Patent Application
20140202235
1. Field of the Invention
The invention relates to filter testing, and specifically relates to filter testing including a combination of particulate matter and fluid during an accelerated life test.
2. Discussion of Prior Art
Filter elements can be used to provide clean fluid, such as air, to or from various devices. Such devices can include gas turbines where clean air over a long service life of the gas turbine is needed. Filter elements such as cartridge filters can be used within an inlet filter house to filter contaminants from an air flow prior to introduction into an associated gas turbine.
Robustness testing of the filter elements often included placing the filter elements into a test rig and injecting some form of particulate matter into test rig air flow. However, these robustness testing results were not effective at predicting the actual performance of the filter elements in actual filtration applications where relatively high amounts of dust and humidity were included in an inlet air flow. Dust and humidity can combine to provide a challenging filtration scenario that is often not accurately predicted by known filter element testing methods. As a result, there are benefits for continual improvements in filter robustness testing methods so as to address these and other issues.
The following summary presents a simplified summary in order to provide a basic understanding of some aspects of the systems and/or methods discussed herein. This summary is not an extensive overview of the systems and/or methods discussed herein. It is not intended to identify key/critical elements or to delineate the scope of such systems and/or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
One aspect of the invention provides a method of testing the robustness of filters. The method includes the step of providing at least one filter element in a test rig. The at least one filter element separates a clean side from a dirty side within the test rig. The method also includes the step of measuring the pressure differential between the clean side and the dirty side. The method further includes the step of increasing the pressure differential between the clean side and the dirty side by filtering particulate matter and fluid from an air flow within the test rig. The method still further includes the step of cleaning the at least one filter element. The method also includes the step of repeating the previous three steps to replicate the conditions the at least one filter element is subjected to during substantially the entire life cycle of the at least one filter element.
Another aspect of the invention provides a method of testing the robustness of filters. The method includes the step of providing at least one filter element in a test rig. The at least one filter element separates a clean side from a dirty side within the test rig. The method also includes the step of measuring the pressure differential between the clean side and the dirty side. The method further includes the step of increasing the pressure differential between the clean side and the dirty side by filtering particulate matter and fluid from an air flow within the test rig. The particulate matter and the fluid combine to form a wet cake on the at least one filter element. The method still further includes the step of cleaning the at least one filter element. The method also includes the step of repeating the previous three steps to replicate the conditions the at least one filter element is subjected to during substantially the entire life cycle of the at least one filter element.
The foregoing and other aspects of the invention will become apparent to those skilled in the art to which the invention relates upon reading the following description with reference to the accompanying drawings, in which:
Example embodiments that incorporate one or more aspects of the invention are described below and illustrated in the drawings. These illustrated examples are not intended to be a limitation on the invention. For example, one or more aspects of the invention can be utilized in other embodiments and even with other types of devices. Moreover, certain terminology is used herein for convenience only and is not to be taken as a limitation on the invention. Still further, in the drawings, the same reference numerals are employed for designating the same elements.
An example of a test rig 10 used in accordance with aspects of the present invention is schematically shown in
Turning to
An example filter 12 installed on the plate 20 is shown. Exterior surfaces 30 of the cylindrical section 26 and the conical section 28 serve as the airflow inlet for the filter 12, while the enlarged, open end of the conical section 28 abuts the respective aperture 24 through the plate 20 and serves as the filter outlet 34. Any suitable means can be used to secure the filter 12 against the plate 20. In one example, an internal tripod structure 36 including legs 38 can be employed to support and reinforce the filter 12. A gasketed, threaded rod 40 can be located on the upstream terminus of the internal tripod structure 36. Mating hardware 44 such as a wing nut, locking nut, etc. can be mounted to the threaded rod 40 to help keep the filter 12 in a desired location against the plate 20. Interaction between the threaded rod 40 and the mating hardware 44 can also be used to apply a force to the filter 12 in a direction generally perpendicular to the plate 20. This force can be used to at least partially compress a seal (not shown) between the filter 12 and the plate 20. The seal helps provide a barrier between a dirty side 48 (upstream) and a clean side 50 (downstream) of the air flow while also helping to prevent fluid (e.g., air) bypassing the filter 12.
