Boiler Drum Level Control

can u provide me some more details abt ur existing system?

DP cell is connected to Kent make indicator through a logic circuit. Indicator reads from -315mm to +315mm. Drum level is measured in left side and right side also. There is two different setups for measurement and control. DP transmitters are of Kent make one and are not smart transmitters.

I'm sure that Kent has a procedure to do these things, Captain. Have you telephoned them?

Dear Chlm,

I can't give you the right answer to an instrument question, since I have no experience in that field, however, I believe zero needs to be the lowest safe water level and that varies with each boiler.

"read the instructions/ call the manufacturer" (PwS)

I use DP transmitters in a laboratory setting. I'm not sure how this "constant head chamber" set-up works.

I think it makes sense to use the lowest safe water level as the zero level, not the centre of the drum.

The way I calibrate them is to connect the low side to a constant water level, say a stilling well and then I conect another stilling well or cylinder to the high side, having a point gauge for accurate water level measurement. I start with both cells at the same level and calibrate to zero at that level, then add water to the high side cylinder, measuring the level accurately each time. Then you can find a corellation between the readout and the differential water level. They are usually quite linear.

Hope this helps somewhat.

Frankston

Am I totally nuts or is your level transmitter hooked up backwards? Shouldn't the H side of the DP cell be on the water end and the L side connected to the steam end?

Is there a possibility of a condensate trap in the steam leg of your drum?

No, you're not nuts. You're absolutely right.

By condensate trap, I mean is there a way to get liquid in the steam leg of the transmitter?

Dear friends,

I think is not a problem where is ubicated the H or L capsule side , if I put the H side on the steam and L side on the water, and the system need use wet leg, when the drum level is zero, the PV showed by the transmitter will be some value as +700 mmwc.

and

If I put the L side on the steam and the H side on the water, using wet leg, when the drum level is zero the PV showed by the transmitter will be some value as -700 mmwc.

Just remember that, the Dp cell transmitter is doing this --> PV = H - L

Rosemount have a good document talking about boiler drum level

http://www2.emersonprocess.com/siteadmincenter/PM%20Rosemount%20Documents/00840-0100-4360.pdf

By the way, They have in its document the H side ubicated in the water. lol

Hope this helps

Regards

JP

It was indicated that there is a shift in the drum level measurements about 100mmwcl. Is it the shift in the normal water level? Upwards or downwards?

Please clarify.

R.Thiyagarajan.

I will look at it this way. Boiler drum consists of steam (at the top half) and water at the bottom.

The impulse line from top (steam side) coming out of the drum condenses into water, hence at a lower pressure than the bottom impulse line, which consists of steam pressure + water pressure.

Therefore this should be connected to the H side of the dP

The problem would be if someone decided to replace this level transmitter and hooked it up correctly and didn't change any of the downstream controls (which are apparently set up backwards too). Your LL shut down would actually be reporting as HH!

Still doesn't explain the shift though which is why I asked about condensate in the steam impulse line. They should be set up to handle that but...