Energy-saving Tips of Bolaite Air Compressor

Compressed air is one of the most widely used power sources in the industrial field. Due to its many advantages such as safety, no harm, good regulation performance and convenient transportation, it is more and more widely used in the fields of modernization and automatic power. However, it is necessary to consume energy for getting high-quality compressed air. In most production enterprises, the energy consumption of compressed air accounts for 10%~35% of the total power consumption. According to the investigation, most compressed air systems, no matter they are new or old, operate in low efficiency, and there are problems such as mismatched equipment, large pipeline loss, system leakage, human demand, incorrect use and improper system control.

Of course, after professional and comprehensive analysis and evaluation of the air system, the compressed air system can save energy by taking appropriate measures, especially up to 10%-50% of electric energy. In today's energy shortage and rising electricity price, such evaluation and transformation not only saves energy, reduces consumption, but also means that it will bring new profit space for enterprises!

Composition of energy consumption and cost of compressed air system

The air compressor is the heart of the air compression station. Now when we refer to the air compressor, we will also think about the compressed air system. The air supply system of the air compressor refers to all equipment from the compressor to the air consumption point. Therefore, the equipment of the whole compressed air system can be divided into the following parts in terms of function:

• Air source generating part: such as the compressor

• Air source treatment part: such as dryer, filter and separator

• Control part: such as various control components

• Gathering and transportation parts: such as air storage tank and pipeline valve

Most of the equipment in the compressed air system is electrically driven, and the electric energy consumed by the air compressor accounts for more than 90% of the total electric energy. For example, there are three 132kW machines (i.e. 24m3/min compressor) in one air compression station, two for operation and one for standby. They run for 8,000 hours every year. The electricity cost is RMB 0.65 /kWh, and the annual electricity cost can be calculated as follows:

132×8000×0.65×2=1,372,800 (RMB)

If the dryer is of refrigerated type, the power of refrigerated air dryer with corresponding treatment capacity is 8.5kW, and the annual electricity cost is:

8.5×8000×0.65×2=88,400 (RMB)

If it is necessary to purchase, establish and maintain the compressed air system, the investment required shall include the initial investment of equipment, spare parts, labor, energy consumption, etc. When examining the capital input allocation of the system in the first year of use, the results are shown in Figure 1:

When considering the total capital input allocation of the system for five years, the results are shown in Figure 2:

From the comparison of the two figures, it can be seen that, with the extension of the service life of a compressed air system, the proportion of its equipment investment is gradually decreasing, while the proportion of operating electricity cost is greatly increasing. In the practical application, a normally operating compressed air system will have a full life cycle of more than 5 years, and some will even have a continuous operation of 15~20 years or more.

Therefore, when considering the investment and return of the compressed air system, we should make a cost analysis of the full life cycle like other mechanical products. In this way, it is easily found that the energy-saving analysis in the compressed air system will bring new equipment management ideas to the enterprises.

Focusing on energy saving of the compressed air system will bring good economic benefits to the enterprises.

Causes of energy waste during operation of the compressed air system

During operation of the compressed air system, there are many causes for energy waste, and the main causes are as follows:

1. Compressor operating load rate:

Generally, the design or selection of air compressors is based on the maximum load condition (i.e. 100% load). This is also a general principle to be observed. However, the working conditions are changeable and the load of the production line is uneven in actual use. Investigation and data show that the load rate of the general compressed air system is 60 ~ 70%.

United States Department of Energy's survey of compressor load percentages for companies using compressed air worldwide is shown in Figure 3:

Taking China as an example, the full load rate of the equipment is 66%, that is, the equipment operates in unloading mode for another 34% of the time. At this time, even if the best conventional regulation mode is adopted, the power consumption of screw air compressor is still 20 ~ 45% of full load power. The oil-free screw compressor has a lower value, while the oil screw compressor has a higher power consumption.

Using the above example (an oil-lubricated screw compressor with a power of 132kW and an exhaust volume of 24m3/min), we compare its power consumption under full load operation with that under 66% load operation in loading/unloading mode, and assume that when operating in loading/unloading mode, the power consumption at unloading mode is generally 35% of that at full load.

It can be seen from the figures in Table 1 that when the load rate is 66%, its power consumption and electricity cost are still 78% of those at full load. That is to say, 22% of the power at full load is wasted. When the compressor runs at 66% load rate, the power waste ratio accounts for 15% of the actual power.

According to the evaluation and investigation of many compressor users in China, it is found that this kind of waste is very common in the Chinese market, so this is a matter of concern.

2. Setting problems of operating parameters between compressors in compressed air system:

There is a lot of equipment in one compressed air system. Generally, multiple compressors run together, equipped with standby machines. When the compressor is running, the gas consumption changes. How to coordinate the changing parameters is a matter of concern. When their parameters are not properly set, it will also cause great power waste.

