Optimizing the network of preheat converters of distillation unit 80 of Abadan refinery using pinch technology

Dissertation

Master's degree

Department: Chemical Engineering

Abstract.

In the design of the heat exchanger network, the designer usually considers high operational flexibility in the presented plan. However, some of the changes that occur in the operating conditions of the process after the design, determine the need to modify the existing network. The purpose of the network modification is to design an economic network by taking into account the operational limitations and appropriate to the new operating conditions. Two common methods in network modification and revision are pinch design method and mathematical programming method. Pinch's method is time-consuming and solves the problem based on the experience and judgment of the designer and with a manual approach. While the mathematical programming method is faster and the application of the designer's taste is less. This method seeks the most optimal solution for network modification with a precise approach. In this research, the combination of two mathematical optimization methods and pinch method, which are based on thermodynamic analysis and practical design, was used to modify the 80th distillation unit of Ibadan Refinery. In the targeting stage, the physical properties of the currents are considered variable with temperature, and each current is divided into several sub-currents that have similar physical properties. By applying the pinch technology and changing ?T(Min), no change has been made in the arrangement of the heat exchanger network, and by reviewing and re-examining the network, it was concluded that the design of the heat exchanger network is a threshold issue, and to increase the heat recovery between the process flows, the network structure should not change in any way because it is in its best state, but since the area used by the heat exchanger network is more than the actual area required for the capacity is 90,000 barrels per day, it can be reduced by reducing the investment cost by 7 shells.

Keywords:

Thermal integration, heat exchanger network, corrective design, optimization, operating mode

1                   Chapter 1

1-1             Necessity of conducting research

With the increase in the price of energy carriers and the energy crisis since the beginning of the seventies, as well as high energy consumption in the industrial sector, energy saving in industries, especially process and chemical industries, is essential. Also, due to the high consumption of gasoline and the discussion of self-sufficiency in the production of gasoline by the country's refineries, the improvement and optimization of the gasoline units of the oil refineries has been considered. This led to the invention of various methods to save energy consumption and also reuse wasted energy in a process. Increasing fuel prices, decreasing fossil fuel resources and the need to maintain the environment are factors that show the importance of optimal recovery of thermal energy and prevention of energy waste in various industries. Today, optimal energy consumption has been proposed as one of the main indicators in evaluating the development of societies. The high intensity of energy consumption in chemical processes causes an increase in production and operation costs as well as a decrease in the efficiency of material extraction in industrial products. Also, considering the importance of heat exchanger network design as one of the important parts of process design, the heat exchanger network of this unit has been investigated from the perspective of thermal integration. This study has been done with two approaches in the form of modifying the existing network and redesigning the network. In redesigning the network, the goal is to minimize the level of heat transfer or the total annual cost of the unit. While the purpose of reviewing and modifying the existing network is to minimize the investment return period after implementing the changes made in the network. The two common methods in designing and modifying the heat exchanger network are the pinch design method and the mathematical programming method. The operating mode of the network is also checked to check the efficiency of the design when the operating conditions change. The reduction of the overall heat transfer coefficient due to the formation of deposits, changes in the inlet temperature or the mass flow rate of the process flows are among the operational parameters whose effect is checked in the network.. In this thesis, the combination of two mathematical optimization methods and the pinch method, which are based on thermodynamic analysis and functional design, have been used in order to redesign and modify the network. Along with its initial development in universities, the pinch technology has also been used in industrial processes, and today it is referred to as a complete technology in academic and industrial centers. Efficient analysis is to check the performance of energy systems and process units. Relying on the results based on this analysis, identifying the critical points of the process and optimizing the energy of the unit by correcting these critical points, the maximum desired results will be achieved. Pinch analysis, in addition to determining faulty heat exchangers, suggests a solution and network of suitable heat exchangers. In the meantime, energy optimization in unit 80 has been investigated. 1-2 Research method: In the thesis, unit 80 of the Abadan refinery's distillation tower is simulated by Aspen hysys refinery software and the simulation results are compared with real values. In the next step, the simulated version is linked to the Aspen hysys Analyzer V7.2 software (the same as HX-NET software) and the network of heat exchangers is drawn in the environment of this software. By evaluating the above network with the help of pinch technology, the possibility of network modification is checked and the necessary suggestions are provided. The method used in Aspen hysys Analyzer V7.2 software is a combination of two mathematical methods and pinch method. The two pinch design methods and the mathematical programming method are among the most widely used methods for network modification.

1-3             Thesis structure:

The studies and analyzes carried out in this research are presented in the form of 5 chapters as follows:

In the first chapter, after a short introduction about the importance of unit energy optimization 80, the method carried out in this study to reduce energy consumption and modify the heat exchanger network of this unit is stated.

In the second chapter, the background of the pinch analysis method and its initial definitions are stated with reference to the history of conducting studies of this analysis and as a criterion for evaluating energy systems and determining the critical points of the process.

In the third chapter, the pinch analysis method in the integration of processes, The goals and principles and criteria of the pinch method are stated in the modification of the heat exchanger network and the optimization of processes using pinch technology. In this chapter, after describing the history of the development of this refinery unit, the types of processes and specifications of the feed and product of this unit are stated.

In the fifth chapter, the results of pinch analysis and other studies conducted in unit 80 of Abadan are given, and in the rest of the chapter, the modification of the heat exchanger network of the unit is stated, and at the end of the chapter, the conclusion of this research and suggestions for future works and studies are stated. 

Abstract

Heat exchanger network (HEN) designs usually feature a high degree of operational flexibility; however some of the subsequent changes made to the operation of processes are so severe that they require retrofit of the original HEN. The retrofit objective is to produce a cost-effective HEN design, subject to any design and operating constraints, which is suitable for the new operating conditions. The two most often used methods in a HEN retrofit are the pinch design method and the mathematical programming method. The pinch method is more time consuming and results are based on the experience and judgment of the designer, but offers more "hands-on" approach to the problem. While the mathematical programming method is less time consuming and has a detailed approach to finding the solution, it requires less user interaction. This study combines mathematical optimization techniques with pinch method, based on thermodynamic analysis and practical engineering, to efficiently solve industrial size retrofit of unit 80 Abadan plant. In targeting step, values ??of physical properties considered various with temperature along each stream.