Energy saving of compressed air system & application of auto drain
August 3, 2016
Foreword
Energy depleting, the trend of high prices cannot be avoided. "Greenhouse effect" cause extreme weather, also cause the global disasters. Mankind has realized that if we do not improve the current situation, the extinction of the global village seems just around the corner, therefore, the international energy conservation is in full swing.
Prior to the end of October 2015, there are 155 countries commit to suppress global warming.
According to the UN report "World Climate Conference" in Paris, the objectives and requirements for the reduction of ninety percent. This will help realize the magnitude of global warming at 2 ° C within the control.
Carbon dioxide is one of the main culprit of global warming, it is generated from power generation process, and hence, reducing the electricity consumption will help "greenhouse gases" decrement.
Compressed air system (air compressor and related equipment) used in industry is very common, it is as indispensable as water and electricity. But it is high energy consumption and low efficiency system, rarely attention by people.
Since power costs of many machinery and equipment for production are included in electricity cost of factory, majority users usually ignore power costs of compressed air systems which accounted for 80% of operating costs.
Improving the energy efficiency of compressed air system, not only can reduce production costs and increase competitiveness for industries, also can decrease “greenhouse gas" emissions for environments.
【Keyword】Air compressor, Energy saving of compressed air system, Motorized ball valve zero air loss auto drain
Not just condensate
Air compressor suck ambient air into air end and compress for manufacturing plants use. Ambient air contains a lot of water vapor, when air has been compressed, the volume of air becomes smaller and density increases. After cooling, the water vapor over-saturated and turn into liquid.
Ambient air contains many impurities, even toxic substances, especially near industrial areas with higher concentration of impurities. After compressed, the density will be increased. Due to process of high temperature compression, some harmful substances will be melt in, and cause a low PH value and corrosive condensate.
Where is condensate?
Generally compressed air system layout in a factory will be: Air compressor - Separator - Air tank – Coarse filter – Refrigeration dryer – Fine filter. (Fig. 1)
Usually, the compressed air process does not produce condensate, but after cooling, when the air temperature is below the pressure dew point, the water vapor in the air would turn to liquid. The following figure is the condensate distribution of a normal compressed air system.
(Fig.1) Condensate distribution of compressed air systems
Source: Super Air Compressor Technology Co., Ltd. (www.super-air.com.tw/en)
Why does air tank turn into water tank?
When cooler of air compressor operate properly, most of water vapor in the compressed air has condensed into liquid water at the outlet end of cooler. If install a high-performance separator and auto drain, there are about 80% water vapor sucked by air compressor can be removed. But for cost considerations, only a small part of manufacturers install these devices, while some of them use a simple device, but most of compressor manufacturers do not have these design. So most of condensate moving downstream, air tank thus accumulated a large amount of condensate.
The real situation in factories, users often install an auto drain at the bottom of air tank. But due to high humidity, air tank get rust easily and auto drain under the tank usually block by rusts, resulting in the entire air tank turn into a water bucket. Or, if users do not trust auto drain, discharging water by slightly open ball valve at the bottom of the tank, but in fact, it discharge a lot of expensive energy - compressed air instead of water.
The main reason of bad product and equipment failure -- Condensate
If users installed an auto drain which has poor function or without installed any drain, they have a lower initial purchase cost. However, when use these drains, moisture contents in the compressed air is too high, and causes to make cylinders and pneumatic equipment rusting and failure, the solenoid valve coil burned, coating cannot be painted, powder agglomeration cannot convey, filter element blockage, poor refrigeration dryer performance, centrifuge blade damage ... and so on. Hence, we can say more than 90% of malfunctions of pneumatic equipment are caused by condensate in the air. Saving money from auto drain not only pay more cost in maintenance, produce bad products, but also result tragic losses of late delivery and damage reputation, indeed runs the risk!
Leaking air, leak the competitiveness of enterprises
Air compressor is a very common equipment in industry, almost every modern plant uses it. Once it shut down, just like working without water and electricity, the production line will be paralyzed.
However, since air is everywhere and inexhaustible, and power cost in factory includes a lot of machinery equipment and lighting expenses, most users ignore the high cost of compressed air.
The energy conversion of compressed air is very low, only about 25%. Thus, compressed air is the most expensive energy in factories. According to the US Department of Energy, the compressed air system without implement of energy improvements and check has about 20% ~ 30% leakage.
The whole power consumption amounted in China 2014 was 5,523 billion kWh, the industry accounted for 70% (study from Bureau of China Standard 2005), power of motor accounted for 70% power consumption of industry, and air compressor occupied about 18% power of motor, so a year consumption of air compressor can roughly calculate:
5,523 billion kWh * 70% * 70% * 18% = 487 billion kWh
If we calculate by the standard of US Department of Energy, the leakage of the whole air compressor system in China will reach 122 billion kWh (487 billion kWh * 25%)
(Fig.2) Percentage of power consumption used in variety of industrial equipment
Source: Super Air Compressor Technology Co., Ltd. (www.super-air.com.tw/en)
Obvious and obscure air leak
Seal ring, quick connectors, flanges sheet gaskets, rubber pneumatic cylinder ring and control valve, all these belong to insignificant leaking. Available to use soap bubbles or ultrasonic leak detector to ascertain leaking and maintenance.
Leaking in condensate drainage of centrifugal compressor, adsorption dryers, vortex cooler, manual drain valve and auto drain are obvious. Users understand the leakage is serious, but choose to ignore leaking due to the limit of existing equipment, technical, financial constraints, and wrong conception about compressed air value.
Especially the drain valve under the tank and the intercoolers of centrifugal compressor are two of the most serious mistakes of discharge. Generally, users would like to discharge condensate by increase the valve opened degree to exchange the operation safety and to have a higher quality of compressed air. But in this discharging way, a lot of expensive air discharge with condensate.
Compressed air is constantly generated by air compressor and disappeared from manual valve. Incorrect operation is not only let energy consumption ratio of air compressor too high, but also increase the compressed air unit costs.
Apparently, condensate in the compressed air not only influence pneumatic equipment operation, affect production and prolong the manufacturing time, but also boosted business costs and reduce competitiveness.
Restriction of traditional drains
In theory, condensate within the compressed air system can be removed through auto drain. However, the traditional auto drain, whether mechanical type, electrical type (timer + solenoid valve) or level control with solenoid vale drains, have many structural defects.
For example: level control with solenoid valve type have a small discharging diameter which clogged up with rust frequently and the diaphragm broken easily.
Mechanical types have many loose parts immersed in condensate, less discharging volume caused frequent movement, and narrow discharging channel clogged in a short time. All above situations leading users have stereotype of low reliability within traditional auto drains.
There are many leaking points in compressed air system, auto drain is the easiest way to solve it. For a long time, users know the risk of the leaking, but can’t find a proper way to overcome.
Features of good auto drains
Compressed air systems become more and more important in industry, and auto drains are indispensable part of compressed air systems. Therefore, good auto drains must have the following features:
1. Energy Saving
Discharge water only without compressed air loss
Compressed air is the most expensive energy in the factory, hence the basic requirement of auto drains must be drainage water without compressed air loss.
2. Efficient
Maximum discharging volume and low operation frequency = Long life span
3. Reliable
Condensate storage tank should not have moving parts, due to the condensate is extremely dirty and corrosive, non-active components within the tank can reduce the failure rate and improve reliability.
4. Safe
Auto drain is the smallest accessary but has an impact on the operation and quality of application of compressed air system. Therefore, to check working status of auto drains, remote monitoring function is required.
Comparison table of drains
Theory of level control with motorized ball valve auto drain
The volume of condensate in the compressed air system change due to the environmental factors.
The only way to reach the requirement of energy saving is to let level sensor detect and decide drain time. Ball valve drain with large and straight line water channel, can discharge water without contaminate accumulate. The rotating angle positioning and speed control of ball valve are the newest technical in drain market.
The theory of ball valve zero air loss auto drain with condensate discharged by level sensor as follow:
(1)Sensor detects high water level and discharge condensate by opening the ball valve automatically.
(2)Condensate discharged, and sensor detects low level, CPU send signal to close motorized ball valve.
(3)Water Seal prevents air leakage when the ball valve fully closed. Reached the outcome only drain water, no air loss.
(Fig.3)Theory of level control with motorized ball valve auto drain
Source: Super Air Compressor Technology Co., Ltd.? (www.super-air.com.tw/en)
How to choose zero air loss auto drain
Usually floating type or Timing control drains only have one model. In the end, users misunderstand that one model can use in all type of compressed air system.
To choose ball valve zero air loss auto drains with level control, besides the aforementioned function: energy saving, efficient, reliable, and safe, also have to consider about below:
· Ambient temperature
· Ambient relative humidity
· Air flow of compressor
· Air pressure
· Air temperature after cooling
The above five variables will change the amount of condensate, and will affect the selection of drains. In order to save initial purchase costs, users often choose a smaller model. Once choosing smaller drains, not only shorten drains’ lifespan owing to the increasing operation times but also let drains overload, cause condensate moving toward downstream. In order to obviate the above condition, before purchasing an auto drain, users have to choose an appropriate size of auto drain by calculate the amount of condensate.
Because condensate contains small amounts of lubricants in lubrication system of air compressor, so the PH value of condensate is approximately neutral. Generally the main body of auto drain made by aluminum which can meet the requirement. However, in the oil-free air compressors, there is no lubricants to help neutralized PH value. Carbon dioxide and harmful substances in the air may dissolve in condensate. Hence, auto drains which used to oil-free compressed air system should be made of stainless steel to prevent corrosion or rust damage and affect drains function.
