[webinar] Embracing Digital Transformation in Maintenance & Plant Operations | March 13 at 10AM EST – Register Now
Best Practices for Compressor Storage
Best Practices for Compressor Storage
Robert C. Neely, Cummins-Wagner Co., Inc.
Understanding best practices for compressor storage for a lubricated trim compressor with load/unload controls is critical for optimized performance.
Air receivers store compressed air and are used to temporarily satisfy fluctuations in plant air demand. There are other benefits of a wet receiver such as cooling and cleaning the air before it enters the air treatment equipment. Storage benefits highlighted below apply to all compressor control types:
Prevents frequent cycling of the compressor which reduces maintenance costs and saves energy
Collects condensate, which may pass downstream from the compressor discharge
Provides radiant cooling of the compressed air to reduce moisture content (oil aerosols and water) and assist the operation of the dryer
Reduces pulsations in pressure from the discharge of a reciprocating compressor
Helps to stabilize fluctuations in system pressure
Stores compressed air as potential energy to supply sufficient air for large surge demands.
When installing a lubricated trim compressor with load/unload controls, it is imperative to also install a wet receiver and ensure adequate total system capacitance. System capacitance is defined as total storage among all receivers and associated compressed air piping. A load/unload compressor, without a wet receiver, will experience shortened inlet valve and air-end life due to rapid cycling. This behavior will occur even when an appropriately sized dry receiver is installed in the system.
The storage recommendation for lubricated compressors with load/unload controls is 5 to 10 gallons per cubic per per minute (cfm) output of the compressor. If the compressor operates load/unload and is a base-load machine, then ensure its discharge air flows through a wet receiver and there is adequate total system capacitance for the trim compressor.
Other compressor control offerings from manufacturers include: modulation, variable displacement and variable speed drive (VSD). When not factoring in surge loads, these machines do not require any more than 3 to 5 gallons of total system storage per cfm output of the compressor. VSD machines require even less storage at 1 to 2 gallons/cfm depending on their turndown capabilities.
A dry receiver is useful for storing clean and dry air. It can be located directly downstream of the air treatment equipment or anywhere in the facility to supply air for specific surge loads. Many dust collectors have dry receivers incorporated into their design to assist in partially satisfying their demand event.
If located directly downstream of the air treatment equipment, a dry receiver can store air at a higher pressure than the plant requires and handle fluctuations in demand through a pressure/flow controller. This is useful especially if the demand exceeds the capacity of the air treatment equipment.
The cycle frequency of a load/unload compressor depends on variables such as the pressure band differential, the total system capacitance, the load percentage of the compressor and most importantly, if a wet receiver is installed downstream of the compressor. When a wet receiver does not exist, the compressor will reload more quickly and more often than if a wet receiver did exist. This is due to the pressure drop associated across air treatment equipment.
If there is a 5 psig pressure drop and the compressor operates on a 10 psig pressure differential, then upon the compressor unloading, it will quickly realize downstream pressure of 5 psig less than its unload setting. This artificially reduces the pressure band from 10 psig to 5 psig, and the compressor cycles twice as much. With a wet receiver installed, the pressure would not rapidly drop. The larger the wet receiver, the longer the compressor cycle time. The longer cycle time directly equates to a reduction in frequency of depressurizing the lubricant sump.
For example, Figure 1 shows the energy profile of a lubricated compressor with load/unload controls. In this case, the compressor has roughly, a 90-second cycle frequency (30 seconds loaded, 60 seconds unloaded). Even upon being unloaded for 60 seconds, the energy consumption of the compressor decreased only 35%. The slow reduction in energy upon unloading is due to the compressor slowly blowing down the lubricant sump. More storage capacity is required to fully unload the compressor and to lower cycle frequency.
The higher the cycle frequency, the less efficient the compressor runs at reduced loads, especially if it is a lubricated compressor. The changes to the power versus flow characteristics with changing storage receiver sizes are shown in Figure 1.
To optimize the performance of a lubricated compressor running as a trim machine with load/unload controls, ensure a wet receiver is installed and that there is a total of 5 to 10 gallons/cfm of total system capacitance. Regardless of compressor control type, should the facility experience large demand events, install additional receivers as necessary near the location of the event(s). Use the equation illustrated in figure 3 to correctly size the receiver.
A motor brush is not a brush at all in the traditional sense. It is actually a carbon or graphite cube, commonly held in place by a spring, that acts as a conductor between the electrified stationary and rotating parts of a motor. The whole brush assembly is made up of a carbon block, one or more shunts, a spring and a holder. The carbon blocks are easily replaceable and are therefore intended as a wear part to prevent damage to more costly motor components.
