appa institute steam plant modeling€¢ discussion of a model of a simple two pipe system •...

APPA Institute – Session 323 EU © GLHN Architects & Engineers, Inc.

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Utilities InfrastructureSteam Plant Modeling

APPA Institute for

Facilities Management

Bill Nelson PE

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Purpose of Today’s Presentation

• To provide a broad understanding of software for modeling piping systems

• To provide a basis of comparison of some available software

• Review applications of modeling to steam systems

• Discussion of a model of a simple two pipe system

• Investigate effects of modifications to a basic system

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Agenda

• Software Overview

• Example Software

• Comparison Attributes

• Selected Comparisons

• Unique Aspects of Steam Modeling

• Applications to maintenance/operations

• Simple Two Pipe System Models

• University of Arizona Case Study

wnelson

Typewritten Text

Jan 2016


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Software Overview

• Desired Features– Flowsheet w/ Graphic User Interface (GUI)

• Represent schematic piping system

• Drawing tools & component icons

• Text boxes

• Snap to grid capability

– Hyperlinks in Flowsheet• Access to electronic data

• Export to CAD

• Link to spreadsheet calcs

• Access to the WEB

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Software Overview

Flowsheet

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Software Overview

Hyperlink


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Software Overview

• Desired Features– Calculation engine

• Fluid data lookup

• Import pump/valve catalogs

• Display pipeline flow rates/pressure drops

• Display pump curves at selection point

• Multiple scenario capability

– Share Information• Create reports in .pdf, HTML or Word

• Export Flowsheets to CAD

• Export to Excel

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Software OverviewDesired Features

Pump Curves

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Software OverviewDesired Features

Print / Export


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Software Overview

• Life of Plant Application– Design Engineer

• Size/optimize piping/equipment

• Balance flow rates

• Run multiple scenarios

• Develop costs

– Contractor• Evaluate/incorporate effect of field changes

• Determine flushing paths/volumes

• Evaluate startup/commissioning process

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Software Overview

• Life of Plant Application– Plant Engineer

• Evaluate effect of increased output

• Anticipate system expansion requirements

• Determine effect of piping/equipment failure

– Maintenance/Plant Operations• Troubleshooting

• Determine effect of equipment isolation for repair

• Ensure optimum system operation

• Evaluate valve/controller operation

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Example Software

Sinda/Fluint www.crtech.comPipe Flo Pro www.eng-software.comFlow Master v7 www.flowmaster.comFluid Flow ^3 www.accutech2000.comSinet Engrs Aid www.epcon.comFlowvent www.flomerics.comPipe Flow www.pipeflow.co.ukFlow of Fluids www.flowoffluids.comFathom 7 www.aft.com


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Comparison Attributes

• Tutorials/training available

• Heat transfer calculations

• Pipe heat loss calculations

• Liquid/vapor/gas capability

• Flow mixing capability

• Auto phase state determination

• Modular architecture

• Tech support

• Service contract

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Selected Comparisons

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Heat Loss Capability

• Allows estimate of energy lost through insulation on piping

• Applications– Estimating the added insulation required to reach a target loss (say 5-10% of total boiler capacity

– Estimating avoided cost of fuel from re-insulating

– Allows comparisons to other steam production methods


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Condensing Boilers

• Concept– Condensing boilers have greater efficiency

– Requires modular boilers at each building

– Avoids line losses associated with central plants

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Condensing Boilers

• Disadvantages– Inflexible fuel supply

– Gas supply lines to all campus buildings

– Cannot take advantage of diversity

– Combustion process in each building

– Modular condensing boiler capacities are limited to about 4,000 MBH

– Greater maintenance cost/more maintenance personnel

– Requirement for firm capacity can double boiler cost

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Line Loss ComparisonStandard vs. Condensing Boilers

• Basis for Comparison– 180,000 MBH campus system

– 5000 heating degree days

– 23 deg F average winter design temp

– 500,000 MMBtu/yr heating load

•Annual Loss Comparison– 100,000 MMBtu for standard boiler in central plant (20% of heating load)

– 25,000 MMBtu for condensing boilers distributed on campus (5% of heating load)


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Line Loss ComparisonStandard vs. Condensing Boilers

• Annual $ Loss Comparison– Assuming 75% efficiency for standard boiler in central plant, and 20% line loss required boiler input is 830,000 Mmbtu/yr. At $8/MMBtu, natural gas cost is $6,700,000/yr.

– Assuming 90% efficiency for condensing boilers distributed on campus, with a 5%line loss required boiler input is 580,000 MMBtu/yr. At $8/MMBtu, the natural gas cost is $4,700,000/yr.

– Avoided cost of condensing boilers is $2,000,000/yr. This weighs against the greater cost of installation/maintenance.

