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APPLICATIONSINTRODUCTION

Varec Biogas reserves the right to change product design and specifications without notice.Copyright © 2009 by Varec Biogas a Division of Westech Industrial Inc. 1

INTRODUCTIONVarec Biogas offers a wide range ofbiogas safety and handling equipment.Biogas is typically produced during thebiological breakdown of organic solidsthrough anaerobic digestion. The gasgenerated through this process is anenergy source which can be collectedand utilized, or can be safely burned.Biogas is a highly moist mixture ofgases consisting of approximately 55 to70% methane, 25 to 35% carbondioxide and trace amounts of nitrogenand hydrogen sulfide. Biogas recoveredmay be used in a multitude of ways.Biogas can be used to run a boiler forheating the anaerobic digester or theplant. Biogas can also be used to run anengine-generator to generate electricity.

Anaerobic digestion is one of the mostsafe and effective methods of treatingbiosolids from municipal and industrialwastewater. It is an ideal method inmeeting strict environmental regulationsin highly urban areas. The anaerobicprocess occurs in closed vessels(digesters), or covered ponds orlagoons. Soluble organics are convertedto methane (CH4) and carbon dioxide(CO2) in a two-step process.

Landfills also generate biogas naturallyas buried organic refuse biodegrades.

BIOGAS SAFETY & HANDLING SYSTEMBiogas collection and utilization is animportant part of the anaerobic digestionprocess. The low heat content gas issaturated, and contains elementsharmful to personnel. Biogas is alsocorrosive to piping and equipment.

It is important to handle biogas properlyto ensure a protected environment. Thekey aspect of design is to recognize thatbiogas handling equipment operates asa system. The following providesgeneral guidelines for the design and

selection of a complete biogas safetyand handling system. With over sevendecades of experience and service tothe industry, Varec Biogas is proud of itshigh-quality worldwide performancerecord.

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APPLICATIONS

Varec Biogas reserves the right to change product design and specifications without notice.Copyright © 2009 by Varec Biogas a Division of Westech Industrial Inc.2

APPLICATIONSSYSTEM FLOW DIAGRAMS

SYSTEM FLOW DIAGRAMSSYSTEM FLOWBiogas is produced within the digester at a rate that createsenough pressure to move gas through the piping system. Insome systems, this gas is first recirculated to the primarydigester to assist in mixing the digester contents.

1. DIAGRAM ITypical lay-out of Digester outlet.

2. DIAGRAM IIDirected to the boiler for digester heating or plant heating.

3. DIAGRAM IIIUsed as fuel for internal combustion or in gas turbine engines to(a) pump wastewater and biosolids; (b) operate blowers and compressors; and (c) generate electricity.

4. DIAGRAM IVStored in a gas holder to accumulate and be used as fuel for internal combustion or in gas turbine engines to (a) pump wastewater and biosolids; (b) operate blowers and compressors; and (c) generate electricity.

5. DIAGRAM V(i)Biogas directed to the waste gas burner through the in-line relief valve. In the case of plant upset or a clogged line, the system gas pressure may increase and a method to relieve line pressure is required.

DIAGRAM V(ii)Installation of biogas directed to an enclosed flare.

DIAGRAM I: DIGESTER COVER/GAS HANDLING


Website: www.varec-biogas.com Email: [email protected] 1-866-4BIOGASWebsite: www.varec-biogas.com Email: [email protected] 1-866-4BIOGAS 3

DIAGRAM III: ANAEROBIC DIGESTER TO ENGINE-GENERATOR

DIAGRAM II: ANAEROBIC DIGESTER TO BOILER

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DIAGRAM IV: ANAEROBIC DIGESTER TO GAS HOLDER

DIAGRAM V(i): ANAEROBIC DIGESTER TO WASTE GAS BURNER

APPLICATIONSBIOGAS SYSTEMS

Website: www.varec-biogas.com Email: [email protected] 1-866-4BIOGAS 5

DIAGRAM V(ii): ALTERNATIVE INSTALLATION: ANAEROBIC DIGESTER TO ENCLOSED FLARE

BIOGAS SYSTEMSSYSTEM HYDRAULICS

When sizing the gas piping and equipment, the followingparameters should be considered:

