About our customer
Our client is one of the world’s largest semi-conductor display- and MLED producers, located in Beijing China. Compressed air is mostly used to dry their chips, embed materials into chips/boards, manufacture printed circuit boards, and cool chips during the manufacturing process. In this factory and in the semiconductor industry in general, compressed air purity must be held to the highest standards due to its critical applications. For the best quality products, the manufacturing environment must be free of contaminants and compressed air must be oil-free.
The factory’s compressed air system consists of seven oil-free centrifugal compressors, two oil-free screw compressors, two 15 m3 buffer tanks, four desiccant dryers, and filtration. The system is built in one compressor room at the power plant, with natural air intake through windows. The total air volume requirement at the demand side is approximately 640 m3/min.
There was no energy monitoring system present. The customer had some flow and pressure sensors. The service life of these sensors was more than 10 years, and they were not in use. The measurement data was therefore unreliable.
The factory consumed a lot of compressed air every day and it claimed up to 20% of their total energy consumption. The annual cost for the compressed air system came up to 20 million yuan. The customer felt the burden to improve the compressed air efficiency in the plant.
New compressed air management system
A new compressed air measuring and monitoring system was implemented throughout the factory with:
- 10 Pieces of VPFlowScope Probe 4-in-1 to measure the mass flow, pressure, temperature, and total flow. Seven were installed on the main pipelines going to different departments, while the other three were placed at the machine level.
- 1 Piece of dew point sensor was installed after the dryers.
- An energy monitoring system to collect all the real-time measurement data, analyze, generate reports, and guide the implementation of an energy-saving project.
Findings and solutions
Analyzing all collected measurement data, led to the following diagnoses. Consequently, the data helped to make fact-based decision investments on how to improve the system. And monitoring the situation before and after helped to establish what savings were gained in the end.
The ventilation state of the air compressor station room impacts compressor efficiency.
Environmental conditions of the compressor room can impact the efficiency of the compressors, especially in the case of centrifugal compressors. In this factory, the intake air went through a simple non-woven filter system, which was easily blocked. This resulted in a large negative pressure value in the air compressor station. Even though the filters were replaced weekly, the negative pressure value was in the range of -30Pa to -40Pa. The longer the filter replacement cycle, the larger the negative pressure value. Also, due to the poor ventilation, the room temperature exceeded the allowable range for equipment operation. It is proven that when the air temperature at the compressor inlet decreases by 3°C, the exhaust volume increases by 1%.
Environmental conditions of the compressor room can impact the efficiency of the compressors.
To improve the ventilation of the air compressor station, 10 non-woven filters of 1x2m were added to the sidewall of the room to increase the fresh air supply. As a result, the negative pressure value of the room increased to -10Pa. The temperature on the west side of the air compressor station was reduced by about 1°C, and the temperature on the east side was reduced even by 6-8°C, which greatly improved the operating conditions of the air compressors and dryers.
Each bar lower in pressure saves 7% of energy.
The overall system pressure was set unreasonably high at 7 bar, as not all departments needed this pressure level to function. It costs more energy to keep this pressure streaming into the whole factory. A 6-bar overall system pressure turned out to be sufficient. Just by this improvement, the factory already saved 7% on the energy bill.
Each bar lower in pressure saves 1% of energy.
Adding enough buffer volume to improve compressor controls.
The buffer tank volume was too small, and the system pressure fluctuated significantly (more than 0.5 bar). When the system pressure went under or was equal to 7.0 bar, a cold standby compressor was automatically triggered to start, unload, and stop shortly after. This resulted in extra power consumption without any effect on the compressed air consumption. Two buffer tanks, 12 m3 and 15m3, were added to increase the buffer capacity. This reduced the fluctuation to about 0.2 bar. Combined with the overall pressure level reduction, it prevented the unnecessary trigger of the cold standby compressor.
Adding a buffer tank will help to ease the pressure fluctuation curve.
Changing the desiccant dryers from time-based to dew point-based control has a positive effect on energy consumption.
A dew point sensor was added to the system, close to the factory demand side. It revealed that the dew point in wintertime was very low. The data supported the switch from time-based control to control based upon dew point. When the dew point is -70°C, the dryer towers are activated. The electrical energy and the regeneration gas needed for the regeneration cycle were reduced. The operation mode of the dryer was extended from 8 to 12 hours.
VPInstruments Dew Point sensor provides accurate dew point measurement of your factory’s pipelines.
Through experiment, the measurements combined with the energy monitoring system have proven to be a powerful means to improve the energy efficiency in the factories.
- Thanks to the data from the compressed air monitoring system, the specialists could perform a deep diagnosis. The measurement data is transferred directly to the cloud and is accessible anytime, from any corner of the world. Industry 4.0 is happening and remote monitoring is improving the efficiency of energy management in every way.
- Several energy-saving solutions were taken to improve the energy efficiency of the factory. After each energy-saving action, the real-time data gave evidential feedback, which allows the engineers to conduct data analysis and carry out more resolutions to save energy.
- With all the improvements, the energy savings rate in the factory increased by 13%. The company saves about 455,000 Euro on its electricity bill each year.
Industry 4.0 is happening and remote monitoring is improving the efficiency of energy management in every way.