Circulating Fluidized Bed
Purpose
The Circulating Fluidized Bed (CFB) facility at the University of Utah is designed to study the combustion of standard fuels (coal, natural gas, fuel oil, etc.) and for waste incineration.
Physical Description
The CFB stands approximately 26 ft tall with inner and outer diameters of 10 in and 24 in respectively. It consists of five main sections: the plenum/distributor; the lower bed, the freeboard, the transition/cyclone, and the standpipe. Under circulating operation, solids are separated in the cyclone and returned to the lower bed through the standpipe with either a loopseal or L-valve. A schematic overview of the CFB and its support structure is shown below.
The CFB is designed to operate in both the circulating (fast) and bubbling bed modes. The CFB can be equipped with fuel injectors for co-firing natural gas or coal with low heating-value waste. The table below shows a range of anticipated feed rates for both natural gas and coal.
Firing Condition |
Firing Rate |
(Stoichometric Ratio) |
Fuel Rate |
Required Air Flow |
Natural Gas |
||||
Preheat |
40 |
1.2 |
2.68 |
808 |
Normal |
73.5 |
" |
4.93 |
1484 |
Maximum |
294 |
" |
19.72 |
5936 |
Coal |
||||
Normal |
73.5 |
" |
9.43 |
1557 |
Maximum |
294 |
" |
37.78 |
6230 |
The firing rates shown above represent the normal range of operation for the CFB. However the maximum fuel (coal) loading, based on a fuel/bed-material fraction of 3% and 30 second fuel residence time, would be 190.48 lb/hr of coal, for a firing rate of 672-kW. This represents the firing limit of the bed and would require indirect heat exchange both in the freeboard of the CFB and prior to entering the flue-gas exhaust ducting.
