An accident case in the benzene elution section
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At 4:00 p.m. on February 11th, during the shift change, lean oil was supplied to the backup lean oil cooler; the amount wasn’t large, but the temperature was high, around 40°C. The shift handover records and operational logs show that the resistance in the benzene washing tower decreased from 2800 pascals at 3:00 to 2600 pascals. The temperature of the lean oil was measured on the heat exchanger platform; it turned out to be much higher than the 27.5°C at the outlet of the second stage. The temperature of the lean oil after the first stage was 44°C, while the temperatures of the cooling water and circulating water were 10°C and 31°C respectively℃ ； During the production process in the unit, the resistance of the benzene washing tower, the temperature of the lean oil, and its flow rate were all decreasing gradually. By around 21:30, when the temperature of the lean oil dropped to 26.5°C, the cooling water flow to the secondary lean oil cooler was reduced to the minimum level; yet the temperature continued to drop. When it reached 25.8°C, the flow rate of the lean oil began to decrease. At that time, the resistance of the benzene washing tower was around 2200 pascals, and my first impression was that the cooler was about to get clogged. I then reduced the valve opening at the oil outlet of the second heat exchanger to the minimum; the flow rate indicated “71” at that point. After that, I opened the outlet valve of the pump fully. The temperature of the lean oil after the secondary stage increased slightly, but then dropped again. The flow rate was now “51.7”, and the temperature was 19.8°C. The temperature after the primary stage was 38°C (as shown on the on-site instruments). After this situation occurred, I closed the inlet and outlet valves for the cooling water used in the secondary lean oil cooler, drained the water from there, and replaced it with steam. Approximately fifteen minutes later, the flow rate and temperature of the lean oil began to rise slowly again ； At around 0:25, after the second stage, the temperature of the lean oil rose to 34°C and when the flow rate of the lean oil was at “85”, steam supply was stopped and water was introduced. Within less than 3 minutes, the temperature of the lean oil increased to 40.8°C and its flow rate rose to “90”. By 0:40, the temperature of the lean oil was reduced to around 28°C; at that time, the resistance in the benzene washing tower was around 2500 Pascals ； That’s how things happened. I believe the reason for the poor performance of the lean oil cooler in this case is as follows: 1. The temperature of the lean oil after the second stage is not equal to the temperature of the lean oil entering the benzene washing tower. Since oil flows directly through the second heat exchanger, the temperature of the oil entering the tower is relatively high, which melts some of the crystals inside the benzene washing tower. As a result, the oil has poor flowability and its flow rate decreases during cooling ； 2. The second heat exchanger draws away a large portion of the pressure from the oil-poor pump during the production process, resulting in insufficient pressure in the oil channel within the second stage of oil-poor cooling and an exacerbation of the low flow rate issue ； This post was last edited by ryn on 2009-2-13 11:41]
1. Insulation and thermal insulation work must be carried out after the hydraulic testing, airtightness testing, and other various tests of the equipment and pipelines are completed. 2. Before construction, the work area must be cleaned. 3. Insulation, cooling materials, or auxiliary materials must be protected from rain and moisture; proper storage is necessary. During construction, prevent these materials from getting wet or exposed to rain. 4. The thickness for heat retention and insulation shall be in accordance with the requirements specified for each device and pipeline in the design drawings. 5. It is necessary to ensure that the nameplate and other markings on the equipment remain visible even after insulation work is completed; sealing material should be applied to the surrounding insulation material. 6. In areas where the equipment and pipes are made of stainless steel, waterproof perlite insulation material is generally used. 7. For bonding foam polystyrene insulation materials, ethanol-based acetates and vinyl-based bonding materials are used. 8. Try to avoid carrying out work in rainy weather. 9. The protective layer can be installed only after the insulation material is fully dry. 10. Since rainwater may seep in at the cuts in the protective layer, a sealing material needs to be applied. 11. The insulation covers for inspection holes, manholes, valves, flanges, and filters shall be of a removable type.
Another point is: when the oil temperature drops and continues to decline, it is very important to be able to detect in a timely manner any signs that the heat exchanger might get clogged – early detection is crucial!