Simulation of Kraft Black Liquor Gasification - A Comparative Look at Performance and Economics, 2001 Engineering / Finishing & Converting Conference Proceedings

J. Cantrell--The Tomlinson recovery boiler is the current conventional technology for recovering cooking chemicals and energy from black liquor. Air-blown pressurized black liquor gasification with combined cycle represents one of several gasification-based technologies that offers future promise as a replacement for the Tomlinson recovery boiler. The focus of this study is to compare air-blown gasification with combined cycle technology directly to that of the Tomlinson recovery boiler. Hence, the study scope is limited to a gasification island based on a 70 MW gas turbine and heat recovery steam generator that matches the process steam output of a Tomlinson recovery boiler for a mill producing 1300 mtpd of oven-dry pulp. Process data, needed for the performance and economic comparisons, came from simulation runs using the CADSIM Plus process simulation platform.

Air-blown high temperature black liquor gasification with combine cycle (BLGCC) requires about 22% additional heat input to achieve the same process steam requirements as the Tomlinson recovery boiler. The air-blown BLGCC net power output is 2.5 times the output of the Tomlinson system. Air-blown BLGCC has a slight overall efficiency advantage over the Tomlinson recovery boiler (64% vs. 62% based on the simulation results presented in this paper). Preliminary economics show that air-blown pressurized BLGCC becomes more economically feasible when compared to a new recovery boiler installation. A major rebuild generally does not provide enough economic incentive for BLGCC unless the rebuild costs are substantial (>$150 per annual metric ton) or unless purchased power costs are high (>4.5¢ per kWh). In the case of a recovery boiler replacement, air-blown BLGCC can offer a very attractive incremental rate of return, although learning curve risk factors can potentially reduce this return.