| Polyvinyl Chloride(PVC for short),together with PE,PP,PS and ABS are collectively known as the five most commonly used resin in the world.PVC is the first in China and the second around the world in this category.Our company uses joint method to produce PVC: 300,000 ton/year by calcium carbide method and 500,000 ton/year by ethylene method.Balanced oxychlorination process from EVC company,low-temperature chlorination process and oxychlorination process are all applied in ethylene method.In our company,capacity of electrolytic ion membrane in upper stream is further expanded while capacity in drying section is not added accordingly.As a result,moisture content in chlorine transported to VCM plant from electrolysis plant is occasionally over standard.This issue has not been thoroughly solved because of stable production and high cost.If mositure content in chlorine is over standard in VCM plant,a strong corrosive substance,hydrogen chloride,will be produced in low-temperature reactor.It can cause serious damage to equipment,even leads to leakage accident.If low-temperature reactor stops production due to corrosive damage or leakage,the upper and lower production stream will be greatly affected.Therefore,research for corrosive leakage in low-temperature reactor is an important and urgent task.This thesis aims to find out reasons for low-temperature chlorination reactor leakage through corrosive leakage data analysis,put forwards improvement methods from process operation and equipment perspectives.It is hoped that this research result can be used in real production to guarantee safe,stable,long-term and smooth running of low-temperature chlorination reactor.Main achievements are as below:1.Adding real-time analyzer to monitor free chlorine on discharge pipeline of low-temperature chlorination reactor: Duty of our electrolysis plant is high and often leads to over standard of moisture in chlorine.Besides,this device is not suitable for our process condition,free chlorine analyzer doesn't work well and can't provide accurate moisture content of free chlorine.2.Install ethylene analyzer on exhaust device of low-temperature chlorination reactor.It can greatly reduce discharging amount of ethylene,effectively control free chlorine content in optimal scope to make least opportunity for corrosion in low-temperature chlorination reactor and its cooling unit.Through real time monitor of ethylene analyzer,reacting proportion can be accurately controlled and discharged ethylene reduced,finally more economy benefits obtained.3.Install automatic temperature regulating valve on circulting water pipe of low-temperature chlorination reactor: this can guarantee stable temperature of LTC.Average over-standard temperature of LTC/year is reduced from 35 to 5 after renovation,effectively reduces corrosive leakage caused by over temperature which usually is due to delayed manual regulating.4.When pressure is normal in control reactor,monitor p H value of return water of cooling equipment in real time,then determine whether there is leakage in cooling unit of low-temperature chlorination reactor.This method is effective and practical.Also,this method can help find leakage in low-temperature chlorination reactor.5.Changing material of cooling unit of LTC by colomony and adding 80 cm long iron heads on tube plate can effectively improve anti-corrosive performance of cooling unit.Under this condition,p H value of return water is 8,concentration of free chlorine in reactor discharge is around 400 ppm,concentration of iron ion is around 8.3ppm,ethylene in discharge gas is below 3% and average purity of dichloroethane reaches 99.6%.This unit is running well and fulfills innovation expectation. |
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