There are two main methods that cover a wide area of biomass conversion technologies, thermochemical conversion and biochemical conversion. To obtain the energy, the combustion factor is key for both technologies. Hardware biomass conversion systems can be stationary or mobile. Mobile hardware systems are generally used in rural areas to supply power to a small number of households, such as in a town, or to power small to medium-sized rural businesses. However, the principle for both stationary and mobile hardware combustion systems is similar.
Combustion can be carried out by means of a furnace or a boiler. A furnace (direct combustion) is one of the simplest methods used to obtain energy by burning biomass materials in a chamber to obtain heat in the form of hot gases released.
A biomass boiler can be used to transform heat into steam, this steam is used to turn the turbine to generate electricity.
There are three different types of boilers:
1. Stack burners
2. Stationary or mobile grill combustors
3. Fluidized bed combustors
The ‘direct shot’ can be divided into four different methods. These methods are called Pile Burner, Spreader Stoker, Fluidized Bed, and Suspension.
The other method is gasification, which can be divided into five different sub-branches, that is, biogasification, landfill gas, pyrolysis, thermal gasification, and microscale biomass.
Direct combustion, gasification, pyrolysis and methanol production are included in the “thermochemical” conversion process. On the other hand, anaerobic digestion and ethanol production are included in the “biochemical” type of conversion process. Biodiesel production is included in the “chemical” conversion process.
Various uses can be made of the biogas produced by anaerobic digestion or pyrolysis. These are:
1. Fuel for internal combustion engines
2. Produce heat for commercial and domestic needs.
3. As a transportation fuel
The following are three different methods of obtaining gases, as an energy source, from biomass materials.
Gasification
Gasification is described as the process of converting the organic fraction of biomass at higher temperatures and with the presence of air, into a mixture of gases with a fuel value and more variation than the original solid biomass. This gas can be burned to produce heat and steam, and it can be used in internal combustion engines or gas turbines to produce electricity and mechanical energy. The production of electricity through gas turbines combined with steam cycles is reported to be the most efficient and economical use of the gaseous product. Several biomass gasification processes have been developed (and / or are under development) for electricity generation that offer advantages over direct burning, such as higher efficiency and cleaner emissions. Many of the gasification systems are currently in the demonstration stage, and the development of these efficient systems for electricity production is essential: the BIGCC (Biomass Integrated Gasification and Combined Cycle) and BIG-STIG (Gas Turbine) plants. with Integrated Biogas Gasification Steam Injection) can achieve efficiencies of 42-47%. In the last fifteen years, important advances have been made in the field of biomass gasification, especially in the field of medium and large-scale electricity production. Gas cleaning to improve gas quality is a crucial issue in both combustion and gasification systems, and requires measures such as reducing emissions and removing particles and tars.
Anaerobic digestion
Anaerobic digestion is the decomposition of wet and green biomass through bacterial action in the absence of air. Broadly speaking, the anaerobic digestion process is made up of four main biological and chemical stages:
1. Hydrolysis
2. Acidogenesis
3. Acetogenesis
4. Methanogenesis
It generally has a mixed gas production of methane (CH4) and carbon dioxide (CO2), called biogas. Landfill gas is the result of the anaerobic digestion of municipal solid waste buried in landfills. Methane gas produced in landfills eventually escapes into the atmosphere. However, the gas can be extracted by inserting perforated pipes into the landfill.
There are a number of benefits related to anaerobic digestion; These can be described under the environmental benefits, rather than the technical or commercial aspect. Anaerobic digestion reduces methane emissions and can provide a good treatment system for organic waste and consequently can prevent groundwater contamination and reduce the local environment odor associated with this waste.
‘The Government should review its current strategy for the anaerobic digestion sector. In doing so, we recommend that you consider practical and financial mechanisms to encourage the expansion of UK DA capacity, while ensuring that new DA systems offer the optimal balance between biogas production and prevention of uncontrolled methane emissions. ‘. (Working group on biomass. 2005).
Pyrolysis
In a temperature range of 300 to 700 ° C and in the absence of oxygen, the chemical decomposition of organic materials by heating is a process called pyrolysis. However, in most cases and in practical terms, the presence of oxygen cannot be completely eliminated.
The end result of the pyrolysis process is that organic materials are transformed into gases and leave a solid residue (coke) formed by coal and ash. Biomass gasification can also be integrated with fuel cells. Furthermore, through pyrolysis, a solid biomass can be liquefied by “direct hydrothermal liquefaction” (USDE, 2005). One of the main benefits of flash pyrolysis is that fuel production has been separated from power generation. This type of method is still in the demonstration stage. Since the development is still in the early stages, like the rest of the bio-oil improvement processes, there is still a need to neutralize the negative aspects, such as corrosivity and low calorific value. Together with existing systems, pyrolysis can be used for large-scale electricity production.
Najib Altawell
