Process for high temperature peroxide bleaching of pulp with cool discharge
First Claim
1. A process for bleaching cellulosic pulp, comprising:
- providing a stream of cellulosic pulp;
adding to the stream of cellulosic pulp at least one composition for bleaching;
bleaching the stream of cellulosic pulp in a pressure vessel at a temperature at or above about 212°
F. and the atmospheric flash point of the cellulosic pulp to form a stream of bleached cellulosic pulp;
cooling the stream of bleached cellulosic pulp prior to discharge from the pressure vessel by adding at least a portion of a cooled filtrate stream to the stream of bleached cellulosic pulp to form a cooled stream of bleached cellulosic pulp that is at a temperature below the atmospheric flash point of the bleached cellulosic pulp,dewatering the cooled stream of bleached cellulosic pulp to obtain a bleached cellulosic pulp residue stream and a hot filtrate stream; and
forming the cooled filtrate stream by cooling the hot filtrate stream.
5 Assignments
0 Petitions
Accused Products
Abstract
A process for high temperature peroxide bleaching of pulp in which pulp is retained at high temperature and pressure to increase bleaching activity but in which the pulp is cooled prior to discharge from the pressure vessel below the flash point thereby resulting in lower energy, nonviolent discharge. Through the use of a heat exchanger, the cooling of the pulp can be performed using recycled filtrate containing residual peroxide, which encourages further bleaching during atmospheric retention. The heat exchanger is also used to heat a water stream, which can be used earlier in the pulping process, resulting in cost savings because energy within the system is retained to a greater degree.
-
Citations
58 Claims
-
1. A process for bleaching cellulosic pulp, comprising:
-
providing a stream of cellulosic pulp; adding to the stream of cellulosic pulp at least one composition for bleaching; bleaching the stream of cellulosic pulp in a pressure vessel at a temperature at or above about 212°
F. and the atmospheric flash point of the cellulosic pulp to form a stream of bleached cellulosic pulp;cooling the stream of bleached cellulosic pulp prior to discharge from the pressure vessel by adding at least a portion of a cooled filtrate stream to the stream of bleached cellulosic pulp to form a cooled stream of bleached cellulosic pulp that is at a temperature below the atmospheric flash point of the bleached cellulosic pulp, dewatering the cooled stream of bleached cellulosic pulp to obtain a bleached cellulosic pulp residue stream and a hot filtrate stream; and forming the cooled filtrate stream by cooling the hot filtrate stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 56, 57, 58)
-
-
54. A process for bleaching cellulosic pulp, comprising:
-
providing a cellulosic pulp; heating the cellulosic pulp, wherein the heating comprises the steps of; injecting steam at atmospheric pressure; increasing the pressure of the cellulosic pulp to above atmospheric pressure; and injecting high pressure steam at raised pressure; adding to the cellulosic pulp at least one composition for bleaching comprising at least hydrogen peroxide; mixing the at least one composition and cellulosic pulp; retaining the cellulosic pulp in a pressure vessel in a pressurized state at or above about 212°
F. and the atmospheric flash point of the cellulosic pulp;cooling the cellulosic pulp prior to discharge from the pressure vessel to a temperature below the atmospheric flash point of the cellulosic pulp using a cooled filtrate; discharging the cellulosic pulp to a substantially reduced pressure; retaining the cellulosic pulp at said reduced pressure; further diluting the cellulosic pulp using the cooled filtrate; dewatering the cellulosic pulp with a press to obtain a dewatered cellulosic pulp and a hot filtrate; clarifying the hot filtrate; cooling the hot filtrate using a heat exchanger to obtain the cooled filtrate; recycling the cooled filtrate for use in cooling and diluting the cellulosic pulp; heating a process water stream with heat obtained from the heat exchanger; and recycling the heated process water stream.
-
-
55. A process for bleaching cellulosic pulp, comprising:
-
providing a cellulosic pulp; thickening the cellulosic pulp using a disk thickener; further thickening the cellulosic pulp using a press; after thickening the cellulosic pulp, diluting and heating the cellulosic pulp using a recycled hot filtrate; further heating the cellulosic pulp, wherein the heating comprises the steps of; injecting low pressure steam at atmospheric pressure; increasing the pressure of the cellulosic pulp to above atmospheric pressure; and injecting high pressure steam at raised pressure; adding to the cellulosic pulp at least one composition for bleaching comprising hydrogen peroxide; mixing the at least one composition and the cellulosic pulp; retaining the cellulosic pulp in a pressure vessel in a pressurized state; bleaching the cellulosic pulp in the pressurized state at a temperature at or above about 212°
F. and the atmospheric flash point of the cellulosic pulp;cooling the cellulosic pulp prior to discharge from the pressure vessel to a temperature below the atmospheric flash point of the cellulosic pulp using a cooled filtrate; discharging the cellulosic pulp to atmospheric pressure; retaining the cellulosic pulp at atmospheric pressure; further diluting the cellulosic pulp using the cooled filtrate; dewatering the cellulosic pulp with a press to obtain a dewatered cellulosic pulp and a hot filtrate; clarifying the hot filtrate; recycling a portion of the hot filtrate for use in diluting and heating the cellulosic pulp; cooling the non-recycled hot filtrate using a heat exchanger to obtain the cooled filtrate; recycling the cooled filtrate for use in cooling and diluting the cellulosic pulp; heating a process water stream with heat obtained from the heat exchanger; and recycling the heated process water stream.
-
Specification