The production of cement and lime involves fossil fuels and produces harmful greenhouse gases. Industry could change this, if a technology could be developed that could use solar power for high temperature industrial processes. The EU-funded SOLPART project has built laboratory-scale reactors that use a solar-powered process to meet this need. When we think of CO2 emissions, we tend to think of power stations, electricity and hundreds of thousands of vehicles pumping out harmful pollution. But other industries also pump tonnes of CO2 out into the atmosphere each year. One of these is the construction industry, which produces the lime used in large quantities in limestone products, cement, concrete and mortar. The construction industry is not far behind energy producers, households and the transport industry in terms of how much CO2 it produces. In fact, the cement industry is responsible for between 5 per cent and 6 per cent of the world’s CO2 emissions each year [about 1 tonne/CO2 per tonne of clinker],” said SOLPART project co-ordinator Gilles Flamant, an engineer whose field of expertise is solar energy and applications to heat, power and fuel production. “The SOLPART project’s high-temperature solar process could significantly cut CO2 emissions and fuel consumption, while saving companies money,” emphasised Flamant. “The use of solar power in the cement and lime production process would save about 0.15 litres of fuel per kilogram of lime produced,” he added.

How it works – chemical processes driven by solar energy

Utility providers already use concentrated solar energy to produce electricity and heat, but solar power heats water in homes at less than 100°C. “The SOLPART project wants to take the efficiency of solar power to much higher temperatures – between 900°C and 950°C,” explained Flamant. High-temperature processes could be used to produce carbonate particles from limestone, which is essentially calcium carbonate. To produce lime for use in the cement industry, industries must heat the limestone to 900-1000°C to break it down. The heat causes the limestone (CaCO3(s)) to lose carbon dioxide (CO2(g)) and turns it into quicklime – calcium oxide (CaO(s)). Industry typically burns fuel to achieve such high temperatures, but this produces greenhouse gas emissions. The project aims to replace the fuel used in this process – which are responsible for 40 per cent of total CO2 emissions – with solar heat. “Even though fewer emissions are produced in the cement production process, using a solar process to produce cement would reduce CO2 emissions by as much as 20 per cent,” he pointed out.

The technology – building and testing solar reactors

For this high-temperature chemical reaction to take place, researchers need the right equipment. As part of the project, they have already constructed two laboratory-scale solar reactors to break down calcium carbonate in lime and cement production. The rotary kiln is in Germany (the German Aerospace Center, Cologne) and the fluidised bed reactor is in France (the French National Centre for Scientific Research, Paris). In the SOLPART concept, the solar reactor supplies hot reacted particles to a particle storage container to simulate the industrial process operating 24 hours a day. “Laboratory testing of these 10 KiloWatt reactors has started and will continue over the course of 2017,” said Flamant. Once the testing process is complete, the project team will decide which reactor to scale up for the next phase of the project. The next reactor will be between three and five times bigger than the current laboratory reactors. Once work in the SOLPART project is complete, the engineers could start building an industrial pilot with a 500 KiloWatt to 1 MegaWatt reactor in a follow on project. This would enable them to use and integrate solar technology into the large-scale production of cement and lime, and possibly even other materials.