Case Analysis | 6 Reasons For High Air Compressor System Energy Consumption

В настоящий момент, the air compressor system energy consumption accounts for about 6% ~ 9% of country’s total power generation. It ranks third in high power consumption equipment after fans and water pumps. Сейчас, energy is increasingly tight. Energy saving is an inevitable subject in the air compressor industry. Поэтому, it is very import to control the air compressor system energy consumption.  

Compressed air system case

В настоящее время, the compressed air system contain the following equipment: 5 sets of oil injected screw air compressors and 5 sets of heat regeneration combination desiccant air dryers. The system design pressure is 1.0 МПа. The maximum air flow is about 7300 Нм3/ч. And design dew point of осушитель сжатого воздуха≤-40℃. The air compressor pressure setting range is 0.86 ~ 0.93 МПа. The average dosage is about 3500 Нм3/ч. The dew point of desiccant air dryer for compressor is about -60°C. Transport them to various air sites through the pipe network. Max air flow of 1#~5# air compressors are as follows: 1152 Нм3/ч, 1074 Нм3/ч, 1074 Нм3/ч, 1326 Nm3/h and 2760 Нм3/ч. Кроме того, the rated power is as follows: 110 кВт, 112 кВт, 112 кВт, 132 kW and 250 кВт. Среди них, 1# is vsd air compressor. And 2#~5# are power frequency compressors. The rated air capacity of 1#~4# combination adsorption dryer is 1380 Нм3/ч. They are rated at 11.5 кВт. Кроме того, the air capacity of the 5# combination absorption dryer is 3000 Нм3/ч. Its power rating is 26 кВт. В настоящий момент, operation mode of the air compressor system is blow: 5# воздушный компрессор + 2# или 3# воздушный компрессор. Three combination regenerative air dryers are running. Another 2 dryers are on standby. The energy consumption of air compressor system is about 288100 (kW·h)/month. It is equivalent to about 400 (kW·h)/час. So the energy consumption per unit air supply is 0.114 (kW·h) /Нм3. Refer to JB/T 50159 “Energy Classification of Compressed Air Stations” to judge. The power consumption index is only third. Operational efficiency is very low. So there is a lot of room for improvement in system performance.  

Why is the energy consumption of the air compressor system high?

The high energy consumption of compressed air is mainly due to the following reasons:

(1) Improper combination of air compressors

В настоящий момент, the air compressor combination is not reasonable. Use large flow power frequency compressor (5#) with small air volume power frequency compressor (2# или 3#). Кроме того, the air-use sites are scattered. They are more than 20. Кроме, the air use is irregular. Поэтому, the total air consumption fluctuates greatly. The amplitude exceeds 20%. Более того, air compressor loading and unloading frequently. And the motor idling often occurs. The energy consumption during unloading is high. На него приходится около 20% ~ 35% of the full load energy consumption of air compressor system. Поэтому, the operation efficiency is low.

(2) Air compressor set pressure is too high

В настоящий момент, there is only one air-use site that requires the pressure of ≥0.8 MPa. Its usage accounts for about 10% of the total. Other air sites require pressure ≥ 0.70 МПа. But the terminal centralized supply. Поэтому, set outlet pressure range at 0.86~0.93 MPa. Overcome filter resistance and pipe resistance. Окончательно, the air terminal pressure is ≥ 0.81 МПа. We need to meet the high pressure needs of a small volume site. Increase the air compressor set pressure by 0.1 МПа. This is clearly unreasonable.

(3) Energy consumption of air compressor dryer is high

We need to make sure the dew point meets requirements. Поэтому, the system uses 5 micro-heat combination dryers for drying. The dryer operation consumes a lot of regeneration air. Расход воздуха составляет около 7%. This occurs during desiccant heating and cold purge. Фактически, this is the energy consumption of air compressor system. Plus the electricity consumed by the electric heater. Compared with other dryers, the combination dryer consumes higher energy. Assume that the dew point of the compressed air is -60°C. The energy consumption comparison of different dryers is shown in below Table 1. Take the combination dryer with air capacity of 1380Nm3/h as an example. The unit energy consumption is calculated as 0.1(kW·h)/Нм3. It can be seen from Table 1: The energy consumption of the micro-heat combination dryer (second type) is high. Это о 5 times that of the traditional waste heat regeneration combined dryer (third type). Кроме того, это о 10 times that of the new type of waste heat regeneration combined dryer (fifth type). It is only lower than the heatless combination dryer (first type). В системе воздушного компрессора, the energy consumption is more than 9%. A single unit can exceed 12 kW of the third type dryer. Так 3 units consume more than 36 кВт. В настоящий момент, the overall energy consumption of air compressor system is about 400 кВт.

(4) Large pressure loss in compressed air system

The compressed air system was completed in batches. The piping layout is complex. Pipe resistance is great. Besides in order to ensure the air quality, installed many precision filters. Есть 20 pcs in total. There are also filters inside the dryers. Поэтому, the pressure loss of this air compressor system reaches 0.05 МПа.

(5) There is a air leakage in the air compressor system

There are more than ten system equipments. Более того, the pipeline network is complicated. The main pipeline is over 600 м. There are more than 20 air-use sites. There are many locations where leaks can occur. О 2% of air leakage are found based on operating conditions and flow comparisons. This also affects the air compressor system energy consumption.