1. Biogas production flow capacity.

2. Pipe diameter, length and fitting - The Water EnvironmentFederation (WEF Manual of Practice No.FD - 8)recommends that piping should be sized with a maximumgas velocity below 12 ft/s (3.7 m/s). This velocity will preventliquid and solid carry-over which damages equipment.Additionally, the number of pipe bends and long piping runsshould be minimized to reduce pressure losses.

3. Maximum digester cover design pressure can be calculatedby determining the amount of gas produced by the digester.Gas production may be estimated using various publishedcalculations. Select the pipe size necessary to stay withinthe recommended velocity requirements. Determine thepressure loss on the gas line leading to the inlet of the gasutilization equipment. The sum of the pressure required atthe inlet of the gas utilization equipment and the pressuredrop through the line determines the minimum operatingpressure necessary beneath the digester cover.

4. Determine required pressure losses through each piece ofequipment to maintain low pressure drop across the entiresystem.

5. The operating pressure necessary for all gas utilizationequipment.

6. All gas piping should be sloped a minimum of 2% for properdrainage. Drip traps should be located at all low points, andin long pipe runs.

In more complex systems, it is necessary to determine theminimum inlet pressures and pressure drops for each linebefore calculating the cover pressure. A gas storage devicemay be necessary to handle loads during periods of low gasproduction.

MATERIALS

The gas system must utilize materials which are corrosion-resistant to H2S and to the overall plant environment. Most gashandling equipment is available in low copper cast aluminum,which has proven to be extremely corrosion-resistant in biogasapplications.

If fabricated steel is used, a protective coating should beconsidered. For example, bitumastic coating or coal tar epoxy isextremely corrosion-resistant. Units can also be hot-dippedgalvanized by the manufacturer, or field painted with acorrosion-resistant coating system. If units manufactured ofcarbon steel are not installed immediately, proper storage andhandling must be considered.

Stainless steel is the material of choice for corrosion resistanceand overall product longevity.

NFPA-820 rated fiberglass can also be used to constructvessels, e.g., H2S scrubbers.

Heat-resistant materials are important for the waste gas burner.Some units utilize stainless steel in areas of the waste gasburner exposed to elevated temperatures. A protective layer ofinsulation for carbon steel stacks in enclosed flares is a morecost-effective method than using an all stainless steel chamber.

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Liquids and Solids HandlingThe biogas is saturated as it leaves the digester, covered pondor lagoon. Moisture and sediment should be removed to avoiddamaging downstream equipment. A Condensate andSediment Trap with drip trap should be located immediatelydownstream of the digester, or covered pond or lagoon. Referto 233 and 246 Series for further information.

If large amounts of condensate are expected, installation of acondensate accumulator at the lowest point of the gas pipingshould be considered to assist in lowering operation andmaintenance cost. Refer to 248 Series for further information.

Foam ProblemsFoaming in the digester may cause operation and safetyproblems. Foam can clog the gas handling equipment, such asthe flame arresters. The following are recommendations toproperly handle foaming problems in the digester.

1. Pressure and vacuum relief (PVR) valves with flamearresters are installed on digester covers. In instances whenfoam clogs the flame arresters, it may prevent the PVRvalves from relieving pressure or vacuum build-up in thevessel. Emergency pressure or vacuum relief can beaccomplished through the installation of emergency reliefmanhole covers. Refer to 400W Series for more information.

2. It is important to prevent foam from entering the main biogastrain leaving the digesters. An effective method is to install afoam separator immediately downstream of the digester.Refer to 231 Series for more information.

