31 replies to this topic

[JArchy123]

I am required to heat water to 650oC before it enters the reactor. I was told to use a heat exchanger but what heating fluid would I use. I determined that a compressor is required to increase the steam from 1 bar pressure to 3 bar pressure as this is also required for the reactor and the outlet steam temperature of this is 389.61^oC.

[latexman]

Are you saying water/steam enters RX at 650 C and 3 barg and exits the RX at 389.61 C?

To heat to 650 C, take a look at using hot oil/Dowtherm.

[JArchy123]

For heating the steam at 389.61 to 650^oC

[JArchy123]

I had a look at the Dowtherm HTF but they went up to 750^oF 

[breizh]

Hi ,

You may want to google :Molten salt heat transfer fluid

 

With so little info it's impossible to give a meaningful answer !

 

Breizh

[Bobby Strain]

It's probably a tiny laboratory scale. So, electric heat is good.

 

Bobby

[Pilesar]

I do not believe there exists any practical process that requires pure steam at 3 bar and 650 C before being added to a reactor. If you were to provide more information, you might get a usable response. Are you trying to answer a specific question from the professor or is this a process you are inventing? What is the context? Why are you 'required' to heat water to nonsensical conditions? 

 

See above paragraph for my main comment. Secondary comments follow. 

 

1) You should never need a compressor to get steam from 1 bar to 3 bar. When steam is heated, it increases in volume or pressure. There is a 'gas law' to describe the phenomenon. Typically, steam is generated at a higher pressure and the pressure is reduced as needed for the application. You would use a pump to put water to the steam generator.

 

2) The process you describe already has a hot heat transfer medium -- the reactor contents! The reactor products will need to be cooled and heat probably can be exchanged against the reactor feed. 

 

3) Heat is going into the process from somewhere. What is the hot utility? These high temperatures can be traced back to a combustion or electrical heating or nuclear reaction. Find the hot utility and exchange heat against it. 

 

4) Is this question related to steam reforming of methane? Typically, the steam is generated at very high pressure and superheated in the convection coils of the steam reformer. Superheat is limited well below 650 C. The hydrocarbon feed is heated in a separate convection coil. Steam is mixed with the hydrocarbon feed and the mixture is then heated further to the reaction temperature.

[JArchy123]

Yeah, it is a steam reforming reaction. The lecturer told me to model the reactor as a heat exchanger (which required cooling to maintain an operating pressure of 650^oC) but he told me that I also have to model the heating of the inlet components that being methane and steam to 650^oC and 3 bar.

[JArchy123]

 

I do not believe there exists any practical process that requires pure steam at 3 bar and 650 C before being added to a reactor. If you were to provide more information, you might get a usable response. Are you trying to answer a specific question from the professor or is this a process you are inventing? What is the context? Why are you 'required' to heat water to nonsensical conditions? 

 

See above paragraph for my main comment. Secondary comments follow. 

 

1) You should never need a compressor to get steam from 1 bar to 3 bar. When steam is heated, it increases in volume or pressure. There is a 'gas law' to describe the phenomenon. Typically, steam is generated at a higher pressure and the pressure is reduced as needed for the application. You would use a pump to put water to the steam generator.

 

2) The process you describe already has a hot heat transfer medium -- the reactor contents! The reactor products will need to be cooled and heat probably can be exchanged against the reactor feed. 

 

3) Heat is going into the process from somewhere. What is the hot utility? These high temperatures can be traced back to a combustion or electrical heating or nuclear reaction. Find the hot utility and exchange heat against it. 

 

4) Is this question related to steam reforming of methane? Typically, the steam is generated at very high pressure and superheated in the convection coils of the steam reformer. Superheat is limited well below 650 C. The hydrocarbon feed is heated in a separate convection coil. Steam is mixed with the hydrocarbon feed and the mixture is then heated further to the reaction temperature.

 

Are you saying that the hydrocarbon stream requires heating but the steam does not

[Bobby Strain]

All we are doing is guessing because we don't have any information. So, we are probably of no help.

 

Bobby

[JArchy123]

What information do you need?

[latexman]

You are not sharing vital information. It took you 4 posts to tell us you are modeling a steam-methane reforming process.

There’s lots of information on this process on the www. I hope you have Googled it and researched thoroughly.

[JArchy123]

This is an individual section of the group project. We completed a mass balance and energy balance as a group and I have designed the reactor and its internal heating but just have some problems with the pre-heating of the inlet streams, that's the one problem. 

 

Basically, all I need explained is if pre-heating of the methane and steam is required before entering the reactor which is keeping the operating temperature 650^oC. So the reactants and products will be 650^oC.

Edited by JArchy123, 22 January 2022 - 09:08 PM.

[latexman]

https://www.google.c...=F2-8la4sUihW_M

There are many, many steam-methane reforming PFDs to be had. It appears the reformer in most of them is a fired unit, and there are one or more “cross exchangers” to preheat feeds and conserve energy.

[JArchy123]

It seems like a lot of the pre-treatment for the steam and methane but it looks like they aren't quite specific. For example, one says steam generator

[latexman]

And some of the reformers look like they are doing double duty to preheat feeds and reform.

[JArchy123]

I only have a certain time limit so the lecturer is trying to make it as simple as possible. A heat exchanger is the simplest one to design as it is something we have designed multiple times if something is too complicated, I don't have to design it but state what the equipment and explain it's utilisation. 

 

Also what is meant by 'double duty'?

[latexman]

See how this reformer also pre-heats the purified HC + steam and then the unpurified HC before exhausting to atmosphere:

https://www.google.c...=F2-8la4sUihW_M

It’s doing triple duty. Reformer and two pre-heaters.

[JArchy123]

Thanks for the reply. I just don't know what pre-heaters to use. 

[JArchy123]

I think the plan is to pre-heat the methane and then add the steam to the methane before it enters the reactor

[JArchy123]

Hi ,

You may want to google :Molten salt heat transfer fluid

 

With so little info it's impossible to give a meaningful answer !

 

Breizh

Also with a molten salt heat transfer fluid would the piping not need to be ceramic lined to prevent corrosion.

[JArchy123]

I have attached all the information I know below. Also One Shell, one tube pass.

Attached Files

•  Design.png   263.13KB   0 downloads

Edited by JArchy123, 24 January 2022 - 12:47 AM.

[Pilesar]

In the classic steam reformers I designed with tubular reactors, no feed was brought to reaction temperature before entering the reactor. The feeds (nat gas and steam) were heated individually in coils of the convection section of the furnace, then mixed together and heated in more coils of the convection section, then entered the reactor tubes containing catalyst in the radiant section of the same furnace where the reactants were brought up together to reaction temperature. It would have made no economical sense to heat the steam up to the reaction temperature before mixing with the natural gas. Your sketch does not seem to take account of the highly endothermic nature of this reaction. How do you intend to continually add heat to this reactor in order to maintain temperature? There are lots of examples of these reactors in the real world and your research seems insufficient.

[JArchy123]

Yeah, basically even though it is highly endothermic, it was calculated through ASPEN and by hand calculations that the reactor requires cooling (It was something like -10000 kW). Don't ask me how this is but this was something that my group calculated before the individual section of the project so I kind of have to stick with it as this is expected that we continue on with the original data. Since we have already calculated this with the feed coming in at 650^oC, I also kind of have to stick with the pre-heating of the feed before entering the reactor as this has already been established. Even though this is all wrong, I have to stick with it all as this was what was determined previously.

[Bobby Strain]

Something is drastically wrong with your calculations. If you were to peer into a reformer furnace you would observe red. So, you should start over. Otherwise you will only learn through failure.

 

Bobby