1、1Residualheat Utilization and Optimal Reformation in PVC productionAbstract： The paper takes the actual problems of target enterprises in PVC production as an example. The paper transforms residual-heat waste status in production and optimizes the key equipment， cooling water system of internal cool
2、ed of polymerization reactor， which not only reduces energy waster and reaction time of single reactor， but also improves production efficiency. So it saves energy for target enterprises and makes considerable economic benefit. Key words： PVC， residual-heat utilization， polymerization reactor 1 Intr
3、oduction PVC is an important organic synthesis material in China. It is widely applied to the fields of industry， construction， agriculture， electric power and package. For the product category of PVC， it belongs to three synthetic materials， synthetic resin， synthetic fiber and synthetic resin in s
4、ynthetic rubber. The production and sales of it is only after polyethylene in the world 1. However， China is the country 2producing and consuming the most PVC in the world， so the production technology of PVC has great influence on China. Polymerization reactor is one of the most important equipment
5、 in a set of production equipment of PVC. The technology of polymerization reactor has direct influence on the quality and production of PVC. Therefore， the quality of polymerization reactor has close relationship with economic benefit of enterprises. As a large energy consumer， low energy utilizati
6、on is a problem which cant be ignored in China. The average residual-heat utilization rate in each industry has reached to 7.3%， but the recovery rate of residual heat resources is only 34.9%， which indicates that residual heat resources have great potentials 2. For residual-heat waste status in pro
7、duction of target PVC enterprises， the paper optimizes the production process， which improves the economic benefit and energy utilization rate of target enterprises. 2 Situation of PVC Industries in China At present， PVC industries in China have been in the industrial environment of global completio
8、n， Asian integrated completion and domestic low-degree completion. With the expansion and emergency of new chlorine-alkali enterprises， 3the global chlorine-alkali enterprises have been in the era of supply exceeding demand. For example， the chlorine-alkali enterprises continued the growth trend in
9、China last year. The productivity of caustic soda increased by 3.23 million t/a and reached to 37.36 million， which increased by 9.5% compared with that in last year. The annual yield was 26.986 million t， which increased by 3.8%. In last year， the production efficiency of PVC increased by 1. 72 mil
10、lion t/a， and reached to 23.41 million， which increased by 8.2% compared with that in the last year. The annual yield was 13.178 million t， which increased by 0.5%3. The chlorine-alkali enterprises faces complicated and strict survival environment in China. Influenced by sustainable growth of produc
11、tivity， weakness of downstream demand， increase of comprehensive cost and poor export， chlorine-alkali enterprises face great survival pressure， and the overall efficiency of the industry decreases. Many enterprises take the production mode of using alkali to supplement chlorine， but it has no good
12、effect. With the decrease of caustic soda market in China， the price of PVC products has no evident increase， which makes the survival status of chlorine-alkali enterprises deteriorated. The issue of Enhancing Calcium 4Carbide Manufacture PVC and Pollution Control of Mercury limits the application o
13、f high-mercury catalyst， and it demands the PVC enterprises must use low- mercury catalyst 4. It makes the enterprises increase the relevant manpower and financial investment， which increases the burden of enterprises. Therefore， it is has great significance for enterprises to improve productivity a
14、nd improve energy utilization efficiency. 3 System Overview 1.Introduction of target enterprises The selected target enterprise is a military enterprise established in 1996. The enterprise was transformed into company system from factory system in 1996. In 2010， the enterprise became a state-owned e
15、nterprise， and the annual sales revenue was more than 4 billion yuan. It is a large state-owned industrial enterprise which is predominated by chlorina alkali chemical industry and is equipped with thermoelectricity， cement， PVC deep process and photovoltaic industry. The annual scale of the leading
16、 products including ionic membrane caustic soda and PVC resin is 540000 tons and 500000 tons. There is an owned cogeneration power plant with 152000 KW of installed capacity and a carbide slag producing cement enterprise with annual output of 1 million tons. And it 5has complete production structure
17、. 2 Factory before transformation 2.1 Heat-thermal waster status in drying section The target enterprise has the matched power plant. In order to make PVC production easy， the power plant transports some steam with high temperature and high pressure to dry processes of PVC production for application
18、. In PVC production process of target enterprise， the drying processes use vortex drying bed. The production principle of vortex drying bed is using high temperature and hot air to make PVC resin dry in cyclone drying tower. And the heat air is from air heater. The vortex drying bed has the characte
19、ristics of easy process， great processing capacity， few of dead angles and easy to be cleaned， which has evident function to improve productivity of equipment and product quality. But the disadvantage is that steam consumption is great， which is very evident. The best consumption level of vortex dry
20、ing bed is 0.5t/t?PVC. But the difference of technical level， operational norms and regional environment makes the consumption of steam different. In the production process in winter in the northern area， the steam consumption is greater. According to the actual situation of target enterprises， 6aft
