stay Tube furnace The process of cracking and producing ethylene has a long history. The tubular furnace is quick flange sealed. Only one fixture can complete the flange connection. It is convenient to place and retrieve materials, avoid air leakage caused by manual operation of bolt seals, reduce installation flange may damage heating pipe, and tube furnace is its core equipment. In order to meet the requirements of high temperature, short residence time and low hydrocarbon partial pressure of hydrocarbon cracking reaction, and to improve the thermal intensity and efficiency of the furnace, the structure of furnace and cracking furnace tube was continuously improved. The heat intensity of the tubular furnace is 290-375 MJ / (M2 · h), the thermal efficiency is 92% - 93%, the residence time is less than 0.1 s, and the outlet temperature of the tubular furnace is 900 ℃.
The process can be divided into two parts: cracking and quenching fractionation
1. The pyrolysis and pyrolysis raw materials are preheated, mixed with superheated steam (or dilution steam) in a certain proportion (depending on the raw materials), heated to 500-600 ° C through the convection section of the tubular furnace, and then enter the radiation chamber. The medium was heated to 780 to 900 ° C and ruptured. In order to prevent the secondary reaction of pyrolysis products, the pyrolysis products from the radiation section enter the quenching boiler to rapidly reduce the temperature and generate high-pressure steam through heat exchange to recover heat.
2 quenching fractionation is cooled in a quenching boiler, the pyrolysis products are cooled to 350-600 ° C, and then further cooled to separate the product fractions. The pyrolysis products from the quenching boiler are in direct contact with the quenching oil injected into the quencher, and the temperature is reduced to about 200-220 ° C. then, the pyrolysis products enter the distillation system to obtain cracked tar, cracked diesel oil, cracked gasoline and cracked products. Natural gas and other products. The cracked gas is pressurized by the compressor and enters the gas separation unit.
Cracking feedstock and product distribution: the cracking feedstock of tubular furnace is light hydrocarbon recovered from natural gas, oilfield associated gas and refinery gas, mainly including ethane, propane, butane and carbon five fractions. For different feedstocks, the cracking process parameters are different, and the distribution of cracking products under suitable conditions is also different. The general rule is that the yield of ethylene decreases with the increase of relative density of raw materials. When diesel feedstock is used, the heavier the fraction is, the more complex the cracking technology is, and the coking in the cracking furnace tube is increased, thus shortening the operation cycle. The higher the temperature, the shorter the residence time, the lower the partial pressure of hydrocarbon and the higher the ethylene yield.