Hydrogen Sulfide RemovalBiogas contains varying amounts of hydrogen sulfide (H2S).H2S is a highly-corrosive substance that can createmaintenance and operation problems. To avoid corrosion, theH2S must be reduced to meet the recommended limit given bythe boiler, compressor, or engine manufacturer. H2S is also atoxic air pollutant that can create a severe odor nuisance evenin minute concentrations. The treatment of biogas for removalof sulfur compounds is increasingly important as regulationsrestricting sulfur emissions become more stringent.

A gas purifier should be installed upstream of boilers,compressors or engine-generators. A flame trap assemblyshould be installed just upstream and downstream of eachpurifier. Refer to 235/236 Series.

Flame PropagationFlame flashbacks in the biogas piping system have a tendencyto propagate. Flame propagation can severely damageequipment.

Flame arresters should be installed 15 feet upstream of allpossible ignition sources. Thermal shut-off valves should beused in conjunction with all in-line arresters. They provideadded protection by shutting off the gas source to the flame.Refer to 5000, 430 and 450 Series for more information.FlamePropagation cont...

Flame arresters should be installed in conjunction with allpressure and vacuum relief valves installed on digester roofs toprevent an external flame from igniting the gas within the tank.Refer to 5810B/5820B Series and the Safety Selector Valvesection.

Gas ControlRegulators provide a means to sequentially direct the gas toutilization equipment such as boilers and engine-generators.Upstream or downstream control may be specified. Refer to180 or 386 Series for more information.

It is important to note that the Model 180 Series Regulatorsconstantly throttle to maintain set upstream or downstreampressure. The Model 386 Series Regulator remains closed untilit’s set pressure is reached.

Check valves should be specified in locations where a reversalof flow would damage rotating equipment or upset the systempressure balance. Refer to 211 Series.

SafetyOccupational health and safety for the plant and personnel iscritical when designing a biogas system. Biogas becomesexplosive when mixed one volume of gas with 5-20 volumes ofair. Proper measures must be taken to ensure that equipment isinstalled to avoid the possibility of an explosion. Someimportant factors to consider are:

1. Flame arresters should be installed as close to the source ofignition as possible. Varec Biogas arresters can be locateda maximum of 15 feet upstream of the ignition source whenused in accordance with UL standards.

2. A flame arrester should be specified in areas where there isa possibility of air ingress off relief valves and vents, as anexample. Where there is an open flame or possiblesparking, e.g., flares, boilers or engine-generators,additional protection utilizing thermal bypass valves andpressure (explosion) relief valves should be specified alongwith the flame arrester. Refer to 430 Series, 450 Series and7100B Series.

3. It is important to check with local building codes,Occupational Health and Safety Association (OSHA)standards, and Fire Protection Codes when determining aninstallation site for waste gas burners or enclosed flares andrelated equipment.

4. All diaphragm-operated valves, manometers, and otherdevices which might vent gas when installed indoors shouldhave provision for vent lines terminating outside thebuilding. A flame check should be specified for installationon vent lines. Refer to 5200 Series.

5. Regular inspections should be made for pressure andvacuum relief devices, flame arresters, and drip traps toensure proper operation. Periodic maintenance is requiredfor efficient overall performance.



EQUIPMENT SELECTION

Website: www.varec-biogas.com Email: [email protected] 1-866-4BIOGAS

A biogas system should have two methods of relieving excessgas to the atmosphere.

Method 1: FLARINGThe waste gas burner is used to safely combust the biogas andreduce irritating odors.

The pipe train to the waste gas burner should consist of thefollowing:

1. A back pressure regulator valve with a flame arrester andthermal bypass shut-off valve. Refer to the 5000, 386, and440 Series for information.

2. A pressure (explosion) relief valve. The pressure (explosion)relief valve is intended to relieve an overpressure condition or pressure shockwave in the pipe caused by a flame flashback. A pressure shockwave results upon ignition and travels ahead of the flame in the pipe. As the flame travels through the pipe, it increases in velocity. At the point where the flame ignites the pressure shockwave, a detonation or explosion occurs. The pressure (explosion) relief valve eliminates the potential for an explosion or detonation from occurring. The installation of a pressure (explosion) relief

valve can be eliminated if the flame arrester will be installed within 15 feet of the waste gas burner in accordance with ULrecommendations. Refer to 7100B Series.

