Combustion of Crop Production Wastes
Development, Investigation and Improvement of a System of Incinerating Crop Production Wastes in Small Capacity Boilers
Tech Area / Field
- ENV-APC/Air Pollution and Control/Environment
- NNE-FUE/Fuels/Non-Nuclear Energy
3 Approved without Funding
Tambov State Technical University, Russia, Tambov reg., Tambov
- NPO Lutch, Russia, Moscow reg., Podolsk
- University of Saskatchewan / Department of Mechanical Engineering, Canada, SK, Saskatoon\nSwedish University of Agricultural Sciences, Sweden, Uppsala
Project summaryPrice rises and limited stocks of traditional energy sources make topical the involvement of various wastes, including crop production wastes, in the fuel balance of communal and industrial energy industry. Calculated estimates show that on average 33 mln tons of winter wheat straws, 1.5–2.0 mln tons of husks from sunflower, rice, millet etc. can be used as fuel in Russia annually. By their heating values (16–18 MJ/kg), these wastes are as good as many grades of domestic coals.
Aims of the Project.
The Project is directed towards the integrated solution of the problems occurring in combustion of crop production wastes. It includes:
- the development of coatings for protection of boilers’ working surfaces from corrosion caused by combustion products of crop production wastes. The coatings should also provide for the possibility of cleaning the working surface both by mechanical means and methods using aggressive media and high temperatures. To solve these problems, it is necessary to develop the coatings’ composition and method of application;
- the development of a process for incinerating pellets of crop wastes combustion. The process should by studied due to several reasons. First, it is necessary to develop such a method of incinerating this kind of fuel, which would enable a maximum reduction of the possibility of ash-and-slug agglomerates in the furnace and on the heating surfaces of the boiler. Second, it is required to develop such a method of incineration, which would enable the maximum burnout of fixed carbon of the fuel and the minimum carry - out of the fuel to provide for the minimum losses of thermal energy due to the mechanical incompleteness of combustion.
Studies to be carried out in the execution of the Project
A. Development of protective coatings and method of their application
Composite materials with the nickel matrix shall be developed for protection of the working surfaces of boilers. As reinforcements, particles of the following materials shall be used:
- tungsten carbide,
- aluminium oxide,
- silicon oxide,
- silicon carbide,
- chromium carbide etc., and their combinations.
Composite material shall be produced using the following scheme: mechanical alloying in planetary mills with formation of granules followed by compaction of composite granules into bulk material. Development of the mechanical alloying regimes will take a considerable time. Nanodiamond powders shall be added to the treated mixtures to improve the mechanical alloying process and to reduce the sticking of processed material to processing tools.
Friction cladding was chosen as the main method of applying coatings for these uses. This method makes it possible to achieve high adhesion of the coating to the base. Herewith, the method does not require any unique equipment or special conditions of application. The method makes it possible to apply the coating to part of the surface, i.e., enables repair of the coating. Cladding is performed by a rotated cylindrical brush. The brush is pressed to a workpiece from coating material (in the Project this material shall be fabricated in the form of a cylinder). During the rotation, the ends of metal brush wires scrape off microscopic particles of material and transfer it to the treated surface, to which the brush is also pressed. As rotation is carried out at a high speed, the rate of the impact of the brush ends on the treated surface is high, which provides for a high force of impact of the microscopic particle of composite material on the surface. This leads to a high strength of adhesion (fusion) of the coating material to the base.
Friction cladding by metal brushes is a relatively new method of applying coatings. There is no experience of applying such coatings in boilers. However, the results of studies of coatings developed for other uses make us certain that such coatings will possess high operational characteristics. However, the research effort for the development of the coatings will be considerable, as it will be necessary to examine numerous variants of coating compositions and application regimes.
Significant part of the Project is directed towards the study of the developed coatings. The studies shall be in two directions: (1) investigation of the structure and properties and (2) investigation of the operational characteristics (heat resistance, high temperature strength, wear resistance, etc.).
In conclusion, we shall fabricate a pilot model of a boiler or part of it with the developed coating.
B. Development of the process of pellets crop production wastes combustion.
We shall develop a process of fluidized-bed combustion of pellets made from crop production wastes. Herewith, the following incineration variants shall be studied:
- combustion of pellets in the fluidized bed of inert material (sand),
- combustion of pellets in the fluidized bed formed by pellets themselves and their solid combustion products (ash, coke),
- combustion of pellets in the fluidized bed of inert material in combination with dry coal wastes (culm, slugs),
- combustion of pellets in the fluidized bed formed by pellets themselves and their solid combustion products in combination with dry coal wastes,
- combustion of pellets in the fluidized bed of inert material in combination with coal slurry prepared from coal slugs,
- combustion of pellets in the fluidized bed formed by pellets themselves and their solid combustion products in combination with coal slurry prepared from coal slugs.
Combustion of pellets in the fluidized bed creates conditions for the most complete burnout of the coke residue and the reduction of fuel losses due to the mechanical incompleteness of combustion. However, agglomerates from particles of the inert agglutinated by melted ashes can be formed in the fluidized bed of inert material. Formation of agglomerates leads to the defluidization and cessation of the burning process. The agglomerate formation process can be suppressed to a significant extent by adding coal wastes (chippings, slugs) into the furnace in the dry form and as coal slurry (which is especially important in combustion of highly watered slurry coals, as it solves the problem of their transportation into the boiler’s furnace. Evidently, agglomeration in the fluidized bed and defluidization can to a significant extent be suppressed in incineration of pellets in the fluidized bed of the pellets and their solid combustion products. However, to be created, such a bed requires high gas rates. These rates can be reduced by the introduction of coal particles (chippings, slugs), both in the dry form and as slurry, into the bed.
- increased service life of small capacity boilers in incineration of crop production wastes;
- composition of the coating for the working surface of the heat exchangers of small capacity boilers;
- method of applying the coating способ нанесения покрытия;
- process of combustion pellets fabricated from crop production wastes, including in combination with dry coal wastes and coal slurry.
Specialists with high qualification will be involved for implementation of the project; it is guarantee of fulfillment of the project on high science and technology level.
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