DETAILED ACTION
Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Continued Examination Under 37 CFR 1.114
A request for continued examination under 37 CFR 1.114, including the fee set forth in 37 CFR 1.17(e), was filed in this application after final rejection. Since this application is eligible for continued examination under 37 CFR 1.114, and the fee set forth in 37 CFR 1.17(e) has been timely paid, the finality of the previous Office action has been withdrawn pursuant to 37 CFR 1.114. Applicant's submission filed on 06/24/2026 has been entered.
Status of the Claims
This action is responsive to the Response to the Final Office Action mailed March 21, 2025, which amends claims 9, 11, and 13, cancels claims 10 and 12, and adds new claims 16-18. The amendment has been entered.
Specification
The specification is objected to because reference numeral 55 is used to designate two different elements: (i) the pressure transmitter located on the shared common discharge header (Spec., paras. 0041, 0043) and (ii) the computerized operations screen of FIG. 4 (Spec., paras. 0045-0047; fig. 4). Each element must be designated by a distinct reference character. See 37 C.F.R. 1.84(p)(4) and MPEP 608.01(o). Appropriate correction is required.
Claim Interpretation
The claims have been reviewed for invocation of 35 U.S.C. 112(f). Claim 9 recites "a computer-based control system communicatively coupled to the plurality of feed compressors and to the pressure transmitter" and "a pressure transmitter located on the shared common discharge header." Although "system" is a generic placeholder capable of invoking 35 U.S.C. 112(f), the recited term is modified by the structural qualifier "computer-based" and by the recited couplings, and "pressure transmitter" is a term understood in the art to denote a definite class of structure. Neither limitation is therefore a means-plus-function limitation.
Accordingly, no claim limitation in claims 9, 11, 13, or 16-18 is being interpreted under 35 U.S.C. 112(f).
Applicant Admitted Prior Art
FIG. 2 of the present application, together with paragraphs 0003-0009 and 0040 of the specification, is treated as Applicant Admitted Prior Art (hereinafter "AAPA"). Paragraph 0040 introduces FIG. 2 as an illustration of a typical prior design setup, and states that prior designs left the control points for the compressor packages separate and distinct, that prior designs operated on a controller/responder basis, and that prior designs used multiple compressors sharing a discharge pressure set point but each controlled from its own individual discharge pressure transmitter. FIG. 2 depicts, as that prior design: a Landfill Gas or BioGas feed drawn by an Inlet Blower, a Sulfur Removal step, three banks of feed compressors labeled Feed Compressors A, Feed Compressors B and Feed Compressors C, a Compressor Slide Value (sic) A, B and C associated respectively with each bank, a combined discharge region labeled Erratic Gas Pressure Area, two Pressure Swing Absorption Vessels downstream of that region, and a Recycle Stream. Paragraphs 0003-0009 further admit that biogas from solid waste landfills is composed primarily of methane and carbon dioxide together with siloxanes, halogenated hydrocarbons, nitrogen and oxygen, and that conventional processing of biogas for biomethane production employs pressure-swing adsorption (PSA) packages, among other separation technologies.
Statements in an application identifying subject matter as prior art are admissions that may be relied upon by the Examiner. See MPEP 2129.
Claim Rejections - 35 USC § 112
The following is a quotation of the first paragraph of 35 U.S.C. 112(a):
(a) IN GENERAL.—The specification shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same, and shall set forth the best mode contemplated by the inventor or joint inventor of carrying out the invention.
The following is a quotation of the first paragraph of pre-AIA 35 U.S.C. 112:
The specification shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same, and shall set forth the best mode contemplated by the inventor of carrying out his invention.
Claims 9, 11, 13, and 16-18 are rejected under 35 U.S.C. 112(a) or 35 U.S.C. 112 (pre-AIA ), first paragraph, as failing to comply with the written description requirement. The claim(s) contains subject matter which was not described in the specification in such a way as to reasonably convey to one skilled in the relevant art that the inventor or a joint inventor, or for applications subject to pre-AIA 35 U.S.C. 112, the inventor(s), at the time the application was filed, had possession of the claimed invention.
Claim 9 recites "monitoring a respective compressor capacity for each feed compressor of the plurality of feed compressors using a pressure transmitter located on the shared common discharge header" in line 8-10, introduces a new matter. The original disclosure describes the pressure transmitter 55 on the shared common discharge header 65 as the element from which a capacity command is issued: all of the compressors react together to one pressure transmitter on the shared common discharge header, and that transmitter sends a capacity command to each of the individual compressors instead of an individual transmitter being provided at each compressor (Spec., para. 0041). The same relationship is described at paragraphs 0038 and 0043, where the discharge control is said to use a common discharge header pressure transmitter combined with a centralized PID control loop. The capacity of each compressor, by contrast, is described as being displayed as the commanded capacity lines 95 and 105 on the computerized operations screen (Spec., paras. 0046-0047; figs. 4, 4A), not as being measured or monitored by the pressure transmitter. A pressure transmitter, as disclosed, senses pressure on the header; it does not sense the capacity of any individual feed compressor. Claim 9 as originally presented recited "regulating the compressor capacity for each feed compressor using a pressure transmitter located on the shared common discharge header." Regulating capacity from the transmitter and monitoring capacity with the transmitter are converse operations, and the original disclosure supports only the former. The amended limitation therefore introduces new matter, and the specification does not reasonably convey possession of a method in which a respective compressor capacity of each feed compressor is monitored using a pressure transmitter located on the shared common discharge header.
