Even 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 as the boiler operation continue, leading to carryover of boiler water into the steam, causing damage to piping, steam traps and even process equipment. The increasing concentration of suspended solids can form sludge, which impairs boiler efficiency and heat transfer capability.
One way to improve efficiency is to review your blowdown practices. This includes the use of an automatic blowdown control system by regulating water volume discharged in relation to the amount of dissolved solids present. This system maintains proper water chemistry within acceptable limits, while minimizing blowdown and reducing energy losses. Cost savings come from the significant reduction in the consumption, disposal, treatment, and heating of water.
The U.S. Department of Energy's Industrial Technologies Program calculated annual cost savings associated with the installation of an automatic blowdown control system that reduced blowdown rate from 8% to 6%. The example below assumes a continuously operating natural gas-fired, 150 psig, and 100,000 lb/hr steam boiler. Makeup water temperature of 60 degrees, with boiler efficiency of 83%, with fuel valued at $3.00 MMBTU was used, and the total water, sewage and treatment costs are $0.004 per gallon.
The annual cost savings in the example above equals:
Boiler Feedwater:
Initial = 100,000 / (1-0.08) = 108,695 lbs/hr
Final = 100,000 / (1-0.060 = 106,383 lbs/hr
Makeup Water Savings = Initial - Final, or 108,695 lbs/hr - 106,383 lbs/hr = 2,312 lbs/hr
Enthalpy of boiler water = 338.5 Btu/lb; for makeup water at 60 degrees = 28 Btu/lb
Thermal Energy Savings = 338.5 - 28= 310.0 Btu/lb
Annual Fuel Savings = 2,312 lbs/hr x 8760 hrs/yr x 310.5 Btu/lb x $3.00/MMBtu / 0.82 x 106 = $23,007
Annual Water and Chemical Savings = 2,312 lbs/hr x 8760 hrs/yr x $0.004/gal / 8.34 lbs/gal = $9,714
Annual Cost Savings = $23,007 + $9,714 = $32,721
If you need additional information about feedwater systems or other ways you can decrease costs, contact Nationwide Boiler today and we are happy to discuss ways to improve your bottom line: 1-800-227-1966.
Boiler Blog | Nationwide Boiler Inc.
1 Operate Boilers At or Close to Design Capacity. This decreases fuel consumption per unit of production and can result in an estimated energy savings range of 1 percent to 5 percent. Likewise, if your facility or plant requires excess capacity, visit the Nationwide Boiler website to obtain a current list of boilers for rent or for sale. Nationwide Boiler provides new and used boilers that can ship immediately, anywhere around the world (conditions apply, contact Nationwide Boiler for details).
2 Reduce Combustion Excess Air. Measure and control air-fuel ratio or oxygen and carbon monoxide content of flue gases from process heating equipment such as furnaces, ovens, and boilers for the entire range of operation. This has an estimated energy savings range of 2 percent to 15 percent. Think about installing a standard low NOx / low excess air burner (compared to an ULN / high excess air burner) on your boiler. Complemented with a Nationwide CataStak™ Selective Catalytic Reduction System (SCR), a new burner retrofit and SCR installation will not only provide immediate energy savings, but will also reduce NOx emissions and decrease your carbon footprint.
3 Clean Heat Transfer Surfaces. Cleaning heat transfer surfaces lowers flue gas temperature and increases efficiency by improving heat transfer. Doing so can save an estimated 1 percent to 5 percent at a moderate cost.
4 Reduce Radiation Losses from Openings. Reducing radiation losses can save an estimated 1 percent to 2.5 percent at a relatively low cost.
5 Use Proper Oven, Furnace or Boiler Insulation to Reduce Wall Heat Losses. Reducing wall losses produces energy savings of 1 percent to 2 percent with only a moderate investment.
6 Insulate Steam Lines Leaving the Boiler as well as Air- or Water-Cooled Surfaces Exposed to the Oven or Furnace Environment. With an estimated energy savings range of 1 percent to 5 percent, piping insulation can be completed for a moderate investment.
7 Install Air Preheaters or Other Heat Recovery Equipment. This type of equipment recovers available heat from exhaust gases and boiler blowdown and transfers it back into the system by preheating. The potential energy savings range id from 1 percent to 25 percent, depending on process temperatures and other variables. Consider a Nationwide Boiler EconoStak Economizer or a Heat Recovery (HR) Blowdown Pak to recover valuable heat that can be reused, allowing you to save money in the long-term.
Adapted from Process Heating Magazine, March 21, 2012.