Petroleum coke is quickly becoming the fuel of choice for many FBC boiler operators, due to its low cost, high availability and high heating value. However, these inherent benefits come with a price, as the high sulfur content of coke requires limestone use as a sorbent for sulfur capture. In some cases, operational problems associated with limestone use have arisen. Fouling, in terms of solid deposits in such boilers are normally thought to occur as a result of interaction with various fuel-ash-derived species within the system. However, detailed examination of the solid deposits demonstrated that the fouling was, most generally, associated with an aggomeration mechanism we have called extended sulfation, i.e., sulfation to near quantitative levels of the limestone sorbent. Carbonation and hydration have also been found to play a role in the agglomeration process at lower temperatures. This paper describes the fouling mechanisms in three circulating fluidized bed boilers firing petroleum coke as the only fuel.
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