Patent Application
20170292522
The subject matter described herein relates in general to compressed air systems and, more particularly, to an improved compressed air system and method of operating same.
Manufacturing and industrial plants typically utilize compressed air as an energy source that may be available throughout the plant. These plants use a compressed air system to provide the compressed air. The demand for compressed air is dynamic may vary throughout the day and from day to day. Compressed air systems are typically sized (and often oversized) based on full load operating conditions and are designed to operate most efficiently at full load. These systems typically use Fixed Speed Drive (FSD) compressors, such as centrifugal compressors which may have one or more stages to achieve the rated full load output in an efficient manner. However, the demand on most compressed air systems varies throughout the day and the system is often operating at less than full load. The loading may be adjusted based on throttling the input to the FSD compressors and any over production of compressed air may be removed by venting compressed air from the system through a blow-off valve. FSD compressors are inefficient at part loads and if not controlled properly a system could have several or all of its FSD compressors simultaneously running at part loads, crippling the overall efficiency. Additionally, venting of compressed air from the system is also inefficient.
Variable Speed Drive (VSD) compressors, such as variable speed screw compressors, use variable speed motors to modulate their output. The advantage of this is that it allows the compressor to have a relatively linear output (cubic feet per minute) to energy (kilowatt) input efficiency curve compared to other mechanisms such as inlet modulation and load/unload operation. This makes VSD compressors useful as trim compressors, supplying the variable demand on top of a stable base demand. However, VSD compressors are not as efficient as FSD compressors at providing a relatively constant output.
A compressed air system that uses both FSD compressors and VSD compressors, however, may result in operational situations where undesirable operation is occurring. Additionally, the FSD compressors may have a limited ability to be repeatedly started and stopped within a given time frame thereby limiting operational flexibility of the compressed air system.
An improved compressed air system utilizes one or more base compressors, such as FSD compressors, to meet the compressed air demands and one or more trim compressors, such as VSD compressors, to meet the variations in the demand. The operation of both the base and trim compressors is controlled to provide improved overall efficiency while meeting the transient load demands. The control can spread the demands over the various base compressors to improve the overall loading on each base compressor. Efficiency metrics can be utilized to control the switching between base and trim compressors. Unloading of a base compressor can be controlled to avoid undesirable changes in system performance.
In one respect, the present disclosure is directed to a compressed air system having an air distribution network, a plurality of base compressors, at least one trim compressor and a control system. Each base compressor has an air outlet coupled to the air distribution network and operable to independently supply a flow of pressurized air to the air distribution network. The at least one trim compressor has an air outlet coupled to the air distribution network and operable to independently supply a flow of pressurized air to the air distribution network. The control system is coupled to the air distribution network, the base compressors, and the at least one trim compressor. The control system monitors the operating condition of the air distribution network and controls the operation of the base compressors and the at least one trim compressor to meet an air demand placed on the air distribution network. The base compressors are arranged an in initial use order that determines the order in which the base compressors will be activated by the controller and upon the deactivation of one of the base compressors the order of the base compressors is changed.
In another respect, the present disclosure is directed to a compressed air system having an air distribution network, a plurality of base compressors, at least one trim compressor and a control system. Each base compressor has an air outlet coupled to the air distribution network and operable to independently supply a flow of pressurized air to the air distribution network. The at least one trim compressor has an air outlet coupled to the air distribution network and operable to independently supply a flow of pressurized air to the air distribution network. The control system monitors the operating condition of the air distribution network and controls the operation of the base compressors and the at least one trim compressor to meet an air demand placed on the air distribution network. The control system replaces operation of one of the base compressors or the at least one trim compressor with operation of a respective trim compressor or base compressor when an efficiency metric exceeds a pre-determined threshold.
