Boiler feedwater illustration

Operators stop steam hammer by dumping either the hot condensate (from a high-pressure steam trap) or the colder condensate (from a low-pressure steam trap) to the sewer. Either way, the condensate is no longer recycled to boiler feedwater. The sort of design required to collect condensate without steam hammer is illustrated in Fig. 12.8. Basically, hot, high-pressure condensate is collected in a... 

Figure 23.8 is a schematic illustration of such a unit. It is desirable for each boiler to have its own economizer. Where one economizer is installed to take the exhaust gases from more than one boiler special considerations must be taken into account. These will include gas-tight isolation dampers. Consideration must be made of flue-gas pressures at varying loads and maximum and minimum combined heat load to match economizer and a pumped feedwater ringmain. Economizers may be used for both forced-draft and induced-draft boilers, and in both cases, the pressure drop through the economizer must be taken into account when sizing the fans. 

Most modem power plants operate on a modification of the Rankine cycle that incorporates feedwater heaters. Water from the condenser, rather than being pumped directly back to the boiler, is first heated by steam extracted from the turbine. This is normally done in several stages, with steam taken from the turbine at several intermediate states of expansion. An arrangement with four feedwater heaters is shown in Fig. 8.5. The operating conditions indicated on this figure and described in the following paragraphs are typical, and are the basis for the illustrative calculations of Example 8.2. 

The figure illustrates a simple system having medium-pressure (MP) and low-pressure (LP) steam. MP steam is consumed in a turbine having two LP-steam exhausts, and E.>. E is held at constant pressure. E may fluctuate and is always lower than that of E. Various steam consumers (boilers, heat exchangers, etc.) are connected to E -So is the first stage of feedwater deara-tion, Si, a stripper open to the atmosphere via a throttling valve. 

Benchmarking the fuel cost for steam generation is an important step in managing the steam system. For a given amount of steam production, the total fuel cost depends on boiler efficiency, steam pressure, fuel type and cost, and feedwater temperature. The benchmark can serve as a tracking tool for monitoring the boiler performance. The benchmark calculations are provided (DOE, 2012), which are briefly illustrated next. 

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