5 replies to this topic

[papillion]

Dear all,

 

I am currently work in ammonia plant, but my bos asked me to help evaluate our CO2 plant due to it's low capacity.

it is an old 1974 plant . the nameplate capacity is 30 ton/day but actual production in 22 ton/hr.

The only documented engineering sheet i found is the PFD. so i did the plant mapping as shown by PFD redrawed in the attachment.

 

After discussion with our teams, there are some issues we found, and i need your opinion on these.

 

1. we decided to upgrade the pipe material in suction of LP and HP case of CO2 compressor from carbon steel to ss. we suspecting that the corrosion product carried to compressor and damage the seat of unloader valve.

2. From other topics i can see that people always say that the CO2 liquid that goes to storage tank is in saturated liquid. in my PFD attached you can see that the design is the saturated liquid CO2 leave the reboiler in 21 kg/cm2g chilled again to -30 degC. the CO2 pressure than reduced to 16 kg/cm2g and sent to storage tank (this condition i'm sure is in subcooled). is this configuration normal for you?

 

The actual condition is that the temperature of reboiler and the CO2 almost the same (-19 degC) which led mw to the third issue.

 

3. Is it true that the refrigeration is not sufficient?

I personally think that the refrigeration is not sufficient because the temperature to the dryer is higher than design, and the CO2 product temperature is only -19degC, same with the reboiler temperature.

This led me to my confusing conclusion that the ammonia circulation is not enough. Why i said confusing is because the operator said that the NH3 Compressor sometimes tripped by OVERLOAD if the CO2 rate increased more than 22 ton/day.

 

 

4. if you can see from the PFD i attached, there were no water separator before CO2 entering dyer. We intend to put a separator/drain facility before the dryer to ease the dryer workload. do you find it practical to put it? or just let the dryer handle it?

 

any opinions are welcomed.

 

 

Attached Files

•  CO2 Compression section.pdf   41.53KB   113 downloads
•  CO2 Refrigeration section.pdf   48.61KB   82 downloads

[Art Montemayor]

Papillon:

 

Please refer to my comments on the attached workbook assembled for this thread and for the purpose of consolidating /documenting further drawings, sketches, comments, and modifications.  Any modifications to the workbook should be done with a Rev number attached to the file name.

 

Additional comments and questions are: 

1. Who designed and built this small ammonia plant?  Is it skid-mounted?
2. I presume that there are no as-built P&ID drawings, vessel fabrication drawings, nor process calculations.  Is this true?
3. I assume you have a steam reformer.  Are you using an MEA CO₂ removal system on the Syn Gas produced?
4. What are the make, capacity, type, and driver of the CO₂ compressor?
5. What are the make, capacity, type, and driver of the NH₃ compressor?
6. What are the size, capacity, and MAWP of the CO₂ storage tank?
7. What are the source, type, and lowest temperature of your cooling system?
8. What is the application of your stored liquid CO₂?  What is the intended use for it?

If you have a water-wash vessel before your CO₂ compressor, it should be practically impossible to have “corrosion products” flowing into your CO₂ compressor suction valves.  I suspect whoever designed the plant thought that MEA would be carried over into the CO₂ compressor and used a water wash to remove it.  This is something that is never used in a well-designed MEA regeneration unit.  Carbon steel piping and vessels are perfectly OK for this application if the process design is done by knowledgeable people.  All you need is a well-designed vapor / liquid separator before the CO₂ compressor.  The “corrosion products” you may be witnessing are mostly rust from the water spray in the water-wash vessel you have.  I also would have liked to have Stainless piping in the many CO₂ plants I operated in the past, but there is no way to logically and rationally justify such an application.  Carbon steel piping has traditionally been used throughout the CO₂ process because it works and is adequate.

 

Liquid CO₂ is stored and transported in the saturated state.  Industrially, there is no need to sub-cool the liquid and it is far easier to vaporize it at its consumption point because the CO₂ is almost always consumed in the gaseous phase.  What is the purpose and use for your CO₂?  If you are selling it or transporting it, there is no purpose in sub-cooling it.  I don’t know the scope of design for your unit nor the basis of the design, so I can’t comment further.

