Abstract:
The present disclosure relates to a system for controlling an extraction of landfill gas flow (LFG) from a plurality of wellheads at a landfill. The system has a first wellhead located at the landfill, a first processor having a first rule set, and a first LFG flow control valve controllable by the first processor. A second wellhead is located at the landfill in a vicinity of the first wellhead and has a second processor and a second LFG flow control valve. The second processor has a second rule set and is operable to control the second LFG flow control valve. The first and second processors use their said rule sets to control the first and second LFG flow control valves, respectively, to control an LFG flow through their said first and second wellheads, respectively.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/024,661, filed on Jul. 15, 2014. The entire disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to wellheads typically used at landfills for the recovery of gasses and fluids, and more particularly to a distributed wellhead system and method by which a performance of each of a plurality of independent wellheads can be monitored and adjustments coordinated to take into account the influence that a change to one specific wellhead may cause to one or more other wellheads within a given area, with a goal of coordinating control over the adjustments made to all of the wellheads to optimize a collective performance of the wellheads. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    A landfill gas (“LFG”) system may consist of many LFG wells connected to a central gas extraction vacuum blower by means of a piping header system. The LFG wells are often used at landfills to extract methane gas that develops below the surface of the landfill from decomposing waste. The vacuum assists in maintaining a desired flow rate of the methane gas out through the wellhead. 
         [0005]    The header system has branches and end points that connect the vacuum blower to all of the LFG wells located across a landfill. Currently each LFG wellhead has a single manually adjustable valve that controls gas flow (i.e., the amount of vacuum applied to the well). Each well has the ability to produce some volume of LFG per unit time. The production of LFG will typically vary at least slightly from well to well, and this well-to-well variance may change over time as well. 
         [0006]    In actual LFG systems the central vacuum source is never able to apply full vacuum to all wellheads equally. This is typically due to blower sizing and head loss in the piping system. Variations in wellhead valve settings will often affect vacuum availability to other wellheads “downstream” from a given wellhead. In other words, a significant change in a valve setting on wellhead A is expected to change the pipe header conditions for wells in the vicinity of wellhead A. Additionally, changes in overall site conditions (macro changes), most notably barometric pressure, can change overall vacuum blower flow rate and rates of apparent gas production from large numbers of wellheads. Wellhead conditions can also change over time, impacting the production of LFG (e.g., water build-up can restrict LFG flow into the well, etc.). The macro changes lead to the necessity of ongoing optimization and adjustment of the manual LFG valves to achieve various control goals (maximize LFG recovery, control LFG emissions, keep oxygen intrusion low, etc.). Such on-going optimization efforts often necessitate frequent trips to each wellhead at a given landfill by a technician in order to check the LFG flow from each wellhead and make the needed adjustments in an attempt to optimize the LFG flow. As will be appreciated, this manpower requirement can sometimes be costly and time consuming, especially at landfills where dozens or more wellheads are in use. 
         [0007]    But perhaps the most significant drawback to present day LFG systems is the inability to factor in the change that an adjustment to the flow valve of one LFG wellhead will make on the LFG flows produced by other LFG wellheads in the vicinity. This variable is typically not considered by technicians when making a flow valve adjustment to each wellhead. Moreover, intelligent information on the real time flow rates from other wellheads is often not readily available to the technician. So situations may exist where a minor adjustment is made by the technician to one specific wellhead (e.g., wellhead “A”) in order to optimize the LFG flow from that well, but this adjustment actually causes a degradation in the flow from one or more other wellheads B and C in the vicinity (e.g., within a 500 ft radius). And then when the technician goes to wellhead B and makes an adjustment to its flow valve, such a change further ends up affecting the LFG flow from wellheads A and C. Thus, it becomes exceedingly difficult, if not impossible, to determine flow valve settings for each of wellheads which optimizes the overall LFG production from all the wells collectively. 
       SUMMARY 
       [0008]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0009]    A system for controlling an extraction of landfill gas flow (LFG) from a plurality of wellheads at a landfill. The system may comprise a first wellhead located at the landfill and having a first processor having a first rule set, and a first LFG flow control valve controllable by the first processor. A second wellhead may be located at the landfill in a vicinity of the first wellhead and may have a second processor and a second LFG flow control valve. The second processor may have a second rule set and be operable to control the second LFG flow control valve. The first and second processors are operable to use their said rule sets to control the first and second LFG flow control valves, respectively, to control an LFG flow through their said first and second wellheads, respectively. 
         [0010]    In another aspect the present disclosure relates to a system for controlling extraction of landfill gas flow (LFG) from a plurality of wellheads at a landfill. The system may comprise a first wellhead located at the landfill and having a first processor, a first rule set and a first communications module. The system may also comprise a second wellhead located at the landfill in a vicinity of the first wellhead, and having a second communications module. The first and second processors may be configured to communicate with one another via the first and second communications modules. The first processor of the first wellhead may be configured to determine a proposed control parameter setting for controlling a first predetermined operating parameter associated with the first wellhead, and to obtain real time information from the second wellhead concerning a second predetermined operating parameter associated with the second wellhead. The first wellhead may use the first processor and the first rule set to analyze the real time information obtained from the second wellhead concerning the second predetermined operating parameter, and when necessary to adjust the proposed control parameter to optimize performance of both the first and second wellheads. 
         [0011]    In still another aspect the present disclosure relates to a method for controlling an extraction of landfill gas flow (LFG) from a plurality of wellheads at a landfill. The method may comprise using a first wellhead located at the landfill and having a first processor and a first communications module. The method may also comprise using a second wellhead located at the landfill in a vicinity of the first wellhead and having a second processor and a second communications module. The second communications module may be used to share second operating information pertaining to an extraction of LFG gas from the second wellhead with the processor of the first wellhead. The first communications module may be used to share first operating information concerning an extraction of LFG gas from the first wellhead with the processor of the second wellhead. The processors of the first and second wellheads may be used to control an extraction of LFG gas from each, in a manner that optimizes an extraction of LFG gas from both of the first and second wellheads. 
         [0012]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0014]      FIG. 1  is a high level block diagram of one embodiment of a distributed wellhead control system in accordance with the present disclosure, wherein each wellhead may communicate with one or more adjacent wellheads via wireless links to reach a consensus on a proposed flow modification to its associated valve before making any flow adjustments, with an effort toward optimizing the LFG flow from all of the wellheads; 
           [0015]      FIG. 2  is another embodiment of the present disclosure in which each wellhead at a worksite (e.g., landfill) is configured to make its own automatic flow adjustment determination, but may also make use of a centralized processor in making flow control adjustments; 
           [0016]      FIG. 3  is another embodiment of the present disclosure in which each of the wellheads make flow control decisions on their own without input from other adjacent wellheads; 
           [0017]      FIG. 4  is a flowchart illustrating various operations that may be performed by the embodiment of  FIG. 3 ; 
           [0018]      FIG. 5  is a flowchart illustrating various operations that may be performed by the embodiment of  FIG. 1 ; and 
           [0019]      FIG. 6  is a flowchart illustrating specific sub-operations that may be performed when executing operation  412  of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0021]    Referring to  FIG. 1  there is shown a distributed wellhead control system  10  in accordance with one embodiment of the present disclosure. In this example the system  10  includes a plurality of wellheads  12   a - 12   n  that may be located at, for example (and without limitation), a landfill. This number may of course vary considerably, and the present disclosure is not limited to use with any specific number of wellheads  12 . However, most landfill applications may be expected to employ typically 50-150 such wellheads  12   a - 12   n . The wellheads  12   a - 12   n  are associated with wells  14 . The wellheads  12   a - 12   n  each are in flow communication with a centralized gas extraction vacuum blower  16  which generates a vacuum that is used by each of the wellheads  12   a - 12   n  to assist in drawing out landfill gas (LFG) from each well  14 . 
