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Briquettes manufacturing

Briquettes manufacturing

The world wide community became worried with the global warming issue, caused by CO2 and other substances emissions, as it arises the problem of forest resources protection, as they are the main CO2 absorbents. The problem of forest resources protection arises the problem of increasing deforestation control together with the problem of wood fuel usage increase which makes the community necessary to think about substitute fuels development. The world wide community and industry experts regard briquette manufacturing technology as the solution for environmental protection – so called clean coal technology which will provide stable briquettes supply thus promoting flood destroy prevention and forest resources preserving.

Let's see the briquettes manufacturing technology in details. Firstly one should specify that industry deals with two types of briquettes: the carbonized and bio ones. The carbonized briquettes manufacturing process consists of two stages: the one of carbonization and the briquettes forming one. The first diagram displays basis process yielding. The carbonization step deals with smokeless semicoke formation, having 20% of volatile substance, done at fluidized bed carbonization furnace on low internal heating temperature (about 450OC of carbonization temperature). Image 2 displays the image of fluidized bed carbonization furnace, which provides highly efficient semicoke carbonization on the low temperature of internal heating. Firstly, the coal is dried (10% or lower surface water content, 5-50 mm of particle size) in a rotary drier. In order to get the coal rid of the dust before it passes to atmosphere the gas that goes off the drier, comes through multi-cyclone. The preliminary dried coal supply is sent to furnace middle section, where it is carbonized with the help of fluidization. Semicoke and carbonization gas, obtained after such process, is taken out from the furnace top. Then, after cooling, the semicoke is sent to the stockyard and the carbonization gas is sent to combustion chamber lines with refractory, where it is mixed with air for further combustion. Then the gas obtained is sent to coal supply drier and near by briquette drier, where it is used as drying heat source for coal supply preliminary heating and formed oval briquettes drying heat source. The carbonization furnace structure is simple, it has no perforated plates or agitators, which eases furnace functioning and upkeep.
The forming stage provides thorough smokeless semicoke (briquette supply, which contains appropriate amount of volatile substance, few ash and sulfur, which emits no smoke and odor) and additional supplies (hydrated lime and clay ) kneading, maintaining the defined kneading ratio. As soon as the mixture obtained had been pulverized, it is mixed with caking add-on together with water addition, done in order to make the substance watery. To even the caking add-on content and to increase the substance ductility, which facilitates easier briquettes forming, the mixture is kneaded again at normal temperature. Then the mixture obtained is transferred to molder where the briquettes are prepared under normal temperature and about 1,000 kg/cm (300-500 kg/cm2) of line pressure. After this continuous drier, designed taking into account process temperature peculiarities, dries them. The process is performed at low temperature as the semicoke has strong ignition properties and ignites the furnace.

Bio briquettes
Bio- briquette is the type of solid fuel, done with the help of coal mixing with 10-25% of vegetable substance (wood bagasse , straws, and haulms of corn) and consequent desulfurizing substance (Ca(OH)2) adding in the proportion, corresponding to coal sulfur content. The bio-briquettes manufacturing under high pressure (1-3 t/cm2) makes coal particles and the fibrous vegetable matter tightly stick to each other. Due to this property they do not separate from each other on combustion which provides vegetable matter double combustion on low ignition temperature and coal supplies usage. Such combustion possess positive ignition and fuel properties, gives small amount of dust and soot emission, promotes sandy combustion ash in order to avoid clinker leaving. Another bio- briquettes plus is that the substance effectively interacts with the sulfur the coal contains, thus providing 60-80% of the sulfur fixing into the ash due to desulfurizing substance sticking to the coal particles. There are many different quality types of coal used for bio -briquettes manufacturing such as: bituminous coal, subbituminous coal, and brown coal. For example the coal cleaning can be highly efficient in case if the low quality coal with big amount of ash and having low calorific capacity is used. Taking into account the fact specified the experts consider bio briquettes technology to be effective for manufacturing of clean fuel which will be used at household and industrial small boilers.

(1) Bio – briquettes manufacturing process. See image three for details.
The coal and biomass are being pulverized to the size of 3 mm or less and then dried. After the substance obtained is kneaded with desulfurizing agent (Ca(OH)2) by means of compression molding in briquettes equipment, working under high pressure. In case of powder coal usage the pulverization may be omitted. Some coal grades may be briquetted with adding some binder. As manufacturing process does not suppose high temperature operations its' structure is centered on dry high pressure briquetting equipment. As the process is simple it does not require profound skills. Plus, it gives the possibility to obtain rigid formed coal the components of which are not separated on combustion, as coal particles and biomass tightly stick to each other due to high pressure briquetting method.
Below we see some comparative characteristics of coal direct and bio- briquettes combustion.
1. The first plus lies in the fact that bio-briquettes combustion diminishes soot and dust generation by one fifth to one tenth in comparison with the coal direct combustion. When operating at low temperature frames the volatile substance does not fully combust as dust and soot generation growth during coal direct combustion. While bio-briquettes combustion technology provides simultaneously low ignition point biomass, coming with the coal to coal particles. This favors volatile substances combustion in low temperature frames designed for combustion, which provides significant reduction of dust and soot generation.
2. Bio-briquettes manufactured by adding of 15-20 % biomass to coal are done at much more shorter ignition time by thus improving the ignition property. Plus they possess favorable combustion characteristics due to secured aeration between briquettes on continuous combustion at fireplace, which confirm their low expansion caking properties. Thus, they have greater combustion sustaining peculiarity ans easier combustion rate fixing, which helps them not to die out at fireplace or other boilers even on air ratio drop down which makes combustion rate to drop down.
3. Such briquettes get rid of the clinker lump formation problem on combustion due to fused ash adhesion in the coal due to fibrous biomass entrance between coal particles and ash passes through grid in form of the sand. This makes aeration secured for combustion status fixing. It help to decrease the quantity of unburnt coal in the ash due to clinkers absence.
4. Bio- briquettes are generated under high compression. Thus, the desulfurizing substances and the coal particles effectively react on combustion as they are tightly stick to each other. The desulfurizing substance adding in the proportion of 2-2 of Ca/S make 60-80% of the sulfur the coal contains to fix in the ash.

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Briquettes manufacturing


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Views: 7401 Added: 24-02-2010