Analysis and control measures of compressed air system in air compressor
1 Establish a compressed air system fire and explosion fault tree
Compressed air system fire and explosion fault tree, simplified fault tree.
2 The minimum cut set and path set of the fault tree
(1) Minimum cut set: refers to a collection of minimum basic events that can cause an overhead event to occur. If any of the smallest cut sets do not occur, the top event will never occur. If there are many gates in the fault tree, the minimum cut set is small, indicating that the system is safe; if there are more gates, the minimum cut set is more, indicating that the system is more dangerous.
(2) Using Boolean algebra, according to the simplified fault tree, find the minimum cut set of the original fault tree.
(3) Minimum path set: refers to the minimum set of paths necessary for the top event not to occur. The basic events in the path concentration do not occur, so that the top event does not occur. There are several sets of paths in the fault tree, and there are several options for controlling the accident to provide a basis for the control of the accident. The more paths in the fault tree, the more secure the system. The method of finding the minimum path set of the fault tree is to use the duality of the minimum cut set to convert the AND gate in the fault tree into an OR gate, or the gate into an AND gate, and the occurrence of the intermediate event does not occur, and then The success tree corresponding to the fault tree, and finally the Boolean algebra is used to find the minimum cut set of the success tree, which is the minimum path set of the fault tree. .
Accident tree analysis result
Through the analysis of the accident tree, it can be seen that there are five possibilities for a fire and explosion accident in the compressed air system. At the same time, we can adopt nine schemes to avoid this accident, and seven of them are to prevent the formation of combustible substances in compressed air; One solution is to prevent the formation of combustion aids; one solution is to prevent the formation of an ignition source. We combine them into three options to analyze and develop relevant preventive measures.
The first option is to control the combustion-supporting substance. Since the air itself is a combustion aid, the first solution cannot be implemented.
The second scheme, through comparison with the fault tree model, we can see that the focus of this scheme is to control compressed air? Oil phenomenon, reducing or timely removing carbon deposits from the system.
The third scheme (X 8, X 9, X 10, X 11, X 12) eliminates the occurrence of an ignition source. Under the current process conditions, the focus of our control is to prevent the occurrence of ignition temperatures.
Control and preventive measures
1 Reduce the phenomenon of compressed air oil and prevent the occurrence of carbon deposits (1) According to JB 5935-99 "Safety Requirements for Compressors for Process Flows" 3.3.2: "Fire and Explosion Requirements for Air Compression Systems"
For the relevant content, oil-free lubricating air compressors should be preferred.
(2) Under the existing conditions, the use and management of compressor lubricants should be strengthened. Strictly follow the requirements of the compressor manual, select special lubricants, and under the premise of ensuring lubrication performance, the flash point of the lubricant should be set to a high limit. For specific requirements, see Table 1 of the chart of GB 12691-90 "Air Compressor Oil". When the lubricant is used for 1a or 4 000h, it must be completely replaced.
(3) Record and count the fuel consumption during the operation of each air compressor. If the fuel consumption is abnormal, thoroughly check the working condition of the air filter of the air compressor. At the same time, according to GB/T13277-91 "Generally used compressed air quality grade" 3.2.3 and Appendix 1, the compressed air quality level used to control the instrument is 3, the total allowable oil content is shown in Table 3, through calculation It can be known whether the fuel consumption of the air compressor is abnormal.
(4) According to the instructions of the air compressor, when the air compressor runs for 4 000h and the air compressor has abnormal fuel consumption, the air compressor oil separator should be replaced in time.
(5) Sewage outlets should be installed in the lower position of pipelines and gas storage equipment, and equipment and pipelines should be drained regularly. At the same time, in accordance with the relevant requirements of the "Guidelines for the Use of UL Series Degreasing Filters", the differential pressure before and after the degreasing filter shall not exceed 0.04 MPa during normal operation, and the filter shall be drained once every 6 hours during operation. When the pressure difference between the use and the filter before and after the filter exceeds 0.08 MPa, the filter element should be replaced.
