Approaches and steps for process package development

Thread Content

The approach and steps for developing process packages: The process package related to YD-liutaize’s integrated chemical technology is the cornerstone of everything, which deterres many professionals in the chemical industry; they find it too complex and complicated to venture into it. Drawing on nearly eight years of practical experience, the author shares personal insights. Comments and corrections from industry professionals are welcome! Development approach and steps: 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 established. 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 effects achieved through several routes are similar; the route with easier-to-implement operating parameters should be chosen preferentially ； 2. Investment ； 3. Energy consumption ； 4. Safety ； 5. Environmental protection ； 6. Requirements for materials ； 7. Product quality ； 8. Whether it constitutes infringement. II. Data collection: Collect basic data through experiments (laboratory tests, pilot tests, scale-up tests, 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. It is well known that the reaction is the soul of the entire system and lies at the very core of the \"onion model\"; if there are problems with it, all other efforts are in vain, and if it is incorrect, the entire benchmark becomes invalid. 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. Research scientists 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 handle 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 production experience. It’s also difficult for technicians who do only production work to perform well, as they lack experience and data in research, development, and 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. In addition, one must also understand the chemical properties of catalysts, such as the reaction conversion rate, selectivity, factors influencing the reaction (including temperature, pressure, flow rate, and component ratios), space velocity, factors affecting catalyst deactivation and poisoning, thermodynamic equilibrium parameters of the reaction, reaction kinetic equations, and the rate-determining steps of the reaction, etc. 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 measures to prevent loss of reaction control. The common separations in separation and recycling 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 disrupt the original gas-liquid equilibrium and achieve separation by changing partial pressures; distillation is the reverse process of absorption. Ordinary distillation relies on boiling points for separation, but 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 analysis based on the specific characteristics 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 processing plants, the single-pass conversion rate for most reactions is not very high. To achieve higher yields, a recycling process must be employed; this applies to plants producing ammonia, urea, ammonium carbonate, coal tar hydrogenation products, melamine, methanol, ethylene glycol, and the like. 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 flow rate and the greater the circulation pressure drop, the higher the energy consumption; there is therefore significant potential for reducing energy use in this area. Generally, the more loops there are, the higher the complexity of the process, and the greater the difficulty of designing, controlling, and operating it. The enthalpy and specific heat values of all substances/flows involved in heat transfer collection technologies, as well as the reaction heats, fusion heats, etc., of 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 essential to go beyond purely theoretical considerations and take into account both operational and process feasibility. Factors such as dew point corrosion, crystallization, blockages, and the impact of gas-liquid phases on catalysts, all resulting from heat exchange, must be thoroughly considered. Regarding momentum transfer, parameters such as the viscosity and vaporization pressure of all flow streams are collected; in two-phase flows, piston flow is avoided, and reasonable equipment layout is used to reduce momentum loss and save energy. III. Development of process simulation packages: Performing full-process simulation is essential. There are two extreme and incorrect views regarding process simulation. Viewpoint 1: Process simulation is universal; everything can be understood by simulating it ； Viewpoint 2: Process simulation is useless; there are too many influencing factors, so it’s impossible to make accurate calculations. 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. Below, the author shares personal opinions based on his own practical experience: 1. Process simulation is extremely helpful for understanding processes; in particular, after conducting a full-process simulation, one’s understanding of the entire system undergoes a qualitative leap ； 2. Process simulation is not merely about input and output; it requires a great deal of manual analysis. Every change in parameters and their influencing factors, as well as the resulting changes throughout the entire system due to a single parameter change, must be analyzed individually. Furthermore, 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 definitely be incorrect. 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 material and energy balance data, as well as physical 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 procedures (the following is in my personal style and for reference only): 1. Determine the methods for assessing physical properties based on those properties ； 2. Starting from the reaction, if the reaction 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 purpose is to make the model predictable, so that it can provide a reliable basis for industrial scale-up ； 3. Address issues related to separation and heat exchange. Based on the data collected earlier and the preliminarily formulated process, perform simulation calculations (including regression of physical property data, analysis and calculation of heat exchangers, etc.). Analyze and correct any problems identified. Additionally, conduct calculations and comparisons for various possible processes to determine the optimal one. Once the optimal process is identified, proceed with optimizing each individual piece of equipment ； 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 profound; to achieve mastery in even just one aspect of it could require an entire lifetime, yet still not be sufficient. IV. After completing the PFD, PID, and equipment data sheets through accurate full-process simulation, a complete material flow diagram (PFD) can be obtained. Referring to the process patterns of typical unit equipment, taking into account the characteristics and requirements of the process, and involving the instrumentation team, the PID control is developed together. The economic flow rate is determined based on the information regarding various 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 accordance with the needs for startup and shutdown, along with the necessary startup and shutdown pipelines. 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 the type of reaction (rapid/slow reaction, gas-liquid reaction/gas-gas reaction/liquid-liquid reaction/gas-solid reaction, catalytic/non-catalytic reaction, etc.), catalyst performance (in the case of catalytic reactions), space velocity, reaction rate, reaction control steps, residence time, mass distribution, heat transfer, and scaling effects, among others. Towers: These include packed towers and tray towers; there are also towers that have both packing and trays within the same structure. 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: Simply import the data from the process simulation into the heat exchanger calculation software for computation. The author generally uses the verification mode in HTRI for calculations. In process simulation, the temperature difference between the hot and cold sides is usually maintained at ≥8°C, with efforts made to avoid temperature crossover. Factors such as fouling heat resistance, cleaning requirements, thermal expansion, and appropriate margins are taken into account. Depending on the climate conditions and water supply situation at the site where the plant is built, air cooling is considered; it is generally used in areas with high heat loads and small temperature differences. 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 site—such as electricity prices, availability of surplus steam, feasibility of installing boilers or captive power plants, coal prices, and other factors—a comprehensive analysis is conducted to determine whether electric drive or steam drive should be adopted. With electric drive, generally speaking, the initial investment for the compressor is low, it occupies less space, and requires minimal operating/maintenance efforts. However, when considering the unit cost of the product, electricity is usually more expensive than steam. When steam drive is used, the compressor generally requires a high initial investment, occupies more space, and involves substantial operational/maintenance work. However, when adjusted for the cost per unit of product, steam is usually cheaper than electricity. Of course, there are some factories that are exceptions; therefore, it is necessary to adapt measures to local conditions – one must not make generalizations! In addition, for systems driven by steam, it is necessary to consider whether the compressor uses total condensation, extraction condensation, or backpressure operation (this needs to be taken into account within the overall plant steam balance). If the compressor employs total condensation or extraction condensation, it is also important to decide whether surface cooling should be done via water cooling or air cooling, as these two methods have different impacts on the compressor’s steam consumption. Separator: Based on the previous calculations, simply organize the equipment data sheet. Storage tanks: These include buffer tanks, intermediate storage tanks, and finished product storage tanks, etc., and are determined based on residence time, storage duration, as well as production operational requirements (such as requirements for manual sampling, sealing of products, and transition between shifts, among others). Other equipment: Non-standard equipment – detailed specifications on external 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. V. Complete the design specifications, instrument specifications, 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, developing 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, and so on. Sixthly, two types of manuals need to be completed: the analysis and testing manual and the operation manual. To complete these manuals, not only a thorough understanding of the manufacturing process is required, but also a large amount of experimental data and results from pilot tests. Furthermore, it is necessary to analyze the involvement of professionals and production technicians in its development; only in this way can the resulting manual be used for staff training, to guide operations during startup and shutdown as well as in accident handling, thus serving a practical purpose.