7 replies to this topic

[process equipment]

Dear all,

Please i'm looking for practical information regarding cracking furnaces, reformers fire heaters of the most common process..like propane, ethane, naphta crackers, and the making of syngas and hydrogen. Futhermore the process principle of radiation and convection section.

Thanks in advance!

PE

[pasquale]

Hi;

For the production of syngas and hydrogen one of the main industrial process is steam reforming.

The main reactions that take place in the reforming furnace are the following (on supposing to use methane as feed):

CH4+H2O=CO+3H2

CO+H2O=CO2+H2

Moreover there are other secondary reaction as coke formation.

There are 3 kind of reforming furnace:

Top fired: with the burners on the top of the furnace near the entrance of the reaction feed

Bottom fired: with the burners on the bottom

Side fired: with the burners distributed on rows along the entire lenght of the reactor tube, this configuration allow a more efficient control of the radiant heat flux transferred to the reactor tube.

In the radiant section of the reforming furnace heat is transferred to the tubes mainly via radiation, the hot gas leaving the radiant section is used in the convection section for heat recovery purpose (steam production, feed preheating).

The reforming reactions take place only in the radiant section of the furnace.

Hope this help.

Pasquale

[djack77494]

pe,
You can find some excellent introductory material regarding the design of fired heaters on the internet. I am not in my office or I could quickly find you a link, but I know that one of the web active engineering consulting companies offers what almost amounts to a full-fledged course on heater. Perhaps another member can supply their name.
Good luck,
Doug

[muchlis nugroho]

Hi,

The steam cracking/reforming reaction is an endothermic one, thus it requires energy. For catalytic tubular reformer, the energy comes from the burners in the radiant section of the furnace (as mentioned by Paquale).

Another type of steam reforming reactor is the pre-reforming reactor. It is a catalytic fixed bed axial or radial type reactor. The process gas enters the "pre-reformer" before it cracked again in the primary reformer (the tubular type). The heat required for endothermic reaction of pre-reformer comes from a heating coil in the convection section of furnace of the primary reformer. So, the process gas (HC + steam) enters the heating coils, then enters the pre-reformer, cracked, then enters the tubular primary reformer, and cracked again. The aim of pre-reformer is to crack heavy HC gas to prolong the lifetime of tubular reformer catalyst.

There is another type of reformer, the secondary reformer/autothermal reformer. This type of reforming reactor is placed after the primary reformer. The secondary reformer is an axial or radial type of catalytic bed reactor. The function of this reactor is to reduced the unreacted ch4 of the outlet of primary reformer in to a minimum number. The heat required for endothermic reaction comes from a combustion reaction inside the reactor. So, there is a combustion reaction inside the reactor besides the reforming reaction. The combustion is coused by injection of oxygen (for H2 & methanol production the injection is pure O2, for Ammonia production the injection is air).

Recent tendency of reformer reactor development is to avoid the use of tubular reactor furnace due to reliability problems.

Rgds,
MNG

[process equipment]

Hi thanks for all the gerenal information..
its quite a bit confusion about first and second reformer. Does reaction take place in convection section. Do you know how to design such a furnace. I like to get more specific information . like studies, design, drawings, heat transfer, process modelling of heat transfer etc.

tahnks in advance

[muchlis nugroho]

Dear PE,

The reaction of secondary reformer is taking place in catalyst bed in a vessel outside the furnace. Actually, may be some reaction can happen in the coil when it absorb heat in the convection section. But it can be considered negligible since there is no catalyst inside the heating coil.

I dont know how to design a furnace for an industrial size tubular reformer, it is a proprietary things. Eventhough you can design it, you will not be able to sell it if you are not working for a wellknown company that has already design a proven well performed reformer furnace.

The process heat transfer modeling is not so hard, you can model it as an isothermal tubular plug flow catalytic reactor. Or you can add some temperatur profile gradient along the tube. Any reformer catalyst vendors may have software to model it, and you may be able to use it if you are in their customer list. But the hard one is in fluid dynamic modeling. You have to model a uniform heat distribution to all of your reactor tubes and a good flame pattern. There are plenty of reactor tubes and burners inside the furnace. And no equipment licensor would be pleased to reveal the design calculation. But theoretically you can design it if you have a Fluid Dynamic Modeling Software.

Rgds,
MNG

[pasquale]

Dear process equipment;

Attached you'll find an article about steam reforming.

It's an overview of the available processes and there are also heat flux and
tube wall temperature profile for the reactor tube.

It's a good article and in the references you'll find other surces of informations.

I hope this help

Pasquale

Rome

[process equipment]

Please help!

thanks for all useful information..because i have to model such a heater in cfd for my company. I dont have proper results because i dont have energy conservation. Somehow my model is not in balance but I tried the heat transer coeffient as boundary condition. Is there any clear guide how to specify the convection heat tranfer coeffient as boundary condition? , coz i'm confuse with the outer surface and inner surface of tubes and what is the magnitude of htc . (outside hot fluegas/inside tubes Hydrocarbon)

Thanks for any help
cheers
PE