Biofuels
Monday, 18 June 2012 14:05

Biomass: a sustainable source of energy

Bio-energy is the term used to describe the many varied ways of utilising biomass to create fuel or feedstock in generating energy. There are various kinds of biomass that can be used for this. This article ventures into selecting a sustainable biomass source to produce energy and explains how one can go about to produce energy using biomass.

biomass a_sustainable_sourceWritten by Nichelle Lemmer

We are entering an era where technology and innovation combined with sustainability enable us to reach a global goal in mitigating and adapting to climate change. Generating bio-energy from different types of biomass means that people can even use harmful gasses to produce energy.

According to the website www.renewableenergyworld.com, people have used bio-energy for thousands of years, ever since they started burning wood to cook food or to keep warm. “Today wood is still our largest biomass energy resource but many other sources of biomass can now be used, including plants, residues from agriculture or forestry, and the organic components of municipal and industrial waste. Even the fumes from landfills can be used as a biomass energy source,” the website states.

According to a research report done by the United Nations Industrial Development Organisation (UNIDO) called Bio-energy for sustainable development in Africa, the agricultural sector in most sub-Saharan countries is dominated by subsistence farming with very low investment levels and yields. The development of modern bio-energy systems offers opportunities for investment and infrastructure improvements in agriculture with the promise to diversify agricultural production and thus to stimulate socio-economic development.

In the report it is stated that in general many African countries have suitable conditions for bio-energy development, such as abundant labour and sufficient available arable land and water resources. “In order to avoid potential negative environmental and socio-economic impacts, effective mechanisms to ensure sustainability need to be put in place,” researchers who worked on the report said. “Several sub-Saharan African countries are currently engaged in the formulation of policies and development plans to guide the development and ensure the sustainability of the bio-energy sector.”

According to the report, many regions’ traditional biomass resources are readily available for the local population. “Their production and use, however, cause a variety of negative impacts, including overuse of natural resources, which is leading to deforestation and health effects, due to indoor air pollution (IAP) disproportionately affecting women and children in the poor areas of developing countries.”

Sustainability and bio-energy

The report states that bio-energy development in Africa should take into account the prevailing land tenure systems in a way that creates benefits for local communities, especially the rural population. For this reason the Competence Platform on EnergynCrop and Agroforestry Systems for Arid and Semi-arid Ecosystems in Africa (COMPETE) was established. The objective of COMPETE is to stimulate sustainable bio-energy implementation in Africa. COMPETE has established a platform for policy dialogue and capacity building in the major multi- and bilateral funding organisations and key stakeholders throughout the bio-energy provision and supply chains.

They developed sustainability guidelines to develop bio-energy in Africa. Under the environmental guidelines they listed the implementation of good agro-ecological practices as a key factor in taking an eco-friendly approach to develop bio-energy.

COMPETE also advises bio-energy project managers to make sure that their projects will not be affecting water supply and quality and don’t change land use, such that it detrimentally affects food security. Under social guidelines COMPETE says  it is important to stimulate community participation in planning especially the participation of women.

Project managers should also make sure that their projects open the door for skills transfer between experts and the community. With reference to economical guidelines, COMPETE says communities should be included in a business model and the project should support the community by adding value to the surrounding area. Improvement in services and infrastructure should also be part of the project’s main objectives. “A project must comply with national policies and  local programmes and plans.” According to COMPETE, one of the most important guidelines to run a successful, sustainable bio-energy project is to respect the land rights of the people, especially in rural communities, and avoid displacement.

Converting biomass to bio-energy

In the past the most common way to capture energy from biomass was to burn it to make heat. The industrial revolution bought new ways to use biomass-fired heat to produce steam power. More recently this biomass-fired steam power has been used to generate electricity. “Burning biomass in conventional boilers can have numerous environmental and air-quality advantages over burning fossil fuels,” says the Union of Concerned Scientists (UCS).

Advances in recent years have shown that there are even more efficient and cleaner ways to use biomass. “It can be converted into liquid fuels or cooked in a process called “gasification” to produce combustible gases, which reduces various kinds of emissions from biomass combustion, especially particulates,” the union explains.