Claim 9 recites "changing, via the computer-based control system, a second compressor slide valve on the second feed compressor from a second position to a third position such that the second feed compressor counteracts a flow disruption from the change in the first compressor slide valve from the stationary position to the first position." The original disclosure describes one, and only one, manner of counteraction: compressor slide valve 35A is jogged in the opposite direction simultaneously from compressor slide valve 35B, so as to counteract the disruption in flow that moving the slide valves would otherwise cause, with the capacity represented by line 95 initially greater and the capacity represented by line 105 initially lower, so that overall header discharge pressure is not affected (Spec., paras. 0014, 0049, 0053; figs. 4, 4A). Every disclosed embodiment requires both (i) movement of the two slide valves in opposite directions and (ii) simultaneity of that movement. Amended claim 9 has removed both requirements. As now written, claim 9 embraces the entire genus of second-valve movements that "counteract" a flow disruption, including movement of the second slide valve in the same direction as the first, movement of a different magnitude, and movement separated in time from the movement of the first slide valve. Disclosure of a single species does not provide written description support for the claimed genus. See MPEP 2163(II)(A)(3)(a)(ii). New claim 16, which requires that the two changes be performed contemporaneously, does not restore the opposite-direction requirement and does not cure the deficiency in claim 9.
Claims 11, 13, and 16-18 are also rejected under 35 U.S.C. 112(b) for being dependent upon a rejected claim.
The following is a quotation of 35 U.S.C. 112(b):
(b) CONCLUSION.—The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention.
The following is a quotation of 35 U.S.C. 112 (pre-AIA ), second paragraph:
The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention.
Claims 9, 11, 13, and 16-18 are rejected under 35 U.S.C. 112(b) or 35 U.S.C. 112 (pre-AIA ), second paragraph, as being indefinite for failing to particularly point out and distinctly claim the subject matter which the inventor or a joint inventor (or for applications subject to pre-AIA 35 U.S.C. 112, the applicant), regards as the invention.
Claim 9 recites "monitoring a respective compressor capacity for each feed compressor of the plurality of feed compressors using a pressure transmitter located on the shared common discharge header" In line 8-10, renders the claim indefinite because a pressure transmitter senses pressure; it does not sense the volumetric capacity of any individual feed compressor. The claim does not state how a respective compressor capacity is derived from, or monitored by means of, a pressure-sensing element, and it cannot be determined whether the recited step requires the capacity of each feed compressor to be measured, to be calculated from the sensed header pressure, or simply to be commanded from the transmitter as the specification describes (Spec., paras. 0038, 0041, 0043). The metes and bounds of the step therefore cannot be ascertained. For examination purposes, the limitation is treated as encompassing any arrangement in which the respective capacity of each feed compressor is determined or set by the control system on the basis of the pressure sensed by a pressure transmitter located on the shared common discharge header.
Claim 9 first establishes, for the first compressor slide valve, "a stationary position" and "a first position." It then recites changing the second compressor slide valve "from a second position to a third position." It cannot be determined from the claim whether the recited "second position" is the same as, or different from, the "stationary position"; whether the second compressor slide valve is ever required to occupy a stationary position; or whether the "third position" bears any defined relationship to the "first position." Because positions of two different slide valves are enumerated in a single ordinal series, the metes and bounds of the claim cannot be ascertained. For examination purposes, the "second position" is treated as any position at which the second compressor slide valve is held immediately before the recited change, and the "third position" is treated as any position of that slide valve different from the second position.
Claim 9 recites "the second feed compressor counteracts a flow disruption" in line 22 renders the claim indefinite because the claim does not state whether the second feed compressor must fully cancel, or need only partially offset, the flow disruption produced by movement of the first compressor slide valve, and recites no measurable reference against which the required degree of counteraction could be judged. Paragraphs 0049 and 0053 of the specification describe the object as countering any flow disruption so that overall header discharge pressure is not affected, but that result is not recited in the claim and the specification supplies no standard of measurement. Neither the claim nor the specification identifies what magnitude of residual disruption is tolerated, and the specification statement that overall header discharge pressure is "not affected" is itself unquantified, so one of ordinary skill would not be apprised of the scope of the limitation with reasonable certainty. The term is therefore a term of degree without an objective boundary. See MPEP 2173.05(b). For examination purposes, any change in the second compressor slide valve that tends to offset the change in flow produced by movement of the first compressor slide valve is treated as satisfying the limitation.
