Chemical looping combustion (CLC) is a breakthrough technology that I reviewed a couple of years ago (CCC/178). In CLC, an oxygen-containing solid such as a metal oxide supplies the oxygen to a fuel, and the spent oxygen ‘carrier’ is separately regenerated by high temperature reaction in an air stream (see below). As there is no direct contact between air and fuel, CO2 recovery is simplified, and there is potential for higher energy efficiency than for conventional CO2 capture systems. I went to the conference to gauge whether the technology had moved on significantly since the 2010 conference.
The conference had some streams concerned with carbonate looping also. This is a regenerable dry scrubbing technology being developed for capturing CO2 from flue gas. About 170 people attended.
Specific points from presented papers
• Much of the work reported was again at university and research institute level
• As at the last conference, there were papers on small-scale laboratory tests to evaluate new oxygen carriers, but fewer than last time
• Laboratory reactor tests using an iron-based carrier showed much of the coal mercury could appear in the fuel reactor gas stream, depending on temperature. This was the first reference to this potential issue. Mercury in the CO2 stream would adversely affect the cryogenic equipment used prior to storage. Another presenter said mercury can be made to remain in the solids.
• There continues to be active participation by industry
• There was now much more emphasis on coal CLC, as opposed to natural gas
• There were this time more tests reported from continuous rigs using coal. Nearly all use interconnected fluidised bed reactors to facilitate mass and energy transfer. CO2 capture at up to 98% has been shown.
• The 1 MWth CLC pilot plant at the University of Darmstadt has now been tested successfully in gasifier mode on one coal using ilmenite oxygen carrier. There was a visit to this plant during the conference. [It also doubles as a carbonate looping system.] • Alstom’s work in the USA on continuous CLC of coal has reached 3 MWth in a plant using CaS/CaSO4 carrier within their limestone-based chemical looping process
• Chemical looping with oxygen uncoupling (CLOU), in which the carrier and temperatures are selected to cause molecular oxygen release before reaction with the fuel, has now been tested in continuous equipment on lignite at up to 1.5 kWth. [This system speeds up the reaction of solid fuels greatly.] • A CLOU plant at 100-200 kWth scale, to use CuO/Cu2O carrier, is being constructed at the University of Utah.
• Alstom believes a 5% point energy penalty for CLC to be realistic. They hope for a 10-50 MW demonstration in 2014
• Design studies for a 450 MWe CLC power plant are continuing under the RFCS ECLAIR project, which also funds the 1 MWth pilot plant at Darmstadt
• A 10 MWth CLC plant, to provide steam for oil sand extraction and fuelled by natural gas, is planned by Cenovus Energy in Canada, operation from 2015-2017
• Sankar Bhattacharya’s team at Monash University are now looking at CLC of lignite
• Pressurised CLC of coals (for use in a combined cycle) is not regarded by most as a feasible option
CLC will not be ready at utility scale until around 2025. Oxygen carriers based on low value or natural materials (e.g. steel rolling mill residues, ilmenite, limestone) are required for coal CLC. There is a need to develop a low-cost CLOU carrier. As well as continuing to show high CO2 capture efficiency (necessitating minimal loss of char from fuel reactor to air reactor), further work on CLC for coal needs to confirm optimal reactor designs and process configurations, adequate carrier lifetime and good carrier/ash separation. These will enable practical solids inventories in the system per MW and limit the make-up of spent carrier and so keep the plant size and cost down. There were few references to economics, but one study indicated a lower cost of electricity than more familiar coal technologies with CO2 capture. The next stage is for scale-up to about 10 times the current, and, although natural gas-fuelled CLC will probably be first to get there, coal CLC is catching up. Carbonate looping would have a different application, and is much closer than CLC to commercial deployment (retrofitted to existing plants).
The social/cultural highlight of the meeting was the conference dinner, aboard a large cruise boat on the Rhine. I have never been on board such a smoothly running vessel. Engines were inaudible and could not be felt except right at the stern. The 4-hour trip covered 56 km from Rüdesheim to Koblenz and gave spectacular views of the many castles, churches and vineyards along the way. It was decades since I had been there, and the views were even better from the river than from the road. As at the last conference, Anders Lyngfelt treated us to some of his unique and amusing chemical looping-related folk songs.