How to install zero air loss condensate drain?
Timing control auto drain discharge water by setting time. When it discharge, pressure inside the systems is higher than atmospheric pressure. Therefore, no matter install time drain above water outlet or inlet pipe of drain bend are no effecting its function, because condensate always goes from higher pressure to lower pressure.
But if entrance of auto drain is higher than the exit of compressed air equipment, condensate cannot flow into the drain due to "air lock" phenomenon (Fig 4), and then the level sensor unable to detect high level, therefore, auto drain cannot operate normally. When this situation occurs, lead users think that auto drain is malfunction.
(Fig.4)Installation of zero air loss auto drain
Source: Super Air Compressor Technology Co., Ltd.? (www.super-air.com.tw/en)
Energy saving example of zero air loss auto drain
A frequency control screw air compressor and auto drain improvement.
This example is a famous screw factory in Taiwan which have 10 production plants, with 22 screw air compressors (100HP & 50HP). For testing energy-efficiency improving of air compressor, in the beginning, we choose a 100HP conventional screw compressor as a basis test machine. Then according to the test results to decide that whether use auto drain in other compressors.
The improving steps are as below:
1.Measurement
2.Energy saving potential calculation
3.Installation and commissioning of revamping project
4.Measure again
5.Final report
1.Measurement
1.1 Original data of single air compressor efficiency and operation power was recorded.
Basic operation data of air compressor:
1.2 To confirm the improve efficiency, the owner of factories selected a specific production line as testing. Air consumption is almost constant throughout the year, and recorded data by themselves.
2. Calculation of energy saving potential
2.1 Power consumption and efficiency before improvement
2.1.1 Energy efficiency ratio of air compressor
Measure of energy efficiency ratio as following:
Energy consumption Measurement record table
Source: Super Air Compressor Technology Co., Ltd.? (www.super-air.com.tw/en)
2.1.2 Measurement of operation power consumption
Graph of operation power consumption
(Fig.5) Graph of operation power consumption
Source: Super Air Compressor Technology Co., Ltd.? (www.super-air.com.tw/en)
Load ratio and power consumption calculation
Load time: 67 %,
Power consumption: 87.5 kW
Unload time: 33 %,
Power consumption: 50.0 kW
Average power consumption: 87.5 × 67 % + 50.0 × 33 % = 75 kW
2.1.3 Measurement data calculation:
Demand air flow: 13.1 x 67% = 8.78 M3/min
Efficiency ratio: 75 kW-hr / (60 x 8.78) = 0.142
2.2 After improving energy Estimated:
2.2.1 Power consumption after frequency control improvement:
(8.78/13.1)* 87.5 kW =58.6 kW
Estimates lowered 1 bar operating pressure can save 6% power consumption:
58.65 kW*6% =3.5 kW
2.2.3 Estimates total power consumption after improvement:
58.6 kW–3.5 Kw = 55.1 Kw
Estimates energy-saving ratio: (75-55.1)/75=26.5%
Estimates energy-saving per year: 8,000 * (75-55.1) = 159,200 (kWh)
Estimates saving power cost per year: 159,200 kWh * 2.5 = 398,000 (NT$)
(Fig.6) Frequency control panel of air compressor
Source: Super Air Compressor Technology Co., Ltd. (www.super-air.com.tw/en)
3. Installation and commissioning of revamping project & 4. Measure again
3.1 Frequency control panel of air compressor installed (Fig.6)
3.2 Measuring operation power consumption (Fig.7)
3.3 Pulse indicate power consumption of air loss caused by timing control auto drain in Fig.7
3.4 Change ball valve type no air loss auto drain from Timing control type (Fig.8)
3.5 Re-measuring operation power consumption (Fig.9)
(Fig.7) Graph of operating power consumption of air compressor
Source: Super Air Compressor Technology Co., Ltd.? (www.super-air.com.tw/en)
(Fig.8) Motorized ball valve zero air loss auto drain
Source: Super Air Compressor Technology Co., Ltd. (www.super-air.com.tw/en)
(Fig.9) Graph of operating power consumption after improving
Source: Super Air Compressor Technology Co., Ltd. (www.super-air.com.tw/en)
From the above cases, we can find out that many people do not care of air leaking, but being years air leaking, the cumulative air loss is extremely huge.
The main reason that zero air loss auto drain cannot popularize is due to the impression of low price of traditional drain. But price of motorized ball valve zero air loss auto drain relate to the cost of compressed air, in fact, just a fraction of all compressed air system.
When the competition between companies getting severe, the industrial not only have to innovation, to reduce costs to enhance competitiveness for market, but also need to comply with environmental requirements of green production methods, improve energy efficiency and reduce greenhouse gas emissions reduction industrial pollution due to economic activities on the global environment and fulfill the obligations Earth citizens.