Thread Content
1 Determine the process route: Except for a small number of new products, the process routes for most domestic chemical technologies have already been basically determined. For the same raw materials and the same product, if there are several process routes available, each route is analyzed and compared separately before a decision is made. It is mainly considered from the following aspects: 1. Parameters such as required temperature and pressure. The results achieved among the various approaches are similar; the approach that makes it easier to set the operational parameters should be given priority ； 2. Investment ； 3. Energy consumption ； 4. Safety ； 5. Environmental protection ； 6. Requirements for materials ； 7. Product quality ； 8. Whether it constitutes infringement. 2 Data collection: Collect basic data through experiments (laboratory, pilot scale, pilot plant, industrial production, etc.) or by consulting various sources such as literature, papers, and technical books, using all possible channels (within legal boundaries). This includes: the physical properties of all substances involved in the technology and the interactions between these substances, as well as all relevant reactions, catalysts, reaction mechanisms, etc. At the same time, pay attention to protecting the intellectual property rights arising throughout the process. // Regarding reactions: As is well known, reactions are the soul of the entire system and lie at the very core of the \"onion model\". If there are problems with them, all other efforts become pointless; if they are incorrect, the entire benchmark is wrong. So, it’s very, very, very important! Reactions are classified according to the presence of a catalyst: catalytic reactions, uncatalyzed reactions ； Classified by phase: homogeneous reactions, heterogeneous reactions. Regardless of the type of reaction, as a process package developer, it is necessary to have a thorough understanding of the reaction, with a clear and precise knowledge of its mechanism. Researchers who are only engaged in laboratory research find it difficult to develop proper process packages, and this is constrained by two factors: the first factor is the lack of engineering experience ； Factor two: Lack of production experience from the industrialization era. Technical personnel who only focus on engineering design also find it difficult to develop a proper process package, due to a lack of understanding of reaction mechanisms and relevant data, as well as a lack of production data and experience. Technical personnel who are only involved in production also find it difficult to do a good job, due to the lack of experience and data in research and development as well as engineering design. In the case of catalytic reactions, process package developers must at least be familiar with the physical properties of catalysts, such as strength, porosity, bulk density, active components, and carrier materials. In addition, it is necessary to understand the chemical properties of catalysts, such as the conversion rate and selectivity of the reaction, factors affecting the reaction (including temperature, pressure, flow rate, component ratios), space velocity, factors that cause catalyst deactivation and poisoning, parameters of reaction thermodynamic equilibrium, reaction kinetic equations, and the steps governing the reaction, among others. Of course, this data can also be provided by the personnel in the project team who specialize in catalyst research and development. In the case of a non-catalytic reaction, it is also necessary to understand the reaction mechanism, factors affecting the reaction, reaction kinetic equations, steps for controlling the reaction, heat absorbed or released, consequences of overheating, and protective measures against reaction runaway. // On separation and recycling // Common separations in chemical plants include gas-liquid separation, absorption, stripping, desorption, distillation, etc. The calculation for ordinary separation tanks is generally based on the diameter of the separated droplets, while high-efficiency separation tanks usually have specific process requirements. The key to absorption is finding the appropriate absorbent. Stripping is used to break the original gas-liquid equilibrium and achieve separation by changing partial pressures. Desorption is the reverse process of absorption. Ordinary distillation relies on boiling points for separation; however, when there are azeotropes or substances with very similar boiling points, special distillation methods such as azeotropic distillation, extractive distillation, or pressure-swapped distillation can be considered. It needs to be determined after analyzing the specific conditions of the substance to be separated. If the binary interaction parameter is missing from the database, it is necessary to measure the gas-liquid equilibrium data or obtain it by consulting relevant literature. Subsequently, a regression analysis of the gas-liquid equilibrium data is performed to determine the binary interaction parameter, thereby enabling accurate separation calculations to be carried out. Circulation is generally divided into gas-phase circulation and liquid-phase circulation, and it is usually carried out to meet the requirements of reactions or separation. In chemical plants, the one-pass conversion rate for most reactions is not high; therefore, a cyclic process must be employed to achieve higher yields, as in the case of plants for ammonia synthesis, urea production, ammonium carbonate synthesis, coal tar hydrogenation, melamine production, methanol production, and ethylene glycol production. Furthermore, for some difficult-to-separate systems, a cyclic approach is also employed in order to achieve high yields and good product quality. The greater the circulation volume and the greater the circulation pressure drop, the higher the energy consumption; there is therefore significant potential for reducing energy consumption in this area. Generally, the