Operation of a Control Valve

Operation of a Control Valve

The Refinery process should have a mean of controlling the pressure , temperature , level through the pipelines in order to get effective separation of the gas and liquids, controlling the mentioned parameters above is done by several equipment installed in the pipelines and equipment , these equipment are divided into 3 major types:

1. Pressure Control 

Well fluids are made up of many components ranging from methane the lightest to very heavy and complex compounds. Whenever there is a pressure drop in fluid pressure, gas is liberated and thus pressure control is important. Pressure is normally controlled with a pressure controller and a back pressure control valve. Pressure controller senses the pressure in the vapor space of the vessel or tank. Back pressure control valve maintains the desired pressure in the vessel by regulating the amount of gas leaving the vapor space. 
If too much gas is liberated, the number of gas molecules in the vapor space decreases, and thus the pressure in the vessel decreases. If too little gas is liberated, the number of gas molecules in the vapor space increases, and thus the pressure in the vessel increases.
this done by pressure control valves used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. this  This enables the direct control of flow rate and the consequential control of pressure.

2. Level Control

Level controller and dump valve is used to control the gas/liquid interface and/or the oil/water interface. Most common forms of level controllers include floats, displacers, and electronic sensing devices. The controller and dump valves are constantly adjusting its opening to ensure that the rate of liquid flowing into the vessel is matched by the rate out of the vessel. If the level begins to rise, the controller signals the liquid dump valve to open and allow liquid to leave the vessel. If the level begins to fall, the controller signals the liquid dump valve to close and decrease the flow of liquid from the vessel.

3. Temperature Control

The way in which the process temperature is controlled varies. In a heater, a temperature controller measures the process temperature and signals a fuel valve to let either more or less fuel to the burner.
In a heat exchanger, the temperature controller could signal a valve to allow more or less of the heating or cooling media to bypass the exchanger.

Stewart, Maurice and Ken Arnold. Gas-Liquid And Liquid-Liquid Separators. 1st ed. Estados Unidos: Gulf Professional Pub., 2009. Print.

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