Boiler Blowdown - Fact Sheet - P2 InfoHouse
Boiler BlowdownEven with the best pretreatment programs, boiler feedwater often contains some degree of impurities,such as suspended and dissolved solids. The impurities can remain and accumulate inside the boiler asthe boiler operation continues. The increasing concentration of dissolved solids may lead to carryoverof boiler water into the steam, causing damage to piping, steam traps and even process equipment. Theincreasing concentration of suspended solids can form sludge, which impairs boiler efficiency and heattransfer capability.To avoid boiler problems, water must be periodically discharged or “blown down” from the boiler tocontrol the concentrations of suspended and total dissolved solids in the boiler. Surface waterblowdown is often done continuously to reduce the level of dissolved solids, and bottom blowdown isperformed periodically to remove sludge from the bottom of the boiler.The importance of boiler blowdown is often overlooked. Improper blowdown can cause increased fuelconsumption, additional chemical treatment requirements, and heat loss. In addition, the blowdownwater has the same temperature and pressure as the boiler water. This blowdown heat can be recoveredand reused in the boiler operations.Boiler Blowdown Benefits Less water, fuel and treatment chemicals needed;Less maintenance and repair cost (minimized carryover and deposits);Saves manual supervision for other tasks (with automatic control);Cleaner and more efficient steam;Reduced operating cost (reduction in consumption, disposal, treatment and heating of water);Minimized energy loss from boiler blowdown can save about 2 percent of a facility’s totalenergy use with an average simple payback of less than one year.Best Operating Practices for Boiler BlowdownN.C. Divisionof Pollution Prevention andEnvironmental AssistanceAs mentioned earlier, insufficient blowdown may cause carryover of boiler water into the steam or theformation of deposits on boiler tubes. Excessive blowdown wastes energy, water and treatmentchemicals. The blowdown amount required is a function of boiler type, steam pressure, chemicaltreatment program, and feedwater quality. The optimum blowdown amount is typically calculated andcontrolled by measuring the conductivity of the boiler feedwater. Conductivity is a viable indicator ofthe overall total dissolved solid concentrations. Typically, blowdown rates range from 4 – 8 percent ofboiler feedwater flow rate, but can be as high as 20 percent with extremely poor quality feedwater.A commonly used ratio for the amount of boiler blowdown required is computed as follows:(919) 715-6500(800) 763-0136Required Blowdown C feedwaterC blowdown
where Cfeedwater the measured concentration of the selected chemical in the feedwaterCblowdown the measured concentration of the same chemical in the blowdownThe maximum recommended concentration limits according to the American Boiler Manufacturers Association(ABMA) is listed in the table below.ABMA Recommended Feedwater Chemistry LimitsBoiler OperatingPressure (psig)Total DissolvedSolids (ppm)Total Alkalinity(ppm)0 - 502,50050051 - 3003,50070015301 - 4503,00060010451 - 6002,5005008601 - 7501,0002003751 - 9007501502901 – 1,0006251251Total Suspended Solids (ppm)The American Society of Mechanical Engineers (ASME) has developed a best operating practices manual for boilerblowdown. The recommended practices are described in Sections VI and VII of the ASME Boiler and Pressure VesselCode. You can identify energy-saving opportunities by comparing your blowdown and makeup water treatmentpractices with the ASME practices. The ASME Boiler and Pressure Vessel Code can be ordered through the ASME Website at http://www.asme.org/bpvc/.Automatic Blowdown ControlsThere are two types of boiler blowdowns: manual and automatic. Plants using manual blowdown must check samplesmany times a day or according to a set schedule, and adjust blowdown accordingly. With manual boiler blowdowncontrol, operators are delayed in knowing when to conduct blowdown or for how long. They cannot immediatelyrespond to the changes in feedwater conditions or variations in steam demand.An automatic blowdown control constantly monitors boiler water conductivity and adjusts the blowdown rateaccordingly to maintain the desired water chemistry. A probe measures the conductivity and provides feedback to thecontroller driving a modulating blowdown valve. An automatic blowdown control can keep the blowdown rateuniformly close to the maximum allowable dissolved solids level, while minimizing blowdown and reducing energylosses.Purchasing and installing an automatic blowdown control system can cost from 2,500 to 6,000 with a mostly 1- to 3year payback period on the investment. A complete system should consist of a low- or high-pressure conductivityprobe, temperature compensation and signal condition equipment, and a blowdown-modulating valve.Boiler Blowdown-2-August 2004
