4 replies to this topic

[wnovaes]

Hi everybody,

How to calculate the minimum booster discharde pump head available in a top high elevation distillation column condenser to avoid gravity flow in return line from exit nozless condenser and how to determine if the condenser is won't in vacuum due the discharge block valve was closed.

Thanks,
William Novaes.

[sgkim]

Instead of increasing the pressure, i think you have to increase the flow rate to the point at which the frictional pressure drop in the CW return line becomes just the same as the static differential pressure from top to the bottom regardless of the system pressure:

(ΔP)static difference ≤ (ΔP)frictional pressure drop in the return pipining at the maximum gravity flow...(1)

If the flow rate is too high to meet the equation (1) then you have to throttle the block valve attached to the CW return header on the ground level to increase the frictional pressure drop thru the valve so that,

(ΔP)static difference ≤ (ΔP)frictional pressure drop in the return piping at present flow + (ΔP)valve pressure difference at present flow ..........(2)

You'd better resort to the latter method.

[wnovaes]

sgkim,

Frist, I thought that as well. But, I wasn't sure. I was in mind to place a Flow Obstruction (Orifice Plate) within the end of the cooling water returne line. Because, to increase the flowrate to balance the friction loses and static head to avaoid the gravity flow in my case is not a good idea therefore the steam consumpition in the collumn reboiler will increase as well.

Thanks,
William Novaes.

[sgkim]

Hi, William Novaes

You don't need to increase the supply pressure. Just increase the return header pressure at the ground level above the static pressure of the return line. Lots of plants solve these problems by locating the CW return end tips in the cooling tower slightly above the highest condenser elevation in the whole plant.

If not, you can't very well increase the pressure at top. The system pressure cannot be incresed by feeding at smaller flow than the discharge flow from a vessel open to atmosphere.

sgkim

Hi!
You can simply provide a funnel at the condenser water discharge at a level just above the condensor. The water will enter the condenser at a pressure above its required pressure drop + discharge head above the condensor outlet. From the funnel it will return by gravity to the cooling tower. This will avoid any suction in the condersor. While you supply cooling water from same pumps to different heat exchangers at different levels, you run the risk creating a syphon at the top most unit. You need to throttle the flow to all units to ensure that water is reaching to the top most unit and it is getting discharged freely into the funnel to avoid any vacuum creation in the top most unit.
Bye

Tirtha

Hi, William Novaes

You don't need to increase the supply pressure. Just increase the return header pressure at the ground level above the static pressure of the return line. Lots of plants solve these problems by locating the CW return end tips in the cooling tower slightly above the highest condenser elevation in the whole plant.

If not, you can't very well increase the pressure at top. The system pressure cannot be incresed by feeding at smaller flow than the discharge flow from a vessel open to atmosphere.

sgkim