Vacuum Process Optimization and Energy Conservation in Chemical Production bookmark0 Wen Yinghuan (Yueyang Petrochemical General Plant Olefin Plant.414014) Viewpoints on vacuum process optimization in chemical production have practical significance for energy saving and consumption reduction - 1 Overview of drying and evaporation in chemical production Chemical units such as distillation and distillation are widely used in vacuum processes and decompression operations for separation. Decompression operation has many advantages, and it is particularly suitable for the separation of heat-sensitive materials.
Decompression can reduce energy consumption while effectively improving product quality and yield. The key to decompression operation is the proper selection of vacuum equipment and the rational choice of vacuum process.
In the chemical production, the decompression operation of the chemical unit such as drying and distillation is generally required to achieve an absolute vacuum of 1.33X101~5.33X102Pa (0.001~4mmHg), which is commonly used in domestic four to six steam injection pumps. Multi-stage steam injection pumps are generally one or two cascaded and then enter the second-stage mixing condenser, followed by sequential injection and renewal of mixed condensation. Evaporation unit decompression operation in chemical production generally requires an absolute pressure of 5.103~1.07X104Pa (0~80mmHg). It is commonly used in China for water jet vacuum pumps and water ring vacuum pumps, and it also uses one to three steam injections. Pump vacuum process.
2 Vacuum process optimization and energy saving in chemical production An example analysis is used for the vacuum decompression operation in chemical production, such as drying, rectification, etc. The use of multi-stage steam jet pump and evaporation unit in chemical production Vacuum decompression operation Use water jet vacuum pump with low efficiency and energy The problem of high consumption requires optimization of its vacuum process to achieve energy saving and consumption reduction. In the following, the vacuum process optimization and energy saving analysis of the polyester chip drying vacuum process reformation and the wastewater monomer recovery evaporation vacuum process transformation of the Yuehua Plant are taken as examples.
2.1 Polyester chip vacuum process transformation and optimization 2.1.1 The original vacuum process This vacuum process has three sets of four steam jet pumps, normal production of a second open and a prepared to obtain 1.33Pa (0.01mmHg column) absolute vacuum, so that The water content in polyester chips drops below 0.6%. The single injection vacuum pump consumes 0.8MPa steam and 850kg/h, and the circulating water consumption is 75m3/h. The main problems in this vacuum process are: reaching the ultimate vacuum time is long; the steam consumption is large; the direct mixing cooling pollutes the circulating water, COD content Increased, it has brought difficulty to circulating water treatment.
After the reformation of polyester chips, the vacuum flow chart uses i water-ring vacuum pumps instead of three-stage and four-stage steam injection pumps. The first and second stage steam injection pumps are indirectly cooled by thin tube water coolers. Water jet vacuum pumps have also been considered in the selection of water ring vacuum pumps because steam jet pumps and water jet vacuum pumps in series are mature vacuum processes, and vacuum processes in which the steam jet pumps and mechanical pumps are connected in series are less commonly used in China; Less demanding and less efficient than being used. The original four-stage steam injection pump starts with a four-stage steam injection pump that can achieve a vacuum of 8.8XlOPaaOOmmHg), and a three-stage steam injection pump can achieve a vacuum of 9.6X14Pa (72QmmHg), all of which need to pass through the front. The secondary steam injection pump and its mixing condenser have large system resistance; while the running water ring type vacuum pump is controlled by the bypass line valve, the extraction main pipe has little resistance to non-condensable gas, and it can quickly reach the vacuum required by the limit, and then input When the secondary and primary steam injection pumps are used, the moisture in the medium evaporates largely and the condensable gases are mainly used. This condensable gas, together with the steam of the same and secondary injection pumps, enters the water cooler to condense into recyclable soft water. At this time, the bypass line valve is closed, and the water ring vacuum pump continues to maintain the non-condensable gas. It not only maintains a high degree of vacuum, but also achieves greater pumping capacity. After the transformation, the pumping capacity is 1.5 times more than the single pumping capacity of the original four-stage steam injection pump. One set of this vacuum process can meet the process requirements.
2.2 monomer recovery vacuum process transformation and optimization monomer recovery process using three-effect continuous evaporation, the third effect of vacuum evaporation, the use of water jet pump facilities require 8.66X monomer recovery before the transformation of the vacuum process flow chart but due to water injection Vacuum pump instead of three), four-stage steam jet pump not 12201 after the transformation of the real process flow chart (/) 111 This vacuum process is simple, but because of the non-condensable gas and condensable gas before entering the water jet pump 60 ~ 70C The temperature of the self-circulating circulating water will rise to more than 60C in a short period of time, and it will not reach the required degree of vacuum; in order to meet the process requirements, a large amount of industrial water with lower temperature has to be added to reduce the circulation. Water temperature, water consumption is quite large.
Vacuum recovery process after monomer recovery and transformation The vacuum process is indirect cooling with a thin tube water cooler, followed by a water ring vacuum pump. At the beginning of the project, without passing through the water cooler, the non-condensable gas was directly pumped by the water ring vacuum pump through the bypass line. The resistance of the pipe network was small, and the vacuum degree of 9.06×1049.20×104 Pa (680,690 mmHg) was quickly reached. With the increase of feed rate and system absolute pressure, the concentration of water vapor increases continuously. The water cooler is used and the bypass line valve is closed. The water vapor can be condensed by the air cooler and discharged through the “atmosphere legâ€. The water ring vacuum pump continues to maintain pumping. The non-condensable gas can obtain a vacuum degree of 8.1049.13XKfPa (670685mmHg) in the working condition. After the modification, the pumping capacity is greatly improved, and the process requirements are better satisfied.
