Methods to drawdown pipe sections with the use or regulation control of flaring and cross-compression technique
A method to drawdown pipe sections with the use or regulation control of flaring and cross-compression technique. The method allows to evacuate a fluid mixture from a drawdown section. The fluid mixture typically contains a liquid phase and a gas phase. The method includes flowing the fluid mixture from the drawdown section towards a separation vessel, and then out of the separation vessel to simultaneously flow the gas phase towards a flare for burning and flow the liquid phase towards one or more pumps towards an adjoining section. The proposed method allows recovering a higher proportion of the fluid mixture, as recycled product, and therefore limiting the combustion of the gas phase towards the atmosphere.
1 . A method to evacuate a gas/liquid mixture from a drawdown section comprising the steps of:
flowing the gas/liquid mixture from the drawdown section into a separation vessel;
allowing the gas/liquid mixture to separate into a liquid phase and a gas phase within the separation vessel;
establishing a liquid level at an interface between the liquid phase and the gas phase;
flowing the gas phase out of the separation vessel through a control valve towards a flare where it is burned, while simultaneously flowing the liquid phase out of the separation vessel through one or more pumps to an adjoining section;
monitoring the liquid level;
controlling the liquid level in response to the monitored level by manipulating the control valve to adjust the flow of the gas phase out of the separation vessel and adjusting the flow rate of the liquid phase out of the separation vessel by manipulating the discharge rate of the one or more pumps in order to maintain the liquid level inside the separation vessel at a predetermined level, or between a minimum and a maximum level; and
injecting an inert gas into the liquid phase after the liquid phase has flowed through the one or more pumps, the injection flow direction of the inert gas being opposite to the flow direction of the liquid phase.
2 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the controlling step is accomplished manually.
3 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the controlling step is automated.
4 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the inert gas is nitrogen.
5 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the predetermined liquid level is between 40% and 60% of a level corresponding to 100% liquid phase.
6 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the minimum liquid level is between 10% and 30% of a level corresponding to 100% liquid phase.
7 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the maximum liquid level is between 70% and 90% of a level corresponding to 100% liquid phase.
8 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the liquid level is monitored with a level indicator.
9 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 1 , wherein the liquid level is monitored with a level controller.
10 . The method to evacuate a gas/liquid mixture from a drawdown section of claim 9 , wherein the level controller provides a feedback signal to manipulate the control valve or to manipulate the one or more pumps.
11 . A system for evacuating a drawdown section comprising:
a separation vessel configured to receive a flow of a gas/liquid mixture from a drawdown section and allow the gas/liquid mixture to separate into a liquid phase and a gas phase within the separation vessel;
a control valve controllable to flow the gas phase out of the separation vessel towards a flare where it is burned;
one or more pumps controllable to flow the liquid phase out of the separation vessel to an adjoining section while the control valve is flowing the gas phase towards the flare;
a liquid level controller configured to perform operations comprising:
monitoring a liquid level within the separation vessel;
actuating the control valve to adjust the flow of the gas phase out of the separation vessel; and
adjusting the flow rate of the liquid phase out of the separation vessel by manipulating the discharge rate of the one or more pumps, wherein the actuating of the control valve and the adjusting of the flow rate of the one or more pumps is configured to maintain the liquid level inside the separation vessel at a predetermined level, or between a minimum and a maximum level; and
a gas injection line configured to inject an inert gas into the liquid phase after the liquid phase has flowed through the one or more pumps in an injection flow direction that is opposite to a flow direction of the liquid phase.
12 . The system for evacuating a drawdown section of claim 11 , wherein the inert gas is nitrogen.
13 . The system for evacuating a drawdown section of claim 11 , wherein the predetermined liquid level is between 40% and 60% of a level corresponding to 100% liquid phase.
14 . The system for evacuating a drawdown section of claim 11 , wherein the minimum liquid level is between 10% and 30% of a level corresponding to 100% liquid phase.
15 . The system for evacuating a drawdown section of claim 11 , wherein the maximum liquid level is between 70% and 90% of a level corresponding to 100% liquid phase.