An Assessment of Black Liquor Gasification Combined Cycles: Part A — Technological Issues and Performance Comparisons

Abstract

Black liquor gasification (BLG) technologies are under active commercial development in the United States and Europe. BLG has been proposed as a future replacement for Tomlinson boilers to provide more efficient, safer, environmentally-friendlier, and more cost-competitive chemical and energy recovery at kraft pulp and paper mills. Also, some pulping process improvements are more readily implemented with BLG than with black liquor combustion. This is Part A of a two-part paper summarizing results of a large study supported by the US Department of Energy, the American Forest and Paper Association, the Southern Company, and the Tennessee Valley Authority to assess performances, emissions, costs and overall benefits of black liquor gasification combined cycle (BLGCC) technology for the U.S. kraft pulp and paper industry. Part A discusses the status of leading black liquor gasification technologies and presents detailed mass and energy balances for BLGCC integrated with a pulp and paper mill producing 1725 metric tons per day of uncoated freesheet paper. The corresponding nominal flow of black liquor solids is 6 million 1bs/day (or 438 MW of contained energy). Mass and energy balances are also presented at a comparable level of detail for state-of-the-art and advanced Tomlinson systems. Tomlinson performances are compared with that for three BLGCC configurations: (i) low-temperature, indirectly-heated gasifier coupled with a medium-power output heavy-duty gas turbine; (ii) high-temperature, oxygen-blown gasifier coupled with a medium-power output gas turbine; (iii) same high-temperature gasifier coupled with a utility-scale gas turbine, where the extra fuel input required to fully load the gas turbine is supplied by natural gas. With state-of-the-art Tomlinson technology, the integrated mill must import approximately 36 MW from the electric grid, which can be reduced to 11.5 MW with an advanced Tomlinson design. Medium-scale BLGCC allows export of 15–20 MW to the grid. This increases to 125 MW when the gasifier is coupled to the utility-scale gas turbine. The superior thermodynamic features of BLGCC are evidenced by the high ratio (0.5–0.9) of extra electricity generated by the BLGCC to extra fossil fuel purchased (higher heating value basis).