more loops there are, the higher the complexity of the process, and the greater the difficulty in designing, controlling, and operating it. // Regarding heat transfer // the enthalpy and specific heat values of all substances/flows involved in the collection process, as well as the heat of reaction, heat of fusion, etc., for all reactions. Heat is recovered through staged heat exchange based on temperature and heat levels within the device (efforts should be made to recover and utilize heat within the device itself; if heat cannot be recovered there, then recovery and utilization should be considered from the perspective of the entire plant). When designing heat exchange networks, it is important to avoid relying solely on theoretical considerations; operational and process feasibility must also be taken into account. Factors such as dew point corrosion, crystallization, blockages, and the impact of gas-liquid phases on catalysts, all resulting from heat exchange, need to be thoroughly considered. // Regarding momentum transfer // Collect parameters such as the viscosity and vaporization pressure of all flow streams; avoid piston flow in two-phase flows, and reduce momentum loss through proper equipment layout to save energy. 3 Process simulation: For the development of process packages, it is essential to carry out full-process simulation. There are two extreme and incorrect views regarding process simulation. Viewpoint 1: Process simulation is omnipotent; everything can be understood by simulating it ； Viewpoint 2: Process simulation is useless; there are too many influencing factors, making it impossible to get accurate results. Both of these views are like trying to understand an elephant by touching it blindly; they do not allow for an objective understanding of simulation software. // Correct understanding of simulation // 1. Process simulation is very helpful for understanding a process; especially after conducting a full-process simulation, there is a qualitative improvement in the understanding of the entire system ； 2. Process simulation is not merely a matter of input and output; it requires extensive manual analysis. Every change in a parameter, its influencing factors, as well as the changes across the entire system resulting from a change in a parameter, all need to be analyzed one by one. In addition, the key data also need to be compared and analyzed with data from experiments, pilot tests, scale-up trials, and industrial production, in order to further refine the model data ； 3. Process simulation is not a panacea; without input, there is no output, and if the input is incorrect, the output will certainly be incorrect as well. Even if the input is correct, the output may still not match the experimental or production data; it is necessary to conduct a thorough analysis of such discrepancies in order to identify the causes of the inconsistency ； 4. The application of process simulation can **shorten the development time of process packages, reduce the amount of experimental work, guide production, and predict trends in data development** ； 5. Through process simulation, complete data on material and energy balances, as well as property parameters, can be obtained, providing fundamental data for engineering design and production ； 6. Various options can be comprehensively compared through simulation to determine the optimal one. // Specific work to be carried out // 1. Determine the property measurement method based on physical properties ； 2. Starting from the reaction, if it is influenced only by thermodynamic equilibrium, then a chemical equilibrium reactor module can be considered, and relevant parameters can be obtained by adjusting the equilibrium temperature difference. If the reaction is influenced not only by thermodynamic equilibrium but also by reaction kinetics, the reaction rate equation and related parameters (including activation energy, pre-exponential factor, adsorption factor, adsorption/reaction equilibrium constants, etc.) are derived through fitting experimental data. These parameters are then used in the reaction module of process simulations, and the simulation results are compared with experimental data for analysis and correction. The aim is to make the model predictable, providing a reliable basis for industrial scale-up ； 3. Address the issues related to separation and heat exchange. Based on the data collected earlier and the initially developed process, perform simulation calculations (including regression of property data, analysis and calculation of heat exchangers, etc.). Analyze and correct any problems that are identified, and simultaneously compare various possible processes to determine the optimal one. Once the optimal process is identified, further optimization of individual equipment is carried out ； 4. Match utility services (keep the specifications as minimal as possible while considering investment). Thus, the simulation work is essentially complete. I hope this casual treatment of the matter will not mislead some people. Because chemical engineering is truly vast and complex; to achieve mastery in even just one aspect of it could require an entire lifetime, yet still might not be sufficient. 