veryone needs energy from fossil fuels in one form or another. They are what keeps us mobile through combustion engines and

through electricity generation, power the gadgets and appliances that have improved our quality of life greatly from something as simple as a light bulb to a supercomputer.

EBy far the greatest primary source of energy used in the world is fossil fuel (coal, oil and natural gas). Oil remains the world leading energy source accounting for 33% of global energy consumption in 2012 followed by

coal at 30% and natural gas at 24%. The rest is split up between hydro, nuclear and other renewables (e.g. biofuel) as shown in Figure 1 [1]. The bulk of the primary sources of energy are predominantly used in electricity generation. This means in the pursuit to solve any issues with primary energy use and sustainability it is essential to scrutinize electricity generation. 67.4% of electricity generation was done using fossil fuels in 2010, mainly coal and gas [2]. Irrespective of the economic benefits of fossil fuels, the environmental impact, especially that coming from carbon dioxide emissions, is impossible to overlook.

The issues

Fossil fuels are carbon based fuel sources which release predominantly carbon dioxide when they go through combustion. Carbon dioxide is a greenhouse gas which means it absorbs and emits radiation within the thermal infrared range in the atmosphere [4]. This process is what keeps earth at a relatively cool temperature. Carbon dioxide makes up almost 80% of anthropogenic (manmade) greenhouse gas emissions [7]. Over the last century the amount of CO2 in the atmosphere has risen,

largely driven by fossil fuel use but also because of land use change and deforestation. Atmospheric

concentrations of CO2 have increased by 35% since the industrial revolution [4]. It has been confirmed by various well respected research groups and the Intergovernmental Panel on Climate Change that global warming is occurring due to human an activity [21]. Evidence of global warming can also be seen in the extreme weather events which have been occurring all over the world in the past decade [8]. The other issue with fossil fuels is their non-renewable nature. From current estimates oil, coal and gas will run out in approximately 52.9, 109 and 55.7 years respectively if energy consumption follows the current trend [1].

Even with these issues, a sustainable energy future will require using all the resources available to us over the short, medium and long term. At the same time, it means producing and utilising all these energy sources in a way that minimises adverse impacts on the environment and maximises economic and social benefit. To make this possible new oil, coal and gas extraction techniques are being developed alongside a rapidly developing renewable energy industry. Various technologies are also being developed to tackle the release of the other by-products of fossil fuel combustion which are also pollutants. By-products such as oxides of sulphur (SOx) and nitrogen (NOx) – and particulate and trace elements, such as mercury [14]. The technologies mainly discussed, will be the ones which tackle the issues of fossil fuels because they still have a high energy density and they will still play a big part in future electricity generation.

Coal

Coal has long dominated as the main fuel for electricity. It has been the fastest growing energy source in the last decade and this is largely driven by the growth of developing economies, mainly China [1]. In 2012 China

NEW AND EMERGING ENERGY SUPPLY TECHNOLOGIES FOR A GREENER FUTURE.

Figure 1: Global energy consumption 2012 [1]

alone accounted for 50.2% of global coal consumption. It is so popular because Coal is the most prevalent and widely distributed fossil fuel, accounting for 64% of globally economically recoverable fossil resources

compared to 19% oil and 17% natural gas [14]. Coal is recoverable across every continent and every region which provides energy security across broad political arenas [9]. Coals abundance and distribution, coupled with its relatively low and

stable price pattern makes it a reliable supply of energy. This makes it a very attractive base load fuel. This means electricity generated from coal is one of the first sources to be dispatched throughout the electric grid. Super critical coal fire power plants are one of the most affordable methods of power generation in China, costing USD 33/MWh compared to USD 50 for hydro, USD 53 for nuclear and USD 71 for wind [17].

The problems of using coal

Even though the market price of coal is low, the true cost is reflected in its impact on the environment and humans. To assess the true cost of coal you have to look at the supply chain, i.e. the mining of coal, combustion and waste disposal.

