OCR Text |
Show into specific shaped- charge fuel with venting holes. The shaped-charge fuel is then burnt in an oven under automatically-controlled optimum temperature and reaction rate to achieve complete combustion into CO 2 with negligible production of undesirable CO, NO , SO , and micro flyash. In this new system, the heat x x transfer rate between the burning fuel and the heat exchanger is controlled by the forced recjrculation rate of the flue gas. The temperature of combustion is automatically maintained at a constant temperature of 1000 o C by reguJating the O 2 or air inflow rate. Indeed, this will be the first time that the combustion of solid fuels is subjected to full automatic control to achieve the optimum combustion characteristic. This technique of combustion is not only suitable for small scale home-heating but also for large scale power-generating systems. Furthermore, most difficulties associated with the present technology of burning fine pulverized-coal are eliminated. TECHNICAL CONSIDERATIONS The explosive nature of combustion for micro-fuel particles is due to the effect of a very large available reaction surface per unit mass. Under this mode of combustion, the burning process takes place in milliseconds which results in a runaway temperature reaching over 2000 o C. Under such a temperature the combustion product is mainly CO instead of CO 2 , Consequently, a large power plant requires a mammoth combustion chamber to provide sufficient resident time for the CO gas to complete a secondary combustion into CO 2 at a lower temperature of 10000 C. Additionally, the high initial temperature of combustion promotes the production of undesirable NO x and SO x gases. A large amount of micro flyash is also produced and tends to accumulate quickly over the surface of heat exchangers, thus negating any advantages associated with a high combustion temperature. In fact, the acid rain problem relating to the runaway combustion temperature is now a serious environmental problem that is crying out for immediate solution. Unfortunately, the present trend of development is still towards the combustion of ever finer particles and ever faster combustion rate, leaving the air pollution problems to be solved as an after thought. Although combustion of atomized fuels is considered to be simple from a hardware point of view, there are no easy solutions in sight to ameliorate the associated undesirable features. Therefore, one is led to reexamine the old subject of flatbed combustion to see if it can be improved for better combustion characteristics. In the past, solid fuel was burnt in a flat bed with random stacking of coal blocks. Combustion took place between the interstices of the blocks. Because of random stacking, many interstices were blocked or too narrow. This resulted in 2 |