How to configure air compressor to achieve better energy saving and emission reduction

1 Air compressor introduction

at present, there are three main types of mainstream air compressors: centrifugal air compressors, screw air compressors, and piston air compressors.

1.1 centrifugal air compressor

the centrifugal air compressor is driven by the impeller to rotate the gas at a high speed, so that the air generates centrifugal force. Due to the pressurization of the air through the impeller, the flow rate and pressure of the air are increased, and compressed air is continuously produced. Centrifugal air compressor features: ① equipment running balance, high operating rate, reliable operation, no friction parts, less maintenance costs. The centrifugal compressor can achieve completely oil-free compression. ③The equipment has large gas production, compact structure, light weight and small footprint. The centrifugal compressor is not suitable for small gas occasions, the pressure ratio can not be too high. ⑤ The stable operating conditions of the centrifugal compressor are relatively narrow, and the adjustment of the gas volume is not economical.

1.2 screw air compressor

the core component of the screw air compressor head is a pair of male and female rotors meshing with each other, and each pair of rotors rotates in reverse to each other to achieve the effect of compressed air. Screw air compressor is characterized by: ① easy to operate. The screw air compressor has a high degree of automation, low requirements for operators, and easy to realize remote operation and unattended operation. ② Reliable operation. The screw air compressor has few parts, simple maintenance, no vulnerable parts, reliable operation and long service life. ③ Strong applicability. The screw air compressor is forced to deliver gas, so the volume flow is not affected by the exhaust pressure, and it can be applied to various working conditions and maintain efficient operation. ④ Good dynamic balance. The screw air compressor has no unbalanced inertial force, the equipment runs smoothly at high speed, and the requirements for the equipment foundation are not high.

1.3 piston compressor

the core components of a piston compressor are composed of a cylinder, an intake and exhaust valve, and a piston that repeatedly moves in the cylinder. The rotation of the crankshaft drives the piston to reciprocate in the cylinder to complete the process of suction, compression and exhaust. The advantages of piston compressors: ①The applicable pressure range is wide. The piston compressor can be designed to work under different pressures, especially in the high pressure or ultra-high pressure range, which cannot be replaced by other compressors. The compression efficiency is high. The process of compressing gas in the piston compressor is a closed system, and its compression efficiency is high. ③Strong adaptability, a wide range of displacement of piston compressors, and the influence of gas density on compressor performance is not as significant as that of speed compressors. Piston compressors of the same specification can be applied to compress other gas media as long as they are slightly modified. The gas with oil, especially for oil lubrication is more significant. The exhaust is not continuous, the gas pressure fluctuations, it is possible to cause the flow pulsation resonance. ⑥ There are more wearing parts and a large amount of maintenance.

2 Compressed air demand analysis

the demand for compressed air involves many factors. How to meet the production demand efficiently and reasonably is mainly analyzed from the aspects of flow, pressure and humidity.

2.1 flow

ideal operating conditions, production and consumption match each other, and the amount of compressed air not only meets the needs, but also does not produce waste. However, in actual operation, in order to meet the fluctuation of production operation, the compressor flow will be too large, the user can not use excessive compressed air, the equipment for load reduction operation, at this time the equipment is no-load or semi-no-load, energy is directly consumed, do useless work.

2.2 pressure

every 0.1 MPa increase or decrease in the discharge pressure of the air compressor will increase or decrease the energy consumption by 6%. For this reason, the exhaust pressure must be reasonably selected according to actual needs, and too much pressure loss margin cannot be left. In addition, the compressed air consumption of pneumatic equipment is also proportional to the pressure level, and a reasonable reduction in pressure can reduce unnecessary compressed air consumption.

2.3 humidity

since most of the equipment has requirements for the water content in the compressed air, the compressed air is generally dried to remove the condensed water. The drying degree of compressed air is usually measured by the pressure dew point temperature. The lower the pressure dew point temperature, the drier the compressed air, and the more energy will be consumed accordingly. The pressure dew point temperature of the freeze dryer is generally 2 ℃ ~ 5 ℃, and the energy consumption is about 1.5 of that of the air compressor. The pressure dew point temperature of the adsorption dryer can reach -50 ℃, and the energy consumption is correspondingly as high as 10% to 15% of the air compressor.

