To do this, one of the five steam boilers that provide energy for the Lacq industrial complex was modified for gas combustion in pure oxygen rather than in air. This is called oxycombustion.

With this technology, combustion emits less smoke and fumes but with a much higher concentration of CO2 (between 90% and 95%), the rest being water vapor. The smoke and fumes from ordinary combustion are more than 70% nitrogen. With oxycombustion the CO2 is easy to recover, while with air combustion the process of separating the very diluted CO2 from large amounts of smoke and gas fumes is more expensive and energy intensive.

The oxycombustion option involved conversion of the boiler (the main change was installation of four new burners) and construction of a cryogenic unit to supply the oxygen.

Pipeline transport

Once the CO2 is recovered, it is washed, compressed to 27 bars and then dehydrated. It is then transported by pipeline to the Rousse gas field 27 kilometers away. The Rousse started producing in 1972 and was operated by Total for more than 30 years.

CO2 storage at Rousse

When the CO2 arrives at Rousse it is compressed again and then injected into a depleted natural gas reservoir 4,500 m below ground.

This reservoir is made of porous rock which becomes impregnated with CO2 (rather like a sponge soaking up liquid) and the gas is then trapped there just as the natural gas (also containing CO2…) was for thousands of years. However, the quantity of CO2 to be injected during the demonstration project is much smaller than the volume of natural gas originally contained in the reservoir.

Above the Rousse reservoir lies a gastight “lid” of thick marl and clay 2,000 meters thick. This formation is more than 35 million years old and remained intact when the Pyrenees were formed. Rousse is geologically isolated from other reservoirs in the region and is not connected to any active aquifer (i.e. porous underground rock impregnated with water). So Rousse offers optimum conditions of long-term safety.