Biomass gasification involves burning of biomass in a limited supply of air to give a combustible gas consisting of carbon monoxide, carbon dioxide, hydrogen, methane, water, nitrogen, along with contaminants like small char particles, ash and tars. The gas is cleaned to make it suitable for use in boilers, engines and turbines to produce heat and power (CHP).
Biomass gasification provides a means of deriving more diverse forms of energy from the thermochemical conversion of biomass than conventional combustion. The basic gasification process involves devolatization, combustion and reduction.
During devolatization, methane and other hydrocarbons are produced from the biomass by the action of heat which leaves a reactive char.
During combustion, the volatiles and char are partially burned in air or oxygen to generate heat and carbon dioxide. In the reduction phase, carbon dioxide absorbs heat and reacts with the remaining char to produce carbon monoxide (producer gas). The presence of water vapour in a gasifier results in the production of hydrogen as a secondary fuel component.
There are two main types of gasifier that can be used to carry out this conversion, fixed bed gasifiers and fluidized bed gasifiers. The conversion of biomass into a combustible gas involves a two-stage process. The first, which is called pyrolysis, takes place below 600°C, when volatile components contained within the biomass are released. These may include organic compounds, hydrogen, carbon monoxide, tars and water vapour.
Pyrolysis leaves a solid residue called char. In the second stage of the gasification process, this char is reacted with steam or burnt in a restricted quantity of air or oxygen to produce further combustible gas. Depending on the precise design of gasifier chosen, the product gas may have a heating value of 6 – 19 MJ/Nm3.
Layout of a Typical Biomass Gasification Plant
The products of gasification are a mixture of carbon monoxide, carbon dioxide, methane, hydrogen and various hydrocarbons, which can then be used directly in gas turbines, and boilers, or used as precursors for synthesising a wide range of other chemicals.
In addition there are a number of methods that can be used to produce higher quality product gases, including indirect heating, oxygen blowing, and pressurisation. After appropriate treatment, the resulting gases can be burned directly for cooking or heat supply, or used in secondary conversion devices, such as internal combustion engines or gas turbines, for producing electricity or shaft power (where it also has the potential for CHP applications).
Oil and gas accounts for over 70% of energy consumed in Nigeria, according to the World Bank. Considering this dependency on fossil oil and possibility of it running out in the future, there should be an urgent intervention to look into other ways to generate energy in Nigeria. The world is moving away gradually from fossil oil and aligning towards sustainable energy resources to substitute conventional fuel, Nigeria should not be exempted from this movement. Biomass, a popular form of renewable energy, is considered as a credible and green alternative source of energy which many developed and developing countries have been maximizing to its potential.
Power generation and supply have been inadequate in Nigeria. This inadequacy of power limits human, commercial and industrial productivity and economic growth . What is the use of infrastructure without constant electricity? Even God created light first. Sustainable and constant supply of power should be one of the priority of government in nation development. Investing in biomass energy will cause an increase in the amount of power generated in Nigeria. Infact, biomass energy has the potential to resolve the energy crisis in the country in the not so distant future.
What is Biomass
The word biomass refers to organic matter (mainly plants) which acts as a source of sustainable and renewable energy. It is a renewable energy source because the plants can be replaced as oppose to the conventional fossil fuel which is not renewable. Biomass energy is a transferred energy from the sun; plants derives energy from the sun through photosynthesis which is further transferred through the food chain to animals’ bodies and their waste.
Biomass has the potential to provide an affordable and sustainable source of energy, while at the same time help in curbing the green house effect. In India the total biomass generation capacity is 8,700 MW according to U.S. of Commerce’s International Trade Administration, whereas the generating capacity in U.S. is 20,156 MW with 178 biomass power plants, according to Biomass Magazine.
Power Sector in Nigeria
Unfortunately, the total installed electricity capacity generated in Nigeria is 12,522 MW, well below the current demand of 98,000MW . The actual output is about 3,800MW, resulting in a demand shortfall of 94,500MW throughout the country. As a result of this wide gap between demand and output, only 45% of Nigeria’s population has access to electricity. Renewable energy contributed 19% of total electricity generated in Nigeria out of which biomass contribution is infinitesimal.
Electricity generation for Nigeria’s grid is largely dominated by two sources; non-renewable thermal (natural gas and coal) and renewable (hydro). Nigeria depends on non-renewable energy despite its vast potential in renewable sources such as solar, wind, biomass and hydro. The total potential of these renewables is estimated at over 68,000MW, which is more than five times the current power output.
Biomass Resources in Nigeria
Biomass can come in different forms like wood and wood waste, agriculture produce and waste, solid waste.
1. Wood
Electricity can be generated with wood and wood product/waste(like sawdust) in modern day through cogeneration, gasification or pyrolysis.
2. Agriculture Residues
In Nigeria, agricultural residues are highly important sources of biomass fuels for both the domestic and industrial sectors. Availability of primary residues for energy application is usually low since collection is difficult and they have other uses as fertilizer, animal feed etc.
However secondary residues are usually available in relatively large quantities at the processing site and may be used as captive energy source for the same processing plant involving minimal transportation and handling cost.
3. Municipal Solid Waste
Back then in secondary school, I learnt that gas could be tapped from septic tank which could further be used for cooking. Any organic waste (like animal waste, human waste) when decomposed by anaerobic microorganisms releases biogas which can be tapped and stored for either cooking or to generate electricity.
Biomass can be used to provide heat and electricity as well as biofuel and biogas for transport. There are enough biomass capacity to meet our demand for electricity and other purposes. From climatic point of view, there is a warm climate in Nigeria which is a good breeding ground for bacteria to grow and decompose the wastes. There are plant and animal growth all year round which in turn create waste and consequently produce biomass.
In November 2016, The Ebonyi State Government took over the United Nations Industrial Development Organization (UNIDO) demonstration biomass gasifier power plant located at the UNIDO Mini -industrial cluster in Ekwashi Ngbo in Ohaukwu Local Government Area of the State. The power plant is to generate 5.5 Megawatt energy using rice husk and other available waste materials available. More of these type of power plants and commitment are needed to utilize the potential of biomass fully.
Why Biomass Energy?
Since biomass makes use of waste to supply energy, it helps in waste management. It also has the potential to supply more energy (10 times) than the one produced from sun and wind. Biomass energy in Nigeria will lead to increase in revenue generation and conserves our foreign exchange. Increase in energy generation will yield more productivity for industries and the rate at which they are shutting down due to the fact that they spend more on power will be reduced to minimal.
Many local factories/companies will spring up and foreign investors will be eager to invest in Nigeria with little concern about power. Establishment of biopower plants will surely create more jobs and indirectly reduce the number of people living in poverty which is increasing everyday at an alarming rate.
Africa’s most populous country needs more than 10 times its current electricity output to guarantee supply for its 198 million people – nearly half of whom have no access at all, according to power minister Babatunde Fashola. Biomass energy potential in Nigeria is promising – with heavy investment, stake holder cooperation and development of indigenous technologies. The deployment of large-scale biomass energy systems will not only significantly increase Nigeria’s electricity capacity but also ease power shortages in the country.
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