The internal tripod structure 36 can be attached by any suitable means to the plate 20 at the end opposite the threaded rod 40. Each leg 38 of the internal tripod structure 36 can be attached to the plate 20 at locations relatively close to the edge of the aperture 24 in the plate 20. In one example, the legs 38 help center the filter 12 over the aperture 24 by engaging an inner surface 54 of the filter 12. In one example, the inner surface 54 of the filter 12 is a surface corresponding to the inside diameter of the filter 12 at the filter outlet 34.
Turning to
Returning to
The test rig 10 includes dust injection equipment 74 configured to introduce dust 76 into the air flow within the test rig 10. The dust injection equipment 74 can include any number of components and/or configurations to inject dust into the air flow and
Similarly, the test rig 10 can include fluid injection equipment 88 configured to inject a fluid into the air flow within the test rig 10. In one example, the fluid injected into the air flow is water 90. The fluid injection equipment 88 can include any number of components and/or configurations to inject water 90 into the air flow and
While not shown, it is to be understood that the dust injection equipment 74 and the fluid injection equipment 88 can be in electrical communication with a controller (not shown). The controller can be used to control the timing of the dust 76 injection and the water 90 injection into the air flow within the test rig 10. Additionally, the controller can also control the amount of dust 76 and water 90 injected into the air flow. The amounts and timing of dust 76 and water 90 injection into the air flow can be controlled dependent upon other factors of the test rig 10 operation including sequencing as will be further described below. In another example, injection of dust 76 and/or water 90 into the air flow may be continuous throughout the robustness test operation.
The test rig 10 may also include a pulse air system 100 to deliver compressed air to the filters 12. As shown in
The test rig 10 can also include a protective filter 114 located within the test rig 10 to remove all or substantially all of any dust 76 that happens to pass from the dirty side 48 to the clean side 50 of the test rig 10. Removing the dust 76 from the air flow prior to the air flow reaching the fan 66 helps eliminate or reduce potential damage resulting from dust contamination and dust impingement to the fan 66 and the equipment that supports the fan. In one example, the protective filter 114 can include a high-efficiency particulate air (HEPA) filter. Typically, HEPA filters must remove 99.97% of all particles greater than 0.3 μm from the air flow passing through the HEPA filter.
An example method of testing the robustness of filters is generally described in
The method further includes the step 220 of measuring the pressure differential between the clean side 50 and the dirty side 48.
The method further includes the step 230 of increasing the pressure differential between the clean side 50 and the dirty side 48 by filtering dust 76, which is one example of a particulate matter, from the air flow within the test rig 10. In one particular example, the filters 12 can filter water 90 from the air flow as well as the dust 76. After a period of filtering operation of the test rig 10, a pressure drop across each of the filters 12 will increase due to the accumulation of particulates, (e.g., dust 76) separated from the particulate-laden air flow and accumulate at the outer surfaces of the filters 12 as shown by particulate layer 120 in
Dust 76 and water 90 are introduced to the air flow via the dust injection equipment 74 and the fluid injection equipment 88, respectively. While not shown, a controller can be used to control the timing and amount of the dust 76 and the water 90 injection into the air flow within the test rig 10. Both the timing and amount of the dust 76 and the water 90 to be injected into the air flow can be dependent upon a particular sequence of operation or other variables. One such variable is the pressure differential between the clean side 50 and the dirty side 48 of the test rig 10 as measured by the clean side pressure sensor 116 and the dirty side pressure sensor 118. The pressure differential can be defined as the pressure sensed by the dirty side pressure sensor 118 minus the pressure sensed by the clean side pressure sensor 116.
For example, at the start of a cartridge filter robustness test, fan 66 can be operated to create an airflow as represented by arrows 16 in
In one particular example, the step 230 of increasing the pressure differential between the clean side 50 and the dirty side 48 continues until the pressure differential reaches a selected magnitude of pressure differential. This magnitude of pressure differential between the clean side 50 and the dirty side 48 of the test rig 10 can be selected to replicate a particular condition that the filters 12 would experience in an actual filtering application. For example, the selected pressure differential can be the maximum anticipated pressure differential that the filters 12 would be subjected to in an actual inlet filter house (not shown). The selected pressure differential can represent the pressure differential that would cause an “alarm state” in an actual filter house, for example, about 1.49 kPa (6-inches water gauge). Another example may include numbers in a range of zero to 3.738 kPa (15-inches water gauge). Further specific examples may include 450 Pa (4.6-inches water gauge) and 1.0 kPa (4-inches water gauge). As such, the controller can create a condition within the test rig 10 replicating the maximum anticipated pressure differential that the filters 12 would be subjected to during an actual filtration application.
In one example of the method, the type of dust 76 and the quantity of water 90 can be selected to replicate particular environmental conditions that may be found in an actual application. For example, the dust 76 can be selected to replicate a particular airborne particulate matter found in a generally dusty environment such as Dubai, UAE. Furthermore, the quantity of water 90 injected into the air flow can be selected to replicate the humidity of a particular environment or fog. Still further, the amount and types of dust 76 and water 90 injected into the air flow can be selected to create a particular mix ratio. For example, selected amounts of dust and water can be chosen to effectively create a particulate layer 120 forming a wet cake (best seen in
The method also includes the step 140 of cleaning the filters 12.
The volume flow from each of the air nozzles 108 at a selected pressure is calculated to be sufficient to overcome the operational filtering flow (e.g., air flow) through the respective filters 12 and to dislodge or remove all or a portion of the dust 76 particulates from the outer surface of the filters 12. It is possible that the reverse cleaning pulse is delivered while the air flow continues to flow around the test rig 10. The cleaning pulse locally overcomes the air flow through the filters 12. It is to be appreciated that the reverse cleaning pulse can be done for all of the filters 12 at one time, or it can be done in any other pattern, such as a top row of two filters 12 and then a bottom row of two filters 12.
The cleaning pulse emerging from the nozzles 108 can create a pressure wave along the longitudinal extent of the filters 12. Due to the suddenly occurring pressure change and the reversal of the flow direction, the filters 12 and the accumulated particulate layer 120 are forced radially outward. The accumulated particulate buildup is separated from the outer surfaces of the filters 12 and can fall to the bottom of the test rig interior.
The method further includes the step 250 which results in repeating steps 220, 230, and 240 until the simulation of the lifetime, or life cycle, of the filters 12 is complete. After the filters 12 have been subjected to the reverse cleaning pulse, the controller can then direct the clean side pressure sensor 116 and the dirty side pressure sensor 118 to measure the pressure differential between the clean side 50 and the dirty side 48. The process can then continue by increasing the pressure differential between the clean side 50 and the dirty side 48 by filtering particulate matter from the air flow within the test rig 10. In one example, the particulate matter can include the dust 76 and the water 90 injected into the air flow as described above. Filtering the particulate matter can continue to increase the pressure differential until the processor stops the dust injection equipment 74 and the fluid injection equipment 88 from injecting dust 76 and water 90 into the air flow. In one example, the controller allows the dust injection equipment 74 to continuously inject dust 76 into the air flow during the robustness test. In this example, it can be desirable to load the filters 12 with the dust 76 and water 90 combination in a wet-cake as quickly as possible in order to subject the filters 12 to a maximum pressure differential in a relatively short period of time. The selected pressure differential can represent the pressure differential that would cause an “alarm state” in an actual filter house, for example, about 1.49 kPa (6-inches water gauge), or any of the above mentioned range/values. The method can then repeat the step 240 of cleaning the filters 12 as previously described.
