Seven stages of chemical technology from creativity to industrialization (Issue 56/Total 100)--General description of process flow

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Seven stages of chemical technology from creativity to industrialization (Issue 56/100 in total) - Technology finalization: The process flow description and the general instruction manual are integrated. Dear friends,: Hello everyone! In the last issue, we talked about HSE and analytical testing, and the three waste emission inventories and sampling system designs were completed. This issue enters the last two of the sixteen core tasks - the preparation of the process flow description and the integration of the general instructions. At this stage, PFD is available, PID is available, equipment data sheet, instrument data sheet, pipeline material grade, boundary condition table, and safety analysis report are all available. These documents were prepared by different disciplines at different times, and now they need to be integrated into a complete set of deliverables that are logically self-consistent, data consistent, and traceable. The process flow description uses words to clearly explain the design intentions on the drawings, while the general instructions put all documents into a unified framework for final cross-checking and document organization. Once these two tasks are completed, the craft package is ready for review. 1. Process flow description is not about looking at pictures. Many people understand process flow description as "looking at the PID and describing the process." This understanding is not wrong, but it is not comprehensive enough. The core value of process flow description is not to repeat the information already on the drawing, but to express the design intention, operational logic and safety considerations behind the drawing. The drawings are for professionals to see, while the process flow description is to provide an entrance to the system for understanding the device for more readers who are not directly involved in the design - the owner's managers, operation training instructors, and future driving teams. Process flow description usually includes the following parts. Process principles and technical characteristics. Use words to systematically explain the physical and chemical principles of the entire process. If there is a chemical reaction, the main reaction and main side reaction equations should be listed to explain the reaction mechanism. Complex processes use block diagrams to represent the interrelationships of various stages. The technical characteristics section should give a summary description of the unique advantages of this technology - not to say "low energy consumption" in general, but to say "how many tons of steam are consumed per ton of product, how many percent lower than the tons of traditional processes. The main reason for the reduction is what scheme is used to recover what heat." Only with data, comparisons and measures can it be convincing. Logistics trend detailed. According to the actual flow direction of the logistics in the device, starting from the boundary area feed pipeline, the state changes and destinations that occur when passing through each piece of equipment are described in turn. The description of each flow stream must completely correspond to the pipeline number and logistics number on the PFD and PID. If a reader takes the process flow description and compares it with the PID and finds that a pipeline mentioned in the description cannot be found on the PID - this is an unqualified explanation. Description of operating conditions. List the main control indicators of each key operating point under different operating conditions. Normal operating conditions, start-up conditions, the difference between the initial and final stages of catalyst use, the difference between maximum load and minimum load - these parameter differences under different operating conditions must be reflected in the process description. Many process instructions only write the parameters under normal operating conditions, but the parameters during driving are completely different from those during normal operation. The operator will be in trouble when using this instruction to prepare for driving. Overview of the control scheme and description of auxiliary systems. Outline all main and special control loop principles in the process, and explain the interlocking parking principles and steps under accident conditions. For the interlocking system, there is no need to repeat every AND gate or gate on the interlocking logic diagram, but it is necessary to clearly explain the triggering conditions and action consequences of the interlocking - what situations will trigger the interlocking, which valves will act after triggering, what state the device enters, and what the operator should do. The functions of auxiliary systems such as start-up and shutdown auxiliary pipelines, purge systems, exhaust systems, and defective product processing systems also need to be described in detail here. 2. Consistency of graphics and text: The lifeline of process flow description The most fundamental quality standard of process flow description is: Any data, any device tag, or any pipeline description that appears in the text must be found on the PFD or PID. This requirement sounds natural, but in actual implementation it can easily go wrong. The source of inconsistency is often that after a certain revision, only the picture is changed but not the description, or only the description is changed but not the picture. For example, the heat load of a certain heat exchanger on the PFD was adjusted after an optimization, and the old data was still written in the process flow description. A certain auxiliary pipeline was added after a PID review, but the process description was not updated. The way to avoid inconsistencies is not to rely on people to be more careful, but to establish a process. Before finalizing the process package, designate a dedicated person to check the consistency of the graphics and text - take the process flow description, compare the PID and PFD sentence by sentence, and mark the one-to-one correspondence one by one. If no correspondence can be found, it is inconsistent and must be corrected. Although this verification is time-consuming, it is much more cost-effective than having to go back and rework after delivery when it is discovered that the graphics and text do not match, leading to errors in the downstream design. I have a little habit when checking the consistency of pictures and texts.: Print out the process flow instructions and outline them sentence by sentence with a red pen. Every time you see a device tag, find the corresponding position on the PID and mark it with a mark. Every time you see an operating parameter, find the corresponding data on the PFD or equipment data sheet and check it again. After checking the process flow description, the PID and PFD should be covered with verification marks. This method may seem stupid, but it often finds a lot of problems—some errors cannot be found even with careful electronic review. 