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A brief discussion on energy-saving and emission reduction approaches for PVC production. Tianjin Botian Chemical Co., Ltd. has a PVC production capacity of 250,000 t/a, mainly using the calcium carbide method. Relying on scientific and technological progress, the company vigorously develops circular economy, carries out technical research, speeds up pollution control, improves the recycling rate of waste residue and waste water, ensures that waste water and waste gas discharge meet standards, and achieves energy conservation and emission reduction in PVC production. 1. Improve the reuse rate of water resources. Water is a resource in short supply in our country. Improving the reuse rate of water resources and reducing wastewater discharge are the most effective measures to ensure the reduction of COD and other pollutants. In the production process of polyvinyl chloride, there is a large amount of water consumption and drainage, and the task of preventing and controlling wastewater pollution is also very heavy. There is great potential for implementing circular economy. 1.1 Indirect cooling water recycling: A large amount of indirect cooling water is used in the production of PVC. It is all well water, does not contain any pollutants, and can be fully recycled. Over the years, the company has taken advantage of the construction of new, renovation and expansion projects to build a large number of indirect cooling wastewater cooling and recycling devices, so that all indirect cooling water for PVC production can be reused. The indirect cooling water recycling amount is 177673.92m3/d., of which the acetylene process is 72336m3/d. ； Vinyl chloride process 19732.08m3/d ； Synthesis process 12392.64m3/d ； PVC polymerization process 44691.12m3/d ； EPVC process 25239.6m3/d: The nitrogen and oxygen station process is 3282.48m3/d, which reduces the consumption of fresh water. 1.2 Multi-stage series utilization of process wastewater Water sources for multi-stage series reuse in polyvinyl chloride production include indirect cooling water such as ammonia compressors in refrigeration stations, synthetic compressors, and finished product centrifuges, sulfur-containing wastewater from acetylene generators, and polymerized mother liquor water. The multi-stage series water utilization volume is 12902.76m3/d, which reduces the fresh water consumption and wastewater discharge. The recycling of process wastewater is the main way to reduce wastewater and pollutant emissions. It mainly includes sulfur-containing wastewater from acetylene generator and polymerized mother liquor water. Sulfur-containing wastewater is the wastewater produced by pressing out the carbide slag slurry discharged from the bottom of the acetylene generator through a chamber filter press. It is alkaline. Among them, COD is about 360mg/L, sulfide is about 20mg/L, and suspended solids is about 260mg/L. The contents are all relatively high, making it very difficult to meet emission standards. Measures have been taken to return the acetylene generator for reuse. Except for part of the sulfur-containing wastewater that is sent to the plant's sewage system to neutralize the acidic wastewater of the entire plant, most of it (about 2.52 million t/a) is returned to the acetylene generator for reuse. The amount of polymerized mother liquor water produced is about 105%, which contains about 430 mg/L COD and about 120 mg/L suspended solids. Because the batching water used in the polymerization kettle is ion-free water, the quality of the mother liquor produced is very good, and all of it is recycled and reused. There are three main reuse channels. One of them supplies water for spraying at the top of the air stripping tower to replace the original 35t/h ion-free water. ； The second one is to send water to the hydrogen chloride synthesis furnace to replace the original 35t/h well water. ； Its three-delivery sodium hypochlorite preparation system replaces the original 35t/h curved well water. To sum up, the reuse of sulfur-containing wastewater can reduce COD emissions by 900t, suspended solids by 650t, and sulfide emissions by 50t per year. The reuse of polymerization mother liquor water can reduce COD emissions by 380t, suspended solids by 100t, and recover 600t of finished materials every year. At present, the reuse rate of PVC industrial water reaches over 96%. The schematic diagram of the recycling process of sulfur-containing wastewater and mother liquor water is shown in Figure 1 (omitted). 1.3 Mercury-containing wastewater The vinyl chloride synthesis produced by the closed-circuit calcium carbide method of polyvinyl chloride uses mercury catalyst as a catalyst. When the converter catalyst overturns, a vacuum pump needs to be used to extract the mercury catalyst, resulting in mercury-containing wastewater from the vacuum pump shaft seal. Mercury is a scarce resource. It is only mined in small quantities in China and is mainly supplied by imports. Moreover, mercury is a type of pollutant. If mercury-containing wastewater is discharged, it will not only cause environmental pollution, but also cause a waste of scarce resources. To this end, mercury-containing wastewater is subject to mercury adsorption recovery and wastewater recycling and reuse measures, and is transferred to units with hazardous waste management licenses for recycling. At the same time, zero discharge of mercury-containing wastewater is achieved to achieve the purpose of energy conservation and emission reduction. The schematic diagram of the recycling process of mercury-containing wastewater is shown in Figure 2 (omitted). 2 Pay attention to industrial wastewater treatment. The wastewater discharged during the production process of polyvinyl chloride paste resin in the chlor-alkali industry mainly comes from washing tank water, VCM recovery system drainage and catalyst dissolution tank drainage, etc. The water volume is about 9t/h, among which the main pollutants are COD and SS. Under normal production conditions, the COD concentration in wastewater is approximately 1500mg/L ； SS concentration is unstable, ranging from 1500 to 4500 mg/L during normal production. Due to the small particle size and high concentration of suspended solids, it is difficult to settle in the sedimentation tank and is not conducive to filtering. Direct discharge will make a large amount of paste resin waste in the water unable to settle. Not only does it cause a waste of materials and an increase in costs, but the excessive discharge of COD and SS also pollutes the water environment. To this end, a set of 20t/h sewage treatment equipment was built, using chemical coagulation technology. The production wastewater is collected from the sewage ditch into the dosing mixing tank. After adding flocculant and stirring for 5-10 minutes, the lift pump is turned on to pump the water to the integrated water purifier for settling. ； The settled wastewater is discharged to the main plant sewage neutralization tank, and the sludge is discharged to the sludge thickening tank for settlement and then transported to the box-type plate and frame filter press by a screw pump for filtering. ； The filter cake filtered out is sold as waste, and a small amount of filtrate is returned to the dosing mixing tank. The treated sewage achieves compliance with discharge standards (COD