         [0022]    Each wellhead  12   a - 12   n  may include a flow control valve  18  for regulating the vacuum applied by its associated wellhead. A processor  20  may have memory  22 , or the memory  22  may be independent of the processor. The memory  22  may be used to store a rule set  24 . The rule set  24  may include one or more algorithms that may be run by the processor  20  which enable the associated wellhead  12   a - 12   n  to automatically determine a setting for its flow control valve. A wireless, short range communications module  26  (i.e., transceiver), for example a BLUETOOTH® wireless protocol communications module or a ZIGBEE® wireless protocol communications module, may be included to provide bidirectional communications capability to each wellhead  12   a - 12   n . In a typical application the communications module  26  may have a range, for example, of 500 feet, and therefore may enable communications with all other wellheads which are within a 500 foot radius. Obviously the range may vary based on several considerations such as the power of the transmitter section of the communications module  26 , any line of sight obstructions, topography, the wireless protocol used, etc. However, most typically, a communications radius of 300-500 feet is readily achievable. 
         [0023]    The system  10  provides the significant advantage of enabling each of the wellheads  12   a - 12   n  to query one or more of its adjacent wellheads to determine, essentially in real time, various control parameters such as the amount of vacuum being drawn by other nearby wellheads, flow control valve settings being used by other nearby wellheads, etc., which would be important and helpful for a given one of the wellheads  12   a - 12   n  to know before making any adjustment to its own flow control valve  18 . This is because an adjustment made to the flow control valve  18  of one of the wellheads, for example wellhead  12   a , may affect the flow of LFG being withdrawn by its adjacent wellheads, for example wellheads  12   b  and  12   c . Without knowing the real time flow rates of wellheads  12   b  and  12   c  and the flow control valve settings being used by those wellheads, the effect on the flow of LFG out from wellheads  12   b  and  12   c  cannot be taken into consideration when adjusting the flow control valve  18  of wellhead  12   a . But the present system  10  enables this important information to be obtained by the processor  20  using its communications module  26  and interrogating its nearby wellheads, which is done essentially in real time. Using the rule set  24 , the processor  20  is able to more accurately determine the degree of adjustment that should be made to its flow control valve  18  in a manner that will eliminate or minimize adverse effects on the flows of LFG being produced through its nearby wellheads, which in this example would be wellheads  12   b  and  12   c . Likewise, the processors  20  associated with wellheads  12   b  and  12   c  will perform the same analysis before making any adjustments to their associated flow control valves  18 . In this manner the overall production of LFG from all the wellheads  12   a - 12   n  is optimized. 
         [0024]      FIG. 2  shows a system  100  in accordance with another embodiment of the present disclosure which is somewhat similar to the system  10 , but which also incorporates a centralized processor/communications interface  128 . Components in common with those referenced in connection with the system  10  are identified by reference numbers increased by 100 over those used in  FIG. 1 . The system  100  may use its centralized processor/communications interface  128  to perform some or all of the computations that would otherwise be performed by the rule set  124  to assist each wellhead  112   a - 112   n  in determining needed adjustments to its respective flow control valve. The use of the centralized processor/communications interface  128  may help to enable integration with other external “macro” data, site-wide historical data for maps, communications to other external applications and/or responsible parties (alarms, etc.); easier “on-the-fly” modification of control schemes, and other data sources in general. 
         [0025]      FIG. 3  illustrates a system  200  in accordance with another embodiment of the present disclosure. Components in common with those described in connection with the system  10  are denoted with reference numbers increased by 200 over those used in  FIG. 1 . With the system  200 , the wellheads  212   a - 212   n  do not communicate with adjacent wellheads, but nevertheless each is provided with the ability to use its own stored rule set/algorithm  224  to make automatic flow adjustments to its respective flow control  18  valve without any involvement from a technician. Thus, this embodiment provides for standalone installation and operation. It can also be used with only some wells at the site, and is likely to be less expensive overall to implement than the embodiments of  FIG. 1 or 2 . 
         [0026]    Turning now to  FIG. 4  a flowchart  300  illustrates one example of operations that may be implemented using the rule set  224  to control a single wellhead  212  without taking into account the influence on measured readings being caused by adjacent wellheads  212 . Thus, the flowchart  300  corresponds to the operation of the system  200  shown in  FIG. 3 . At operation  302  a set point goal (Ng) is designated for a selected variable. The variable may be any particular variable that one wishes to monitor and control, for example LFG flow, applied vacuum, flow+vacuum, temperature, etc. For this example it will be assumed that LFG flow is the variable that is being controlled. At operation  304  the high and low limits for the LFG flow are set (Nmin and Nmax). At operation  306  the accuracy bandwidth (i.e., measurement tolerance) Ntol is set. At operation  308  the amount of change (Ndelta) to the measured set point (P) to be implemented in a single control step is defined. Operations  302 - 308  thus represent operations for configuring the parameters which will be helpful and/or required to control each wellhead  212   a - 212   n.    
