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摘要：一个好的压缩空气系统设计对于半导体芯片厂是非常重要的。这篇论文主要是介绍压缩空气系统的设计思路。 本文主要讲述一下内容: 总体目标、气体要求、扩充策略、维护保养、空气流通、气体品质与压力、系统中的压力损失、系统框架等。
关键字：压缩空气；压力；容量；质量
Abstract: A well designed compressed air system is very important for a semiconductor wafer Fab operation. This paper gave the designer of compressed air system design. The following topics covered in this paper: Overall objective, Air demand, Expansion strategy, Maintenance considerations, Ventilation, Air quality, Air pressure, Pressure Loss in Air System, Information needed by supplier, Air Receiver Sizing, System Layout. Even you are designing a new compressed air system or you want to get your exist system expanded, you will find this paper is helpful for your project.
Key Words: Air compressor; Pressure; Capacity; Quality
Compressed Air System Design
I Overall objective of compressed air system design
Meet average air demand
Meet peak air demand
Provides the quality of air needed for the application
Provides at least the minimum required air pressure
Provide capability for future expansion
Provide capability for easy maintenance
Provides sufficient ventilation
Keep the project cost within budget
Minimize operation cost
II Air demand
Air demand can be determined from flow measurements or by observation of exist compressor load factors in an existing system. An air survey can be done on an existing system or for a proposed system to determine air demand. If an existing system has the compressors running at 100% use factor and is still not maintaining design pressure, PLANT REQUIRED CAPACITY CHART located in this section can be used to determine how much additional capacity is required to bring the pressure back up to the design point.
For example: if existing plant capacity is 2000 scfm, existing pressure is 90 psi, but the required pressure is 110 psi. We assume load factor is 100%,the additional capacity required for each 1000 scfm (existing) can be
200scfm€? =400scfm
Determined in the chart : 200scfm/1000scfm. So the total additional capacity is :Total required capacity is 2400 scfm, as shown in the above chart.
III Expansion strategy
One approach to future expansion requirements is to oversize the existing system. This may take the form of one or more compressors designed to run at less than full load to meet present demand allowing for increased air production in the future. It may also take the form of installing one or more additional compressors the are on standby until needed. Another approach is to design the compressor room and piping system such that additional compression equipments can be added later.
IV Maintenance considerations
All compressors require routine preventive maintenance and nearly all compressors eventually experience an unexpected outage. If the cost to an outage is extreme, it is wise to consider a stand-by compressor in the system. When maintenance is required, it is necessary to have sufficient room to work on the compressor system. Make sure there is enough clearance around and above the components to facilitate maintenance. Minimum clearances can be obtained from the equipment supplier for specific item, Overhead lifting capability is useful.
If the compressor intake is located indoors, sufficient air must be available to pass through the intake filter and into the compressor. This need for ventilation, however, is minor compared to the ventilation required for removal of heat. It is generally true that:
□An air cooled compressor rejects about 42.4 BTU/Min per BHP to the air around itself.
□A water cooled compressor rejects between 13% and 30% of that amount (the rest is rejected to the cooling water). Based on a 330 BHP compressor:
Get specific heat rejection data from the equipment manufacturer in order to determine ventilation requirement.
The specific heat of air at 14.7 psia, 60Deg F is 0.018336 BUT/CUBIC FT-DEG F. In order to ventilate a room for a 330 BHP air cooled unit allowing a 10 DEG F temperature rise in the cooling air would require the following;
(330 X 42.4 BTU/MIN)X(CUBIC FT-DEG F/0.018336 BTU)/(10 DEG F)=76,309 CFM OF VENTILATING AIR
V Air quality / pressure
The quality of is determined by it's intended use. Dew point requirements can be addressed with aftercoolers and dryers. Oil content can be addressed with oil free compressors or filtration. Particulate matter can be addressed with piping materials and filtration. Refer to the manufacturer's catalog to select the aftercooler, dryer and filter.
Determine air pressure requirements at the point of use. Most air pressure requirements are satisfied by selection of the proper compressor design pressure and a properly designed piping system. Low pressure requirements are often satisfied from the plant air system through a pressure regulator. When constant pressure is required at the point of use and normal system pressure fluctuations are a problem, a point of use pressure regulator is generally the solution. In this last case system pressure must be designed to always be above the desired pressure after the regulator.
