Block’s Indicator of Sustainable Growth

by Ray Block

There is already enough evidence worldwide that CO2 storage will work well, if the geological structures selected for permanent storage are depleted oil and gas reservoirs, coal seams or saline aquifers.

 

However, carbon capture is another matter in the battle for clean coal. There are currently at least three pilot plants testing different technologies for CO2 removal. One of these, the Schwarze Pumpe project in East Germany is the first pilot plant in the world to demonstrate the technology of oxy-combustion, also known as oxy-fuel firing.

 

The Swedish company, Vattenfall, which operates the existing high emission lignite-fired 1600MW power plant in Eastern Germany has chosen the French company Alstom, a major world supplier of power generating equipment to install a 30 MW pulverized coal demonstration pilot next door to the large power plant. The test procedure is to demonstrate the complete oxy- fuel chain, starting with oxygen production and ending with CO2 purification and compression.

 

As described in Power Engineer- IT Automation, the Schwarze Pumpe demonstration project was launched in September 2008, with the construction of the plant and commissioning of the boiler. In the first test period, lignite is the focus of the testing, and in the second test period, bituminous coal will be used.

 

The tests will concentrate on data relating to heat transfer, combustion efficiency, emissions, dynamic behaviour, plant design, performance, cost and economics for both new and retrofit applications. Pumping in pure ogygen to burn the fuel and processing the emissions consumes about 14 per cent of the test plant’s generating capacity, and road transport costs for the CO2 will further substantially reduce the technology’s efficiency.

 

A pilot plant for pre combustion of CO2 involves the Spanish power company Elcogas in Puertollana. The research organisation Bellona visited Elcogas early in 2008. With a budget of 18.5 million euros funded by government and the consortium of nine industrial companies owning the company, the construction and testing of the world’s first pre-combustion technology for CO2 removal is about to begin.

 

The 14 MW thermal plant to be commissioned in the first half of 2009 is being integrated with the existing 335 MW power plant, and achieves a net efficiency of 42.5 per cent. This is 10 to 15 per cent higher than existing conventional power plants. It is fitted out with a IGCC (integrated gasification combined cycle) power generation unit, only one of the first four IGCC plants to go into service worldwide.

 

Pre combustion capture systems remove CO2 prior to combustion, which is achieved via gasification of coal. This produces a synthetic gas (syn gas), which is primarily a mixture of carbon monoxide, methane and hydrogen. Before combustion, the syn gas is reacted with steam to produce CO2, which is subsequently scrubbed from the gas stream, usually by a physical or chemical absorption process. The result is a hydrogen rich fuel. Pre combustion systems are intended  to work in conjunction with IGCC technology.

 

The third pilot devoted to post combustion capture (PCC) of CO2 involves an international agreement by Australia’s scientific and industrial research organisation, CSIRO with China’s Thermal Power Research Institute (TPRI). TPRI will install, commission and operate a PCC pilot plant at the Huaneng Beijing co-generation power plant. CSIRO’s involvement in post combustion is the second such project for the research group. They are also involved in a PCC pilot plant installation at Delta Electricity’s Munmorah power station on the central coast of the Australian state of NSW.

 

As described in the blog Chemical Engineering World (May 12 2008), PCC is a process that uses a liquid to capture C02 from power station flue gases. It is a key technology that can potentially reduce emissions from existing and future coal fired stations by more than 85 per cent. In a traditional power plant, coal is pulverised and burnt to produce high pressure steam. Flue gases leaving the boiler are filtered to remove dust and then vented to the atmosphere. These gases contain around 10-15 per cent CO2.

 

Flue gas is cooled and cleaned, then fed into the bottom section of a CO2 absorber. It then passes through an absorbing solution containing a chemical to capture the CO2,. and the clean flue gas, virtually 100 per cent nitrogen is released into the atmosphere. The CO2 is then removed from the absorbing solution by steam heating to allow the absorber to be reused. The CO2 is compressed and cooled to form a liquid, which is then available for transport and permanent storage.

 

The benefits of PCC is that it can be retrofitted to existing plants and is a prospective means of substantially reducing greenhouse intensity.

 

A summary of the three methods for capturing CO2 was produced by the European research group TAB. Working paper No 120 November  2007 finds advantages in each of the technologies, but counterbalanced with disadvantages at the same time.

 

Ø      As already stated, the post combustion process can be integrated into existing industrial processes and power plants. But this is offset by relatively high costs and energy losses. A lot of research is needed to increase efficiency, particularly for further developing the solvents used, but also to improve the process integration and to optimise its deployment in power plants.

Ø      Pre combustion has a lower energy requirement and offers the advantage of producing hydrogen or synthetic fuels from coal with relatively low C02 intensity. The big negative is the great complexity of the plant and its operation. The key components are highly efficient hydrogen turbines, which are currently in the pilot stage of development.

Ø      The oxyfuel process has the advantage that a relatively high concentration of CO2 is available, and the flue gas stream to be processed is much smaller than for the other processes. But the big disadvantage is the high use of energy and the considerable costs involved.

 

There are other alternative separation processes, but these are going to take a long while to develop. Such as the use of fuel cells, the Zeca process and “chemical looping combustion”. In the meantime, a good 10 years or so may be necessary to get the CO2 separation processes to work effectively with zero or near zero emissions. But one thing is certain. Developing clean coal is a worthy ambition, but very costly.

 

 

 

 

 

 

 

 

y Ray Block

Posted under Carbon Abatement Scheme, Climate Change, Global Warming