Energy Tips – Steam Steam Ti p Sheet #26B • Jul y 2007 Industrial Techno l og i es Program Suggested Actions Consi derat i ons When Se l ect i ng a Condensi ng Economi zer • Determine your boiler capacity, Boilers equipped with condensing economizers can have an overall efficiency that combustion efficiency, stack gas exceeds 90%. A condensing economizer can increase overall heat recovery and steam temperature, annual hours of system efficiency by up to 10% by reducing the flue gas temperature below its dew operation, and annual fuel consumption. point, resulting in improved effectiveness of waste heat recovery. • Identify in-plant uses for low- This tip sheet is a companion to one entitled Consider Installing a Condensing temperature heated water (plant Economizer, and discusses two types of condensing economizer: indirect and direct space heating, boiler makeup water heating, preheating, or contact. process requirements). An indirect contact condensing economizer (see Figure 1) removes heat from hot flue • Verify the thermal requirements gases by passing them through one or more shell-and-tube or tubular heat exchangers. that can be met through This economizer can heat fluids to a temperature of 200°F while achieving exit gas installing a condensing economizer, and potential annual temperatures as low as 75°F. The indirect contact economizer is able to preheat water fuel energy and cost savings. to a higher outlet or process supply temperature than the direct contact economizer. The condensing economizer must be designed to withstand corrosion from condensed • Determine the cost-effectiveness water vapor produced by the combustion of hydrocarbon fuels such as natural gas or of a condensing economizer, ensuring that system changes are light oils. The condensed water vapor is acidic and must be neutralized if it is to be evaluated and modifications are discharged into the sewer system or used as process water. included in the design (e.g., mist eliminator, heat exchangers). Stack Temperature Simple paybacks for condensing 100-120˚F economizer proj ects are often less than 2 years. 200˚F Temperature Controller Boiler make-up water or hot Damper process water load

Flue gas 325˚F Resources from boiler after 45-85˚F heat exchange U.S. Department of Energy— in feed-water economizer DOE’s software, the Steam Pump System Assessment Tool and Steam System Scoping Tool, can Figure 1. Indirect contact condensing economizer help you evaluate and identify Another heat recovery option is to use a direct contact condensing economizer steam system improvements. (see Figure 2), which consists of a vapor-conditioning chamber followed by a In addition, refer to Improving countercurrent spray chamber. In the spray chamber, small droplets of cool liquid Steam System Performance: come into direct contact with the hot flue gas, providing a non-fouling heat transfer A Sourcebook for Industry for surface. The liquid droplets cool the stack gas, condense and disentrain the water more information on steam vapor. The spray chamber may be equipped with packing to improve contact between system efficiency opportunities. the water spray and hot gas. A mist eliminator is required to prevent carryover of small droplets. The direct contact design offers high heat transfer coupled with water Visit the BestPractices Web site recovery capability since heated water can be collected for boiler feedwater, space at www.eere.energy.gov/ industry / heating, or plant process needs. Recovered water will be acidic and may require bestpractices to access these and treatment prior to use, such as membrane technology, external heat exchangers, or pH many other industrial efficiency control. resources and information on training. The site must have substantial heating requirements for low-temperature process or cold make-up water if a direct contact condensing economizer is to be a viable heat recovery alternative. Because direct contact condensing economizers operate BestPracti ces i s part of the I ndustr ial close to atmospheric pressure, altitude and flue gas temperature limit makeup water Technol og i es Program I ndustr i es of the Future strategy, whi ch he l ps the country’s temperature to 110°F to 140°F. most energy-i ntens i ve i ndustr i es i mprove Flue gas outlet thei r compet iti veness. BestPracti ces br i ngs 100˚F together emergi ng techno l og i es and best energy-management practi ces to he lp Spray Water inlet compani es beg in i mprov i ng energy effici ency, 95˚F envi ronmenta l performance, and productivi ty right now.

BestPracti ces emphas i zes p l ant systems, Heat Exchanger Packed bed of where si gn ifi cant eff ici ency i mprovements 90˚F stainless steel and savi ngs can be achi eved. I ndustry ga i ns pall rings easy access to near-term and l ong-term Boiler make-up water or other sol ut i ons for i mprov i ng the performance of Flue gas inlet hot water load motor, steam, compressed ai r, and process heati ng systems. I n add iti on, the I ndustr ial 135˚F Assessment Centers provi de comprehensi ve 325˚F 140˚F industr ial energy eva l uat i ons to sma ll - and medi um-s i ze manufacturers. Pump Blow-down

Figure 2. D i rect contact condensi ng econom i zer w i th packed bed and external heat exchanger FOR ADDITIONAL INFORMATION, PLEASE CONTACT: When considering whether to install a condensing economizer, evaluate changes in system operating parameters. These economizers preheat boiler makeup water EERE I nformat i on Center and reduce deaerator steam requirements, thereby providing more steam for plant 1-877-EERE-I NF processes. The energy savings potential is decreased if the maj ority of the deaerator (1-877-337-3463) steam is supplied from blowdown heat recovery. The condensing economizer could www.eere.energy.gov also limit or decrease backpressure steam turbine energy production if the turbine discharge is used to balance a low-pressure header. The reduction in stack gas exit Industr ial Techno l og i es Program temperature reduces plume buoyancy and must be considered when modeling Energy Effici ency and Renewabl e Energy pollutant dispersion. Performance characteristics of both indirect and direct contact U.S. Department of Energy economizers are summarized in the table below. Washi ngton, DC 20585-0121 www.eere.energy.gov/i ndustry Compari son of Condensi ng Heat Recovery Economi zers Performance Characteri st ic Direct Contact Ind i rect Contact Maxi mum Outlet Water Temperature 140°F 200°F Minimum F l ue Gas Temperature 75°F 75°F Percent Removal of Hum idi ty from F l ue Gas 85% 35% (Approx i mate ) Need for Heat Exchanger Depends on Appli cat i on No Yes ( when no heat Recovery of Water i n F l ue Gas Possible (si te spec ific) 1,2 exchanger i s used ) 1,2 Footpri nt per MMBtu/ hr of Heat Recovery Site spec ific Site spec ific Permi ss ibl e Fue l s Burned i n Bo il er Natural Gas Yes1 Yes A STRONG EP NERGY ORTFOLIO Light O il Yes2 Yes2 FOR A SA TRONG MERICA 1. Water treatment required if water of condensation is reused. Special corrosion-resistant materials or coatings may be required on heat exchange surfaces. Energy efficiency and clean, renewable energy will mean a stronger economy, a 2. Water treatment required if water of condensation is reused. More acidic due to SOx in solution. Special corrosion- cleaner environment, and greater energy resistant materials or coatings are required on heat exchange surfaces. independence for America. Working Condensing economizers require site-specific engineering and design, and a thorough with a wide array of state, community, industry, and university partners, the U.S. understanding of the effect their operation will have on the existing steam system and Department of Energy’s Office of Energy water chemistry. Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies. For additional information on condensing economizers, refer to Feedwater Economizers for Waste Heat Recovery. For additional information on industrial DOE/GO-102006-2337 steam system efficiency, refer toImproving Steam System Performance: July 2007 A Sourcebook for Industry. All publications are available from the EERE Steam Tip Sheet #26B Information Center at (877) 337-3463. Revi sed from DOE / GO-102002-1504 • March 2002