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Minimizing Boiler Blowdown and Decreasing Costs



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.

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Tuesday, 18 September 2018