Method of controlling flare gas recovery system

Abstract

The present invention relates to a method of controlling a flare gas recovery system, which meets all possible operational scenarios in a primary oil processing plant in a completely continuous, stable and transparent manner for the operator. In particular, the steps performed in the method proposed here include Initialization and Checking the availability of the main compressor, and Monitoring the system inlet pressure and Adjusting the compressor request. More precisely, the method described by the present invention is capable of operating in four operating modes, which comprise: a) a volume accumulation scenario for startup, referring to a system switched on with no compressor yet operating; b) a low burn scenario, referring to a system connected with a single compressor in operation; c) a high burn scenario, referring to a system connected with two compressors in operation; and d) a scenario of high sequential burns, referring to a system connected in “switch mode” between compressors.

1 . METHOD OF CONTROLLING FLARE GAS RECOVERY SYSTEM, characterized by comprising the steps of:
 Step A) Initialization and Verification of main compressor availability, and   Step B) Monitoring the system inlet pressure and Adjustment of compressor request.   
     
     
         2 . METHOD, according to  claim 1 , characterized by controlling flare gas recovery systems in:
 a volume accumulation scenario for startup, referring to a system switched on with no compressors still in operation,   a low burn scenario, referring to a system connected with a single compressor in operation,   a high burn scenario, referring to a system connected with two compressors in operation, and   a scenario of high sequential burns, referring to a system connected in “switch mode” between compressors.   
     
     
         3 . METHOD, according to  claim 1 , characterized by acting in the control of gas compression systems composed of liquid ring type compressors and their sealing accessory and three-phase separation systems, optionally composed of one or more compressors depending on the volume of gas to be recovered and the target recovery scenarios,
 wherein the systems optionally further comprise electric motors, automation panel to implement interlocking and control logic, knock-out vessels at the base of the flare to accumulate gas from primary processing and support the separation of liquid and vapor phases, quick opening valves, rupture discs, and PV valve for load control and gas recirculation from compressor discharge to suction.   
     
     
         4 . METHOD, according to  claim 1 , characterized in that Step A) initially considers an accumulation of volume to enter a steady state at the expected “startup” time, wherein the initial suction pressure is recognized at the point where it is high enough for the final discharge pressure to reach an adequate value, ensuring a steady state, within X seconds after starting the compressor, applying the real gas equation PV=n ZRT within the stipulated parameters. 
     
     
         5 . METHOD, according to  claim 4 , characterized in that in Step A) once the flare gas recovery system is connected, it is checked whether there is a compressor determined as the main compressor, so that if there is no compressor determined as the main one, the method invites the user to define a main compressor, and if a main compressor has already been determined, the method leads to the filling of the system referring to the two compressors, by the formation of the liquid ring of the compressors,
 wherein the method sequentially leads to the closure of the flare valves, with the flare gas recovery system subjected to control already in operation.   
     
     
         6 . METHOD, according to  claim 1 , characterized in that in Step B)
 after closing the flare valve in step A), the method leads to monitoring the pressure at the inlet of the system subjected to control through a pressure sensor, so that if it is identified that the system inlet pressure is greater than Ps (min), the method leads to the activation of the main compressor, and if it is identified that the system inlet pressure is not greater than Ps (min), monitoring of the system inlet pressure continues to be carried out,   wherein when it is identified that the system inlet pressure is greater than Ps (min) and the main compressor is turned on, the system inlet pressure is also monitored, so that if the inlet pressure is greater than Ps (max) and the PV recycle valve is closed for more than T seconds, the backup compressor is turned on, and if not, monitoring of the system inlet pressure remains in operation,   wherein, upon activation of the backup compressor, the method leads to checking whether the “switch mode” mode is activated, where if it is not activated, the method remains monitoring the system inlet pressure, while the switch mode is activated, the backup and main compressors are led to alternate this primary and secondary positioning, and   wherein, following the alternation between compressors, monitoring of the system inlet pressure continues to be carried out, so that it is checked whether the PV recycle valve has an opening greater than PVopen % for more than Ta seconds, where if it is concluded that yes, the backup compressor is turned off and the first analysis is returned to check the need to activate the backup compressor, while if not, the method leads to remaining monitoring the system inlet pressure.   
     
     
         7 . METHOD, according to  claim 1 , characterized by additionally and in parallel to the steps discussed A) and B), the method performs a stop control of the flare gas recovery system in a predictive way, wherein if it is identified that system depressurization is not supported by recovery, the system is forcibly stopped.