The mining causes widespread deforestation due to the excavation, soil erosion and pollution. Miners also suffer from Coal Workers’ Pneumoconiosis, colloquially known as black lung disease. Working in a coal mine overtime will lead to the accumulation of dust in the lungs which will cause many health problems [15]. The combustion of coal releases more of the anthropogenic CO2 released into the atmosphere than any other fossil fuel. These include sulphur and nitrogen oxides and particulate trace elements such as mercury. These pollutants when released lead to the formation of photochemical smog and acid rain [15]. The waste from coal combustion known collectively as Coal

Combustion Wastes (CCW). These are mostly ash which is toxic and often laced with lead, arsenic and cadmium. When placed in a landfill, these can seep into the ground and contaminate ground water [15].

The solution

The answer to solving these issues will come through the development of efficient technologies which reduce the waste produced at each stage and neutralise the adverse environmental impact. Legislation has led to the development of technologies which remove the particulates from coal combustion and this has proven effective [12]. A considerable amount of the waste from coal power plants is also recycled. Fly ash and bottom ash are used in concrete and blended cement and boiler slag is used in grit/roofing granules [22].

More efficient coal use

By making electricity generation more efficient the amount of coal per megawatt will be reduced which in turn would reduce the effect of coal on the environment. Current pulverised coal fired plants (PCF) are mostly sub-critical power plants [17]. Significant efficiency improvements and reduction in CO2 can be achieved if these are replaced by higher efficiency supercritical (SC) and ultra-supercritical plants (USC) which operate at higher pressure and temperatures. Another alternative would be Integrated Gasification Combined cycle plants (IGCC) which also offer improved efficiency. IGCC plants use a gasifier to convert coal to syngas, which drives a combined cycle turbine. The average PCF plant efficiency is currently 33% compared to 45% for the more efficient SC, USC and IGCC plants [9]. Highly efficient modern power plants also emit up to 40% less CO2 than the previous coal plants [9]. As a result improving the efficiency of the oldest and most inefficient plants would reduce CO2 emissions from coal use by 27% representing nearly a 7% reduction in global CO2 emissions [9]. With greater efficiency, comes greater running cost but the benefits to the environment outweigh this.

Carbon capture and storage

Figure 3: Carbon capture and storage [16]

These plants are also easier to fit with carbon capture and storage technology (CCS) which can reduce CO2

emissions to the atmosphere by 80-90%. This involves capturing CO2 that would otherwise be released to the atmosphere and injecting it to be stored in deep geographical formations. There are several ways to carry out carbon capture [16].

Capture

Post combustion – directly separating CO2 from regular flue gas after the combustion process. The flue gas is cooled and treated to remove particulate matter. Once cooled, the gas enters an absorber which consists of a liquid solvent (usually chilled ammonia) which absorbs the CO2. The CO2

- rich solution is then sent to a stripper where it is separated into two gases: the pure amine gas, which is recycled into the stripper and a CO2 stream which is then dehydrated, compressed and sent to storage [16].

Pre- combustion – carbon and hydrogen are separated prior to combustion. In this process, air is purified to extract pure oxygen (O2). The O2 is then sent to the gasifier where it reacts with the fuel source (coal/natural gas) to create a synthesis gas, or syngas. The syngas is purified which leaves a mixture of hydrogen (H2) and

carbon monoxide (CO). Steam is then added to a shift reactor which converts the CO to CO2 and H2. The H2 gas stream can be burned cleanly to produce steam to run the turbines for electricity generation. The pure CO2 stream is then dehydrated, compressed and sent to storage [16].

Oxyfuel Combustion – also involves purifying the air to extract pure O2. The coal is then combusted with pure O2 which is used to create steam to run the turbines for electricity generation. The flue gas produced will have a very high concentration of CO2 due to the absence of nitrogen (N2). This can then be captured as in post combustion capture, then stored [16].

Post combustion and oxyfuel capture can be retrofitted to existing power stations and new power plants constructed over the next 10-20 years [21]. Pre combustion on the other hand requires utilising IGCC cannot be retrofitted but it makes coal potentially more flexible because the hydrogen produced can also be used in hydrogen fuel cell transportation [21].

