Patent CA-3069063-A1 (CA)
Title: System and methdo for controlling and introducing a flow of vent gases into the fuel supply of a natural gas engine
Inventor: HARTMAN RALPH R
IPC: F02B43/12
Filed: 2020-01-21
Abstract: ABSTRACT OF THE DESCRIPTION  The present invention is directed to a means and method to inlet zero to low pressure vented, fugitive or exhausted gas volumes and discharge those volumes into the existing fuel gas supply systems of a natural gas fueled engine. To this end, greenhouse gases such as methane are recovered and prevented from escaping into the atmosphere. The use of parts and components common to industry innovatively arranged and configured to sequentially enable a parallel train of two or more gas to gas ejectors of same or differing flow volume capabilities will provide industry a vented gas containment solution with a large capacity variance that is readily retrofittable or will suitably integrate with new equipment packaging. This invention will prove the control and small quantity recovery of vented gases economical where the cost and configurability of a conventional vapor recovery compressor or similar systems would be considered impractical due to high capital and operating costs. A typical installation for this invention would be a gas compression unit or station where vented and fugitive gases are collected and accumulated by means current and common to industry such as seal pots, tanks and knock-out vessels and routed to the inlet port on one or more gas to gas ejectors. The use of a seal pot is depicted and discussed herein. A seal pot is a preferred type of tank in that is provides a trap space for gases, a siphon drain arrangement to manage liquids and immersion tube(s) which effectively isolate the individual sources of vented gas to eliminate the possibility of pressure communication between sources. Typical sources for vented gases are reciprocating compressor rod packings, compressor cylinder distance pieces, actuators, valve positioners and other instrumentation and source components on and off the compressor skid. To facilitate the operation of the embodied invention, a high pressure motive gas of 350 to 500 psig would be supplied from an appropriate point in the gas compression or production process to ensure correct ratio of motive to suction gas for effective ejector operation. Motive gas pressure would be controlled by a pressure regulating device and connected to each individual ejector via an operated valve. These valves will be opened sequentially and Date Recue/Date Received 2020-04-29 corresponding ejectors activated as warranted by suction gas pressure and system design parameters. As the motive gas enters and passes through the ejector, gathered suction gas volumes are drawn in, the ejector will then discharge the combined high pressure motive gas and low pressure suction gas volumes at a design controlled pressure into fuel gas system of a natural gas fuelled engine. Uniquely, the gas discharged will not require any significant capability modification to existing engine fuel gas systems beyond provisioning a connection port. Discharged gas volumes are introduced downstream of engine fuel gas pressure regulators on turbocharged engines at a pressure sufficient to admit discharged volumes into existing fuel gas streams. Introducing discharge volumes upstream of engine fuel gas pressure regulator(s) will also be an option primarily on normally aspirated engines.  Original equipment combustion air and fuel gas management systems will continue to function as intended. The addition of air to fuel ratio control systems is not required as existing engine fuel gas pressure and volume control devices are sufficient to maintain desired fuel supply as intended in natural gas fuelled engines of all combustion types, including but not limited to lean burn, lean turbulent, lean pre-chamber and conventional rich burn designs (stoichiometric). A method of sequentially activating and deactivating the ejectors allows for variable flow volumes. A flow control computer with programmable and configurable Al &  DO may be used to manage control of motive gas activation solenoid valves, suction gas pressure sensing and metering, system alarms and communication. A simple control system might be preferred;  such as an electric switch gage or electric pilot controller with milliamp input and output triggering a relayed actuator. Two or more ejectors would be sequentially activated as initiated by suction pressure ranges and required system throughput capacity. Ejectors will be of a constant-area double-choke subsonic configuration and engineered and arranged to function under variable and unique design conditions. Should unusual discharge conditions or hinderances occur, or a sudden burst of suction gas volumes larger that total system design capacity, a set-pressure cracking check valve will open and release suction gas to vent or flare.  Should vented gas volumes reduce to a point where negative gauge pressure may be realized, a recycle device is employed to provide a method of maintaining a minimum suction pressure by routing a portion of ejector discharge volumes back into device suction port.  A pressure relief Date Recue/Date Received 2020-04-29 valve exhausting to atmosphere or flare is a last fail-safe should discharge pressures reach a critical high value. This invention would be more attractive than current market offerings of vent gas evacuation via electric drive vacuum pumps or compressors; lower operating costs would be expected as there are no rotating components such as electric motors or positive displacement compressors that require lubrication and life-cycle wear maintenance. Lower capital costs would be expected as there will be no requirement for A.C. motor electrical supply to be installed. The embodied method of introducing vent gas volumes into the engine fuel gas supply rather than engine combustion air is preferred in that existing engine fuel pressure regulation devices are sufficient to maintain intended engine operability, no additional air to fuel ratio control systems are required as would be with vent gas into engine air intake systems. In addition, utilization of a ejector inherently produces a suction or vacuum effect at the vent gas inlet port whereas other system use a differential pressure at engine air intake downstream of air filter(s) to vent gas and may cause an undesirable backpressure on venting systems and components. Other attributes of this invention include provision for the safe operation and control of this apparatus in a multitude of gas compositions, site specific pressure and volume conditions and control scenarios. A vacuum breaker in employed to manage minimum inlet pressure with make-up volumes recycled from the discharge stream. A back pressure regulator will provide constant discharge pressure and stable throughput volumes to minimize existing engine fuel gas pressure regulator, fuel valve and air fuel mixer actions. It is required the fuel consumption volume of the engine be of a volume large enough to accommodate the additional system discharge volume. To that end, a means to manage system engagement and disengagement is required. On a turbo charged engine sensing engine manifold boost pressure is an effective method; set point calculation will initiate system to operate only when engine load is sufficient to warrant the introduction of system discharge gas volumes into the engine fuel piping downstream of the fuel gas regulator. On naturally aspirated and draw-through carbureted engine arrangements, system discharge volumes are Date Recue/Date Received 2020-04-29 introduced upstream of fuel gas regulator; an aspect of the means and system embodied herein is a high discharge pressure switch which will prevent system discharge flows until engine fuel system pressure drop to a point low enough to satisfy switch and initiate system operation. All configurations will require one or more ¨ depending on applicable codes or regulations ¨ fuel gas shut off valves be installed to prevent any possible flow of fuel gas at unit shut down events. The ubiquitous limitation of variable volume capability through a single ejector will be eliminated by optionally utilizing an arrangement of two or more ejectors individually sized to application and activated into duty as variable requirement demand and programmed control philosophies dictate. This innovative approach to capacity control allows significant turn-up and turn-down vent gas volume capture and throughput to containment recovery. By activating additional ejectors in a parallel arrangement based on suction pressure value measurement this apparatus will successfully manage vent gas volume increases and decrease while minimizing over-pressure atmospheric releases and low volume recycle actions. Date Recue/Date Received 2020-04-29