LPG storage Tank for storing Carbon Dioxide

[vntgpt]

We are setting up a plant where CO2 will be used in gaseous form at pressure of 6kg/cm2 and temperature 25-35 deg Celsius. We will use approximately 10MT to 15MT of CO2/month initially. We already have 3 LPG storage tanks of 30MT,& 2 nos. 20MT. I wish to know if we can use these tanks to store CO2 with modifications (insulations)? The design pressure of these tanks is 14.76 kg/cm2 and what I got to know from various sources, LCO2 is generally stored in vessels having pressure range of 22 kg/cm2 to 28 kg/cm2. To use the CO2 in gaseous form, what kind of machinery do we need, if we purchase liquid CO2? Please help.

 

[cheute79]

Off topic, I hate to see a perfectly good units system being destroyed by that awful "g-sub-c" correction because someone decides to use mass units for pressure units. Let's all go back to using "slugs". But that isn't your fault.

On topic, you have 2 issues. 1) you need to vaporize liquid CO2, and 2) you need to assure that the pressure of the gas is reduced by at least 35% before it gets to your storage tank.

The LPG tanks don't care if they are filled with CO2 or LPG, as long as it is dry, the temperature is over something like -15° to -20°C, the pressure never exceeds their rating, and they are protected from impact.

Typical LPG tanks are fabricated of carbon steel. Yours could be special, and made of austenitic stainless or aluminum or titanium. You don't say. If they are of carbon steel or non-austenitic stainless, they must be protected from getting too cold, because those materials lose about 50% (+/- 10%) of their "toughness" (more or less, impact resistence) at -15° to -20°C. So, you must have vaporizors that are designed and sized to assure that all the liquid is flashed off AND heated to at least ambient temperature before reaching your tanks. However, the vaporizers will only reduce the pressure slightly. So you will need a pressure reducing valve system and an intermediate tank that is rated at the full pressure or the LCO2.

 

[dcasto]

lets see now, MT is metric tonnes? a 30 MT vessel will hold in english units 16,000 gallons of propane, which is 2140 ft^3. CO2 at 100 psai and 80F has a density of .786 lb/cf. This means your tank will hold .75MT of CO2, because its a gas. To get the CO2 liquid, you'll have to run refrigerated tanks.

At 14 kg/cm^2, the tanks will have operate at -27C, right at the tanks minimum temperature. Next, CO2 weight more than water at these conditions. The foundations and tank stress are not normall designed to have the weight of water in the vessel and tank could collasps with over twice the mass than they were designed for.

 

[MortenA]

if you wish to look at a reliable source of pure co2 data take a look here:

http://www.union.dk

If you wish to have liquid co2 at amb temperature youneed a pressure higher than 70 barg.

Best regards

Morten

 

[nhliew]

1) You need to check the material to see if the design code allows operation at those temperatures. Then, you have to requalify your tanks to run at higher pressure. This involves recalculating the stresses and treating the tanks to another hydrotest at higher pressure. Some authority approval may be required, depending on where your tanks are located.
2) You will need to get a vaporizer if you store liquid CO2 but need it in gaseous form.

 

[CH5OH]

that sounds like a semi pressurised tank, so you need a reliquefaction plant;basically a compressor (reciprocating)a heat exchanger and some spray nozzles at the top of the tank (to cool down the boil off CO2). you suck out the boil off gasses from the storage tank, compress them, cool them down (liquify them and then you pump the liquid CO2 to the spray nozzles at the top of the tank. to regulate the temperature of CO2 supply, you mix the outlet gas from compressor with the outlet gas of the tank.sounds simple but does require a lot of calculation. the cut in of the compressor is defined by the maximum allowed pressure of the tank, the cut out by the lowest allowable temperature.you probably end up with a multistage compression cycle, and a few intermediate coolers,much depending how fancy (efficient) you want it,the insulation of the tank and so on.But then again if the rate of boil off is about the same as your consumption and you have a reliable supply, you don't need a reliquefaction unit.