Scientists from Tomsk Polytechnic University are developing a technology for obtaining liquid fuel from coal wastes for thermal power stations (TPSs). This fuel is 10 times more environmentally friendly and resolves two problems at once: reducing the amount of anthropogenic emissions of TPSs and efficiently disposing of wastes from coal processing and beneficiation. The research team of the Department of Automation of Thermal Power Processes led by Professor Pavel Strizhak shares its outcomes.
As Pavel Strizhak notes, thermal power stations generate up to 40 to 45 percent of the world's electricity; they are also the sources of five contaminants that account for 90 to 95 percent of all atmospheric emissions such as cinder particles, sulfur oxides, nitrogen and carbon oxides, as well as water vapor. Operating TPSs release carbon dioxide (CO2), which scientists consider as the main cause of the greenhouse gas effect. Particles of volatile cinder released into the atmosphere may also contain other compounds, in particular, heavy metals. Gaseous products of organic fuel combustion may also include toxic and carcinogenic microelements, carcinogenic hydrocarbons and other harmful substances.
'People believe the most dangerous are the emissions of sulfur and nitrogen oxides which, when merged with atmospheric moisture, oxidize, thus forming weak solutions of sulfuric and nitrous acids. They are the main causes of acid rains.
The increase of concentration of nitrogen oxides contributes to the destruction of the ozone layer, which protects our planet from ultraviolet radiation,' says Pavel Strizhak.
To reduce anthropogenic impacts on the environment and the amount of pollutants emitted into the atmosphere, TPU scientists suggest the production of carbon water slurry containing petrochemical (CWSP) fuel compositions from wastes produced by coal beneficiation or oil refining.
'They are liquid fuel compositions, 80 percent of which are coal-processing products. We use four groups of substances as major components: solid combustible components out of low-rank coals and coal-processing wastes, liquid combustible components, and water and plasticizers (stabilizers). The resulting fuel represents a viscous mass that will be burnt in boiler units,' says Pavel Strizhak.
Each of the four components cannot be used as fuel in the power industry, but together, they form fuel comparable to traditional coal with reduced economic and environmental impact.
The outcomes of the study have been published in the Journal of Hazardous Materials.
The study compares the effect of hard coal combustion and carbon water slurry containing petrochemical fuels (CWSP) based on coal processing wastes (filter cakes), which are widespread in the world power industry.
'We burnt these two fuels at temperatures from 500 to 1000 C. For the first time, it was shown that the concentration of sulfur and nitrogen oxide is significantly lower when burning CWSP compared to traditional coals,' says Pavel Strizhak.
The output performance (ignition delay, minimum threshold ignition temperature, maximum combustion temperature) of CWSPs and coal was very similar.
'The results obtained open great opportunities for the wide use of CWSP suspensions as cheap, energy-efficient and environmentally friendly fuel compared to traditional coals. Using liquid fuels based on coal processing products, manufacturers will be able to reduce the volume of mining and development of new deposits. This, in turn, will save resources and reduce the damage to the environment,' says Pavel Strizhak.
The development will allow coal producers to process coal beneficiation wastes and burn them directly on site to generate power that will reduce costs for collection and transportation of hazardous wastes. The technology has been already tested at one coal production enterprise of the Kemerovo Region.
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Margarita A. Dmitrienko et al, Environmental indicators of the combustion of prospective coal water slurry containing petrochemicals, Journal of Hazardous Materials (2017). DOI: 10.1016/j.jhazmat.2017.05.031