Improving Energy Performance Of Diesel Hydrogenation Process

The consumption of diesel as a fuel is very huge,and the severity in environmental pollution makes environmental regulations more stringent.Diesel hydrogenation is the most important technical means of producing clean diesel,whose application is very extensive.In the production process,diesel hydrogenation reaction occurs under high temperature and high pressure conditions,so that the raw material oil needs to be heated to about 400 ℃,which requires a lot of energy consumption.At the same time,diesel products need to be cooled to about 50 ℃.Therefore,the energy performance will have a huge impact on the whole process.Pinch technology in search for bottlenecks have very mature applications.In this thesis,pinch technology is used to analyze the energy consumption for two sets of diesel hydrogenation processes.According to the difference in the Grand Composite Curve of the two diesel hydrogenation processes,the process conditions which affect energy consumption are analyzed.Optimization of heat exchanger networks is carried out using pinch technology.The process is simulated and optimized by Aspen Plus.In view of the heat exchanger network of a diesel oil hydrogenation process,the pinch technology is used to find out the unreasonable heat transfer,and two schemes are put forward: the largest heat recovery scheme and by-producing steam scheme.The largest heat recovery scheme can save 11166 kW energy.The by-producing steam scheme can save 11166 kW,and at the same time produce 3.5 t/h of medium pressure steam,at the cost of consuming 3.6 t/h low pressure steam.Finally,from the view of economics and the rationality of energy use on the two schemes,a simple assessment is made and found that the by-producing steam scheme’s payback period is relatively longer,but its energy utilization is more reasonable.The optimization of process conditions for the diesel hydrogenation process contains two parts: optimization of feed temperature and optimization of the fractionation system.Raising the feed temperature can reduce the energy consumption,and a specific energy saving means is given in this thesis,that is to by-producing steam.The relationship between the feed temperature and the amount of steam produced is determined.The distillation system of the diesel hydrogenation process is a double column process.The pressure,steam volume and steam temperature of the stripping tower are studied in this thesis.It is found that if the operating pressure of the stripping tower can be reduced,the stripping steam consumption can be reduced under the premise of satisfying the stripping requirement.Increase of the stripping steam and the stripping steam temperature can reduce the heat load of the subsequent distillation tower,so that the energy consumption of the reboiler is reduced.Based on the two aspects,reducing the stripper pressure will make the overall fractionation system reduce energy consumption.