         [0027]    At operation  310  a monitoring/control sequence of operation begins by obtaining a currently measured set point value (P) for the LFG flow. At operation  312  an initial check may be made to determine if the current Ndelta should be kept or modified. Modification may be made at operation  312   a  by using any suitable logic. For example, if a certain number of passes have already been made attempting to adjust the set point goal (Ngoal) to a new value, it may be more desirable to alter the Ndelta value to provide a greater magnitude of change, per pass, than what was initially set for Ndelta. This may enable the system  10  to respond even more quickly and efficiently to reach and maintain a new determined value for Ngoal when significant adjustments to the set point (P) are required. 
         [0028]    At operation  314  a check is made to obtain the current set point value (P). In this example the current set point value relates to a real time rate of LFG flow which was obtained by measurement. If the current set point (P) value is not within the predetermined minimum and maximum limits, then the set point is set equal to the set point goal (Ng at operation  315 ). This ensures that the set point P will always be set virtually immediately back to the set point goal (Ng) in the event it is detected to be outside of some predetermined range. 
         [0029]    At operation  314 , if P is detected to be within the predetermined minimum and maximum limits, then a check is made at operation  316  if P is within the preset error tolerance range ((Ng−Ntol)≦P≦(Ng+Ntol)). If the current set point value (P) is within the predefined error tolerance range, then a loop is made back to operation  310 . If the check at operation  316  indicates that the current set point value is outside of the predefined error tolerance range, then a check is made to see if P is less than the difference of Ng-Ntol at operation  318 . If the check at operation  318  produces a “Yes” answer, then the current set point (P) is reset such that P=P+Ndelta at operation  320 . This produces a new value of the current set point (P) which is within the predefined error tolerance range. 
         [0030]    If the check at operation  318  produces a “No” answer, then a check is made at operation  322  to determine if P is above the maximum allowable point defined by Ng+Ntol. If it is, then at operation  324  the current value for the set point is reset to reduce it by the value of Ndelta (P=P−Ndelta). A loop is then made back to operation  310 . The method of flowchart  300  thus maintains the current set point (P) within a predefined tolerance range, as well as adjusts the current set point (P) in the event it is detected to be just outside (i.e., either above or below) the predefined error tolerance (Ntol) value. 
         [0031]    Referring now to  FIG. 5 , a flowchart  400  is shown in accordance with a method of controlling each of the wellheads  12   a - 12   n  shown in  FIG. 1 . The method shown in  FIG. 5  is able to obtain and use information from a plurality of wellheads  12  when making determinations as to what adjustments are needed to the flow control valve  18  of a given one of the wellheads. For this example it will be assumed that wellhead  12   a  is the specific wellhead which is being examined and adjusted. Other ones of the wellheads will be referred to simply as “nodes” (e.g., wellhead  12   b  is “Node B”, the set point goal for node B is (Ng(B)), etc.). 
         [0032]    Operations  402 - 408  are identical to operations  302 - 308  discussed in connection with  FIG. 4 . At operation  410  the current set point value (P) is obtained. At operation  412  a determination is made as to whether to keep the current value of Ndelta and/or Ngoal, in the same manner as described for operation  312 . If such a change is needed it may be implemented via operation  412   a.    
