Energy Optimization Of Distillation And Heat Exchange System In Oil Refining Process

According to “three-link” theory, any chemical process is composed of threesub-systems of heat exchange, distillation/reaction and utility. In this paper, some issues onprocess integration concerned with heat exchange, distillation, interaction between heatexchange and distillation, as well as utility have been researched, respectively.On heat exchange: three corrections are applied to improve the SimultaneousOptimization Synthesis Approach (SOSA) of heat exchangers network (HEN). Firstly thetemperature-dependent characteristic of process streams is considered in calculating theirheat capacities, which were regarded as constant value in a defined temperature interval;secondly the splitters and mixers of streams located in the network are listed in investmentitem, resulting in the more detailed cost calculation of HEN; thirdly a group of heuristic rulesis suggested to cancel those MINLP superstructure matches impossible in engineering andthermodynamics before the optimization calculation, making the simultaneous optimizationson both investment cost and utility consumption charge available.On distillation:1. A general method on multivariable operation optimization of ansimple petroleum fractional column is built, where a strict plate-by-plate enthalpy calculationis used to abort the assumption of permanent molecule flow in the distillation process, andthe factor of pressure drop is also considered in the calculation of plate temperatures,resulting in higher model accuracy, especially to vacuum distillation system.2. A method forthe operation optimization of fractional system aided by process simulation technology isdeveloped. In its way, the calculation of complicated Jacobi matrix can be avoided byreplacing dY/dXwith Y/Xwhich are obtained by simulation(X stands forindependent variable, and Y for state variable), making it become available for us toconveniently get the Generalize Reduced Gradient XNofX Nand the optimal step size(X N1XN (XN)X N). Especially, the Transfer Matrix (TM) developed in thismethod can help us to reduce the simulation workload greatly.3. Based on the carbon balance principal of chemical reaction, a method of calculating the stoichiometriccoefficients of reactants and resultants in lump hydrocracking reaction has been suggestedwith use of the distribution function of the Stangeland’s model for modeling hydrocrackingprocess of petroleum distillates. Consequently, the hydrogen consumption of individual lumpreaction process can be calculated accurately, resulting in a correct estimation on reactionheat amount, material balance and energy balance of every lump reaction process.On coordination optimization of heat exchange&distillation: the distribution ofpumparound heat in a complex distillation column is investigated, an three-level adjustingstrategy covering total tower, upper&under parts, single pumparound, respectively, issuggested. Based on the linearization treatment of temperature and flowrate disturbances, therunning equation of HEN was developed, it exposes the interaction mechanism of HEN andtell us how to achieve the optimal final temperature of the target stream by adjusting thepumparound parameters. Meanwhile, this paper also gives a method to carry out thecoordination optimization between heat exchanger sun-system and distillation sub-system,where HEN and column’s structure changes as well as adjustment of pumparoundparameters are permitted, the revamped Dhulesia interpolating model and new-built HENsimulation model are used to monitor side product qualities and network behavior during theadjustment.On utility: first a conception of “generalized utility” is suggested. It puts processfurnaces located in process units into the unified utility system from the view of energyapplication, enriching the heat integration of utility tremendously and making systemsolution available. Combining the Grand Composite Curve （GCC）of Pinch Technology anoptimal energy integration case and the corresponding estimation standard of energy usageon utility system are developed. The standard can tell us ideal aims on fuel consumption andpower generation in the generalized utility. For example, under the condition of warrantingthe minimum heat supply to the process system, how much the minimum fuel consumptionshould be when no power generation? How much again when keeping the current powerproduction unchanged? And how much the maximum power generation when keeping thepresent fuel consumption constant? And how much the minimum fuel and the maximumpower should be to a new-designed utility? In addition, a heat integration method between process furnace and gas turbine is developed to copy with the concentration of fuel ingeneralized utility. The method has been computer-programmed and is available to both newsystem construction and revamp of existing system. Meanwhile, a three-parameterevaluation skill is suggested to the integration case.