Full-circulation, hot cyclone, and compact-type CFBC boilers are the only designs that have accumulated adequate references and data. For utility applications, these are the only acceptable configurations. Other technologies have not managed to move into this space.

Although very large boilers of 460 MW are built to even supercritical (SC) conditions, most references pertain to fuels that are difficult to burn in PF, such as petroleum coke,

Peat, and anthracite, or combination fuels such as coal with lignite, wood waste, pith, and so on. More difficult environmental conditions have helped CFBC boilers become the boilers of choice.

Figure 12.32 traces the growth of CFBC technology over the years. Although it is specific to FWC it represents the general pattern.

A typical 125 MW boiler unit for lignite is shown in Figure 12.33. This is a hot cyclone design with one cyclone on either side. The next major size was 250 MW where the furnace was designed in a pant-leg fashion adopted in designs of larger boilers. There are two cyclones on either side of the boiler (Figure 12.34).

Several utility boilers have been built by FWC. The largest compact boiler is for 460 MWe in Poland, using coal, coal slurry, and biomass as fuels and employing, for the first time, SC conditions in CFBC. This unit is designed to generate main and reheat steam at

• 370/307 kg/s (1332/1105 tph)

• 27.5/5.5 MPa (280.5/5.6 kg/cm2)

• 565/580°C from feed water temperature (FWT) at 290°C

The boiler employs four sets of compact separators on either side, as shown in Figure 12.35.