Abstract:
A system is provided for removing particulate matter from a particulate collection device utilized to collect particulate matter from a flue gas stream. The system includes a pressure vessel for storing a pressurized gaseous medium in an interior area defined by the pressure vessel. A first pressure sensor is in communication with the interior area and configured to measure pressure therein. A particulate collection device for collecting particulate matter from a flue gas stream includes a conduit in communication with the pressure vessel. A valve is disposed in the conduit and adapted to open to release a pulse of the pressurized gaseous medium from the pressure vessel into the particulate collection device. A control system is in communication with the valve and the first pressure sensor, and includes a controller configured to operate the valve based upon at least one pressure measurement received from the first pressure sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims benefit under 35 U.S.C. §119(e) of co-pending U.S. Provisional Patent Application No. 61/617,377 entitled “SYSTEM AND METHOD OF CLEANING PARTICULATE COLLECTION DEVICES USED IN A FLUE GAS PROCESSING SYSTEM,” filed Mar. 29, 2012, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure is generally directed to particulate collection devices used in a flue gas processing system. More particularly, the present disclosure is directed to a system and a method for removing particulate matter from the particulate collection device with the use of pressurized fluid pulses having a controlled release based upon pressure in a pressurized fluid supply vessel. 
       BACKGROUND 
       [0003]    Combustion of fossil fuels typically produces an exhaust gas stream (commonly referred to as a “flue gas stream”) that contains contaminants, such as sulfur oxides (SOx), nitrogen oxides (NOx), mercury, and carbon containing species, as well as particulate matter such as dust or fly ash. To meet requirements established under certain laws and protocols, plants that burn fossil fuels subject the resultant flue gas stream to various processes and systems to reduce or eliminate the amount of contaminants present in the flue gas stream prior to releasing the flue gas stream to the atmosphere. 
         [0004]    Many flue gas stream treatment systems employ at least one particulate collection device to remove particulate matter from the flue gas stream. One example of a particulate collection device is a fabric filter, through which the flue gas stream flows. The filters include media formed into filter cartridges or filter bags. The particulate-laden flue gas stream flows through the filters while the particulate contaminants are trapped thereon. The filtered flue gas stream is then subjected to another process for further contaminant removal, or is released to the atmosphere. 
         [0005]    Over time, the filters collect a significant amount of particulate matter resulting in an accumulated build-up of particulate matter on the filter. The increasing build-up of particulate matter causes an increase in pressure drop across the filters, which in turn increases the energy consumed to generate an effective flow of flue gas through the filters. Accordingly, the filters need to be periodically cleaned to remove the build-up of particulate matter thereon. 
         [0006]    A disadvantage of known methods and apparatus to periodically clean the filters is, in case of off-line cleaning, the amount of time it takes to shut down at least a portion of the plant in order to clean the filter(s). Another disadvantage of known cleaning methods and apparatus is the unsynchronized manner in which certain filters have to be cleaned. That is, in plants utilizing multiple filters or multiple filter compartments, the various filter elements may need to be cleaned in a specific order and at a specific time interval. Further disadvantages of known systems and processes include reduced filter life and higher than desired emissions of particulate matter in the released flue gas stream. What is therefore desired is a uniform method by which the filters can be cleaned in an efficient manner that does not disrupt the operation of the plant as a whole and results in longer filter life and lower emissions of particulate matter. 
       SUMMARY 
       [0007]    According to aspects illustrated herein, there is provided a system for removing particulate matter from a particulate collection device utilized to collect particulate matter from a flue gas stream. The system includes a pressure vessel for storing a pressurized gaseous medium in an interior area defined by the pressure vessel. A first pressure sensor is in communication with the interior area and configured to measure pressure therein. A particulate collection device for collecting particulate matter from a flue gas stream includes a conduit in communication with the pressure vessel. A valve is disposed in the conduit and adapted to open to release a pulse of the pressurized gaseous medium from the pressure vessel into the particulate collection device. A control system is in communication with the valve and the first pressure sensor, and includes a controller configured to operate the valve based upon at least one pressure measurement received from the first pressure sensor. 
