25 replies to this topic

[asad daud]

Hi all

Can any one tell me where to find the information about upsets faced in running of the ammonia plants throughout the world.
For example

What happens if air compressor trips during normal running.

Regards

Asad.

[pawan]

What is your objective? The Ammonia industry is so old that you can have hundreds of incidents available over many decades. So its not possible to give all in this forum as a FEED to MOUTH.

If you want to discuss any specific problem I am always ready based on my 8 years experience in Ammonia & Urea industry.

[asad daud]

Dear Pawan

You are right that there are a number of problems that could arise in an Ammonia plant.

I wanted some discussion on handling those problmes.

Lets start with the problems arising out of tripping of process air compressor.
What can be the possible affects of this tripping on the other parts of the plant?
What actions will be needed to ensure the safe operation after that?
For how long, if possible, plant can be kept in operation?
How much reduction in the front end load will be required?

If compressor's tripping is for a short time, how should air to be given back into the secondary reformer?

Pratical experinces will help me complile a set of instructions for better operation.

My best regards to everyone who will help me in this work.

Asad.

[Jiten_process]

what you are asking is very generalize topic...

visit this site...they have good information regarding ammonia plant

http://www.chemengse...h-articles.html

Edited by Jiten_process, 26 June 2010 - 10:03 AM.

[Chem01]

I have 9 years of working experience at Ammonia plant including complete re-engineerin of an old Ammonia plant. Every Ammonia plant is different in terms of some key areas including CO2 absorption.
When I was junior our GM used to ask these questions, like you have mentioend here.
Air compressor tripping has effect on second. reformer o/l temperature, immediate decrease in steam production from waste heat boiler, change in heat duty of reboilers in catacarb / benfield or mdea sections.
A decrease in CO2 in process gas forces Urea to decrease their plant load. A change in Mol.weight (as N2 source is now cut) can upset Synthesis compressor to surging and it should be tripped. Ammonia plant front end load must be decreased to avoid wastage of process gas as now Ammonia production will stop.
You must decrease plant load, and look for steam balance of your plant.
See how the mol. wt of gas is changing now after air comporessor tripping.
Check how much differenc in mol. wt is tolerated b/w recycle nad makup stage of your plant syn gas compressor.
What actions you can take at CO2 absorption section, you need to decrease circulation now. How the pressure across hydraulic turbine in benfield/catacarb section is changing?
Load reduction / increase takes time, try to maintain like 80 % load if immediate restart of air comp is possible.
At what minimum possible load you can operate your Ammonia plant with what reason?
Air introduction back into sec. refomer has some potential risks, you must always give air as per standard procedures, i.e. gradually to avoid explosion.
Plant operators do not wish to keep LTS and methanator in service if air compressor trips, you must know why..
Steam injection into air coil is also important, verify its flow by area operators, life of air coil is shorten otherwise.
Let me know if you need more info....
regards,

Edited by Chem01, 30 June 2010 - 06:42 AM.

[asad daud]

Dear Chem01

This is the right answer, which I was looking for.
You must have worked in operation side.
It will still be better if I can find some written emergency procedures from somewhere.

You must have worked at Engro or FFC-3.

I do remember that some where in pakistan, surging of process air compressor resulted in damagimg of the secondary reformer. Do you have any such information?

What are you doing at present? Can I know your name?

It will be great to benifit from your experience.
I am new to this forum, still learning to use this site.

Regards.

Asad.

[steamreformer]

Dear Chem01/pawan/jiten
Its really nice to see good explanation from all of you , well i want to start a new problem though its new for forum but in ammonia plants across the globe it take place , well do u have any reasons why the bypass control valve of reformed gas boiler in outlet of sec reformer will close fully , and if yes then what are the possible ways to solve the issue, actually if it closes fully then our control of maintaining the refomed gas temp was lost and it will effect the HTS catalyst.

Regards
sahil

[pawan]

Sahil
Again your question is incomplete. You said - Why the bypass control valve of reformed gas boiler in outlet of sec reformer will close fully - My question is what is the situation? Why it will close?

So please specify your situation & objective.

[asad daud]

Dear Sahil

Please keep in mind that there are different control methods for maintaining HTS temperature.
One of the methods is the one you have discribed here.
It is the combination of a control valve and a by pass valve.
Other methods include contol by a single valve only, with out and additional by-pass valve.

