【Original】I’m involved in the major maintenance plan for a small private chemical plant

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This post was last edited by Small and on 2017-8-18 at 13:45. Major Repair Plan: This repair is a small-scale, specialized emergency repair effort. The main objectives of this repair are as follows: First, to restore the original process design for alkali washing and absorption in the three towers, in order to absorb and wash hydrogen sulfide and thereby reduce its concentration in the exhaust gases; the washed liquid that has become saturated after absorption is then recycled. It is hoped that in future operations, progress can be made toward meeting the standard outlined in the process design plan, which aims for virtually no emissions of waste gases or liquids, so that ultimately there will be essentially no waste gases or liquids in the synthetic acid hydrolysis stage. (Three wastes refer to: waste liquids, waste gases, and waste solids.) 1. Install two neutralization towers, and inspect the absorption tray plates and gas-liquid distributors inside these towers, in order to prevent pollution caused by damaged components of the gas-liquid distributors or design flaws that might result in some gas escaping from the tower without being cleaned first. 2. Thoroughly inspect and maintain the three alkaline wash absorption circulation pumps to ensure the effectiveness of the wash absorption liquid, thereby guaranteeing effective absorption of hydrogen sulfide in the exhaust gases. (Note: In the original process design, hydrogen sulfide exhaust gas is absorbed in a series configuration using one tower and two additional towers, passing through two neutralization towers. After being absorbed in two stages, it is drawn out via a dedicated exhaust fan and discharged through a 25-meter-high chimney. Hydrogen gas, on the other hand, is cleaned and absorbed in a washing absorption tower, meaning three towers in total, before being discharged through the chimney. All three of these neutralization towers are essential; without them, it is not possible to meet the basic standards for exhaust gas emissions.) Whether the three washing pumps are operating properly has a direct impact on the efficiency of exhaust gas washing and absorption. Just because a pump is running does not necessarily mean it is functioning correctly; without monitoring flow rates, it is generally necessary to determine whether the pump is reaching its operating pressure by checking the inlet and outlet pressures. Therefore, the outlet pressure gauge for the pump that was under repair should be reinstated this time, with any other missing components being added gradually as repairs are carried out. By the way, pressure gauges and thermometers are the most crucial and essential safety devices in chemical plants; in terms of importance, pressure gauges come first. Low-pressure and normal-pressure equipment do not mean that displaying pressure is meaningless; it is only meaningful to monitor the operating temperature after knowing the operating pressure. The operating pressure is not merely a safety accessory; here it represents a process parameter. 3. Conduct thorough maintenance on the two exhaust fans. (It should be noted first that the exhaust fan is not merely used for discharging waste gas; it is related to the operating pressure of the reaction vessel at that time, and it plays a role in promoting or suppressing the acidification reaction. It is necessary to restore the pressure gauge at its inlet – also known as an air pressure gauge or vacuum gauge – in order to monitor the pressure during the acidification reaction in the reaction vessel while exhaust air is being expelled.) The motor base, impeller, casing, and pipelines of the exhaust fan all need to be thoroughly inspected to prevent issues such as an unstable foundation or pipeline leaks. Areas that are deformed, cracked, or hardened must be replaced and repaired promptly to prevent hydrogen sulfide and hydrogen from leaking out or air from entering the pipes. The former poses a risk of poisoning, while the latter may cause an explosion. 4. Check the control circuit to ensure it is in good condition; inspect the installation of the pipelines for the three towers, identify potential hazards, troubleshoot any faults, and finally conduct a parallel test run of the three towers. Once everything is satisfactory, they can be put into standby mode. Second, inspect the ten acidification reactors and test the connected gas-liquid pipelines for leaks, addressing any issues found. (The synthesis reactors from No. 1 to No. 4 should also be checked for leaks.) Among reactors No. 5 to No. 14, many are operating with defects; some can no longer be used in production, and the problems are mainly due to leaks, cracked ceramic components, detached or malfunctioning agitators, and so on. (It’s a device that operates at normal pressure, at moderate temperatures, and for a limited duration of time; we should carefully analyze the reasons behind this, work together as a team, and focus our efforts on identifying the issues in installation, operation, and maintenance.) ) Third, the boiler feed water pump should be thoroughly overhauled, reinstalled firmly, and leveled and aligned. Restore the export pressure gauge. Fourth, inspect the two vacuum systems, carry out maintenance on the motors, pump bodies, and pipelines, and check for leaks. Fifth, restore and reconfigure safety markings, designate hazardous areas, improve safety accessories, and add additional safety measures such as night lighting, loading platforms, and fences. Check other centrifugal pumps and diaphragm pumps; a check valve should be installed at the pump outlet. Prevent backflow of the medium at the moment the pump stops, which could cause fluid mixing and damage to the rotating components. Safety equipment to be prepared for major repairs: 16 safety helmets, 5 sets of safety belts, 1 set of air or oxygen respirators, 2 sets of gas masks, 2 sets of rubber suits, 10 pairs of rubber boots, 26 pairs of acid-resistant rubber gloves, and 50 pairs of canvas gloves. 10 kilograms of cotton yarn and cloth, three sets of brooms and baskets. 30 sets each of steel scaffolding at 6 meters, 3 meters, and 2 meters lengths, 300 sets of fasteners, and 6 walkboards. The office has prepared some bottled water, and the cafeteria has stocked enough food for groups of four or more people; the standard of meals will be raised during these days. Three to four single beds along with corresponding mattresses, sheets, and pillows have been prepared. Major maintenance of mechanical equipment is carried out by specialized teams. Employees of our factory work in shifts, with one shift working each day to assist with the maintenance efforts, providing support in terms of process operations, such as shutting down systems, flushing them, and replacing fluids. They also help with transporting materials, ensure safety, learn the techniques for maintaining equipment, understand the characteristics of the equipment in their respective positions, and improve their own operational skills. The plan is tentatively set for nine days: production will stop on 4/1, resume on April 5 after the Qingming Festival, and normal operations will be resumed on April 14. 2017/3/30 Regarding the hazards and recommendations related to hydrogen sulfide emissions: This facility generates large amounts of hydrogen sulfide gas during the acidification stage, along with a small amount of hydrogen gas. Since there are no analytical data available, estimates can only be made based on chemical reaction equations. During the acidification process, the main component of the exhaust gas is hydrogen sulfide, accounting for about 50–90% of the gas phase; hydrogen makes up around 2–5%. Additionally, some aerosolized hydrochloric acid and some aerosolized synthetic mother liquor may also be carried away with the gas stream. This creates the \"smoke\" that we can see with our eyes; (both hydrogen and hydrogen sulfide are colorless and transparent, so what we see is actually aerosolized acidic droplets.) The concentration of hydrogen sulfide in pipes can be as high as 50–90%, while even a concentration of 0.1% in the air is sufficient to cause instantaneous death in humans and animals – death occurs within one or two seconds, and there is no way to save them. **The concentration allowed under environmental regulations is below 10 ppm/L. This device uses an alkaline solution in three towers for absorption and washing. The key factors are maintaining the concentration of the absorption solution, its flow rate, as well as ensuring adequate contact area between the gas and liquid, the contact time, the absorption temperature, pressure, and so on. Therefore, it is essential to ensure the proper functioning of the entire washing and absorption system. Moreover, the vacuum pressure generated during the washing and drainage process also represents the reaction pressure in the acidification process, and it has a significant impact on the progress of this reaction. (The acidification reaction is a process involving an increase in volume; from this perspective, an increase in vacuum level should be favorable for the main reaction, although further consideration is needed. ) With careful and precise operation, it is possible to achieve the designed values, that is, environmentally friendly emissions.