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Petrochemical process system energy, steam system optimization technology advantages

I. Energy optimization method for petrochemical process system

After many years of research and practice of petrochemical process system energy optimization method, Blueprint Engineering (Qingdao) Co., Ltd. has established and integrated the core competitiveness of the design institute, and organized and integrated Houston Mobil Oil Company, Tsinghua University, South China University of Technology, China University of Petroleum and other units. The strongest professors and expert teams in the field, after two years of unremitting efforts, gradually established the following petrochemical process energy optimization method (referred to as the five-step method).
Petrochemical process energy optimization method

The following is a brief description.
1. The whole plant can plan
    Before the specific energy optimization study of each device and system unit, combined with the overall process, product plan, raw material situation, energy consumption structure, near-term development plan, general plan layout and energy consumption in surrounding areas, the total process analysis and linearity Planning as a means to carry out the overall energy planning of the whole plant, to determine the maximum efficiency production process plan and the best energy consumption structure of the whole plant by principle, and to point out the direction and key points for the subsequent energy optimization research.
2. Heat and heat supply between devices
The heat balance of each device is different due to the different processes. Some devices have a lot of heat, and some devices lack energy. If it is limited to the internal heat integration of a single set of devices, it will inevitably lead to low energy utilization efficiency and large cooling load of the heat excess device, while the heat shortage device needs to consume a large amount of high energy level public works. Therefore, it is necessary to break the limitations of the device, according to the principle of “synchronization, proper temperature, suitable load, easy to arrange”, the direct thermal joint between the devices is implemented, and the heat of the thermal surplus device is directly sent to the adjacent and synchronously running heat-deficient device. . The research method is based on a comprehensive investigation of the process characteristics, energy distribution and overall layout of each device, and develops a preliminary joint scheme, and then establishes the energy model of the combined device, and implements the system solution to determine the final thermal joint solution. Including the quantity, quality and depth of joint energy.
Inter-supply relationships are widespread in petrochemical processes. However, due to various reasons and excessive pursuit of safety limits, traditional processes mostly use cold discharge and cold feed, that is, the intermediate product of the upstream device first heats and cools in the device, and then through the intermediate tank area, steam heating and The temperate is then delivered to the downstream unit via an intermediate pump or heat exchanged or further heated by the industrial furnace to a specified process temperature. The process not only repeats heat exchange and cooling, but also consumes heated steam and pump work in the tank area. Therefore, under certain auxiliary process conditions and safety measures, it is necessary to carry out hot discharge/hot feed between the synchronously operated devices. In addition to reducing the repetitive cooling, the most important is to use the medium and low temperature of the intermediate materials in the upstream device. The bit energy replaces the high-energy heating load of the downstream device to achieve energy upgrade utilization. The focus of the study is on the direct supply temperature of the intermediate material as a variable, optimized by the upstream and downstream devices to determine the optimal feed temperature.
3, the device internal energy optimization
     First of all, the first and second steps mentioned above, that is, the total energy planning of the whole plant and the heat integration between the devices and the completion of the hot discharge, the boundary conditions of the device energy optimization have been reasonably determined, and it is no longer an isolated device optimization. It will be in line with the overall goal of the plant and related equipment. This is very important, otherwise it will be lost, that is, the energy consumption of a certain device is reduced, but the energy consumption of other devices or units or systems is increased.
      Energy optimization of the plant is the basis of energy optimization throughout the plant. The content is extremely extensive, mainly including material efficiency optimization (such as improving yield, upgrading product quality, avoiding repeated processing, avoiding high quality and low use of energy and raw materials, and recycling high-value components such as light. Hydrocarbon, hydrogen, steam condensate, etc.), local process or process adjustment (such as shutting down a section, integrating the same section of the plant, etc.), optimization of operating parameters (such as adjusting furnace outlet temperature, tower pressure, blowing volume, fractionation tower) Reflow parameters and reflux heat transfer, etc.), process logistics heat transfer process optimization (including steam production, process optimization), low temperature waste heat recovery process optimization. To this end, it is necessary to establish a rigorous full-process simulation model for each plant, and use advanced and mature technologies and equipment under the guidance of the process energy synthesis theory, combined with the specific process and equipment and space conditions of the device. The technical and economic comparison will finally determine the optimization plan that is practical and synergistic with the overall goal of the whole plant.
4, the whole plant low temperature heat system utilization
After the energy optimization of the third step is completed, the utilization of the internal process heat of the device has been optimized. In other words, the heat has been used to the maximum extent of the process, the total amount of waste heat has been minimized, and the collection process (mainly the low temperature of the hot water medium) The heat collection process has also been established, so the use of waste heat should be implemented next.
The environmental temperature constraints and process heat-promoting characteristics determine that the petrochemical production process will inevitably generate a large amount of low-temperature waste heat, and they are many points, wide and highly dispersed. At the same time, the heat traps that can consume low-temperature waste heat in the petrochemical process are also discretely distributed, and quite a part of the heat. The load of the well also changes with the ambient temperature, which determines that the waste heat recovery and utilization cannot be “point-to-point” and must be “face-to-face”. It must be based on a comprehensive study of the low temperature waste heat and low temperature heat trap characteristics of the whole plant (heat traps should also include The surrounding users of the plant) proposed practical and effective system solutions, especially the use of hot water for long-distance safe transportation, large specific volume and high boiling point, and established the low-temperature waste heat recovery and utilization of the whole plant with hot water as the medium. system. From the practice of many years, there may be more than one such hot water system. It is necessary to establish several sub-regions and sub-functions. They are relatively independent and complement each other. Therefore, the research focuses on the topology of hot water flow and hot water. The system adapts to the flexibility of ambient temperature changes, the coordination between subsystems, and the coordination of operation between the hot water system and the waste heat recovery device.
Low-temperature heat utilization is the energy optimization of the device. It is naturally one of the footholds of the whole system optimization. It is the continuation and guarantee of the energy optimization of the device. If it is not implemented or implemented poorly, many device optimization and system optimization measures become "Half-pull" cannot be implemented and should be highly valued.
5, the entire plant steam power system optimization
After the completion of the previous four studies, the whole plant steam balance will undoubtedly undergo profound changes, so steam system optimization is an objective requirement for process energy optimization. There are three research priorities. a) optimization of steam production and use of various process units and units; (2) optimization of steam pipe network throughout the plant; and (3) optimization of steam power system operation focusing on thermal power plants. The first study was actually completed in the internal energy optimization study of the plant, which gave the minimum process steam demand of the whole plant; the main content of the second study was to adjust the steam pipe network structure of the whole plant and improve the steam delivery quality to achieve the minimum. Steam transmission loss; the third study is to determine the best normal operation plan and emergency adjustment plan based on the actual situation of thermal power plant boilers and turbines under the principle of “heat setting”. In addition, optimization of fresh water, demineralized water, deoxygenated water, and condensate systems associated with steam systems should also be covered.
Petrochemical process steam system optimization method