However, few people pay attention to the matching of equipment parameters of compressed air system at present. Since the system has been changing all the time, how to fully match the supply and demand in dynamic changes requires a large amount of tracking and research on the system equipment. Therefore, commissioning personnel shall not only have good professional knowledge, but also have a high sense of responsibility.

The following figure shows the current variation curve of a system with only two compressors. This system is composed of one 75kW compressor (represented by the curve above) and one 30kW compressor (represented by the curve below). It works for 350 days a year and 24 hours a day. The unit price of electricity cost is RMB 0.65 /kWh. The current curve during its operation is shown in Figure 4:

Current curve before setting

It can be clearly seen from the figure that in this system, the operation control mode of the two compressors is the conventional loading and unloading control of the machine. As the coordination setting is not well performed, the two compressors are respectively converted to loading and unloading in accordance with their own pressure settings. Figure 5 shows the compressor operation curve after resetting:

Current curve after resetting

It can be seen from Figure 5 that after adjustment, the main machine runs smoothly, the loading and unloading frequency is greatly reduced, and the startup time of the standby machine is also greatly reduced.

According to the calculation, before the parameters are adjusted, the annual electricity cost is about RMB 586,000, of which RMB 74,000 is wasted, so the energy-saving potential is also obvious. However, the solution is to simply reset the pressure!

3. Leakage of the compressed air system

Leakage is a common phenomenon in each compressed air system. The leakage of compressed air mainly occurs at the pipe joints, such as flanges, joints, quick plugs, etc. According to data, the leakage ratio of ordinary factories is above 20%. Table 2 shows the waste caused by leakage points with a diameter of 1mm2 when the pressure is 0.7MPa and the unit price of electricity cost is RMB 0.65 /kWhr:

From the above two sets of figures, we can know a fact that the waste caused by leakage in the compressed air system is also considerable. If solving the problem with care, we will surely have a good energy-saving effect.

Solutions for energy saving of the compressed air system

According to the composition of energy consumption of the compressed air system and the reasons for waste mentioned above, it is found that the energy saving of the compressed air system can be finally reflected in the energy consumption, especially the power consumption. Although the compressor is the equipment with the most power consumption in the compressed air system, the energy-saving space in the compressed air system is not necessarily all in the compressor itself. The problem of equipment flow configuration, the problem of cooperation of several machines and even the use of compressed air at the final use point will lead to the waste of system energy.

Therefore, it is crucial to select the compressor for energy-saving operation in a compressed air system. If the energy-saving problem of the system is discussed, our focus should be shifted from focusing on the compressor itself to the performance of the system. Only in this way can we truly find the reason for the biggest waste of the system and correct it.

The key problem of energy saving of the compressed air system is to find the root cause of system waste and accurately analyze the value of system energy-saving potential. To this end, we understand the user's on-site use, record some necessary data and implement data analysis, perform professional and comprehensive air system analysis, and implement relevant measures properly, so that the energy savings can reach 10%-50%.

The provision of a comprehensive solution for the compressed air system should start with a professional evaluation of the compressed air system. The difficulties and inefficiency problems encountered during the operation of modern compressed air systems are always complex and unattainable. Proper evaluation is the only channel for dynamic management and making compressed air system components fully effective. This is a process of providing comprehensive solutions for the entire compressed air system of users from the compressor to the use point, providing users with a compressed air system with high energy efficiency, increasing system stability, improving compressed air quality and ensuring normal output of compressed air. This is also the future development direction of the compressed air industry.

In the past period, the problem of power shortage has become a "bottleneck" restricting the development of the national economy. Many enterprises are forced to cut off power to maintain the normal operation of the whole society. Therefore, the energy and efficiency problems of the compressed air system have become a special topic at present and have been paid attention to by some enterprises and research units. Some domestic government units involved in energy saving have gradually transferred their work centers to the energy saving of the compressed air system.

Energy is part of the product cost, and in some products, energy cost accounts for a high proportion. It is obvious that the more energy is consumed in the production process, the higher the cost, the smaller the profit space and the smaller the competitive advantage in price. At present, the vast majority of enterprises in China have extensive management, high consumption, large waste, poor economic benefits and lack of competitiveness. Energy conservation and consumption reduction, and energy efficiency improvement have become important means for high energy-consuming enterprises to improve international competitiveness. The Chinese government attaches great importance to technological development and transformation focusing on energy saving and consumption reduction, and provides financial support. Its purpose is to encourage enterprises to reduce production costs and improve their competitiveness in the international market through energy conservation and consumption reduction in fierce market competition.