Piping Design For HE Upgrade

[bldickin]

I was charged with replacing a shell and tube (single pass, counterflow) Heat Exchanger with a plate and frame heat exhanger. The plate and frame is 1/3 the length of the old, will have 14" piping, and has all connections on one side. The old HE had 20" for the hot side and 26" for cold with connections on both ends. My question revolves around placing reducers in the current system to make it down to 14". The cold side doesn't matter as much because that system has double capacity needed. The hot side however (20" to 14" reducer needed) will need more thought. The current system on both sides has a 20" gate valve to about 3' of pipe into the HE. The new system will have a gate valve then 25' of pipe and a couple elbows into the HE. Would I be better off keeping the 20" gate valve (in good condition) necking down immediately after the valve and making my run in 14" ( cheaper pipe wise) or necking down closer to the HE, or necking down with the longest run immediately following the reducer? I am not worried as much about the pressure drop across this part of the system as I am the wear on the valves and elbows and the flow characteristics as it enters the new HE.

Thank you for any insight.

 

[GHartmann]

First I would want to look at the velocities and relative pressure drops (dp / 100 ft) in the larger lines. Many times the shell and tube exchangers will have oversize nozzles to limit impingment on the shell side. The tube side nozzles may just match the bundle diameter.

Depending on how the velocity analysis looks, you may want to consider asking for some oversized nozzles on your plate and frame exchanger.

I think you answered your own question based on your assessment of your pressure drop restritions.

However, given the large differences in size I would want to look closely for any case requiring the larger line sizes. The original lines were sized as 20" and 26" and I would want to look into that.

Good luck