Second-Generation Pressurized Fluidized Bed Combustion Research and Development

A team of companies, led by Foster Wheeler Development Corporation (FWDC) and consisting of Gilbeni Commonwealth, Institute of Gas Technology, the Power Generation Business Unit of Westinghouse Electric Corporation, and the Science & Technology Center of Westinghouse Electric Corporation has been developing an advanced second-age D. Crittion pressurized fluidized-bed combustion system. A carbonizer is an essential element of this system. The primary responsibility of IGT in this program was to develop a carbonizer model for scale-up which initially utilized data available in the literature and was subsequently updated with actual data generated in the carbonizer pilot plant during the component testing. Prior to the carbonizer pilot plant testing at FWDC, an extensive literature search was conducted, and correlations were developed for predicting yields of various species as a function of coal properties and carbonizer operating parameters. Based on these correlations. a computer model for the carbonizer was developed. This model could simulate a bubbling or a circulating fluidized-bed reactor with or without fines recycle in which the coal and ambient could be introduced into the fluidized-bed region and/or into the freeboard region of the carbonizer. During the period beginning November 1991 and ending September 1992, a series of tests were conducted at FWDC in a fluidized..bed coal carbonizer to determine its performance characteristics. The carbonizer was operated for 533 hours in a jetting fluidized-bed configuration during which 36 set points (steady-state periods) were achieved. Testing was completed with four different fuels, namely, Pittsburgh No.8 bituminous coal, Illinois No.6 bituminous coal, Wyoming Eagle Butte subbituminous coal, and petroleum coke; a total of 83 tons of feedstock was consumed. In addition, an exploratory carbonizer test in a circulating fluidized-bed configuration entailing four set points and 9.9 tons of two different fuels (Pittsburgh No.8 bituminous coal and petroleum coke) was completed. Sorbent (dolomite or limestone) was also fed to the carbonizer during each of the set points to capture sulfur. Extensive data were collected on the feed and product stream compositions, heating values, temperatures, and flow rates. With this data, elemental and energy balances were computed to evaluate and confirm the accuracy of the data. The carbonizer data were not as self-consistent as could be desired (balance closure imperfection). A software package, called BALAID, bas been developed by Science Ventures, Inc., of California. which reconciles the data by applying conservation laws and other equality and inequality constraints. Adjustments are made to all the species flows, temperatures, and variable species compositions with the adjustments weighted according to the statistical variance of each variable. A maximum-likelihood set of reconciled values is computed in which all the elemental and energy balances close exactly. This approach takes advantage of all the available measurement information as well as information embodied in the conservation laws and in the estimated quality of the measurements. The program utilizes advanced principles in statistics. numerical techniques. and constrained nonlinear optimization theory. This program was successfully applied to reconcile the carbonizer data. The reconciled data for the carbonizer. \\oillie operating in the jetting fluidized-bed configuration were rigorously analyzed, correlations were developed.. and the model was updated accordingly. The model was then used for simulating each of the 36 early-state periods achieved in the pilot plant. Any correlations were also developed that were not in the forms present in the existing model. Incorporation of these new correlations m the model would have required significant changes in the computer code. and Would have required additional resources. These correlations. if incorporated into the model. could have improved its predictive capabilities.

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