One of the oldest and most common ways of converting biomass to electricity is to burn it to produce steam, which turns a turbine that produces electricity. “The problem with the direct combustion of biomass is that much of the energy is wasted and that it can cause some pollution if it is not carefully controlled,” says UCS. “Direct combustion can be done  using only biomass in a plant made to burn another fuel, usually coal.”

 

Co-firing

UCS further explains that an approach that may increase the use of biomass energy in the short term is to mix it with coal and burn it at a power plant designed for coal, a process known as co-firing. “Through gasification, biomass can also be co-fired at natural gas-powered plants.”

According to the union, the benefits associated with biomass co-firing can include lower operating costs, reductions of harmful emissions like sulfur and mercury, greater energy security and, with the use of beneficial biomass, lower carbon emissions. “Co-firing is also one of the more economically viable ways to increase biomass power generation today, since it can be done with modifications to existing facilities.”

Combined heat and power (CHP)

Direct combustion of biomass to produce electricity, also produces heat that can be used to heat buildings or for industrial processes. “Because they use heat energy that would otherwise be wasted, CHP facilities can be significantly more efficient than direct combustion systems, but it is not always possible or economical to find customers in need of heat in close proximity to power plants,” says UCS.

Biomass gasification

UCS further explains that by heating biomass in the presence of a carefully controlled amount of oxygen and under pressure, it can be converted into a mixture of hydrogen and carbon monoxide called syngas. “This syngas is often refined to remove contaminants.” Equipment can also be added to separate and remove the carbon dioxide in a concentrated form. “The syngas can then be run directly through a gas turbine or burned and run through a steam turbine to produce electricity,” the union adds. “Biomass gasification is generally cleaner and more efficient than direct combustion of biomass. Syngas can also be further processed to make liquid biofuels or other useful chemicals.”

Anaerobic digestion

According to UCS, biogas can be generated by a process called anaerobic digestion. The gas can then be used as a source of energy. Biogas is created by using micro-organisms to break down biomass to produce methane and carbon dioxide. “This can occur in a carefully controlled way in anaerobic digesters used to process any organic waste for example sewage, animal manure or food waste.”

In addition to generating biogas, which displaces natural gas from fossil-fuel sources, such collection processes keep the methane from escaping to the atmosphere, reducing emissions of a powerful global warming gas.

Manure can be converted into renewable energy through anaerobic digesters, combustion or gasification. According to the union, dairy farms can for example convert cow manure using biogas digesters to produce biogas.

Farmers can use the biogas in three ways. They can use the biogas on-site as a replacement for the farm’s own natural gas or LP gas use, scrub the biogas removing contaminant gases, pressurise it and inject it into nearby natural gas pipelines (this has never been done in South Africa), or burn it to heat water producing steam that runs a turbine generating renewable electricity for use on-site or feed onto the local grid. “The best application of biogas from manure will be determined by the opportunity to displace natural gas or LP gas use, local energy markets and state and federal incentives,” says UCS.

Poultry litter can also be digested to produce biogas or combusted to produce renewable electricity, either directly or through gasification, which improves efficiency and reduces emissions.

Biogas energy systems

Marisa Naude, sales and marketing manager of Agama Energy, says there is a widespread ignorance of biogas in the South African market. According to her, the regulatory environment is also unclear and adds to the confusion. “Regulations like the Waste Act (especially with regard to sewage being classified as hazardous waste irrespective of quantity), the Water Act and National Environmental Management Act  all have an impact on the need for environmental impact assessments (EIA) for biogas installations affecting installation costs and some of the legislation is contradictory,” she says.

Naude says  clients are often looking to generate electricity from gas, whereas using gas directly for heating and cooking is a far more efficient way to use the energy available. “Over 50% of the energy value of the gas gets lost as heat when generating electricity from biogas. Generating electricity and then selling it onto the grid is very complex as it requires agreements with Eskom that may not be granted,” she adds. She advises large commercial clients to do a prefeasibility study during which one should look at the business case for a biogas digester at a specific site. “Make sure there is an accessible regular supply of waste available in the future and plan on what will be done with the overflow water from the digester,” she adds.

