Bio-Briquettes

Bio-briquettes (biomass briquettes) are a biofuel substitute to coal and charcoal. They are used to heat industrial boilers in order to produce electricity from steam. The most common use of biobriquettes is in the developing world, where energy sources are not as widely available. There has been a move to the use of briquettes in the developed world throngh the nse of co-firing, when the briquettes are combined with coal in order to create the heat supplied to the boiler. This reduces carbon dioxide emissions by partially replacing coal used in power plants with materials that are already contained in the carbon cycle. 

Boilers in power plants (Chapter 15) are traditionally heated by the combustion of coal, but if co-firing is implemented, the carbon dioxide emissions decrease while still maintaining the heat inputted to the boiler. Implementing co-firing requires few modifications to the current characteristics to power plants, as only the furl for the boiler is changed. 

Manufacturers mainly use three methods to create the briquettes, each depending on the way the biomass is dried out. Although biomass briquettes are usually manufactured, biomass has been used throughout history all over the world from simply starting campfires to the mass generation of electricity. 

Bio-briquette combustion decreases the generation of dust and soot to one-fifth to one-tenth that of direct coal combustion. Direct coal combustion increases the generation of dust and soot because the volatile matter released at low temperatures (200°C-400°C [390°F-750°F]) does not completely combust To the contrary, bio-briquettes simultaneously combust the low ignition point biomass, which permeates the coal particles, assuring the combustion of volatile matter at low combustion tanperatures. As a result, the amount of generated dust and soot is significantly reduced. 

Bio-briquettes prepared by blending biomass with coal have a significantly shorter ignition time. In addition, because of the low expansibility and caking property of bio-briquettes, sufficient air flow is maintained between the briquettes during continuous combustion such as in a fireplace. As a result, the bio-briquettes have superior combustion-sustaining properties and do not die ont in a fireplace or other heater even when the air supply is decreased. This makes it easy to adjust the combustion rate. 

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In the shows the basics of the bio-briquette production process (Figure 17.3), the raw materials, coal and biomass, are pulverized to a size of approximately 3 mm or smaller and then dried. The dried mixture is further blended with a desulfurizing agent, such as slaked lime [Ca(OH)2]. 

The bio-briquettes are formed under high compressive force. Because of this, the desulfurizing agent and the coal particles strongly adhere to each other, and they effectively react during combustion. With the addition of a desulfurizing agent at a ratio of approximately 1.2 2 of Ca/S, 60%-80% of the sulfur in the coal is fixed in the ash. 

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