(6) Regularly clean the air filter of the air compressor to keep the inhaled air clean, and ensure that the content of solid particles in the air meets the requirements of Appendix A of GB/T 13277-91 "General Compressed Air Quality Grade".
(7) Control the circulating water pressure between 0.2MPa and 0.6MPa, and the temperature should not be higher than 30 °C to ensure effective cooling of compressed air.
The compressor air outlet air temperature should be less than 40 °C.
(8) All equipment, pipelines and storage tanks in the system should be regularly repaired and cleaned. The cleaning time is determined according to the specific use conditions, generally no more than 1a, if found? When the oil and carbon deposits are serious, the frequency of inspection and maintenance should be encrypted.
(9) The desiccant desiccant should be replaced to avoid the accumulation of carbon deposits. According to the instructions of the dryer, the desiccant should be completely replaced every year; or when the dew point of the compressed air frequently exceeds the standard during operation, the desiccant should also be replaced. This can effectively reduce the carbon deposition on the surface of the desiccant. In order to understand this situation more timely, it is recommended to increase the instrument Feng Shui dew point online testing equipment.
2 prevent the occurrence of ignition temperature
(1) Strengthen the daily inspection of the air compressor system and master the operating status of the air compressor and dryer. View and record the operating parameters of the air compressor, and whether there are alarms such as over-temperature and over-pressure. Ensure that the air compressor over temperature (100 ° C) alarm, (105 ° C) shutdown function is normal.
(2) Regularly check and verify the air compressor, dryer body thermometer, thermocouple or other temperature sensing device to ensure the normal operation of the control system. Among them, the temperature measuring device of the PE-12.5/8-A micro heating regenerative compressed air dryer is a pressure type temperature sensor. The current calibration equipment cannot check and verify such instruments. It is recommended to purchase related equipment. To ensure that the temperature sensor is intact and accurate.
(3) At present, the operating room of the air compressor and dryer is invisible, and the operating state of the dryer and various operating parameters cannot be viewed at all. It is recommended to additionally increase the DCS temperature monitoring for the dryer heater and drying tower; At the same time, it is recommended to upload the operating parameters of the air compressor and dryer to the central control room, so as to timely understand the operation status of the equipment and avoid the phenomenon of over-temperature of the equipment.
(4) Since the dryer has a low pressure protection function, the control system stops working when the intake pressure is lower than 25 MPa, and the system automatically resumes operation when the intake pressure is higher than 0.45 MPa. Therefore, in normal operation, the intake pressure should be guaranteed to reach 0.45 MPa to ensure the normal operation of the pneumatic valve of the dryer.
(5) Reasonably set the heating range of the dryer heater, which is currently set to the heater inlet temperature of 90 ° C and the outlet temperature of 180 ° C. It is recommended to strengthen the management of the dryer controller and prohibit arbitrary changes to this setting.
(6) During the operation of the dryer, it is forbidden to close the regenerative pressure regulating valve to prevent the heater from overheating and burning.
(7) Regularly clean and replace the dryer drying tower silencer to ensure timely discharge of hot and cold air during the regeneration and cooling of the dryer to prevent heat accumulation and temperature rise in the drying tower.
(8) Every year, the solenoid valve, pneumatic valve, single-flow valve and pneumatic pipeline of the dryer should be inspected and maintained regularly to ensure smooth air passage, flexible valve action and good sealing condition to prevent malfunction of pneumatic valve and single-flow valve. The internal leakage causes the regeneration of the drying tower and the failure of the cooling process to prevent the occurrence of over-temperature accidents.
Conclusion
In the actual production process, as long as we truly recognize the hazards of air compression system accidents, we must pay attention to and constantly improve and standardize the safety technology management of compressed air stations to reduce compressed air. The oil phenomenon can timely remove the carbon deposits in the system and prevent the occurrence of ignition temperature, which can effectively prevent the accident of the air compressor system.
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