The revamping of aged boilers by replacing major portions of them with new, more-efficient equipment is not a new phenomenon. In the past, retrofits and upgrades were spread out over several years to meet specified capital budgets governed by regulated rates of return. Pollution from hundreds of aging coal-fired power plants in China is a major threat to global warming as well as to the world's environment. Increasing energy efficiency and reducing atmospheric pollution are the two major tasks of Chinese government policy. China started to shut down small size coal fired boilers a few years ago because of their low efficiency and high pollution. Building new power plants with pollution controls is an obvious way to reach the power objective, however the initial investment is very high and it is difficult for a developing country like China to undertake. As an alternative a good choice would be to revamp old coal-fired boilers so as to increase their efficiency and reduce gaseous emission at lower cost compared to building a new boiler. Revamping old boiler with clean coal combustion technology is developing in China, as the requirement on emissions became stricter and stricter. Several revamping designs are presented and compared for a 50 ton/hr old coal-fired boiler. The old pulverized combustion boiler was retrofitted to a circulating fluidized bed boiler with its high combustion efficient and low emissions. Technically, selection of separator and recycle system is the key in the revamping process. Revamping designs including two-stage separators, high temperature cyclone, high temperature square cyclone and horizontal heat exchanger square cyclone plans are presented. Advantages and disadvantages of those plans are compared. Several key components such as a separator, an ash cooler and an external heat exchanger, used in revamping designs are also discussed.
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