Pumps – Processes
Reexamination Certificate
2001-08-20
2003-11-25
Walberg, Teresa (Department: 3742)
Pumps
Processes
C417S286000, C137S002000, C137S487500, C137S565130
Reexamination Certificate
active
06652240
ABSTRACT:
TECHNICAL FIELD
This invention relates to a compressor system and more particularly, to a compressor control system and method of operating a compressor system comprising multiple throttled inlet rotary screw compressors.
BACKGROUND
Compressed fluids, such as air, are commonly used in an industrial environment and serve as a power source for various machines and tools. The actual demand for such compressed fluids typically fluctuates throughout the course of a standard work day due to the varying load requirements of each machine and tool. In order to fulfill the demand for a wide variation in load level, the system for supplying the compressed fluid typically includes a plurality of various sized compressors. The compressors are usually connected in parallel and/or series in order to produce a total capacity that can adequately satisfy the anticipated demand.
The compressors are typically started in sequence beginning with the smallest sized compressor and ending with the largest sized compressor. Thereafter, the compressors are cycled “on” or “off” (i.e., loaded or unloaded) in response to the pressure demands required by the load(s) within the system. For example, in an industrial environment, the activation of one or more pneumatically powered tools connected to a compressed air system results in an outflow of compressed air, thereby reducing the overall system pressure. In order to maintain the desired system pressure, it may be necessary to load another compressor onto the system. Similarly, if a machine requiring compressed air is turned “off”, the system will have an over abundance of pressurized fluid, thereby increasing the system pressure. Hence, it may be necessary to unload one or more compressors. The issue, therefore, becomes which compressor should be loaded or unloaded (i.e., added or removed from the compressor system).
A pressure responsive control system typically includes a controller that is wired to measure the system pressure. When the system pressure drops below or climbs above a predetermined pressure set-point, the controller loads or unloads the next available compressor. This process is repeated as often as necessary, or until all of the compressors are either loaded or unloaded, in order to compensate for the change in system demand. Similarly, rather than controlling the compressor system in response to the system pressure, the compressor system could be responsive to a flow sensor that measures the fluid flow.
Whether responding to the system pressure or fluid flow within the system, it may be advantageous to initially sequence the loading and unloading of the compressors in order to produce an electrically efficient compressor system. Particularly, the operator of the system may recognize that the load requirements increase as the day progresses. Therefore, certain compressors are loaded and/or unloaded accordingly such that the pressure or flow capacity of the system increases to satisfy the anticipated load requirements. In other words, the sequence is typically based upon an estimate of the anticipated system demand such that the estimate is close as possible to the actual system requirements. The goal of estimating the actual system demand and loading the appropriately sized compressors is to provide a moderately efficient system by minimizing the unused capacity of the system, thereby minimizing the wasteful use of electrical power.
After initially loading the compressors according to the sequence, the compressors are loaded and/or unloaded in response to the pressure or fluid flow sensors to more particularly satisfy the demands of the system. For example, if after the initial sequence of compressors is loaded and the system senses that it requires additional pressure, an additional compressor may be loaded to the system to satisfy the immediate demand. Likewise, if the system senses that it has an over abundant pressure capacity, a compressor may be unloaded to reduce the overall system pressure.
However, controlling the compressor system solely in response to the pressure differential between the actual system pressure and the pressure requirement of the system may not be as electrically efficient as originally believed. Specifically, although the system may produce fluid with sufficient pressure, the volume of fluid being produced may be inadequate or substantially excessive in comparison to what is actually required. Similarly, controlling the compressor system solely in response to a change in the fluid flow rate may not be the most electrically efficient control method because although the system may produce the required volume of fluid, the pressure of fluid being produced may be substantially higher or lower than what is actually required.
Additionally, compressors may require a significant amount of time to produce fluid at their rated pressure capacity and flow rate. Moreover, during such period, the compressors utilize a significant amount of electrical energy, which translates into a high operating cost. Furthermore, upon the compressors attaining their rated capacity, the present control systems do not insure that the appropriate blend of compressors is loaded to the system in order to produce the most suitable pressure and volumetric flow rate capacity. In other words, controlling the compressors in response solely to a change in pressure or fluid flow may produce excessive amounts thereof. These unnecessary quantities of fluid flow and pressure are the by products of the compressors utilizing an over abundance electrical energy. Thus, controlling the compressors in response solely to a change in pressure or fluid flow utilizes an unwarranted amount of electrical power, thereby producing an inefficient compressor control system.
OBJECTS OF THE INVENTION
It is an object of the invention to produce a more efficient compressor control system.
It is an other object of the invention to produce a compressor control system that does not merely control the operation of compressors as a function of the system pressure.
It is an other object of the invention to produce a compressor control system that does not merely control the operation of the compressors as a function of the system's volumetric flow rate capacity.
It is a further object of the invention to produce a compressor control system comprising of a plurality of throttled inlet rotary screw compressors.
It is a further object of the invention to produce a compressor control system comprising a plurality of throttled inlet rotary screw compressors, wherein the control system does not control the operation of the compressors by sensing only the compressor systems pressure or its volumetric flow rate.
It is even a further object of the invention to produce a control system for a plurality of throttled inlet rotary screw compressors, wherein the control system does not utilize a flow meter to determine the compressor system's volumetric flow rate.
SUMMARY OF THE INVENTION
The present invention is a more efficient compressor control system and a more efficient method of operating a multiple compressor system because the method and control system are a function of both the system pressure and the volumetric flow rate of the system. Thus, a compressor is loaded or unloaded from the compressor system after sensing both the actual pressure and volumetric flow rate of air within the compressor system. The actual flow rate of the compressor system is compared to the online flow rate capacity, and the set-point pressure is compared to the actual pressure of the compressor system. Upon completing these two comparisons, a determination is made as to which, if any, compressors should be loaded or unloaded. These two comparisons allow the control system to load or unload the compressor that will produce the most efficient compressor system. If the pressure of the compressor system is greater than the pressure set-point and the flow rate capacity for one of the compressors is less than the excess flow rate for the compressor system, that particular compressor will be unloaded fro
Day Jones
Harper Blaney
Patel Vinod D.
Scales Air Compressor
Walberg Teresa
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