Indirect / direct steam desuperheater Query 1

[nli2]

Deal all,
one query regarding to steam desuperheater.
1. system description
3rd party High pressure steam 40 barg into Plant Battery limit, reduce the pressure to 17 barg with PSV installed downstream, then feed to one dedicate heat exchanger through another control valve which controled by heat exchanger process side. this exhanger tube use copper/nickel alloy materail.
this exchanger steam consumption is pretty small, say 300 kg/hr. This exchanger is the only user for this steam, however, it is the most important exchanger of the plant.

2. facing issue
It is Superheat steam into the heat exchanger chest. then temperature quickly decreased to saturated temperature @ the chest pressure. we are losing some heat transfer area with low efficiency, but this is not an issue due to heat exchanger overdesign. The actual issue is: tube mental temperature exceeds its limit based on tube material, this is due to the superheat steam temperature, not due to the satureated steam temp @chest pressure.

We plan to design a desuperheater to solve this issue instead of change tube material.

3. Query of desuperheater.
there is direct /indirect desuperheater. for direct type, the injected condensate amount is pretty small and need higher pressure than the requried steam pressure. and i do not have such high pressure condensate and not willing to install a booster pump only for such small usage.
i am looking for any type of indirect desuperheater which may solve my issue? How doest this indirect desuperheater work? Any recommended vendors?

Any help on this query will be highly apprecited.

thanks in advance.

NL

 

[Drexl]

Hi,

I indirect de-superheater is basically a shell-tube HEX. Steam in the tubes and cooling water in the shell and some regulating equipment. I think Spirax Sarco make them on demand.

 

[nli2]

We do the hand calculation again and find the super heat is quite small, less than 4 C over the saturated temperature. This small degree of superheat can be removed readily in the first part of the heating surface. Thus, this is not an concern any more.

Drexl, Still thank you a lot for the input.

 

[25362]

If I'm not wrong in reading the tables, an isenthlapic expansion from saturated steam at 40 barg to superheated steam at 17 barg results in more than 80^oC superheat.

 

[nli2]

25362, The calculation method is based on Spirax Sarco website.

http://www.spiraxsarco.com/resource...iples-and-heat-transfer/superheated-steam.asp

Example 2.3.5 Superheat created by a control valve.

Steam property is based on ASME STEAM TABLE.

 

[25362]

To nli2, I'm sorry, you are right and I'm wrong. As I said, my weak eyes read enthalpy for the 40 barg steam and then internal energy (not enthalpy) for the 17 barg steam.