3. Waste gas burner. Refer to the Burners & Flares section.

IMPORTANTConsult your local air pollution authorities for information onemission requirements before specifying the type of wastegas burner to use. In cases where stack emissions areregulated or where visible flame is unacceptable, anenclosed flare may be specified. A gas pipe train leading toEnclosed Flares differ slightly from what is described here.Refer to 244E or 249 Series for more information.

4. A drip trap should be installed on the 1/2’” NPT connection provided with the flame arrester if the flame arrester will be installed on a horizontal pipe run. When the flame arrester or trap assembly is installed vertically, then provisions should be made to install drip trap on the lower point of the gas piping to the waste gas burner. Refer to 246 or 247 Series for more information.

Cold Weather Conditions1. The gas train and equipment installed outdoors must be

insulated. Heat tracing should also be considered. Biogasis wet and dirty, and condensate will have a tendency tofreeze in cold weather conditions. This lowers plantefficiency.

2. The pressure-relief regulator (386 Series Back PressureRegulator) installed on the waste gas burner train should beeither:

a. Installed indoors to ensure proper operation of the pressure sensing line. The sensing line tap-in on the main gas line should be at least 10 feet away from the regulator.

b. If installed outdoors, provisions should be made to protect the regulator from cold weather. A special insulating jacket can be specified. Heat tracing should also be considered. In extreme cold weather conditions, the sensing line tubing should be insulated and/or heat traced.

Refer to 386 Series and Insulating Jacket literature for further information.

3. Since the flame arrester or flame trap assembly isrecommended for installation within 15 feet of the burner,and will typically be located outdoors, a special insulatingjacket can be specified. Heat tracing should also beconsidered in extreme cold weather conditions. Refer toInsulating Jacket data sheets for further information.

4. The pressure-vacuum relief valves installed on top of adigester cover should be specified with the “all-weather”feature. This includes special anti-freeze coating applied tothe seat ring tip, pallet periphery and stem and guide posts.In addition to specifying the “all-weather” feature, thepressure-vacuum relief valve and flame arrester should be:

a. Provided with a special insulating jacket. Refer to Insulating Jacket literature for more information.

b. Installed in an insulated or heated shelter or enclosure, with a pressure relief pipe-away option. The pipe-away option allows biogas to be relieved to the atmosphere through a pipe connection one size larger than the process connection. The heated or insulated shelter should have enough ventilation to meet vacuum relief requirements. Refer to 5810B/5820B Series for more information.

5. Drip traps should be located indoors wherever possible. Iflocated outdoors, they should be insulated against freezing.Refer to 246 Series, 247 Series and Insulating Jacketliterature for further information.

Humid Conditions1. Field paint a corrosion-resistant coating on equipment that is

manufactured with fabricated carbon steel.

2. Consider utilizing stainless steel hardware (nuts and bolts)on equipment to prevent rusting. Rusted hardware can bedifficult to maintain.


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EXTREME WEATHER CONSIDERATIONS

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Method 1: FLARING cont...Alternative Installation: Diagram V(i)

In cold weather conditions, and in cases where it posesdifficulty in installing a relief valve and flame trap assembly asone unit within 15 feet (4.5 meters) of the waste gas burner, thefollowing is the recommended installation:

1. A back pressure regulator should be installed indoors so thecold weather does not affect its pressure sensing line. Thereare no distance constraints when installing a back pressureregulator on the gas train to the waste gas burner. Refer to386 Series.

TIPThe pressure sensing line of the back pressure regulator willprovide more accurate readings when installed further awayfrom the waste gas burner.

2. A flame trap assembly should be installed within 15 feet ofthe waste gas burner per UL requirements. Refer to 430 and450 Series for further information. In cold weatherconditions, it is good practice to insulate the flame trapassembly. Refer to Insulating Jacket data sheets for furtherinformation.

