Compressed air is widely used in various fields of industrial production as a clean, environmentally friendly and convenient energy source. As a secondary energy source, the power consumption of compressed air itself is very alarming, averaging 15% to 30% of the total power consumption of the enterprise. However, most companies have not paid much attention to compressed air. They were once considered to be free or very cheap. of. It is inevitable to waste compressed air under this concept, which is manifested in many aspects such as equipment configuration, operation, use, transportation, and management. As energy prices continue to rise, the energy consumption of compressed air is valued by more and more companies and is beginning to be included in the unit cost of the product. Due to the lack of professional knowledge and experience, how to reduce the energy consumption of compressors and improve the utilization of compressed air has become a difficult problem for enterprises. Nanjing Energy-saving Technology Service Center seeks energy-saving potential through testing of air compressor system, and proposes economic operation plan to help enterprises save energy and reduce consumption.
2 Air compressor system introduction
The compressed air required by each production department of an electronic tube factory is mainly provided by the air compressor station of the plant, and the air compressor station is now equipped with 6 piston air compressors. Due to the different quality requirements of compressed air in various production departments, the air compressor station starts from the energy-saving purpose, and separates the compressed air into two separate subsystems: purified compressed air and unpurified compressed air. See the schematic diagram of the compressed air system.
Each air compressor station is equipped with a first-stage gas production pressure, a secondary gas production pressure, a motor current field indicator and a pressure overload alarm for each air compressor unit. The air compressor station controls the gas production volume and pressure stability by manually changing the opening degree of the air compressor inlet valve to control the first-stage exhaust pressure. The air compressor station is continuously operated in three shifts. According to the current demand for compressed air, it is usually necessary to open four 20 m 3 /min air compressors or one 40 m 3 /min and two 20 m 3 /min air compressors between 7:00 and 22:00 on weekdays. machine. The annual power consumption of the air compressor station is 3,609,700 kWh, and the annual output of compressed air is 1,504,670 m3.
3 test and analysis
3.1 test results
According to the statistics of gas production and electricity consumption of the monthly air compressor station in the previous year, the average unit consumption of compressed air of enterprises is 0.204 kWh/m 3 (including electricity for cold dryer, lighting, control instruments, etc.), deducted from cold. The power consumption of the dryer is about 0.196 kWh/m 3 . Corporate compressed air usage is roughly between 60 m 3 /min and 70 m 3 /min. Compressed air output pressure can meet the normal operation of gas equipment in the range of 0.65~0.72 MPa during the day and 0.58~0.64 MPa during the night. The pressure point of the first, second and third branch plants of the company is 0.40.65 MPa, and the pressure of the four-point plant is 0.60.65 MPa.
3.2 Analysis
After analyzing the test data, it can be seen that:
(1) The compressed air of the plant is regulated and supplied with gas. The supply pressure is set at 0.65~0.70 MPa. Due to the failure to implement automatic control, when the gas equipment changes frequently, the pressure fluctuation range cannot be achieved at 0.65. The fluctuation within ~0.70 MPa reflects the room for the pressure setting of the company's air compressor station to be lowered.
(2) There is energy saving space for the operation of the dryer. On-line flow meter monitoring shows that the company needs to purify compressed air volume less than 40 m 3 /min. The plant also opens two cold dryers to purify compressed air, which is unreasonable. The air quality of the two dryers is not the same, one dew point is 2.2 °C, and the other dew point is 0.5 °C. The purified compressed air is mixed and used, resulting in waste of energy in the dryer.
(3) The internal pipeline resistance of individual gas units is relatively large. For example, the pressure of the plant entering the plant is 0.62 MPa, and the pressure drop at the inlet point of the equipment is 0.51 MPa. Within a linear distance of 30 m, the pressure drop is as high as 0.11 MPa.
(4) The air filter of the intake pipe has not been repaired for a long time, and the filter has more ash accumulation. The filter on the air compressor is seriously damaged, which reduces the air quality at the inlet of the air compressor, resulting in the existence of the sealed piston ring of the air compressor. Pulling phenomenon, it is estimated that the cylinder body will also have traces of strain, which affects the sealing characteristics of gas compression.
(5) On-site investigation found that the two air compressor drive systems were defective, lacking a belt, and the individual belts were loose.
(6) The operation of the air compressor has been more than 20 years, and some technical indicators have not reached the original factory value, and the gas production is about 80% to 90% of the factory value. The experiment found that when the intake valve is closed, the no-load current of the unit is too large.
(7) The air aftercooler cools the compressed air less. The compressed air temperature after the cooler is at 44 ° C and the temperature is as high as 72 ° C. The condensate drain pipes of several aftercoolers are blocked.
(8) In order to meet the demand for increased gas consumption, the air compressor station has been adjusted several times, resulting in a messy supply line in the station, and some pipeline layouts are not consistent.
Reason.
(9) The existence of the original gas gas station caused the environmental quality of the air compressor station to be poor, which caused the air filter to be installed indoors, which easily caused the inlet air temperature to be high.
4 suggestions
4.1 Work that can be done on an existing basis
(1) Strengthen communication with each branch factory, according to the test pressure curve, realistically determine the gas supply pressure, so as to ensure normal production and save energy, the four-point plant uses less gas, requires high gas pressure and is away from the air compressor station. At the farthest, a small air compressor can be specially configured for its use of gas to obtain a large reduction in the supply pressure of the entire compressed air system.
(2) Renovate the internal compressed air line of the three-point plant to reduce internal pressure loss.
(3) Replace the damaged air filter, establish and implement a regular maintenance system for the air filter and the aftercooler, improve the air quality at the inlet of the air compressor, reduce the air resistance at the inlet, and make the compressed air cool well. Enter the cold dryer at about 40 °C for purification treatment or enter the gas tank.
(4) Carry out the maintenance work of the dryer, and solve the problem that the dew point of the compressed air after the purification of the two dryers is large.
(5) According to the quality requirements of purifying compressed air dew point, try to run the dry-drying machine with one standby mode to save power consumption and compressed air consumption when the dryer is running. According to the on-site investigation, the air compressor running time of 40 m 3 /min is about 18.5 h/d, and the annual running time is 1 620 h. After one use and one standby, the electric energy can be saved to 10 530 kWh.
4.2 Work included in planning and organization of implementation
(1) Starting from the long-term development of the enterprise and reducing the operating cost of the air compressor station, considering the net value of the main equipment of the air compressor station, the air compressor station transformation project will be carried out. Determine the size of the air compressor station (air supply), model (oil-free / oil-based, piston / screw) and configuration (recommended with current gas volume 20 m 3 /min × 3 + 10 m 3 / min × 3 Improve existing pipeline layout, determine more reasonable and tidy air supply pipelines in the station; determine compressed air quality requirements, configure appropriate purification equipment to achieve economic operation; select appropriate working pressure to determine economical and reasonable air compressor Operation control mode. It is recommended to use one machine to control pressure and flow through loading and unloading or variable frequency speed regulation, and other machines are in full load operation mode.
(2) The implementation of the air compressor station transformation only meets the national standard (0.114 kWh/m 3 ) per cubic meter of compressed air power consumption, and the average electricity price of the enterprise is 0.66 yuan / kWh. The annual cost savings are: 0.66 × (0.196 - 0.114) × 15046771=811.4 million RMB
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