Consulting-Specifying Engineer - August 2007 - (Page A2)

STE GH & AND S GENE I N S IA M T S P O W EIR S U E S R AT I O N E N E RGY SOLUTION S CE NTE R Recovering Waste Heat from Boilers The Next Step in Energy Efficiency AT A GLANCE ❯ Rising energy costs make heat recovery attractive also avoids thermal discharge problems oday’s industrial process or energy manager continually looks for ways to reduce plant energy usage. Owners conduct facility reviews to ﬁnd ways to save energy in steam systems, including ﬁnding leaks and repairing steam traps, improving insulation levels and shutting down or setting to standby equipment not being used actively. In the United States, the Save Energy Now program from the Dept. of Energy’s (DOE) Ofﬁce of Energy Efﬁciency and Renewable Energy (EERE) has demonstrated signiﬁcant energy savings with rigorous industrial site assessments. After adjustments are made to existing equipment and practices, an owner might ask, “Are there other things we can do to reduce our energy usage?” For many industrial users of natural gas, an ideal next step may be boiler heat recovery systems. ❯ Blowdown heat recovery ❯ Stack heat recovery uses T spray tower or condensing economizer a portion of the boiler water is continuously or periodically removed to control levels of dissolved and suspended solids. Blowdown helps avoid both scaling and internal corrosion. Blowdown may remove anywhere from 1% to 20% of the boiler water in each cycle, depending on feedwater conditions and individual boiler characteristics. ENERGY LOSSES IN BLOWDOWN PROCESS From an energy perspective the boiler blowdown process, though necessary, is a loser. A boiler system suffers an efﬁciency penalty from 1% to 5% through the thermal energy lost in the blowdown stream. This water stream is pressurized and at temperatures well above the boiling point at atmospheric pressure, thus a portion of it will ﬂash to steam when released to the atmosphere, which wastes energy. An additional problem is that most municipal wastewater systems will not accept discharges of the remaining hot blowdown water, so it has to be cooled or diluted to meet the typical maximum temperature of the receiving sewer system. ON THE COVER Two natural gas fueled Waukesha engines, Model VHP F3521G, rated at 500 hp each drive two vertical turbine water booster pumps. These are used to pull water at 6,500 gpm from a reservoir to serve the water system of the City of Huntington Beach in California. Photo courtesy James Myers, Valley Power Systems Inc. Gas Technology is a trademark of Energy Solutions Center, Inc. and is published in cooperation with Reed Business Information. Gas Technology is an educational supplement from the Energy Solutions Center, 400 N. Capitol St., N.W., Washington, DC 20001. Phone: (202) 824-7150. Web site: www.energysolutionscenter.org. David Weiss, Executive Director. Comments may be directed to: Gas Technology Editor, Plant Engineering Magazine, 2000 Clearwater Dr., Oak Brook, IL 60523. Phone: (630) 288-8789. Printed in the USA. TWO AREAS OF ENERGY SAVING The modern industrial boiler is a result of more than 200 years of development, so further gains in the efﬁciency of the boiler itself are likely to be modest. However there are potentially signiﬁcant energy improvements in the boiler system. Two areas worth consideration are boiler blowdown heat recovery and exhaust stack heat recovery. Boiler blowdown is essential in nearly all boilers. It is the operation whereby WEBSITES www.aircompressor.org www.poweronsite.org www.gasairconditioning.org www.cleanboiler.org www.energysolutionscenter.org USE HEAT RECOVERY TO TEMPER BLOWDOWN WATER A solution increasingly being adopted is the use of blowdown water heat recovery. The blowdown goes through a heat exchanger, where it transfers most of its thermal energy to a cold make-up water A2 http://www.energysolutionscenter.org http://www.aircompressor.org http://www.poweronsite.org http://www.gasairconditioning.org http://www.cleanboiler.org http://www.energysolutionscenter.org

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - August 2007

Contents M/E Roundtable Giants 100 Pullout Poster Giants Stand Tall: CSE Giants 100 Report Electrical Design for Tall Buildings HVAC and Fire Safety for Elevator Systems How to Beat the Codes GAS Technology Supplement Recovering Waste Heat from Boilers New Applications for Tankless Water Heating Systmes Techniques Improve for Powder Coating MDF New Tools Available for Heat Treating Steel Direct Drive Engines

Consulting-Specifying Engineer - August 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.