Notes on the Start of Alkylation Operation

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Records of the Alkylation Unit’s Commissioning: From construction to operation, all those involved demonstrated admirable qualities such as hard work, selfless dedication, and a willingness to learn. However, some mistakes were still made during the process. To prevent similar issues from occurring again, the following records are kept: 1. When the alkylation oil was circulated, olefins entered the system, causing a sudden rise in the reactor temperature. Passes through: the feed tank of the isobutane removal tower, the isobutane removal tower, the n-butane removal tower, and the water dehydration unit for the alkylation oil circulation water; sampling and analysis are conducted – no water is present, with an olefin content of 28%. Sample addition for further analysis is required, aiming for an olefin content of 0%. After the acid circulation in the reactor returned to normal, laboratory analysis showed that the alkylated oil was in good condition. A small amount of this alkylated oil was introduced into the reaction vessel, and the temperature rose rapidly; it was determined that water in the pipes was causing this phenomenon. More oil was added, and the temperature reached 40°C, showing signs of stabilization, which indicated that all the water had been removed. To lower the temperature, oil was pumped from the refining coalescer feed pump P2004 into the refining coalescer. After passing through heat exchanger E1005, water was used to cool the mixture before it was sent back to the reactor. However, the temperature continued to rise until it finally stabilized at 60°C. Subsequent sampling and analysis confirmed that the alkylated oil was normal. When the alkylated oil was mixed with 98% acid in a 1:1 ratio in a container, a reaction occurred, with the temperature reaching up to 80°C. Multiple samples were taken, and two of them contained olefins, at levels of 11% and 3% respectively; all the other samples were normal. Treatment: The acid concentration has been reduced; new acid has been added. The alkylated oil continues to circulate in order to remove the acid that has accumulated in various locations as a result of cooling during circulation. Alkylated oil is replenished once again, and it can be poured in only after on-site tests show normal results, aside from laboratory tests. Cause analysis: The inlet of the alkylation oil pump in the tank farm shares the same pipeline as that used for loading 93# gasoline; the pipeline was not properly purged or improper operations were carried out. Eliminate: multiple sampling, on-site experiments. II. Leakage in the E6001 gasket: After the waste acid heater stopped discharging acid, the operator closed the manual valve at the E6001 outlet on-site, while the control room shut down the acid discharge control valve; subsequently, the switch for the waste acid heater was turned off. However, the temperature had already risen to 86°C, and no one noticed this. Eventually, a leakage occurred in the gasket at the E6001 outlet, causing acid mist to spray out over a distance of about 15 meters. People wearing protective gear closed the nearest valve to E6001. Once the acid leakage stopped, the gasket was replaced, and leaks were found in several areas, which were then tightened to prevent further leakage. Reason: 1. The heater was not turned off in time ； 2. After the acid removal process is complete, both ends are closed, resulting in pressure buildup ； 3. The soft PTFE is used for the E6001 outlet pump; it cannot withstand high temperatures or pressures. III. Over-temperature at the compressor outlet: When the inlet flow rate of the compressor dropped to 12,630 m3/h, it was necessary to prevent backflow, and the backflow valve was opened to 35% of its maximum capacity. As the inlet flow rate increased to 18,080 m3/h, the temperature at the inlet rose rapidly from 16°C to 100°C, while the outlet temperature reached 150°C (both sensors reached their full scale). This condition of full-scale temperatures at the inlet and outlet persisted for 31 minutes. At that point, the cooling system was activated at the compressor inlet, and the backflow valve was reduced in size; normal operation was restored after 10 minutes. Approximately 15 minutes after the over-temperature occurred, one of the air-cooling tubes at the compressor outlet was damaged, resulting in an increase in the compressor’s seal leakage rate by 10 m3/h. Reason: The compressor inlet temperature was not taken into account during the operation. IV. Acid leakage occurred three times when the same operation was performed at the same location. During the process of draining and replenishing acid, the drain valve of the acid tank was not closed, which caused the acid in the tank to flow into the acid tank and overflow through the vent. Reason: An incident analysis was not conducted promptly after the acid run, and no training was provided in a timely manner. V. After 10 days of operation, severe corrosion occurred in the impellers and pump casings of the acid pumps. After approximately 10 days of operation of the alkylation unit, the ring seals of the two new small acid pumps were corroded; the impellers of the new large acid pumps were severely corroded, and the pump casings suffered from corrosion-related leaks. Reason: To save on costs during construction, the material used for the impeller and pump casing was downgraded to carbon steel, which resulted in a high maintenance rate for the pumps and prevented them from functioning properly, thus severely affecting normal production. VI. All valves with a DN40 size or smaller in this installation are welded valves, which makes it more difficult to replace them in the future. VII. During the initial construction phase, metal wound gaskets shall be used exclusively; later on, soft PTFE gaskets will be substituted. PTFE gaskets cannot withstand high temperatures or pressures, so metal wound PTFE gaskets are to be used. VIII. During construction, the manufacturer was not required to weld the acid-oil distributor joints at the correct angles, which makes assembly on site quite difficult. 9. The tank transfer line in the spherical tank area is inflexible, making it difficult to mix raw materials and resulting in a passive production process.