Energy Conservation Research Of Ethylene Plant

The ethylene industry is the foundation of a country’s chemical industry.The development level of the ethylene industry generally represents a country’s petrochemical industry strength.In our country,there are not so many large-scale ethylene plants,most of them are middle or small-scale plants.In addition,light cracking feeds are short.For above-mentioned reasons,the energy consumption of the ethylene industry in China is higher than that abroad.Therefore,study of energy conservation in the ethylene industry is very important.In this thesis,pinch technology is used to analyze optimize the energy system of a certain ethylene plant.The HEN(heat exchanger network)of the plant is divided into two parts,cold HEN and hot HEN.Using Aspen energy analyzer we find that the pinch of the hot HEN is 175℃,the minimum heating utility is 26960 kW,and the minimum cooling utility is 152700 kW.Compared with real energy consumption,the energy saving potential is 51.8%.As for the cold HEN,the energy saving potential is 5.9%.Then the recovery of reaction heat,high temperature waste heat recovery of cracking gas and energy use of columns are analyzed,and effective modification schemes are proposed.Five heat exchangers need to be replaced,decreasing heating utility 25787 kW,with equipment investment around 2.4 million,and the payback period is less than one month.In this thesis,aimed at the unreasonable waste heat recovery of ethylene plants,namely,the heat of the cracking gas with high temperature is degraded directly to lower temperature during the recovery,a new process is proposed,in which the vacuum gas oil is sprayed into the hot cracking gas to recover the heat of the cracking gas from waste heat boilers.In the new process through multi-level heat recovery and reasonable energy utilization,the steam value is increased.The refrigeration configurations are compared between cascade refrigeration system and tertiary refrigeration system.Aspen Hysys is used to simulate the ternary ethylene refrigeration system,and then analyse exergy loss.Some unreasonable refrigeration configuration is found,and some effective energy-saving suggestions are presented for different equipments.This work combines the ethylene cryogenic separation process with the LNG gasification process,so that LNG light hydrocarbon separation can be treated as cold source,and ethylene separation process can be treated as a cold sink.In this way,the cold utility demand in the ethylene cryogenic separation and the heat utility demand in the LNG gasification process are both reduced.The light hydrocarbons from LNG separation process can be a perfect cracking feed for the ethylene plant.This work can be a guideline for energy conservation in ethylene plants.