A bit of concrete thinking

During my second year at University I worked for two months in a cement plant as part of the “practical experience” element of my chemical engineering studies. This was about 30 years ago and in those days nobody talked about CO2 – I don’t recall any mention of the CO2 footprint of cement or the overall impact of the industry on the environment (nor, for that matter, when I worked for the local electricity generator – mainly coal – a year later).

Today, CO2 emissions have a very high profile in the cement industry. The CO2 intensity of cement manufacture is one of the main issues being addressed by the Cement Sustainability Initiative (CSI) formed under the auspices of the WBCSD. Of course there are good reasons why this is necessary – the manufacture of a tonne of cement can deliver up to three quarters of a tonne of CO2 released into the atmosphere. This comes from two sources;

  1. The chemical reaction that converts limestone into cement, which results in ~0.42 tonnes of CO2 per tonne of cement produced;
  2. The energy required in the cement plant to drive the conversion, which varies significantly depending on efficiency and fuel types, but for a modern cement plant 0.3 tonnes of CO2 per tonne of cement is probably a fair number. Some are better but equally some are worse, although the CSI is doing much in this area.

I think that the issue with cement is not so much the impact it is having today (although with global production of some 2.7 billion tonnes total emissions are about 4%) but the impact this industry will have over the rest of this century. A simple analysis shows that the industry must also deliver on some very substantial reductions in the relatively near future.

Cement (and the concrete it is used to make) is quite literally the backbone of our civilization. It is hard to imagine the cities we have built existing without cement. But with production growing rapidly as new cities spring up across the developing world, a very substantial emissions impact is in store for us.

Current estimates show cement production reaching over 5 billion tonnes per annum by 2030. Let’s also assume that after that it continues to grow, but plateaus between 7 and 8 billion tonnes per annum in the second half of the century. That will mean a total cumulative cement production between now and the end of the century of more than half a trillion tonnes.

In a previous posting I discussed the issue of cumulative CO2 emissions as the better measure of what must be managed, rather than emissions in any given year. The researchers who presented this concept made the point that to stay under 2⁰ C we should limit total carbon emissions to 1 trillion tonnes, or 3.7 trillion tonnes of CO2 – of which we have now used half. So we have 1.8 trillion tonnes of CO2 emissions left at the very maximum (there were various confidence level reasons why they thought we should actually aim for less than this, but I will work with the upper limit).

Society has now recognised that the oil, gas and coal industries must develop technologies such as carbon dioxide capture and storage (CCS) in response to this. But the fossil fuel industry won’t be on its own. Industries like cement are going to have to respond as well, and energy efficiency is not going to get them there.

The half trillion tonnes of cement could lead to total CO2 emissions this century of some 400 billion tonnes, or about 22% of the available emissions space. Even the chemical process emissions on their own would use up some 13% of the total (assuming a zero emission alternative fuel is used – e.g. bio derived).

So it seems to me that the cement industry and probably some other industries as well are also going to have to develop CCS solutions. One of the issues faced by this industry could be cost. Whilst sequestering all the CO2 emissions associated with a barrel of oil might amount to a third or less of the cost of that barrel (assuming $60 per tonne for CCS in the long term and 0.3 tonnes of CO2 per barrel and oil at current prices), in the case of cement which costs something like $60 per tonne, the implication is an 80% price rise.

This presents the industry with quite a challenge.