The waste gas burner pipe train should be sized to handle themaximum amount of gas produced by the digester.

Method 1: FLARING cont...Alternative Installation: Diagram V(i) cont...

It is important that the burner pilot remains continuously lit whilethe biogas is flaring to ensure safe disposal. The pilot gassupply can be either biogas, natural gas or propane. Utilizingnatural gas or propane ensures a more reliable pilot and isespecially critical in areas with high winds. Auto-start ignitionand pilot flame monitoring are recommended features. Refer tothe Flare Section of this catalog when choosing the type ofburner suited for your application.

Method 2: PRESSURE AND VACUUM RELIEF ONDIGESTER OR GAS HOLDER COVER

The second means for emergency relief is through theinstallation of pressure and vacuum relief valves on the digestercover, or biogas holder. A minimum of two pressure/vacuumrelief valves with flame arresters are recommended. Each set oftwo should be installed with a Safety Selector Valve, as shownon the diagrams provided. The Safety Selector Valve providesa means to isolate one set of equipment while performingmaintenance on another. Refer to 2010B/2020B, 5810B/5820Band Safety Selector Valve data sheets for more information.

EMERGENCY RELIEF CONT...

DIGESTER ACCESS

Digester contents are often sampled to provide plant operatorsan evaluation of process efficiency. At least two 8” (200 mm)quick-opening sampling hatch covers should be mounted onsampling wells on each digester cover. When digesters arecleaned, roof access is required. It is advisable to provide atleast two large diameter gas-tight manholes with quick-openingcovers. Refer to 42, 4310, 220, 220W, 400W, and 220VP formore information.

To successfully operate the biogas system, gas production andline pressure must be carefully monitored.

When floating digester covers are used, the Digester should beequipped with position indicators. Cover level may betransmitted to grade or control room by mechanical or electricalmeans. High and low level alarms should be considered toprotect the covers from structural damage. Refer to 2592Series.

Manometers should be installed in each pipe train to monitorthe system pressure. Gas flowmeters should be located at eachdigester, and in the main header. Meters should also beinstalled to measure flow to each biogas utilization equipment.Refer to 217 Series and 219 Series for more information onmanometers.

PROCESS MONITORING


The data presented in this bulletin is for general information only. Manufacture is not responsible for acceptability of these products in relation to system requirements. Patents and PatentsPending in U.S. and foreign countries. All rights reserved. Printed in USA. Varec Biogas reserves the right to change product design and specifications without notice. © 2009

www.varec-biogas.com

1-866-4BIOGAS

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1-866-4BIOGAS

The landfill gas (LFG) handling system is similar to a biogas handling system with an anaerobic digester, or a covered lagoon orpond. Landfill gas composition is generally more susceptible to fluctuations in Btu content. LFG may be collected and flared. In largerlandfills the gas may be utilized.

In landfills, a compressor is specified to draw-off gas from the gas collection wells. The compressor suction is generally of largediameter to minimize the vacuum required to obtain the gas. Some leachate treatment systems use an aerobic reactor whichproduces a digester-type gas.

The use of covered lagoons or ponds in place of anaerobic digesters is another method of wastewater treatment. This biogashandling system is similar to systems utilizing anaerobic digesters, except with covered lagoons or ponds, a blower is normallyrequired to boost the pressure of the gas collected from the lagoon or pond.

COVERED LAGOON AND POND APPLICATIONS

LANDFILL GAS APPLICATIONS

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FIELD SERVICE

The data presented in this bulletin is for general information only. Manufacture is not responsible for acceptability of these products in relation to system requirements. Patents and Patents

Pending in U.S. and foreign countries. All rights reserved. Printed in USA. Varec Biogas reserves the right to change product design and specifications without notice. © 2009.

