Nigeria: Wood Waste to the Rescue

The Niger Delta region of Nigeria is home to most of the country's oil wells, but it could be its wood resources that bring power to the people Credit: Terry Whalebone Being an oil-rich country, Nigeria's energy supply is primarily fossil-based. The unequal distribution of oil wealth, along with agitation for self-determination and resource control, has led to the sabotage of oil installations. However, a recent study has shown that combined with the use of micro-grids, the 1.8 million tonnes per year of wood waste produced by the lumber industry in Nigeria could help ease the situation with the supply of 1.3 TWh of electricity. By Kehinde Oluoti, Godswill Megwai, Anita Pettersson, Tobias Richards Nigeria is the world's sixth largest producer of oil, with exports of crude forming the backbone of its economy. The Niger Delta region is home to most of the Nigerian oil wells, but the area has failed so far to enjoy the benefits of such huge revenues. Most basic amenities are nowhere to be found when compared with other parts of the country. The situation has led to agitation, with oil pipelines being vandalised, as well as sabotage and abductions. The disruption caused has led to many power stations losing their supply of natural gas, dramatically decreasing and even completely halting power generation. Considering the non-renewable nature of fossil energy, coupled with never ending agitation for resource control in the Niger Delta regions, the solution to power problems in Nigeria may be a new renewable option. Biomass resources such as municipal solid waste and animal waste, agricultural crops and residues, as well as forestry resources, are common in Nigeria. Given that they are widely available, especially wood waste, there is a large potential for their use in producing biofuel. Wood Waste to the Rescue As a whole, the country has a total of around 11.1 million hectares of forest and 5.5 million hectares of other wooded land. As such, wood waste from these huge landmasses could be explored as fuel for power generation purposes. The country's landscape is varied, as is the climate, from humid and sub-humid in the south, to semi-arid in the north. The considerably high annual volume of rainfall allows the government-controlled forest reserves to thrive extensively throughout the country. The major wood processing industries in Nigeria are typically large capacity facilities, such as sawmills, plywood mills, pulp and paper plants. However, there are also quite large numbers of small-scale wood companies manufacturing wooden products such as furniture, and many cabinet makers and carpenters. Sawmills, by their very nature, generate considerable amounts of waste - sawdust, off-cuts, wood backs, plain shavings, rejects, etc. In the absence of proper disposal methods, these wastes are burnt in the open air, dumped along the bank of streams and rivers or left on any available space to rot. Estimates of the amount of sawdust generated in Nigeria range from around 1.8 million tonnes per annum to 5.2 million tonnes. As the demand for wood and its products increases, the volume of wastes being generated increases too. Hence, one of the environmental problems facing cities and towns today is the proper disposal of the wastes being generated daily by the ever increasing activities of sawmills. Meanwhile, the huge volume of wood waste generated in and around Nigerian cities and towns poses environmental and health challenges. It can however be utilised directly as fuel by public and private power facilities. Environmental Impact of Wood Waste Currently, prominent environmental problems caused by the poor management of wood waste include emission into the air of toxic and non-toxic particulates. Further, emissions from veneer dryer machines affect workers and others living in the vicinity and are a serious health hazard. It has also been estimated that 136 kg of carbon dioxide equivalents (CO2e) are emitted per tonne of chips that are dried naturally in piles for a period of six months. Inland waters in Nigeria are also polluted by organic discharges from sawmills and other wood processing factories sited near streams and canals. Pollutants, such as inert solids, originate from wood shavings and leachates. When released into an aquatic environment they cause a reduction in light penetration which in turn, limits the productivity of, and causes impairment to, the organisms living in that particular ecosystem. However, wood waste from sawmills could be used in a variety of ways, including the production of particleboard, mushrooms, charcoal, chemicals, enzymes and briquettes. Alternatively, together with bark, it can be used as fuel for producing energy. Promoting Renewables The Nigerian Government has over the years rolled out several policies and regulatory frameworks to promote rural electrification and power generation using renewable sources of energy. For example, all energy sectors are covered The National Energy Policy (NEP), 2003. The main targets for the power sector are (a) to ensure that 75% of the population has access to electricity by 2020, (b) to provide electricity to cities and local government headquarters by 2010, and (c) to promote the participation of the private sector. Under the policy the country's renewable energy resources are to be promoted, as is a decentralised energy supply based on renewable resources. Further to the NEP, the Electricity Power Sector Reform Act (EPSR), 2005 reiterates the Federal Government's