VI Pressure loss in air systems
Determine air pressure requirements at the point of use. Most air pressure requirements are satisfied by selection of the proper compressor design pressure and a properly designed piping system. Low pressure requirements are often satisfied from the plant air system through a pressure regulator, when constant pressure is required at the point of use and normal system pressure fluctuations are problem, a point of use pressure regulator is generally the solution. In this last case system pressure must be designed to always be above the desired pressure after the regulator.
Pressure Loss in Air Systems
Pressure drops for components such as aftercoolers, dryers and filters should be obtained from the manufacturer. The expected pressure drop through the piping system can be estimated using the pressure loss tables and equivalent length table.
VII Information needed by supplier
The supplier should be given the following design conditions:
Barometer=psia
Inlet air temperature=Deg F
Relative humidity=%
Cooling water temperature=Deg F (if applicable)
Discharge pressure=psig
Air Flow=ICFM or ACFM or SCFM
Definitions:
ICFM - Inlet Cubic Feet per Minute. This is a measurement of the air entering the compressor.
ACFM - actual Cubic Feet per Minute. This is measurement of actual air delivered, referred to inlet conditions.
SCFM-Standard Cubic Feet per Minute Delivered. This is a measure of delivered capacity rapacity referred to some standard set of conditions. The most common set of standard conditions are 14.7psia, 60 Deg F and 0% relative humidity.
The supplier should also be given the minimum and maximum inlet air temperatures. If it is a water cooled application, Minimum and maximum cooling water temperatures should also be stated.
VIII Air Receiver Sizing
The air receiver size can be determined based on manufacturer's recommendation or system requirements.
The following formula can be used to size a tank based on system needs.
V: Receiver Capacity, in Cubic Feet
T: Compressor off line time prior to loading, in Minutes
P2: Final Receiver Pressure when the compressor just be off ling, in psig
P1: Initial Receiver Pressure when the compressor starts, in psig
C: Actual Compressor Delivery, ACFM
Pa: Atmospheric pressure, PSIA
IX System Layout
The following picture shows the general layout for compressed air system.
作者简介：张榕，男，汉族，天津人；中级工程师，中芯国际集成电路制造（天津）有限公司，研究方向：机电/控制/洁净室。
注：本文中所涉及到的图表、注解、公式等内容请以PDF格式阅读原文
关键字：压缩空气；压力；容量；质量
Abstract: A well designed compressed air system is very important for a semiconductor wafer Fab operation. This paper gave the designer of compressed air system design. The following topics covered in this paper: Overall objective, Air demand, Expansion strategy, Maintenance considerations, Ventilation, Air quality, Air pressure, Pressure Loss in Air System, Information needed by supplier, Air Receiver Sizing, System Layout. Even you are designing a new compressed air system or you want to get your exist system expanded, you will find this paper is helpful for your project.
Key Words: Air compressor; Pressure; Capacity; Quality
Compressed Air System Design
I Overall objective of compressed air system design
Meet average air demand
Meet peak air demand
Provides the quality of air needed for the application
Provides at least the minimum required air pressure
Provide capability for future expansion
Provide capability for easy maintenance
Provides sufficient ventilation
Keep the project cost within budget
Minimize operation cost
II Air demand
Air demand can be determined from flow measurements or by observation of exist compressor load factors in an existing system. An air survey can be done on an existing system or for a proposed system to determine air demand. If an existing system has the compressors running at 100% use factor and is still not maintaining design pressure, PLANT REQUIRED CAPACITY CHART located in this section can be used to determine how much additional capacity is required to bring the pressure back up to the design point.
For example: if existing plant capacity is 2000 scfm, existing pressure is 90 psi, but the required pressure is 110 psi. We assume load factor is 100%,the additional capacity required for each 1000 scfm (existing) can be
200scfm€? =400scfm
Determined in the chart : 200scfm/1000scfm. So the total additional capacity is :Total required capacity is 2400 scfm, as shown in the above chart.
III Expansion strategy
One approach to future expansion requirements is to oversize the existing system. This may take the form of one or more compressors designed to run at less than full load to meet present demand allowing for increased air production in the future. It may also take the form of installing one or more additional compressors the are on standby until needed. Another approach is to design the compressor room and piping system such that additional compression equipments can be added later.
