API PLAN 23 - Cooler configuration

[planck121]

Hi,
For API plan 23 in boiler feed water application or any application in general. Is is better to have the cooler orientation horizontal or vertical. Is there a preference for one over the other (i.e in terms of rate of cooling etc) or are both orientations acceptable (any documentation mentioning this) I know API 682 has no mention explicitly.

Secondly, I have seen a block valve on some horizontal cooler configurations on the outlet line from the seal to the cooler. What is the purpose of the block valve. They are not there on the vertical. If it is to do with venting. Can you not vent the horizontal without a block valve. Because there are application where the block valve is not there on a horizontal cooler and they still work or vent fine.

Thanks

 

[JJPellin]

We allow coolers to be installed in either orientation. I personally prefer the horizontal arrangement. I have never seen any documentation that gives an explicit preference of one over the other. We require the additional block valve in the horizontal installations in order to make sure that the cooler is properly vented.

Our typical cooler is a coil of tubes inside a shell. The boiler feed water is in the tubes and the cooling water is in the shell. When you install the cooler in the vertical direction, every portion of every wrap of the coils in the cooler will tend to vent to the high point. Starting at any point inside the cooler tubes, it is always up-hill to the high point vent. This allows the cooler to be vented without the additional block valve.

When the cooler is installed in the horizontal direction, there is a local high point in every wrap of the coil within the cooler. It takes more flow to remove all of these air pockets. That is the reason for the extra block valve. When you open the high point vent on the top line (which should be the line from the seal up to the cooler) the flow can come from two possible directions. It can come directly from the pump seal up the top line to the high point. Or, it can come from the seal up the lower line, through all of the wraps of the coil of the cooler. Since flow tends to take the path of least resistance, most of the flow will come from the seal and not pass through the cooler. If you vent the cooler very well, for a long time, you will probably still vent out all of the air bubbles. But, it is difficult to be sure.

By adding the extra block valve, you can be more certain of getting all of the air vented out of the cooler. The block valve must be installed in the upper line such that the high point vent is between the block valve and the cooler. You should vent the high point once with this valve open. Then you close the valve and vent again. When you vent with the valve closed, all of the flow must pass through every loop of the cooler coil to get to the high point. This is a more certain vent to remove all of the air pockets. Then you should open the block valve and vent again.

I guess I prefer the horizontal installation because it seems line a shorter path with the best advantage for the thermo-siphon affect. In the vertical installation, the hot fluid has to rise up to the high point and then drop down into the cooler. Since heat tends to rise, this short section of piping is opposing thermo-siphon. I know that thermo-siphon still works in this configuration. But, the horizontal installation seems to me like it should work better. The price you pay for this advantage is the possible problem with venting out each wrap of the coil within the cooler. But, by adding the additional block valve and using the correct procedure, you overcome this possible disadvantage.


Johnny Pellin

 

[planck121]

Thanks for an excellent answer Johnny. Certainly clarifies the senereio quite well.

 

[flexibox]

Just one more thing to add to Johnny's comments, check where the cooler is mounted. I have seen cooles mounted below the Pump Centre Line and that could create other venting problems.

PS: I did not se the attachment.

 

[HoustonMechEngr]

I have a question regarding the cooling water side of the API plan 21/23 system. What is the preferred industry approach to flow control? Do you recommend a simple orifice or a flow control valve? In addition, I would think a simple flow indicator on the outlet line would be suitable (Per API 682). Do you recommend flow monitoring on the cooling water side of the system and is flow indication required on both the supply/return lines?

 

[JJPellin]

For the water side of the cooler, I see no reason to make it complicated. I prefer to orifice the water flow if any restriction is needed. In our plant the supply and return pressures are fairly stable. If there is any question about water flow, a site flow indicator on the return line could be installed. We used this on elevated applications where flow is less certain. I am not aware of any benefit for duplicate flow indications on the supply and return.

Johnny Pellin