Claim 11 recites "monitoring, by the computer-based control system, that the shared common discharge header at a header discharge pressure that is within a predetermined deadband boundary range" renders the claim indefinite because it cannot be determined whether the recited step requires monitoring the header discharge pressure, verifying that the header discharge pressure lies within the deadband, or maintaining the header discharge pressure within the deadband as originally recited. For examination purposes, the limitation is treated as "monitoring, by the computer-based control system, that the shared common discharge header is at a header discharge pressure that is within a predetermined deadband boundary range."
Claim 13 recites "changing a respective current position of at least one feed compressor of the plurality of feed compressors ... to a respective different position." Two defects are present. First, "a respective current position" of a feed compressor lacks antecedent basis; the claims recite positions of compressor slide valves, not positions of feed compressors. Second, a feed compressor is a machine, not a valve, and it is unclear whether Applicant intends to change the physical location of the feed compressor itself or, as described throughout the specification, the position of the compressor slide valve carried by that feed compressor (Spec., paras. 0013, 0044, 0046). For examination purposes, the limitation is treated as "changing a respective current position of a compressor slide valve on at least one feed compressor of the plurality of feed compressors to a respective different position."
Claim 16 recites "wherein the changing each respective position of the first compressor slide valve and the second compressor slide valve is performed contemporaneously" renders the claim indefinite because the limitation "the changing each respective position" lacks antecedent basis, because claim 9 recites changing the first compressor slide valve from a stationary position to a first position and changing the second compressor slide valve from a second position to a third position, and does not recite a "respective position" of either slide valve. It is further unclear whether "contemporaneously" requires the two changes to begin at the same instant, to overlap in time, or merely to occur within some unspecified interval of one another. For examination purposes, the limitation is treated as requiring that the two changes overlap in time.
Claims 17 and 18 are also rejected under 35 U.S.C. 112(b) as depending from a rejected claim.
Claim Rejections - 35 USC § 103
In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status.
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
The factual inquiries for establishing a background for determining obviousness under 35 U.S.C. 103 are summarized as follows:
1. Determining the scope and contents of the prior art.
2. Ascertaining the differences between the prior art and the claims at issue.
3. Resolving the level of ordinary skill in the pertinent art.
4. Considering objective evidence present in the application indicating obviousness or nonobviousness.
Claims 9, 11, 13, and 16-18 are rejected under 35 U.S.C. 103 as being unpatentable over Applicant Admitted Prior Art (AAPA) in view of Itou et al. (US 2003/0053906 A1) in view of Mountford et al. (US 6,629,645 B2), and further in view of Centers et al. (US 6,533,552 B2).
In regard to claim 9, AAPA teaches a method of controlling compressor operations for a plurality of feed compressors (Feed Compressors A, Feed Compressors B and Feed Compressors C) in a facility for treating biogas to recover renewable natural gas (the prior RNG recovery facility of fig. 2) comprising:
receiving, at the facility, a landfill gas stream comprising biogas (the Landfill Gas or BioGas stream drawn by the Inlet Blower and delivered through Sulfur Removal to the feed compressors) (paras. 0003-0005, 0040; fig. 2);
operating the plurality of feed compressors such that each compressor of the plurality of compressors discharges to a shared common discharge header (the combined discharge region labeled Erratic Gas Pressure Area, into which Feed Compressors A, B and C discharge in parallel upstream of the Pressure Swing Absorption Vessels), wherein the plurality of feed compressors comprises a first feed compressor (Feed Compressors A) and a second feed compressor (Feed Compressors B) (para. 0040; fig. 2);
a first compressor slide valve on the first feed compressor (Compressor Slide Value A) and a second compressor slide valve on the second feed compressor (Compressor Slide Value B), each regulating the volume capacity of its respective feed compressor and each held at a position to hold that feed compressor at a given volume capacity (para. 0040; fig. 2); and
a compressor capacity for each feed compressor that is regulated on discharge pressure control (the discharge pressure set point common to the compressor packages of the prior design) (para. 0040; fig. 2).
AAPA does not explicitly teach monitoring a respective compressor capacity for each feed compressor of the plurality of feed compressors using a pressure transmitter located on the shared common discharge header, as that limitation is construed in the rejection under 35 U.S.C. 112(b) above; nor changing, via a computer-based control system communicatively coupled to the plurality of feed compressors and to the pressure transmitter, a second compressor slide valve on the second feed compressor from a second position to a third position such that the second feed compressor counteracts a flow disruption from the change in the first compressor slide valve, or returning the second compressor slide valve to the second position.