3. Integration of General Instructions: After each individual document from scattered documents to complete document technology package is compiled, it needs to be integrated into the unified framework of the master specification. This is not simply to pile all the files together and make a directory, but to reorganize them according to logical levels to ensure that the reference relationships between files are clear and coherent. The content of the general instruction manual needs to follow a certain logical sequence so that readers can understand the process step by step. Usually starts with the design basics - project definition, installation size, product specifications, boundary conditions, standard specifications based on which the design is based ； Then there is the process description - process principle, process description, operating conditions ； Next is the material properties table - a summary of the physical property data of all materials ； Then there are the PFD and logistics data tables-three balance calculation results ； Then there is the pipe material grade index table - the selection criteria for pipe materials and specifications. ； Next is the PID - the complete piping and instrumentation flow diagram of the device ； Then there is the boundary area conditions table - the handover conditions for all materials and public works entering and leaving the boundary area. ； Then there is the process equipment data sheet and equipment list ； Then there is the instrument data sheet and interlocking logic diagram ； Finally, there are recommended equipment layout drawings, analysis and laboratory instructions, and hygiene, safety and environmental protection instructions. During the integration process of the general instructions, there are several core cross-checks that must be completed. The first is the data consistency check between PFD, equipment data table, instrument data table and PID. Is the same temperature or pressure exactly the same in the four documents? Starting from the PFD, select a key stream, write down its temperature and pressure, and then trace the equipment data sheet into which the stream enters, the instrument data sheet on the equipment, and the pipelines and valves on the PID - in such a closed loop, any inconsistencies will be exposed. The second is the consistency check between the boundary condition table and PID. For every material and public project entry in and out of the boundary zone on the boundary condition table, the corresponding boundary symbol can be found on the PID. If a certain stock of material is listed on the boundary condition table, but the corresponding entry and exit mark cannot be found on the PID, that is a problem that needs to be corrected. The third is the consistency check between the interlocking logic diagram and the instrument data table. Each sensor tag and actuator tag on the interlocking diagram has a corresponding record in the instrument data sheet. Does the interlock trigger value match the instrument range? For example, if the interlock trigger value is 500 degrees, the instrument range should cover at least 600 degrees. Otherwise, when the interlock is triggered, the instrument has exceeded the range and cannot accurately measure. 4. Internal proofreading: After integrating the three general instructions of self-schooling, cross-schooling, and review, it needs to go through internal proofreading before it is officially submitted to the final version for review. Internal proofreading is a step-by-step process within the compilation team and is divided into three levels. Self-examination is the compiler's self-examination against the compilation rules. This is the most basic level, but it is also the easiest to go through. Preparers often have blind spots when it comes to what they write - subconsciously they know what is being expressed here, so they cannot see the ambiguity in what they write. When self-study, you have to force yourself to look at the documents from the perspective of someone who is completely unfamiliar with the project. If this is my first time getting this craft kit, can I understand what is written here? Is the source of this data indicated? Is this label likely to cause ambiguity? Mutual schooling is an effective means to break blind spots. Have another engineer in the same field proofread the document. He can see problems that you can't. When drawing PIDs by myself, I habitually omit the auxiliary pipelines and the operational steps that I habitually skip - these habitual omissions become obvious in the eyes of people who are collaborating with each other. Cross-schooling is not about finding fault, it is about using another pair of eyes to make up for one's blind spots. Review is the final technical check. The reviewer is usually a senior reviewer with sufficient engineering experience to be able to view the entire process package from a global perspective. The value of a reviewer does not lie in discovering clerical errors in the data, but in discovering logical flaws at the plan level. Whether this operating condition is realistic during driving conditions, whether this safety interlock setting value covers the most unfavorable scenarios, and whether this heat exchange network will cause problems in extremely cold conditions in winter - these questions require sufficient technical accumulation to be able to ask. 5. Quality self-inspection checklist before final delivery Before delivering the final version for review, there are several key self-inspections that are worth completing one by one. File integrity check. Compare SHSG-052-2003 and the delivery list agreed in the technical annex of this project to check one by one whether there are any missing documents or missing content items. Although the format of some data sheets is complete, the key parameters are left blank or written "determined by the manufacturer" - this should not appear in the process package stage, because the positioning of the process package is to set standards, set the key process parameters, and the manufacturer will select within the parameter range. Image and text consistency check. Whether the corresponding relationship between the process description and PFD and PID is consistent, whether the nozzle number is consistent with the equipment data sheet, and whether the interlocking logic diagram is consistent with the instrument data sheet. I have repeatedly emphasized this point before, but it is worth saying again - many engineering projects have troubles after delivery, and the root cause is that the graphics and text of the delivery documents are inconsistent. Data traceability check. Can every key data on the PFD be traced back to pilot data packages or process simulation calculations? If the traceability chain is broken, data becomes sourceless water. During the final review, the review experts will definitely ask about the source of the key data. If they cannot answer the question, they will not pass the review. Next issue preview No. 57: Review of the final version of the technology package and document delivery. The internal review of the technology package has been completed, and the integration of the master instructions has been completed. Next is the last major review of the entire technical finalization stage - the final version review. Who will participate, what will be reviewed, how the review comments will be graded, and what will happen after the document is signed. Expand next issue.