         [0033]    If the inquiry at operation  412  produces a “No” answer, then at operation  414  a check is made if there is a change in a consensus P(A), that is, a change in the consensus of the current set point for Wellhead  12   a  for near neighbors (e.g., Nodes B and C). If the answer to this operation is “Yes”, then operations sequence  415  is performed. With brief reference to  FIG. 6 , operations sequence  415  involves initially connecting to the near neighbors (e.g., wellheads  12   b  and  12   c , or Nodes B and C) and making a query for a consensus P(Node) table change request(s), as noted at operation  416 . By this operation wellhead  12   a  (i.e., Node A) is requesting from wellheads  12   a  and  12   b  any change request(s) that have been submitted by wellheads  12   b  and  12   c  (Nodes B and C) since wellhead  12   a  made its last set point (P) adjustment. At operation  418  a determination is made if in fact there was at least one P(Node) change request (i.e., a request from either wellhead  12   b  or  12   c ). If so, then at operation  420  the processor  20  of wellhead  12   a  determines a modification to the set point (P(A)) and proposes a new consensus P(A) to the processors  20  of wellheads  12   b  and  12   c . At operation  422  the processor  20  of wellhead  12   a  determines if the processors of wellheads  12   ba  and  12   c  have accepted the proposed new consensus set point (P(A)) and have transmitted notification of their acceptances back to the processor  20  of wellhead  12   a . If one or more of the wellheads  12   b  and  12   c  have not accepted the proposed new consensus set point (P(A)), then at operation  424  processor  20  of wellhead  12   a  may create a new consensus set point (P(A)), and operations  416 - 422  are repeated. Operations  416 - 422  are repeated until a “Yes” answer is received by processor  20  of wellhead  12   a  from the processors of wellheads  12   b  and  12   c  agreeing to the newly proposed consensus set point (P(A)). At operation  426 , then a consensus (P(Node)) table for each of the wellheads  12   a ,  12   b  and  12   c  is updated with the value of the new set point (P). 
         [0034]    Generally a proposed set-point may be rejected if it is too extreme and known to impact the near well&#39;s set-point. Such information may be known through historical near well change vs. local change database tables. So the methodology described in  FIG. 5  may start with a more extreme proposed set point change proposal and then back it down until a point is reached where a specific, proposed new set point is accepted by the processors  20  of the adjacent wellheads  12   b  and  12   c . The rule set  24  can also keep track of acceptance versus rejection from each nearby wellhead  12   b  and  12   c , and also modify a proposed starting point based on these historical statistics. 
         [0035]    Returning now to  FIG. 5 , if the inquiry at operation  414  indicates that there is no change in the consensus set point value that is presently being used by wellhead  12   a  (P(A)), then at operation  428  a check is made by processor  20  of wellhead  12   a  to see if the set point P(A) for wellhead  12   a  is within the predefined minimum and maximum limits. If it is not, then at operation  430  P(A) is set equal to the set point goal (Ng(A)), and a loop is made back to re-perform operation  410 . 
         [0036]    If the check at operation  428  indicates that P(A) is within the predefined upper and lower limits, then at operation  432  a check is made by the processor  20  of wellhead  12   a  to determine if P(A) is within the predefined error tolerances. If it is, then a loop is made back to re-perform operation  410 . 
         [0037]    If the check at operation  432  indicates that P(A) for wellhead  12   a  is not within the predefined error tolerances, then a check is made by the processor  20  of wellhead  12   a  at operation  434  to determine if P(A) is less than the difference between Ng(A)−Ntol. If it is, then at operation  436  the current set point P(A) for wellhead  12   a  is set equal to P(A)+Ndelta(A) by the processor  20 , and a loop is made back to re-perform operation  410 . 
         [0038]    If the check at operation  434  produces a “No” answer, then at operation  438  a check is made by processor  20  of wellhead  12   a  to determine if P(A) for wellhead A is above the predefined tolerance limit (i.e., P(A) (Ng(A)+Ntol)). If it is, then at operation  440  the processor  20  of wellhead  12   a  sets P(A) equal to P(A)−Ndelta(A), and a loop is made back to re-perform operation  410 . 
         [0039]    The present system and method thus enables communications between a plurality of wellheads at a worksite so that proposed changes to the flow valve settings at each wellhead can be communicated to other nearby wellheads and a consensus reached as to precisely what degree of change should be made to optimize the LFG flow from all the wellheads. The system and method may substantially reduce, or eliminate, the situations where a change is made to one wellhead, which is believed to optimize its LFG flow performance, but because the effect of this change on other nearby wells is not known or checked, the change degrades the LFG flow performance from one or more nearby wells. Since the monitoring and LFG flow changes implemented to each of the wellheads is made automatically, the need for a technician to physically travel out to each wellhead to check the LFG flow performance and make adjustments thereto, is eliminated or at least substantially reduced. 
         [0040]    While various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.