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This post was last edited by xiouxingzhe on 2026-6-17 22:40 The seven stages of chemical technology from creativity to industrialization (Issue 44/100 in total) - Technology finalization: Equipment selection and data sheets for containers, pumps, compressors and other sea friends: Hello everyone! In the previous issue, we talked about the selection and design of towers and heat exchangers. This issue wraps up the equipment selection section—containers, pumps, compressors, and other equipment such as filters, mixers, and vacuum pumps. Although these devices are not the "heart" of the device like reactors and towers, any selection error may lead to unstable device operation, high energy consumption and even safety accidents. 1. The residence time and size of the container The main process parameter of the container is the volume, which depends on the residence time and medium flow rate. How to determine the residence time of the tower top reflux tank? I usually choose 5 to 10 minutes at 50% liquid level. The horizontal reflux tank has a large gas-liquid separation space and is easy to arrange, so it is used more frequently. The residence time of the feed buffer tank depends on the stability of the upstream feed and the downstream tolerance of flow fluctuations. If the upstream is continuously stable, 10 to 15 minutes is usually enough. If the upstream incoming material is intermittent or the fluctuation is relatively large, it may take half an hour or even longer. After determining the size of the container, there are a few details worth noting. The number of manholes and handholes must meet the maintenance needs - at least one manhole for the tower top reflux tank, and two manholes may be needed for large-volume storage tanks. The drain port should be set at the lowest point to ensure that materials can be drained cleanly during maintenance. The vent should be set at the highest point to avoid dangerous gas accumulation. Liquid-liquid mixtures with possible stratification also need to be equipped with upper and lower discharge ports. The most common problem in container design is not miscalculating the volume, but ignoring the fluctuation range during operation. It takes time for the liquid level regulating valve to respond, and small fluctuations upstream and downstream will accumulate in the container. If the volume happens to be stuck at the theoretical minimum value, the liquid level often alarms or even interlocks during actual operation. Therefore, the design volume of the container usually leaves a certain margin based on the calculated value, which is not a waste, but provides a buffer space for operations. 2. Pump lift calculation and NPSH. The pump needs to provide parameters such as flow rate, lift, NPSH, and recommended form during the process package stage. How to determine the traffic margin? Usually, 10% to 15% is added to the normal flow rate as the design flow rate. This margin is used to absorb operating fluctuations and adapt to flow changes under different operating conditions. But it should not be too large - if the margin is too large, the pump will run in the low-efficiency zone for a long time, which will waste energy and affect the life of the impeller. The calculation of head is not just the pressure difference between the pump inlet and outlet equipment plus the elevation difference. Pipe friction resistance, local resistance of pipe fittings (elbows, tees, valves), pressure drop of regulating valves, pressure drops of heat exchangers, pressure drops of flow meters and filters - all these resistance losses must be accounted for. The longer the pipeline, the smaller the diameter, and the higher the flow rate, the greater the proportion of resistance loss in the total lift. If this part is ignored, the outlet pressure of the pump will be low during actual operation and the flow rate will not reach the design value. The parameter of NPSH is easily ignored by young engineers. The effective NPSH at the pump inlet must be greater than the NPSH required by the pump, otherwise the pump will experience cavitation - large vibrations, loud noises, and the impeller will be damaged quickly. The calculation of effective NPSH depends on the absolute pressure of the liquid level at the pump inlet, the level difference from the liquid level to the pump inlet, the resistance loss of the suction pipeline and the saturated vapor pressure of the medium. The installation height of the tower bottom pump and the height of the tower skirt serve this purpose - the higher the skirt, the greater the level difference between the liquid level at the bottom of the tower and the pump inlet, and the more sufficient the effective NPSH. After the pump selection is completed, prepare a data sheet for each pump: No., name, quantity, type, operating conditions and design conditions, flow rate, lift, NPSH, material, motor power, nozzle table. Every parameter on the data sheet can be derived from PFD and momentum balance calculations. 