Storage

After the capture of the CO2 the storage becomes the next issue to deal with. The geographical features being considered for CO2 storage fall into three categories; deep saline formations, depleted oil and gas fields and unmineable coal seams. The Intergovernmental Panel on Climate Change (IPCC) special report on carbon capture and storage found that the risk of leakage was very likely to be less than 1 % over 100 years [21].

Deep saline formations – Very large, porous rock formations typically atleast 800m below the

surface and containing water that is unusable because of its high mineral

content and/or salt. This saltwater is around 10 times saltier than ocean water and it’s trapped by impermeable rock called “cap rock” for millions of years. CO2 injected

Figure 4: carbon storage potential [21]

into the formation is contained beneath the cap rock and over time it will dissolve into the saline water. Saline formations have the largest storage potential but are the least well explored [21].

Depleted Oil and Gasfields – well explored and have proven ability to store hydrocarbons over a long period of time. CO2 is already widely used in Enhanced Oil Recovery (EOR) from mature oil fields [18]. Injecting CO2

into an existing oil field reduces the oils viscosity making it flow easier, and also acts as a pressurising agent pushing more oil out of the rock. In EOR, the CO2 can therefore have a positive commercial value [21].

Unmineable coal seams – when the CO2 is injected into the seam it is adsorbed by the coal in preference to other gases e.g. methane which are displaced. This is feasible when used in conjunction with Enhanced Coal Bed Methane (ECBM) because the methane released can be captured and used as a very clean fuel source [18].

CCS has great potential in creating a sustainable energy future but it is still a relatively new field which still requires a lot of research and development. The first commercial example was setup as recent as 2000 in Weyburn oil field in Midale, Canada. Figure 5 shows the different stages each aspect of CCS is on in

developmental terms. Carbon capture can also be used in any fossil fuel power plant such as a natural gas plant [21].

Natural Gas

Natural gas has been widely discussed as a less carbon- intensive alternative to coal. It is the second most used fuel source having a 22.2% share in electricity generation [1]. Coal production in 2012 increased by only 2.5% (lower than the usual trend) which is mostly due to a large increase of natural gas consumption of 4.1% in the US [11]. Combustion of natural gas releases around 50% less CO2 than coal per unit of electricity output and significantly less SO2 which means before the wider implementation of CCS, natural gas is a better option for electricity generation [12]. In 2008, in the US only 21% of natural gas fired electricity was generated by steam turbine plants and simple cycle turbine plants which are relatively inefficient [11]. 79% was produced by combined

turbine plants, which use waste heat to run steam turbines boasting efficiencies on average 49% which is much higher than coal plants. It is widely considered as a “potential bridge fuel” for addressing climate change and transitioning into a future powered by low-carbon renewables [20]. An issue could be the possibility of natural gas running out but new gas extraction techniques are being developed to allow access to this cleaner source of fuel.

Figure 5: Stages of develoment of CCS [21]

Fracking

Figure 6: hydraulic fracturing [12]

The main method which has been in news headlines recently is hydraulic fracturing also known as fracking. Fracking gives us access to previously uneconomical shale gas which is just natural gas that is trapped within shale formations [12]. Shales are fine-grained sedimentary rocks that can be rich sources of natural gas. Shown in Figure 6, fracking is a technique in which water, chemicals and sand are pumped into these shales to unlock the hydrocarbons trapped by opening cracks (fractures) in the rock and allowing natural gas to flow from the shale into a well. It is necessary to use fracking in conjunction with horizontal drilling because shale gas does not usually flow to the well rapidly and commercial quantities cannot be produced, fracking makes the rapid flow possible [12].

Issues with Hydraulic fracturing

However, there are some environmental issues which are associated with fracking. Firstly, fracturing wells require large amounts of water and this significant use of water may lead to water shortages and it may affect aquatic life [19]. Second, if not managed properly, hydraulic fracturing

fluid, which contains hazardous chemicals such as lead or radium, can be released leaks or spills [19]. Fracking also produces large amounts of waste water, which may contain dissolved chemicals and other contaminants that would require treatment before disposal [19]. Lastly, fracking causes small earthquakes, but these are almost always too small to cause concern. However, along with natural gas, fracking fluids and formation water are returned to the surface. These waters have to be injected back into the deep wells which can cause earthquakes large enough to be felt and may cause damage [19].

