Boiler continued heat recovery

Further savings can be made by the use of a suitable blowdown (BD) water flash steam and heat recovery (FSHR) system. Such systems are standard equipment on large power boilers but are less common on smaller plant. However, the FS component (and often the HR component as well) can usually be justified for smaller systems because the capital cost payback of such equipment generally is less than 12 months and such systems continue to save fuel and high-quality water year after year. 

Flash steam and heat recovery systems perform more efficiently if a continuous source of blowdown is provided. Depending on boiler pressure, the potential BW blowdown recovery is up to 25% of the blowdown volume recovered as flash steam and up to 75% of the heat content recovered. The flash steam can be passed to a LP steam line or sent back to a deaerator or feed tank, where it provides both FW heating and a replacement for MU water. 

AVT Barg BD BDHR BF BOF BOOM BOP BS W BSI BTA Btu/lb BW BWR BX CA CANDUR CDI CFH CFR CHA CHF CHZ Cl CIP CMC CMC CMC COC All-Volatile treatment bar (pressure), gravity blowdown blowdown and heat recovery system blast furnace basic oxygen furnace boiler build, own, operate, maintain balance of plant basic sediment and water British Standards Institution benzotriazole British thermal unit(s) per pound boiler water boiling water reactor base-exchange water softener cellulose acetate Canadian deuterium reactor continuous deionization critical heat flux Code of Federal Regulations cyclohexylamine critical heat-flux carbohydrazide cast iron boiler clean-in-place carboxymethylcellulose (sodium) carboxy-methylcellulose critical miscelle concentration cycle of concentration... 

The TDS content of BFW should be minimized by upstream treating. In former days, hot lime water softening was employed. In most modern process units, ion exchange resin is used to demineralize BFW. "Blowdown" is the water that is drained out of the boiler to control the accumulations of TDS or silicates in the boiler. My old design value for this flow was 10 percent of the makeup BFW flow. Two types of blowdown from a boiler are used continuous blowdown from the steam drum, and intermittent blowdown from the mud drum both will reduce silica. Note that with the continuous blowdown, heat recovery equipment may be economically justified. 

The recoveiy of heat from waste gas in a waste heat boiler involves the combined operation of two processes, however. The drawback is that the waste heat boiler has to be shut down when- ever the kiln is stopped. This must be taken into consideration in the design and operation of the boiler. On the other hand, it should be possible to continue operating the kiln in the event of a fault or shutdown of the heat recoveiy system, without any adverse effects upon the burning process in the kila In my report I want to deal more particnlarly with the recovery of heat from waste gases in waste heat boilers. And I want to point out that a waste heat boiler should be considered only if there is no other possibility of utilizing the heat. 

The most economical options for landfill gas utilization are direct uses such as process heat and boiler fuel, where the end users are in close proximity (no more thanl.6-3.2 km [1-2 miles]) from the landfill, and whose gas supply needs closely match production at the landfill. In practice, end users are infrequently located near landfills and rarely require continuous fuel in the amounts produced [16]. As of 1992, there were 21 landfills (less than 20% of total energy recovery projects) with use of landfill gas as heating fuel [17]. 

---