BACKGROUND OF THE INVENTION

Lignite is a form of fossil fuel that is very abundant in the soil of many countries. Large quantities are produced for example in China, the USA, Russia, Germany, Poland, the Czech Republic, Canada, and Australia, for use in industry and in municipal power plants. However, the burning of lignite, especially in the last few decades, has been found to cause serious environmental problems.

Nonetheless, the recent shutdown of nuclear power in Germany for example, together with many other factors, including lignite's relatively low cost and well-known methods of production as well as abundant availability of the raw material, have drawn attention to this energy source. For example, the Swedish energy company Vattenfall produces large quantities of lignite from its quarries in Germany. Since lignite (also known as "Brown coal") has also attracted the attention of environmentalists and authorities, new methods of production and use are needed. Therefore, it is now necessary to examine the development of new processing options.

The main problems among the environmental effects of lignite include

- emission of greenhouse gases, oxides of carbon

- release of sulphur gases

- acid effects

- various heavy metals and other toxic compounds

- polyphenols, such as lignins, that degrade with difficulty in the environment

- the eutrophication effect of waste water from quarries and enrichment plants

- problems caused by coal dust

Potential treatment methods must therefore, in particular, improve the manageability and reduce the environmental impact of lignite in relation to the above-mentioned factors a) in an economically advantageous fashion and b) in such a way that the constituents of lignite can be better recovered. At the same time, attention must also be paid to c) the ecological sustainability of treatment processes, and d) reduction of local environmental pressures, as well as e) global effects, such as greenhouse gases and acidification. Previous studies on the use of microbes in reducing the environmental impact of lignite utilization or related wastewater treatment have been done e.g. with anaerobic methane bacteria (Kuschk et al. 2010). More broadly, microbiological processing of coal has been studied, for example, in Australia (Midgley et al. 2010). Various kinds of pre-treatment, such as hydrogen peroxide, have succeeded in oxidizing organic acids and other compounds from coal, such as methanol, formic acid, glycolic acid and malonic acid (Miura, et al 1996).

Laboratory studies by Finnoflag Oy have produced considerable amounts of several potential biochemical products, such as 2,3-butanediol (Hakalehto 2009 Hakalehto et al. 2008, 2013). By special processes, the same studies also succeeded for instance in forming butanol with the aid of Clostridium acetobutylicum bacteria (Hakalehto 2014). Also, significant amounts of carbon, hydrogen, and hydrogen sulphide were emitted.

The present invention describes a fermentation process aiming to clean lignite (Figure 1), with the purpose of improving the usability of lignite in energy production from the viewpoint of environmental protection, process technology, and overall economic advantage. Characteristic of the equipment used is that its operation is adjusted and optimized by measuring and adjusting the composition and flow rates of gas flows. In this case, the subject of adjustment may be gas flows led from both combustion and fermentation processes.

DESCRIPTION OF THE INVENTION If one wishes to treat lignite with microbes, it must first be crushed or pulverised, which in any event falls within the normal treatment process (Fa/ara & Twardowski 1999). Also, the moisture content of lignite can vary considerably, so that an elevated moisture content lowers the calorific value. Bacteria obtained as natural strains, for example from the purification plant processes in a wood-processing factory or from the effluent of a food production facility, can in turn produce combustible organic compounds in the liquid phase, which raise calorific value and other characteristics of combustion.

Gaseous substances formed in micro-biological processes, such as H ₂ and H ₂ S can be led from the solution, so that utilization of their energy content can be developed. Methods have also been developed for industrial desulphurization. In the method and apparatus contained in the present invention the above-mentioned gases can be led in a controlled manner into a combustion chamber, in which they can contribute to the combustion of coal. Naturally, this requires their dilution in order to prevent explosive effects. This dilution can be carried out by means of exhaust gases from combustion, in which the oxygen content is also significantly reduced. Before the gas mixture thus formed is led into the combustion chamber, its composition must be carefully measured.

Carboniferous combustion gases can also be led into bioprocessing, where they prevent the escape of carbon beyond reach of the microbes by raising the partial pressure of carbon oxides. At the same time, soluble carbon can be assimilated into the bioprocess using various microbial strains derived and enriched from natural sources or from waste materials.

For the bioprocess itself, concentrated atmospheric nitrogen gas, if necessary with added carbon dioxide, can be used as an anaerobic carrier gas and in starting the process. Using the method and apparatus contained in the present invention, sulphur can be extracted and evaporated from lignite, while at the same time the microbes also increase the calorific value of the coal suspension.

The essential features of the invention are depicted in Figure 1 , an apparatus and method according to the invention being implemented as follows:

1. lignite is ground and/or pulverised

2. waste liquor or other organic material is added, which contains the necessary microbial strains (usually, these are naturally enriched in the said liquor or material)

3. suitable conditions are adjusted for the bioprocess (fermentation)

4. the carrier gas is led into the process (at least during start-up)

5. the gas released by the process is led through the dilution unit and into the combustion chamber 6. gases released by the coal burning plant during combustion are used to dilute the gases

7. the same gases can also be led to the bioprocess, which may be phased in such a way that when the gas cools while heating and dissolving into the suspension in phase 1, they also hygienise the process liquor

8. additional microbes may be used, as needed, in the later stages of the process 9. combustible liquids formed in the bioprocess can be used in the combustion of coal, or they can be separated and cleaned for chemical processing

Using the method and apparatus contained by the invention, the objectives of environmental process engineering can be achieved, because the quantities of emitted sulphur and greenhouse gases are reduced. At the same time, the energy efficiency of coal use increases, and the hydrogen gas and hydrogen sulphide released in the bioprocess can also be used in the production of energy. The latter can also be collected as valuable elemental sulphur. Carbon capture is particularly efficient, and thus the same investment in raw material can be made to produce much more energy in the longer term.

References

Fafara Z., Twardowski K., 1999. Analiza zmiennosci wilgotnosci naturalnej w^gli brunatnych. Zeszyty Naukowe Politechniki Slqskiej. Gornictwo, z. 243, nr kol. 1436: 45 - 53.

Hakalehto, E. 2009. US Patent Application No.: 12/522,258. Filed: 6 July 2009. Title:

Biotechnical and microbiological production method and equipment.

Hakalehto, E., Humppi, T., & Paakkanen, H. 2008. Dualistic acidic and neutral glucose

fermentation balance in small intestine: Simulation in vitro. Pathophysiology, 15, 21 1-220.

Hakalehto, E., Jaaskelainen, A., Humppi, T., & Heitto, L. 2013. Production of energy and chemicals from biomasses by micro-organisms. In: Dalhquist, E. (Ed.): Biomass as energy source: resources, systems and applications. CRC Press, Taylor & Francis Group, London, UK.

Hakalehto, E. 2014. Enhanced microbial process in the sustainable fuel production. In: Jinyue, Y (ed.). Handbook of clean energy systems. Wiley JR & Sons., USA and UK. In Print.

Kuschk, P., Stottmeister, U., Liu, Y.-J., Wiessner, A., Kastner, M. & Muller, R.-A. 2010. Batch methanogenic fermentation experiments of wastewater from a brown coal low-temperature coke plant. J Environ. Sci. 22: 192-197.

Midgley, D.J., Hendry, P., Pinetown, K.L., Fuentes, D., Gong, S, Mitchell, D.L. & Faiz, M. 2010. Characterisation of a microbial community associated with a deep, coal seam methane reservoir in the Gippsland Basin, Australia. Int. J. Coal Geol. 82: 232-239.

Miura ,K., Mae , K., Okutsu, H. , & Mizutani, N. 1996. New oxidative degradation method for producing fatty acids in high yields and high selectivity from low-rank coals. Energy Fuels

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