4. Complete the PFD, PID, and equipment data sheets. After accurate full-process simulation, a complete material flow diagram (PFD) can be obtained. Referencing the process patterns of typical unit equipment, taking into account the characteristics and requirements of the process, and involving the instrumentation team, a PID control system is developed together. The economic flow rate is determined based on the information regarding various flow streams shown on the PFD; pipe pressure drops are calculated, and then the pipe diameter is determined. Considerations such as purging, catalyst heating and reduction/ shutdown protection, pre-sulfidization, etc., are taken into account in line with the needs for starting up and shutting down the system, along with the necessary lines for these operations. Design calculations are carried out for all equipment; for standardized equipment, detailed parameters and material selection principles are specified, while for custom-made equipment, dimensions, size, height, internal components, etc. are calculated. // Reactor // It is determined based on a comprehensive consideration of the reaction factors, including: reaction type (fast/slow reaction, gas-liquid reaction/gas-gas reaction/liquid-liquid reaction/gas-solid reaction, catalytic/non-catalytic reaction, etc.), catalyst performance (if it is a catalytic reaction), space velocity, reaction rate, reaction control steps, residence time, mass distribution, heat transfer, scale-up effects, and other factors. // Column types // Include packed columns and tray columns; there are also columns that have both packing and trays within them. Packed towers generally have low pressure drops, while tray towers have higher pressure drops. Packed towers usually require a higher spray density compared to tray towers. Additionally, the properties of the material being processed also have a significant impact on the choice of tower type. Based on the separation requirements, the feed position is optimized, the reflux ratio and the number of theoretical plates are adjusted; an appropriate flooding coefficient is selected according to the properties of the material, and calculations for the tower are carried out to determine the gas-liquid phase loads, liquid holdup, spray density, and pressure drop for each tray/packing element. // Heat exchanger // Import the data from the process simulation into the heat exchanger calculation software to carry out the calculations. Calculations are generally carried out using the verification mode in HTRI. In process simulation, the temperature difference between the hot and cold sides is usually maintained at ≥8°C; attempts are made to avoid temperature crossover. Factors such as fouling heat resistance, the need for cleaning, thermal expansion, and appropriate margins are taken into account. Depending on the climate conditions and water supply situation at the site where the plant will be built, air cooling may be employed, as it is generally used in situations where the heat load is high and the temperature difference is small. High-efficiency heat exchangers are considered for applications with high heat exchange requirements, a small temperature difference between the hot and cold sides, low pressure drop requirements, and limited space constraints. // Compressor // The type of compressor is determined based on the volume of gas, pressure ratio, and the composition of the gas being transported. Based on the specific conditions of the plant, such as electricity prices, the availability of steam, the possibility of installing boilers or a captive power plant, coal prices, and other factors, an decision is made as to whether to use electric drive or steam drive after comprehensive analysis. When electric drive is used, the compressor generally requires a lower initial investment, occupies less space, and involves less work in operation/maintenance. However, when adjusted for the unit price of the product, electricity is usually more expensive than steam. If steam drive is used, generally the initial investment in compressors is high, they require a large amount of space, and there is a lot of work involved in operation and maintenance. However, when the cost per unit of product is taken into account, steam is usually cheaper than electricity. Of course, there are also some factories that are exceptions; therefore, it is necessary to adapt measures to local conditions – one must never make generalizations! In addition, for systems driven by steam, it is necessary to consider whether the compressor uses a full condensation, extraction condensation, or back-pressure type (this needs to be taken into account within the overall plant steam balance). If the compressor employs full condensation or extraction condensation, it is also necessary to decide whether surface cooling should be achieved through water cooling or air cooling, as these two methods have different effects on the compressor’s steam consumption. // Separator // Based on the previous calculations, simply organize the equipment data sheet. // Storage tanks // Includes buffer tanks, intermediate storage tanks, finished product storage tanks, etc., which are determined based on residence time, storage duration, as well as production operational requirements (such as requirements for manual sampling, product sealing, shift handover, etc.). // Other equipment // Non-standard equipment; detailed specifications regarding dimensions, types of internal components, as well as detailed parameters and process parameters are required ； For shaping equipment, detailed process parameters, process requirements, material selection principles, etc. should be specified. 5. Complete the design specifications, instrument specification sheets, interlock instructions, recommended equipment layout diagrams, etc. At this stage, refer to the requirements outlined in the SHSG 052-2003 Process Design Package for petrochemical plants (a comprehensive set of technical specifications) and carry out each task in accordance with those requirements. Of course, this involves a wide range of knowledge areas and high standards; in addition to process-related aspects, it also covers equipment, instruments, hygiene, safety, environmental protection, analysis, piping materials, layout, production, and more. Therefore, creating a good, mature process package that can be applied in practice truly cannot be accomplished by an individual alone. It must be supported by a good team, one that includes experts in research and development, technology, engineering, production, etc. To complete the two manuals – the analysis and testing manual and the operation manual – thorough understanding of the manufacturing process is necessary, in addition to a large amount of experimental data and results from pilot tests.