To maintain solids at an acceptable level, water is removed from the boiler system. This water bleed-off, termed “blowdown,” from industrial boilers is an important part of boiler operations. Achieving the right amount of blowdown is critical. As with cooling towers, insufficient blowdown can lead to excessive buildup of impurities. Too much blowdown can lead to wasted water, treatment chemicals and energy. Blowdown is released from beneath the water surface in the boiler’s steam drum, mud drum, bottom header or from the bottom of the boiler. Surface water blowdown is often done continuously to reduce the level of dissolved solids, and bottom blowdown is performed periodically to remove sludge from the bottom of the boiler. Additionally, the blowdown heat can be used to increase the overall efficiency of the system. The optimum amount of blowdown required is a function of boiler type, steam pressure, chemical treatment program and feedwater quality. Because supply water quality varies from place to place, no hard and fast rules exist as to the exact volume of blowdown required. Blowdown rates can very from one percent (of feedwater flow) to as much as 20 percent, with the typical range of four to eight percent. Blowdown amount is typically calculated and controlled by measuring the conductivity of the boiler feed and blowdown water.  Conductivity is a viable indicator of the overall total dissolved solid concentration.

Facility managers should know the optimum operating parameters for their boiler water quality. While optimizing boiler water treatment and control procedures can conserve water, more importantly, they will maintain proper boiler performance, extend life and save energy. The American Boiler Manufacturers Association and American Society of Mechanical Engineers have developed guidelines for water purity controls in boilers. These can be used as a starting point for determining boiler blowdown needs.

Operating the boiler below these levels requires more blowdown, wasting water and energy, thus increasing the cost of operation. The total dissolved solids are the sum of all naturally occurring minerals dissolved in supply water and any treatment chemicals added to the system.

Improving condensate return is another way to minimize blowdown water and maximize cycles of concentration at which a boiler operates. By increasing condensate return, operators will increase the concentration cycles, decrease chemical usage, decrease blowdown and conserve the heat value of the high-temperature condensate. A well-functioning steam trap inspection programis essential to maximizing condensate return.  When steam traps exceed condensate temperature, the trap is leaking steam. Use infrared temperature gun/device to check this. Steam lines and traps should be checked for leaks periodically and repairs should be scheduled. Such repairs are typically very cost effective because of the potential for energy savings. Condensate return systems and automatic shut-off controls should be considered for boiler systems not utilizing them. Consultation can be conducted with boiler vendors, service providers and other technical assistance providers.