A new natural gas compressor unit (G3608LE-WH74) is added to an air-to-air recovery project in a domestic oilfield. The unit is an in-line 8-cylinder gas-driven compressor unit. The engine part is CATERPILLAR's product, and the compressor part is a US company SUPERIOP natural gas. The compressor product series is assembled by a domestic equipment company. The unit's driving power is 2370HP (1767KW), the speed range is 600-1000RPM, the single unit is designed to have a displacement of 20x104Nm3/d. The unit adopts four-stage compression, and the final exhaust pressure is 11-12 MPa. Two sets of units and built The natural gas booster system forms a parallel operation and is mutually redundant. The WH74 compressor cylinder and the air packing are forcedly lubricated by the oiler using Mobil 600W lubricating oil.
The unit was put into operation in May 2011. In August 2011, due to the high shutdown temperature of the three-stage exhaust gas, it was found that the oil film on the cylinder wall was too thin, and there was no lubrication at all. The longitudinal pull marks and rust spots in the inner cavity were very clear, not enough. The oil filling margin; there are tensile marks on the cylinder and the piston body.
2 Analysis of the cause of the failure The WH74 unit has been running for more than 1,000 hours since it was put into operation. The preliminary analysis caused the formation of the lubricating oil film in the three-stage cylinder due to insufficient oil supply or poor oil supply.
2.1 Analysis of the reasons for insufficient oil supply The original design of the compressor of the WH74 unit is composed of a worm gear mechanism, a camshaft, a 3/8" and a 3/16" oil pump, and a 3/8" injection. The oil pump supplies oil to the cylinders and packings of the first, second and third stage compression cylinders. A 3/16" oil pump supplies the four stage compression cylinders and the packing. After the 3/8" oil pump comes out, it will be divided into two ways. After passing through the main distribution block 60S, it will pass again (T means double action, S means single action). The distribution block supplies oil to the first and second stage cylinders and packing, and the other way is passed. After the main distribution block 25S, the oil is supplied to the three-stage cylinder and the packing through the 12S+12S+12S distribution block. The four-stage compression cylinder and the packing are high in working pressure, and the original design adopts a single 3/16" note. The oil pump supplies oil. After the oil pump is pumped out, it supplies oil to the four-stage cylinder and packing through the 12S+12S+12T distribution block. The overall design of this model has less oil injection, resulting in insufficient overall oil injection.
Since the gas discharge pressure of the three-stage cylinder is about 4.0 MPa, the ratio of the two-stage exhaust pressure is higher, so the amount of oil entering the third-stage cylinder is less than that of the two-stage cylinder. As a result, the three-stage cylinder block is seriously deficient in oil.
2.2 Analysis of the reasons for poor oil supply The overhead fuel tank and the oiler for the oil filling of the compressor oiler are directly connected through the oil filling pipeline (tube diameter: 13mm), and no oil collector is installed in the middle. If the oil filling pipeline is slightly blocked, the lubricating oil of the overhead fuel tank cannot be replenished in time, which may cause the overall oil supply to be poor; especially in the cold winter, the outdoor minimum temperature in the area reaches -25, although there is a plumbing system in the room. There is an electric heating cable outside the pipeline, but due to the thick consistency of the lubricating oil, the situation of poor oil supply still occurs from time to time.
3 Troubleshooting of the failure of a fuel injection system In order to solve the problem of insufficient oil supply and poor oil supply, the redesign of the two-in-one unit oil injection system was mainly to increase the two-in-one 3/8" oil injection pump and one oil collector. Change the original 3/16" oil pump to a 3/8" oil pump and adjust the distribution block. The specific modification is as follows: oil is supplied to the primary cylinder and packing separately; (2) the second level is increased by a 3/8 "The oil pump supplies oil to the cylinder and packing through the 60S+60S+12S distribution block; (3) adds a 3/8" oil pump to the third stage and supplies oil to the cylinder and packing through the 60S+60S+12S distribution block; (4) Change the original 3/16" oil pump of the 4th grade into a 3/8" oil pump and supply oil to the cylinder and packing through the 12S+12S+12T distribution block; (5) Maintain the original overhead fuel tank to the oiler When the pipe diameter is constant, install an oil collector on the upper end of the oiler (see the oil collector parts drawing). The oil collector can pre-store a small amount of lubricating oil, which is equivalent to a small pipeline oil storage device. When the fuel tank cannot supply oil to the oiler in time, this part of the lubricating oil can be replenished in time; especially in winter.
4The effect of the transformation is to calculate the oil injection quantity before and after the transformation of the WH74 unit. According to the model of the distribution block, the oil quantity in one stroke of the distributor can be calculated, and then according to the time statistics of one stroke of the oil-free flow switch, the unit can be calculated. Daily oil injection. The specific algorithm is as follows: Take SMX-4 (35T-16S-16T-08S) allocation block group as an example: query manual allocation block allocation oil quantity to get: 35T (0.02); means double action, S means single action, the allocation The oil injection amount of the block 1 stroke = 0.02x2+0.02+0.01x2+0.01 =0.09 cubic inches. If the stroke is 15 seconds (the oil flow switch does not flash for 15 seconds), the daily oil injection amount is 24x60x60+15x0. 09 = 518.4 cubic inches. According to this method, the daily oil consumption of the injection system of the WH74 compressor unit calculated before this method is shown in Table 1. Table 1 Daily fuel consumption (unit: cubic inch) series distribution block composition (oil consumption) - total stroke The amount of oil consumed per stroke consumes 12 seconds per day. 3 steps, 12 seconds, 4 steps, 6 seconds. From the data in Table 1, it can be seen that the modified three-stage compression cylinders and packings provide the same method to calculate the modified WH74 compressor. The oil filling system of the unit has a small amount of oil per oil, which results in obvious longitudinal pull marks and oil consumption in the inner cavity, as shown in Table 2.
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Table 2 Daily fuel consumption (unit: cubic inch) series distribution block composition (oil consumption) - total stroke oil consumption per stroke consumption time per day oil consumption 1 level 8 seconds 2 level 12 seconds 3 level 12 From the data of Table 2, it can be seen from the data of Table 2 that the oil injection amount of the 3rd and 4th grades after the transformation has a large increase, the oil film on the inner wall of the third-stage cylinder is evenly formed, and the lubrication of the oil film and the packing of each cylinder is improved.
5 Conclusion After the two units were rebuilt with oil injection system, they have been operating normally for about 8,000 hours. The maintenance personnel checked the oil film and packing lubrication of the cylinders at intervals of 1000 hours. It was found that the oil film on the cylinder wall was in good condition, and the oil ring and piston ring wear were also within the normal range, which fully met the requirements. The technical transformation has improved the aging time of the compressor, increased the load capacity of the unit, and reduced the amount of natural gas venting during the shutdown period, thereby reducing environmental pollution and saving resources.
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