(2b) Chemical Looping Gasification - A Study on Calcination/Carbonation Looping Cycle

At present there are no two minds on the fact that we are facing a great environmental challenge in the form of global warming and climate change caused by higher concentration of carbon dioxide in atmosphere which in turn is produced from combustion of fossil fuels. But the present economy is all carbon based, so issues right now is how easily we can shift from this carbon based economy to renewable based without compromising on the energy need. For that do we have the technology to capture carbon dioxide as well as provide us with the energy we wanted? To overcome this challenge author’s has come up with the concept of Chemical Looping Gasification. It produces hydrogen rich gas from the biomass using steam gasification technology which can be used for fuel cell technology, as well captures carbon dioxide during the process and regenerates it producing the pure stream of carbon dioxide for direct sequestration.

The system consists of two reactors: one is a bubbling fluidized bed gasifier and another is a circulating fluidized bed regenerator. The fuel is fed into the gasifier that receives calcium oxide from the regenerator and steam from an external source. During gasification, the carbon dioxide produced will be captured by the calcium oxide that makes up the bubbling fluidized bed. Immediate removal of the reaction products, CO₂ from the system will increase the rate of water-gas shift reaction, and therefore yield higher hydrogen. The calcium carbonate formed in the gasifier will move into a circulating/Transport regenerator where it decomposes (calcines) into calcium oxide and carbon dioxide. The calcium oxide is returned to the gasifier, and the carbon dioxide is taken for sequestration. A pilot plant of 5 kW capacities has been built and the tests are underway.

However the limitation is imposed by the loss in the activity of the sorbent CaO for capturing carbon dioxide which may be due to sintering of the sorbent, deposition of tar and char around the sorbents. To identify the loss in activity of the sorbent, an experiment is being conducted by taking the sample going into and out of the gasifier. Sample going into will shows the capacity of regeneration while coming out will give the absorbing capacity. SEM technique will be used to analyse the samples and identify the sintering rate. The results from this experiment will be presented in this paper.