If there is a combination of by-pass and control valve, then these rules should be followed.
The usual case is that opening of the valves are so set that their total is 100 %.
If by-pass valve is 25 % open then cotrol valve is also 75 % open.
If by-pass valve is 50 % open then cotrol valve is also 50 % open.
If by-pass valve is 75 % open then cotrol valve is also 25 % open.

This is done to avoid blocking of gas flow through primary reformer, and hence avoiding low flow tripping.

Temperature is usually controlled through the combination of the openings of these valves.
If HTS temp is running low then Main control valve and by-pass valve's openings are so adjusted that hot process gas exchange less heat while passing through the waste heat exchangers, down stream of secondary reformer. Less heat exchange will increse the temp of the gas going into HTS.

Your concern is the loss of control.
This question can be fully answered if the exact flow diagram is known.
Pawan has rightly pointed out that a little more information is needed to answer your question in full.

Regards.

Asad.

[Chem01]

Asad,
Yes I have worked in operations at FFC-1. I have started my own engg company now.
I am compiling data for Ammonia plant to give free info to lot of youngsters, It may take 6 months - 1 year. A forum dedicated to Ammonia will also be started.
There was a site nh3.org that we've been referring, but the site administrator closed it. Now the site dispay, it was hijacked.

Sahil,
The waste heat boiler o/l temp control is different at differnt plants based on its design. The explaination asad has given for the 2 valves is typical for KBR/Kellogg plants. While there are other designs where only one control valve is installed at the bypass. This is the case when bypass is internal to the WHB.
The bypass closure (like any other valve) is a possibility based on its fail safe position and if instrument air fails. In some plants there is a lockup provided, which avoid its full closure, at the same plant where I was working. Emergency air supply is also sometimes provided via a cylinder to keep its position fixed. Hand jack is also installed but lock up is affective to avoid full closure.

Regards,

[steamreformer]

Dear Chem01

first of all thanks to you for starting a dedicated ammonia site and it will certainly fill the gap.

i totally agree with u and u are right, i am talking about one bypass that is internal bypass of waste heat boiler like what we have in haldor topsoe design,you give most of the possible causes for any control valve to close but my problem is that it is not a sudden closure of control valve , i am observing a gradual closure from full open to full close with in period of couple of months, certainly it is depending on the waste heat boiler temperature setpoint, my exp list certain factor for this as

1)fouling of waste heat boiler tubes
2)detachment of control valve from inside

so thats why i am looking for more reasons from you expereanced guys, i have ruled out the possibility of fouling of waste heat boiler.
as u have mentioned you have lot of data and case studies can u share with me some article on teh said subject.

thanks for all of your concerns towards solving the issue in ammonia industry

sahil

[asad daud]

Dear Sahil

Is there a load variation in your plant?
Is high pressure steam drum's pressure kept constant throughout the year?

It is not usual to consider fouling in such waste heat exchangers.
Fouling can be resulted if BFW's quality is low.
But if BFW's quality is low, it will result in leaking of exchanger because the temps and heat flux is of very high magnitude in such an exchanger.

One other thing that is coming to my mind is refractory or catalyst carry over into the "Hot" side, that is, the process gas side of the waste haet exchanger.

What is the capacity of your plant?
what are all the process conditions?

what is the range of temp drop during the normal running year?

Answering the above questions will help you look into the matter more deeply.

Regards.

Asad.

[Chem01]

sahil,
How much change you are observing in valve opening? In say last 3 months the vave has closed from 70 to 60 % or what?
Clearly the closure of this valve is unusual and you must have verified the closure physically in area.
Still your HTS inlet temp is same (how much is that?),,,,
Is there any increase in sc. reformer o/l temp?
How much steam let down has changed (let down of 100 bar) since its closure?
Try to relate any other process parameters with its closure and let us know.

Deatchment of control valve from isnide? If you can physically see the stem position has changed then there must be some process side reason.
I can try to give you case studies,,,after 10th July may be...i am on traveling these days.