2.4 lubrication

in the process of working, air compressors are classified according to whether the air is mixed with lubricating oil, and can be divided into two categories: oil-type and oil-free. The participation of lubricating oil significantly improves the volumetric efficiency of the air compressor. Therefore, from the perspective of energy saving, the energy efficiency of oil-type air compressor is much higher than that of oil-free air compressor. And more importantly, the price of oil-free machine is 1 times more expensive than oil lubrication equipment. In addition to the oxygen compressor and other special requirements of the work, the compressor selection should choose oil lubrication equipment, matching the corresponding post-processing equipment, to meet the needs of gas users.

3 Selection of air compressor and post-processing equipment

3.1 compressor type selection

production of low-pressure compressed air (below 1.6 MPa): when the compressed air usage is stable and ≥ 100 m & sup3; /min, it is recommended to use centrifugal compressor, when the compressed air volume is not continuously supplied or the compressed air usage is <100 m & sup3; /min, it is recommended to use screw compressor. The reason is that the centrifugal compressor runs stably with large flow, low energy consumption and simple maintenance. However, if the user's energy consumption changes, the centrifugal compressor is prone to wheezing and gasping, affecting the normal operation of the equipment. Start and stop complex, can not meet the use. The screw compressor is easy to adjust automatically and is more flexible. Medium pressure compressor, the choice is more diverse. Due to the continuous progress of technology, screw compressor has been able to reach 4 MPa, so in the field of medium pressure 1.6 MPa ~ 4 MPa, screw compressor, piston compressor and screw-piston combination compressor can be selected according to the needs. According to practical experience, it is recommended to give priority to screw compressors to reduce operating costs. The production of high-pressure compressed air (above 4 MPa) shall be carried out with piston compressors. It is recommended to use a low-pressure screw machine to produce low-pressure air and perform secondary pressurization of the piston machine to obtain high-pressure compressed air, thereby reducing the cost of piston machine spare parts.

3.2 post-processing type selection

dryer selection: cold dryer can make the pressure dew point reach 3 ℃ ~ 5 ℃, to meet the general needs. The advantages are low energy consumption and high cleanliness of compressed air after treatment. The adsorption dryer can make the pressure dew point reach -40 ℃ or even lower to meet the more demanding drying needs, but the corresponding energy consumption is high. Due to the desiccant, the cleanliness is affected. It should be pointed out that the adsorption dryer needs to consume part of the compressed air (the regeneration air consumption of the non-heat suction dryer is as high as 12% ~ 15%, even the regeneration air consumption of the micro-heat suction dryer is as high as 7% ~ 8%), so the user who chooses the adsorption dryer should set aside the corresponding margin for the compressor selection.

Selection of oil remover: ordinary filter element oil remover and activated carbon filter do not consume electricity, but catalytic oxidation oil removal equipment needs electricity. However, it should be noted that such oil removal equipment can be directly connected to the back end of oil-lubricated air compressor to realize the same oil-free state as oil-free air compressor, thus the purchase cost and operation cost of catalytic oxidation oil-lubricated air compressor with energy-saving oil-lubricated air compressor are obviously lower, the total energy consumption and cost can be reduced by about 25%.