“Another misconception that also influences the decision to invest in a biogas energy system is that clients often expect a much higher energy yield per unit of feedstock than is possible,” says Naude. That is already mentioned above “Clients tend to underestimate the capital cost involved. Many companies have an existing budget for running costs like electricity, heating and cooling, but struggle to budget for capital costs to finance something that will be paid back out of the running costs over a period,” she explains. 

She says there are several benefits that one can expect a biogas digester to deliver on. “It provides energy savings, energy security, reduced carbon  emissions, on-site waste management, and the possibility of recycling waste water.” She further explains that a company with an excess of waste like animal manure, offal or food waste that is expensive to dispose of, can definitely benefit from investing in a biogas digester. “They must then find a thermal use for the gas, like heating animal pens, pasteurising milk or cooking. There is also the  possibility of using the nutrient-rich water leaving the digester for irrigating crops or of purifying it further (higher capital cost), and re-using it in industrial processes,” she adds.

Urban waste

According to the union, people generate biomass waste in many forms, including urban wood waste such as tree trimmings, shipping pallets and clean, untreated leftover construction wood, as well as clean, biodegradable portions of garbage like paper that cannot be recycled, food and yard waste.

This scientific community states that a related process happens in a less-controlled manner in landfills, as biomass in the garbage breaks down. “In addition, methane can be captured from landfills or produced in the operation of sewage treatment plants and used for heat and power, reducing air pollution and emissions of global warming gases,” UCS concludes.

Selecting a beneficial crop to produce energy

UCS notes that if developed properly, certain crops can and should supply increasing amounts of bio-energy. “In fact, in numerous analyses of how America can transition to a clean energy future, sustainable biomass is a critical renewable resource,” the union says.

It further explains that like all energy sources, bio-energy has environmental risks that need to be mitigated. “If not managed carefully, biomass crops for energy can be harvested at unsustainable rates, damage ecosystems, produce harmful air pollution, consume large amounts of water and produce net greenhouse emissions,” UCS states.

According to the union, most scientists believe there is a wide range of biomass crops that can be produced sustainably and with minimal harm, while reducing the overall impacts and risks of the current energy system. “Implementing proper policy is essential to securing the benefits of biomass and avoiding its risks,” the union adds.

Selecting a biomass crop that is not harmful to the environment can be done. It is just a matter of choosing a feedstock that adheres to sustainable principles.

UCS says one can choose an energy source that doesn’t compete with food crops for land, use portions of crop residue such as wheat straw or corn stover or use sustainably-harvested wood and forest residues. Then one can also venture into using clean municipal and industrial wastes. “Among beneficial resources, the most effective and sustainable biomass resources will vary from region to region and also depend on the efficiency of converting biomass to its final application, be it for electricity generation, biofuels, bioproducts or or heat,” the union says.  

According to UCS, energy crops can be grown on farms in large quantities and in ways that don’t displace or otherwise reduce food production. These crops can be grown on marginal lands or pastures or as double crops that fit into rotations with food crops. The union further states that depending on soils and slope, a certain fraction of crop residues should be left in the field to maintain cover against erosion and to recycle nutrients. “In most cases some fraction of crop residues can be collected for renewable energy in a sustainable manner. Food processing also produces many usable residues.”

Woody biomass

Bark, sawdust and other by-products of milling timber and making paper are currently the largest source of biomass-based heat and renewable electricity. “Lumber, pulp and paper mills use it for both heat and power,” says UCS. “In addition, shavings produced during the manufacturing of wood products and organic sludge (or ‘liquor’) from pulp and paper mills are biomass resources. Some of these ‘mill residues’ could be available for the additional generation of renewable electricity.”

UCS further explains that beyond these conventional types of woody biomass, there are additional sources of woody biomass that could be used for renewable energy. “With a proper policy these additional sources could be sustainably harvested and make a significant contribution towards renewable energy generation.”

Opportunities to turn various kinds of biomass into a potentially useful source of energy are endless. Although bio-energy is a sustainable and energy-efficient way of producing energy, one should still adopt eco-friendly measures  when harvesting biomass or feedstock for such a project. The future looks bright for this industry as it complements the vision of the South African government to transition into a low carbon economy.

Full acknowledgement and thanks are given to the United Nations Industry Development Organisation, Agama Energy and the Union of Concerned Scientists for the information given to write this article.