Air heaters are used in a few waste heat boilers for preheating combustion air. Incineration plants and reformer furnaces also use preheated air. Decades ago they were used in boilers that fired solid, liquid, and gaseous fuels. However, with NOx limitations for all kinds of fuels, they are now used only if the combustion of […]

Packaged fire tube boilers (Fig. 3.3) generate low pressure saturated steam, generally below 300psig. Above this pressure, the thickness of the corrugated central furnace (referred to as Morrison pipe) becomes larger and it is difficult to make the corrugations. The corrugations help to reduce the thickness of the furnace, which operates at a high metal […]

Good water chemistry is important for minimizing corrosion and the formation of scale in boilers. Steam-side cleanliness should be maintained in water tube as well as fire tube boilers. Plant engineers should do the following on a regular basis: 1. Maintain proper boiler water chemistry in the drum according to ABMA or ASME guidelines by […]

Soot blowing is often resorted to in coal-fired or heavy oil-fired boilers. In packaged boilers, both steam and air have been used as the blowing media, and both have been effective with heavy oil firing. Rotary blowers are sometimes used with distillate oil firing. Steam-blowing systems must have a minimum blowing pressure of 170-200 psig […]

Flue gas recirculation affects the oxygen in the wind-box by diluting it. One may measure the oxygen values to evaluate the FGR rate used. TABLE 3.8 Effect of FGR on Boiler Performance Load (%) 100 100 50 50 Excess air, % 15 15 15 15 FGR, % 0 15 0 15 Combustion, temp, °F 3,230 […]

Flue gas recirculation is widely used as a method of NOx control because it reduces the flame temperature and thus lowers NOx formation as discussed in Chapter 4. The effect of FGR on boiler performance is quite significant. Not only is the gas temperature profile across the boiler different, but the steam tempera­ture and gas […]

Steam generators have been fired with both distillate fuel oils and residual oils. The design of the boiler does not change much for distillate oil firing compared to gas firing. The fouling factor used is moderately higher, 0.003-0.005 ft2 h °F/Btu, compared to 0.001 ft2 h °F/Btu for gas firing; rotary soot blowers located at […]

Unlike HRSGs, packaged boilers, fortunately, do not have to deal with the issue of steaming. The reason is illustrated in Fig. 3.25, which shows the temperature FIgure 3.25 Economizer temperature pick-up in boiler versus HRSG. Profiles of the economizer of the boiler whose performance is given above and an HRSG. Because of the small ratio […]

If we look at Table 3.4 For performance of a boiler at, say, 100% load, we see that the gas temperature leaving the evaporator is 739°F and leaving the economizer it is 327°F. Now if the economizer is removed from service, can we assume that the exit gas temperature will still be 739°F? The answer […]

Plant engineers are interested in knowing how a given boiler performs at various loads. The variables affecting its performance are the fuel, amount of excess air, FGR rate, and steam parameters. Tables 3.4 And 3.7 Show how boiler performance varies with load on gas and oil firing. Figure 3.24 Shows the results in graph form. […]