PRODUCTION OF HYDROCARBONS FROM FAST PYROLYSIS OF KRAFT BLACK LIQUOR: INTEGRATION WITH A KRAFT MILL

A proprietary thermochemical process, trade-named Emerald Process [1], is being developed for producing chemical feedstock from Kraft black liquor through fast pyrolysis, catalytic upgrading, and separation. The objective of this process is to leverage the harvesting and processing infrastructure of the modern Kraft mill to produce chemical feedstocks in large quantity in addition to cellulose. Integration of the new process with existing and new Kraft mills is key to obtaining maximum economic synergy. In the proposed process, the fast pyrolysis step takes place in a fluidized bed, where part of the high-solids Kraft black liquor stream is pyrolyzed. The fine droplets of heavy black liquor coat the solid particles in the circulating bed, while a fluidizable char with favourable particle size distribution and friability is produced in the bed. A small portion of the char particles, separated by cyclones, is oxidized in a solids heater and returned to the pyrolysis reactor to supply the heat required for drying, heating, and pyrolysis. The balance of the char, also containing the bulk of the inorganics, is reintroduced to the black liquor for recovery in a Tomlinson furnace to maintain the chemical balance and support both chemical reduction and steam production in the boiler. The raw pyrolysis gas is upgraded in a catalytic reactor to improve the bio-oil yield of aromatics. After separation of the upgraded hydrocarbon product, the non-condensable gases are returned to the recovery boiler. Following a summary of results with a 10-cm-diameter fluidized-bed system, this paper will present mass and energy flows for a modern Kraft mill using the new process and discuss the implications for new mill design and char firing methods in the recovery boiler. An assessment of the economic and environmental merits of this process will be presented.