1 question raised When the Datong Coal Mine Group Corporation's city gas combined production of 50,000 t/a methanol was designed, the 5 000 m 3 cabinet in the plant was used as a storage and buffer cabinet for methanol feed gas. After the project was put into production, the 5,000 m3 cabinet had many shortcomings in operation. When the gas production fluctuates, it is easy to have insufficient or excess gas source. The normal demand for methanol is 6 000 m3 / h. The 5 000 m3 cabinet not only has small capacity, but also has a small lifting range and a low buffering capacity. If the adjustment is not timely, the contradiction between production and supply often occurs, which seriously affects the normal production of methanol, and also limits the normal production of gas. In order to ensure the stability of methanol production, we changed the 50,000 m3 wet cabinet to the buffer cabinet in March 2007. After the operation, the buffer capacity of the buffer cabinet was greatly improved, and the peaking capacity of the gas cabinet was increased to make the gas for methanol production. The flow rate is stable, the methanol production has reached the highest output since it was put into production, and the expected target has been achieved. At the same time, due to the stability of the gas source, good economic benefits have been achieved in the energy saving and consumption reduction of methanol production, which is beneficial to the adjustment and ensure the supply of methanol. The production of stable gas flow, stable production and high production ensure the annual production volume, and provide guarantee for the city gas joint production of 50,000 t / a methanol. Before the 50,000 m3 wet cabinet was not rebuilt, the wet cabinet and the dry cabinet were used as the common gas storage cabinet of the city gas. The two were connected through the pipeline. At the peak, the two cabinets provided the gas source for the compressor at the same time. After the peak, the gas was replenished from the dry cabinet to the wet. The cabinet raises the wet cabinet to a stable height of 27 m. After the 50,000 m 3 wet cabinet is changed to the buffer cabinet, the original wet cabinet inlet and outlet pipes are disconnected from the wet cabinet through the valve, the wet cabinet exits the city gas operation system, and the dry cabinet is operated as the only gas storage cabinet of the city gas alone, carbonization The produced gas is purified and all enter the dry cabinet. The gas required for the compressor inlet is supplied by the dry cabinet outlet pipe. After the wet cabinet was changed to the buffer cabinet, the operation was stable. However, from May 2007, a compressor station continuously appeared more than 10 sound abnormalities in a short period of time, the cylinder operation failure, etc., and the failure rate was significantly higher than before. At the same time, the inlet pipe often has negative pressure when the peak gas is supplied. The compressor is the key equipment in the purification workshop and is responsible for the pressure delivery of the gas. The integrity of machinery and equipment has always been a top priority for the workshop, especially during the peak period. Since 7 compressors are the equipment at the time of construction, they have been running continuously for many years. Coupled with the continuous increase of gas users in recent years, the amount of transportation at the peak is increasing. In addition to the start of the second pressurization station, a pressurization station still has to Open 4 machines. In order to ensure peak gas supply and alleviate peak supply pressure, spare equipment may be turned on at any time due to insufficient pressure and failure. In the work, we require that the operating and standby equipment have a good rate of more than 95%. If there is a continuous bad machine failure, the number of compressor repairs will increase, which will result in insufficient peak supply and even depressurization, so that the produced gas cannot be normally pumped. To the user, this is related to the tens of thousands of people eating problems in the entire group of companies. To this end, the workshop pays attention to the operation of gas supply during peak hours, and on the other hand, it has added manpower to intensify maintenance. During the maintenance, it was found that the compressor was seriously damaged by the piston, the crosshead and the cylinder every time, and each time the cylinder had water inflow, the water in the cylinder was the main cause of compressor damage. Due to the damage of the piston and the cylinder, the replacement repair cycle is lengthened. The price of the compressor is 300,000 yuan/set, and the replacement of the crosshead, the piston and the cylinder requires tens of thousands of yuan each time. The compressor continuously fails in multiple times at the same time, which not only increases the conveying pressure and operating cost, but also brings hidden dangers to safe production and normal gas supply. Compressor failure statistics. 2 transformation method The compressor is in normal operation, and water is forbidden in the inlet pipe and in the cylinder. The working principle of the compressor is: consisting of vertical and horizontal cylinders, through the reciprocating motion of the piston, the gas is pressurized and sent to the distribution pipe network. Since the piston is running at high speed in the cylinder, the two frictions must be lubricated by the water jacket and the added lubricating oil. The lubricating oil reduces friction by lubrication and protects the piston and the cylinder. After the water is introduced into the cylinder, the compression ratio of the water is very small, and the dead space between the piston and the cylinder head is only 2 mm to 3 mm. Therefore, once the cylinder enters the water, a cylinder crash corresponding to the piston and the cylinder head occurs. If it is light, it will damage the piston, the piston rod and the crosshead. If it is heavy, it will damage the