In yet another respect, the present disclosure is directed to a compressed air system having an air distribution network, a plurality of base compressors, at least one trim compressor and a control system. Each base compressor has an air outlet coupled to the air distribution network and operable to independently supply a flow of pressurized air to the air distribution network. The at least one trim compressor has an air outlet coupled to the air distribution network and operable to independently supply a flow of pressurized air to the air distribution network. The control system monitors the operating condition of the air distribution network and controls the operation of the base compressors and the at least one trim compressor to meet an air demand placed on the air distribution network. When the control system determines that there is excess air production and seeks to stop operation of a base compressor, the control system initiates an unload test. The unload test includes reducing the output pressure of an operating base compressor by a predetermined increment in a series of steps and monitoring the pressure of the air distribution network relative to a predetermined threshold at each step. The control system stops operation of the associated base compressor if the pressure remains above the predetermined threshold and maintains operation of the associated base compressor if the pressure drops below the predetermined threshold.
This detailed description relates to compressed air systems that utilize one or more base compressors, such as FSD compressors, to meet the compressed air demands and one or more trim compressors, such as VSD compressors, to meet the variations in the demand. The operation of both the base and trim compressors may be controlled to provide improved overall efficiency while meeting the transient load demands. The control scheme may spread the demands over the various base compressors to improve the overall loading on each base compressor. Efficiency metrics may be utilized to control the switching between base and trim compressors. Unloading of a base compressor may be controlled to avoid undesirable changes in system performance.
Detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are intended only as exemplary. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the aspects herein in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of possible implementations. Various embodiments are shown in the Figures, but the embodiments are not limited to the illustrated structure or application.
It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details.
In one or more arrangements, a compressed air system 20 may include a plurality of compressors to meet the air demand. System 20 may include a plurality of base compressors 22 which may be configured to provide a majority of the compressed air demand placed on system 20. Base compressors 22 may be fixed speed drive (FSD) compressors, such as multi-stage centrifugal compressors. Exemplary FSD compressors may include Ingersoll Rand CENTAC brand compressors available from Ingersoll Rand. Each base compressor 22 has an air inlet 24 which may have a throttling device 26 operable to throttle the air flow into base compressor 22. Each base compressor 22 has an air outlet 28 that is coupled to an air distribution network 30 of system 20. A blow-off device 32 may be operatively coupled to each outlet 28 to allow excess compressed air to be released. Blow-off devices 32 may be located adjacent the associated base compressor 22 or at a remote location. The number of base compressors 22 can vary based on the desired capacity system 20. As shown in
System 20 may include one or more trim compressors 34 which may be configured to provide compressed air to supplement the compressed air provided by base compressors 22 to meet the air demand. Trim compressors 34 may be variable speed drive (VSD) compressors, such as screw compressors. Exemplary VSD compressors may include Ingersoll Rand Sierra brand and Atlas Copco ZR315 brand compressor available from Ingersoll Rand and Atlas Copco, respectively. Each trim compressor 34 has an air inlet 36 that supplies air to trim compressor 34. Each trim compressor 34 has an air outlet 38 that is coupled to an air distribution network 30 of system 20. As shown in
System 20 may include a master controller 42 that is operable to control the operation of system 20 to meet the air demand. Master controller 42 may be operatively connected to each base compressor 22, trim compressors 34, and the associated components, such as throttling devices 26 and blow-off devices 32. For example, in some arrangements master controller 42 may be connected to base controllers 33 and trim controllers 40 to command and control the operation of system 20 while in other arrangements master controller 42 may alternatively or in addition be directly connected to each component of system 20 to command and control the operation of system 20. Accordingly, the specific arrangement and connections of the controllers can be varied as desired. Additionally, while operation of the various components of system 20 may be referred to with reference to a particular controller, such as base controller 33, trim controller 40 and/or master controller 42, it should be appreciated that the particular reference is merely exemplary in nature and the operation may be controlled by commands from a controller other than that recited.
Each base controller 33 may control the operation of the associated base compressor 22, throttling device 26 and blow-off device 32. For example, base controller 33 can set the operating parameters (desired volume of compressed air, output air pressure, etc.) and command the starting and stopping of base compressor 22, the throttling of input air by throttling device 26 and the venting of excess air production by blow-off device 32. The operating conditions for each base compressor 22 and its associated components may be reported/communicated to master controller 42 by the associated base controller 33. Additionally, master controller 42 may provide commands to each base controller 33 that dictate how each base compressor 22 is operated.
