Much work has been done in investigating technologies for capturing CO2 from cement plants as a necessary and effective means of reducing CO2 emissions. But the question remains: what do we do with the CO2 once we have captured it? This article will take a look at some of the many ways that companies and organisations have decided to tackle the problem of what to do with the captured CO2, and discuss their potential viability for the cement industry.
Before we begin the discussion of carbon utilisation, however, we should briefly discuss carbon storage or sequestration. A large amount of research, mostly carried out by governmental groups and the utilities industry, has gone into how we can store captured CO2 in geological formations. The primary sites for this storage are usually (but not exclusively) limited to deep saline aquifers, previously (or nearly) depleted oil and gas reservoirs, and unmineable coal beds. While deep saline aquifers hold the highest storage potential (anywhere between 400 and 10 000 Gt of CO2),1 there is relatively less knowledge about storing CO2 in aquifers over the better known physics and chemistry of storing the CO2 in coal beds and oil and gas reservoirs. In fact, using CO2 for enhanced oil recovery (EOR) has been occurring for a number of years, with projects situated globally – although the vast majority of the projects are located in either the US or Canada.
While sequestration may very well be a solution for how to manage a portion of our captured CO2 emissions, there are some very real concerns with this prospect. Chief among them is the potential for CO2 leakage. CO2 leakage would not only nullify the previous efforts of capturing the CO2, but could also lead to serious environmental consequences in the surrounding area, including acidification and the pollution induced by the mobilisation of heavy metals.2 Due to these consequences, effective monitoring techniques and technologies will need to be developed in order to establish what the potential long-term effects of geological CO2 storage will be. Because of the amount of CO2 being stored, along with the geological timeline, any leakage rates above 0.1% per year would render climate control attempts ineffective.3
With these concerns in mind, we can see how it is necessary to look at other forms of carbon storage, mainly by using the carbon in commercial activities to produce useful products while also eliminating our emissions.
While there are many ways that CO2 has already been put to use in industry, such as fire suppression, carbonated beverages, refrigerants and the aforementioned EOR, there are three areas of carbon utilisation that are of particular interest to the cement industry: mineral carbonates, direct chemical products, and algal and microbial consumption of CO2, with the end result of a variety of products. Each of these areas produces a different end product, with varying degrees of utility or economic benefit.
The main idea when it comes to mineral carbonates is to expose or introduce the captured CO2 to some form of mineral in order to form a solid, inorganic mineral carbonate (e.g. calcium to make calcium carbonate CaCO3). These minerals are highly stable, chemically altering the CO2 such that even if the materials were broken up, the CO2 would not be released. Mineralisation is being explored as a means to permanently sequester CO2. However, this is not considered a beneficial use as a product of value is not being created.
Currently, there are many companies and universities that are working with the above principles to introduce new products to the market. Three companies that are closely associated with the construction industry are: Calera,4 Solidia,5 and Carbon Cure,6 all three of which are creating calcium carbonates used in building materials.
1. International Energy Agency Report. Improvements in power generation with post-combustion capture of CO2. IEA Greenhouse Gas R&D Programmes, PH4/33; 2004.
2. Elzahabi, M., Yong, RN., ‘pH in?uence on sorption characteristics of heavy metal in the vadose zone’, Eng. Geol. 2001; 60:61–8.
3. Enting I.G., Etheridge, D.M., Fielding M.J., ‘A perturbation analysis of the climate bene?t from geosequestration of carbon dioxide’, Int. J. Greenhouse Gas Control 2008; 2:289 – 96.
This is part one of a three-part article written by John Kilne and Charles Kline for World Cement’s August 2015 issue and abridged for the website. Subscribers can read the full issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Check back tomorrow for part two of the article on www.worldcement.com.
Read the article online at: https://www.worldcement.com/the-americas/29122015/carbon-utilisation-part-one-8/