cylinder block, and there may be a major accident that the machine is destroyed. During the overhaul, it was found that the water jacket did not damage the water leakage. There was water in the cylinder and the air outlet pipe, and then there was water in the inlet pipe, indicating that the water was in the pipeline. After the high-temperature gas from carbonization is subjected to a series of purification processes such as primary cooling, ammonia washing, and desulfurization, most of the tar, moisture, and impurities in the gas are removed, but some moisture still exists, and the pipeline is continuously transported in the gas. The lengthening gradually condenses and gathers in the pipeline. A condensate tank is provided in the gas pipe to prevent condensation from accumulating at the lowest point of the pipe. The function of the condensate tank is to collect the condensate in the pipeline gas, collect it and collect it regularly by the pump truck. If it is not pumped away in time, it will increase more and more, reducing the effective cross-sectional area of ​​the pipeline. Reduce the flow rate of the gas unit section. Especially in the lower part of the pipeline, it will affect the gas transportation. When the peak gas supply, the inlet pipe often has a negative pressure phenomenon, indicating that the gas flow of the dry pipe outlet pipe is insufficient at the peak. According to the theoretical calculation, the pipeline of the dry cabinet outlet DN800 can fully meet the peak gas supply requirements. The insufficient flow indicates that the pipeline may have condensed water accumulation, which makes the pipe diameter smaller and affects the gas transportation. By understanding the pumping situation, the water in the condensate tank after the renovation is much less than the original, and sometimes there is no water. Through inspection of the drawings and on-the-spot investigation, it was found that the connecting pipe between the outlet of the dry cabinet and the outlet of the wet cabinet had sunk, and the condensate tank was not at the lowest point. The condensed water condensed at the lowest point of the connected pipeline and was not concentrated in the condensate tank. The condensed water in the pipe cannot be discharged, and the continuous accumulation makes the effective pipe diameter of the gas pipe small. The gas pipe that originally entered the wet cabinet is the welded pipe of DN500, and the gas outlet pipe of the dry cabinet is the welded pipe of DN800. When the condensed water is condensed at the lowest point, it flows into the condensate tank. When the gas is supplied at the same time, the gas flow of the dry pipe of the dry cabinet is not large. The condensation water accumulated in the pipeline has little effect, so no abnormality can be seen. After the dry cabinet is operated alone, the connecting pipe becomes the only pipe for conveying the gas. The condensed water in the gas accumulates at a new low point and cannot enter the condensate tank. The accumulated condensed water occupies the effective pipe diameter, so that the flow rate is reduced. When the peak gas supply increases, the demand for gas in the compressor increases, so that the supply of gas in the compressor is in short supply, and a negative pressure is formed. At the same time, as the gas volume increases, the condensed water accumulated in the pipeline will be continuously taken out along with the gas into the compressor. Caused damage to the compressor. We drilled a hole at the sinking point and found a lot of condensate and found the cause of the problem. In order to solve this problem, we propose to add the condensate water in the connecting pipe section of the condensate tank at the lowest point and connect the original wet pipe intake pipe and the air outlet pipe to form a double-line gas supply to increase the gas volume. Install a condensate tank at the new lowest point to increase the effective pipe diameter of the connecting pipe to avoid the condensed water entering the compressor with the gas at the peak gas supply, causing damage to the compressor; and adding water at the lowest point of the connection. Seal and release the water accumulated in the connected pipeline in time. The change of the outlet pipe of the dry cabinet from single-line gas supply to double-line gas supply not only increases the supply pipe diameter of the gas, but also reduces the burden on the dry pipe outlet pipe during peak hours. It is also necessary to meet the increasing demand of gas users and gas in the future. By demonstrating that this scheme is simple and feasible, it will be completed on December 25 after 10 days of efforts. 3 transformation effect After the completion of the project, the compressor has been running smoothly. Check that no water is found in the intake pipe, and there is no negative pressure in the intake pipe, indicating that the method and measures are completely correct. Through this transformation, not only the unused inlet and outlet pipes of the original wet cabinet were effectively utilized, but the gas output from the dry cabinet at the peak time was effectively diverted, the supply pressure at the peak gas consumption was reduced, and the condensation in the pipeline was avoided. Water enters the compressor, ensuring the normal operation of the compressor and prolonging the service life of the compressor; accumulating experience in compressor operation, saving a lot of equipment costs and maintenance costs, and more importantly ensuring safe production and normal operation. Continuous gas supply. 4 Conclusion Through this transformation, we realized that it is necessary to rationally design the diameter of the pipe and the position of the condensate tank in the transportation of gas. At the same time, in the future work, it is necessary to strengthen the management of the condensate tank and eliminate the condensate in time. Ensure that the conveying equipment is in good condition and supply air normally.
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