Black liquor gasification. Consequences for pulping process and energy balance.

摘要

An investigation has been made with the aim to describe black liquor gasification processes and their effects in the kraft mill, the potential for increased electrical power production and requirements for research and development. There are two types of liquor gasification processes. Liquor gasification at high temperature, above 850 deg C, gives sodium sulphide carbonate smelt/green liquor and reduced gas as main products. An example is the Chemrec process. Liquor gasification at low temperature, below 800 deg C, gives sodium carbonate in solid form and reduced gas, i.a. with all sulphur in the form of H(sub 2)S. Examples are the MTCI process and ABB's process. The latter allows the handling of sulphur and sodium in separate streams. Consequently, there is a possibility for advanced modified kraft pulp cooking in two stages, with one high sulphidity and one low sulphidity liquor. More research is needed regarding the liquor gasification processes themselves, such as black liquor properties and -atomization, the chemistry of liquor gasification and alkali gasification/dust formation. Studies of pressurized black liquor gasification and energy and heat systems, both combined and hybrid systems need to be undertaken. Electric power production in a kraft pulp mill is estimated to become 1400-1600 kWh per tonne pulp, compared to a conventional system 1200-1300 kWh ptp. The former production figure could be increased by extending gas turbine, boiler and steam system efficiencies to their technical potential, according to the KTH studies. A future integrated pulp and paper mill can, with margin, be supplied with heat and electricity through this type of liquor and energy recovery.