         [0008]    According to further aspects illustrated herein, there is provided a method for removing particulate matter from a particulate collection device utilized to collect particulate matter from a flue gas stream. The method comprises: providing a pressure vessel for storing a pressurized gaseous medium in an interior area defined by the pressure vessel; providing a particulate collection device for collecting particulate matter from the flue gas stream; providing a conduit in communication with the interior area of the pressure vessel, the conduit having a valve in communication with the particulate collection device; operating the valve and supplying a first pulse of the pressurized gaseous medium to the particulate collection device initiating when the pressurized gaseous medium in the pressure vessel is at a first pressure and terminating when the pressurized gaseous medium in the pressure vessel is at a second pressure. 
         [0009]    The above described and other features are exemplified by the following figures and in the detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Referring now to the figures which are exemplary embodiments and wherein like elements are numbered alike: 
           [0011]      FIG. 1  discloses a schematic side-view of a tubular filter with a device for pressurized air pulse cleaning and control equipment adapted for carrying out the method according to the invention. 
           [0012]      FIG. 2  discloses schematically a view from above of the tubular filter of  FIG. 1  without the control equipment. 
           [0013]      FIG. 3  discloses a graph illustrating the varying pressure of a pressurized air tank caused by variation of the initial pressure in the tank and the opening and closing of a valve during rapid cleaning sequences. 
           [0014]      FIG. 4  discloses a graph illustrating the pressure of a pressurized air tank caused by variation of the initial pressure in the tank and the opening and closing of a valve during rapid cleaning sequences. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    As further described below with reference to  FIGS. 1 and 2 , a particulate collection device  102  comprising a plurality of filter elements  106  arranged to extract particulate matter  114  out of a flue gas stream  112  is cleaned by pressurized air pulses or cleaning pulses. 
         [0016]    The frequency, maximum pressure and duration of the pressurized air pulses are measured and subsequently selected for cleaning a first plurality of filter elements  106  in order to minimize the total emission of dust and particulates therefrom. After each pressurized air pulse, a maximum value for an instantaneous emission of dust, referred to as an “emission peak,” is determined. The emission peak is used for selecting the frequency, maximum pressure, and/or the duration of the pressurized air pulses for cleaning a second plurality of filter elements  106  in a sequence during a continued cleaning operation. Such a method for cleaning a similar particulate collection device  102 , namely a barrier filter, is shown and described in U.S. Pat. No. 6,749,665 issued to Bjarno et al. and assigned to Alstom Power N.V., the disclosure of which is incorporated herein by reference in its entirety. 
         [0017]      FIG. 1  and  FIG. 2  illustrate a system  100  for removing particulate matter from the particulate collection device  102 . In one embodiment the particulate collection device  102  is a filter and such filter preferably is fabricated from woven fabric or felt. In another embodiment, the particulate collection device  102  comprises a barrier filter  104  having one or a plurality of filter elements  106  in the form of one or a plurality of filter tubes  142 . In one embodiment, the filter elements  106  are fabricated from woven fabric or felt. In one embodiment, the filter tubes  142  similarly are fabricated from woven fabric or felt. In one embodiment, the filter tubes  142  comprise a filter medium  143  defining an interior area  144  bounded by the filter medium  143 . The particulate collection device  102  may be positioned inside a baghouse (not shown) together with one or more other particulate collection devices. The particulate collection device  102  is positioned in the flow of the flue gas stream  112 , which contains, among other things, particulate matter  114  that is generated by for example the combustion of a fossil fuel or from other processes (not shown). Particulate matter  114  may include, for example, fly ash, dust and the like. 
         [0018]    As the flue gas stream  112  flows through the particulate collection device  102 , the particulate matter  114  in the flue gas stream  112  collects on the particulate collection device  102 , thereby removing the particulate  114  from the flue gas stream  112 . A filtered flue gas stream  116  is released to the atmosphere via a stack (not shown) or subjected to further processing (not shown) to remove other contaminants such as SOx and/or NOx, and the like. Over time, the particulate matter  114  collected on the particulate collection device  102  builds up and decreases the efficiency of the flue gas cleaning process of system  100 . 