Through the above five-step research, the problems and solutions of the whole plant energy use are basically determined.
It can be seen that the method has the following characteristics:
1) Systematic. The first, fourth and fifth steps in the figure belong to the whole plant large system optimization, the second step belongs to the partial optimization including several sets of devices, and only the third step is the device level optimization. The whole process goes from the global to the device and from the device to the whole plant, so the problems found and the proposed improvements are comprehensive and synergistic.
2) Quantitative. The entire process, whether it is to analyze problems or develop improvement measures, is based on rigorous full-process simulation calculations to meet actual engineering needs.
3) Integration. All reasonable and mature technologies and processes can be integrated into the method.
The project summing up the above technology “Comprehensive optimization of process industrial energy system and engineering application in the petrochemical industry table” won the first prize of Guangdong Science and Technology Progress Award.
 Second, the device energy optimization method
It can be seen that device energy optimization is the basis of system optimization. After years of practice, we have summarized the following device energy optimization methods.
 Device energy optimization method
The following is a brief description.
1. Understand the basic situation of the device. Mainly through the inspection of operating procedures, relevant design documents / drawings and on-site investigations, etc., to understand the general map of the device and site layout, major equipment models, etc., to provide a basis for subsequent calculations;
2. Field operation simulation fitting. Due to the limited measurement methods, the data that the device DCS and the field table can give are extremely limited, and some of the data may be wrong, so it is impossible to perform accurate energy analysis on existing processes and operations based on these data. It is impossible to propose appropriate improvements. Our method is:
1 Use general large-scale commercial process simulation software such as PRO/II, ASPEN PLUS, HTRI, etc. to establish a full-process simulation model of the device;
2 Implement simulation calculations, and continuously adjust thermodynamic methods, equipment efficiency, dirt thermal resistance and possible process losses in the calculation process, and try to make the calculation results consistent with the field data; if they are consistent, the calculation parameters are simulated to simulate the actual operation. The problems found in this way are real and quantitative, and the improvement measures proposed next are also reliable.
After the simulation is fitted, we can get the maximum amount of data. Taking the heat exchanger as an example, the Reynolds number Rei and Reo inside and outside the tube can be obtained; the heat transfer film coefficients αi and αo inside and outside the tube; the fluid flow velocity ui and uo inside and outside the tube; the fluid flow pressure drop ΔPi and △Po inside and outside the tube; Thermal coefficient K; logarithmic mean temperature difference LMTD; temperature difference correction factor Ft; heat load Q; heat exchange area A; process efficiency k0. Obviously, they are not available on the spot table and DCS. With this data, we can get a more comprehensive understanding of the energy consumption of the heat exchanger.
The simulation of the fitting process is critical and is the basis for the correct analysis of the problem and the proposed measures, and of course the most time consuming.
3. Summarize the main problems in the energy consumption of the device. Since the second-step simulation allows us to obtain the most abundant quantitative data, it is possible to perform energy analysis under the guidance of the scientific energy theory.
4. Develop an energy optimization plan. Usually according to the difficulty level, according to the convenience of cooperation with other devices and units, according to the actual situation on the site (including spatial location, etc.), as well as the possible shutdown maintenance period and near-term planning, from shallow to deep, from simple to complex A number of programs are reviewed by Party A.
5. Conduct a technical and economic analysis of the plan, estimate the project quantity, investment amount, energy saving quantity and benefit of each plan, and clearly give the recommended plan.

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