NOVELTY - A gas purification process (P1) involves: feeding a gas stream to be purified for to an upstream side of a compression stage and compressing the gas; subjecting the compressed gas stream and liquid stream to liquid scrubbing, where the liquid scrubbing stage provides at least one downstream gas/liquid stream outputs; directing the liquid stream output to two flashers operating in series, a first flasher and a second flasher; and recycling the respective flashed gas output streams into the gas stream to be purified, either upstream and/or downstream, of the compression stage.    USE - As gas purification process useful for reducing methane slip in biogas upgrade (claimed).    ADVANTAGE - The utilization of the pressures of the flashed gases from the flashers enables the re-injection of such gases at points in the process which minimize the need to completely recompress the flashed gas to the same requirements as the raw gas inflow or input or raw supplied gas to the process. The flash units enable retrieval of desirable gaseous components to be recovered and contribute to the overall yield of a purified or processed gas stream. The flash vessel design enables the biogas upgrading plant to achieve significantly lower methane slip without compromising production capacity further.    DETAILED DESCRIPTION - A gas purification process (P1) involves: feeding a gas stream to be purified for to an upstream side of a compression stage and compressing the gas; supplying a liquid stream and the compressed gas stream to a liquid scrubbing stage, and contacting the compressed gas stream with the liquid stream, where the liquid scrubbing stage provides at least one downstream gas stream output and at least one downstream liquid stream output, and following the liquid scrubbing stage; directing the at least one liquid stream output to two flashers operating in series, a first flasher and a second flasher, where each of the flashers generating a recyclable flashed gas output stream from the liquid stream; and recycling the respective flashed gas output streams into the gas stream to be purified, either upstream and/or downstream, of the compression stage, and the flashed gas is recycled into the gas stream at the respective flashed gas pressures of the respective flashers. INDEPENDENT CLAIMS are included for the following:    (1) a gas purification plant comprising: a first compressor to receive a gas inflow, a scrubber or scrubber sequence (scrubber) to receive the gas flow stream from the second compressor and to provide a gas outflow stream (e.g. as the purified gas), a first flasher to receive the liquid outflow with any entrained gas from the scrubber, and a second flasher to receive the liquid with some entrained gas from the first flasher, where the second flasher feeds at least some its flashed gas stream as an additional infeed to the first compressor, and the first flasher recycles at least some its flashed gas stream as an additional infeed inter-stage to the first compressor;    (2) a biogas processing plant including at least two in series feed supply gas compression stages in advance of a scrubber, the provision of two downstream and in-series flashers, each providing a gas recycle feed at different pressure to allow: the recycling of gas from the first and downstream more flasher, at a pressure more compatible with the inlet pressure of gas at the first compression stage, to the first compression stage, and the recycling of gas from the second and upstream more flasher, at a pressure more compatible with the inlet pressure of gas at a second compression stage, to a second compression stage;    (3) a biogas upgrading system comprising: a lower operating pressure second flasher downstream of a higher operating pressure first flasher, and a recycle gas output from which is at least partially fed back into the system for introduction into the flow of feed supply gas entering a first compression stage of the system;    (4) a water flooded screw (WFS) type compressor including an additional intake for a recycle gas feed;    (5) a biogas upgrade system comprising a scrubber upstream of multi stage flashing taking place in at least two flashing vessels and a stripper downstream of the multistage flashing, where a first and second of the flashing vessels are in a vertical disposition relative to each other and/or the stripper and/or flasher to tend towards operating the system with minimal slip; or a first and second of the flashing vessels are in a vertical disposition relative to each other and/or the stripper and/or flasher to tend towards operating the last of the flash vessels at or greater to the pressure at the outlet of the preceding flasher less static pressure head defined by the vertical disposition; or a first flashing vessel is located below a second the flashing vessels that is downstream of the first flashing vessel; or a first flashing vessel is located at a vertical disposition relative a second the flashing vessels that is downstream of the first flashing vessel such that the operating pressure in the first flashing vessel is higher than in the second flashing vessel; and    (6) reducing the operating pressure, in a multi stage flash process of a biogas upgrade system that includes at least two in series flash vessels, in a downstream of the flash vessels by placing the or the upstream flash vessels at an appropriate elevation relative to the downstream of the flash vessels.