         [0019]    As further shown in  FIGS. 1 and 2 , the particulate collection device  102  comprises a tubular filter  105  having a housing  122 , an inlet  123  through which the flue gas stream  112  passes, and an outlet  124  through which the filtered flue gas stream  116  passes. The tubular filter  105  is divided into a first section or a raw gas chamber  125  for receiving the incoming flue gas stream  112  from the inlet  123 ; and a pure gas chamber  126  positioned proximate to an intermediate wall  127 . The pure gas chamber  126  collects the filtered flue gas stream  116  and passes it to the outlet  124 . The intermediate wall  127  supports the plurality of filter tubes  142 . In one embodiment as shown in  FIG. 2 , the plurality of filter tubes  142  are configured in four rows  210 ,  220 ,  230 , and  240 , and each row  210 ,  220 ,  230 ,  240  includes four filter tubes  142 . As shown in  FIG. 1 , the flue gas stream  112  flows into and through the raw gas chamber  125 , and through the filter medium  143  into the interior area  144  of the filter tubes  142 . Particulate matter  114  in the flue gas stream  112  collects on the filter medium  143  of the filter tubes  142 . The filtered flue gas stream  116 , having a reduced particulate matter content, collects in the pure gas chamber  126  and passes from the housing  122  of the tubular filter  105  through the outlet  124 . 
         [0020]    As further shown in  FIG. 1 , a subsystem  80  is in fluid communication with the tubular filter  120  to provide for cleaning the filter tubes  142  by means of pressurized air pulses. At least one distributing pipe  140  extends into the pure gas chamber  126 . The distributing pipe  140  defines at least one discharge port  145  extending at least partially into the pure gas chamber  126 . In one embodiment, each of the discharge ports  145  comprises a nozzle  141  located substantially centrally above each filter tube  142 . For example, the nozzle  141  is positioned at a discharge portion of the filter tube  142  proximate to the distributing pipe  140 . While the nozzle  141  is shown and described as being located substantially centrally above each filter tube  142  and positioned at a discharge portion of the filter tube  142  proximate to the distributing pipe  140 , the present invention is not limited in this regard as the nozzle  141  may be located substantially centrally at any position within the interior area  144  defined by the filter medium  143  of the filter tubes  142  without departing from the broader aspects of the invention. As shown in  FIG. 2 , each row  210 ,  220 ,  230 ,  240  of the filter tubes  142  is in fluid communication with at least one distributing pipe  140  having a nozzle  141  located substantially centrally above each filter tube  142 . Each row  210 ,  220 ,  230 ,  240  further includes a respective valve member or valve  211 ,  212 ,  213  and  214  in fluid communication with, and controlling the flow through, a respective distributing pipe  140 A,  140 B,  140 C and  140 D. 
         [0021]    A pressure vessel such as a pressurized air tank  81  is in fluid communication with an overpressure source, for instance a compressor (not shown), via a first conduit  83 . The pressurized air tank  81  stores a pressurized gaseous medium  81 A in an interior area  81 B defined by the tank  81 . A stream of the pressurized gaseous medium  81 A such as an air stream  82  is passed to the air tank  81  via a second conduit  84  as selectively determined by a control member  93 . The air stream  82  is passed into the tubular filter  120  via a third conduit  85 . In one embodiment, portions  82 A,  82 B,  82 C and  82 D of the air stream  82  are passed respectively to the valves  211 ,  212 ,  213 ,  214  via a respective fourth conduit  85 A,  85 B,  85 C and  85 D. Each valve  211 ,  212 ,  213 ,  214  selectively passes the respective portion  82 A,  82 B,  82 C,  82 D of the air stream  82  to its respective distributing pipe  140 A,  140 B,  140 C,  140 D. The nozzle  141  located substantially centrally above each filter tube  142  ejects a pressurized pulse such as a pressurized air pulse  86  into a respective filter tube  142  as determined by the system  100  as further described below. The pressurized air pulse  86  is released from the nozzle  141  in short, high powered pulses for contact with the filter tubes  142  in order to dislodge at least a portion of the particulate matter  114  from the filter tubes  142 . While the pressurized pulse is shown and described as a pressurized air pulse  86 , the present invention is not limited in this regard as the pressurized pulse may comprise, for example, a pressurized pulse of a suitable alternative gas or other medium, without departing from the broader aspects of the invention. 
         [0022]    As described above, the frequency, maximum pressure and duration of the pressurized air pulses are measured and subsequently selected for cleaning a particular plurality of filter elements  106  in order to minimize the total emission of dust and particulates therefrom. Such operating parameters are measured or obtained via one or more measurement devices  92  including, but not limited to, pressure sensors, particulate mass concentration samplers, and flow meters. In one embodiment, the measurement devices  92  comprise transducers  94  for measuring the pressure in the raw gas chamber  125 , one or more transducers  95  for measuring the pressure in the pure gas chamber  126 , one or more transducers  96  for measuring the dust concentration in the outlet  124 , and one or more transducers  97  for measuring the pressure in the tank  81 . Optionally, one or more additional transducers (not shown) may be employed for measuring the gas volume flow through the tubular filter  105 . While the measurement devices  92  are shown and described as comprising one or more transducers  94 ,  95 ,  96 ,  97 , the present invention is not limited in this regard as the measurement devices  92  may comprise, for example, pressure gauges, electronic pressure sensors, pressure transmitters, pressure senders, pressure indicators and the like, without departing from the broader aspects of the invention. 
