Patent RU-2768837-C1 (RU)
Inventor: ARNO OLEG BORISOVICH
IPC: E21B43/34
Filed: 2021-06-02
Granted: 2022-03-24
Abstract: FIELD: oil, gas and coke-chemical industry. 
     SUBSTANCE: invention relates to production and preparation of gas and gas condensate for long-distance transport, in particular, to automatic maintenance of density of unstable gas condensate (UGC) using turboexpander units (TEU) in installations of low-temperature gas separation (hereinafter referred to as plant) of northern oil and gas condensate fields (OGCF) of RF, supplied to the main condensate pipeline (MCP). Method includes cleaning of gas-condensate mixture coming from production wells from mechanical impurities in separator of the first separation stage and separation of gas-condensate mixture at UGC, gas and water solution of inhibitor (WSI), with subsequent removal of UGC and WSI in separator of liquids (SL). Further, the WSI is diverted from the SL for inhibitor regeneration to the inhibitor regeneration shop, and the UGC is supplied by a pump to the MCP. Weathering gas from the SL is used for own needs, or is compressed and pumped into the MCP, or is utilized. Density of UGC is monitored by APCS by means of UGC density sensor and controls it. Simultaneously, the APCS controls the gas temperature at the outlet of the low-temperature separator, automatically maintaining it by controlling the turbo-expanding assembly rotor speed, which is set by a cascade of two PID controllers implemented on the basis of the APCS of the plant. For this purpose, to the input of setting SP of the PID density maintenance controller at the output of the SL, APCS sends the signal of setting density of the UGC is supplied, the value of which is set by the service personnel. And to the PV feedback input of the same PID controller the signal of the actual density of the UGC is sent from the sensor installed at the SL output. By comparing these signals, the PID controller generates at its output the CV rotor rotation frequency setting signal, which provides the necessary cooling of the gas-liquid mixture supplied to the input of the low-temperature separator, and ensuring achievement of the required density of the UGC at the output of the liquid lubricant. Signal of this setting from the CV output is supplied to the input of the SP setting of the PID controller for controlling the rotor rotation speed of the turbo-expanding assembly. Simultaneously, a signal of the actual rotation speed of the turbo-expanding assembly rotor is sent to the PV feedback input of this PID controller from the turbo-expanding assembly rotor speed sensor. Comparing the signals arriving at the inputs, the PID controller for controlling the rotor rotation speed of the turbo-expanding assembly generates a CV control signal at its output, which is installed at the outlet of the turbo-expanding assembly turbine. Parallel to the specified cascade of PID-regulators there installed is the second cascade of PID-regulators, also implemented on the basis of APCS. This cascade controls the flow rate of the produced mixture supplied to the inlet of the installation. Each of these two cascades of PID-regulators is equipped with a Start/Stop input, by applying a logic “zero” signal, the APCS imposes a prohibition on the operation of the cascade, and by sending a logic “one” signal, switches it into operation. At that, the first cascade of PID-regulators controls the technological process from the moment of installation start-up and until then, until the working member of the KR, which controls the flow rate of gas passing through the turbo-expanding assembly turbine, reaches one of its extreme positions, is completely open or closed to the maximum allowable value. As soon as the working element of this KR is in one of extreme positions, APCS blocks operation of the first stage of PID-regulators, having sent a logical “zero” signal to its Start/Stop input. Simultaneously, the APCS sends a logic “one” signal to the Start/Stop input of the second cascade of PID controllers, allowing it to control the flow rate of the produced gas-liquid mixture supplied to the input of the installation using a KR installed at its input. Owing to such switching, the APCS maintains the specified density of the UGC supplied from the SL to the MCP. After switching control of maintaining density of UGC from one cascade of PID controllers to another, APCS generates a message to operator on transition of installation to new operating mode. 
     EFFECT: proposed method allows to improve quality of accepted control decisions at plant by exclusion of human factor from control of technological process of UGC density maintenance, reduction of probability of occurrence of complications and accidents in MCP. 
     4 cl, 2 dwg