Equalizing line between two steam "polishers" connected in parallel

[Mike4chemic]

Hello,
In our power plant we have two similar steam "polishers" connected in parallel installed upstream of a Steam Turbine.
Due to asymmetry of the polishers inlet two-phase (steam quality is about 99.8 % w), and steam outlet pipelines ,the polishers are operated at the different loads. The pressure drop difference between two polishers (vapor phase) is about 2 psid.
As a result (I assume), the polishers are operated at the different liquid level ( please see the attached scetch).
There is 20" equalizing line connected between two polishers.
What is the optimal way to equalize liquid level between two polishers ? Why the existing equalizing line does not solve the problem ?
Due to layout accessibility we can't install the throttling valves at the separators inlet and steam outlet side.

Thanks in advanve,Mike

 

[BigInch]

Looks like it might work better in equalizing liquid levels if the balancing line was connected to the bottoms of the two vessels.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Mike4chemic]

BigInch,
Thanks for your reply.
The question is if the balancing line connected to the bottoms of the two vessel as you suggested can equalize levels between the two vessels operated at the different vapor pressure? The 1st separator is operated at 236 psig (separator with high liquid level), 2nd is operated at 238 psig (low liquid level). The pressures are measured at the vapor phase.
My thought was to install a throttling valve at the condensate outlet from the low level separator and thus to equalize level with the high level separator. Can it help?

Thanks in advance, Mike

 

[BigInch]

I'm outside of my area with steam, but I'll try to help anyway. At least until somebody else kicks in.

What do you think is causing the difference in liquid levels?

Is the cause thermo related, more steam condensing on one side than the other, due to temperature. Are both vessels at the same temperature?

What's the 322 & 278 numbers? Unit looks like "kpm", but I don't know what that unit represents.

Is there some difference in piping symetry that could be responsible?
What's the physical layout look like?
Both tanks at the same elevation?
Is there a difference in the height of A's liquid surface level vs the B tank.



"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Mike4chemic]

I'll try to explain the issue more clearly. We have two steam/water seaparators located upstream of a steam turbine. It function is to separate steam (quality about 99.8 %w) from traces of water before entering to the steam turbine.
The separators are connected in parallel but due to asymmetry of the steam inlet and outlet lines are operated at the different steam loads. My assumption is based on the measurements of the steam flow from each separators. The 1st separator recieves about 322 kph(146 t/hr) of steam and 2nd separator recieves 278 kph (126 t/hr) of steam. The separation pressure inside the 1st separator is 236 psig and 238 psi inside the 2nd separator.
As seems to be the difference of the pressures stems from the different steam loads/pressure drop throught the separators.
The separated condensate is collected at the bottom part of the separators and evacuated by pump. Condensate outlet lines from each separator connected together upstream of the pump.
There is a difference in the height of 1st separator liquid surface level vs the 2nd separator. 1st level is about 67% and 2nd is 35%.
Both separators are at the same elevation.

 

[BigInch]

It would appear to me that you must install some kind of a restriction in the line from "A", or install a balance line below the minimum liquid levels in the tanks.

I think if the flows are not balanced, even if you did manage to equalize the condensate levels, you would soon develop more condensate in A than B once again.

Will they not equalize levels when the condensate pump suction valves are open, but the pump is stopped? I think they would, as long as those line diameters were large enough.

If the tanks are at the same level, then a 2 psi difference in operating pressure would account for about 2 psi / 0.43 psi/ft = 4.65 feet of difference in condensate surface level elevations. Is that what you see now?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Mike4chemic]

You meant we need to install some kind of a restriction in the line from "B" (low level separator),not from "A" ?
The phenomenon of the different levels also exists when pump is run and is stop. Therefore, as I wrote before, my thought was to install a throttling valve at the condensate outlet from the low level separator "B" "to add" 2 psi pressure drop and thus to equalize level with the high level separator. Can it help?
Why a balance line installed below the minimum liquid levels in the tanks would help,since now the separators connected together from the liquid side and it does not help.

 

[BigInch]

I am feeling like the imbalance in liquid levels is caused by a NON-symetrical piping arangement.

The steam flow:

Install a restriction in the 322 kpm steam outlet line to slow the flow in the A system, that will increase the flow through the B system.

Condensate flow:

For pump out, install a restriction in the condensate line from B and that should increase the condensate taken from A.

Is the condensate pump running continuously?
Is the difference in fluid levels near my calculated value of 4.5 feet?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Mike4chemic]

Yes,The pump pump running continuously.The difference in fluid levels is about 5 feet.

 

[1gibson]

Equalizing pressure is only part of the solution. The assumption that a line connecting them will equalize liquid levels is only valid if the vessels are at the same temperature. I assume that is not the case?

 

[BigInch]

I think that they are very nearly the same temperature, since they have nearly the same pressure and I've already explained the difference in liquid level by only considering the pressure difference.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek