE

Kadant Johnson Corp. Armstrong

WIKA Instrument Corp. Chicago Electric

Pamarco Bill Nikkel

Lateral Corrugator Contact Information

Michael Schaepe

Institute of Paper Sci & Tech @GT

500 10th St, NW

Atlanta, GA 30332-0620

404-894-6640

[email protected]

Web site www.ipst.gatech.edu/research/projects/corrugating.html

Energy Observation Press Dewatering Improvement

Many mills are using advanced technology press fabrics, optimizing nip geometry, and other techniques to increase web dryness entering the dryers.

TIP 0404-52, press section optimization, provides guidelines.

Relative Cost of Water RemovalSpec

ific

Cost

of

Wate

r R

emoval

Gravity

Fabric Tension

Vacuum

Mechanical

Compression

Evapora

tion

Water Removal kg/kg fibers

124 2.25 1.25

Former Presses Dryers

$0.014/ton $0.019/ton $22.00/ton

* Source Pressing Principles Dr. Ivan Pikulik Paprican 2002

Containerboard Press Solids vsSteam Consumption

35

40

45

50

55

2000 3000 4000 5000 6000Steam Consumption lb/t

Press Solids %

Corrugated Medium

Improved Speed and Reduced Steam Usage

2.10

2.15

2.20

2.25

2.30

2.35

2.40

2.45

2.50

2.55

Supplier A Supplier B AstenJohnson Stylus

Steam Usage (klb/ton)

1960

1980

2000

2020

2040

2060

2080

2100

2120

Machine Speed (fpm)

Steam Usage (klb/ton) Machine Speed (fpm)

Machine ran 3.5% faster

while using 10% less steam

Potential Annual Value = $1.9 MM

Engineered Density Technology


Using fresh water at 40 to 70oF for press fabric conditioning. Press dryness 43.8% with 1,200 pli last press.

Comments Recommended shower water temperature is 130oF.

Lower temperature cools sheet, reduces press dewatering, and provides less efficient fabric conditioning.

Whitewater Filter

How Does It Work ?

Filtrate

FILTER MEDIA

SUPPORT SCREEN

INNER DISC

FLOW

1

2

3

Shower Water Filter

Vessel is full of process water and operates at low pressure

(0,1 - 0,3 bar)

Disks are completely submerged and slowly rotate

Rotation speed increases as vessel pressure increases

Clean filtrate passes through the media to central hollow shaft

Disks are continuously cleaned in three stages :

A. Filter cake is doctored off and pumped away (if necessary)

B. Clean filtrate is pulled back through media removing debris

C. Oscillating high pressure, submerged shower cleans the

media

BRUSH SHOWERS

Brush ShowerBrush Shower


Have to run two dry end pulper agitators full time to slush winder trim.

Comment

Pulper modifications will permit operation with one agitator and provide $75,000 annual savings.

Energy Efficient Repulper Rotor Blade

Energy is a Controllable Operating Expense !

Batch Repulper Power ResponseThree Day Comparison

Summary of Energy SavingsBatch Repulper

0.05/kWh0.05/kWhEnergy Cost (USD)

28,035Cost Savings (USD)

560,700kWh/year saved

1,885,4502,446,150kWh/350 day year

5,3876,989kWh/day

20.820.8Motor hours/day

259336Avg. Consumption (kW)

265368Peak Consumption (kW)

Low Energy Rotor

Conventional Rotor

Energy Observation Kraft Specialty Machine

Whitewater system is too small so mill water is used in pulper when running purchased pulp.

Comment:

Larger whitewater system would permit using whitewater for pulp dilution.


Sheet follows second/last press fabric ~ 10 feet after press nip

Comment: Estimated sheet rewet is 2 to 3 percentage points that equates to 4,000 to 6,000 lb/hr increase in dryer steam consumption.

Mill is looking at different press fabric designs and ways to get sheet off fabric without compromising runnability.

Press Rewet

Single FeltRewet

Single FeltRewet Minimized

Double FeltRewet Minimized


Rebuilt refiners and changed to spiral logarithmic refiner plates.

Comment:

Rebuilds increased plate life and capacity.

Plate changes reduced energy consumption by 10% at comparable strength and freeness.

Logarithmic Spiral DesignLogarithmic Spiral Design

SpiralSpiral Refiner Plate BenefitsRefiner Plate Benefits

Better StrengthBetter Strength

Average Experience: 5Average Experience: 5--10% 10% ImprovementImprovement

Comparable Energy ConsumptionComparable Energy Consumption

Energy SavingsEnergy Savings

Average Experience: 10% Average Experience: 10% ReductionReduction

Comparable Strength and CSFComparable Strength and CSF

Energy Saving Reduced Diameter Plate Designs

No load: Wasted energy required just to spin a refiner rotor in a pulp slurry

No Load Equation (HP): = (3.083 X 10-13)(Dia4.249)(RPM3)

42 Refiner @ 514 Rpm = 330 Hp no-load

38 Reduced diameter plate @ same 514 Rpm = 215 Hp no-load

Energy Observation Specialty Kraft Paper Mill

Has many vacuum pumps manufactured before 1960 that are energy inefficient (high hp and seal water flow).

Comment

Pumps should be replaced (not rebuilt) when capacity falls below 80% of design.

Nash Vacuum Pump Comparison

0.0400.0450.051Hp/cfm

160180205Horsepower

65 gpm60 gpm 100 gpmSeal Water

327400257RPM

4,000@204,000@204,000@20CFM@in Hg

1984-1960-19841930-1960Vintage

904M2CL4002H4408Model

Energy Observation Stacked Dryer Cylinders

Pro Less machine direction space required.

Better for heat recovery.

Con Higher radiant heat loss (7 vs 3%?).

Difficult to apply fabrics.

More difficult to thread and remove broke.

Mechanical stability of frames.

STACKED

DRYER

SECTION

THREE-TIER

DRYER

SECTION

Energy Optimization Low Energy Mode

When drying or speed limited: Lower whitewater temperature.

Turn off/reduce steam flow to steam showers.

Lower temperature or turn off PV and VA systems if does not cause sweating or moisture profile to get worse.

Reduce steam pressures in wet end dryers that flash to condenser.

Relative Steam Application Efficiency

Pounds Steam Per ExtraPound Water Removed

Heating White Water 5 to 10

Fourdrinier Steambox 3 to 5

Press Steambox 1 to 2?

Dryers 1.3

IR Temperature Gun

Identify leaks in steam system: Vent valves Condensate system Steam traps

Relative dryer temperatures Sheet temperatures Fresh water, whitewater, shower, and effluent water temperatures Flat black paint required to get emissivity right.

Leaking valves in fresh water make-up

Appendix

Information in TIP 0404-63

TAPPI TIP 0404-63 Paper Machine Energy Conservation

Five Basic Principles

1. Minimize amount of water evaporated in the dryers.

2. Minimize amount of steam condensed outside the dryers.

3. Maximize condensate return flow and pressure.

4. Minimize electrical consumption for key users.

5. Monitor and manage energy consumption and cost.

Energy Monitoring

Meter energy flows to each machine. Establish key energy parameters. Highlight variables that affect energy consumption. Include energy parameters in operator rounds and

centerlining. Provide information to operators, engineers, and

managers to encourage continuous improvement. Discuss energy cost and conservation in production

meetings. Conduct periodic checks of key systems. Benchmark machine operation.

Utility Monitoring

Pressure, temperature, and flow for each steam header.

Electricity consumption for each machine.

Natural gas consumption.

Water flows and temperatures-mill water, water from other areas of the mill, and sewer.

Compressed air pressure and flow.

Condensate return flow and temperature.

Calculate Specific Energy Indices

Steam consumption-lb steam/ton paper

Electricity consumption-kWh/t

Natural gas consumption-Kscfm/t

Total energy consumption- MM Btu/ton

Water consumption-gal/ton

Compressed air consumption-kscf/ton

Condensate return-%

Total energy cost-$/ton

Paper Machine Energy Targets

Fine Paper and Bleached Board

75-8075-80%Condensate Return

180180o FPV Supply Temperature

1.21.2Lb steam/lb water evap

Drying Steam

5.05.0%Reel Moisture

3.03.0%Size Press Moisture

4242/45%Press Solids

2522%Couch Solids

2,0002,000Gal/tonWater Consumption

7.06.0MMBtu/tonTotal Energy Cons.

350350kWh/tonElectricity Consumption

4,4004,000Lb/tonTotal Steam Consumption

8487%Overall Machine Efficiency

9093%First Quality

9393%Uptime

Bleached BoardFineGrade

UnitsIndex

Paper Machine Energy Targets Linerboard and Medium


180180oFPV Supply Temperature


Drying Steam

9.07.5%Reel Moisture

42/5042/50%Press Solids

2727%Couch Solids






9797%First Quality

9494%Uptime

Corrugating MediumLinerGrade

UnitsIndex

Paper Machine Energy Targets

Pulp Machines



Drying Steam

7.510%Reel Moisture

4550%Press Solids

2828%Couch Solids






9799%First Quality

9595%Uptime

Fluff PulpMarket PulpGrade

UnitsIndex

Key Energy Factors

Venting from dryer thermocompressor or cascade sections.

Condenser water valve output/condensate flow.

Differential pressures.

Wire pit steam valve position.

Basis weight versus standard.

Press section weir flows.

Moisture to size press.

Key Energy Factors (cont)

Size press starch solids. Pocket ventilation temperature. Temperatures in hood exhaust heat recovery system.

Warm water flow from pulp mill. Mill water leakage into whitewater system.

Winter/summer operating strategy for machine room ventilation.

Any additional steam venting.

Energy Survey Guidelines

Keys to identifying opportunities and successfully implementing recommendations.

Suggested frequency of additional detailed surveys-steam and condensate, steam traps, refining, pressing, vacuum systems, steam showers, hood air and heat recovery systems, compressed air, etc.

Additional Surveys

Steam trap surveys (annual) Compressed air system

surveys (annual) Refining optimization (on-

going) and mechanical surveys (annual)

Showering surveys (every 2 years)

Press section optimization (on-going)

Press section nip surveys (every 2-3 years)

Vacuum pump boroscopes or orifice plate testing (annual)

Vacuum system surveys/optimization (every 3 years)

Thermography to check for leaks and hot spots (annual)

Steambox surveys (annual) Dryer steam and condensate

system surveys (annual) Hood air system surveys

(annual) Machine room ventilation

studies (every 5 years) Pulp dryer

maintenance/capacity reviews (annual)

Tissue machine hood balances/inspections (annual)

Energy Optimization Reduce Evaporation of Water

Increase press exit dryness. Optimize press fabrics and roll cover designs. Reduce basis weight. Trim sheet at wet end on narrow deckle grades.

Improve moisture profiles. Reduce over-drying before size press. Increase starch solids with metering size presses.

Increase re

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