BIO-ENERGY

 

Dr. Shahida Rafique

Department of Applied Physics, Electronics and Communication Engineering

University of Dhaka

Dhaka-1000, Bangladesh

 

Bio-Energy:

 

Biomass is the result of photosynthetic conversion of solar energy and CO2 into the chemical and physical components of plant material. Energy produced from various ways from biomass is the bio-energy. Biomass is the only combustible carbon resource that is carbon neutral. 11% of world primary energy use is derived from bio-energy. Estimates for world bio-energy potential appeared to be 450 EJ in 2050. Biomass can be mixed with coal to reduce environmental emissions. Technical efficiency is enhanced when bio-energy is used in combined heat and power (CHP) applications. Bio-energy works within the Earth's carbon balance and can contribute to the maintenance of biodiversity. Biogas production from biomass is shown in Figure 1. Production process of biogas is shown in Figure 2. From production to consumption of biogas is shown in Figure 3. Organic waste is mixed up with water. The mixture is heated and placed in the digester tanks where bacteria transform the nutritive substratum into methane and CO2. Methane is the component that is used to produce biogas. The biogas is cleaned from the CO2, vapor, H2S and then compressed. The pipeline then conveys biogas.

 

Production of Biogas

Biogas can be produced from solid wastes, sewage, agro-industrial wastewaters by microbes during methanogenic anaerobic fermentation. Other types of bio-fuels such as, methyl esters may be mixed with standard patrol or diesel to give bio-diesel. Bio-fuels can be produced locally with local resources and technology. There are different technologies available for methane production and to recover biogas. To use it in vehicles, it must be purified to 96 to 100% methane by removing or separating CO2, moisture, H2S and other corrosive components in the gas. The purified gas is then compressed to a pressure of 200 to 250 bars for use in the vehicles.

 

Biogas is produced from organic waste being decomposed by microorganisms. Decomposition is anaerobic that it takes place in an oxygen-free atmosphere. The digestion process of organic waste produces mainly methane and CO2. Several types of organic waste can be used provided that the amount of N2 and carbon are sufficient.

 

Production Process of Biogas:

• •         The waste is composed of low-risk material.

• •         The waste material is mixed up with sufficient water. In order to slow down the digestion process, the waste is mixed with manure from farms.

• •         The mixture is then heated and placed in digestion tanks, where bacteria transform the nutritive substratum into methane and CO2.

• •         Methane is the component that is used to produce biogas. Biogas is then cleaned from CO2, vapor and trace-levels of H2S. The cleaning technique is absorption technique.

• •         When cleaned, biogas is conveyed by pipeline at a pressure of 4 bars to the compression center.

• •         It is then compressed to 200 bars.

 

 

 

Biogas Production from Biomass.    

 

 

 

 

From Production to Consumption of Biogas.

 

 

 

Production Process of Biogas.

 

 

Schematic diagram of gasification and liquefaction plant. Organic waste such as swine feces are introduced into a coil that is heated using a downdraft burner. This causes the material to decompose into hydrogen and carbon monoxide, which, after cleanup, is catalytically combined into a liquid fuel such as ethanol or diesel. Residual heat from the downdraft burner is first used to generated superheated steam, which is injected with the organic material. Remaining heat is used to pre-dry the organic waste. Ash remaining after gasification is collected using a cyclone.

Production of Hydrogen from Biomass by Gasification Process

 

• •         The biomass feedstock is first dried and sized.

• •         The feedstock is then gasified to produce syngas, mainly composed of CO, hydrogen, CO2, steam, some methane and small quantities of hydrocarbons.

• •         The syngas is then cleaned, and hydrocarbons are converted to CO and hydrogen by steam reforming.

• •         The reformed gas then undergoes shift reactions. Two shift reactors in series, the first at 4500C and the second at 2300C are used to react the CO with steam to form hydrogen.

• •         Hydrogen is then recovered from the gas steam by pressure swing absorption (PSA - PSA desorbs all the gases except hydrogen).

• •         97% of the hydrogen passing through the PSA is recovered which has 99.999% purity.

• •         The hydrogen can then be liquefied or compressed for transport.

 

    Gasification and gas cleaning equipment is still at the pre-commercial stage. Reforming, shift reaction and PSA equipment is commercially available at large-scale, and is widely used for industrial hydrogen production, mainly from natural gas.