In the heat exchange network,fouling is a frequent operation problem in the operation of the heat exchanger.The fouling problem in the heat exchanger can be optimized by three measures such as changing the flow rate of the heat exchanger,adjusting the split ratio,and regularly carrying out off-line scale removal treatment on the heat exchanger.These three optimization methods have their own advantages and disadvantages as well as limitations.Both the crude oil preheat network and circulating water network are common in industry.When optimizing such cases,the fouling and pressure drop problems must be taken into consideration.The pressure drop causes an increase in pump power consumption.The fouling rate is a dynamic process,which is related to the parameters such as flow rate and wall temperature.The scale rate of the high temperature crude oil can be described using the Polley scale threshold model.The fouling rate of water in circulating water network is based on the related water fouling model.They are essentially the result of the competition of settlement and suppression.If the temperature is too high and the flow rate is too low,the fouling rate will be increased.In chapter 4 and 5 in this paper,under different operation cycles and different physical parameters of crude oil,the atmospheric and vacuum preheating network of crude oil considering fouling and pressure drop is studied,use these three methods separately,the temperature parameters are calculated by NTU element method,and the optimization of the heat exchange network of the fixed structure is realized by applying the stimulated annealing algorithm.The results show that the three methods can reduce the annual total cost to varying degrees,and the energy saving benefit and optimization strategy will change with different operation cycles and different physical parameters.The flow rate optimization method is quite suitable for oil cases where the operation cycle is not very long or the fouling is slight.The energy saving effect of flow rate optimization method is always better than that of shunt ratio optimization method.For cases where the operation cycle is too long or the fouling is serious,the optimization method of scale removal cycle is always the best optimization strategy.In addition,two optimization schemes of the circulating water network are also discussed in this paper.The results show that the scheme of adjusting the initial mass flow rate can bring better energy saving benefit than the optimization scheme of adjusting the mass flow rate every month on the premise of completing the heat transfer task of each heat exchanger during the operation cycle. |