Method for treating liquid flows at a chemical pulp mill
First Claim
1. A method of treating liquid flows at a chemical pulp mill comprising:
- alkaline cooking to produce brown stock pulp,washing the produced brown stock pulp using successive essentially closed liquid cycles, which include a last liquid cycle, wherein wash liquid flows through the liquid cycles counter-currently to the flow of the brown stock pulp through the successive essentially closed liquid cycles;
bleaching the washed brown stock pulp in a pulp bleaching plant using ECF-bleaching, in which chloride-containing effluents are formed,treating the chloride-containing effluents with a biological agent to reduce organic matter in the chloride-containing effluents,returning at least twenty percent (20%) of the treated chloride-containing effluents flow to the pulp mill, wherein at least a portion of the returned treated chloride-containing effluents are used as wash liquid in the last liquid cycle of the brown stock pulp washing step, andwash liquid effluent from the successive essentially closed liquid cycles is treated in a recovery boiler which separates chlorides from the wash liquid effluent.
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Accused Products
Abstract
A method for treating liquid flows at a chemical pulp mill including at least an alkaline cooking process for producing pulp, brown stock treatment with essentially closed liquid cycles, a pulp bleaching plant using ECF-bleaching, a chemical recovery plant comprising a chemical recovery boiler, and effluent purification. Chloride-containing bleaching plant effluents are led to the effluent purification, where they are treated in order to decrease the organic matter content thereof. At least 20% of the purified effluent is returned to a pulp mill process and purified effluent is used in a last washing stage included in brown stock treatment. In the brown stock treatment the liquid flow is passed counter-currently to evaporation, wherefrom it is led for treatment to a recovery boiler process, wherein a separation process for chlorides is arranged for controlling the chloride level of the liquor cycle.
13 Citations
19 Claims
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1. A method of treating liquid flows at a chemical pulp mill comprising:
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alkaline cooking to produce brown stock pulp, washing the produced brown stock pulp using successive essentially closed liquid cycles, which include a last liquid cycle, wherein wash liquid flows through the liquid cycles counter-currently to the flow of the brown stock pulp through the successive essentially closed liquid cycles; bleaching the washed brown stock pulp in a pulp bleaching plant using ECF-bleaching, in which chloride-containing effluents are formed, treating the chloride-containing effluents with a biological agent to reduce organic matter in the chloride-containing effluents, returning at least twenty percent (20%) of the treated chloride-containing effluents flow to the pulp mill, wherein at least a portion of the returned treated chloride-containing effluents are used as wash liquid in the last liquid cycle of the brown stock pulp washing step, and wash liquid effluent from the successive essentially closed liquid cycles is treated in a recovery boiler which separates chlorides from the wash liquid effluent. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A method of treating liquid flows at a chemical pulp mill comprising:
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alkaline cooking of cellulosic material to produce brown stock pulp, washing the produced brown stock pulp in a succession of closed liquid wash cycles, wherein wash liquid flows through the wash cycles in a counter-current direction to a flow direction of the produced brown stock pulp through the wash cycles; bleaching the washed brown stock pulp in a pulp bleaching plant using ECF-bleaching and discharging chloride-containing effluent formed during bleaching; purifying the discharged chloride-containing effluent with a biological agent to reduce organic matter in the chloride-containing effluent to produce a reduced chloride-containing effluent, and returning at least a portion of the reduced chloride-containing effluent as the wash liquid for a last wash cycle of the wash cycles.
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Specification