Technology Idea of the Week

Finding alternative energy sources to produce cheaper electricity for households and businesses is becoming a huge business but what about carbon intensive industrial processes as well?

Cement Processing 

Making cement is one of these intensive industrial processes. After water, cement is the second most consumed substance on the planet: each person uses about 3 tonnes per year (Environment Publications, UNEP, 2010). It is one of the main materials in essentially every construction project including buildings, bridges, reservoirs and roads. We often do not see the extent to which concrete is used in construction for example The Shard has concrete foundations reach down 53m: approximately 1/6 of the buildings height (Ingenia Engineering, 2012). In 2010 the global production of cement produced about 3 billion tonnes of CO2, accounting for 5% of global emissions (TIME, 2010). The diagram below shows a very simplified outline of the process where raw materials (gypsum/limestone) are heated in a kiln to produce cement and give off CO2 emissions.

Cement Production - image courtesy of CO2CRC

The Energy Demands 

This is a summary of the main energy demands - summarised from Madool et al 2011, Renewable Energy Reviews 

• Extraction and crushing of raw materials before going into the kiln (green on diagram below)
• Heating the kiln to ~1440°C (purple on diagram)
• Final grinding of the clinker into a fine grey powder which can be added to fluid to make cement (blue on diagram below)
• Other auxiliary needs such as transportation of raw materials (red on diagram) 
• On average, producing 1 ton of cement produces just under 1 ton of CO2

Energy Distribution in Cement Manufactoring - Madool et al 2011, Renewable Energy Reviews 

New Innovations 

1. Using the by product - one way to reduce the energy costs of cement which has become common in the last few years is to use the 'slag'. This is the waste product from the production of Portland Cement and was previously thrown away creating the distinctive 'slag heaps'. However, it is now often used in combination with pure cement for example the foundations of The Shard use 70% slag and only 30% Portland Limestone (Ingenia Engineering, 2012). This dramatically reduces the cost of building and the CO2 emissions. 

2. Waterproofing cement - cement is rarely recycled because as water seeps in it reacts with the calcium carbonate (limestone) and causes it to slowly breakdown. This is the same chemical reaction that forms limestone caves, karst landscapes, stalactites and stalagmites. If we could waterproof cement and prevent the breakdown we would not have use new cement in every building. This is what the company Hycrete are aiming to do. A hydrophobic mixture is poured over the cement to reduce the absorption of water to less than 1% (Hycrete Admixtures). This is a bit like pouring oil over it except cheaper and more sustainable!

3. New Formulas - both the above solutions really help to reduce the energy demands of cement production but the ultimate goal would be to produce carbon neutral cement. This is what Novacem is aiming to do. Based on research from Imperial College London, a new type of cement based on magnesium silicate rather than calcium carbonate has been created. This absorbs CO2 as it solidifies: almost three times as much than the traditional formula. This could actually result in the cement industry being a net absorber of CO2 rather than emitter (Imperial College, Novacem Research). In addition, the by products of production can be used and it is waterproof. Almost too good to be true! 

Tackling big industrial processes is a really important part of finding energy solutions. It would take an awful lot of wind farms to see the same benefit as creating a carbon negative cement.