Moving Beyond the Status Quo [ PDF ]

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Mitigating Industrial Black Carbon Through Energy Recycling

Mak Dukan

Alleviating climate change is often viewed as an endeavor that will impose huge costs on our economies. Furthermore, the incongruity between measures and effects means that programs implemented today may not produce noticeable results for a century or more. In order to gain wider public support, climate mitigation strategies must focus on producing tangible results. Reducing black carbon emissions by using energy recycling techniques is a profitable and quick way of alleviating the short term effects of global warming. Adopting these technologies in the US could also have implications for climate negotiations, as the US would show a commitment to lowering its own emissions.

Black carbon

Black carbon is one of the main residues of soot emitted from incomplete combustion of fossil fuels and biomass. A growing body of evidence indicates that black carbon plays a significant role in increasing radiative forcing that drives climate change. In fact, studies suggest that on a per unit basis, black carbon warms the atmosphere hundreds of times as much as CO2, despite lasting in the atmosphere for only a few weeks (i). Its effect on the polar regions is even greater, as the dark soot particles settle on ice and snow, forming thin black rugs that absorb sunlight. This reduces the reflection of solar radiation back into space and contributes to warming (ii). Black carbon has direct negative effects on health and agriculture (iii) and its short atmospheric life cycle of a few weeks means that its removal would result in an immediate decrease in warming.

The largest sources of black carbon come from open burning of forest and savanna, inefficient combustion of diesel engines and burning fuel for residential heating and cooking. Around 10 percent of global black carbon is emitted from the industrial sector (iv). Although industrial emissions of black carbon play a relatively small role globally, figure 1 indicates they constitute a major part of emissions in China and to a smaller but still significant degree in India. Each black carbon source has a different warming effect, which depends on the ratio of black carbon particles to other pollutants that exhibit a cooling effect. After diesel emissions, industrial processes are one of the largest annual contributors to the warming effect from black carbon. Within the industrial sector, research indicates that cokemaking is among the largest sources of industrial black carbon emissions (v).

Metallurgical coke is one of the main inputs in steel production and is used to fuel blast furnaces that reduce iron ore to pig iron. Coke is produced by heating coal in an oxygen-free environment inside a coke oven. This process, called coking, is conducted in order to purify coal from its volatile components. Once this is achieved, the material remaining is a carbon mass called coke. The separated volatile components form coke oven gas, which is either vented into the atmosphere or directed to a separate chemical recovery plant where it is refined into by-products (vi).

The latter refers to By-product Cokemaking and is common to developed countries like the US, where environmental regulations are strict. Bond et al. (2004) (vii) approximate black carbon emissions from By-product coke production to be smaller by a factor of four than the emissions from "beehive" coke ovens, a traditional method still used in some developing regions. Beehive ovens are the dirtiest form of Non Recovery Cokemaking, which includes all methods that do not recover the coke oven gas to produce by-products. While some of these facilities vent coke oven gas into the atmosphere, some innovative plants use the gas's heat to produce electricity. This process, called Heat Recovery Cokemaking, has been determined to be the cleanest form of cokemaking. It is estimated that the production of one ton of coke through modern methods emits between 0.7 to 7.4 kilograms of particulate matter into the atmosphere, compared with at least 20 kilograms per ton emitted from beehive ovens (viii), (ix). Although it is unknown to what extent this includes black carbon, it likely constitutes a significant part.

The rapid economic development of China and India has increased their demand for steel, which consequently increases demand for coke. China produces about half of the world’s steel and about the same share of the world’s coke (x). This gives China an essential role in crafting global policies to reduce black carbon. An additional concern arises from the fact that in 2004, China still produced 35 million tons of coke using beehive ovens (xi), the dirtiest form of cokemaking. Although this is less than a sixth of China’s 255 millions tons of total production, it amounts to almost the entire coke production of Japan, the world’s second largest coke producer after China (xii). Considering the effects that black carbon emissions from coke production have on the environment, targeting the coking industry, and especially beehive ovens, should be of primary concern.

Energy recycling

Energy recycling is a term used to describe a process that utilizes waste energy, such as exhaust heat from the coke oven or a blast furnace, to produce electricity. During the process, the waste heat is converted into high pressure steam and diverted to a steam turbine. Moving high pressure steam through the turbine blades creates rotational energy which is then converted into electricity using a generator. The produced electricity can be used on site by the manufacturing plant or it can be sold to other users. Industries that have the highest energy recovery potential are steel, glass, cement and petrochemicals (xiii).

The potential of recovering waste heat in the US is great. It is estimated that recycling industrial energy waste could generate as much as 10 percent of U.S. electricity (xiv). In 2005 the combined electricity output of the Mittal Steel coking plant in Indiana and its nearby rival U.S. Steel that utilizes the same energy recycling technology, was greater than the entire U.S. output of solar photovoltaic energy that year (xv).

Besides increasing energy efficiency, energy recycling reduces black carbon emissions and mitigates other pollutants. Furthermore, this technology increases business competitiveness as it lowers operational costs. It is estimated that by recycling waste heat, the Mittal Steel plant saves up to $110 million per year, while the capital costs of building such a plant are estimated at $165 million (xvi). That being said, the initial investment in waste heat recycling technology is repaid in less than two years while substantially reducing the impact on the environment.