 

In the present engineering generation I continue to see more young engineers depending upon the data and information given to them by plant operators.  Based on my many years of operations in the field I seriously advise you to NOT DEPEND ON DATA OR CONCLUSIONS given by operators when analyzing a process problem.  Operations engineers are the “owners” of the process (the single point of responsibility) and should be the ones who generate such data for further analysis and conclusions.  The ammonia compressors can shut down for other reasons besides capacity overload.  Before arriving at such a conclusion, the operations engineer(s) should have a complete set of actual, operating data on the unit before it shut down.  It may be true that the ammonia compressors are overloaded, but a heat and material balance should be generated in order to analyze the current load being imposed on them, taking into consideration their ability to handle and vary the capacity.  The official and certified capacity for the ammonia compressors should be obtained from the manufacturer (if available) or calculated from physical data and information.

 

My curiosity on the origins of this plant (designer & builder) is based on what I read.  Any experienced process engineer knows that when a water-saturated gas is cooled, there will be water condensate formed and it is imperative to remove this liquid immediately after the cooler.  In fact, this is a method used quite often in order to minimize the size of the downstream adsorber dryer unit used to reduce the water content down to approximately -90 ^oF dew point using activated alumina.  The absence of a well-designed knock out separator before the adsorbent dryer unit (I have to assume you have an adsorbent type dryer) reveals the design as one done by inexperienced engineers and suspect of other flaws and errors.  It is imperative that you have a well-designed water separator before the dryers.  That is why I solicit information on its origins and design.

 

 Papillon's CO2 Recovery Plant.xlsx   358.38KB   93 downloads

[papillion]

Art:

 

Thank you for your response, below are some additional information as you need,

 

1. Who designed and built this small ammonia plant?  Is it skid-mounted?

The designer of 30 MTPD CO2 liquid plant was “Gases Industriales” from Argentine in 1974 (a very vintage plant).

Yes it is skid mounted, divided into the CO2 compresion, and the refrigeration, each around about 20 X 13 X 16 foot (L x W x H). So compact that there are no operational access to the intercoolers located above.

1. I presume that there are no as-built P&ID drawings, vessel fabrication drawings, nor process calculations.  Is this true?

Yes this is the most troublesome obstacle. I had spent one week digging engineering document I could found. The only document I can found is a shabby PFD. I redraw the drawing and design conditions attached based on this PFD. I can’t see any compressor nameplate anymore since the bad habit of the painter is to paint everything they can paint, including nameplate.

1. I assume you have a steam reformer.  Are you using an MEA CO₂ removal system on the Syn Gas produced?

The CO2 removal in the ammonia plant using benfield (K2CO3) solution.

1. What are the make, capacity, type, and driver of the CO₂ compressor?

The type is oil free reciprocating (CO2, and ammonia), with motor driven. As for the OEM, and rated conditions, they erased it with painting the nameplate, but from the operator remembrance, I think they mean Ingersoll.

1. What are the make, capacity, type, and driver of the NH₃ compressor?

Identical comment with no 4.

1. What are the size, capacity, and MAWP of the CO₂ storage tank?

The capacity is 160 metric ton. Design pressure 20 bar, test pressure 26 (I assumed the MAWP  equal to design pressure).

1. What are the source, type, and lowest temperature of your cooling system?

We use open type cooling water (rarely 86 degF, normally 90 degF, highest 94 degF)

1. What is the application of your stored liquid CO₂?  What is the intended use for it?

Liquid CO2 sold to beverage factory and chemical plant by truck, small amount sent to dry ice unit.

 

Another point:

1. Wet CO2 have a corrosion impact to carbon steel material. We had witnessed it frequently (CS CO2 piping to Urea plant suffering from this corrosion also). As for the water scrubber we already programmed it to be replaced with SS water scrubber since it already thinning and frequent shutdown for patching the leaking scrubber. Hopefully, potential rust from the water spray as you mentioned shall be eliminated too.

I’m not sure about the existing design of KO drums, they just sized around 0,5 ft Diamter x 1,5 ft Height (for 30 MTPD CO2 liquid), is it common?

