8 replies to this topic

[A mukherjee]

Hi everybody,
I just want to know why CO2 plant is operated at around 18-20 barg pressure.
I have read that such pressure creates a situation which is favorable for liquefaction.
I am in confusion about it,as any pressure above 5 bar would have been sufficient to get liquified CO2.
Can anybody explain in detail why such high pressure is required?
I'll furnish details of the process if required.
Regards,
Arpan

[A mukherjee]

Is any more info required?

[Art Montemayor]

Arpan:

Through the years, I have written extensively on CO₂ generation plants and the operating pressures employed therein. The pressure at which most (if not practically all) CO₂ plants produce their product (and store it) is at approximately 250 -265 psig.

I have detailed out the reasons for arriving at that pressure in many other threads and the majority of the reasons is that it is related to the thermodynamics of phase equilibria.

You say that any pressure above 5 bar (75 psia) would be sufficient to get liquefied CO₂ – and you are correct, because that happens to be the Triple Point for CO₂. However, your confusion is due to the fact that you are not taking into consideration what would be the optimum and most practical:

1. Commercial refrigerant to liquefy the product;

2. Commercial, available storage tank material to withstand the related -53 ^oC saturated temperature.

The 250 psig storage selected corresponds to using conventional ammonia as a refrigerant and conventional 2-state reciprocating compressors to develop the 250 psig (starting with 5 psig suction on the first stage). The resulting -8 ^oF (-22 ^oC) fits in very well with conventional, available steel such as A516 Grade 70 that can easily withstand -20 ^oF.

I hope this resolves your confusion.

[thaqrhys]

Dear Art Montemayor,

As you are rich of experience in CO2. I'd like to ask your favor for dealing with this problem.

I want to liquefy CO2 gas. The process description as follow :

1. Dry CO2 gas enters Diaphragm Compressor and the gas outlet is 17 barg; 32 deg.C.
2. Compressed CO2 gas is cooled using Water-Glycol (-25 deg.C) in a BPHE, the CO2 gas exits at approx. -12 deg.C
3. The CO2 gas continues to be cooled using R-507 in a Shell-Tube HE and exits at -45 deg.C.

After I checked in CO2 Phase Diagram, CO2 will be in liquid at 17 barg; -30 deg.C. So I believe that my process will produce Liquid CO2.

The problem is :
1. Is my process is correct ?
2. If I want to put the liquefied CO2 into the CO2 cylinder, can I simply cool the CO2 cylinder and connects it to the CO2 liquefaction system ? Or I have to pumped using Liquid CO2 Pump (until 200 barg) and puts it into a Storage Tank ?

Thank you for your kind attention and looking forward to hearing any news from you.

thaqrhys

[Art Montemayor]

thaqrhys:

I am going to assume you are a graduated, professional chemical engineer. Because of that, I expect you to give ALL the basic data and background related to your query.

• Why do you use a diaphragm compressor instead of a conventional, 2-stage reciprocating compressor or a screw compressor? I have never found or heard a need for a diaphragm compressor for this type of service.
• Why do you resort to cooling with 2-stage cooling and liquefaction (glycol + water followed by R-507)? Why don’t you simply use what has always been used to produce the liquid CO₂ at 17 barg and -22.9 ^oC: cool the compressor discharge gas with cooling water and follow this with a conventional 2-stage ammonia refrigeration cycle?

The glycol and R-507 are just more complications and cost more. The ammonia system is environmentally the best you can use and the most efficient refrigerant to boot. I am not criticizing your process decisions, but simply pointing out that there is a simpler, more efficient, and more economical way to do it and it is being done every day in industry.

Contrary to what you state, the liquid CO2 at 17 barg is saturated and at -22.9 ^oC. Look at the attached Excel workbook.

To fill CO₂ cylinders with stored Liquid CO₂ at 17 barg and -22.9 ^oC, what has always been done is to fill each cylinder with a measured amount of liquid CO₂ (usually 25 kg in the USA, using conventional CO₂ cylinders). The amount of fill is measured using a weigh scale. What is done in a professional operation is to use two weigh scales and fill the cylinders one at a time. A special, liquid CO2 pump is used for this operation.

You don’t furnish complete basic data or a schematic flow diagram showing your process, so that’s about all I can comment on.
 CO2 Thermophysical Properties.xlsx   15.99KB   63 downloads

[thaqrhys]

Dear Art Montemayor,

First of all, I do highly appreciate for your reply and the suggestions.

Answering your questions :

• I chose Diaphragm Compressor because besides CO2, there are several gases in minor amount ( less than 2% v/v of total volume ) which are blended with CO2, then to be liquefied and stored in cylinders.
• I didn’t consider the ammonia refrigeration cycle at all. Could you recommend some good literatures regarding this refrigeration system ? The ammonia system will be applied for the next production unit.
• Herewith I attach you the PFD. Please inform me what are the basic data you require ?

Thanks and waiting for your further news.

Attached Files

•  PFD_CO2-LIQUID.pdf   254.76KB   64 downloads

[thaqrhys]

Dear Art Montemayor,

 

Regarding my post dated December 16th, 2012 about CO2 Liquefaction Process.

 

I use Water+Glycol as the 1st stage cooling and the result is not satisfying at all.

It happened that the Water+Glycol mixture freezes and block the Glycol Pump.

 

And, another problem is the CO2 gas inlet is rich with water content over 5%. So, I plan to install Refrigerant Air Dryer followed by Desiccant Dryer before enters the Compressor. 