3. Compressor procurement data sheet The compressor mainly provides a procurement data sheet in the process package stage, and does not require detailed structural design - that is the responsibility of the compressor manufacturer. Procurement data sheet needs to be provided: Composition of the intake air - mole fraction of each component ； Inlet air temperature, pressure, and flow rate—normal values and possible fluctuation ranges ； Outlet required pressure and temperature ； If there is interstage cooling or post-cooling, the specifications and temperature of the cooling medium. Special reminder here: The composition of the intake air must be complete and accurate. Trace components—even inert gases containing less than one percent—can affect compressor performance and discharge temperature more than imagined. Because inert gas will accumulate in the circulation loop, it will cause changes in the molecular weight of the incoming air, thereby affecting the performance curve of the compressor. In addition, the fluctuation ranges of inlet pressure and temperature must also be clearly marked, and the compressor selection must cover the most unfavorable working conditions—usually summer conditions when the inlet air temperature is the highest and the inlet pressure is the lowest. The compressor data sheet should also indicate whether frequency conversion adjustment is required, whether one is required for use and one for standby, noise limits and vibration limits. If there are special installation requirements - such as the need for an independent foundation or the need for a soundproof enclosure - these should also be noted. 4. Other equipment In addition to containers, pumps, and compressors, the process package also involves many other equipment. The stirrer is used in the reactor and the mixing tank. The process professional needs to provide the purpose of stirring, material properties, and operating conditions. The specific selection and power calculation of the stirrer are usually completed by the stirrer manufacturer. The process package stage mainly provides conditions. The filter needs to provide filtration accuracy, processing capacity, operating temperature and pressure, and allowable pressure drop. The filtration accuracy is not as fine as possible - if it is too fine, it will cause frequent clogging, frequent backwashing, and high operating costs. Reasonable accuracy is the minimum accuracy required to meet downstream equipment protection or product quality requirements. The vacuum pump needs to provide the pumping volume, the required vacuum degree, and the composition of the pumped gas. Special attention should be paid to the design of vacuum systems: If there are condensable components in the pumped gas, a condenser must be installed in front of the vacuum pump to prevent condensable gas from condensing in the pump and causing damage to the pump. If the gas is corrosive, the pump material and sealing fluid need to be selected accordingly. The selection ideas for these devices are actually similar.: First clarify the process requirements, then determine the key parameters, and finally compile the data sheet. The data sheet of each piece of equipment must have a source for the parameters and a basis for model selection. 5. Equipment data table summary and equipment list After the selection calculation and data table preparation of each piece of equipment are completed, the key information of all equipment is summarized into an equipment list. The equipment list is a direct input for subsequent equipment layout design.: The overall dimensions determine the frame span and floor height, the weight determines the foundation and hoisting plan, and the orientation of the pipe opening determines the pipeline direction. The list includes at least the tag number, name, quantity, type, key dimensions, material, weight, operating conditions and design conditions. Cross-checking is also required between data tables. The discharge temperature of the reactor and the feed temperature of its downstream heat exchanger should be consistent on the two data sheets. The flow rate of the pump and the material balance data of the pipeline in which it is located should be consistent. The heat load of the heat exchanger and the heat balance sheet should be consistent. This cross-check may seem trivial, but many design errors occur at these interfaces. The finished product of equipment selection is a complete set of data sheets and calculations behind the data sheets. The data sheet is for downstream design, and the calculation sheet is for archiving for future reference. If there is a problem with the equipment during the operation of the device in the future, the calculation sheet can be used to review the original selection basis and analyze whether the problem lies in the design assumptions or the manufacturing and installation process. Next issue preview No. 45: PID preparation - from control intention to engineering realization and equipment selection, all are completed, and the key parameters of all equipment have been determined. Next, enter the eighth core task of process package preparation-PID preparation. PID is the document with the highest information density in the process package. It refines every line and every control intention on the PFD into specific pipelines, valves, instruments and interlocks. Starting from this period, three periods will be used to carry out the preparation and review of PID in detail. In the next issue, we will talk about PID page planning and information density control.