How to sequester carbon dioxide and produce natural gas

A scientist at the Indian Institute of Technology, Madras, has a solution for two vexing problems — ‘climate change’ and ‘energy security’ — in one go.

Do you want to find a home for carbon dioxide captured from industry sources? Do you also want to produce natural gas — the cleanest of fossil fuels — from the abundant gas hydrate reserves that India has under its seas?

Prof Rajnish Kumar of the Department of Chemical Engineering, IIT-M, has just completed a GAIL-funded project which shows it is possible to first separate carbon dioxide, in an almost pure form, from the flue gases of industries, particularly coal-fired thermal plants. The next step is to inject the carbon dioxide into the gas hydrate zones, whereupon the carbon dioxide molecules push out the resident methane molecules and take their place. The methane can be tapped off.

Hydrates are a mixture of water and a gas, defined as “a solid, ice-like form of water that contains gas molecules in its molecular cavities”.

Kumar’s process for separating carbon dioxide from flue gases is simple enough — cool it to 1.5 degrees Centigrade and pressurise it to 30 bars, and let it react with water. Carbon dioxide will separate out to form carbon dioxide hydrates.

Next, if you depressurise the chamber, (nearly) pure carbon dioxide will separate from the hydrates.

So far so good, but what do you do with the carbon dioxide? You have to find a permanent home for it, to prevent it from messing with the planet’s climate, right?

For this, Kumar suggests it could be injected into the methane hydrate zone.

India has mind-boggling amounts of natural gas in the form of hydrates — of the order of 2,000 trillion cubic feet. The Krishna-Godavari basin alone has about 134 tcft.

For decades, the National Gas Hydrate Programme has been racking its brains over how to get the gas out of the hydrates.

Kumar says you only need to inject the carbon dioxide, and the gas will do the rest. It will kick out the methane, which can be tapped off, as in any gas field. The carbon dioxide will remain there forever.

His project report is currently with GAIL.

A few questions remain to be answered. First of all, don’t you need energy to get the flue gases to 1.5 degrees Centigrade and 30 bars?

Kumar is confident it is still economically viable.

Second, you produce natural gas (methane), which is still a fossil fuel. In today’s world, all fossil fuels are enemies of mankind.

The answer to that is: Methane is the best among all fossil fuels — far better than coal. Carbon dioxide capture and storage is a costly affair. In a coal-fired thermal power plant, it could take up 25 per cent of the power produced by the plant.

Methane mined from gas hydrates can pay for it. But, importantly, the net carbon dioxide emission will be less than the unabated emissions from thermal plants.

The conventional way of carbon capture and sequestration has been through the use of chemicals called amines. The problem here is that you have to spend a lot of energy to recover the amines. In contrast, separating carbon dioxide from carbon dioxide hydrates costs practically nothing.