When we use DP Transmitter for measuring drum level, why we install condensate pot in the line from the upper tapping. Which line should be connected to H and which line to L of the DP transmitter

 

The purpose of condensate pot in the upper tap of the drum is to condensate the steam/moisture inside the pot into liquid, by this way it will keep the level of liquid on the H line of the DP transmitter.

regard,
fx bambang

 

Dear,
The answer to your first qs when we use dp transmitters for drum level. in the past we were using dp transmitters all the way and now a days there other types of electrode measurements for this purposes. so measuring the level in steam drums with dp tx are conventional. It is not necessary to use dp tx and there are no specific guide lines to use dp tx for level measurements.

Answwer to the second qs is:
to put the condensate pot in the upper leg which is called high leg in this application. this is reverse in non condensating vapour closed vessel level measurements for which high leg is bottom tapping.

First off all u should know the measurements of levels.
1. open tank level measurements: only one leg is envisaged a dp transmitter high is connected to the tapping.low is left to the atmoshere. or a low range gauge pressure transmitter can also do the purpose.

2. Closed vessel non condensate cvapour liquids measurements: if a dp transmitter bottom tapping is connected to high and top to low of the tx. no condensate pot is required.

3. closed vessel condensate vapour liquid level measurements : a dp tx with a condensate pot on top tapping connected to the high of tx and bottom tapping to the low of the tx.

now ur qs of condensate pot in the upper tapping for closed condensable vapour liquid level measurements is ...to fill with the water drawn from the lower tapping after the flushing maintenance of the tx and while startups, and after shutdowns etc and stabilizes the liquid all over the upper impulse line by closing the upper tapping valve.

here the qs is why u need to pour and fill the liquid in upper tapping??? why we just leave the upper tapping impulse with out filling the water??? u can leave like this and allow the condensate to form while the convection of vapour heat takes place to the atmosphere and vapour condensates on it is own, this process may take long time and while this process u may not able to read the tx reading correct. and also allowing hte hot steam may damage the tx diaphram. ther eis another usage of the condensate pot as seal pot to isolate the process from reaching the tx element.

finally by filling up the upper leg with the liquid is to eliminate the error by liquid condensation in the upper leg.
so by filling it up with the liquid and callibrating tx as req u will get the right out put.
ok by by conact me if u have any more doubts on this.

 

For this application, Are there particular reason to put the dp tx high to the top tapping?

 

u always talk about steam getting condensed inside the condensate pot. why not the other way? isn't there any possibility of water inside the H leg being vaporized absorbing heat from steam. In that case the water level of H leg will not be a constant. can u plz give me an explanation since i really want to solve that to my self

 

> u always talk about steam getting condensed inside the condensate pot. why not the other way? isn't there any
> possibility of water inside the H leg being vaporized absorbing heat from steam. In that case the water level of H
> leg will not be a constant. can u plz give me an explanation since i really want to solve that to my self

At the pressure (equal to drum pressure) and the temperature at which the H leg is, steam will condense. The excess condensate will drain back in to the drum, thus maintaining constant level in the H leg.

 

The issue has to due to the impulse tubing from the process taps to the DP transmitter. Since variable liquid levels on both sides of the transmitter will affect the differential pressure reading, you need to ensure one side remains constant. That side is called the reference leg, and a condensate pot is attached to ensure sufficient steam condenses to maintain a set level. Therefore, the only changing level is the drum level.

Since most people want drum level indication to numerically increase as level goes up, the low side of the DP transmitter is attached to the reference leg, while the high side to the lower tap on the boiler (reference leg goes to the high tap).

The transmitter is generally calibrated in "H20 and runs from a negative value "height of reference leg" to zero. That value is often converted in the control system to provide a zero indication at normal operating water level (or some variance thereof).