Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
(OP)
Dear all,
In my design, water will be heated by hot gas from liquid state to gas state to get high temperature steam.
In order to meet the compact requirement, is there a possibility to complete the whole heating process inside just on shell and tube HEX?
I am using the Bell-Delaware method to design the HEX, and am now confusing about how to deal with the calculation.
The water side will experience three phases and could you please give me some advice about how to conduct the calculation, or show me some reference materials on this issue?
Thank you.
In my design, water will be heated by hot gas from liquid state to gas state to get high temperature steam.
In order to meet the compact requirement, is there a possibility to complete the whole heating process inside just on shell and tube HEX?
I am using the Bell-Delaware method to design the HEX, and am now confusing about how to deal with the calculation.
The water side will experience three phases and could you please give me some advice about how to conduct the calculation, or show me some reference materials on this issue?
Thank you.





RE: Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"
RE: Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
RE: Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
Typical design process is to split up the HX into these 3 heating duties and evaluat ethe HX area to derive the surface area required for each - a few iterations of the entire thermal calc may be required to match estimated terminal temps in each zone to match the calculated - quite involved if you do this manually.
RE: Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
RE: Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
Your "feedwater" to this "boiler" will have to be regulated and at proper pressure when entering. Not sure what pressures are involved here, but you may need a high-head pump and valve, similar to the feedwater valve on a high-pressure boiler. Now, how to control the pump??? On/off, continuous with VFD or small bypass??
Will this water need to be pre-heated/deaerated and chemically treated?
Low water cutoffs, similar to a boiler?? What happens if the unit is dry with only the hot gas and then you introduce water? Will there be thermal shock or violent flash?
What regulates the hot gas into the heat exchanger? I'm sure it doesn't run wild.
As you mentioned, you are in the process of sizing the unit. Sounds like this hot gas will not condense during this process, so you are limited to a sensible temperature change on the hot gas side, which may require a lot more heat transfer area that you think.
I'm sure I am missing some other safety items (like relief valves and other controls) but this is all I can come up with on the spot.
RE: Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?
If you do not have a lot of available pump pressure, then the device would likely need to be subdivided into at least 2 systems, with at least one intervening mix header. The likely location of the mix header would be at the saturated steam location, but designed to permit occasional 2-phase flow. One such header design is the water fed from the upstream circuit feeds the bottom centerline of the small intermediate header, and the header discharges to the second section through tubes along the side centerline.
"Nobody expects the Spanish Inquisition!"
RE: Is it possible to complete the whole preheat-evaporate-supheat process inside just one HEX?