(6) Electronic timing drainer consumes a lot of air

Есть 27 pcs of drainer in the compressed air system. They can automatically drain according to the season. Однако, compressed air is always discharged during the draining process. In spring and summer, the drainage interval is 1 мин. 5 s each time. Кроме того, in autumn and winter, the drainage interval is 3 минуты. 15 s each time. So average annual drainage interval is 2 мин. 10 s each time. The diameter of the drain core is about 4 мм. The discharge of a single drain is about 0.25 Нм3/ч. Most of them are air. Calculated at 90%. Air loss is about 0.23 Нм3/ч. A total of about 6 Нм3/ч. So about 50,000 Nm3 of compressed air is wasted throughout the year.

Plans to change the energy consumption of air compressor system

(1) Adjust the air compressor combination

Give several different combinations of air compressors to supply air. And count the operating energy consumption. The energy consumption per unit of air production is shown in Table 2. Фактически, the combination includes the desiccant dryer and рефрижераторный осушитель воздуха.

Dryer Type	Расход воздуха (/Номинальный воздушный поток)	Power Loss (кВт)	Power Consumption (кВт)	Суммарная мощность (кВт)
Heatless Regeneration Combination Dryer	о 14%	19.3	0.5	19.8
Micro Heat Regeneration Combination Dryer	о 7%	9.7	5.8	15.5
Heated Regeneration Combination Dryer	о 4%	5.5	8	13.5
Traditional Waste Heat Regeneration Combination Dryer	о 2%	2.8	0.5	3.3
New Type Waste Heat Regeneration Combination Dryer	0	0	1.5	1.5

Combination Type	Air Compressor System Energy Consumption (KW*h)/час	Unit Energy Consumption (KW*h)/Nm³
5#+1#	345.6	0.0987
5# + 2# или 3# (The combination that has been always used)	358.3	0.1024
5# + 4#	360.5	0.103
1#+2#+3#+4#	362.9	0.1037

It can be seen from Table 2: the energy consumption of the combination 5#+1# is the lowest. 1#+2#+3#+4# has the highest energy consumption. The former reduces the energy consumption by about 3.5% compared with the second type.

Energy consumption analysis of air compressor combination

The air compressors load and unload according to the pipe pressure. Иногда, the actual air consumption is greater than the air supply. В это время, the pipe pressure will gradually decrease. Once below the loading set pressure, air compressor starts loading at full capacity. Кроме того, sometimes the actual air consumption is less than the air supply. В это время, the pipe pressure will gradually increase. Once exceed unloading set pressure, the compressor begins to unload. В это время, the intake valve closes. And the vent valve opens. Vent the high pressure air from the exhaust end to the inlet end. Reduce the inlet and outlet pressure ratio at no-load. В это время, the energy consumption accounts for about 20% к 35% of the full load state. The difference is that the motor speed of power frequency compressor is constant. So it can’t adjust air volume. Changes in the pipe pressure will cause the valves to operate frequently. Окончательно, it will reduce the operation efficiency of air compressor. Кроме, it will affect the stability of the air supply pressure. Однако, the motor speed of VSD compressor can adjust independently. The adjustment range is generally 60%~100%. The intake valve and vent valve operate very little. It can effectively reduce the idling of air compressor system and energy consumption. Air supply pressure is also very stable. Поэтому, we plan to use the combination of 5# + 1# воздушный компрессор. Между ними, в 1# air compressor is variable speed.

(2) Different regional pressure supply

Add a new compressed air system. Supply air separately for the high-pressure air use site. The compressed air terminal operates at reduced pressure. Reduce the air compressor pressure from 0.86~0.93 MPa to 0.76~0.83 MPa. Energy consumption formula: E=∫ Edt=∫PaQaln(p/pa)dt Па: atmospheric pressure absolute pressure Qa: volume flow in atmospheric state p: absolute pressure of air compressor outlet t: time Either variable can reduce air compressor system energy consumption. Assume the flow and time remain unchanged. For every 0.1 MPa decrease in pressure, energy consumption decreases by about 7%~8%. The new adding compressed air system is as follows: include 2 sets oil-free screw VSD compressors and 2 sets combination dryers. The design working pressure is 1.0 МПа. Each max air capacity is 1068 Нм3/ч. Use permanent magnet variable frequency motor. It can start and stop arbitrarily. And the times is unlimited.

(3) Use GM zero air consumption smart drainer

Don’t use the electronic timing drain again. Change it to GM smart zero air consumption drainer. Its working principle is as follows: condensate flows into the drain. The fluid level in the chamber keeps rising. When reaching high level, the level sensor signals. Activate the solenoid valve to start draining. The condensate level drops to a low level. В это время, the sensor sends a signal. Close the solenoid valve to stop draining. The liquid level is still slightly above the drain port. It will form a liquid seal. So prevent the compressed air from escaping. Then it achieves the effect of zero air consumption. Judging from the actual situation on site, there is no air emission during GM drainer working. It really eliminates the unnecessary energy consumption of the air compressor system.

Energy consumption performance of the air compressor system after change

System change completes. The monthly operation energy consumption of the compressed air station is about 239,906 (kW·h). The new adding energy consumption is about 25205 (kW·h). Таким образом, total is 265111 (kW·h)/month. Before change, the monthly energy consumption was 288100 (kW·h)/month. Поэтому, it saves energy by 22989 (kW·h). It reduce air compressor ystem energy consumption by about 8%. The energy saving effect is very obvious. В заключение, we should monitor the compressed air system frequently. And need maintain the air compressor, сушилка, filters and pipeline well. Кроме того, the system also needs to be optimized and upgraded. So it can reduce the energy consumption of the air compressor system.