         [0023]    The control member  93 , transducers  94 ,  95 ,  96 ,  97 , and the valves  211 ,  212 ,  213 ,  214  are in electrical communication with a control system or control apparatus  90 , and can transmit and receive electrical signals therebetween. The control apparatus  90  comprises a device capable of receiving and transmitting information and/or commands from a user or another device, storing information, and responding to information and/or commands entered by a user or another device. The control apparatus  90 , control member  93 , transducers  94 ,  95 ,  96 ,  97 , and valves  211 ,  212 ,  213 ,  214 , are electronically coupled to one another through wires or other physical conduits or via a wireless manner. 
         [0024]    In one embodiment, the control apparatus  90  comprises a Programmable Logic Controller (“PLC”)  190 , referred to herein as the controller  190 , for selecting the frequency, maximum pressure and duration of the pressurized air pulses for cleaning a plurality of filter elements  106 , based on one or more signals received respectively from the transducers  94 ,  95 ,  96 ,  97 , and transmitting signals respectively to the valves  211 ,  212 ,  213 ,  214  for operation thereof. The controller  190  is configured to receive and transmit multiple signals simultaneously, at elevated temperature ranges, and having a resistance to vibration, impact and electrical noise. While the control apparatus  90  is shown and described as comprising a controller  190 , the present invention is not limited in this regard as the control apparatus  90  may comprise, for example, a supervisory control and data acquisition (“SCADA”) system, a distributed control systems (“DCS”), a computer or any type of microprocessor or like programmable control device having software installed therein, a server connected to one or more programmable devices, or any like controller without departing from the broader aspects of the invention. As used herein, the term “computer” encompasses desktops, laptops, tablets, handheld mobile devices, mobile phones, internet ready televisions, and the like. In one embodiment, the control apparatus  90  includes an alarm  91  coupled to the control apparatus  90 . The alarm  91  may be any type of audio, visual, or audio and visual alarm. Alternatively, the alarm  91  may send a signal to a user device such as a computer. The alarm  91  may be triggered, for example, if a measured pressure is higher than a desired or design pressure. 
         [0025]    In operation of the system  100 , the dust-containing flue gas stream  112  passes into the tubular filter  105  through the inlet  123  to the raw gas chamber  125 , through the filter tubes  142 , into the pure gas chamber  126 , and out of the tubular filter  105  through the outlet  124  and is released to the atmosphere via a stack (not shown) or is passed to one or more units of an Air Quality Control System (“AQCS”) (not shown) for control and/or removal of additional particulates from the flue gas. The pressure in the raw gas chamber  125  and in the pure gas chamber  126  is measured, substantially continuously, by the transducers  95  and  96 . During operation, extracted particulates and/or dust forms a dust heap  99  along the outer sides of the filter tubes  142  and subsequently is separated therefrom. As the thickness of the dust heap  99  increases, the pressure drop between the raw gas chamber  125  and the pure gas chamber  126  correspondingly increases. 
         [0026]    When the pressure difference, also referred to as the pressure drop, between the raw gas chamber  125  and the pure gas chamber  126  reaches a first predetermined limit value, for example in the range of about 1400 Pascal (“Pa”), a row  210 ,  220 ,  230 ,  240  of the filter tubes  142  is subjected to a cleaning operation. The subsequent pressure of the raw gas chamber  125  and the pure gas chamber  126  is measured by the transducers  95  and  96 , transmitted to the control apparatus  90 , and the pressure difference between the raw gas chamber  125  and the pure gas chamber  126  is determined. If the pressure difference after the cleaning operation has fallen less than for example 50 Pa, another row  210 ,  220 ,  230 ,  240  of the filter tubes  142  is subjected to a cleaning operation. The described measurement of the resultant difference of pressure between the raw gas chamber  125  and the pure gas chamber  12 , after a row  210 ,  220 ,  230 ,  240  of the filter tubes  142  is subjected to a cleaning operation, is repeated until a desired pressure difference value is achieved. When such a pressure difference value is achieved, the cleaning operation is suspended until the pressure drop over the filter tubes  142  and the dust heap  99 , i.e. the pressure difference between the raw gas chamber  125  and the pure gas chamber  126 , again reaches 1400 Pa. At this occurrence, a row  210 ,  220 ,  230 ,  240  of the filter tubes  142  that was not subjected to a cleaning operation at the previous cleaning occurrence, is now subjected to a cleaning operation in the same manner and in accordance with the operating parameters as described above. 
