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Show Page 6. The particle size of solid fuel or effluent which may be fed into a normal fluidized bed is usually not larger than 1/4" In a spouted fluid bed the maintained velocity of the large jets of air renders them capable of su~porting and burning particles larger than 3/4" to the top of the inverted cone. The solid fuel type availability is, therefore, greatly widened. The air jets are also capable of disintegrating sludges and slurries which may be fed diIectly into the bed near the spout nozzles, or, alternatively, arrive there by recirculation. Operating Hodes The SFBC can be operated either as a thermal oxidizer or as a pyrolizing gasifier. The adiabatic oxidation, a waste material must have a minimum actual heat value of 4000 BTU/lb. Below that, auxiliary fuel addition will be necessary. For gasification, a minimum actual waste heat value of 6500 BTU/lb is necessary. Fluidizing air preheat, superheated steam or oxygen enrichment can be applied to improve gas quality. Other operating process variables are bed temperature, bed loading, bed depth, type of fluidizing material, chemical addition to the bed to absorb harmful effluents and overbed air. Design variables include: mean bed velocity, freeboard velocity, residence time, size and number of spouts, turndown capability. Pilot plant testing may be necessary to optimize process and design variables. Emissions With the exception of particulates, the SFBC is an inherently low producer of harmful emissions such as CO, HmCn, NOx, and SOx (with limestone additon). Halogenated wastes require downstream scrubbing and almost every application will need particulate removal such as venturi scrubber, bag filter or electrostatic precipitator. Capital Payback Energy costs today vary from a low of $2.00/HH BTU to a high of $6.00/MH BTU. Using an average of $4.00/HH and a minimum on stream time of 6000 hrs/yr, everyone million BTU/hr saved is worth $24,OOO/yr. Disposal costs by landfill or commercially operated incinerator vary widely according to the type of waste, transportation distances, quantities and handling problems. Assuming a non-hazardous, organic sludge, pumpable, with an actual heating value of 5000 BTU/lb and a disposal cost of .25/cents/lb. |
