Cyclone-Fired System

Cyclone furnaces are not without disadvantages. The coal used must have a relatively low-sulfur content in order for most of the ash to melt for collection. In addition, high-powered fans are required to move the larger coal pieces and air forcefully through the furnace, and more nitrogen oxide pollutants are produced compared with PCC. Finally, the actual burner requires yearly replacement of its liners due to the erosion caused by the high velocity of the coal. 

A crushed coal feedstock having 95% of 5 pm size is typical. Combustion temperature in the external cyclone furnaces can be anything from 1650°C to over 2000°C (3000°F to 3630°F). In addition, cyclone-fired boilers are suitable for coals with 

The cyclone furnace chambers are mounted outside the main boiler shell, which will have a narrow (or tapered) base, together with an arrangement for slag removal. 

Larger particles are trapped in the molten and sticky layer that covers the entire surface of the cyclone interior, except for the area in front of the air inlets. The coal is fired under conditions of intense heat input, and while the finest particles may pass through the vortex in the center, the larger ones are thrown toward the walls and are recirculated to achieve adequate burnout. 

The combustion gases, residual char, and fly ash pass into a boiler chamber where burnout is completed and there are various stages of heat exchange and heat recovery, producing steam to drive the turbine and generator. As a result of the intense combustion conditions, nitrogen oxide (NOx) formation tends to be considerably higher than in a pulverized coal combustor. 

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Because most of the ash is removed as molten slag, addition of a bottom grate is not necessary.7 However, small TDF is required, because much of the combustion must occur in suspension.7 TDF that is too large to combust completely can get carried over into the boiler or dust collection system, and cause blockage problems.9 Therefore, particle size may inversely determine the amount of TDF that can be used in a cyclone boiler.11 Three cyclone-fired boilers at utilities have burned 1M x 1" TDF in test operation, one at the 2 percent, one at the 5 percent, and one at up to a 10 percent level.3,9,12 One pulp and paper mill plans the use of TDF in a cyclone-fired hog-fuel boiler.13... 

Manter, ])., and R. Tressler A Coal-Air Ratio Control System for a Cyclone Fired Steam Generator, ISA Paper l-CI-61. 

Drying rotary oil- or gas-fired Particulates, SO2, NO, VOC, CO, and smoke Proper combustion controls, fuel-oil preheating where required local exhaust system, cyclone and a scrubber or baghouse... 

Introduction and Statement of Problem. Current techniques to remove particulates in coal fired power plant flues are based on electrostatic precipitators, bag houses, cyclones and wet scrubbers. Typical collection efficiencies of such devices and the far less efficient cyclones are shown in Figure 1 (J,). Of interest is the fact that below 1 micrometer the efficiencies drop off rather precipitously. Work presented by Davies ( ), Figure 2, has shown that the human lower pulmonary system is unfortunately most efficient in absorbing and retaining particles in the 1 micrometer range. These particles are the primary cause of such respiratory ailments as bronchitis, emphysema and lung cancer. 

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