The repetition of the steps of measuring the differential pressure, increasing the differential pressure, and cleaning the filters 12 can continue until the entire anticipated life cycle of the filters 12 is replicated in the test rig 10. Once the simulation of the lifetime of the filters 12 is complete, the method is complete at step 260. In one example, the duration of the test replicates the number of cleaning operations, or reverse cleaning pulses that are experienced by the filters 12. The repetition can be conducted while the differential pressure is at or is relatively close to the maximum anticipated pressure differential subjected to the filters 12 in an actual filtering application. For example, one particular filtration application includes filters with an expected life span of approximately one year (approximately 9,000 hours). During that time, the reverse cleaning pulse operation occurs approximately every 15 minutes, or four times every hour of operation. This results in a filter test about 36,000 times to replicate substantially the entire life cycle of filter 12. Of course, testing for various models of filters 12 that experience different environments in real world applications may have different testing scenarios with different quantities of testing repetitions, and/or different time intervals between reverse cleaning pulse operation.
It is to be appreciated that the described methods of testing the robustness of filters can have relatively short time periods between the reverse cleaning pulses in order to shorten the length of time of the robustness testing. In one example, the reverse cleaning pulses can occur every ten seconds. In another example, the reverse cleaning pulses can occur every 5 seconds. As such, the robustness of the filter 12 over its entire life cycle can be tested in a period of days rather than approximately one to two years. It is to be appreciated that the reduced time between reverse cleaning pulses can require a larger air compressor 106 and/or a large gas storage tank 110 in order to meet the demand of compressed air in comparison to typical pulse air systems associated with actual inlet filter houses. In one example, the test rig 10 can include a 700 kPa (7 bar) air compressor.
The cleaning operation introduces an appreciable amount of stress to the filter media 64, often due to the repeated bending of the filter media 64 during the expansion and contraction of the filter media 64. This repeated bending can lead to micro-folds developing in the filter media 64 which act as stress risers (or stress concentrations). The stress risers can lead to micro-tears in the filter media 64 which can ultimately lead to failure of the filter, thereby allowing particulate matter to move from the dirty side of an inlet filter house to the clean side of an inlet filter house and potentially damage downstream equipment such as a gas turbine and/or its components.
The described methods of testing the robustness of filters 12 enables a test that includes a relatively high quantity of reverse cleaning pulses within a relatively short period of time while maintaining a relatively high pressure differential between the clean side 50 and the dirty side 48 of the test rig 10. Testing the filters 12 at the described highest anticipated pressure differential enables the testing party to determine or predict the life expectancy of the filters 12 in what may be termed a worst-case scenario. The worst-case scenario can include a pressure differential at or near the alarm state pressure differential as previously described over the simulated life expectancy or substantially the life expectancy of the filters with a relatively heavy loading of particulate matter on the filter media 64. The described methods of testing the robustness of filters 12 can also enable the manufacturer and end users to have a relatively high level of confidence that the filters 12 are able to filter the desired particulate matter from an air flow in the “worst-case” scenarios for the entire expected life of the filters 12.
Additionally, the relatively heavy loading of particulate matter (e.g., dust and water) on the filter media 64 can create relatively large stress amounts on the filter media 64 during the reverse cleaning pulses, thereby encouraging the creation of stress risers. If and when the stress risers lead to filter failure, the filter media 64 can be evaluated to determine whether the filter media 64 has sufficient mechanical strength to resist tearing during the life cycle of the filter 12 in order to predict the long-term life span of the filter 12. The mechanical strength of the filter media 64 can be evaluated in any of the methods as are known in the art. In one example, the evaluation can simply include examining the filter media 64 for tears, holes, signs of wear, etc.
It is to be appreciated that water is used to wet the filter media 64 and that such wetting can weaken the filter media. For example, some filter media may use binders to hold filter fibers and such binders are soluble in water. Weakening of the filter media can have an effect concerning the robustness testing.
The described methods of testing the robustness of filters 12 also allow evaluation of different pleating methods used to fold the filter media 64. Various failures of the filter media 64 and the location of the failures can help instruct the testing party as to improved methods of pleating the filter media 64. The described testing methods may also help indicate better construction methods for the filters 12.
The invention has been described with reference to the example embodiments described above. Modifications and alterations will occur to others upon a reading and understanding of this specification. Example embodiments incorporating one or more aspects of the invention are intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.