Each trim controller 40 may control the operation of the associated trim compressor 34. For example, trim controller 40 can set the operating parameters (desired volume of compressed air, output air pressure, etc.) and command the starting and stopping of trim compressor 34 and is operating speed. The operating conditions for each trim compressor 34 may be reported/communicated to master controller 42 by the associated trim controller 40. Additionally, master controller 42 may provide commands to each trim controller 40 that dictate how each trim compressor 34 is operated.
Referring now to
Referring now to
Base compressors 22 are an efficient way to provide compressed air at a relatively constant volume at a specific pressure. The output of base compressors 22 can be varied through the use of throttling devices 26 and blow-off devices 32 to try and maintain a constant pressure in distribution network 30, as known in the art. For example, when excess air is being produced by a base compressor 22, which will result in increased air pressure in distribution network 30, throttling device 26 can reduce the air flow into base compressor 22 thereby reducing the output and the resulting contribution to air pressure in distribution network 30. This is also referred to as partial loading. If the pressure is still too high, excess air production can be discharged by the associated blow-off device 32 to further reduce the resulting contribution to air pressure in distribution network 30. However, the use of throttling device 26 (partial loading) and venting via blow-off device 32 are inefficient and increases the operating cost of system 20.
Trim compressors 34 may be more efficient at providing compressed air at a particular volume and pressure as compared to operating a base compressor 22 at partial load and/or venting. Trim compressors 34 may use variable speed motors to modulate their output. The advantage of this is that it allows the compressor to have a relatively linear output (cubic feet per minute) to energy (kilowatt) input efficiency curve compared to other mechanisms such as inlet modulation and load/unload operation. As such, it may be desirable to operate base compressors 22 at a full load (or limited partial loading) and supplement the output with one or more trim compressors 34 to meet the air demands in an overall more efficient manner.
In one or more arrangements, system 20 may be operated such that a majority of a relatively stable air demand is met by the use of base compressors 22 and the remaining air demand is met through the use of one or more trim compressors 34 as necessary. System 20 may select which and how many base compressors 22 to utilize to meet the relatively stable air demand and which and how many trim compressors 34 to utilize to supplement base compressors 22 to meet the air demand. System 20 may select the combination of base and trim compressors 22, 34 to meet desired efficiency goals and/or improve overall efficiency. System 20 may use an efficiency metric to determine the combination of base and trim compressors 22, 34. System 20 may select base compressors 22 to even out the overall usage across all of the base compressors 22. For example, as shown in
In one or more arrangements, system 20 is controlled to provide a desired volume of compressed air at a desired pressure. The air demand (volume demand) can vary as different machines demand differing air flows from air distribution network 30 as they turn on and off. While the air volume demand may change, the required air pressure at which the air is supplied is typically maintained within a limited range to provide for proper operation of the machines using air from system 20. That is, the machines using compressed air from system 20 are configured to perform their associated tasks with air being supplied at a particular pressure. System 20 may be configured to provide the varying air demands at a relatively constant pressure range. By way of example, the desired operating pressure may be 112 psi+/−0.5 psi in distribution network 30. System 20 may monitor the pressure in distribution network 30 and take corrective actions when the pressure deviates from the desired operating pressure. For example, a low pressure warning may be indicated when the pressure is within a low range below the desired operating pressure, such as between 0.6 and 2.9 psi below, and a low pressure alarm may be indicated when the pressure is a predetermined amount below the desired operating pressure, such as 3.0 psi below or greater. The corrective action taken by system 20 can vary based on whether there is a low pressure warning or a low pressure alarm. For example, when a low pressure warning is present, system 20 may look to increase the output of one or more trim compressors 34, initiate operation of another base compressor 22, and/or replace operation of one or more trim compressors 34 with operation of one or more base compressors 22. When a low pressure alarm is present, system 20 may, by way of example, initiate operation of a trim compressor 34, if available, and/or initiate operation of another base compressor 22. A low pressure alarm may require a more drastic or quicker response than a low pressure warning as the pressure in distribution network 30 may be inadequate to meet the needs of the machines utilizing the compressed air.