Regards,

[ETHAN]

Dear members
It is great pleasure for me to join your discussion in ammonia industry ... i'm Chemical engineer in ammonia plant and i need to discuss certain troubleshooting in ammonia plant .... first of all i worked in UHDE Process-designed ammonia plant ....

my point to discussion is the most difficult situation for any plant ..... (POWER FAILURE)
what the right thing to do (Sequence of acting) during the first second after the power failure
what is the main important actions must be done after the power failure ....
what is the kind of state the plant will behave during the power failure ...
what is the right thing to do after diesel engine will put in operation automatically

i wanna catch the deadly red lines during this situations ,,,, 1 ,2, 3

many regards

[steamreformer]

sahil,
How much change you are observing in valve opening? In say last 3 months the vave has closed from 70 to 60 % or what?
Clearly the closure of this valve is unusual and you must have verified the closure physically in area.
Still your HTS inlet temp is same (how much is that?),,,,
Is there any increase in sc. reformer o/l temp?
How much steam let down has changed (let down of 100 bar) since its closure?
Try to relate any other process parameters with its closure and let us know.

Deatchment of control valve from isnide? If you can physically see the stem position has changed then there must be some process side reason.
I can try to give you case studies,,,after 10th July may be...i am on traveling these days.

Regards,

dear asad bhai and chem01 saab,
what mentioned by both of u , i have already checked.
steam drum pr is contant and not incraesed and there is no increase in delta P so fouling is ruled out , chem 01 saab valve position becomes full close from full open in four months.offcourse the opening varies with the plant load.there is no change in let down as steam prod is contant .
i am eagerly waiting for your technical case study report , can u give yr email id for communication .

regards
sahil

[pawan]

Dear Sahil
Its interesting. So you said - Bypass is automatically closing from full open to full close in about 4 months time. During these 4 months, your steam generation is constant and Drum pressure is constant. You also said SR outlet temp is also constant. Is this correct? - Also confirm that it is repeatedly happening.

IF so, we need to understand...

1. what do you do after the complete closure of bypass valve. I mean what makes it fully open again?
2. Have you checked SR outlet composition - methane slip etc.?
3. do you have very high load variation during these 4 months?
4. In which plant you are working right now?

Let me go thru some more analysis & thoughts on this.

[asad daud]

Dear members
It is great pleasure for me to join your discussion in ammonia industry ... i'm Chemical engineer in ammonia plant and i need to discuss certain troubleshooting in ammonia plant .... first of all i worked in UHDE Process-designed ammonia plant ....

my point to discussion is the most difficult situation for any plant ..... (POWER FAILURE)
what the right thing to do (Sequence of acting) during the first second after the power failure
what is the main important actions must be done after the power failure ....
what is the kind of state the plant will behave during the power failure ...
what is the right thing to do after diesel engine will put in operation automatically

i wanna catch the deadly red lines during this situations ,,,, 1 ,2, 3

many regards

Please note that power failure will generate different actions on different plants.
The actions will depend on the facilities available as "back-up" power.

Supposing that the facility available is the steam turbine, first steam is produced in off-site boilers, then this steam is used for generating electricity, then the following case will be true.
Note 1: There is tripping of electrical turbines but not the boilers, so steam is available to run the main cooling water turbine driven pumps.
Note 2: UPS is available to supply power to instrumentation of the boilers.
Note 3: Instrument air supply is through a steam turbine driven compressor.
Note 4: Steam can be given to Ammonia plant from the off-site facility.
Note 5: This steam will be enough for running the primary reformer’s furnace Induced draft fan.
As far as Ammonia plant is concerned, it produces enough steam to run all the turbines, even if electrical power is not available.
The only thing needs to be studied is the availability of cooling water at the right temp to the main condenser.
In cooling tower, the fans are on electrical power, they will trip, on the failure. This will result in the increase in the cooling water supply temp. This will reduce the vacuum in the main condenser, and hence will result in shutting down of the air, syn gas and refrigeration compressors.
Note 6: CO2 removal system's pumps, if running with condensing turbines, will be shutdown. Hence shutting down of the CO2 removal section.
This will result in taking Methonator and LTS out of service and keeping the gas venting at down stream of HTS.
No further change will be required as steam and gas supply to the primary reformer can be continued by using the off-site steam for injecting into the furnace and as well as running the induced draft fan.