FIELD SERVICE

Varec Biogas reserves the right to change product design and specifications without notice.Copyright © 2009 by Varec Biogas a Division of Westech Industrial Inc. 11

INTRODUCTIONBiogas produced from anaerobic digestion is typically wet, dirtyand contains corrosive elements such as hydrogen sulfide. Thegas is flammable and provides a potential safety hazard if nothandled properly. These unique properties of biogas requirespecial consideration to the design of the gas handling system,especially in regard to maintenance and safe operation underall conditions of the anaerobic process. Varec Biogas, theleading total solutions provider of biogas safety and handlingequipment, offers on-site field expertise.

SITE SURVEYSOur Field Service Engineer will survey your existing biogassystem and provide a comprehensive report that will:

• Troubleshoot causes for existing operation problems on your biogas system.

• Recommend an immediate solution to address the existing operations problem, as well as offer a permanent fix.

The site walkthroughs have proven to be a great tool that helpthe plant develop a budget that addresses future needs forrehabilitation and/or upgrade.

MAINTENANCEOur qualified and experienced field service engineers areavailable for professional and timely periodic maintenance ofinstalled Varec Biogas equipment.

It is our aim to provide cost effective periodic maintenanceService so that the Varec Biogas equipment will:

• Perform to factory specifications.

• Produce maximum process uptime.

• Help our customers accomplish their objectives.

PREVENTATIVE MAINTENANCEOur service personnel will visit your facilities on your chosenschedule. A typical schedule is a semi-annual visit. The scopeof work is listed but not limited to the following:

• Inspect the overall condition of the equipment,verify correct operation and make necessary adjustments or calibrations.

• Certify calibration to within the published factory specifications.

• Where necessary, lubricate the mechanical devices, inspect and replace parts of installed Varec Biogas equipment.

• Provide a detailed written report of the findings, including recommended solutions and parts replacement.

• Furnish updated documentation to you at no charge.

Having a Preventative Maintenance Contract provides thecustomer with a predictable yearly operations and maintenancebudget for Varec Biogas equipment. Varec Biogas also offersan optional maintenance contract with a plant where a non-Varec product has been installed. A site survey would be aprerequisite.

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FIELD SERVICE

The data presented in this bulletin is for general information only. Manufacture is not responsible for acceptability of these products in relation to system requirements. Patents and PatentsPending in U.S. and foreign countries. All rights reserved. Printed in USA. Varec Biogas reserves the right to change product design and specifications without notice. © 2009

www.varec-biogas.com

1-866-4BIOGAS

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TRAININGVarec Biogas provides both maintenance and operator trainingon site. Our qualified field service Engineers are lending theirexpertise in digester gas safety equipment and making itavailable at your doorstep. Whether this is your first time usinga particular product or you just need a refresher course, thetraining offers hands-on experience and a complete informationkit as a resource for the future.

At the conclusion of training, operators will have a basiccomprehension of how to efficiently install, calibrate and repairVarec Biogas products thus, minimizing downtime.

Topics include:

• Gas safety equipment specifications

• Safety hazards and precautions

• Installation

• Operation

• Start-up and shut down procedures

• Troubleshooting guidelines

• Preventative maintenance

• Recommended spare parts

• Routine and non-routine emergency procedures

The Varec Biogas instructor will provide all visual aids andtraining manual. A training certificate with date, seminar title,material content and name will be issued.

START-UP SERVICESYou can rely on our field service experts to inspect properinstallation of the Varec Biogas equipment via a comprehensiveinspection checklist. This is vital in achieving desired operatorsafety.

Our field service engineers are also available forcommissioning and start-up assistance of the equipment, andcan lend their proficiency during field testing.

After successful commissioning of the Varec Biogas equipment,our field service engineers can provide necessary training tooperators on the proper care, operation and the requiredpreventative maintenance of the Varec equipment. Each sitevisit is documented with a comprehensive report, and VarecBiogas issues a Certificate of Installation Inspection,Commissioning and Start-Up Assistance. Varec Biogasrecommends a follow-up site visit after a year of equipmentoperation to ensure plant system efficiency.

applications proof 2 - etec applications.pdf · selection of a complete biogas safety ......

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