In one or more arrangements, system 20 may monitor the amount of excess air being discharged by blow-off devices 32. System 20 may initiate a corrective action if the discharged air exceeds a predetermined quantity. For example, system may determine a collective amount of discharged air from all blow-off devices 32 and compare that to a predetermined value. If the collective amount exceeds the predetermined value, system 20 may determine if a more efficient arrangement of base and trim compressors 22, 34 can be operated to meet air demand. System 20 may look at an efficiency metric to determine if it is more efficient to operate a trim compressor 34 or a base compressor 22. The efficiency metric may take into account the efficiency of a base compressor 22 at both full loading and partial loading and the efficiency of a trim compressor 34 at various operational speeds in making a determination about a preferred operational arrangement. In some operational scenarios, it may be more desirable to run a base compressor 22 at partial loading as opposed to a trim compressor 34 at low operational speed. By way of example, one efficiency metric may be a measure of the amount of energy (kilowatt hours) to make 1000 CFM of air at a given psi, such as 112 psi. This metric may be referred to as a KCF number. System 20 may calculate the KCF for a particular compressor (base or trim) and compare that to a predetermined value to ascertain whether to operate a base compressor 22 or a trim compressor 34. By way of example, if a KCF of operating an available and non-running base compressor 22 is greater than 3.5 then system 20 may replace operation of a trim compressor 34 with that base compressor 22. The available and non-running base compressor 22 may be the next available non-running base compressor 22 in a predetermined usage sequence. It should be appreciated that other efficiency metrics may be utilized and that the metric may be a ratio.
In one or more arrangements, system 20 may operate base compressor 22 and trim compressors 34 so that a running trim compressor 34 is the lead adjuster. For example, system 20 may place a demand on running base compressors 22 that are beyond their capabilities (such as a pressure output greater then operationally possible) thereby ensuring that the running base compressors 22 are fully loaded. Adjustments to the air output system 20 may then be accomplished by adjusting the operational speed of a trim compressor 34 to meet the air demand. This arrangement may prevent a fight between adjusting the loading of a running base compressor 22 and adjusting of the operational speed of a trim compressor 34.
Referring now to
Referring now to
Pressure control 62 will then determine if the commanded start sequence failed, as indicated in decision block 82. If the start sequence failed, pressure control 62 will return to step A. If the run sequence did not fail, pressure control 62 will initiate a wait delay timer, as indicated in block 84. The wait delay timer stops further operation of pressure control 62 until the predetermined time period has lapsed. The wait delay timer prevents rapid operation of pressure control 62 and allows time for the operational changes to have some effect. Wait delay timer, by way non-limiting example may be about 30 seconds. Upon the completion of the wait delay timer, pressure control 62 will add 1 to a run counter, as indicated in block 84. The run counter is used to allow operation of system 20 to stabilize and prevent immediate corrective action in the event of a low pressure warning condition, as explained further below. The run counter does not prevent pressure control 62 from initiating another corrective action to address a low pressure alarm situation or an excess blow off condition. After adding 1 to the run counter, pressure control 62 returns to step A.
