reducing emissions from brown coal

http://www.globalccsinstitute.com/insights/authors/dennisvanpuyvelde/2013/07/05/reducing-emissions-brown-coal

Reducing emissions from brown coal
05 Jul 2013 | Dennis Van Puyvelde
While I was on leave in June I attended a workshop on brown coal drying. This was the first seminar session for this year in a series organised by Brown Coal Innovation Australia which supports research, development and demonstration to ensure the ongoing use of Victoria's lignite resources in Australia. Other planned seminars for this year include coal gasification and CCS.

The presentations at the workshop were of high quality and many of them drew on elements of carbon capture. Indeed, I observed a number of synergies between coal drying and carbon capture.

Firstly some background.

Brown coal in Victoria, Australia has around 66% moisture content. This means that each tonne of coal mined produces 2 tonnes of water (the local joke is that it is a water mine contaminated with carbonaceous material). As a result, the coal has a very low calorific value of less than 10GJ/tonne. This results in large power stations (to account for the additional steam) and low energy efficiencies. Drying the coal would improve the overall efficiency of power generation. While Australia's lignites are one of the most 'wettest' around the world, there are many other countries that use lignite, such as Germany, whose lignites only have 55% moisture. So drying of lignites is an important issue around the world to reduce emissions from the ongoing use of lignites.

I was able to obtain a sample of 'dried' brown coal that has been processed. The aim of processing this coal was to be able to develop a product that has an equivalent energy content to black coal. The sample below is from a Victorian brown coal that was dried and extruded to form a type of briquette. Being able to process lignite like this may allow it to be considered as another energy export from Australia and to be used as a substitute fuel in power stations in say Japan, where a lot of Australia's coal exports are used.



Some of the other forms of brown coal utilisation included converting to liquids or slurries.

I came away with the following observations from the workshop.

There are many drying technologies. A review indicated that there are 72 technologies available for the drying of coal. Some are more advanced than others and some of these may never proceed to commercial reality. Similarly, there are many different capture technologies and some of these will have a better success at proceeding to commercial reality compared to others. Some technologies involve squeezing the water out of the coal, others involve heating the coal with steam to remove the water and others require a 1,000 m deep well to remove the water through a combination of pressure and heat.
Both drying and capture are immature technologies and need to progress through two valley of death. The first valley of death addresses the technical issues and a second one addresses commercial issues. Many of the technologies promoted for drying are still addressing technical issues but some of them were at the stage of addressing commercial issues only. Indeed, the only drying technology that is in commercial operation in Australia is that of fluidised bed drying. On the other hand, many of the capture technologies such as post combustion capture using amine type solvents, oxy-combustion and capture from gasification processes have proceeded past the technical issues and the current work in carbon capture is mainly focussed on commercial issues. Nevertheless. there is also ongoing work to address technical issues for second and third generation capture technologies such as MOFs.
Reducing emissions is a portfolio approach. Many organisations often promote the use of a portfolio approach to reducing emissions in order to ensure that the concentration of CO2 in the atmosphere does not exceed 450 ppm . The technologies often talked about are CCS, energy efficiency, nuclear, fuel switching and renewables. However many of these technologies tend to be promoted within certain industries. Indeed, drying of brown coal is a way to improve energy efficiency but it has implications on other technologies such as carbon capture. All these technologies need to be developed in parallel to identify and work with the synergies between the technologies. For example, drying of coal will produce a flue gas with a higher CO2 content and hence have impacts on capture of that CO2 from the resulting flue gas.
Competition between low-emissions technologies. Many of the proposed drying technologies made use of the waste heat available at power stations. Indeed, many of the cost reductions for carbon capture also include better integration between the capture plant and the power station, and this often uses the same heat sources as those proposed for the drying of lignite. A holistic approach needs to be considered to ensure the integration of either and/or both capture and drying achieves the maximum reduction in CO2 reduction per unit of usable energy produced.
A banker does not have a technologist view of technology. One of the plenary presentations showed the audience (mainly technologists) how a financier would look at projects for coal drying. The first thing the financiers will consider is the financial model. i.e. does it make sense. Then they would proceed to determine whether the technology would deliver as estimated. This is difficult for first of a kind technologies such as coal drying but also carbon capture since the financial world does not have experience with these technologies. Hence they are considered as high risk - from a financiers perspective anyway. Focussing on achievements at pilot and demonstration plants is essential to make the case. Finally the financier would consider whether the market would exist well beyond the terms of the loans. For example, they would want to be sure that there is a market for dried coal for at least 25 years if they were to provide funding over a 20 year period. This also implies ensuring that the product from the process fits into the market. This was quite unique to brown coal as it may be difficult to sell a partially dried coal with a calorific value of 22 GJ/ tonne into a market that required a calorific value of 26 GJ/tonne.
There are many things to be learnt by taking a broader approach to the energy industry rather than focussing specifically on your own technology area such as solar PV or post combustion capture. Indeed, it is widely recognised that the only way we will be able to restrict global emissions to less than 450 ppm CO2 is through a portfolio approach. More cross sectional effort is needed to identify how the different components of this portfolio can work together and support each other.

For brown coal, the drying of brown coal will have benefits in that it will reduce the emissions from the use of brown coal but it may also create additional opportunities for using brown coal as an alternate fuel source that can be exported.