21、er the steam with high temperature and high pressure makes heat exchange with cold air in air heater， the cold air becomes high-temperature air for drying process. After the high-temperature steam receives heat exchange， some become condensed water， and most steams become low-pressure steam as tail
22、gas to be discharged into air， which means that most heat is wasted as steam condensate and low-pressure steam， which causes severe loss. Therefore， it is necessary to effectively make use of the lost energy. 2.2 Efficiency of polymerization workshop is not good The project of 200000 tons of PVC of
23、the target enterprise in the paper was established in August 2006 and was put into production. Polymerization reactor is the key large-scale equipment in polymerization workshop. The enterprise uses 70m?polymerization reactor. And the structure chart is as follows. 1.transmission；2impeller；3 agitati
24、ng shaft；4 reactor；5 half-pipe jacket；6 safety device；7manhole；8 spray device；9 inner cooling tube；10 baiting valve Figure： 70m?agitated reactor 5 The heat-transfer capability of polymerization reactor is one of the key factors restricting production capacity 6. The 7polymerization reactor of target
25、 factory uses two-way cooling device. One way is cooling in half-pipe jacket outside of polymerization reactor. And the other way is cooling in four inner cooling pipes inside polymerization reactor. Two-way cooling water uses circulating water for cooling， but circulating water is restricted by nat
26、ural conditions. For target enterprises， the average reaction time of PVC5 polymerization reactor is from 340min to 350min， and the temperature of circulation water is from 24 to 25. Under the condition that jacket of polymerization reactor and regulating valve of inner cooling pipe are nearly open，
27、 the polymerization time long， and the temperature and pressure of polymerization reactor in reaction process rises， which not only needs to reduce the temperature in polymerization reactor by fetching water， but also needs to reduce the usage of initiator. And the reaction time delays， which is not
28、 good for production. In June， July， August and September， the external temperature is high， and the temperature of circulation water rises to 28. Too high temperature of circulation water makes the time of PVC monomer polymerization in the operation process longer than that in winter， which serious
29、ly affects production efficiency. Therefore， reducing 8reaction temperature of polymerization reactor and reducing polymerization time has great significance to improve production efficiency in polymerization stage. 3. Transformation method In order to save energy， reduce emission and improve the be
30、nefit of enterprises， according to the characteristics of target enterprise， we make appropriate transformation on enterprises. Firstly， in order to use the waste heat expelled in drying process of PVC production， we add a steam double-effect lithium bromide absorption cooling-water machine in dryin
31、g process， and use the heat provided by waste heat to produce cooling water with the temperature of 7. And the produced cooling water is sent to polymerization workshop in PVC production for reducing the reaction temperature of polymerization reactor. 3.1 Utilization and transformation of waste heat
32、 in drying section The data provided by target enterprises indicates that the temperature of the waste gas exhausted in drying section is 160180， the pressure is 0.18MPa and the quantity of steam is 710kg/h. From the data provided in the table， we see that the quantity of steam which can be used is
33、about 710kg/h. According 9to refrigeration air conditioner equipment manual and the data provided by the relevant manufacturers 7， RCW-032-type steam double-effect lithium bromide absorption cooling-water machine is selected （parameters are shown in the following table）. The normal steam demand with
34、 normal operation is 704kg/h， and the quantity of steam provided in drying section of target enterprise can meet the demand. The refrigerating capacity of the unit is 563kW， the working pressure is 0.4MPa， and cooling water of 7 is provided with 163m?/h. 3.2 Transformation of cooling water in polyme
35、rization workshop In order to improve heat-transfer capability and production efficiency of polymerization reactor， the paper makes improvement on the original working conditions， as follows. An inlet is added to the original circulating water pipe. And the water with the temperature of 7 which is p
36、roduced in steam double-effect lithium bromide absorption cooling-water machine is led into inner cooling pipe of polymerization reactor for cooling water in inner cooling pipe. The cooling water with the temperature of 7 replaces industrial circulation water to be led into inner cooling pipe. As th
37、e temperature of cooling water is low， the heat transfer temperature difference is 10great， the heat transferring effect is better， which reduces the reaction temperature of polymerization reactor. As shown in the following figure， before transforming cooling water system in polymerization section，
38、the industrial circulating water required by reactor is provided by the circulating water station， and the original working condition has no branch A， B and C. The circulating water is send to reactor by D pipeline of water pump， which cools polymerization reaction. After transformation， branch C pr
39、oviding cooling water with the temperature of 7is added， which reduces the reaction time of polymerization reactor. 1 Steam double-effect lithium bromide absorption cooling-water machine 2Circulation water station 3 circulating water pump 4 Reactor In the figure， branch A is from drying section and
40、provides high-temperature steam. Branch C provides the cooling water with the temperature of 7 which is provided by lithium bromide chiller， and it is used to cool inner cooling tube of polymerization reactor. Branch D is the industrial circulating water provided by industrial circulating water station， and is used to cool half-pipe jacket outside of polymerization reactor. F is the exit of reactor. In order to be safe， while
