Efficiency of radiant section of steam reformer

[dhproeng]

I want to calculate the efficiency of radiant section of steam reformer but from process side when i calculate the heat of reaction for steam reforming reaction and shift reaction it increases than supplied from fuel side. Please anybody can help me in this regard how to calcultae heat of reaction for reactions taking place in reforming.

Thanks

[ibrahim]

I think you are missing something in those calculations. First evaluate the heat of reforming reaction, based on delta conversion of methane and higher hydrocarbons. Same calculations will be done with shift reaction. Remember to incorporate proper percent conversions. Heat balance of other side would be critical as you would also have coils installed in that reformer. So if you have any temperature measurement at outlet of radiant section, that would help. Calculate fuel energy based on LHV of that composition and evaluate heat transfer based on delta T. The delta between both values will dictate the efficiency.

hope this will help.

[whaider]

Can you post some details of your specific case.
As It seems odd to me.

[dhproeng]

Thanks for ur concern,
I have calculated heat of reforming reaction by the differnce of heat of formation of products and reactants and also include the sensible heat at reformer temperature i.e. 1450 F. While feed is entering at 850 F. Reactants will go from 850 F to 77 F then break and then form the products and will absorb heat to 1450 F. Refrence is David M. Himmelblau, Basic Priciples and Calculations in Chemical Engineering (6th Edition), page # 444-450. OR Chemical Reaction Engineering by Levenspile, page # 208.
But this gives me higher answer as compared to input. Is there some differnce for heat of reaction for equilibrium reactions and also can u tell me the heat of reaction for reforming reaction. The given in literature is very low.

[whaider]

You are right in your approach.
Can you give me following data and I may be able to send you a spread sheet.

1) Reformer inlet analysis (Wetbasis)
2) Reformer outlet analysis
3) Flue gas analysis
4) Flue gas temperature before any convection coil & after radiant section. (SInce these temperature indication are unreliable mostly you may consider to verify these by heat balance across 1st convection coil)
5) Fuel gas flow and composition
6) Temperatures reformer inlet and outlet
7) Process gas flow rate

[dhproeng]

Reformer inlet analysis (Wetbasis)
N2= 2.26%, H2= 1.07%, CH4= 20.45%, Ar= 0.0048, CO2= 0.469% C2H6= 0.2417%, C3H8= 0.0641%, n-C4H10= 0.015%, i-C4H10= 0.016% n-C5H12= 0.0055, i-C5H12= 0.00764 %, C6H14= 0.0629%, H2O= 75.31% Total Lb-Moles= 7066.4
2) Reformer outlet analysis
N2= 1.75 %, H2= 39.73%, CH4= 5.69%, Ar= 0.00373, CO2= 6.42%, CO= 5.10 %, H2O= 41.27%
3) Flue gas analysis
We only measure O2= 4.60 % and CO2= 8.42 % others are found by assuming excess oxygen at inlet and equalize CO2 % by material balance.
4) Flue gas temperature before any convection coil & after radiant section. (SInce these temperature indication are unreliable mostly you may consider to verify these by heat balance across 1st convection coil)
1748.86 F
5) Fuel gas flow and composition
N2= 8.23%, CH4= 87.971%, , CO2= 2.019% C2H6= 1.039%, C3H8= 0.276%, n-C4H10= 0.0066%, i-C4H10= 0.0069% n-C5H12= 0.
024%, i-C5H12= 0.033 %, C6H14= 0.279%, FLOW 457090.63 SCFH, 1206.04 Lb-moles/hr as 1 Lb-moles= 379 SCFH at our codition.
6) Temperatures reformer inlet and outlet
Reformer Inlet= 900 F, Tube Outlet Temperature= 1445, Transfer Line = 1465 F
7) Process gas flow rate
1744.03 Lb-moles/hr

Thanks for ur concern, any material from ur side will be wellcomed.

[ibrahim]

apart from what whaider is doing for you, you can use following figures that i used to use during my rough calculations;
heat of reforming reaction, based on CH4 delta only: 88700 BTU/lb-mol at 900°F
heat of shift reaction, based on CO2 delta only: 17700 BTU/lb-mol at 900°F
Only add sensible energy for 1450 - 900 F. although it will be rough calculations yet it will give you an idea of where you went wrong.

[ibrahim]

and yes, delta is the difference of their dry basis compositions at inlet and outlet of reformer.

[dhproeng]

please Mr. whaider, can u send me the spread sheet. My email is w4u734@gmail.com thanks for ur concer

[dhproeng]

Mr. Ibrahim, u r saying that heat of reaction at 900 F, it means reforming reaction starts at 900 F while literature says that it starts at 1200 F, pls. clarify that at what temperature reaction starts and where equilibrium plays its role and in sensible heat which contenets will be cosider for calculation from 900-1400 F.