5 replies to this topic

[hasanasif]

Dear All I have recently set up a carbon dioxide recovery plant on a natural gas fired boiler.

In order to liquify the carbon dioxide I need to compress the gas close to 21 bars however the suction pressure available is 1-2 millibar. Please advise if any compressor would do the job for me, or if there is any alternative.

 

 

Looking forward to your help people

 

Thanks,

Hasan

[Muhammad Waqas]

Hasan.

compressor of how much capacity are you looking ? In other words what is the capacity of your plant >

[Art Montemayor]

Hasan:

 

As I previously stated, you fail to furnish all the customary and required basic data in order to address your request for help.

 

What is needed is:

1) All your basic data - complete with capacities and utilities identification;

2) A detailed flow diagram of your proposed process;

3) Why do you state that you need 21 bars of pressure in order to liquefy the CO2?  Is that gauge or absolute pressure?

4) Are you using a 2-stage reciprocating compressor with intercoolers and an adsorption dryer on the discharge of the 2nd stage?

5) Why do you state that you will only have 2 millibars of CO2 suction pressure?  If you are using a boiler to produce a flue gas that will be treated with an amine solution ( as is the common, normal manner) to selectively capture the CO2, then you will generate 6-10 psig of recovered CO2 pressure (345 - 690 millibarg).  How are you generating your CO2?

 

Not just any compressor will do.  You have to select your compression and refrigeration needs first.  Normally, a 2-stage compressor is used (lubed or non-lube).  Then, you employ a 2-stage NH3 vapor compression system to liquefy the dry product.

 

You could also employ a 3-stage CO2 compressor without any NH3 refrigeration.  It all depends on what process you have selected.  That is what you have not told us.  We need ALL your basic data in order to help you.  If you don't supply it, we can't help you.  We can only guess.  As engineers we don't "guess"; we furnish specific answers.

[hasanasif]

Dear Art,

 

Thank You for your response. I am not an engineer, I am an owner of a textile factory and we have set up a co2 recovery plant based on the boiler flue stack. I will give a  brief review of the process. Flue gas is  drawn from the boiler exhaust and is washed with water in the scrubbing tower after which it goes into the absorber using a vaccum blower where co2 is absorbed by counter flowing Mono Ethanol Amine. The rich solution passes via a heat exchanger and goes into the reboiler where steam is used to release co2 from the rich stream. The co2 is cooled using condensors and goes into the pottasium tank. After that the gas co2 is fed into a balloon of 75m3. For liquification I have a Mehrar compressor TZW 50 which is two stage oil free compressor. After the second stage of compression I have installed a condensor to further cool the CO2 and a header is made to remove any moisture before entering the activated almunia based dryer. For liquification purpose I am using R404a and not ammonia as the plant is very small 80kg/hour. I have few questions to ask:

 

1) The inlet pressure entering the balloon is 2-3 millibar ( I have installed a millibar meter on the line) which means I will have to shut down the compressor after a few minutes or the compressor will suck air into the system. What can I do to solve this problem? Can I use an inverter to reduce the speed?

 

2) What size of alumnia balls should I use in the dryer?

 

3) Till what temp do i heat the dryer for regeneration purpose? 

 

Regards,

Hasan

[Art Montemayor]

Hasan:

 

As I requested last month, what we need in order to discuss this topic in a clear, accurate, detailed, and positive manner without any mistakes or misconceptions is:

1. All your basic data - complete with capacities and utilities identification; since you are not an engineer, this data is the capacity of CO₂ (kg/hr) recovered from the flue gas, the CO₂ purity sought, the storage conditions of the produced liquid CO₂, the designer and fabricator of your MEA recovery plant process, the %MEA (wt.) solution used, the temperature and pressure of the MEA Stripper reboiler, the liters/min of MEA solution circulated, and the temperature and pressure of the gaseous CO₂ exiting the CO₂ cooler on the MEA Stripper outlet.
2. A detailed flow diagram of your proposed process – complete with temperatures and pressures indicated.

If you are recovering the CO₂ from an existing flue gas out of an existing boiler, you are going to require some low pressure steam for the MEA reboiler tube bundle in order to regenerate the rich MEA into lean MEA.  I presume you are using some steam from the existing boiler.

 

What do you mean by a “header is made to remove any moisture”?  You probably mean a vapor-liquid separator, since headers don't remove moisture.  Your lack of process knowledge makes it important to have at least a detailed flow diagram before discussing your plant.  Otherwise, we will spend a lot of useless and confusing time exchanging information among ourselves.

 

Your statement that your compressor has only 2-3 millibar (gauge or absolute pressure?) of suction does not make any sense at all.  That is why I need to know who designed and built this small plant.  If what you say is true, you are saddled with a ridiculous situation.  As I have previously stated, if you are using a boiler to produce a flue gas that is treated with an amine solution ( as is the common, normal manner) to selectively capture the CO₂, then you are generating 6-10 psig of recovered CO₂ pressure (345 - 690 millibarg) in the outlet of the MEA stripper tower.  That is a process fact.  If your plant is wasting that available pressure, you obviously have a flawed and silly design.

 

I have always used ¼” activated alumina spheres in my CO₂ adsorber dryers.  If that is what you mean to ask, then that is my response.

 

I have always designed my CO₂ adsorbers to generate a minimum of 500 ^oF in the regeneration gas.  The regenerated bed should achieve a temperature of 450 ^oF.  These temperatures depend on the type of adsorber dryer arrangement you have and the cycles you are employing.  That is why I require a detailed flow diagram of the plant.  Otherwise we are wasting time and effort in discussing something we don’t even have a decent description of.

 

Additionally, if it takes you 3 weeks to reply, consider that it may also take that long for our members to reply to you.  If your need is not urgent or important, then please tell us.  I have assumed your request to be a serious one and that it required timely response and accurate information.  That is why my responses have been rapid and detailed.

[hasanasif]

Dear Art,

 

Hope you are doing well. Sorry for the delayed response last time

I am trying to get all this data for you. As soon as i find them out I will let you know.

 

Thanks

 

Regards,

Hasan