Shanghai Chlor-alkali Technology Innovation, Renovation, and Tri-tech Measures to Achieve VCM Standard Emissions

Before 2010, the residual VCM (vinyl chloride monomer) in the drying tail gas of Shanghai chlor-alkali chemical PVC (polyvinyl chloride) paste resin device remained at 100-200 mg/g, far exceeding the national standard. After 2010, Shanghai Chlor-Alkali Chemical increased the technological breakthroughs and innovation and transformation. At present, the VCM residue in the drying tail gas of three sets of PVC paste resin devices is basically controlled at 15 to 20 mg/g, which is far below the national standard.

In the PVC production process, VCM raw materials must be used for the polymerization reaction, and VCM is a particularly harmful chemical substance that can cause a series of diseases such as cancer. The state has strict requirements for the VCM residue standard in the drying tail gas of PVC equipment, and the requirement must be less than 36 mg/g. Before 2010, almost all VCM residues in drying tail gas of PVC paste resin devices in China exceeded national environmental standards.

For the suspension PVC production device, due to the polymerization using a dispersion system, and the particles generated by the reaction are large, the dispersion system can be adjusted to increase the porosity of the particles, and the high temperature countercurrent of the stripper can be used to strip the PVC slurry. In this way, the VCM residue in the dry exhaust gas will reach the national standard. The emulsifier is used in the polymerization reaction of the PVC paste resin device. The particles generated by the reaction are very small, and the PVC slurry cannot be stripped of VCM residues by high-temperature countercurrent stripping. Therefore, the VCM residue that is generally in the dried slurry is relatively high, resulting in the VCM residue in the dry tail gas exceeding the national standard.

The innovative technologies adopted by the plant mainly include three aspects: First, the vacuum degree of the PVC slurry in the PVC paste resin installation equipment is increased to facilitate the removal of VCM from the slurry. In order to reduce the PVC slurry out of the equipment caused by the increase in vacuum, resulting in increased unit consumption and difficulty in wastewater treatment, an anti-foaming agent was added to the corresponding equipment for defoaming, and additional equipment was installed in the corresponding equipment to eliminate foaming. The device helps defoam the PVC slurry left by the mechanical defoamer after defoaming. The second is to install special equipment on the feed pipe in the heating equipment so that the VCM residue of the slurry can be taken out better and faster. The third is to add or improve special temperature-control heating facilities to ensure that VCM residues in PVC slurry are removed more efficiently. The combination of the three measures not only makes the VCM residue in the tail gas of the PVC paste resin device far lower than the national standard, but also has little effect on the product quality and the labor intensity of the workers due to the skillful design of the technology, and is worthy of reference for the manufacturers.

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