2 replies to this topic

[abantikag]

Presently i am facing problem in deciding set point values of hot well levels in surface condenser in a power plant.We are having surface condenser  with five levels; High High,High,Normal,Low & Low Low.

 

1) Generally we try to maintain hot well level at 0 MM or normal level.

2) If hot well level falls below 0 mm, normal make up valve will open and allow DM water to condenser in order to maintain normal level.At Low level this normal make up valve will be fully opened.

3) If hot well level goes below Low Level, emergency make up valve will open to bring back the liquid level in normal level.At low low level Condensate extraction pump will trip.At this Normal Makeup Valve & Emergency Make up valve will be in fully open condition.

4) Similarly at high level a dumping valve will open and allow excess water from condenser to be dumped in Condensate Storage Tank and try to bring back the hot well level in normal value.

5) At high high level the steam inlet to condenser will be closed to avoid overflow.

 

Can anybody please tell me how can i decide the high High,High,Low , & Low Low level set point. Is there any guideline for this?

[fallah]

abantikag,

 

Suppose the overall height of the hot well is 40.00" (1 m) then the estimated level set points are as follows:

 

High High: 30.00" (120% of the Normal)

High: 25.50" (102% of the Normal)

Normal: 25.00"

Low: 7.50" (30% of the Normal)

Low Low: 3.00" (Pump Trip)

 

Note that what dictates the Low Low level set point is the NPSHR of the condensate extraction pump...

[riven]

It depends on the sump dimension and how much capacity in the sump assuming no makeup but the general levels as proposed above are ok. There are numerous examples of process design basis documents out there which will give you recommendations on this. However you could do some maths.

 

Example

On the LL level to trip the pumps, look at where your suction pipe is in the tower. Obviously the trip will not be lower than the top of the suction pipe with some margin for error. So if you are at 0.6m, makeup fails and your suction pipe is at 0.2m, knowing the evaporation from the tower (& leaks etc) and volume, you could put a mathematical basis on that. There is no reason then to do this for all levels starting from the general points as given.