Can we clean coal?
Carolina Johansson
Despite environmental concerns, coal is the world’s fastest growing fuel, according the BP 2008 Statistical Review of World Energy. Coal is plentiful and cheap compared with fossil fuels such as oil and gas.
In the United States, which has the world’s largest coal reserves, more than half of the electricity produced comes from coal-fired power plants. On a global scale, coal provides about 40 per cent of the electricity consumed, but as the economies of China and India continue to grow and industrialise this share is likely to increase further, according to the International Energy Agency (IEA).
Meanwhile, coal-fired power plants account for as much as a third of the world’s man-made carbon dioxide emissions, believed to be the root cause of global warming. For this reason, limiting CO2 emissions has been high on the global agenda to reverse climate change.
Finding and developing renewable energy sources is one way to tackle the problem, but it will be a long time before these new technologies are sufficiently developed to provide a serious alternative to fossil fuels. “Even with rapid development of alternative energy sources, coal will continue to be important for at least the next 50 years,” says Geoffrey Morrison, programme manager at the London-based IEA Clean Coal Centre.
“It’s vital to invest in ways of burning coal more cleanly, particularly with regard to the removal of carbon dioxide.”
Growing concern over CO2 emissions and tougher legislation to minimize them have spawned intensive research into technologies to enable cleaner coal production.Clean coal initiatives basically seek to reduce emissions from coal-fired power plants by employing technologies that facilitate the capture of carbon dioxide. They also address the issue of permanent storage of carbon.
“Carbon capture and storage (CCS) has to be part of any serious and affordable climate change strategy,” says Milton Catelin, chief executive of the London-based World Coal Institute. “The IEA tells us that stabilising emissions without CCS is impossible. If governments are serious about tackling climate change, then they need to get serious about investing in all low-carbon technologies, including CCS.”
There are three technologies available today for carbon capture – pre-combustion, post-combustion and oxy-fuel combustion. Pre-combustion capture involves gasification, or turning coal into a synthesis gas comprising hydrogen and carbon.
The technology, termed “integrated gasification combined cycle” (IGCC), was first successfully demonstrated on a commercial scale at the Cool Water Project in Southern California in the 1980s. There are currently a few commercial-size, coal-based IGCC plants in the United States and Europe, and some pilot projects are being launched, particularly in the US. While the technology holds promise, it requires investment in a dedicated new plant, which makes it relatively expensive.
The two other carbon-capture technologies may be retrofitted into existing power plants and power stations. One is oxy-fuel combustion, which involves burning fossil fuels in pure oxygen, resulting in an exhaust stream with a high concentration of CO2 and water vapour. These are then separated by condensation. The other is post-combustion capture, which involves removing CO2 from flue gases after hydrocarbon combustion.
Each of these three carbon-capture technologies has pros and cons, according to Morrison. “Pre-combustion capture on IGCC has the lowest energy penalty (reduction of net electric output), but IGCC is not yet in widespread commercial use,” he explains. “Oxy-fuel and post-combustion capture have higher energy penalties, but they can be potentially applied to existing plants. This is important, given the high inventory of existing pulverized coal-fired plants.”
All three of the technologies need to be further demonstrated and tested, he says. And all of them are at present less cost-efficient than traditional coal burning.Europe currently has several programmes in place to demonstrate carbon capture and storage. The US is developing similar programmes, China is catching up fast, and in Australia a number of small-scale CCS demonstration projects are under way.
“Most people in the industry expect CCS to be commercially demonstrated by 2020,” says Morrison. There are cost and regulatory uncertainties connected to CCS technology. The issue of clean coal is also controversial, and some environmental groups and others would rather see money invested in renewable technologies.
However, the world energy demand is projected to grow by 55 per cent between 2005 and 2030, and renewable technologies are just not sufficiently developed to really make a difference.
“Climate change is a serious issue and requires serious funding in all low-carbon technologies – renewables, energy efficiency, nuclear and CCS,” says Catelin. “The UN Intergovernmental Panel on Climate Change maintains that CCS could contribute 55 percent of all emission reductions by 2100.”
He says public investments in CCS represent excellent value for money. “One large-scale CCS power plant can supply the equivalent low-carbon electricity of 1,400 wind turbines,” Catelin says. “The truth is, the world is investing far too little in CCS and other low-carbon technologies.”
Courtesy: here/Alfa Laval
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