With the advantages of short process flow and less investment, the cracking unit which takes light hydrocarbon as the raw material provides a new way for the revamping and expansion of ethylene plant by petrochemical enterprises. Taking a light hydrocarbon cracking project planned and constructed by an enterprise as an example, this paper puts forward three categories and six different construction schemes for comparison and selection based on the supporting conditions and development strategy, uses PIMS process planning platform system to calculate the material balance of the schemes, discusses the engineering schemes for process units and utilities, analyzes the investment and benefits of different schemes, and draws preliminary research conclusions and suggestions.

Through the comparison of yield characteristics of ethylene plant with different raw materials, the particularity of ethane cracking is shown. Based on a 1000 KTA ethane cracking plant and the assumed prices of natural gas, ethane and electricity, the hydrogen recovery cost of ethane cracking plant is obtained. If natural gas is used as the substitute heat for hydrogen, the hydrogen recovery cost depends on the price of natural gas. In regions where the natural gas price is high, the hydrogen recovery cost is relatively high and the market competitiveness is weak. If ethane is used as the substitute heat for hydrogen, when the ethane price is low, the hydrogen recovery cost of ethane cracking is close to that of coal to hydrogen, showing strong market competitiveness.

	The traditional startup method of styrene extraction unit is generally divided into reverse startup and sequential startup. The reverse startup is to prepare
styrene products in advance and fill them into the system. The sequential startup is to start up the unit with C8/C9 raw materials according
to the sequence of the process. This paper introduces the third startup method for styrene extraction unit, i.e., firstly filling mixed xylene into C8/C9 cutting tower for oil flushing, then sending the mixed xylene to extraction
system after the hot flushing with solvent, and finally sending the mixed xylene to decolorization and refining system to get through the entire process
for oil flushing. After the oil flushing with mixed xylene, the frequency of filter cleaning during normal feeding process is greatly reduced, and the risk of
styrene polymerization caused by equipment failure during startup is reduced.At the same time, the process parameters have been optimized to the best state
during the oil flushing with mixed xylene, providing favorable conditions for the production of qualified styrene products.

Petroleum benzene is one of the important basic chemicals, and its industrial production process is realized in aromatics extraction unit. Most of its raw materials come from pyrolysis gasoline hydrogenation unit, accounting for more than 50% of petroleum benzene products. With the rapid development of the chemical industry, the requirements for sulfur content of benzene products in chemical market become higher and higher. Sulfur exists in benzene products mainly in the form of thiophene, and the thiophene content of products can be approximately characterized by total sulfur content. Because the physical properties of thiophene and benzene are similar, it is difficult to separate them by distillation in industrial production, and hydrodesulfurization is mostly adopted. By analyzing the chemical reaction process of thiophene removal of pyrolysis gasoline by hydrogenation and comparing the total sulfur content of hydrogenated gasoline products under different process conditions, the optimal operating conditions that can meet the sulfur content of products with the existing technologies and process conditions are obtained.

This paper analyzes and finds out the reasons for the problems of process water system in the ethylene plant at SINOPEC Tianjin Company, including the decrease in overhead stripping steam in process water stripper, the drop in overhead temperature and the over high oil content of process water. The boiler in the process water stripper is treated to increase the overhead temperature, reduce the oil content of process water, avoid the pollution of sewage system, reduce the low-pressure steam makeup, reduce the energy consumption of ethylene plant, and reduce the blowdown of dilution steam.

This paper introduces the abnormal operation of pyrolysis gas dryer in the 1000 kt/a ethylene plant at PetroChina Dushanzi Petrochemical Company caused by the decrease in adsorption and dehydration performance after the agent was re-screened and re-filled for the bed leakage in 2016. The reasons for the abnormal operation of pyrolysis gas dryer is analyzed, and some corresponding measures are taken to ensure the stable, safe and long-term operation of the ethylene plant under high load.

The emptying of quench system during the overhaul of ethylene plant has always been the difficulty and control point of plant shutdown. After two rounds of revamping and expansion, there were many changes on the site of the ethylene plant of SINOPEC Qilu Company, bringing a lot of difficulties to the emptying of quench system. In view of the characteristics of quench system including a large number of equipment, complex process and heavy oil products, related processes were prepared in advance, all the disciplines coordinated with each other, and the emptying replacement speed and quality of the system were improved through scheme optimization. On the premise of recovering oil products from oily sewage as far as possible, the low-emission emptying replacement of quench system were achieved in 8 days.

The operation cycle of the heavy oil cracking furnace at SINOPEC Zhenhai Refining & Chemical Company has reached more than 120 days, but at the end of the operation, the fuel consumption increases, the output of ultra-high pressure steam decreases and the energy consumption increases under the same feeding quantity. The energy consumption required for coke burning of cracking furnace is calculated, the ratio of feed to fuel and the ratio of ultra-high pressure steam output to fuel consumption during the whole operation cycle are analyzed, and the average data every 10 days of the 50 days before operation and that of the 50 days after operation are compared. The results show that the objectives of planned decoking and lower total energy consumption of the ethylene plant can be achieved through reasonable arrangement of operation cycle.

 The structure characteristics and working principle of transfer line valve in the cracking furnace of the 220 kt/a ethylene plant at PetroChina Dushanzi Petrochemical Company are analyzed. The effect of anti-scorching steam on transfer line valve and the causes of the blockage of anti-scorching steam line are analyzed. By taking a series of measures including installing flanges downstream the steam line valve and upstream the injection point hand valve, installing heat tracing for steam lines and strengthening daily maintenance, the hidden danger of anti-scorching steam line blockage of transfer line valve was successfully eliminated.

Condenser is the core equipment of condensate system of extraction condensing steam turbine. The condensate system is under negative pressure during normal operation, and the change of working state of condenser directly affects the working efficiency of steam turbine. In this paper, the on-line cleaning and leakage elimination process of the condenser in steam turbine of cracking gas compressor in the 200 kt/a ethylene plant at SINOPEC Tianjin Company is introduced, and some improvement suggestions are put forward for on-line monitoring and other deficiencies.