The operation of alkali recovery and middle stage

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The operation experience of wheat straw pulp alkali recovery and middle stage water treatment system of Huatai Group

● the production test undertaking unit of the national "Ninth Five Year Plan" key research project "research and development of wheat straw pulp black liquor alkali recovery technology"

● the "model project" of pollution control promoted by the State Economic and Trade Commission and the State Environmental Protection Administration to the whole country

● wheat straw pulp black liquor alkali recovery not only has environmental benefits, but also realizes profits

● the middle stage water meets the discharge standard, and the treatment cost is only 0 6 yuan/m3

Xu Shoufu, deputy editor of Huatai people, special appointment of this magazine. Abstract: Based on the first set of 100t/d alkali recovery and 40000 m3/d middle water treatment projects, Huatai Group has built the second set of 160t/d alkali recovery and 60000 m3/D middle water treatment projects. This paper mainly introduces the technological process, technical equipment, progressiveness, production and operation experience of the second set of new projects

key words: wheat straw pulp black liquor; Alkali recovery; Combustion method; Middle water; Aerobic biochemical technology; Technical equipment; improvement; Operating experience

Huatai Group is a national super large enterprise with an annual output of 400000 tons of machine-made paper and paperboard. In 2001, its sales revenue reached 1.1 billion yuan, profit and tax 255 million yuan, and its economic benefits achieved stable and sustained growth. While accelerating the development of the enterprise, based on the sustainable development of the enterprise, we always regard pollution control as the "Life Project" of the enterprise, and actively introduce new technologies, new processes and new equipment. Its alkali recovery project and middle water treatment project have been promoted nationwide as "model projects" by the Ministry of science and technology, the former Light Industry Bureau, the State Environmental Protection Administration and other departments

in 1995, a total investment of 50million yuan was added to the 100t/d alkali recovery project, which was completed and put into operation in August 1997. The oil gun was thrown away in seven days, realizing the spontaneous combustion of black liquor, and becoming one of the first projects in China with the most normal operation of wheat straw pulp black liquor project and getting rid of losses. On this basis, a 160t/d alkali recovery project is added. On the basis of summarizing the operation experience of the first set of alkali recovery (editor's note: it has been published in the second issue of this journal in 1999), the project has made continuous improvements in equipment and process, so that it can achieve profit and loss balance at the same time. At present, the black liquor extraction rate and alkali recovery rate have reached 88.5% and 78.3% respectively. The average daily alkali recovery is 30t, and the monthly benefit is more than 60000 yuan

40000 m3/D phase I intermediate water treatment project was installed and put into operation in June 1998, with a total investment of 50million yuan. The advanced technology and equipment of Swedish Prak company were introduced, and the treatment technology combining physics and biochemistry was adopted, including pretreatment system, aeration system, sludge reflux system, secondary sedimentation tank and other units (editor's note: it has been introduced in detail in the third issue of this journal in 1999). In 2001, the second phase of the middle water project was constructed, which was completed before the 160000 ton paper project was put into operation and put into operation in September 2001. The investment of the second phase project is more than 80 million yuan, and the equipment and technology of Swedish Prak company, Austrian Andritz company and American Baker company are introduced, with a daily sewage treatment capacity of 60000 m3/d. The total sewage treatment capacity of the middle section has reached 100000 m3/D, making it the paper-making enterprise with the largest water treatment capacity and the most advanced equipment in China

treatment this paper mainly introduces the operation experience of 160t/d alkali recovery project and 60000 m3/D middle section water treatment project of Huatai Group

1 160t/d alkali recovery system

main equipment selection:

Huatai main long tube evaporator 3 × 1000m2, 3 sets of

Huatai main single chamber plate evaporator 1000m2, 1 set of

Huatai main three chamber plate evaporator 3 × 550m2, properly tighten the connecting rib between the oil tank and the oil pipe, 1 set

Huatai main plate condenser 360m2, 1 set

Huatai main black liquor jet furnace 170t/d solid, 1 set

Huatai main disc evaporator 1 set

Huatai main electrostatic precipitator 1 set

Huatai main causticizer 6 sets

1.1 operation experience of extraction section

1.1 adopt the new process of continuous cooking and continuous bleaching.The, The extraction rate and quality of black liquor have been greatly improved.

Huatai has successively added 100t/d and 130t/d continuous steaming and bleaching projects, and eliminated the backward ball steaming and intermittent bleaching. The new process of continuous cooking and continuous bleaching not only solves the quality problem of pulp, but also effectively ensures the supply quality of alkali recovery black liquor. Its advantages are as follows: dry and wet preparation are combined to remove most of the sediment and stones in wheat straw. After wet preparation, the content of SiO2 can be reduced by 3% - 4%, which improves the expansion performance of black liquor to a certain extent, reduces the viscosity of black liquor, and facilitates the drying and expansion combustion of black liquor in the combustion furnace continuous cooking technology is adopted to effectively control the phenomenon of over steaming and raw meal of black pulp and make the cooking of pulp more uniform. At the same time, because the content of fine fibers in the black liquor is greatly reduced, the time for the fibers to scale on the evaporator board and in the tube is delayed, and the phenomenon of "false" increase in the viscosity of the black liquor and blockage of the black liquor spray gun caused by the increase of the concentration of the dilute black liquor after being concentrated to the combustion section is reduced after adopting dry and wet material preparation and continuous steaming technology, the proportion of inorganic and organic substances is relatively reduced, so that the lignin content that can provide heat can make the whole experimental process more smooth and further increase, thus stabilizing the combustion of black liquor the use of continuous steaming technology can properly control the degree of steaming, increase the water filtration of the slurry, especially the use of cold spraying, and reduce the beating degree by more than 5 ° SR when compared with hot spraying, so as to protect the fiber precision. High concentration of black liquor (above 6.5 ° be ′/85 ℃) was obtained while improving the detergency

1.1.2 improve the extraction equipment of drum vacuum washer to improve the quality of black liquor

Huatai has made the following improvements in process and equipment in order to improve the quality of black liquor and reduce operating costs: (1) change semi closed washing screening to fully closed washing screening; (2) Four washing machines are connected in series, and five are connected in series for countercurrent washing; (3) Replace the conventional fiber filter with imported pressure screen; (4) Cancel the conventional instrument control and replace it with PLC system control; (5) Cancel domestic instrument valves and replace them with imported instrument valves to ensure the normal operation of the system. At the same time, the operation method of low slurry level, slow speed, high vacuum and uniform sizing is adopted

through improvement, all indicators of Huatai black liquor have exceeded the design requirements. The concentration is above 6.5 ° be ′/85 ℃, the extraction rate of black liquor is 88.5%, the fiber content in black liquor is less than 10mg/l, and the residual alkali after black pulp washing is less than 0.1g/l, so that the quality of black liquor and the cleanliness of pulp are taken into account

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