IV Maintenance considerations
All compressors require routine preventive maintenance and nearly all compressors eventually experience an unexpected outage. If the cost to an outage is extreme, it is wise to consider a stand-by compressor in the system. When maintenance is required, it is necessary to have sufficient room to work on the compressor system. Make sure there is enough clearance around and above the components to facilitate maintenance. Minimum clearances can be obtained from the equipment supplier for specific item, Overhead lifting capability is useful.
If the compressor intake is located indoors, sufficient air must be available to pass through the intake filter and into the compressor. This need for ventilation, however, is minor compared to the ventilation required for removal of heat. It is generally true that:
□An air cooled compressor rejects about 42.4 BTU/Min per BHP to the air around itself.
□A water cooled compressor rejects between 13% and 30% of that amount (the rest is rejected to the cooling water). Based on a 330 BHP compressor:
Get specific heat rejection data from the equipment manufacturer in order to determine ventilation requirement.
The specific heat of air at 14.7 psia, 60Deg F is 0.018336 BUT/CUBIC FT-DEG F. In order to ventilate a room for a 330 BHP air cooled unit allowing a 10 DEG F temperature rise in the cooling air would require the following;
(330 X 42.4 BTU/MIN)X(CUBIC FT-DEG F/0.018336 BTU)/(10 DEG F)=76,309 CFM OF VENTILATING AIR
V Air quality / pressure
The quality of is determined by it's intended use. Dew point requirements can be addressed with aftercoolers and dryers. Oil content can be addressed with oil free compressors or filtration. Particulate matter can be addressed with piping materials and filtration. Refer to the manufacturer's catalog to select the aftercooler, dryer and filter.
Determine air pressure requirements at the point of use. Most air pressure requirements are satisfied by selection of the proper compressor design pressure and a properly designed piping system. Low pressure requirements are often satisfied from the plant air system through a pressure regulator. When constant pressure is required at the point of use and normal system pressure fluctuations are a problem, a point of use pressure regulator is generally the solution. In this last case system pressure must be designed to always be above the desired pressure after the regulator.
VI Pressure loss in air systems
Determine air pressure requirements at the point of use. Most air pressure requirements are satisfied by selection of the proper compressor design pressure and a properly designed piping system. Low pressure requirements are often satisfied from the plant air system through a pressure regulator, when constant pressure is required at the point of use and normal system pressure fluctuations are problem, a point of use pressure regulator is generally the solution. In this last case system pressure must be designed to always be above the desired pressure after the regulator.
Pressure Loss in Air Systems
Pressure drops for components such as aftercoolers, dryers and filters should be obtained from the manufacturer. The expected pressure drop through the piping system can be estimated using the pressure loss tables and equivalent length table.
VII Information needed by supplier
The supplier should be given the following design conditions:
Barometer=psia
Inlet air temperature=Deg F
Relative humidity=%
Cooling water temperature=Deg F (if applicable)
Discharge pressure=psig
Air Flow=ICFM or ACFM or SCFM
Definitions:
ICFM - Inlet Cubic Feet per Minute. This is a measurement of the air entering the compressor.
ACFM - actual Cubic Feet per Minute. This is measurement of actual air delivered, referred to inlet conditions.
SCFM-Standard Cubic Feet per Minute Delivered. This is a measure of delivered capacity rapacity referred to some standard set of conditions. The most common set of standard conditions are 14.7psia, 60 Deg F and 0% relative humidity.
The supplier should also be given the minimum and maximum inlet air temperatures. If it is a water cooled application, Minimum and maximum cooling water temperatures should also be stated.
VIII Air Receiver Sizing
The air receiver size can be determined based on manufacturer's recommendation or system requirements.
The following formula can be used to size a tank based on system needs.
V: Receiver Capacity, in Cubic Feet
T: Compressor off line time prior to loading, in Minutes
P2: Final Receiver Pressure when the compressor just be off ling, in psig
P1: Initial Receiver Pressure when the compressor starts, in psig
C: Actual Compressor Delivery, ACFM
Pa: Atmospheric pressure, PSIA
IX System Layout
The following picture shows the general layout for compressed air system.
作者简介：张榕，男，汉族，天津人；中级工程师，中芯国际集成电路制造（天津）有限公司，研究方向：机电/控制/洁净室。
注：本文中所涉及到的图表、注解、公式等内容请以PDF格式阅读原文