Alternatives

If extraction methods are made safer, natural gas electricity generation could be a method of slowing down climate change. A more permanent option would be to eliminate carbon dioxide completely and use renewable energy such as biofuels, solar, hydro or wind generated electricity. Although the adoption is on the rise in the developed world. Many developing countries will opt for fossil fuels because they’re cheaper to produce [13]. Hydro power has proved he most successful and is well implemented but it requires that there is an existing large water bodt. Other problems are that solar and wind farms require land which could be used for farming purposes. Solar and wind energy is also not consistent so storage methods will need to be developed.

Energy storage through hydrogen

Figure 7: Energy storage through hydrogen

One of the storage methods being developed acquires inspiration from plants [13]. This is called the artificial leaf concept. Instead of using photocells to generate electricity directly from sunlight, you deploy a chemical reaction that stores solar energy in the form of hydrogen, which you can then use in a hydrogen fuel cell to generate electricity [13]. This is still in the developmental stage and the main issue is in trying to find a

combination of materials that give you a cost effective reaction which would allow large scale implementation [13]. These carbon neutral electricity generation methods are in no doubt the key to tackling climate change but a lot of research is necessary to make them a sustainable affordable energy source [13]. It is perhaps the reason to consider separate primary energy which doesn’t produce greenhouse gases, nuclear energy.

Nuclear

Global nuclear output fell by 6.9% in 2012, the largest decline on record, mostly due to and 89% decline in nuclear output in Japan [1]. This happened due to a tsunami which devastated japan and cause a meltdown at the Fukushima plant. One year after the disaster all 52 nuclear reactors were shut down leaving only 2 [5]. Authority to restart these power plants was given to the local governments but in all case they decided against it. This was heavily due to public opinion. Problems with nuclear power include the possibility of these accidents, radioactive waste disposal and the possibility of terrorist attack, which would occur due to terrorists stealing the enriched nuclear materials. This has led to Germany deciding to close all its reactors by 2022 and Italy banning nuclear power completely. Nuclear power is also relatively expensive and the decommissioning of a plant can take years [5].

Better safer nuclear

Figure 8: Travelling wave reactor [23]

All these issues stem from the materials used as a fuel source. Today’s light water reactors use thermal energy produced from the fission uranium (U-235) [23]. The Enrichment of U-235 releases U-238 as a by-product and this is currently set aside as waste. A company called TerraPower are currently in the development stages of a travelling wave reactor (TWR) which uses this U-238 as its fuel source. For conventional nuclear energy plants, U-235 is used because U-238 is considered too weak of an energy source [23]. A new method can be used to extract the latent energy from U-238, making it a perfect source of energy for the TWR. The poorly splitting isotope of uranium (U-238) can be converted to easily splitting plutonium given the investment of a single neutron [23]. When a second neutron comes around, the newly transformed plutonium will readily split and produce energy. While this concept is used by breeder reactors via recycling, TWRs do not require the plutonium to be removed from the reactor and refabricated into new fuel. The power effectively moves from the part of the core that’s active to the part of the core that has just produced enough fuel to sustain a chain reaction. A travelling wave reactor can run for 40+ years without refuelling, produces 7 times less waste and rely on natural physics for safe shut down without human involvement. This will also reduce the waste from the nuclear legacy of the word [23].

The travelling wave reactor is not the only nuclear technology being considered for providing energy in the future. There are other types of fast breeder reactors being considered such as the thorium fuel reactors and high temperature reactors such as molten salt reactors (MSRs) and others. Each of the alternatives offers a different set of advantages, including improved safety, reduced waste, less risk of weapons proliferation, and improved operating efficiencies. Nuclear fusion could even be on the cards in the future. The National Ignition Facility (NIF) in California USA in 2013 was the first facility to achieve an important milestone in the commercialisation of fusion by producing more energy than the energy applied. With more research and development into nuclear technology it could be a sustainable energy source for the future [4].

