Shandong Huayuan Lantian Paper Co., Ltd. was established in June 1998 1 1. It has successively won more than 60 honorary titles at or above the provincial level, such as the Quality Management Award of the Ministry of Light Industry, the National Advanced Unit of Light Industry and Environmental Protection, and the National 100 Maximum and Best Benefit Papermaking Enterprise. This paper introduces that Huayuan Lantian Paper Company reformed the original pulping system and alkali recovery system, strengthened environmental protection, and finally realized the simultaneous improvement of economic, environmental and social benefits. 1 Pulp System Reconstruction Project 1. 1 Project Background and Reconstruction Scheme In 2007, China's pulp output was about 2 1 10,000 tons, of which non-wood fiber pulp accounted for 24%, and rice-wheat straw pulp accounted for the highest proportion. Due to the shortage of wood resources in China, it is difficult to completely change the existing raw material structure in a short time. For a long time, pulping and papermaking with rice and wheat straw fiber as raw material will still occupy a very important position. The company's 60t/d wheat straw pulp production line was completed and put into operation in 1978. At present, it is very backward, with high pollution load, and it is difficult to improve the quality and grade of products. In addition, the company has two sets of 37.5 tons/day and 75 tons/day alkali recovery furnaces and a set of 20,000 cubic meters/day middle-stage wastewater treatment facilities, which laid the foundation for the technical transformation of the pulping system. Therefore, in order to improve the quality of straw pulp and reduce material consumption, energy consumption and pollution load, the original pulping system was completely reformed. The original cooking bleaching system was transformed into a continuous cooking four-stage bleaching system, and the original 37.5t/d alkali recovery furnace was replaced with a 75t/d alkali recovery furnace. Adding evaporation and causticization system to improve the quality of bleached wheat straw pulp is beneficial to alkali recovery, economic operation of middle-stage wastewater and environmental protection. 1.2 transform the production technology and main processes of the pulping system, including dry and wet preparation, continuous cooking, washing and bleaching. 2. alkali recovery system renovation project 2. 1 alkali recovery system upgrading and renovation project, with an investment of 757,300 yuan. First, the primary and secondary air systems are reformed, including adding primary and secondary fans, air heaters and three groups of air preheaters. , and remove the original economizer; Secondly, the lining height and furnace building area are increased; The third is to improve the black liquor heating system and carry out supporting transformation. After modification, the temperature of primary and secondary air is increased from 140℃- 150℃ to above 250℃. Besides the fuel consumption of the combustion pad and lifting pad, the oil gun runs normally and throws oil, and the monthly fuel consumption is reduced from 450-500 tons to 100- 150 tons. When the furnace temperature of black liquor is increased from 98℃ to about 105℃, the solid concentration of black liquor increases and the viscosity decreases. The daily treatment capacity of dilute black liquor is increased from about 600m3 to 850 m3-900m3, which reduces the scattering of alkali ash. The daily recovery of caustic soda is 5 tons, and the annual recovery of caustic soda is 1700 tons. In addition, the solid treatment capacity of black liquor is increased, which reduces the environmental pollution. 2.2 Newly-built 75t/d straw pulp alkali recovery project In order to reduce environmental pollution and strictly implement industrial pollution discharge standards, the company newly-built 75t/d straw pulp alkali recovery project, which is the second set of alkali recovery environmental protection project supporting the company's continuous cooking straw pulp production line. It includes evaporation, combustion and causticization. The evaporation section adopts a five-body five-effect full-plate evaporator combined evaporation station. The first effect adopts three chambers (two chambers evaporate concentrated black liquor, one chamber is washed with dilute black liquor, and it is switched regularly), and the other four effects are single chambers, with a total evaporation area of 38 1.4m 2 and an evaporation capacity of 37.42 t/h; A new type of straw pulp black liquor incinerator is used in the combustion section, with a daily capacity of100t (10%-15%). The disc evaporator and electrostatic precipitator are used to recover alkali, and the dust removal efficiency is over 96%. The causticizing section is a continuous causticizing process, which adopts the combined process of tubular filter press, three series continuous causticizers, three clarifiers and two pre-hung white mud filters. After the transformation is completed and put into production, the black liquor treatment capacity can reach more than 900 tons; The extraction rate of black liquor is increased from 80% to 90%; The alkali recovery rate is increased from 58% to over 72%; The 75T/D alkali recovery system can recover caustic soda 19.94 tons per day, and the system wastewater pollution load can be reduced by 80%-84%, and the annual recovery of caustic soda is 66 10 tons. The influent COD concentration of sewage treatment plant decreased from 2200mg/l to1800mg/L. 3. The original middle-stage water treatment system of sewage treatment system company, which treated 20,000 cubic meters of wastewater every day, adopted two-stage biochemical treatment technologies, namely, first-stage chemical flocculation and sedimentation treatment and second-stage biological treatment. 4. The measures taken in the technical renovation project of wastewater and waste gas treatment and the results achieved are 4. 1. The total investment of the pulping system upgrading project and two alkali recovery projects is 60.6 million yuan, of which the investment in environmental protection facilities is 21160,000 yuan, accounting for 34.92% of the total investment. The following governance and monitoring measures have been taken. 4. 1. 1 In order to reduce the load of the middle water treatment plant, the grass washing water is purified and reused separately during the preparation of wet materials; The closed high concentration screening technology is adopted in the washing process, which can effectively alleviate the shortage of water resources; In the bleaching process, environmental protection bleaching with less chlorine and less hydrogen peroxide is adopted, which greatly reduces the pollution load; The white water of paper machine is reused for pulp washing through the company's white water recovery system (which has been built and operated) to reduce external drainage; Alkali recovery and evaporation and reuse of clarified condensate also reduce the water treatment load in the middle section. 4. 1.2 For flue gas treatment, the electrostatic precipitator of disc evaporator is used for flue gas dust removal in alkali recovery. The high-temperature flue gas generated by the combustion of organic matter in black liquor is discharged after heat exchange through boiler water wall, tube bundle, economizer and tubular air preheater, and then exchanges heat with black liquor in disc evaporator to concentrate black liquor; The alkali ash with larger particles in the flue gas settles in the black liquor, and the flue gas temperature drops to 140℃- 150℃, and enters the electrostatic precipitator, and the dust removal rate is over 96%. The purified flue gas is introduced into an 80-meter chimney and discharged up to the standard. 4. 1.3 The evaporation process of alkali recovery adopts five-effect full-plate evaporator combined with evaporation station. During production, each room is cleaned regularly with dilute black liquor to reduce the plate scale during evaporation of concentrated solution, maintain and improve the evaporation intensity without stopping the machine, prolong the maintenance period and reduce the operating cost. 4. 1.4 The middle-stage water treatment plant adopts the COD on-line monitor produced by Qingdao Evergrande Company to monitor the treated sewage on-line, monitor the operation status and pollution load of the treatment facilities, and realize the regular monitoring of wastewater discharge. 4.2 The obtained effect has been improved, the alkali recovery rate has been increased to more than 72%, and the final dryness of white mud can reach more than 55%, which is convenient for transportation. The transformation pays attention to the investment of environmental protection funds, and its wastewater treatment effect is obvious. See Table 2 for the discharge load of sewage field before and after technical transformation:
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