Potential for black carbon reductions

As mentioned, Non Recovery Cokemaking plants vent the extremely dirty coke oven gas into the atmosphere. Besides containing various pollutants, this gas is hot. In other words it contains an abundance of heat energy that is being needlessly wasted. The excess heat contained in coke oven gas could be recycled or converted into another form of energy, such as electricity. In the process of recycling waste heat from coke oven gas, mentioned previously as Heat Recovery Cokemaking, fugitive air emissions which result from the long hours of baking coal are incinerated inside the coke ovens, thereby destroying virtually all organic compounds (xvii), including black carbon particles.

Although the excess emissions could also be reduced by converting a Non Recovery into a By-product Cokemaking plant, recycling waste heat eradicates more emissions and eliminates the need for a separate chemical recovery plant. In addition, it is estimated that a one million ton-per-year heat recovery coke facility can generate approximately 100MW of electricity (xviii). Given that the average yearly consumption of a US household is around 11,000 kWh (xix), this would be enough to power approximately 77,000 US homes.

Further black carbon emission reductions are achieved by decreasing the use of fossil fuels. A plant that produces an additional 100MW of electricity by recovering its exhaust heat avoids the greenhouse gas and black carbon emissions that would result from mining, transporting and combusting coal or oil to produce the same 100MW.

Conclusion

Cokemaking may be the biggest source of industrial black carbon emissions. Recycling waste heat from coke ovens could lower these emissions. The reductions would range depending on the cokemaking process in use, but the largest reductions would be achieved in China, where beehive coke production is still used on a mass scale.

Additional black carbon reductions in the US would be much lower than China’s, because the US utilizes mainly By-product Cokemaking which emits much less black carbon than beehive coking. But this does not mean the US should not take the lead in adopting energy recycling technologies in coke production and on a wider scale. Recovering industrial waste heat would benefit the US economy by increasing the productivity of energy use, lowering dependence on fossil fuel imports and increasing competitiveness. In addition, the US would gain credibility in climate negotiations, especially when urging developing countries to lower their emissions.

If energy recycling becomes as widely commercialized in the US as in some parts of Europe, it could more easily be transferred to countries such as China and India, where the potential to reduce black carbon emissions from cokemaking is greatest. Reductions in black carbon emissions could be enormous, with an immediate reduction in global warming.

References

i. MacCracken M., (2009) “The Achievable Path to Climate Protection," Climate Alert, Autumn 2009.

ii. Topping J., (2009) “A Message From the President," Climate Alert, Autumn 2009.

iii. Bachman J., (2009) “Black Carbon: A Science/Policy Primer,” PEW Center on Global Climate Change

iv. Bond, T. C. 2009. Black carbon: Emission sources & prioritization, Presentation to the ICCT Black Carbon Workshop, London, U.K. PDF.

v. Bond, T. C., D. G. Streets, K. F. Yarber, S. M. Nelson, J.-H. Woo, and Z. Klimont (2004). “A technology-based global inventory of black and organic carbon emissions from combustion.” J. Geophys. Res. 109, D14203, p 13

vi. Environmental Protection Agency, “Metallurgical Industry”, AP 42, Volume I, Fifth Edition, Chapter webpages. PDF

vii. Bond et al (2004) p 13

viii. The World Bank (1998), “Pollution Prevention and Abatement Handbook, Coke Manufacturing.”

ix. In addition it is estimated that coke oven gas is a source of 2.9 kg of Sox (ranging from 0.2 to 6.5 kg), 1.4 kg of nitrogen oxides (NOx), 0.1 kg of ammonia, and 3 kg of VOCs (including 2 kg of benzene).

x. NationMaster, Energy Statistics - Coke Oven Coke, Production (2005) By Country.

xi. Zhang G., Zheng P., (2005) “Study on the Development of Coke Industry in China”, China-USA Business Review, Volume 4, No.7

xii. NationMaster, Energy Statistics - Coke Oven Coke, Production (2005) By Country.

xiii. Lowe M., Gereffi G., (2007) “Manufacturing Climate Solutions, Chapter 7: Recycling Industrial Waste Energy,” Center on Globalization, Governance & Competitiveness

xiv. Ayers R.U., Ayers E.H., (2009) “Crossing the Energy Divide: Moving from Fossil Fuel Dependence to a Clean-Energy Future,” Wharton School Publishing, p 42

xv. Ayers R.U., Ayers E.H., (2009), p 33

xvi. Casten T.R., “Recycling Energy to Reduce Costs and Mitigate Climate Change,” Recycled Energy Development , LLC

xvii. Waddell R., Westbrook R., “Heat – Recovery Cokemaking presentation,” p18, Sun Coke Co.

xviii. Sun Coke Co. Power Generation (Cogeneration).

xix. US Energy Information Administration, "Frequently Asked Questions – Electricity," 25 March 2010.

SPRING 2010 Climate Alert

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