If back-up power is sufficient to keep running the cooling tower fans, then there will be no need to shut down anything. Load reduction of 10 % to 20 % can keep conditions under control.

Suppose the electrical generation in by a gas turbine, and then steam generation at the off-site facilities will follow the electrical generation.
• Tripping of electrical power will mean loss of steam as well.
o In that case Ammonia plant will have to be shutdown immediately.
o First syn-gas compressor will be shut down.
o Then refrigeration compressor will be stopped.
o The process air compressor will be stopped.
o Methonator and HTS will be taken out of service.
o Process gas will be vented down stream of HTS.
o CO2 removal system will be stopped.
o Steam will not be available from the off-site, so gas will be cut to the primary reformer.
o All the fuel supplies to the furnaces will be stopped, as there will be no steam or electrical power available to run the Induced draft fan of primary reformer.

[steamreformer]

sahil,
How much change you are observing in valve opening? In say last 3 months the vave has closed from 70 to 60 % or what?
Clearly the closure of this valve is unusual and you must have verified the closure physically in area.
Still your HTS inlet temp is same (how much is that?),,,,
Is there any increase in sc. reformer o/l temp?
How much steam let down has changed (let down of 100 bar) since its closure?
Try to relate any other process parameters with its closure and let us know.

Deatchment of control valve from isnide? If you can physically see the stem position has changed then there must be some process side reason.
I can try to give you case studies,,,after 10th July may be...i am on traveling these days.

Regards,

Hello Chem01
greetings, hope u have finish your tour , i am eagerly waiting for the case studies which u promised.

i have also one request from moderators of this site , can we have facility of online conversation with the members which are online ?

regards

[Chem01]

Steamreformer,
I've tried to get production loss report data from an old dvd, but it doesnt seems to be recoverable.
Pl. find attached one of the incident of sec. reofmer and lesson learned.
Regards,

Attached Files

•  sec reformer incident.pdf   412.95KB   158 downloads

[ETHAN]

Dear members

I need some help to understand the relation between the Recycle flow and make up flow in the synthesis loop of ammonia synthesis plant
the effect of Inert gases and elevated temp of the make up gas on the volumetric flow rate and the efficiency of the compression in synthesis gas compressor....
also i want to ask about the physical properties of ammonia at mixing point of make up gas with recycle gas
and in comparison with separation point at the separator of ammonia liquid in synthesis loop ........

thanks

[pawan]

Ethan
Too many questions in one post - Confusing & Complex.
So will be better if you put them one by one.

To Answer your first question -
The relation between make up gas & recycle flow is dependent on many factors e.g. conversion in the reactor, inerts level, hydrogen recovery & recycle from purge, operating parameters, system pressure drop etc. Generally for a Haldor Topsoe S-200 loop, The recycle flow is around 4 to 4.5 times of the Make Up flow in Nm3/Hr.

Remember one thing for ammonia synthesis loop - Loop Pressure depends on COnversion in Ammonia Converter AND Conversion depends on Loop Pressure - Yes & this is true because of one compressor for Recycle & make up flow.

Rest I will answer later on.

[ETHAN]

thanks sir ...............
sorry for confusing you

go on ........ i need to listen .....

thanks again

[jigs1403]

Dear CHEM01,

I HAVE JUST JOINED a SYNTHESIS GAS PLAN WHICH WAS RECENTLY RECOMMISIONED..... Now i have number of queries regarding the operation... how shud i start asking? i mean how to adress my queries....

[steamreformer]

Dear CHEM01,

I HAVE JUST JOINED a SYNTHESIS GAS PLAN WHICH WAS RECENTLY RECOMMISIONED..... Now i have number of queries regarding the operation... how shud i start asking? i mean how to adress my queries....

Dear chem01
i hope by this time your ammonia forum is ready will u share with us the website with u s.
regards
steamreformer

[Chem01]

Jigs,
You can ask here any relevant questions.
Steamrefomer,
Site is http://www.rotunds.com
The link for Ammonia/Urea forum is also mentioned there. I have started the site with a vision to put related info on Ammonia/Urea and other fertilizers.
Thanks,
ETHAN,
Did you go through manual of synthesis loop, who is licensor of your plant? Appreciated if you ask some sepcific queries.
Regards,