| 摘要 |
Black liquor from a cellulose pulp processing plant is treated, including by using a direct contact (cascade) evaporator, without need for oxidizing the black liquor, without substantial sulphur emissions at the cascade evaporator, and by maximizing the solids content of the black liquor so that the loss of heating value of the black liquor is minimized. The black liquor is heated under temperature and time conditions sufficient to drive off most of the organic sulphur compounds as off gases, which gases are converted primarily to methane and hydrogen sulfide, with the methane separated by selective absorption in white liquor. The black liquor is then stripped of most remaining sulfur by bringing it into stripping contact with flue gases from the recovery boiler, the flue gases taken from downstream of the direct contact evaporator. After stripping, the solids content of the black liquor is increased (as by passing it to another evaporator), then it is led into association with the cascade evaporator, and then passed into the recovery boiler where it is combusted. The sulphur constituents of the off gases from the stripping operation are also passed into contact with white liquor.
|
