Thermal Expansion Valves and Pressure Control Instead of Temperature Control

What sort of equipment do "they" operate? What are "their" processes?

My questions concern the process of an oil and gas plant.

The TXV is at the outlet of a heat exchanger, the fluid inside is HC condensate which is being heated.

The pressure control which I talked about is at the outlet of a condenser with sour water as the fluid inside. I realised that pressure transmitter has been used at this place instead of temperature transmitter, although it is the temperature which is supposed to be measured. Someone told me it's because of the sensitivity of the case and that it's difficult to control the temperature, but pressure is preffered as it gives a wider domain in controlling. They are afraid with a small delay in temperature measuring and controlling, the pressure might suddenly go down and vacuum happen.

I want to know where are the places in which this kind of controlling is preferred?

Thank you

Not off topic. It's of high relevance to the original posted question.

Without access to a P&ID, it is only possible to state that the location for such control is at similar sorts of installations where these particular fluids and heat exchange is taking place.

In a single component closed system pressure and temperature are uniquely linked. Controlling pressure controls temperature. Mechanical pressure responsive valves can act immediately locally.

The simplest example is a domestic pressure cooker. Though it is the temperature that cooks it is a dead weight pressure regulator that is used as a control element.

bioramani

Concerning the pressure control: On Condensing Units which are prone to be in a positive or negative pressure state. Level is often measured here as well through differential between High & Low (wet or dry) This is seen more often on condensers off of steam turbines.

1. The thermal relief valve is provided to allow the expansion of the entrained liquid if the inlet and outlet valves are closed by mistake and heat exchanger is put on. Liquid being incompressible can damage the equipment on closed heating.

2. Pressure control and temperature control are different functions. In the case of some fluids pressure control will also lead to temperature control as in the case of saturated steam.

Controlled Pressure is part of the stablization process of products in some materials during the manufacturing process.

Expansion valves are used at the out let of a condenser of a refrigeration machine to regulate the flow of the liquid refrigerant and to reduce the condenser pressure to evaporator pressure. It is constant enthalpy process.In reverse Carnot cycle turbine is used for expansion.

In a distillation column temperature and pressure are directly related, if you fix one the other is also fixed. A change in the temperature at the reboiler will cause a change in temperature of the overheads, eventually and by the same amount, but it will also change the pressure, but one would see the change in pressure more quickly than a change in temperature of the overheads. I believe it is more desirable from a control point to use pressure over temperature when the components being separated by distillation have very close boiling points.

The thermal expansion valve is a safety valve, in case of blocked in flow, the cooling fluid will be relieved if.