 

I always avoid using operator data to do evaluations, because I know how they gathered and record the data (but their experiences still are valuable information). That is why I still questioning about the overload claim from the operator. Unfortunately there is no online monitoring, moreover data historian, event summary, and OEM data in this vintage plant to debate that point scientifically. I usually done the logsheet record personally for evaluation purpose, and for the data attached, I used calibrated instrument as noted in the Excel attached.

 

The CO2 Plant located 400 meter from Ammonia Plant, and operated by different section. Mostly CO2 leaving CO2 stripper (in Ammonia Plant) is in saturated condition with moisture (demin water and sometimes contaminated with K2CO3/Absorbent). Along the line to the CO2 Plant, some of moisture condensed and causing serious corrosion.

 

We have limited engineer, until recently we all concentrated to the Big brother Ammonia and Urea. Now the little brother, CO2 Plant, get the attention, and thus we do the mapping of CO2 plant. And yes we found it strange too, why decades ago they do not give separator before the Dryer.

 

You gave me a solid reason to not try so hard to make the CO2 subcooled. I will inform my other team.

Attached Files

•  Papillon's CO2 Recovery Plant-Rev 1.xlsx   533.86KB   42 downloads

Edited by papillion, 18 June 2013 - 11:26 AM.

[Art Montemayor]

 

Papillion:

 

Thank you for the detailed background and information on your CO₂ unit.  With this additional information I now have a clearer and more accurate picture of what you have inherited.  I still lack data and information, but let’s handle that as we come to the specific topic because from what I can deduce, you have your hands full.

 

I am from the era before Gases Industriales was formed but I am familiar with their efforts in trying to design and sell compact ammonia plants.  I had my doubts as to their success and they have disappeared from the industrial scene.  I believe you already know that and the fact that you can’t obtain any information from them since they no longer exist.  Nevertheless, you can succeed in making your unit as efficient as you can and do this in-house.  If you have an Ingersoll-Rand CO₂ compressor and a similar NH3 compressor, you have the basic core equipment and it should be very sound and rugged if they are Ingersoll-Rand compressors.  I am attaching some old I-R catalogs and I hope you can recognize the type of compressor you have from these.  Ingersoll-Rand was acquired by Dresser Industries and is now called Dresser-Rand.  There is a chance that if you can identify the model and serial number of your compressor(s) you might be able to obtain capacity information and other data from Dresser-Rand.  If you are unable to get information from D-R, then you / we can calculate the estimated compressor capacity by knowing the compressor rpm, cylinder bore, rod diameter, and end clearance.  All these are measurable in the field.  Look over the brochures and see if you have a PHE, ESH, or HSE model.  Also, please give details on your NH₃ compressor.  Is the ammonia compression also handled by the same compressor, but on different throws?  It is unfortunate that you have non-lube design compressors.  This, in my opinion, was a dumb mistake on the part of the plant designers.  It is, in my opinion, a waste of money and a decision made by un-experienced people.  CO₂ and NH₃ compressors that are oil-lubricated operate much more reliably and with much, much less maintenance – especially with respect to the piston rings.  I would hope that your compressors could be back-modified to oil lubricated rings because that could give you additional capacity.

 

As I had guessed, your unit was designed by persons not experienced in processing compressed gases – regardless of what they claimed.  The results of their expertise is revealed in the unit you inherited.  I also suspected a skid-mounted unit that was cheaply put together to save on space and steel.  This unfortunately has compacted all the equipment together and made maintenance on the equipment a nightmare.  I had to deal with such badly designed units in my early years and I paid a heavy price in sleepless nights and weekends spent in the plant.  However, these problems led to my education and experience in resolving such difficult tasks in the field without the aid or assistance of other engineers.  This will also be an enriching and profitable experience for you if you so decide to tackle these bad problems.  I offer you my help as you need it.