23 Vacuum process reformation, energy-saving analysis after optimization Energy-saving and energy-saving after vacuum process reformation and optimization are very significant. The energy-saving efficiency analysis is performed before and after the polyester chip vacuum process and monomer recovery vacuum process transformation.
2.3.1 Direct Economic Benefits The vacuum process of a four-stage steam injection pump is compared with the vacuum process of a series of one-stage and two-stage steam injection pumps connected to a series of water ring vacuum pumps. The latter can consume less than 0.3t/h of steam. The power consumption is 8.25kWh, the consumption of industrial water is 4 5m3/h, the consumption of circulating water is 25m3/h, and the soft water recovery is 0.7t/h. After the renovation, one set of four-stage steam injection pumps is opened, which can save 0.85t/h steam. Save 75m3/h of circulating cooling water. After the reformation of the monomer recovery vacuum process, the industrial water consumption is reduced by 22m3/h, the consumption of circulating water is increased by 60m3/h, and soft water is recovered by 0.3t/h. The electricity consumption is basically the same. Polyester drying vacuum process and monomer recovery vacuum process can save steam 1.15t/h, recycling soft water 1 Wei save fresh water a! 7. h, consumption of circulating water 10m3/h. According to the energy price at the time of Yuehua: steam 50 yuan / t, soft water 4 yuan / t, fresh water 0.6 yuan / m3, electricity 0.5 yuan / kWh, circulating water 0 15 Yuan/m3 calculation, can save 66.37 yuan per hour, the whole year according to 300d start time calculation can save 477,800 yuan.
2.3.2 Indirect economic benefits After vacuum process optimization, the vacuum degree is improved, and the time to reach the ultimate vacuum is shortened, creating conditions for improving product quality and production. Polyester chips have a short residence time at 100 C drying temperature, and the yield is improved. The polyphenol color is guaranteed and the quality goes up, improving the first-rate product rate of spinning. The recovery of monomer in wastewater increases.
The thin tube tube water cooler replaces the soda-mixed water cooler and eliminates chemical and chemical fiber tail gas materials from entering the circulating water system, reducing the COD content in the circulating water and creating conditions for circulating water treatment. Qualified circulating water can improve the heat exchange efficiency of the water cooler and thus enter a virtuous cycle. From the aspect of circulating water, it can ensure the production and quality of chemical products.
3 Optimization trend of vacuum process in chemical production The vacuum process in chemical production is a small part of the whole chemical unit installation. Generally only a certain degree of vacuum is required to satisfy the operation of the chemical unit installation, and the process analysis is not taken seriously. In the current period when domestic jet vacuum pumps are very inefficient and difficult to improve, only the use of relatively high-efficiency mechanical pumps and the recombination of new vacuum processes are used to compensate. This is the trend of vacuum process optimization. For the vacuum system of pumped air (non-condensable gas), it is required to obtain a vacuum process of a steam jet pump cooling a series piston vacuum pump or an air-cooled Roots vacuum pump via a thin tube heat exchanger. Outside of chemical production in China, a vacuum process using a three-stage triple-leaf air-cooled Roots pump is used to obtain an absolute pressure vacuum plastic additive manual of 0.11 Pa (7.5×1037.5×10 −2 mmHg). Translated by Chen Zhenxing. Beijing: Sinopec 5 Wang Yuanhong. Flame retardant chemistry and its application. Shanghai: Shanghai Science and Technology Publishing 6 Li Jian. Plasticization of wood. Wood Industry, 1992 (6) 7 Rowan St. The combustion process of wooden materials and its flame retardant treatment. Building wood-based panels, 1994 (2) 8 Wang Xiaoyan. Floor wood fire retardant technology and its application . In the inorganic salt industry, 1995 (4) 2627 (continued from page 44) column), the vacuum vacuum process of series-connected water ring vacuum pumps can be cooled by thin-tube heat exchangers using one or two stage steam jet pumps. In the production of small devices can be directly used rotary vane vacuum pump, can obtain a 13.3Pa (0.1mmHg column) absolute vacuum; if you need a higher degree of vacuum and contains a lot of condensable gases, you can use one, two The steam jet pump cools the vacuum process of the tandem rotary vane vacuum pump via a thin tube heat exchanger to obtain an absolute vacuum of 0.133 Pa (1×103 mmHg). Chemical production is especially a chemical production unit that integrates chemical units such as drying, distillation, and evaporation, and is operated under reduced pressure. The potential for vacuum process optimization is even greater. Low-grade, by-product steam can be used as steam for steam injection pumps. The “edge water†with a certain residual pressure or repressurization can be used as a water jet vacuum pump or a water jet condensing vacuum pump. It is possible to use less contaminated, lower temperature water as the makeup water for the water jet vacuum pump or the water jet condensing vacuum pump circulating water seal tank. Thin tube heat exchangers can be used to reduce the temperature of extraction by industrial circulating cooling water, the condensable gases can be condensed in time, the capacity of non-condensable gases can be increased, and the time for reaching the ultimate vacuum can be shortened to increase the production capacity and product quality. The space advantage device can increase the height of the “atmosphere leg†of the water jet vacuum pump and the water jet condensate pump to increase its authority and reduce the pressure of the power water. Should be based on actual production and specific analysis, reasonable choice, scientific collocation and the correct choice of vacuum equipment and reasonable choice of vacuum technology. However, the problem of “cavitation corrosion†of wet pumps such as water ring vacuum pumps must be taken into consideration when using a mechanical vacuum pump in extreme vacuum conditions. In addition, the problem of resistance drop of the vacuum pipeline, the handling of the turning point of the condensed water downcomer, etc. should be caused. Enough attention.
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