Black Liquor Gasification: Evaluation of Past Experience in Order to Define the Roadmap of the Future Pathway, 2002 Fall Technical Conference

2002 TAPPI Fall Conference & Trade Fair September 8 - 11, 2002 San Diego, CA Abstract A number of promising black liquor gasification (BLG) technologies have been evaluated from bench scale to demonstration unit testing over the last two decades with somewhat encouraging results, however with a number of process limitations. The most well known and documented process systems include those based upon steam reforming with indirect heating and entrained flow gasifier design. Two additional promising technologies include the pressurized circulating fluidized bed and perhaps the spouting fluidized bed design.

Key design characteristics, technological challenges, process concerns, benefits and a potential future BLG process configuration will be discussed for several of what should be termed developmental gasification technologies. Oxygen or air blown, pressurized black liquor gasification, with combined cycle (BLGCC) energy recovery, may begin to replace Tomlinson styled recovery boilers in the next four to eight years. This timing will depend upon development strategies, the cost of power, government based financial incentives and key consortium support from major utility and forest products companies. The potential applicability of BLGCC incremental power generation to renewable energy incentives and voluntary emission reduction incentives, noted in the new energy bill, would be very attractive possibilities.

Operation of a circulating bed, pressurized Transport Reactor, shows particular promise as a key element of an efficient BLGCC process system. The use of an amphoteric compound, such as modified rutile titanium dioxide has the potential to allow both high operating temperature, >950 °C, while avoiding sodium compound smelting, creating opportunities for direct causticization by continuous removal, slaking and re-injection of circulating media. Gasification temperatures noted, in combination with sufficient reactor retention time, would also be fundamental for minimization of organic tars content in generated syn-gas.

Subsequent hot fuel gas processing with recovery of elemental sulfur allows generation of clean fuel gas, without troublesome condensates, rich in organic tars. Use of hot fuel gas desulfurization, enables opportunities for heat recovery options not open to the process systems of other technologies. High temperature waste heat recovery improves process efficiency and economics.