 

The lack of engineering calculations and documentation is yet another obstacle that you have to overcome.  You must start to compile and document everything you can see, measure, and identify in the field.  Start making specific data sheets for every piece of equipment in your plant.  Organize a logical and detailed engineering file that you can keep handy and up-to-date.  Start by making a list of every PSV and safety relief device in your plant.  This is the highest priority.  Proceed on to compressors, motors, heat exchangers, pumps, etc., etc.  This effort will pay you back in the future.  I write this with first-hand, personal experience.  Additionally, start a detailed heat and mass balance on your refrigeration system.  This is important in order to identify the actual and potential capacity of your ammonia system.  Note Rev2 of the workbook and the different ammonia systems.  Your ammonia PFD is not clear and needs to be simplified as I show in my PFDs.  If you need help on generating the heat and mass balance, let me know and I’ll show you how it is done.

 

Designing and fabricating a vapor-liquid separator for your adsorption dryer unit is no problem.  All you need is some seamless carbon steel pipe and pipe caps.  I would guess you would use a 10” to 12” size (maximum).  However, a detailed design can be done easily.  Do you have local steel fabrication shops that can fabricate a pressure vessel?  I believe you should.

 

I am very sure that your CO₂ storage tank is working with saturated liquid CO₂.  I don’t see how you could justify sub-cooling the tank contents.  Your carbonated beverage clients and your liquid transport tanks are all – I am sure – designed for saturated liquid CO₂.  You should normally not be required to sub-cool your liquid CO₂.  This type of process thinking is – again – a mistake made by inexperienced design engineers.  More on this topic in later posts.

 

There is a possibility that you may be able to obtain further cooling from your refrigeration system as well as more capacity from the CO₂ compressors.  But we need the detailed sizes, identification, diameters, strokes, clearances, etc. in order to be able to tell if the compressors can yield more capacity.

 

Yes, you are correct; wet CO₂ is corrosive to steel.  However, the wet CO₂ must be in water solution.  In other words, you should not have LIQUID water in contact with CO₂ gas because it forms carbonic acid – the corrosive ingredient.  You should not be having carbonic acid corrosion in your piping and heat exchangers if you are separating any water from the CO₂ gas as soon as it is formed in the process – as in the CO₂ pre-cooler immediately before the CO₂ dryer.  That is why I recommend you install a water separator and drainer at that spot.

 

Let me know your thoughts and if you want to start immediately on the NH₃ heat and mass balance.

Also, submit photos of the equipment if you can in order to get an accurate idea of the installation and equipment.

 

 Papillon's CO2 Recovery Plant-Rev 2.xlsx   687.18KB   56 downloads

 ESH-ESV Gas Compressors.pdf   2.08MB   61 downloads

 HSE Balanced-Opposed Process Compressors.pdf   1.79MB   51 downloads

 PHE Model 2041-PHEcomp.pdf   996.42KB   49 downloads

 

[Art Montemayor]

Papillion:

 

Please study the attached PFD found in the workbook.  Check and correct any errors, omissions or mistaken information.

 

I have done this rather quickly and in-between family duties with my visiting grandchildren - so I apologize for the poor quality.   I will clean it up and improve it if it is going to be of any value.  I have used your original PFD as a source and the reported process data you cited.  Please verify that this is correct.  As you can see, there is a lot of additional process information that is still lacking in order to make a complete and detailed heat and mass balance of your ammonia system.  However, it is the mimimum requirement in order to establish your process base line for future and existing process work on this unit.

 

Please indicate if you are interested in proceeding further on this topic.

 Papillion PFD.xlsx   49.35KB   55 downloads

[papillion]

Art,

 

I'm sorry I can't reply you sooner, I've been out of office the last two weeks, and i just have 3 days in office tomorrow before leave again, and my boss asked me to prepared data for furnace coil cleaning service company in these three days (cleaning with peletized dry ice, i think you familiar with that).

The flowsheet you generate are far better than mine. For the temperature, pressure, and mass flow, that’s all that I can obtain. I have revised some of the data in the PFD you gave.

Both compressor (CO2 and NH3) are HSE type based on brochures you gave. I will try digging more information on the compressor tomorrow.

The CO2 composition (inlet of CO2 compressor 1^st stage) is as follow:

(%dry wt basis)

CO2  99,71 %

N2       0,03 %

H2       0,27 %

Yes we have workshop to fabricate the water separator in here, and I think you are right, we just need to keep it simple.

Attached Files

•  Papillion PFD rev 1.xls   375.5KB   45 downloads