Seven stages of chemical technology from creativity to industrialization (Issue 41/Total 100)--PFD Milestone Review

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This post was last edited by xiouxingzhe on 2026-6-14 22:37 The seven stages of chemical technology from creativity to industrialization (Issue 41/100 in total) - Technology finalization: PFD Milestone Review Dear Haiyou Friends: Hello everyone! In the last issue, we talked about the preparation of PFD - the results of the three-balance calculation are all condensed on this drawing. This issue talks about a more critical action: Milestone Review of PFD. Just because the PFD has been painted, does not mean it is ready for use. The review process failed, and all previous calculations and drawings were only in "draft" status. After passing the review, the PFD is officially frozen and becomes the only data benchmark for all subsequent downstream work. The importance of this review cannot be overstated. so to speak: The quality of PFD review directly determines the fate of the project. The PFD that has passed the review is a technical document that can withstand scrutiny. ； The PFD that is just a formality in the review process is a hidden danger buried in the downstream design from time to time. 1. Purpose of evaluation: Not just "finding faults" Many people understand review as "finding problems". This understanding is not wrong, but it is not comprehensive. The core purpose of the PFD review is to confirm two things. First, confirm that every data on the PFD has a reliable source. Second, confirm that the process plan is technically sound and engineering feasible. “"Data has a source" means that every temperature, pressure, flow rate, heat load, and utility consumption on the PFD can be traced back to the pilot data package or process simulation calculation results. It's not written on the head, nor copied and pasted from other projects. “"The plan is established" means that this process is not only feasible in theory, but also has no insurmountable obstacles in project implementation. The purpose of the review is not to find anyone's fault, but to expose all the problems that should be exposed during the drawing stage. If you find a problem on the drawing, you can change the data and calculate it again, and the cost is almost zero. It was not until the construction stage that there was a problem with the data on the PFD, and the cost of rework would be dozens or hundreds of times. 2. Who will participate in the review? The PFD review cannot just be done by the craft majors behind closed doors. I usually recommend inviting the following people to attend. The core members of the process package preparation team are the person in charge of process simulation, the person in charge of equipment, and the person in charge of instrumentation. They are most familiar with the data on the PFD and must be able to explain the source and calculation basis of each data. Owner's representative. What they focus on is whether investment and consumption indicators are within acceptable ranges, and whether product solutions and device scale meet market demand. Technology provider, if any. They focused on whether the data in the pilot data package was accurately converted to the PFD and whether the design conditions of the core reaction and separation units were within the operating window verified by the data package. Equipment experts. What they are concerned about is whether there is a feasible equipment solution for the equipment operating conditions marked on the PFD - if the reactor operating temperature exceeds the allowable range of conventional materials, what special materials or cooling measures are required. Instrumentation expert. Pay attention to whether the key control scheme marked on the PFD is achievable, and whether the temperature and pressure conditions at the measurement and control points exceed the applicable range of conventional instruments. Driving expert. It is best to have someone with more driving experience participate. What they are concerned about is whether the operating conditions and operating flexibility marked on the PFD are reasonable—whether the difference between startup conditions and normal operating conditions is fully considered, and whether the material direction during shutdown and accident conditions is clearly planned. Materials expert. For highly corrosive systems, the opinions of material experts are very important - whether corrosive components have been missed and whether there is any risk of erosion caused by multi-phase flow. This review team seems to have many people, but each role has an irreplaceable perspective. Process majors cannot see problems in equipment manufacturing, equipment experts cannot see problems in operation and maintenance, and driving experts can see details that designers would never think of while sitting in the office. Without any perspective, the review will have a blind spot (of course, in reality, one person may be responsible for multiple roles. In this case, please review from different perspectives). 3. What to review During the review meeting, take the PFD and compare it with the pilot data package and process calculation sheet to conduct an item-by-item review. The core review content includes the following aspects. First, three balance the accuracy and traceability of data. This is the most basic and core content of the review. Randomly check the temperature, pressure, and flow data of key logistics, and ask the source of each data - is it directly quoted from the pilot data package, or is it calculated through process simulation? If it is obtained by simulation calculation, what thermodynamic equation is chosen? Where do the interaction parameters come from? What is the convergence criterion? If the source of a certain data is unclear, or the logic cannot withstand scrutiny, it must be returned for re-verification. This is not to find fault, but to ensure that every data on the PFD has a solid physical and engineering foundation. Second, the rationality and completeness of the process plan. Look at the entire process to see if there is room for optimization – are there any unnecessary “sandwich” operations of heating, then cooling and then heating again? Is the reflux ratio of a certain distillation tower too high? Is the hot and cold logistics matching of