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Applications

• Boiler Outages– How to rebalance to feed critical buildings

– Which buildings lose service first

• Pipe Breaks– How to reroute steam to critical buildings

– Effect/benefit of looped feeds

• Trouble Shoot Low Pressure– Can find pinch points

– Help establish routes for additional feeds

• Evaluate System Modifications– Find low cost solutions

– Determine minimum material/costs

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Steam Model Aspects

• Supply modeling is straightforward

• Condensate return modeling difficult

• Difficult to model loss of boiler capacity or boiler staging

• Cannot predict problems with pitch

• Cannot model trap operation

• Cannot model water hammer

• Models control valves using actual valve data from catalogs

• Cannot model startup


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Steam Model Aspects (cont’d)

• Models buildings as a single load with a second order curve

• Static model-does not follow load changes over time

• Load changes can be modeled as discrete load points

• Boilers modeled as infinite source at set pressure

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Modeling Procedure

• Obtain campus steam piping site diagram, in CAD if possible

• Verify pipe lengths (easy in CAD)

• Verify pipe diameter/material

• List the fittings and valves in each run (good approximations)

• Model each building as a single load

• Insert valve data that best represents existing valve control action

• Select actual boiler plant supply pressure for infinite supply source

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Steam Pipe Velocity


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Two Pipe Campus Model

• Small campus

• Six steam heated buildings

• Four buildings on a loop

• Scenarios– Existing system-as operated for years

– Effect of low pressure

– Effect of pipe breakage

– Effect of increased loads

– Effect of resizing some piping

– Effect of pipe breakage on resized system

– Effect of low flow on resized system

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Example Campus

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Existing SystemNo Text for Clarity


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Existing-As Operated

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Existing SystemLow Pressure

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Existing SystemBroken Pipe


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Existing SystemIncreased Load

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Existing SystemIncreased Loads

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Existing system Notes

• Significant variability in supply pressure between buildings

• Supply pressure dropped drastically to all buildings under increased load

• Velocity in main to loop increased from 7680 fpm to 8640

• Velocity in loop increased from 7260 fpm to 9720


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Resized SystemIncreased Load

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Resized SystemBroken Pipe

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Resized SystemLow Pressure


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Resized SystemIncreased Loads

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Resized System Notes

• Building supply pressure variability significantly reduced

• Supply pressures to all buildings increased

• Main to loop velocity dropped back to 5900 fpm

• Loop velocity dropped back to 5160 fpm

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Campus Model Notes

• Existing system designed according to velocity charts, resulting in pressure variability due to lengths of run

• Resized system attempted to achieve a balanced pressure at all buildings

• Resizing can mean replacing piping or running parallel feeders to critical locations


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U of A Case Study

• Campus Overview– Refer to Campus map

– Black lines are unchanged existing tunnels

– Orange lines are recently added interconnects

– Red lines are proposed resizing and interconnects

– Yellow circles are selected buildings for analysis

m

41Bio. Sci. W

Coronado Hall

AnthropologyOld Main

Gila Hall

Elec. & Comp. Engineering

AME

Cancer Ctr.

Drachman Hall

Life Sci. N.

CRP

Ina Gittings

Opt. Sci.

McClelland Hall

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U of A Case Study

• Steam system description– Two Steam plants: AHSC (north) and CHRP (south)

– Plants are now interconnected and operated cooperatively

– 5 miles of steam piping and tunnels

– 100 psig supply pressure

– Two pipe system (steam supply and condensate return)

– Condensate equalizer system


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U of A Case Study

• Current operation– Historically, plants and distribution were separate

– Recent interconnect tied plants together

– Plants now operated cooperatively feeding campus together

– As a result, distribution has improved significantly

– Standard deviation of inlet pressures dropped from 23.5 to 5.6

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U of A Case Study

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U of A Case Study

• Planned new loads– Refer to campus map

– Total of five new block loads

– Buildings constructed in three phases over 20 years

– Additional 10,000,000 sq ft

– Additional 164,000 lb/hr

– Current piping system unable to handle new loads

– Proposed new interconnect shows some improvement


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U of A Case Study

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U of A Case Study

• Final solution– Resize 5th st. tunnel from 6” to 10”

– Resize northwest tunnel from 6” to 8”

– Build new 10” interconnect

– Standard deviation of building inlet pressures drops to 5.9

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U of A Case Study


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U of A Case Study

• Cost of upgrades– New proposed 10” interconnecting tunnel…………………..$33,500,000

– Resize Northwest tunnel from 6” to 8”………………………….$3,500,000

– Resize 5th street tunnel from 6” to 10”………………………..$3,100,000

– New boilers…………..$10,600,000

– Total……………………$50,700,000

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U of A Case Study

• Other lessons learned– Increasing supply pressure to 125 psig had little effect

– Upsizing the new interconnect tunnel to 12” from 10” had little effect

– Upsizing the 5th street and Northwest tunnels to 12” had little effect

– Adding the new interconnect alone was not the final answer

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appa institute steam plant modeling€¢ discussion of a model of a simple two pipe system •...

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