Referring now to
Upon the completion of the start delay timer, pressure control 62 again determines if a low pressure warning is active, as indicated in decision block 100. If there is no low pressure warning, pressure control 62 moves to step D in
Referring now to
Once an available base compressor 22 has been ascertained, pressure control 62 initiates a base delay timer, as indicated in block 126. Base delay timer prevents pressure control 62 from initiating operation of a base compressor 22 for a predetermined time period. By way of example, base delay timer may be 1 minute. After completion of base delay timer, pressure control 62 will command the operation of the associated available base compressor (base compressor available from decision blocks 120-124), as indicated in block 128. Pressure control 62 will then ascertain if trim compressor 2 is running, as indicated in decision block 130. If trim compressor 2 is running, pressure control 62 will commend operation of trim compressor 2 to stop, as indicated in block 132. If trim compressor 2 is not running or once trim compressor 2 has been commanded to stop, pressure control 62 will move to step E in
Thus, as illustrated in
Referring now to
If there is not a system imbalance, pressure control 62 will look to turn off a trim compressor 34 if possible. Pressure control 62 will determine if trim compressor 2 is running, as indicated in decision block 150, and if trim compressor 2 is running pressure control 62 will command that operation of trim compressor 2 be stopped, as indicated in block 152. If pressure control 62 determines that trim compressor 2 is not running, pressure control 62 will determine if trim compressor 1 is running, as indicated in decision block 154, and if trim compressor 1 is running pressure control 62 will command that operation of trim compressor 1 be stopped, as indicated in block 156. In the event that neither trim compressor 2 nor trim compressor 1 is running, pressure control 62 will move to step G in
Referring now to
Referring now to
If an unload abort condition does not occur and upon the completion of the unload test and unload timer, pressure control 62 will initiate an unload delay timer, as indicated in block 190. The unload delay timer provides a delay prior to beginning the full unloading of base compressor 1. By way of example, the unload delay timer may be 3 to 5 minutes. Upon the completion of the unload delay timer, pressure control 62 will initiate unloading of base compressor 1, as indicated in block 192. To initiate the unloading, pressure control 62 can command that the operation of base compressor 1 be stopped with the intent of reaching a fully unloaded and de-energized condition. Pressure control 62 monitors the pressure in distribution network 30 during the unloading and ascertains if a low pressure warming or alarm is activated, as indicated in decision block 194. Activation of a low pressure warning or alarm is indicative of the need for the operation of base compressor 1 to meet the air demand. If a low pressure warning or alarm is activated, pressure control 62 initiates a reload delay timer, as indicated in block 196. The reload delay timer delays the re-energizing of base compressor 1 to allow the motor to fully stop and avoid damage by re-energizing too soon. By way of example, the reload delay timers may be about 15-30 seconds. Upon completion of the reload delay timer, pressure control 62 commands the operation of base compressor 1, as indicated in block 198, and then moves to step E in
If pressure control 62 determines that there is not a low pressure situation, as indicated in decision block 194, a stop delay timer is initiated, as indicated in block 200. The stop delay allows for a delay before pressure control 62 turns off base compressor 1. When the stop delay is timer is completed, pressure control 62 turns off base compressor 1, as indicated in block 202, and again ascertains if a low pressure warning or alarm condition exists, as indicated in decision block 204. If a low pressure situation exists, pressure control 62 moves to block 196 and proceeds as discussed above to rectify the condition. If a low pressure condition does not exist, as determined in decision block 204, pressure control 62 moves to step I in
Referring now to
Upon completion of the switching, pressure control 62 will determine if the shifted base compressor 1 (the compressor that moved from position 1 to position 4 in this example) is still running, as indicated in decision block 222. If the shifted base compressor 1 is still running, pressure control 62 will again command its operation to stop, as indicated in block 224. Once pressure control 62 determines that shifted base compressor 1 is no running, a wait delay timer is initiated, as indicated in block 226. The wait delay timer may the same as that discussed above with reference to block 160. Upon completion of the wait delay timer, pressure control 62 sets the run counter to 0, as indicated in block 228, and returns to step A in
It will be appreciated that arrangements described herein can provide numerous benefits, including one or more of the benefits mentioned herein. For example, arrangements described herein can provide for a distribution of the loading across multiple base compressors. Additionally, the system can choose between the use of a trim compressor or a base compressor by using a metric, which may be related to efficiency and which may not necessarily be limited to only selecting the most efficient arrangement. Moreover, the system can selectively remove a base compressor by unloading the base compressor in stages to ascertain if undesirable operation results from the removal. Thus, the various arrangements may provide numerous benefits.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Dimensions, types of materials, orientations of the various components, and the number and positions of the various components described herein are intended to define parameters of certain embodiments, and are by no means limiting and are merely exemplary embodiments. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means “plus-function format and are not intended to be interpreted based on 35 U.S.C. 112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. The terms “a” and “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e. open language). The phrase “at least one of . . . and . . . ” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. As an example, the phrase “at least one of A, B and C” includes A only, B only, C only, or any combination thereof (e.g. AB, AC, BC or ABC). The term “operatively connected” as used throughout this description, can include direct or indirect connections, including connections without direct physical contact.
Aspects herein can be embodied in other forms without departing from the spirit or essential attributes thereof. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.
