System and method for distributed control of multiple wellheads

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.

FIELD

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

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.

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.

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.

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

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.

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.

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.

DETAILED DESCRIPTION

Referring toFIG. 1there is shown a distributed wellhead control system10in accordance with one embodiment of the present disclosure. In this example the system10includes a plurality of wellheads12a-12nthat 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 wellheads12. However, most landfill applications may be expected to employ typically 50-150 such wellheads12a-12n. The wellheads12a-12nare associated with wells14. The wellheads12a-12neach are in flow communication with a centralized gas extraction vacuum blower16which generates a vacuum that is used by each of the wellheads12a-12nto assist in drawing out landfill gas (LFG) from each well14.

Each wellhead12a-12nmay include a flow control valve18for regulating the vacuum applied by its associated wellhead. A processor20may have memory22, or the memory22may be independent of the processor. The memory22may be used to store a rule set24. The rule set24may include one or more algorithms that may be run by the processor20which enable the associated wellhead12a-12nto automatically determine a setting for its flow control valve. A wireless, short range communications module26(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 wellhead12a-12n. In a typical application the communications module26may 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 module26, any line of sight obstructions, topography, the wireless protocol used, etc. However, most typically, a communications radius of 300-500 feet is readily achievable.

The system10provides the significant advantage of enabling each of the wellheads12a-12nto 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 wellheads12a-12nto know before making any adjustment to its own flow control valve18. This is because an adjustment made to the flow control valve18of one of the wellheads, for example wellhead12a, may affect the flow of LFG being withdrawn by its adjacent wellheads, for example wellheads12band12c. Without knowing the real time flow rates of wellheads12band12cand the flow control valve settings being used by those wellheads, the effect on the flow of LFG out from wellheads12band12ccannot be taken into consideration when adjusting the flow control valve18of wellhead12a. But the present system10enables this important information to be obtained by the processor20using its communications module26and interrogating its nearby wellheads, which is done essentially in real time. Using the rule set24, the processor20is able to more accurately determine the degree of adjustment that should be made to its flow control valve18in 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 wellheads12band12c. Likewise, the processors20associated with wellheads12band12cwill perform the same analysis before making any adjustments to their associated flow control valves18. In this manner the overall production of LFG from all the wellheads12a-12nis optimized.

FIG. 2shows a system100in accordance with another embodiment of the present disclosure which is somewhat similar to the system10, but which also incorporates a centralized processor/communications interface128. Components in common with those referenced in connection with the system10are identified by reference numbers increased by 100 over those used inFIG. 1. The system100may use its centralized processor/communications interface128to perform some or all of the computations that would otherwise be performed by the rule set124to assist each wellhead112a-112nin determining needed adjustments to its respective flow control valve. The use of the centralized processor/communications interface128may 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.

FIG. 3illustrates a system200in accordance with another embodiment of the present disclosure. Components in common with those described in connection with the system10are denoted with reference numbers increased by 200 over those used inFIG. 1. With the system200, the wellheads212a-212ndo not communicate with adjacent wellheads, but nevertheless each is provided with the ability to use its own stored rule set/algorithm224to make automatic flow adjustments to its respective flow control18valve 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 ofFIG. 1 or 2.

Turning now toFIG. 4a flowchart300illustrates one example of operations that may be implemented using the rule set224to control a single wellhead212without taking into account the influence on measured readings being caused by adjacent wellheads212. Thus, the flowchart300corresponds to the operation of the system200shown inFIG. 3. At operation302a 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 operation304the high and low limits for the LFG flow are set (Nmin and Nmax). At operation306the accuracy bandwidth (i.e., measurement tolerance) Ntol is set. At operation308the amount of change (Ndelta) to the measured set point (P) to be implemented in a single control step is defined. Operations302-308thus represent operations for configuring the parameters which will be helpful and/or required to control each wellhead212a-212n.

At operation310a monitoring/control sequence of operation begins by obtaining a currently measured set point value (P) for the LFG flow. At operation312an initial check may be made to determine if the current Ndelta should be kept or modified. Modification may be made at operation312aby 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 system10to 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.

At operation314a 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 operation315). 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.

At operation314, if P is detected to be within the predetermined minimum and maximum limits, then a check is made at operation316if 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 operation310. If the check at operation316indicates 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 operation318. If the check at operation318produces a “Yes” answer, then the current set point (P) is reset such that P=P+Ndelta at operation320. This produces a new value of the current set point (P) which is within the predefined error tolerance range.