         [0027]    During operation, a first pressure of the tank  81  is obtained before the controller  190  initiates a cleaning occurrence or a cleaning sequence based upon the pressure difference between the raw gas chamber  125  and the pure gas chamber  126  as described above. A second pressure of the tank  81  is obtained upon termination of the cleaning sequence by the controller  190 , again based upon the resultant pressure difference between the raw gas chamber  125  and the pure gas chamber  126 . During the cleaning sequence, at least one valve  211 ,  212 ,  213 ,  214  is selectively opened by the controller  190  for a predetermined duration or time. Operating parameters for each valve  211 ,  212 ,  213 ,  214  are selectively determined by the controller  190  and are based upon a comparison of, a ratio of, or a difference between or any mathematical model incorporating, the first and second pressure of the tank  81 . For example, the controller  190  operates the valve  211 ,  212 ,  213 ,  214  to achieve the second pressure, a certain desirable resultant or second pressure, in the tank  81  as measured by transducers  97 . The pressure in the tank  81  is measured when the at least one valve  211 ,  212 ,  213 ,  214  has closed and such measured pressure is compared to the desirable pressure in the tank  81  and a setpoint is calculated for the selected valve. The next time the selected valve  211 ,  212 ,  213 ,  214  is operated, the opening time is adjusted for that particular valve  211 ,  212 ,  213 ,  214 . For example, if the second pressure in the tank  81  was too low after the previous cleaning sequence, then the opening time of the particular valve  211 ,  212 ,  213 ,  214  will be reduced the next time it is selected to be operated by the controller  190 . Correspondingly, if the end pressure in the tank  81  was too high after the previous cleaning sequence, then the opening time of the particular valve  211 ,  212 ,  213 ,  214  will be increased the next time it is selected to be operated by the controller  190 . 
         [0028]    Accordingly, the second pressure in the tank  81  is measured after each cleaning sequence that engages a particular valve  211 ,  212 ,  213 , or  214 , and such second pressure measurements are used for selecting the frequency and/or the duration of the next cleaning sequence that again engages the particular valve  211 ,  212 ,  213 , or  214 . In one embodiment, a variation in the second pressure in the tank  81  at a particular duration of a cleaning sequence for a particular valve  211 ,  212 ,  213 , or  214  is monitored, and the alarm  91  coupled to the control apparatus  90  is triggered when the variation in such second pressure in the tank  81  exceeds a predetermined value. In another embodiment, a variation in the second pressure in the tank  81  at a particular duration of a cleaning sequence for a particular valve  211 ,  212 ,  213 , or  214  is monitored, and a maximum duration of the cleaning sequence is set when the variation in such second pressure in the tank  81  exceeds a predetermined value. 
         [0029]    In one embodiment, a required cleaning sequence duration to achieve a predetermined second pressure in the tank  81  for a particular valve  211 ,  212 ,  213 , or  214  is monitored, and the alarm  91  coupled to the control apparatus  90  is triggered when the cleaning sequence duration to achieve such second pressure in the tank  81  is lower than a predetermined value. In one embodiment, a required cleaning sequence duration to achieve a predetermined second pressure in the tank  81  for a particular valve  211 ,  212 ,  213 , or  214  is monitored, and a maximum duration of the cleaning sequence is set when the cleaning sequence duration to achieve such second pressure in the tank  81  is lower than a predetermined value. 
         [0030]    In one embodiment, the pressure difference (or pressure drop) between the raw gas chamber  125  and the pure gas chamber  126  is measured substantially continuously and each row  210 ,  220 ,  230 ,  240  of the filter tubes  142  is cleaned in a predetermined order such that the cleaning of a particular row  210 ,  220 ,  230 ,  240  of the filter tubes  142  occurs when the pressure difference (or pressure drop) reaches a first determined limit value. In addition, when the first pressure in the tank  81  is lower than a predetermined value, the second pressure in the tank  81  is increased to achieve a predetermined first pressure in the tank  81  at the next cleaning sequence. 
