What is clean coal?
The UK Government hasn’t specifically made clean coal one of the solutions that will help achieve 2020 emissions targets and beyond – rather clean coal is one of the possible projects that is linked to Carbon Capture & Storage (CCS) initiatives that are currently in the pipeline. More about public policy later.
The clean coal process seeks to reduce harsh environmental effects by using multiple technologies to clean coal and contain its emissions. For example now CCS involves capturing the carbon dioxide, preventing the greenhouse gas entering the atmosphere or the coal can be cleaned before it is burned. However many of the approaches are yet to be made available on a large commercial scale because of the costs involved. This section focuses specifically on clean coal but there are other solutionsCCS and washing coal, for example, are one of the solutions.
Current conventional coal technology
The combustion and the subsequent emissions from conventional coal fire power stations is one least environmentally free ways to generate electricity. When coal is burned, it produces emissions that contribute to global warming, create acid rain and pollute water. For example burning coal emits the following: sulphur dioxide (acid rain); nitrogen oxides (ground-level ozone) and particulates (affects people’s respiratory systems). Although Nuclear Power can have devastating effects if things go wrong at the power station or if toxic waste is not properly disposed off (very low probability), the emitting process doesn’t have the impact on the environment that coal burning has.
Clean coal technologies available
The best known technology which seeks to capture and store the CO2 away from the power plant that has created it. There are several ways the CO2 can be stored and are either geologic or oceanic solutions. An example of geologic, is where the CO2 can be pumped into disused coal fields. This then displaces the methane which can be used as fuel for other purposes. CO2 can be pumped into and stored into saline aquifer. Finally CO2 can be pumped into oil fields, helping maintain the pressure and making that process easier for extraction.
Oceanic storage is a technology that is still in its infancy and involves injecting liquid CO2 into water which is between 500 to 3,000 meters deep. The expectation is that the CO2 would dissolves under pressure. The snag to this process is that it may impact the pH of the water and therefore harm marine habitats.
When coal burns, it releases carbon dioxide and other emissions in flue gas. This is most prominent when seeing large plumes of smoke coming out of the power station chimneys. The Coal Washing process looks to clean the material and purify it before it burns. This type of coal preparation removes unwanted minerals by mixing crushed coal with a liquid and allowing the impurities to separate and settle.
Another system, looks to control the coal burn to minimize emissions of sulphur dioxide, nitrogen oxides and other trace greenhouse gases. Wet scrubbers, or flue gas desulphurisation systems, remove sulphur dioxide, a major cause of acid rain, by spraying flue gas with limestone and water. The mixture reacts with the sulphur dioxide to form synthetic gypsum, a component of drywall.
Low Nitrogen oxide burners reduce the creation of nitrogen oxides, by restricting the amount of oxygen available in the hottest part of the combustion chamber where the coal is burned. This minimises the formation of the gas and requires less post-combustion treatment.
Electrostatic precipitators remove more than 99% of the particulates from the flue gas. The system operates by charging particles with an electrical field and then capturing them on collection plates. These particulates if not removed aggravate asthma and cause respiratory ailments.
The process of gasification avoids burning coal altogether. With integrated gasification combined cycle (IGCC) systems, steam and hot pressurised air or oxygen combine with coal in a reaction that forces carbon molecules apart. This results in the creation of syngas which is a mixture of carbon monoxide and hydrogen (primary). These substances are then cleaned and burned in a gas turbine to make electricity. The heat energy from the gas turbine also powers a steam turbine. In effect an IGCC power plant can create two forms of energy, which means they have the potential to have much higher levels of fuel efficiency. According to US Dept. of Energy, this level of efficiency is as high as 50%.
Future development of the industry
Coal is still the most cost effective fuel for electricity production as the alternative forms cannot replace a power source this cheap and plentiful in supply. Therefore clean coal technology offers an opportunity to mitigate the increasingly severe climactic effects of coal emissions with some of the process explored in the previous sections. The Vattenfall-Schwarze Pumpe plant in Germany is a common example of a power plant that uses carbon capture technology.
However as some of the technologies are not yet commercially viable, clean coal is still in development to be part of the ‘zero-emissions’ solution. For example Utilities in the UK will not always trade-off more technology to help the environment versus the technology that is commercially viable. In 2009 the Secretary of State for the Dept. of Energy & Climate Change (DECC) gave the go-ahead to a funding mechanism to fund carbon capture projects for the next generation of Coal Fire Power plants and keep the UK as a global leader in this technology. With the current administration the DECC set a target to have at least four working, commercial CCS projects running by 2020 (some could be on gas fired or coal fired power stations). At the moment there are six projects in that have cleared the European Investment Bank financing hurdles and are up for being able to receive some of the €5bn Carbon Credits available to support a max of eight European projects in total. In addition to that, the DECC has now pledged a further £1bn of funding support to help get the first project up and operational.
Cleaning coal and storing its emissions significantly increases the cost of producing a Kw/h of electricity for an otherwise cheap fuel. However some of the by-products from the clean coal have helped the industry sell on residual products such as gypsum or commercial Co2 for fizzy soda. The clean coal industry would be helped by increasing the charging on carbon (e.g. carbon trading that is commercially stable), which would increase the financial viability of the technology.