3.3 gas tank selection

the air storage tank is generally placed between the compressor and the dryer, and its functions are: ①The air is pre-cooled, the moisture and impurities in the compressed air are roughly separated, the workload of the post-processing equipment is reduced, the energy efficiency of the equipment is improved, and the energy saving effect is achieved. ② weaken the reciprocating pulse airflow of the piston air compressor to stabilize the air pressure and ensure the smooth and continuous supply of compressed air. ③ Gas storage regulation, balance the imbalance between air consumption and air supply in a short period of time in the system. When the air compressor is unexpectedly shut down, the gas storage tank can be used as an emergency gas source for a short period of time. ④ Provide a larger system capacity to prevent frequent loading and unloading of compressor equipment and improve equipment life. According to the amount of compressed air, if the air consumption matches the output of the compressor, the selection of the air storage tank can be smaller. If the amount of compressed air does not match the production, the air storage tank should be larger to meet the user's demand during fluctuations. Empirical formula for selecting the volume of air storage tank: V = 10NQ/P, where: V is the volume of air storage tank, m & sup3; ;Q is the flow rate of air compressor, m & sup3; /min;P is the gas storage pressure (absolute pressure) of the gas storage tank, MPa;N is the redundancy coefficient, the value of stable gas consumption is 1, the value of frequent fluctuation is 2~3, and the value of frequent fluctuation is more than 4.

4 Energy-saving measures

for large gas users, the construction of large-scale air compression station, to meet the requirements of large-scale air test, accurate supply. The classification of compressed air for different purposes is designed to meet the needs of users without excessive energy consumption. For compressed air with remote distribution or special needs (such as low pressure, small flow rate and high cleanliness required by precision equipment such as processing center), if the pipeline is drawn from the air compression station for special transportation, the cost is high, the pressure drop is large, and the energy consumption is high. Therefore, for the low-pressure air supply of such equipment, air compressor and post-processing equipment should be installed nearby to reduce the loss along the way and meet the needs of a small amount of compressed air.

4.1 communication facilities

in view of the long distance between the gas consuming unit and the air compressor station, the production and consumption cannot be well coordinated and matched. Therefore, perfect communication equipment should be built during the construction period to coordinate and match the kinetic energy production and user needs, including information such as flow, pressure, humidity, etc., so as to achieve maximum accurate matching, set expenditure according to needs, and achieve energy saving effect. Users and air compressor station construction signal regulation and feedback information, timely control of production operation. At present, compressed air production and users through simple scheduling, for example, compressed air is used from 9: 00 to 12: 00 on a certain day. If the user test is completed at 11: 00 and the air compressor station does not receive feedback, it will continue to run for 30 minutes before gradually shutting down. This will cause waste of energy. Take a 300 kW equipment as an example, consuming 150 kWh more electricity each time.

4.2 equipment selection

the principle of compressor equipment selection should be based on the ability to meet the user's parameter requirements, try to achieve the power frequency load, and reduce the energy waste caused by excessive purification of the compressor no-load post-processing equipment. For example, dew point temperatures of 3°C and 10°C are most likely not to be significantly different in use. However, the energy consumption difference between the two is 10 times, the choice of dryer must be selected according to the actual situation, do not deliberately force too low pressure dew point temperature, so according to the user test requirements, matching the appropriate pressure and drying equipment, and according to the demand for reasonable supply in order to maximize energy saving. Combined with the actual situation of industrial enterprises with large fluctuations in energy production, in the selection of compressor equipment, multiple similar equipment in parallel operation, it is appropriate to use a variable frequency compressor for load adjustment, to ensure that the load changes can also make efficient use of energy. The rest of the compressor equipment works at power frequency to achieve the most energy-saving operation effect, and the fluctuation adjustment with frequency conversion meets the matching problem between production and users.

4.3 heat recovery

compressors generate a lot of heat energy during operation, and compressed air is often heated during testing. This allows compressed air to carry not only pressure potential energy, but also a large amount of heat energy. However, in the current production process of Singapore Airlines, the heat energy attached to compressed air is directly discharged. The recovery of this part of the heat energy has many practical applications, such as: winter heating needs, cleaning and heating in the heat meter treatment.

4.4 energy outsourcing model

explore the operation mode of energy outsourcing, and look for the possibility of overall outsourcing under the condition of accurate statistics of kinetic energy usage, so as to reduce operating costs and save manpower. Due to the different conditions of each unit, the production energy of various products is uneven. Therefore, in the exploration of energy outsourcing, we should find a suitable energy outsourcing model for this unit according to local conditions.