4 replies to this topic

[Danielisimo]

Hello,

 

I am specifying a Fuel Gas Performance Heater for a Combined Cycle following GE recommendations, from this document:

 

https://powergen.gep...ed-gas-fuel.pdf

 

Every equipment in this document has its explanation except why specify 2 series units instead of 1. Does anyone know the reason?

 

I was talking with a co-worker and he thinks it is a way to minimize water entering in the gas system in case of failure, but it doesn't convince me (it just can work for the first unit, water has to go through the first shell to the second one), and I find more likely a failure in the second unit because of greater temperatures.

 

Could it be related to with gas shell speed improving thermal efficiency? (i am just trying to guess )

 

thank you for your comments.

[shan]

It seems to me that the upstream exchanger(gas/steam) is to recover the steam latent heat and downstream exchanger (gas/water) is to recover the condensate sensitive heat. The two body design is to prevent tube side two phase flow.

[Danielisimo]

It seems to me that the upstream exchanger(gas/steam) is to recover the steam latent heat and downstream exchanger (gas/water) is to recover the condensate sensitive heat. The two body design is to prevent tube side two phase flow.

 

Hi Shan,

 

Thanks for your reply. I think both heat exchangers are gas/water, the water inlet (in the particular case of GE paper) comes from IP economizer, I suppose that stream should be a bit subcooled. Anyway, in my particular case, I have a water stream.

[shan]

There is steam flash out when you letdown pressure of IP condensate.

[Danielisimo]

Correct me if I wrong. I am just a junior engineer eager to learn.

 

This is what I understand:

 

In the flow diagram just after the IP inlet, there is an FV valve and another downstream of the second heat exchanger. These 2 FV are on/off valves in case of unavailability of HRSG or tube leakage. Downstream of last FV valve there is a TCV valve to control water flow with Gas temperature, and then the outlet to atmospheric condensate tank. As this is just part of the diagram, I think downstream of this outlet there is a Pressure Reducing Valve to match atmospheric pressure. So, you keep the pressure in tubes and avoid flash out and mixed flow in the first heat exchanger (*).

 

As i said, please correct me I am just want to learn as much as I can.

 

 

(*) GE paper extract: "With water pressure being higher than gas pressure, this configuration insures that gas will not enter the feedwater system following tube leak or rupture."