         [0031]    At least one of the valves  211 ,  212 ,  213 ,  214  is selected to be operated by the controller  190  for each cleaning sequence initiated by the controller  190 . The operating parameters for selection and sequential operation (i.e., opening and closing) of the valves  211 ,  212 ,  213 ,  214  during each cleaning sequence is based upon data received and transmitted between the controller  190 , the transducer  97  (i.e., the first and second pressure measurements in the tank  81 ), and the selected valve(s)  211 ,  212 ,  213 ,  214 . The initiation of each cleaning cycle by the controller  190  is based upon data received and transmitted between the controller  190  and the transducers  95  and  96  (i.e., the pressure difference between the raw gas chamber  125  and the pure gas chamber  126 ). 
         [0032]    As shown in  FIG. 1 , the nozzle  141  is positioned above the filter tube  142  such that when the pressurized air pulse  86  is ejected from the nozzle  141 , it is directed into contact with the filter tube  142  to dislodge particulate matter  114  collected on the filter tube  142 . Optionally, the nozzle  141  may be positioned inside the filter tube  142 . By placing the nozzle  141  inside the filter tube  142 , the pressurized air pulse  86  is ejected from the nozzle  141  and expands the filter tube  142  at high speed so that the particulate matter  114  collected on the outside of the filter tube  142  is dislodged when the filter tube  142 stops at its maximum, most expanded, dimensions. 
         [0033]    The above-described cleaning operation having cleaning sequences further serves to identify malfunctioning valves  211 ,  212 ,  213 ,  214  that require an exceptionally long time to close. Such valves  211 ,  212 ,  213 ,  214  are identified by the control apparatus  90 . Depending on a desired mode of operation of the system  100 , the malfunctioning valve  211 ,  212 ,  213 ,  214  is operated with a higher second pressure in the tank  81  or is removed from service and/or flagged as defective. The opening time of each valve  211 ,  212 ,  213 ,  214  is continuously measured and monitored. If the opening time is shorter than a first predetermined value, and at the same time the achieved second pressure in the tank  81  after a cleaning sequence is lower than a second predetermined value, the valve  211 ,  212 ,  213 ,  214  will be identified by the control apparatus  90  as malfunctioning. 
         [0034]    The above-described cleaning operation having cleaning sequences also serves to identify malfunctioning valves  211 ,  212 ,  213 ,  214  that exhibit a large variation in second pressure in the tank  81  after a cleaning sequence. Again, such valves  211 ,  212 ,  213 ,  214  are identified by the control apparatus  90 . Depending on a desired mode of operation of the system  100 , the malfunctioning valve  211 ,  212 ,  213 ,  214  is operated with a higher second pressure in the tank  81  or is removed from service and/or flagged as defective. The opening time of each valve  211 ,  212 ,  213 ,  214  is continuously measured and monitored. If the range of the opening time is larger than a third predetermined value, or if other suitable measured or calculated statistics, or other operating parameters that signify a variation in the opening time exceeds a fourth predetermined value, the valve  211 ,  212 ,  213 ,  214  will be identified by the control apparatus  90  as malfunctioning. In one embodiment, a variation in the second pressure in the tank  81  at a particular duration of a cleaning sequence for a particular valve  211 ,  212 ,  213 , or  214  is monitored, and the particular valve  211 ,  212 ,  213 , or  214  is taken out of service when the variation in such second pressure in the tank  81  exceeds a predetermined value. In one embodiment, a required cleaning sequence duration to achieve a predetermined second pressure in the tank  81  for a particular valve  211 ,  212 ,  213 , or  214  is monitored, and the particular valve  211 ,  212 ,  213 , or  214  is taken out of service when the pulse duration to achieve such second pressure in the tank  81  is lower than a predetermined value. 
         [0035]    The above-described cleaning operation having cleaning sequences provides a flue gas stream cleaning process that can be strategically and specifically targeted to those particulate collection devices  102  in need of cleaning. Such a system and process results in fewer plant shutdowns for cleaning. Additionally, such a system and process extends the life of the particulate collection devices  102  since each particulate collection device  102  is cleaned only when necessary. 
