Fluid bed boilers

Fluiaized-Bea Boilers As explained in the earlier discussion of coal combustion equipment, the furnace of a fluid-bed boiler has a unique design. The system as a whole, however, consists mainly of standard equipment items, adapted to suit process requirements. The... 

Fluid bed boilers have also been applied as a cure to sulfur dioxide air pollution from power plants. Various schemes have been developed in which combustion of a sulfur containing fuel takes place in a fluidized bed of particles which absorb or react with sulfur dioxide. The particles are usually regenerated to recover sulfur, which often has enough by-product value to make a significant contribution to process economics. 

Cast iron sectional boilers Steel boilers Electrode boilers Steam generators Vertical shell boilers Horizontal shell boilers Watertube boilers Waste heat boilers Fluid bed boilers... 

Hawaii Napier grass, sorghum Circulating fluid-bed boilers, fermentation Power and ethanol 4856 23 ... 

There have been a great many studies of heat transfer in fluidized beds of large particles, which are important for the design of fluid-bed boilers. The maximum coefficients are lower than with type A solids, and some experiments show a gradual decrease in h with increasing dp and a minimum hat dp = 2 3 mm [28]. Extensive data are presented in books [29,30] and in the proceedings of the Engineering Foundation Conferences on Fluidization. 

Fluidized-bed combustors can be either atmospheric or pressurized (Yeager and Preston, 1986). The atmospheric type operates at normal atmospheric pressure while the pressurized type operates at pressures 6-16 times higher than normal atmospheric pressure. The pressurized fluid-bed boiler offers a higher efficiency and less waste products than the atmospheric fluid-bed boiler. There is also a circulating (entrained) bed combustor which allows for finer coal feed, better fuel mixing, higher efficiency, as weU as an increased sulfur dioxide capture. 

Over the same time period of 20 years, a tremendous progress has been made to the development of Fluidized Bed Combustion (FBC) technology, as an improved alternative to the conventional coal-fired boiler technology. By 1985 more than 160 industrial fluidized bed boilers were in operation in the Western nations with about 50 firms selling fluid bed boilers all over the world (Yerushalmi, 1986). 

TEMMINK, H.M.G. and MEULINK, J., Operating experiences with the TNO 2M X 1 M atmospheric fluid bed boiler facility. Proc. 3id European Coal Utilisation Conf., Oct. 11-13, 1983, Amsterdam, Vol. 2, 99-123. 

The gas, along with entrained ash and char particles, which are subjected to further gasification in the large space above the fluid bed, exit the gasifier at 954—1010°C. The hot gas is passed through a waste-heat boiler to recover the sensible heat, and then through a dry cyclone. SoHd particles are removed in both units. The gas is further cooled and cleaned by wet scmbbing, and if required, an electrostatic precipitator is included in the gas-treatment stream. 

St. Joe Minerals Corporation uses a fluid-bed roaster to finish the roasting at 950°C of material that has been deleaded in a modified multiple-hearth furnace operated with insufficient oxidation (34). First, sulfur is reduced from 31 to 22% and lead from 0.5 to 0.013%. Somewhat aggregated, the product is hammer-milled before final roasting. Half of the calcined product is bed overflow and special hot cyclones before the boiler remove the other half total sulfur is ca 1.5%. Boiler and precipitator dusts are higher in sulfur, lead, etc, and are separated. 

Carbonyl sulfide can be either a starting or intermediate material (108—110), or it can be used as a fluidizing gas in a carbon fluid-bed process (111). Making carbon disulfide from boiler flue gas by catalyticaHy reducing SO2 with CO to COS, and then converting COS to CS2 over an alumina catalyst has been proposed (112). 

The chamber is externally insulated and clad. Combustion equipment for solid fuel may be spreader or traveling-grate stokers or by pulverized fuel or fluid bed. Oil and gas burners may be fitted either as main or auxiliary firing equipment. The boilers will incorporate superheaters, economizers and, where necessary, air preheaters, grit arresters, and gas-cleaning equipment to meet clean air legislation. 

The deep bed, as its name implies, is similar to the shallow bed but in this case may be up to 3 meters deep in its fluidized state, making it suitable only for large boilers. Similarly, the recirculating fluid bed is only applicable to large watertube boilers. 

In the composite boiler, a watertube chamber directly connected to a single-pass shell boiler forms the combustion space housing the fluid bed. In order to fluidize the bed the fan power required would be greater than that with other forms of firing equipment. 

Anderson, B. A., and Lechner, B., Local Lateral Distribution of Heat Transfer on Tube Surface of Membrane Walls in CFB Boiler, Circ. Fluid. Bed Tech IV, 311-318 (1993)... 

Radauer, H. G., Glatzer, A., and Linzer, w., A Model Combining Convective and Radiative Heat Transfer in CFB Boilers, Circ. Fluid. Bed Tech. V, 9 (1996)... 

The Institute s primary interests, however, were the fast-bed boiler and the fluid catalytic cracker regenerator. 

Crouse, F. W., Nazemi, A. H., and Lewis, J. P. Performance Analysis of a Pressurized Circulating Fluidized Bed Boiler Combined Cycle Power Plant, Proc. Int. Conf. Fluid. Bed Combust., Volume Data 1982, 7th(l), p. 232 (1983). 

Combustion Boilers, Proc. Int. Conf. Fluid. Bed Combust., Volume Data 1982, 7th(2), p. 1136. 

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