If the check at operation318produces a “No” answer, then a check is made at operation322to determine if P is above the maximum allowable point defined by Ng+Ntol. If it is, then at operation324the 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 operation310. The method of flowchart300thus 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.

Referring now toFIG. 5, a flowchart400is shown in accordance with a method of controlling each of the wellheads12a-12nshown inFIG. 1. The method shown inFIG. 5is able to obtain and use information from a plurality of wellheads12when making determinations as to what adjustments are needed to the flow control valve18of a given one of the wellheads. For this example it will be assumed that wellhead12ais the specific wellhead which is being examined and adjusted. Other ones of the wellheads will be referred to simply as “nodes” (e.g., wellhead12bis “Node B”, the set point goal for node B is (Ng(B)), etc.).

Operations402-408are identical to operations302-308discussed in connection withFIG. 4. At operation410the current set point value (P) is obtained. At operation412a determination is made as to whether to keep the current value of Ndelta and/or Ngoal, in the same manner as described for operation312. If such a change is needed it may be implemented via operation412a.

If the inquiry at operation412produces a “No” answer, then at operation414a 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 Wellhead12afor near neighbors (e.g., Nodes B and C). If the answer to this operation is “Yes”, then operations sequence415is performed. With brief reference toFIG. 6, operations sequence415involves initially connecting to the near neighbors (e.g., wellheads12band12c, or Nodes B and C) and making a query for a consensus P(Node) table change request(s), as noted at operation416. By this operation wellhead12a(i.e., Node A) is requesting from wellheads12aand12bany change request(s) that have been submitted by wellheads12band12c(Nodes B and C) since wellhead12amade its last set point (P) adjustment. At operation418a determination is made if in fact there was at least one P(Node) change request (i.e., a request from either wellhead12bor12c). If so, then at operation420the processor20of wellhead12adetermines a modification to the set point (P(A)) and proposes a new consensus P(A) to the processors20of wellheads12band12c. At operation422the processor20of wellhead12adetermines if the processors of wellheads12baand12chave accepted the proposed new consensus set point (P(A)) and have transmitted notification of their acceptances back to the processor20of wellhead12a. If one or more of the wellheads12band12chave not accepted the proposed new consensus set point (P(A)), then at operation424processor20of wellhead12amay create a new consensus set point (P(A)), and operations416-422are repeated. Operations416-422are repeated until a “Yes” answer is received by processor20of wellhead12afrom the processors of wellheads12band12cagreeing to the newly proposed consensus set point (P(A)). At operation426, then a consensus (P(Node)) table for each of the wellheads12a,12band12cis updated with the value of the new set point (P).

Generally a proposed set-point may be rejected if it is too extreme and known to impact the near well's set-point. Such information may be known through historical near well change vs. local change database tables. So the methodology described inFIG. 5may 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 processors20of the adjacent wellheads12band12c. The rule set24can also keep track of acceptance versus rejection from each nearby wellhead12band12c, and also modify a proposed starting point based on these historical statistics.

Returning now toFIG. 5, if the inquiry at operation414indicates that there is no change in the consensus set point value that is presently being used by wellhead12a(P(A)), then at operation428a check is made by processor20of wellhead12ato see if the set point P(A) for wellhead12ais within the predefined minimum and maximum limits. If it is not, then at operation430P(A) is set equal to the set point goal (Ng(A)), and a loop is made back to re-perform operation410.

If the check at operation428indicates that P(A) is within the predefined upper and lower limits, then at operation432a check is made by the processor20of wellhead12ato determine if P(A) is within the predefined error tolerances. If it is, then a loop is made back to re-perform operation410.

If the check at operation432indicates that P(A) for wellhead12ais not within the predefined error tolerances, then a check is made by the processor20of wellhead12aat operation434to determine if P(A) is less than the difference between Ng(A)−Ntol. If it is, then at operation436the current set point P(A) for wellhead12ais set equal to P(A)+Ndelta(A) by the processor20, and a loop is made back to re-perform operation410.

If the check at operation434produces a “No” answer, then at operation438a check is made by processor20of wellhead12ato 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 operation440the processor20of wellhead12asets P(A) equal to P(A)−Ndelta(A), and a loop is made back to re-perform operation410.

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.