plan to increase access to electricity in rural areas from 40% in 2005 to 75% in 2015. In addition, the Nigerian Renewable Electricity Policy (NREP), 2006 was set to 1) elevate biomass as an alternative energy resource in rural areas in particular; 2) enhance efficient use of agricultural residues, animal and human waste as sources of energy; and 3) to decrease health hazards by less biomass and agricultural residues being incinerated in the open. Finally, the Renewable Energy Master Plan (REMP), 2007 foresees increasing the country's electrification demand to a total of 14,000 MW by 2015 of which around 701 MW (5%) would be from renewable sources. It is also envisaged that by 2025 the total electricity demand will have increased to around 29,000 MW, with renewable sources constituting up to 10%. The plan targets contributions to the electricity supply mix from biomass sources of around 50 MW by 2015 and 400 MW by 2025. The plan includes the 2 MW and 5 MW wood waste power plants in Ogun and Ondo States, respectively. Suitable Sites When siting a wood waste fuelled power plant it is important to consider transportation costs for the fuel. It is thus suggested that wood waste to energy plants be located close to sawmills and other similar wood working industries. Efforts should also be made to provide adequate space for the supply and storage of fuel. A detailed technical/economic feasibility study should be conducted on any sites identified, and an appropriate business plan for the further development of these sites formulated. The study should include detailed work on the historical, and seasonal, generation of biomass at the site to ensure the sustainable operation. Year round operating patterns of the related industrial activities, including operational variations during the various seasons (rainy, dry, peak, off-peak, etc.), should be studied to obtain an accurate idea of the availability of the feedstock. In producing the feasibility study an assessment of the electricity demand from all the nearby consumers, and their current electricity sources, should be carried out in order to assess the prospect of selling the electricity to them. By using a mini-grid system individual entrepreneurs can become small power companies, meeting the needs of a small neighbourhood or a cluster of businesses. Such a system enhances the distribution of power to isolated areas not connected to, or far from, the national grid. Gasification Typically, internal combustion engines are used in the energy facilities found rural areas of developing countries such as Nigeria. However, technologies such as gasification could present make other options attractive. Many developing countries are either in the process of evaluating biomass gasification technology, or are already introducing small-scale biomass gasifiers. Besides using wood as fuel for cooking, gasification of these resources offers a better option for producing power, heat and biofuels for a wider variety of applications. With renewed focus on producing energy from wood waste, it is both possible and encouraging to know that wood waste can be processed using the existing infrastructure and equipment associated with fossil fuels such as coal. Wood waste is typically gasified at relatively high pressure, usually higher than 30 bars, and at a temperature as high as 1500°K (1226°C). During the process it reacts with a gasifier agent (steam/oxygen) to produce raw synthetic gas (CO + H2), hydrogen and some other minor byproducts. This syngas is cleaned and eventually used to generate electricity. Different wood fuels give different energy outputs. In the case of waste woods from forestry versus biomass crops, the energy output of the latter is 24%, while for the former with its lower moisture content is 18% - 25%. The choice of gasifier for use in biomass conversion is highly dependent on its capacity, the physical and chemical characteristics of the biomass fuel in question and the intended application. Although there are several designs and models of gasifiers, the generic configurations are the same, and include an updraft or countercurrent, a downdraft or concurrent gasifier, a cross draft and a fluidised bed. Wood waste often contains a lot of tars, which form various compounds and mix with the product gas during reactions in the gasifier. The best way of solving these problems for small-scale units is by making use of a downdraft gasifier, which also suffers less from environmental criticisms as the organic component in the condensate is low. The acid and other tarry products from the fuel pass through a glowing bed of charcoal on their way down the downdraft gasifier configuration and are converted into permanent gases: hydrogen, carbon dioxide, carbon monoxide and methane. This leads to an almost complete breakdown of the tar, thus producing a virtually tar-free gas suitable for use by an engine. Evaluation of Biowaste to Energy Technologies For the purposes of the study, the generating technologies selected for analysis were: internal combustion engine, gas turbine, micro-gas turbine, Stirling engine and steam turbine. The electrical efficiency and economic feasibility of these technologies were investigated for the small-scale production of power using wood waste as the fuel. Furthermore, the total cost of installation and operations, electricity production (thermodynamics) and economic analysis are considered as being suitable for detailed evaluation and comparison between each technology with regards to estimating