However, Itou teaches a plurality of compressors (A0, B0, C0, D0) connected in parallel, each having a capacity-regulating valve at its suction side (inlet guide vanes 50a, 50b) that adjusts the amount of gas taken into the compressor main body (60a, 60b) (paras. 0009-0010, 0018; fig. 1); a single discharge-pressure detection means of the compressor system (pressure gauge 90) provided downstream of the junction position of the parallel compressors on the common discharge conduit, its signal being transmitted to the controller over a signal line (54) (paras. 0009, 0020; fig. 1); a computer-based controller (10) communicatively coupled to each compressor by signal cables (51a, 52a, 53a) and to the discharge-pressure detection means (90), which issues a rotation-angle instruction to each capacity-regulating valve (50a, 50b) so that the discharge pressure of the system is brought to a predetermined pressure, thereby regulating and tracking the capacity of every compressor from that one transmitter (paras. 0009-0010, 0020-0021, 0025, 0031, 0037; fig. 1); a change in the capacity-regulating valve of a first compressor (50a of A0) that abruptly reduces the flow rate of the compressor system (para. 0028; fig. 2); and a corresponding change of the capacity-regulating valves of the remaining compressors (50b of B0, C0, D0) in the opposite sense, opening them so that the abruptly falling discharge flow rate is turned back to the flow rate obtaining at the time before the first change, thereby counteracting the flow disruption caused by the first compressor (paras. 0028, 0031-0032; fig. 2), those valves thereafter being rotated back once the flow rate recovers to the predetermined flow rate equal to that before the change (para. 0030; fig. 2).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have modified the RNG recovery facility of AAPA to monitor and regulate the capacity of each feed compressor from a single pressure transmitter located on the shared common discharge header by way of a computer-based control system coupled to the feed compressors and to that transmitter, and to offset a capacity change made at the first feed compressor by an opposing capacity change at the second feed compressor followed by a return of the second compressor slide valve to its prior position, as taught by Itou, in order to achieve partial load operation easily by means of a simple control and to obtain effective operation of plural parallel compressors even when the suction conditions and the individual states of each compressor change (Itou, paras. 0004, 0048). One of ordinary skill would have been motivated to make this modification because AAPA expressly identifies the separate and distinct control points of the prior compressor packages, and the individual per-compressor discharge pressure transmitters, as the cause of gas pressure swings and of the Erratic Gas Pressure Area downstream of the feed compressors (AAPA, para. 0040; fig. 2), and Itou identifies the same failure mode in parallel compressor banks and resolves it by centralizing discharge-pressure control (Itou, paras. 0003-0005). See MPEP 2143(I)(A).
AAPA, as modified above, does not explicitly teach changing, via a computer-based control system, a first compressor slide valve on the first feed compressor from a stationary position to a first position in response to the first compressor slide valve being at the stationary position for a pre-determined period of time, or returning the first compressor slide valve on the first feed compressor to the stationary position.
However, Mountford teaches a valve (2) having a valve member (20) with a sealing face (26) against which resilient cup seals (22, 24) press, a valve servo (4) for moving the valve, and a control system (6) that operates the valve servo in response to a control signal (col. 7, lines 1-11; col. 20, lines 25-56; figs. 1-3); that where such a valve is left unoperated for a long period the seal material begins to adhere to the sealing surface, the stiction effect causes the operating torque to rise with time, and the valve may jam in the position at which it was left (col. 20, lines 25-38); a control system (6) that includes a timer and monitors how long it has been since the valve (2) was last operated, and that, when the time since last operation exceeds a predetermined limit, operates the valve servo (4) so as to move the valve (2) from the position at which it has been standing, the movement needing to be only enough to slide the resilient seal in either direction (col. 7, lines 1-11; col. 20, lines 42-56; fig. 1); and a servo routine in which the control system (6) drives the valve (2) in one direction past a position registered by a detector (54) and then reverses the valve servo (4) until the valve (2) returns past that same position (col. 19, line 59 to col. 20, line 24; fig. 1).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have further modified AAPA to change the first compressor slide valve on the first feed compressor from its stationary position to a first position in response to that slide valve having remained at the stationary position for a pre-determined period of time, and thereafter to return that slide valve to the stationary position, as taught by Mountford, in order to keep the seal from adhering to its sealing surface, to prevent the valve from jamming in the position at which it was left, and to avoid the rise in operating torque and the strain placed on the valve servo and operating mechanism that follow prolonged inactivity (Mountford, col. 7, lines 1-11; col. 20, lines 25-56).
A compressor slide valve regulates the built-in volume ratio for the capacity of its compressor and therefore alters the flow that compressor delivers whenever it is moved (Centers, col. 1), so the commanded movement of the first compressor slide valve produces the very flow disruption that the second feed compressor is operated to counteract in the manner set out above. One of ordinary skill would have been motivated to make this modification because the sticking of a capacity-control valve was a problem already recognized within the compressor art itself: Centers states that the opening and closing of the capacity valve of a rotary screw compressor is unreliable due to friction, corrosion and other environmental factors which often derogate the positioning of the valve (Centers, col. 1), and identifies the prevention of valve sticking and erratic valve timing as the very reason for adopting a positively driven capacity valve (Centers, col. 10). AAPA presents that recognized problem in its most acute form, because its compressor slide valves are held at a fixed position in order to hold each feed compressor at a given volume capacity and are therefore moved only occasionally (AAPA, para. 0040; fig. 2), and the gas in which those slide valves sit is a landfill gas or biogas admitted to carry siloxanes, halogenated hydrocarbons and other contaminants (AAPA, paras. 0005-0006). See MPEP 2143(I)(C).
In regard to claim 11, AAPA, as modified above, teaches the method of claim 9, including a computer-based control system communicatively coupled to the plurality of feed compressors and to a pressure transmitter located on the shared common discharge header. AAPA does not explicitly teach monitoring, by the computer-based control system, that the shared common discharge header is at a header discharge pressure that is within a predetermined deadband boundary range.
However, Centers teaches an electronic control system (104) for a rotary screw compressor (102) whose output capacity is varied by four capacity-reduction lift valves (322, 324, 326, 328) and an inlet valve (336), the system including a line pressure transducer (204, 308) installed in the pressurized line served by the compressor and a system processor (502) executing firmware stored on the microprocessor board (500) (cols. 5-7, 12; figs. 1-3, 5a-5i); a continuous run mode in which the processor holds the compressor motor (214) at constant speed and uses an adjustable pressure deadband algorithm to match compressor output to system demand, the operation being governed by dynamically calculated pressure ranges rather than by the measured service air pressure value directly (col. 19); a series of overlapping pressure deadbands whose width is calculated by the control system from an operator-entered full-load pressure and unloaded pressure (col. 21; fig. 9); a monitoring operation in which the sensed line pressure is compared against the start point and the close point of each deadband and no capacity valve is actuated so long as the sensed pressure remains within the band (col. 21; fig. 9); and a plurality of such compressor systems (100) feeding the same distribution system, their control systems (104) being networked so that the compressors are coordinated to hold a common target pressure (Abstract; cols. 25-27; figs. 8, 11).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have modified AAPA so that the computer-based control system monitors that the shared common discharge header is at a header discharge pressure within a predetermined deadband boundary range, as taught by Centers, in order to prevent rapid and needless cycling of the compressor capacity controls during periods of reduced demand and to stabilize system pressure (Centers, col. 4; cols. 19-20).
In regard to claim 13, AAPA, as modified above, teaches the method of claim 11, but does not explicitly teach receiving, from the pressure transmitter, a signal indicating that a current header discharge pressure is outside the predetermined deadband boundary range; and, in response to the signal, changing a respective current position of a compressor slide valve on at least one feed compressor of the plurality of feed compressors to a respective different position.
However, Centers teaches that the line pressure sensed by the line pressure transducer (204) is delivered to the system processor (502) through the analog-to-digital converter (556) and is continuously compared against the boundaries of the pressure deadbands (cols. 16, 21; figs. 5i, 9); that when the sensed pressure passes beyond the start point of a band the corresponding capacity valve is opened and kept open, and when the sensed pressure falls below the close point of that band the valve, if open, is closed, the inlet valve (336) being closed when the sensed pressure exceeds its close point and opened when the sensed pressure falls below its open point, so that a capacity-control valve of at least one compressor is driven from its current position to a different position in response to the pressure leaving the band (col. 21; fig. 9); and that where several compressor systems (100) are networked on one distribution system, the valves on the other networked machines are automatically adjusted to compensate for a capacity reduction taken at one machine (col. 29; fig. 11).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have modified AAPA to receive from the pressure transmitter on the shared common discharge header a signal indicating that the current header discharge pressure lies outside the predetermined deadband boundary range and, in response to that signal, to change the current position of a compressor slide valve on at least one feed compressor to a different position, as taught by Centers, in order to bring the header pressure back within the band and thereby maintain the desired pressure in the system served by the compressors (Centers, Abstract; col. 21).
In regard to claim 16, AAPA, as modified above, teaches the method of claim 9, but does not explicitly teach that the changing of each respective position of the first compressor slide valve and the second compressor slide valve is performed contemporaneously.
However, Itou teaches that the controller (10) instructs the vanes of the capacity-regulating valves (50a, 50b) of the compressor main bodies (60a, 60b) to rotate so that the flow rates of the parallel compressors (A0-D0) are changed simultaneously, and that the controller closes the capacity-regulating valves of the several compressors simultaneously and controls those sets to rotate their vanes at the same time (paras. 0025, 0039; figs. 1, 2).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have modified AAPA so that the change of the first compressor slide valve and the change of the second compressor slide valve are performed contemporaneously, as taught by Itou, in order to obtain a stable operation of parallel compressors of the same capacity and type by means of a simple control method and to suppress the power consumed (Itou, para. 0047).
In regard to claim 17, AAPA, as modified above, teaches the method of claim 9, but AAPA does not explicitly teach that the pre-determined period of time is at least 8 hours.
However, Mountford teaches that the predetermined period after which the control system (6) automatically operates the valve (2) to prevent stiction is at least 24 hours, and discloses in the alternative a period of approximately 30 hours, a period of approximately 20 hours, and automatic movement once every week, while stating that there is little need for automatic operation within 12 hours (col. 7, line 12; col. 20, line 57 to col. 21, line 4). Each of these disclosed periods falls within the claimed range of at least 8 hours.
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have set the pre-determined period of time of AAPA at least 8 hours, as taught by Mountford, in order to keep the seals of the valve from sticking to the sealing surface while operating the valve no more often than is necessary to do so (Mountford, col. 7, line 12; col. 20, line 57 to col. 21, line 4). One of ordinary skill would have been motivated to make this modification because the length of the idle interval that is tolerated before a jog is commanded is a result-effective variable that trades the risk of the slide valve seizing against needless actuator wear and needless disturbance of the header discharge condition of AAPA (AAPA, para. 0040; fig. 2), and the discovery of an optimum or workable value of a result-effective variable is ordinarily within the skill of the art. See MPEP 2143(I)(E).
In regard to claim 18, AAPA, as modified above, teaches the method of claim 9 comprising receiving, at a pressure swing adsorption unit (the Pressure Swing Absorption Vessels downstream of the Erratic Gas Pressure Area), output gas from the plurality of feed compressors (the compressed Landfill Gas or BioGas discharged in common by Feed Compressors A, B and C) (paras. 0007-0008, 0040; fig. 2).
Claims 9, 11, 13, and 16-18 are rejected under 35 U.S.C. 103 as being unpatentable over Centers et al. (US 6,533,552 B2) in view of Mitariten (US 2007/0068386 A1) in view of Itou et al. (US 2003/0053906 A1) and further in view of Mountford et al. (US 6,629,645 B2).
In regard to claim 9, Centers teaches a method of controlling compressor operations for a plurality of feed compressors (a plurality of compressor systems 100, each comprising an oil-flooded rotary screw compressor 102 and an electronic control system 104, up to sixteen of which are joined in a peer-to-peer network and feed the same distribution system) comprising:
operating the plurality of feed compressors such that each compressor of the plurality of compressors discharges to a shared common discharge header (the common service air distribution system into which every networked compressor system 100 delivers through its reservoir air output 337 and service air output 346, the network mode being provided for the case of multiple machines installed in one location and fed into a header), wherein the plurality of feed compressors comprises a first feed compressor (the compressor system 100 bearing sequence designation A) and a second feed compressor (the compressor system 100 bearing sequence designation B) (Abstract; cols. 9-10, 25-27, 30; figs. 3, 8, 11);
a first compressor slide valve on the first feed compressor and a second compressor slide valve on the second feed compressor, a rotary screw compressor of this kind being provided with valves for regulating the built-in volume ratio for the capacity of the compressor and slide valves being used where continued regulation is required, and the position of such a valve being commanded electronically to vary compressor output and hold pressure at a selected setpoint (cols. 1-2, 5-6; figs. 1, 3);
monitoring a respective compressor capacity for each feed compressor of the plurality of feed compressors using a pressure transmitter (each electronic control system 104 transmitting to every other the current load setting of its machine, including the actuation condition of each capacity valve, together with the line pressure measured at its line pressure transducer 204, each machine determining its proximity to the target pressure from the average of those readings, the network algorithms being capacity-based rather than pressure-based) (cols. 25-27, 29-30; figs. 5i, 8, 11);
changing, via a computer-based control system communicatively coupled to the plurality of feed compressors and to the pressure transmitter (the networked electronic control systems 104, each built on a microprocessor board 500 carrying system processor 502, joined by the ARCnet peer-to-peer network connection 213, and each connected to a line pressure transducer 204), a first compressor slide valve on the first feed compressor from the position at which it has been standing to a different position (cols. 6-8, 12-13, 19-21; figs. 2, 5a-5i, 8, 9); and
changing a second compressor slide valve on the second feed compressor from a second position to a third position such that the second feed compressor counteracts a flow disruption from the change made at the first feed compressor, the valves on the other networked machines being automatically adjusted to compensate for the capacity reduction taken at the first machine (col. 29; fig. 11).
Centers does not explicitly teach a method of controlling compressor operations for a plurality of feed compressors in a facility for treating biogas to recover renewable natural gas, or receiving, at the facility, a landfill gas stream comprising biogas.
However, Mitariten teaches a landfill (2) from which a gas stream (4) consisting primarily of methane, carbon dioxide, air, water, siloxanes, volatile organic compounds and other trace elements is extracted through a gathering system of piping at a pressure from sub-atmospheric to 25 psig (para. 0022; the FIGURE); a compressor (6) that pressurizes the landfill gas stream (4) to a feed pressure of about 60 to 200 psig because that gathering pressure is too low for feed to the downstream separation process (para. 0022; the FIGURE); and a compressed landfill gas stream (8) directed to a pressure swing adsorption process (10) containing two to four adsorbent vessels, from which a methane-rich product stream (12) containing at least about 65 volume percent methane and substantially free of siloxanes, volatile organic compounds and water is recovered (para. 0022; the FIGURE).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have applied the parallel compressor control method of Centers to a facility receiving a landfill gas stream comprising biogas and treating it to recover renewable natural gas, as taught by Mitariten, in order to raise the gathered landfill gas from its low gathering pressure to the feed pressure required by the downstream separation process and thereby upgrade the gas to a pipeline-quality methane product (Mitariten, para. 0022). One of ordinary skill would have been motivated to make this modification because Centers states that although its apparatus and methods are particularly applicable to rotary screw compressors supplying industrial compressed air, the methods may be applied to other types of compressors in other applications (Centers, col. 5), and the compression duty Mitariten identifies is the same duty Centers controls. See MPEP 2143(I)(A).
Centers, as modified above, does not explicitly teach that the pressure transmitter is located on the shared common discharge header, or returning the second compressor slide valve on the second feed compressor to the second position.
However, Itou teaches a single discharge-pressure detection means of the compressor system (pressure gauge 90) provided downstream of the junction position of the parallel compressors on the common discharge conduit, its signal being transmitted to the controller (10) over a signal line (54), the controller issuing a rotation-angle instruction to the capacity-regulating valve (50a, 50b) of each compressor so that the discharge pressure of the system is brought to a predetermined pressure and the capacity of every compressor is thereby regulated and tracked from that one transmitter (paras. 0009-0010, 0020-0021, 0025, 0031, 0037; fig. 1); and return of the compensating capacity-regulating valves (50b) toward their prior condition once the flow rate recovers to the predetermined flow rate equal to that obtaining before the change (para. 0030; fig. 2).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have modified Centers to locate the pressure transmitter on the shared common discharge header and to regulate and monitor the capacity of every feed compressor from that transmitter, and to return the second compressor slide valve to its prior position once the flow has recovered, as taught by Itou, in order to achieve partial load operation easily by means of a simple control and to obtain effective operation of plural parallel compressors even when the suction conditions and the individual states of each compressor change (Itou, paras. 0004, 0048).
Centers, as modified above, does not explicitly teach changing the first compressor slide valve on the first feed compressor from a stationary position to a first position in response to the first compressor slide valve being at the stationary position for a pre-determined period of time, or returning the first compressor slide valve to the stationary position.
However, Mountford teaches a valve (2) having a valve member (20) with a sealing face (26) against which resilient cup seals (22, 24) press, a valve servo (4) for moving the valve, and a control system (6) that operates the valve servo in response to a control signal (col. 7, lines 1-11; col. 20, lines 25-56; figs. 1-3); that where such a valve is left unoperated for a long period the seal material begins to adhere to the sealing surface, the stiction effect causes the operating torque to rise with time, and the valve may jam in the position at which it was left (col. 20, lines 25-38); a control system (6) that includes a timer and monitors how long it has been since the valve (2) was last operated, and that, when the time since last operation exceeds a predetermined limit, operates the valve servo (4) so as to move the valve (2) from the position at which it has been standing, the movement needing to be only enough to slide the resilient seal in either direction (col. 7, lines 1-11; col. 20, lines 42-56; fig. 1); and a servo routine in which the control system (6) drives the valve (2) in one direction past a position registered by a detector (54) and then reverses the valve servo (4) until the valve (2) returns past that same position (col. 19, line 59 to col. 20, line 24; fig. 1).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have further modified Centers to change the first compressor slide valve from its stationary position to a first position in response to that slide valve having remained at the stationary position for a pre-determined period of time, and thereafter to return that slide valve to the stationary position, as taught by Mountford, in order to keep the seal from adhering to its sealing surface, to prevent the valve from jamming in the position at which it was left, and to avoid the rise in operating torque and the strain placed on the valve servo and operating mechanism that follow prolonged inactivity (Mountford, col. 7, lines 1-11; col. 20, lines 25-56). A compressor slide valve regulates the built-in volume ratio for the capacity of its compressor and therefore alters the flow that compressor delivers whenever it is moved (Centers, col. 1), so the commanded movement of the first compressor slide valve produces the very flow disruption that the second feed compressor is operated to counteract in the manner set out above. One of ordinary skill would have been motivated to make this modification because Centers identifies the very problem Mountford solves: it states that the opening and closing of the capacity valve of a rotary screw compressor is unreliable due to friction, corrosion and other environmental factors which often derogate the positioning of the valve (Centers, col. 1), and identifies the prevention of valve sticking and erratic valve timing as the reason for adopting a positively driven capacity valve (Centers, col. 10), while the landfill gas of Mitariten in which such a valve would sit carries siloxanes, volatile organic compounds and water (Mitariten, para. 0022). See KSR, 550 U.S. 398; MPEP 2143(I)(C).
