Multi-cyclones

Based on the experience of these 75 t/h boilers, a 220 t/h CFBC boiler has been designed and is now being fabricated. A two-stage channel separator, as shown in Fig. 39, is used on these CFBC boilers. This is followed by multi-cyclones. By using this combination of gas-solid separators, and with fly ash reburn, the combustion efficiency has reached 97.5% for a 12,000-kJ/kg low-grade coal. 

For particle cleanup cyclones, impact separators, fabric and fiber filters, granular beds, and electrostatic percipitators for low-temperature gas cleaning have been widely used in the industry. However, for hot gas filtration with ceramic filters, the long-term durability, alkali corrosion, cleanability, thermal shock, and particulate penetration into filter media has been recognized as major concerns. Traditional bag filters are sensitive to high ten erature and hot particles, electrostatic percipitators have a relatively high cost of installation in smaller plants and multi-cyclone cleaners are not sufficiently efficient to meet the new purification demands. 

Inorganic coarse material goes down and accumulates at the bottom of the reactors, then is discharged periodically through the bottom valves. Fine inorganic particles such as ash are exhausted with the flue gas from the top of the regenerator and are caught by the multi-cyclone and electrostatic precipitator. 

Ash. Two kinds of ash are discharged by this process. One of them is coarse inorganic matter which is taken from the bottom of the reactors, the other one is fine particle ash discharged from the multi-cyclone and the EP. The coarse material contains very little organic material because it remains in the reactors for a long time. Organic or combustible matter in fine ash is also small. It is less than two-percent as shown in Table-VII. 

In the quarrying process, drilling is the main potential source of dust. The air carrying pulverised rock up the hole may be de-dusted using multi-cyclones, but the use of bag filters is the preferred control method. The collected dust should be disposed to tip in sealed bags, or should be wetted to avoid its becoming air-borne when blasting. 

The raw coal (10% or lower surface water content, 5-50 mm particle size) is preliminarily dried in a rotary dryer. The gas exhausted from the dryer passes through a multi-cyclone to remove the dust before venting the gas to the atmosphere. The most efficient process for carbonizing semicoke and one that retains approximately 20% of the volatile matter in the semicoke is the internal-heating, low-temperature fluidized-bed carbonization furnace (Chapter 16). 

Multi-cyclones occupy less space on plan than multiple cyclones of equal performance. Besides, because of their small diameter the individual cyclones achieve more powerful centrifugal action and thus attain higher efficiencies. In... 

Both reactor types are quite complicated firom a construction tube bundles in both reactor types have to be constructed to temperature variations that occur when the process is started, reactor requires a special distributor, and multi-cyclones catalyst in the bed. The tubular reactor requires a support each pipe. Nevertheless both reactor types find wide application Here we shall consider the fixed bed reactor with wall cooling, cooling causes radial temperature gradients, that in its... 

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