Pulverized fuel firing involves a distinct milling plant and firing equipment. Milling deals with size reduction, while firing relates to combustion. 1. The milling plant consists of A. Feeders to feed coal from bunkers to mills or pulverizers B. Mills to grind the crushed coal C. Pipes to transport the ground coal to burners 2. […]

Pulverized fuel (PF) firing is the most dominant type because of its great versatility and scalability. Since coal and lignites are the most competitive fuels in large parts of the world, the growth and dominance of PF firing for the last eight decades has almost been unassail­able. The bulk of power generation has been and […]

Developed in France in the 1950s and patented as Ignifluid technology, these boilers gained a rapid acceptance after the oil crisis in the 1970s and 1980s. Although the other FBC boilers were still under development, this type of fluidized bed boiler was fully ready and in use across the globe. Ignifluid technology can be considered […]

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 […]

Process The classical or the full-circulation CFBC process involves • Operating at higher velocities of —4 to 7 m/s • Using high ash recirculation for uniform temperature profile • Controlling the combustor temperature near optimum desulfurization temperature • Employing staged combustion to limit NOx • Releasing high heat rates in plant areas closer to PF […]

Process Figure 12.5 depicts a typical underfeed bubbling bed boiler. There is a bottom/grid/distribu­tion plate consisting of sand/ash and fuel. Evenly spaced air and fuel nozzles as well as ash nozzles for ash discharge are attached to the bottom plate. After preheating, air is admit­ted to fluidize the bed, followed by the fuel feeding. The […]

Characteristics of FBC Boiler • Combustibles form only —3% of bed material, and the remainder consists of fuel ash, inerts, and limestone (if used). • In high-ash applications, usually with ash >15% in the fuel, no inert material addi­tion may be required to stabilize the bed, as the fuel ash is sufficient to replenish the […]

FBC are available in bubbling, circulating, and expanding bed (which is in between) types, depending on the in-bed gas velocity and mean particle size. Each of the systems is separately described after the following discussion on the fundamentals of fluidization technique. Fluidization When gas is passed through a chamber with a bed of solids resting […]

Fluidized bed combustion (FBC) is burning of various solid fuels in the fluidized state—a condition where a gas-solid mixture behaves like a free-flowing fluid. Mass burning (MB) and traveling grate (TG) stokers burn solid fuel in static mode with the fuel resting on a grate, whereas pulverized fuel (PF) firing burns the fuel in suspension […]

The big stoker market today focuses on bagasse, wood, and biofuel firing, with coal firing having gone to the industrial boiler market. Bagasse-fired boilers for process and cogen have capacities as large as 250 tph and pressures reaching 130 bar and temperatures of 540°C. Similarly wood-firing in cold climates has been employing large stoker-fired boil­ers. […]