electrical efficiency. If not properly managed wood waste can be problematic for waterways and rivers Credit: Terry Whalebone However, most of the technologies are yet to be commercialised, so information on operating conditions and parameters makes the evaluations possible. Furthermore, for the purpose of comparison, wood waste in the form of sawdust from the Ile-Ife City in Nigeria was used as the feedstock. Electrical Performance The electrical efficiency of each technology was evaluated for the reference plants based on the energy value of the fuel and process modification in some of the technologies. The study found, that based on reference conditions, the internal combustion engine has a better electric output than the other technologies at 33%. It was found that the gas turbine had a lower efficiency of 29% based on the conditions. However it should be noted that depending on the conditions this could be increased to around 35%. The micro gas turbine, which operates at a pressure as high as 6 bar, has an electrical performance of 30%, which can be increased to 31% when operating with an electric output below the 500 kW range. This indicates that micro scale production using a micro gas turbine gives a better electric performance. The Stirling engine power system indicates an electric efficiency of 20% from a nominal electric output range of 10 - 150 kW irrespective of the fact that it has yet to be widely commercialised. Based on the reference plant, the steam turbine had an electrical efficiency of 23%. Economic Evaluation In assessing economic performance many fixed and working capital costs were considered and mathematically modelled. The fixed capital cost includes the purchase of equipment, installation, labour, contingency funds, and all other costs associated with building the power plant. The estimate shows that both the internal combustion engine and Stirling power plants have a low fixed capital cost when compared to the other technologies. Additionally, the fixed capital costs of gas turbine and steam turbine plants indicate that they are mostly designed for centralised or large scale power generation. Furthermore, the cost per unit of small power plants is more than that of large facilities. In terms of working capital, or running costs, the estimates took into account the cost of start-up operation of the power plant and the first few months of operation. The estimated hourly start-up cost ($/kWh) for a micro gas turbine, gas turbine, internal combustion engine, Stirling engine and steam turbine is 0.33, 0.35, 0.16, 0.18 and 0.35 respectively. The total of working capital cost was assumed to be 20% of the fixed capital cost which covers the operating and maintenance costs, salaries and other costs pertaining to operations. It is clear from these estimates that gas turbine and steam turbine technologies require more capital compared to the others. Micro gas turbines require roughly the same capital per kW as the gas turbine for the start-up operation, whereas the start-up is low for both internal combustion and Stirling engines, which suggests that both technologies can be considered as being economically feasible for generating power from waste wood on a small scale. Environmental Evaluation The combination of feedstock and the combustion technology determine the variability in the level of emissions associated with biomass power plants. Common pollutants from such plants include nitrogen oxide, sulfur dioxide, carbon monoxide, and particulate materials such as soot and ash. Gasifier systems equipped with electrostatic precipitators can, however, help reduce emissions of NOx CO2 and particulates. The level of NOX emissions are affected significantly by the temperature of the flame as well as by the amount of Nitrogen that is present in the fuel. Other significant factors include the level of excess air and the temperature of the combustion air. Particulate materials are controlled effectively through the use of high-grade fuels, and an efficient gasifier set-up that is well adjusted and maintained. A set of notable NOX control measures has been the primary focus of research and development in controlling emissions from biomass power systems, and include the control of emissions from the combustion process, fuel gas recirculation (FGR), low excess air (LEA) firing, burner modification, and water/steam. Conclusions Nigeria would benefit from incentives to convert wood waste into power. It would reduce air pollution and, ultimately, help reduce emissions of greenhouse gases. Further, the decision of the Nigerian Government to introduce policies and regulations aimed at enhancing the proper and formal propagation of mini-grids for producing power from wood waste is commendable. The problem of supplying to rural localities that are not connected to the national grid would be solved by the diligent installation of mini-grid systems coupled with proper management, finance and adequate feasibility studies of site suitability and the electricity requirements of the host localities. The implementation of such systems would give rise to a huge opportunity for Nigeria to both reduce the environmental impact of huge quantities of waste wood, while generating much needed renewable energy. Kehinde Oluoti, Godswill Megwai, Anita Pettersson and Tobias Richards are PhD Students at the Swedish Center for Resource Recovery, University of Boras, Sweden Email: kehinde.oluoti@hb.se, More Waste Management World Articles Waste Management World Issue Archives