Changing from manual blowdown control to automatic control can reduce a boiler’s energy use by 2 – 5 percent andreduce blowdown water losses by up to 20 percent.Blowdown Heat Recovery UnitsIn addition to proper blowdown practices, including the use of automatic blowdown control, reducing cost and heatloss associated with boiler blowdown can also be achieved through recovering the heat/energy in the blowdown. Theblowdown water has the same temperature and pressure as the boiler water. Before this high-energy waste is discharged,the resident heat in blowdown can be recovered with a flash tank, a heat exchanger, or the combination of the two. Anyboiler with continuous surface water blowdown exceeding 5 percent of the steam generation rate is a good candidate forblowdown waste heat recovery. A boiler blowdown heat recovery project at Augusta Newsprint Mill saved the company 31,000 in fuel costs and 14,000 MMBtu in energy annually.To learn how to calculate your energy recovery potential, please see the fact sheets on Boiler Blowdown EnergyRecovery s/wint2003 boiler.shtml) and Recover Heat from BoilerBlowdown at recovery.pdf).Flash Tank SystemThe flash tank system shown in the figure below can be used when expense and complexity must be reduced to aminimum. In this system, the blowdowns from the boilers are sent through a flash tank, where they are converted intolow-pressure steam. This low-pressure steam is most typically used in deaerators or makeup water heaters.Schematics of a Flash Tank SystemFlashed SteamBoiler 1Condensate ReturnMakeup WaterBoiler 2FlashTankBoiler 3DeaeratorBlowdown to DischargeFeedwater to boilersFlash Tank – Heat Exchanger SystemThe system shown below consists of a flash tank and a heat exchanger. The temperature of the blowdown leaving theflash tank is usually still above 220 F. The heat of this flash blowdown can be used to heat makeup water by sending itthrough the heat exchanger, while cooling the blowdown at the same time. Heating boiler makeup water saves on fuelcosts. An additional advantage of cooling blowdown is in helping to comply with local codes regulating the discharge ofhigh temperature liquids into the sewer system.Boiler Blowdown-3-August 2004
Schematics of a Flash Tank – Heat Exchanger SystemSteam to Flash TankFlashed SteamFlash TankBlowdownPreheatedMakeupWaterHeat Recovery ExchangerTreatedMakeupWaterCooledBlowdownTo DischargeBlowdown Wastewater PermittingFor information on boiler blowdown wastewater general permitting (in North Carolina), please visit the website for NCDivision of Water Quality at http://h2o.enr.state.nc.us/su/Forms Documents.htm.ConclusionAs mentioned above, the blowdown amount required can be significantly affected by the feedwater quality. Therefore,improving feedwater quality through makeup water treatment and chemical treatment in the boiler system can reduceblowdown rate. For more information on chemical treatments, please see Boiler Chemical nces “Avoiding Boiler Problems.” William L. Reeves. ASHRAE Journal. September 2001 Issue.http://www.ashraejournal.org/ “Boiler Blowdown.” Application Note. Analytical-SIC-4900-02. http://www.us.yokogawa.com/Boiler Blowdown-4-August 2004
“Boiler Blowdown Energy Recovery.” Greg Harrell. Energy Matters Newsletter. Winter 2003 Issue.Department of Energy. Industrial Technologies Program. tters/wint2003 boiler.shtml “Boiler Blowdown Heat Recovery Project Reduces Steam System Energy Losses at Augusta Newsprint.”Forest Products. Best Practices Technical Case Study. Department of Energy. Office of IndustrialTechnologies. http://www.nrel.gov/docs/fy02osti/31697.pdf Boiler Efficiency Improvement. David F. Dyer and Glennon Maples. Fifth Edition. Auburn University.Boiler Efficiency Institute. Auburn, Ala. 1991. “Best Practices – Steam Generation.” Utah Industries of the Future.http://www.uiof.org/best/steam/gen.html “Install an Automatic Blowdown Control System.” Steam Tip Sheet #23. Department of Energy. IndustrialTechnologies Program. April 2004. eam tip 23.pdf “Minimizing Boiler Blowdown.” Steam Tip Sheet #9. Department of Energy. Office of IndustrialTechnologies. Energy Efficiency and Renewable Energy. June imize blowdown.pdf “Recover Heat from Boiler Blowdown.” Steam Tip Sheet #10. Department of Energy. Office of IndustrialTechnologies. Energy Efficiency and Renewable Energy. June y/heat recovery.pdf “Waste Heat Recovery from Boiler Blowdown.” Commercial Energy r Blowdown-5-August 2004
The N.C. Division of Pollution Prevention and Environmental Assistance provides free, non-regulatory technical assistance andeducation on methods to eliminate, reduce, or recycle wastes before they become pollutants or require disposal. Contact DPPEAat (919) 715-6500 or (800) 763-0136 for assistance with issues in this fact sheet or any of your waste reduction concerns.DPPEA-FY04-03Boiler Blowdown-6-August 2004
Purchasing and installing an automatic blowdown control system can cost from 2,500 to 6,000 with a mostly 1- to 3- year payback period on the investment. A complete system should consist of a low- or high-pressure conductivity
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Quench - start 100 - 400 100 - 175 15 - 60 Quench - mid 130 - 500 150 - 200 15 - 50 Quench - end 20 - 120 50 - 200 15 - 20. 9 Delayed Coker Blowdown System Water Reuse October-2017 coking.com Budapest Recycle of Condensed Blowdown Water Cited in Oil & Gas Journal 23-apr-1973 (1) Joliet R
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