A motor brush is not a brush at all in the traditional sense. It is actually a carbon or graphite cube, commonly held in place by a spring, that acts as a conductor between the electrified stationary and rotating parts of a motor. The whole brush assembly is made up of a carbon block, one or more shunts, a spring and a holder. The carbon blocks are easily replaceable and are therefore intended as a wear part to prevent damage to more costly motor components.
In today's global environment, the "one size fits all" approach is used for so many products that we expect it to apply to just about everything. In the mechanical seal industry, one problem with that philosophy is the definition of the word all. Mechanical seals must live in literally every environment under the sun-from extreme hot to extreme cold, wet to dry, solid to gas, acidic to caustic and so on. Until relatively recently, a vast variety of cartridge mechanical seals were needed to accommodate these pump applications.
In today's global environment, the "one size fits all" approach is used for so many products that we expect it to apply to just about everything. In the mechanical seal industry, one problem with that philosophy is the definition of the word all. Mechanical seals must live in literally every environment under the sun-from extreme hot to extreme cold, wet to dry, solid to gas, acidic to caustic and so on. Until relatively recently, a vast variety of cartridge mechanical seals were needed to accommodate these pump applications.
How do control valves work? Control valves regulate the flow of a liquid or gas by opening or closing internal passages. They form part of a control loop used to control a process. The control valves respond to instructions from the controller and adjusts the internal openings accordingly.
How do control valves work? Control valves regulate the flow of a liquid or gas by opening or closing internal passages. They form part of a control loop used to control a process. The control valves respond to instructions from the controller and adjusts the internal openings accordingly.
Use the proper tools and a good pair of eyes to eliminate almost all your belt drive problems. Did you know that premature belt drive failures can be attributed to just a half-dozen commonly encountered problems? Or that all it takes to solve these problems is just a few tools and using your head? Other than normal wear and use, the most common sources of belt drive failures are 1) improper tension, 2) misalignment, 3) handling, 4) hardware, 5) environmental factors, and 6) design factors.
Use the proper tools and a good pair of eyes to eliminate almost all your belt drive problems. Did you know that premature belt drive failures can be attributed to just a half-dozen commonly encountered problems? Or that all it takes to solve these problems is just a few tools and using your head? Other than normal wear and use, the most common sources of belt drive failures are 1) improper tension, 2) misalignment, 3) handling, 4) hardware, 5) environmental factors, and 6) design factors.
ANSI is an acronym used to describe the American National Institute Pump Standard. The standard evolved from the American Voluntary Standard (AVS) that was first proposed by the Manufacturing Chemists Association in the nineteen fifties. It is a set of inch dimensional standards that describe the envelope dimensions of a back pull out, centrifugal pump.
ANSI is an acronym used to describe the American National Institute Pump Standard. The standard evolved from the American Voluntary Standard (AVS) that was first proposed by the Manufacturing Chemists Association in the nineteen fifties. It is a set of inch dimensional standards that describe the envelope dimensions of a back pull out, centrifugal pump.
Process pump reliability logically involves a combination of fluid-related performance and design decisions that focus on engineering materials and the configuration of mechanical components. Recent case studies have pointed out improvement opportunities in the relative design conservatism found in certain process pump models. Combined with deficiencies in the training of personnel, it can be argued that pump reliability has not made as much progress as it perhaps could.
Process pump reliability logically involves a combination of fluid-related performance and design decisions that focus on engineering materials and the configuration of mechanical components. Recent case studies have pointed out improvement opportunities in the relative design conservatism found in certain process pump models. Combined with deficiencies in the training of personnel, it can be argued that pump reliability has not made as much progress as it perhaps could.
The cost of replacement parts, labor, standby inventory, and downtime can have a devastating effect on a plant's bottom line. Eliminating even one of them by drying a compressed air system will offset the cost of installing and operating the equipment. When pneumatic components wear or become corroded as a result of moisture, they consume more compressed air - and lose energy efficiency. When this wear or corrosion becomes great enough, components must be repaired or replaced - increasing operating expense.
The cost of replacement parts, labor, standby inventory, and downtime can have a devastating effect on a plant's bottom line. Eliminating even one of them by drying a compressed air system will offset the cost of installing and operating the equipment. When pneumatic components wear or become corroded as a result of moisture, they consume more compressed air - and lose energy efficiency. When this wear or corrosion becomes great enough, components must be repaired or replaced - increasing operating expense.