the heat exchange network reasonable? Also focus on the integrity of the process – are there any missing ancillary equipment? Is the material direction during start-up, parking and abnormal working conditions reflected on the PFD? Third, review of critical control programs. The core control scheme marked on the PFD is a concentrated expression of the process control intention. The review experts will review: Is the reactor temperature control scheme reasonable? Is it possible to control the temperature of sensitive plates in distillation towers? What is the basis for setting the critical flow ratio control? Is there a more reasonable control strategy? The review focuses on whether the "intention" of the control plan is correct and whether it can meet the requirements of process operations. It does not discuss the specific selection of control valves or the specific configuration of instruments - those are matters in the PID stage. Fourth, a review of operational resilience and boundary conditions. Is the operating elastic range of the design load reasonable? The parameters marked on the PFD are rated operating conditions, but the load may fluctuate between 50% and 110% in actual operation. Are the operating parameters of key equipment under these non-rated operating conditions still within the allowable range? Have the boundary conditions – maximum operating temperature, maximum operating pressure, minimum cooling water temperature, maximum steam pressure – been clarified and reflected in the PFD’s logistics data and equipment operating conditions? 4. Review conclusions and problems discovered at the PFD freeze review meeting shall be recorded according to severity levels. Category A Issue – A significant flaw that affects the viability or safety of the process. Such issues must be re-evaluated after the PFD is revised and cannot be passed directly. Type B questions—questions with insufficient data or that require additional validation. The responsible person will add data or explanations within a time limit, and it will be closed after review and confirmation. Such issues do not require a new review meeting, but a written confirmation record is required. Type C questions - optimization suggestions or improvement suggestions. It is provided as a reference for the compilation team. No modification is mandatory, but it is recommended to take it seriously - the optimization suggestions put forward by review experts are often based on their own years of experience in pitfalls. After all issues are dealt with, the PFD is frozen. Freezing is an important concept. It means that from this moment on, every data, every pipeline, every piece of equipment, and every control scheme on the PFD is no longer allowed to be modified at will. Subsequent equipment data tables, instrument data tables, and PID drawings are all based on this frozen data baseline. Why is freezing so important? Because if there is no freezing mechanism, the PFD will always be in a "fine-tuning" state - today some people say to change the temperature again, and tomorrow some people say to adjust the flow rate again. Each fine-tuning seems to have little impact, but downstream professionals are already working on the old data. If the temperature is changed, the equipment professional needs to re-calculate the material, the instrument professional needs to re-select the model, and the pipeline professional needs to do a new stress analysis - one step affects the whole body. If the PFD does not freeze, downstream work can never actually start. Of course, freezing does not mean that it can never be changed. If problems that must be corrected are indeed discovered during project execution, a formal change management process can be followed - first assess the scope of impact, then modify the PFD, and then notify all downstream professionals to update simultaneously. This process ensures that any modifications are controlled, and there will be no situation where "Major A will make it based on the new data, but Major B doesn't know yet". 5. Frequently Asked Questions in Reviews and Responses Some of the more common issues in PFD reviews will be discussed in advance. One is that the source of data is unclear. When the review experts asked where a certain parameter came from, the compilation team said "it was probably estimated" or "referred to a certain project." This kind of answer will not pass the review. The solution is to sort out the data sources clearly before the review - mark the source next to each key parameter, whether it is a pilot test measurement or a simulation calculation, making it clear at a glance. Another is insufficient discussion of operational resiliency. The review expert asked, "Can this distillation tower still operate stably when the load is reduced to half?" The preparation team was unable to answer for a while. This situation is more common in projects that only run rated working conditions in the pilot stage. This question can be answered easily if there is data on boundary conditions in the pilot test data package. ； If not, the truth will be stated at the review meeting and it will be assessed whether relevant data needs to be supplemented in subsequent stages. Another is the gap in understanding between majors. There is a temperature written on the diagram of the process professional. The equipment expert understood it to be the design temperature, and the instrumentation expert understood it to be the operating temperature. They found that they did not match up. This type of problem exposes the problem of inconsistent definitions of terms and inconsistent labeling habits. The solution is to clearly label the definition of each data in the PFD legend and description - whether it is an operating value or a design value, whether it is normal operating conditions or maximum operating conditions. Next Issue Preview Issue 42: Equipment selection and data sheet - Reactor amplification needs to be done with caution. The PFD is frozen, and the process plan and key parameters have been determined. The next step is to select equipment and compile data sheets one by one based on the data on the PFD. Let’s start with the core and most stressful reactor—what is the core dilemma of reactor amplification, how to judge the controllable physical quantities, and how to choose between different reaction systems. Expand next issue.