Blowdown Ration = 3,200 ÷ (3,200 + 50,000) = 6.0%From the table, the heat recoverable corresponding to a 6% blowdown ratio with a 150-psig boiler operating pressure is 1.7 MMBtu/hr. Since the table is based on a steam production rate of 100,000 lb/hr, the annual savings for this plant are:
Annual Energy Savings = [1.7 MMBtu/hr x (50,000 lb/hr/100,000 lb/hr) x 8,000 hr/yr]/0.80 = 8,500 MMBtu
Annual Cost Savings = 8,500 MMBtu/yr x $8.00/MMBtu = $68,000Blowdown Energy Recovery: Blowdown waste heat can be recovered with a heat exchanger, a flash tank, or flash tank in combination with a heat exchanger. Lowering the pressure in a flash tank allows a portion of the blowdown to be converted into low-pressure steam. This low-pressure steam is most typically used in deaerators. Drain water from the flash tank is then routed through a heat exchanger. Cooling the blowdown has the additional advantage of helping to comply with local codes limiting the discharge of high-temperature liquids into the sewer system. For additional information on heat recovery, contact the team at Campbell-Sevey or download this Steam Tip sheet for suggested actions and resources. This tip is provided by the U.S. Department of Energy – Energy Efficiency and Renewable Energy and originally published by the Industrial Energy Extension Service of Georgia Tech.