In regard to claim 11, Centers, as modified above, teaches the method of claim 9 further comprising monitoring, by the computer-based control system, that the shared common discharge header is at a header discharge pressure that is within a predetermined deadband boundary range (the continuous run mode in which the system processor 502 holds the compressor motor 214 at constant speed and matches output to demand by an adjustable pressure deadband algorithm, the width of each deadband being calculated by the control system from an operator-entered full-load pressure and unloaded pressure, and no capacity valve being actuated so long as the sensed pressure remains between the start point and the close point of the band) (cols. 19, 21; fig. 9).
In regard to claim 13, Centers, as modified above, teaches the method of claim 11 further comprising receiving, from the pressure transmitter, a signal indicating that a current header discharge pressure is outside the predetermined deadband boundary range (the line pressure sensed by the line pressure transducer 204 being delivered to the system processor 502 through the analog-to-digital converter 556 and continuously compared against the boundaries of the pressure deadbands) and, in response to the signal, changing a respective current position of a compressor slide valve on at least one feed compressor of the plurality of feed compressors to a respective different position (the corresponding capacity valve being opened and kept open when the sensed pressure passes the start point of its band, and closed when the sensed pressure falls below the close point of that band) (cols. 16, 21; figs. 5i, 9).
In regard to claim 16, Centers, as modified above, teaches the method of claim 9, but Centers does not explicitly teach that the changing of each respective position of the first compressor slide valve and the second compressor slide valve is performed contemporaneously.
However, Itou teaches that the controller (10) instructs the vanes of the capacity-regulating valves (50a, 50b) of the compressor main bodies (60a, 60b) to rotate so that the flow rates of the parallel compressors (A0-D0) are changed simultaneously, and that the controller closes the capacity-regulating valves of the several compressors simultaneously and controls those sets to rotate their vanes at the same time (paras. 0025, 0039; figs. 1, 2).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have modified Centers so that the change of the first compressor slide valve and the change of the second compressor slide valve are performed contemporaneously, as taught by Itou, in order to obtain a stable operation of parallel compressors of the same capacity and type by means of a simple control method and to suppress the power consumed (Itou, para. 0047).
In regard to claim 17, Centers, as modified above, teaches the method of claim 9, but Centers does not explicitly teach that the pre-determined period of time is at least 8 hours.
However, Mountford teaches that the predetermined period after which the control system (6) automatically operates the valve (2) to prevent stiction is at least 24 hours, and discloses in the alternative a period of approximately 30 hours, a period of approximately 20 hours, and automatic movement once every week, while stating that there is little need for automatic operation within 12 hours (col. 7, line 12; col. 20, line 57 to col. 21, line 4). Each of these disclosed periods falls within the claimed range of at least 8 hours.
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have set the pre-determined period of time of Centers at least 8 hours, as taught by Mountford, in order to keep the seals of the valve from sticking to the sealing surface while operating the valve no more often than is necessary to do so (Mountford, col. 7, line 12; col. 20, line 57 to col. 21, line 4). One of ordinary skill would have been motivated to make this modification because the length of the idle interval tolerated before a jog is commanded is a result-effective variable that trades the risk of the capacity valve seizing against needless actuator wear and needless disturbance of the pressure Centers holds within its deadband (Centers, cols. 19, 21), and the discovery of an optimum or workable value of a result-effective variable is ordinarily within the skill of the art. See MPEP 2143(I)(E).
In regard to claim 18, Centers, as modified above, teaches the method of claim 9, but Centers does not explicitly teach receiving, at a pressure swing adsorption unit, output gas from the plurality of feed compressors.
However, Mitariten teaches that the compressed landfill gas stream (8) leaving the compressor (6) is directed to a pressure swing adsorption process (10) containing two to four adsorbent vessels, in which the compressed stream is contacted with an adsorbent to remove carbon dioxide, water, volatile organic compounds and siloxanes and to yield a methane-rich product stream (12) (para. 0022; the FIGURE).
Therefore, it would have been obvious to one of ordinary skill in the art before the effective filing date of the claimed invention to have modified Centers so that a pressure swing adsorption unit receives the output gas from the plurality of feed compressors, as taught by Mitariten, in order to remove carbon dioxide, nitrogen, water, volatile organic compounds and siloxanes from the compressed landfill gas and recover a methane-rich product stream of pipeline quality (Mitariten, para. 0022).
Response to Arguments
Applicant’s arguments with respect to the amended claims have been considered but are moot in view of the new ground(s) of rejection.
Conclusion
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/W.M/Examiner, Art Unit 3763
/FRANTZ F JULES/Supervisory Patent Examiner, Art Unit 3763
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