12 replies to this topic

[User]

Dear all

please assist,

 

I have a problem with my Steam Methane reformer. The outlet temperature of both chamber is not equal.

 

The details of Reformer:

 

Side-fired reformer with two chamber with 288 tubes with 144 tubes each chamber. with 6 row of burners with each side of each chamber. each rows contains 13burners with average each burners heat-up 8 tubes.

 

Currently for chamber A the outlet temperature is about 906 while in chamber B the outlet temperature is about 913. In normal condition both chamber outlet temperature should be close together.

Some abnormalities is in chamber A there is 1 tube have been cutoff due to hotspot. while in chamber B 2tubes have been cut-off.

the tricky part is in chamber B with higher ROT less burner has been lined-u compare to Chamber A.

I couldn't get it why the ROT of chamber B can be higher than A while there is less Burner lined up.

can anybody clarify me on this.

Thanks.

 

[thorium90]

I wouldnt really be too worried about the outlet temperature difference. At such high temperatures, the probes themselves will re-radiate some heat back out and the temperature may not be 100% precise. Furthermore the difference is just 7C. Not too much worry.

 

I would be more worried about your tubes. I assume you dont have individual valves to each tubes, so when you say cutoff, it means blockage? What about the tube skin temperatures? Hot spots? Have you verified what caused the hot spot? If it is because the adjacent tube is leaking burning gas and burning a hole on that tube that wont be good and might even explain your higher bridgewall temperatures. Any sulphur problems? These tubes are expensive and you have 3 damaged tubes already.. When you have less working tubes, less heat gets removed by the reaction and therefore even with less burners lit, the temperature will be higher.

Edited by thorium90, 24 February 2013 - 12:06 PM.

[User]

We plug out the tubes during our previous TA due to its TMT value to high and the tubes skin is reddish during operation that time.

 

Our Instruments teams already check and validate the Probe is still in good conditions.

I already try to turn off as many burner as possible at chamber B but still couldn't get close ROT to chamber A.

Is there by any chance the combustion air contributed to the ROT. Chamber B combustion air we have throttle to be 50% opening only due to many burners offline.

[thorium90]

You can control the amount of air to each chamber but can you see the flow to each chamber? If you reduce the amount of air, for the same amount of fuel being burnt, the temperature will be higher. Anyway, why is there a need to get the temperature to be exactly the same? You could be more worried about the problem that caused the hotspots on the tubes. Which burners to light and how many simply depends on trying to get the right temperature for the reaction and an even profile, not really to get the same outlet temperature...

Edited by thorium90, 24 February 2013 - 12:20 PM.

[User]

If the temperature variation between the two chambers is 10degrees alarm will triggered. to avoid that thats why im trying to keep it as close as possible.

Furthermore, we will check our TMT value every two nights. One of our initiative to troubleshoot the high TMT problems is we also throttle our Fuel gas valve. Is it advisable to do so?

[TS1979]

It seems that you are really operating the unit at very high temperature. Material specialist should be consulted if the stress at this high temperature is still in the acceptable range. As for the temperature difference, I guess you can throttle the fuel gas to reduce the high outlet temperature. If the alarm is a problem, you may reconfiguration the alarm setting to eliminate the alarm.

[thorium90]

I believe your tubes are the nickel chromium niobium titanium alloys and should have design temperatures of about 1000C. To be frank, I've never heard of the rationale behind the need for a reformer safety trip requirement for a temperature difference of more than 10C between the reformer chambers. I mean I've heard of the high temperature trip but not this. Do enlighten us about the rationale behind the need for such a delta T setting?

 

Tube metal temperatures can also be high because of high plant loads. You can increase SC ratio and reduce the syngas outlet temperature. How is the deviation between tube temperatures? Any adjacent tubes with large temperature differences? Its actually not really advisable to throttle the fuel gas valves, but rather to just turn them off if that area is too hot.

Edited by thorium90, 25 February 2013 - 04:19 AM.

[User]

We wanna keep the ROT at optimum value so that we could get the Methane slip about 4.5-5.5% normally we keep it at 5%. If the ROT is unbalanced the CH4 slip would be higher.

Further more we just wanna keep the heat distribution on both chamber the same so that it wont effects the reaction Mechanism along the tubes.

 

Currently we are operating at our highest load, we wanna maximize our H2 production for downstream reactions.

We being advised by Topsoe Rep. he said that we might try to throttle our fuel gas valve in order to reduce the tendency of higher TMT and it seem to works. but the fuel gas pressure of each chamber is not balanced and its effected the ROT variation.

 

Is there any other method can be done?

 

The deviation between tubes is not consistent but there also a few tubes with same burners have high TMT value and our practise is we light off the burner we dismantle it and service it and fix back. but it seem to happen again the high TMT.

[thorium90]

You already have some of the best experts in reformer design to help you, Topsoe. Perhaps you should seek their advice. You are not using NG for your fuel? Out of curiosity, is your plant in West Port, Selangor, Malaysia?

[User]

We also seek advice from john zink hamworthy their rep said we shouldnt throttle the Fuel gas. Yup, we used some portion of NG as fuel gas as secondary.

But since John Zink and Hamworthy is already merged they hav limited expertise on reformer therefore now we are looking for another combution vendor for advice.

 

Our Plant is located at Terengganu, Malaysia.

[thorium90]

One reason for not throttling fuel gas valve is because if the flow is too low, the flame shape will not be the desired shape, ie: it adds heat to the area but does not help in achieving a desirable profile. So john zink hamworthy designed the burners and Topsoe designed your reformer. I would suggest you listen to Topsoe rep and not the combustion vendor..Operating at high loads does push the plant abit.

Perhaps you might want to put up a list of relevant operating parameters here (if possible)(SC ratio, air flow, feed flow, temperatures, pressure etc etc), others might be able to give some advice too.

[Satyajit]

Dear Misa,

                   10C delta between two chambers is not a big deal. As per Topsoe guidelines, you should try to keep close to 10C difference.

 I guess,your plant is a syngas plant ; so the primary reformer operation is quite critical having CO2 recyced to reformer.

Throttling of burners will increase fuel gas pressure and the impingement of flame as a consequences.

Reducing combustion air flow will also increase flame temperature worsening the condition.

I have following suggestion for you.

1. Do reformer survey : check excess O2 at different level, combustion air and fual gas pressure at different levels.

2. Do TMT at both sides of each chamber and make temperature plot; see your mean temp, deviation, cold and hot zones,and adjust burners.

3. Contact Topsoe technical service department for reformer evaluation

4.Keep maximum burner on line lowering fuel gas header pressure; keep combustion air full open.

5. Keep excess O2 about 2% in flue gas ( wet basis).

6. Upgrade tube materila to Microalloy with design metal temperature upto 1120C. Your current metal temp is about 1020 C I guess.

7. Keep reformer outlet temperature below 900C; allow slightly more methane slip or reduce plant load slightly.

It is possible to simulate the reformer with all data and find out the root cause for tube failure.

Kind regards,

Satyajit

Edited by Satyajit, 26 February 2013 - 01:32 AM.

[User]

Dear Mr. thorium i will comeback to you with the details.

 

Dear mr. sayajit,

 Yes it is a syngas plant.

Thanks for your advice. I will try do all that and update the results later

thank you so much for your reply.