Pressure Transmitter or Pressure Transducer

You might put the pressure transducer at the end of a fairly long run of small pipe/tube, so that the gas is cooled. There may also be various ways of putting a liquid trap in the instrument line.

In addition to #1↑, many transmitter manufacturers can offer process isolation diaphragm arrangements to keep the temperatures away from the instrument. It's worth a few telephone calls to Rosemount, Endress+Hauser, Honeywell, etc. <usual disclaimer> to discuss.

I am sorry I did not mention that Producer Gas also contains Volatile matter in gaseous form which solidifies if cooled

That's a good one Tony. I'll this too once I complete with PWS idea and come back

Are you listening to PWSlack?

Diaphragm seal isolates capillary from the process goop, fill fluid in capillary transmits pressure to transmitter, transmitter is remote mounted from hot process.

Yes Iris, I think I'll go with PWS and come back.

Iris can you throw some light on the photo and the make and details of the Diaphragm isolator? Let me confess I am a Mechanical Engineer and new to this field.

Govind,

I want to ask you the following:

As the presnt one does not work as the temperature of the gas is 500 degrees celcius <--- Below to this temperature the transmitter is working? Is this a old transmitter or brand new? Model/manufacturer?, Maybe It was designed to work with that temperature but you need to isolate the electronic housing or maybe the surrounding area of the transmitter housing increase to values not permitted by the electronic equipment or also by heat transfer directly from the process the temperature is increasing.

Can you put some photo about the issue?

Regards

JP

We are using one from China and it works for few days and then starts all the problem. I would upload the photo and the specifications of the same and it's mounting.

Whoops, I was wrong. Some vendors will spec DC704 to as high as 640°F (my mental memory value), but as Tony pointed out, the process temp was stated in °C, not °F. Dang those units. Remote diaphragm seal with capillary fill fluid is not a player.

Hey Tony, I asume the purge flow is provided through a purge regulator. Is the regulator a constant pressure regulator or a constant flow (differential) regulator?

Ideally, the purge flow rate should be constant. It is possible to use either use a constant-flow regulator, or a constant-pressure regulator followed by a needle valve, for adjusting purge flow rate. A rotameter is a nice accessory to install as well, to indicate the rate of purge flow (also to show when purge stops, if ever the impulse line becomes plugged).

If you choose to use a constant-pressure regulator, the purge gas pressure should be set substantially greater than the process pressure so that the percentage pressure change across the needle valve remains relatively small. That way, purge flow won't change much with process pressure swings.

For example, if the process pressure varies over a range of 0 to 10 PSI, a constant purge gas pressure of only 15 PSI upstream of the needle valve would result in the needle valve seeing a relatively large pressure swing (from 15 PSID to 5 PSID) as the process pressure changes by 10 PSI. However, if the constant purge gas pressure is set to something substantially greater (say 80 PSI), the needle valve will see a proportionately smaller pressure swing (from 80 PSID to 70 PSID) with the result being a more constant purge flow rate. In short, setting a constant-pressure regulator to a high pressure and using a tiny needle valve to restrict flow is a cheap way to make a constant-pressure regulator deliver a (nearly) constant flow rate.