Performance and Preliminary Economics of Black Liquor Gasification . . Combined Cycles for a Range of Kraft Pulp Mill Sizes

The design of a black liquor gasification/combined cycle (BLGCC) power/recovery system requires the selection of a specific gas turbine. There are many different models from which to choose, but with only a fixed set of output ranges that are determined primarily by original design decisions relating to aircraft applications. A perfect match between the fuel requirement of a gas turbine and the fuel that can be generated by gasifying the black liquor available at a kraft mill will be rare. This paper examines the performance and prospective economics of BLGCC systems involving a fixed-size gas turbine at mills with black liquor processing rates corresponding to mill production rates of 500 to 2000 air-dry metric tonnes per day of pulp. Detailed predictions of powerhouse thermodynamic performance are coupled with cost estimates for BLGCC powerhouses (assuming the technology has reached commercially-mature costs) and Tomlinson powerhouses developed with input from the Bechtel Corporation. The analysis indicates that (i) powerhouse capital investment requirements per unit of black liquor processed for BLGCC systems are comparable to those for new Tomlinson systems across the range of mill sizes considered, (ii) the annualized cost (including O&M, fuel, and capital charges) will be higher for a BLGCC system than for a new Tomlinson ~'ystem, but the higher value of the electricity produced, even at an electricity price as low as 3 ~/kWh, will far outweigh the added cost, and (iii) the incremental economics of a BLGCC powerhouse relative to a new Tomlinson powerhouse are optimized when the gas turbine is sized to match the mills' black liquor throughput.