Conclusion

In the short term oil and natural gas will be the main primary sources for electricity generation. This means research and development into the technologies discussed will be essential to tackling climate change. Medium term and moving towards long term, renewables will be the solution and if development of nuclear reactors increases, nuclear energy could be the ultimate source of energy.

References 1. BP (2013). BP Statistical Review of World

Energy June 2013. London: BP. 1-24.2. International Energy Agency (2012). Key

World Energy Statistics. Paris: International Energy Agency . 6-35.

3. Anonymous. (2014). Sustainable energy. Available: http://withouthotair.blogspot.co.uk/. Last accessed 7th Mar 2014.

4. Chris Pash. (2014). The World's Top Scientists: Take Action Now On Climate Change. Available: http://www.businessinsider.com.au/the-worlds-top-scientists-take-action-now-on-climate-change-2014-2. Last accessed 7th Mar 2014.

5. Green Peace. (2011). Nuclear power - the problems. Available: http://www.greenpeace.org.uk/nuclear/problems. Last accessed 7th Mar 2014.

6. Shahriar, S Erkan, T. (2009). When will fossil fuel reserves be diminished?. Energy Policy  . 37 (1), 181-189.

7. Richard Black. (2011). Global warming 'confirmed' by independent study. Available: http://www.bbc.co.uk/news/science-environment-15373071. Last accessed 07 Mar 2014.

8. Fiona Harvey. (2012). Scientists attribute extreme weather to man-made climate change. Available: ccsmanmade-climate-change. Last accessed 07 Mar 2014.

9. World Coal association . (2013). COAL MEETING THE CLIMATE CHALLENGE. Available: http://www.worldcoal.org/coal-the-environment/coal-use-the-environment/improving-efficiencies/. Last accessed 7th Mar 2014.

10. International Energy Agency. (2010). Coal. Available: http://www.iea.org/topics/coal/. Last accessed 7th Mar 2014.

11. U.S. Energy Information Administration. (2012). What is shale gas and why is it important?. Available: http://www.eia.gov/energy_in_brief/article/about_shale_gas.cfm. Last accessed 7th Mar 2014.

12. Fullon M, (2011). Comparing life-cycle greenhouse gas emissions from natural gas and coal. Frankfurt: World Watch Institute. 3-24.

13. Energy Saving Trust. (2007). Getting started with renewables.Available: http://www.energysavingtrust.org.uk/Generating-energy/Getting-started-with-renewables. Last accessed 7th Mar 2014.

14. World Coal Association (2007). COAL MEETING THE CLIMATE CHALLENGE. Richmond: World Coal Institute. 1-36.

15. Short, R (2008). The True Cost of Coal. Amsterdam: Greenpeace International. 8-32.

16. ICO2N. (2008). What is carbon capture and storage - An overview.Available: http://www.ico2n.com/what-is-carbon-capture. Last accessed 7th Mar 2014.

17. Anthony, J. (2006). Modelling New Coal Projects: Supercritical or Subcritical?. Available: Modelling New Coal Projects: Supercritical or Subcritical?. Last accessed 7th Mar 2014.

18. Stephen, F (2010). Storing and Using CO2 for Enhanced Coalbed Methane Recovery in Unmineable Coal Beds of the Northern Appalachian Basin and Parts of the Central Appalachian Basin. 2nd ed. Kentucky : MRCSP. 15-21.

19. Food and water watch . (2012). Fracking, Climate Change and the Water Crisis. Available: http://documents.foodandwaterwatch.org/doc/FrackingClimateWaterBrief.pdf. Last accessed 7th Mar 2014.

20. U.S. Energy Information Administration. (2014). Natural gas . Available: http://www.eia.gov/naturalgas/issuesandtrends/production/2013/?src=Natural-f4. Last accessed 7th Mar 2014.

21. Bert, M (2005). IPCC Special Report on Carbon Dioxide Capture and Storage. New York: Cambridge University Press. 75-100

22. American coal ash association. (2007). uses of coal ash. Available: http://www.coalashfacts.org/. Last accessed 7th Mar 2014.

23. Terrapower.(2013). Travellingwave reactor design. Available: http://terrapower.com/pages/traveling-wave-reactor. Last accessed 7th Mar 2014.