Flash Economizer

Heat Recovery System for Continuous Blowdown

Continuous Blowdown
When a boiler is steaming, solids in the water are left behind in the boiler, increasing concentration. Boiler water treatment with phosphates or chelating agents does not reduce the amount of concentration but it chemically reacts with boiler solids to reduce or eliminate scale forming materials.

If the concentration of solids becomes too high, foaming and priming can occur, and excessive sludge can restrict circulation and heat transfer causing rupturing and blistering of boiler tubes or shell. Since the concentration is greatest at the point of highest steam release, the best location for the continuous blowdown is just below the water level in the boiler.

At this point of highest concentration (about 4” to 6” below the water level), boiler water is continually drained off to reduce the concentrated boiler water. Fresh make-up water with a much lesser concentration is, at the same time taken, into the boiler. While this is the best method of controlling Total Dissolved Solids (T.D.S.) in the boiler, valuable heat can be lost.

The Penn Flash Economizer Saves You Money
Continuous blowdown of 1 gpm on a 150 psig boiler wastes 169,000 BTUs/Hr. This blowdown water, to hot to dump to streams or public sewage, must be cooled to at least 140°F in most locations. Tempering this water with added cold water or just taking the water and dumping it to a hot well or blowdown tank becomes costly because you’re losing both flash steam and hot water which can be recycled into the boiler. This water can be cooled by sending it through a Flash Economizer, which takes the heat out of the continuous blowdown and recycles it back into the make-up water. The drain temperature is reduced to 100-110°F.

With a Flash Economizer most of the heat is recycled back into the boiler. A Flash Economizer saves more BTUs than a conventional heat exchanger. When a percentage of the continuous blowdown flashes into steam in the upper portion of the Flash Economizer, you get 100% recovery of the BTUs in flash stream. Also, with today’s cost of treating make-up water, you reclaim a percentage of the blowdown water in flash stream and put it back into your system. For more information on these savings see Brochure F14.5.

Heat Recovery Process
Continuous blowdown enters tangentially spinning around in the Flash Chamber. Flash steam is released in the center area and recycled into the deaerator or feedwater heater. Every pound of flash steam returns 1156 BTUs into your system which, when taken back to the deaerator or feedwater heater, is condensed. So you not only save BTUs but also make-up water. The remainder of the blowdown water flows directly down to the second area of recovery – the spiral coil heat exchanger. The hot water flows around the coils and heats the make-up water which flows through the coils.

The Penn Flash Economizer is designed for efficient trouble-free operation. Note that the only area in which sludge can accumulate is below the heat transfer area, and that there is no value between the flash area and heat exchanger area to stick or clog. Maintenance is simple with the Flash Economizer. The unit is flanged to simply drop out the lower spiral coil section, clean the copper or stainless coils, and place the unit back in operation without even having to shut the boiler down. This is recommended maintenance at least once a year.

Single and Multiple Boilers
Because the flash process is a natural process continuous blowdown from one boiler or multiple boilers, even operating at different pressures can be taken into one Flash Economizer. They will each flash down to the pressure maintained in the deaerator set by the pressure reducing valve off of the main steam line. The pressure inside the economizer will be the same as in the deaerator or feedwater heater.

Design Features: