ARTang Pressure Transmitter Measures Steam Pressure in Power Station

Pressure is the second most frequently measured process variable in industrial processes, following temperature. Reliable pressure measurement of liquids, steam and gases is an important prerequisite for both the optimisation of procedures and the efficient use of energy and raw materials.

Whenever liquids or gases are moved, stored or processed, values such as (gauge or absolute) pres-sure, differential pressure, level and flow must be measured precisely and reliably. Pressure measurement devices are therefore subject to high requirements.

The amount of energy required to generate steam with a certain pressure in a closed vessel can be calculated from the enthalpy of water plus the vaporisation heat at the respective pressure. The enthalpy is the difference between boiler water temperature and boiling temperature, multiplied with the specific heat and density.

Since steam boilers are under pressure, differential pressure transmitters (e.g. ARTang type AED23) must be used for level measurement in order to compensate for the vessel's overpressure.

To make sure during this differential pressure management that hot steam does not condensate at the colder offset side of the transmitter in an undefined way, leading to a changing water head, a condensate offset vessel is usually added to the measurement system.

Due to the condensate vessel, the water seal/water head on the offset side of the transmitter always has a constant level. This water seal also serves as a reliable temperature barrier which protects the transmitter against the high steam temperature. In the condensate vessel, the water vaporises and accumulates up to a defined, constant level. Excessive condensate will flow back to the vessel.

To make sure a transmitter can be de-installed for inspection without any problems, a triple valve block is installed directly before the transmitter for differential pressure measurement.

This allows the pressure, which may vary between the individual connecting pipes, to achieve identical pressure values through the counterbalance valve while the process is reliably shut off by means of the other two valves. At the same time, the transmitter can be removed from the measuring point without interrupting the process.

When measuring steam, a quintuple valve block combination, i. e. a triple valve block with two separate exhaust valves, is preferably connected in front of the transmitter. In contrast to a compact quintuple valve block, the sepa-ration of the exhaust valves prevents hot steam from getting in contact with the transmitter when exhausting the pipes, thus causing damage to the transmitter.

ARTang pressure and differential pressure transmitters are used for standard applications as well as for demanding applications in automation environments, for monitoring and for safety-related measurements with SIL certification. Hart 4…20mA or Modbus communication are available. The measuring error of the transmitters is 0.075, 0.01 or 0.2 % of rate, depending on the requirement and type.

If you would like any more information about our Pressure Transmitters, please contact us.