         [0036]      FIG. 3  provides a graph of the pressure variability of the pressurized air tank  81  as a function of time. As shown in  FIG. 3 , the pressure in the tank  81  fluctuates with the opening and closing of a valve  211 ,  212 ,  213 ,  214 . In particular, during rapid cleaning sequences, the pressure in the tank  81  may fall below the desired second pressure value. During operation, a first pressure in the tank  81 , for example 3.0 bar designated as Point A, is measured and a cleaning sequence is initiated by the controller  190  as described above. At least one valve  211 ,  212 ,  213 ,  214  is selectively opened for a particular duration based upon the difference between the first pressure in the tank  81 , Point A, and the desired second pressure or second pressure in the tank  81  after the cleaning sequence, for example 1.0 bar designated as Point B. 
         [0037]    During sequential cleaning occurrences, or rapid cleaning sequences as shown in  FIG. 3 , the operating parameters for valve  211 ,  212 ,  213 ,  214  are based on past performance of the selected valve as recorded by the controller  190 . For example, a subsequent cleaning sequence is initiated by the control apparatus  190  as described above. Upon initiation of the cleaning sequence, the first pressure in the tank  81  is 2.5 bar designated as Point A′. Preferably at least one other valve  211 ,  212 ,  213 ,  214  is selectively opened for a particular duration and, in this cleaning sequence, the operating parameters of the selected valve  211 ,  212 ,  213 ,  214  caused such valve to be opened for a particular duration such that a second pressure B′ in the tank  81  is approximately 0.8 bar or less than the desired second pressure Point B by about 20%. Thereafter, a subsequent cleaning sequence is initiated by the control apparatus  190  as described above at a time at which the first pressure in the tank  81  is again 2.5 bar designated as Point A″. Again, preferably at least one other valve  211 ,  212 ,  213 ,  214  is selectively opened for a particular duration and, in this cleaning sequence, the operating parameters of the selected valve  211 ,  212 ,  213 ,  214  caused such valve to be opened for a particular duration such that a second pressure B″ in the tank  81  again is approximately 0.8 bar or less than the desired second pressure Point B by about 20%. 
         [0038]    During rapid cleaning sequences, the pressure of the tank  81  does not fully recover, for example to Point A, because of the opening of a selected valve  211 ,  212 ,  213 ,  214  before pressure in the tank  81  has reached Point A. Under normal operating cleaning sequences (i.e., not rapid cleaning sequences), a desired first pressure of the tank  81 , represented by the line designated as line C, can be achieved such that the tank  81  exhibits a substantially constant first pressure, for example 3.0 bar at Point A and C′. Under such conditions, the desired second pressure of the tank  81 , represented by the line designated as line D, can be achieved such that the tank  81  exhibits a substantially constant second pressure, for example 1.0 bar at Point B and D′. In one embodiment, the operating parameters of a selected valve  211 ,  212 ,  213 ,  214  are set by the controller  190  such that the difference between the first pressure, for example Point A′, and the second pressure, for example Point B′, exceeds a set value, such as for example 1.0 bar, 1.5 bar, 2.0 bar, or some other set value. 
         [0039]      FIG. 4  also provides a graph of the pressure variability of the pressurized air tank  81  as a function of time. As shown in  FIG. 4 , the pressure in the tank  81  fluctuates with the opening of a valve  211 ,  212 ,  213 ,  214 . During operation, a first pressure in the tank  81 , for example 3.0 bar designated as Point E, is measured and a cleaning sequence is initiated by the controller  190  as described above. At least one valve  211 ,  212 ,  213 ,  214  is selectively opened for a particular duration based upon the difference between the first pressure in the tank  81 , Point A, and the desired second pressure or second pressure in the tank  81  after the cleaning sequence, for example 1.0 bar designated as Point B. At least one valve  211 ,  212 ,  213 ,  214  is selectively opened for a particular duration based upon the difference between the first pressure in the tank  81 , Point E, and the desired second pressure or second pressure in the tank  81  after the cleaning sequence, for example 0.5 bar designated as Point F′ located on line F. As further shown in  FIG. 4 , an operating range for each valve  211 ,  212 ,  213 ,  214 , represented by a shaded area G, can designated by the controller  190 . As described above, if the pressure in the tank  81  continues to decrease after the controller  190  transmits a signal to the valve  211 ,  212 ,  213 ,  214  to close, for example to a second pressure of less than 0.25 bar designated as Point E′, the continuing decreasing pressure, or less-than-timely increasing pressure, is likely indicative of a faulty valve. 
         [0040]    While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or matter to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.