 

Based on these two problems, I come up with an idea :

I am planning for the 2nd production line of CO2 Liquefaction, I compress the CO2 gas to 80 barg, 25 deg.C. 

I checked in the CO2 Phase Diagram, CO2 will turn into Liquid phase at mentioned condition.

 

Based on your experience, is this process is common in CO2 liquefaction plant? 

Could you recommend which CO2 Compressor that could meet the phase change requirement ?

 

Thank you for your kind attention and help.

 

Best regards,

Thomas.

[Art Montemayor]

 

Tomasso:

 

I responded to your Dec 16^th query that very same day.  You did not respond to my direct, specific, and detailed questions and comments until Jan 11^th, almost a month later – and even then, you have not furnished any important details and basic data.  Since I was sick with a very bad virus for 2 months, I assumed that you were not interested in gaining any of the expertise and know-how I accumulated for the past 53 years and so I concentrated on improving my health rather than wait around for your basic data.  Three months later, you have returned to the same thread demonstrating that you haven’t read or understood what I wrote – or you simply don’t believe what I have recommended to you.  That’s OK.   Your lack of interest in improving your knowledge about how to produce a lower cost, more profitable, safer, and more efficient CO₂ product is your own handicap.  I have tried to help you, but apparently it hasn’t sunk in.

 

I have written extensive threads and details on all the experience I accumulated over the years in designing, fabricating, installing, and operating various CO₂ plants and even have a U.S. patent on producing Dry Ice automatically.  You can obtain all this experience through our Forum SEARCH engine – for free, and complete with detailed drawings, calculations, and explanations.

 

I have tried to help our members by sharing all my experience and knowledge with them through many years on these Forums.  However, if I am to help you with specifics, then YOU must furnish ALL of your specific information and scope of work.  Those are my terms for helping you and all other members.  I will not furnish you my personal expertise under YOUR terms.  I share my information with all our members – not just with one or two, or with only those I prefer.  That is why we must have a mutual sharing of trust and  understanding when exchanging basic data for experienced engineering help and advice.

 

If you prefer not to divulge or reveal some of your basic data, you can communicate that portion to me through my personal messenger service found on this Forum.  I can understand that you prefer not to reveal where you work or some of the nature of what you are doing because of proprietary information that you do not want to share with potential competitors.  That is OK.  I understand that; but I still have to know certain information to give you the best of my experiences and knowledge and that can be done through the personal messenger.

 

If you are serious in your endeavors and want the best free advice I can offer, I will be happy to share it on the Forum, but I need to know:

 

Are you a graduate chemical engineer?

Where do you work and where will the CO2 production take place?  (if in Italy, then it is in a
country dear to my heart)

Are you an employee of the company doing the investment, or are you a direct owner?

What is your existing CO₂ production like in capacity and size?

Furnish a detailed PFD or preferably a P&ID of the existing plant and identify who designed and fabricated it.  Is the CO₂ generated by combustion of hydrocarbon fuels or is it a by-product of fermentation or other chemical production (like ammonia)?

Who is doing the detailed engineering design for your proposed CO₂ plant?  Where will the
equipment fabrication take place?

What is the end market that you are supplying the product CO₂ for?  Does the CO₂ have to be of “food-grade” purity?

Are you selling/distributing the product CO₂ as a liquid in tonnage quantities at approximately 17.5 barg and -22 ^oC?  Or are you distributing the product in 25 kg cylinders
at 76 barg and 30 ^oC?

 

Please respond to each and every one of my questions and comments.  I will guide my response by your response to my requests.  I will help you as much as you help me.  The quality and quantity of my contribution to your queries will be directly proportional to the quality and quantity of information and specific details you furnish.  There is no area of the CO₂ industry that I have not been directly associated with and with which I am not knowledgeable.  I have advised and consulted on this industry in the past many times and I charge my usual, expensive fees for direct, one-on-one consultations.  However, if I do it through this Forum, I give this service free because I am sharing it with all of its members.

 

Let me know your response and if I can be of help through the Forums.  I await your reply.

Additionally, this thread was started by someone else - who obviously is no longer interested in the topic.  If you want to continue your quest for information, then I strongly recommend you start your own, specific, new thread with the appropriate topic title so that we can all dedicate that thread to your specific needs.

Ciao.

[thaqrhys]

First of all, I really sorry to hear that you've been sick lately. I do really hope you could fully recover soon.

I was late replying to your response because the system you explained compared to the existing system is different.

However, I still have to use the existing process equipments until the production starts and we could expand on the 2nd production line using the system you advised in previous posts.

I am a fresh graduate from Universita di Firenze. I took Bioenergy & Environment as my major and had few years of experinece in the field.

Then, I came back to Indonesia and I work for a private agrochemical company. At this moment they plan to produce a pesticide product which is a mixture of gases. The majority is composed of CO2 gas.

So, the source of CO2 gas comes from CO2 cylinders, then to be mixed with gaseous pyrethroid insecticide, and finally to be liquefied and stored into 50 kg cylinders. That is the main idea.

An engineering consultant designed this sytem but unfortunately the company gone bankrupt and the owner passed away, so before this CO2 liquefaction project has finished, they never continued it and now we ( the owner ) directly continue the project.

I'll be happy to be able to share with other forum members. And I would share all the basic data you needed, but please tell me what are the basic data you require? As I already upload a simplified PFD with operating condition.

Thank you for your kind attention and sharing.