Biomass - Sources of Information and General Introduction


The following is reproduced from the REED Energy Entrepreneur's Toolkit, UNEP, 2005 (original document can be found here)

General Introduction

Biomass accounts for more than 10 percent of global energy use. In parts of the developing world it accounts for up to 90 percent. Biomass is an indigenous fuel source that is often readily available and inexpensive throughout much of Africa. It can also be effectively converted to electricity and heat due to recent technological developments. It is because of these two factors that biomass will most certainly play a significant role in the development of energy sectors across the world.

The two most common types of biomass resources are plant biomass which includes woody and non-woody biomass and processed waste and fuels; and, animal biomass which includes animal manure as a feedstock to generate energy using biogas technologies or directly as a cooking fuel.

Each type of biomass has unique characteristics that make it more or less suitable as a fuel source:
  • Moisture content: This is simply the amount of water found in the resource expressed as a percentage of the total resource weight. The value can range from less than 10 percent, for some straws, up to 70 percent for forest residues. The percentage can be expressed as a portion of the wet, dry, or ash-free matter. Typically, it is measured on a wet basis, however it is important to know and cite the way in which the resource was measured.
  • Ash content: Again, the ash content can be measured on all three bases - wet, dry or ash-free matter. The type used must be reported. It is most common to see the ash content measured as a percentage of the dry matter. In wood, the ash content is around 0.5 percent, for agricultural residues the percent ranges from 5 to 10, and for husks it can be as high as 40 percent. The amount of ash affects the biomass’s behavior when exposed to the high temperatures necessary to convert it to electricity.
  • Volatile matter content: This is the measurement of the amount of the biomass that escapes when heated up to 400 and 500 degrees Celsius. When exposed to high heat, the biomass decomposes into solid char and volatile gases. The volatile content can be as high as 80 percent.
  • Elemental composition: The elements contained in biomass are typically carbon, oxygen and hydrogen with a small amount of nitrogen.
  • Heating value: This property measures the amount of energy that is chemically bound in a standard environment. The heating value is a measurement of the energy (Joules; J) per amount of matter (kilograms; kg). The value cannot be measured directly so it is done according to reference states such as the lower heating value (LHV), measured in a gaseous state and the higher heating value (HHV) measured in its liquid state.
  • Bulk density: This is the weight of the resource per unit of volume. This measurement can be found when the biomass is in zero (0) moisture content state (MC=0), termed the oven-dry-weight basis, or according to its given moisture content (MCw). This property also shows extreme variations from as low as 150 to 200 kg/m3 straws to 600 to 900 kg/m3 for wood. The last two properties, heating value and moisture content together determine the biomass resource’s energy density. The energy density is defined as the potential energy per unit volume. The result is typically one-tenth that of fossil fuels.

Technology Options

The following provides a brief introduction to the various types of biomass technologies that are available for different
biomass resources.
  • Direct Combustion: Biomass such as wood, garbage, manure, straw, and biogas can be burned without processing to produce hot gases for heat or steam. Burning the resource by direct heat is termed direct combustion. Examples of direct combustion range include burning wood in fireplaces, burning garbage in a fluidized bed boiler, producing heat or steam to generate electric power. This is the simplest, most widely used, and often most economical biomass technology especially if the biomass resource is within close proximity.
  • Pyrolysis: Pyrolysis is the thermal degradation of biomass by heat in the absence of oxygen. Biomass resources, such as wood or garbage, are heated to a temperature between 800 and 1400 degrees Fahrenheit, but no oxygen is introduced to support combustion. Pyrolysis results in three products: gas, fuel oil, and charcoal.
  • Anaerobic digestion: Anaerobic digestion converts organic matter to a mixture of methane, the major component of natural gas, and carbon dioxide. Biomass, such as wastewater (sewage), manure, or food processing wastes, is mixed with water and fed into a digester tank without air. Use of this type of technology results in biogas.
  • Gasification: Biomass can be used to produce methane through heating (800 Celsius) or anaerobic digestion. During gasification, about 65% of the energy is captured and converted into combustible gases. The gases are then converted into natural gas, which can be used to fuel vehicles, generate electricity, or again converted into synthetic fuels. This technology is not as commercially viable as direct combustion because it is more costly and more state of the art. The most commonly used types of gasifiers are fixed-bed and fluidized-bed. There are many advantages that gasification technologies have over direct combustion and the other converting technologies. The advantages include increased efficiencies by as much as 50%, variety of suitable biomass resources.
  • Alcohol Fermentation: Fuel alcohol is produced by converting starch to sugar, fermenting the sugar to alcohol, then separating the alcohol water mixture by distillation. Feedstocks such as wheat, barley, potatoes, waste paper, sawdust, and straw contain sugar, starch, or cellulose and can be converted to alcohol by fermentation with yeast. Ethanol, also called ethyl alcohol or grain alcohol, is the alcohol product of fermentation usable for various industrial purposes including alternative fuel for internal combustion engines.
  • Landfill Gas: Landfill gas is generated by the decay (anaerobic digestion) of buried trash and garbage in landfills. When the organic waste decomposes, it generates gas consisting of approximately 50 percent methane, the major component of natural gas.
  • Cogeneration: Cogeneration is the simultaneous production of more than one form of energy using a single fuel and facility. Furnaces, boilers, or engines fueled with biogas can cogenerate electricity for on-site use or sale. Biomass cogeneration has more potential growth than biomass generation alone because cogeneration produces both heat and electricity. Cogeneration results in net fuel use efficiencies of over 60 percent compared to about 37 percent for simple combustion. Electric power generators can become cogenerators by using residual heat from electric generation for process heat, however, waste heat recovery alone is not cogeneration.
  • Co-firing: Co-firing is only possible if using an existing coal-fired power plant. This process is possible by mixing biomass with coal and then burning them together or in different boiler feeds. Advantages of this technology are that it can be the least-cost option and can displace up to 15% of the coal. The typical biomass resources used in this case are wood products.

Overall, one of biomass’s most attractive qualities is its versatility. It can be easily converted to electricity by burning or converted to liquid or gaseous fuel by physical or biological means.

System Costs

Due to numerous variables, it is not reasonable to provide estimate costs for biomass projects. Issues to consider in determining the cost of using a biomass resource include:

  • Crop selection and rotation: Biomass properties will often affect the attractiveness of the resource. For example,the energy density, leaf cover, productivity, water and nutrient requirements, soil erosion susceptibility to disease, effect on biodiversity may increase the cost of converting the resource;
  • Cost and seasonal availability of resource;
  • Storage: It may be possible that you have to collect and store the resource for a period of time, which may be costly;
  • Transport: Costs to get the biomass to the conversion site; and
  • Efficiency: The lower the efficiency of the biomass resource the more land is required. This cost may be a substantial percentage of the total project costs or the land may be economically suited for another activity.
  • Plantation running costs: labor, fertilizer, and herbicides

Advantages

  • Biomass is a renewable source as is receiving a great amount of attention as a possible fuel of the future to combat climate change. This could have a positive impact on the cost, etc.
  • Biomass is often available in large supply in developing countries.
  • Land requirement is not an issue because there is generally a large amount of land area in Africa that cannot be used for other productive uses, but can sustain biomass.
  • A variety of conversion products are available with a wide range of uses.

Disadvantages

Biomass is often left out as a fuel for the future for the following reasons:

  • Associated with health related problems in developing countries mainly from particulates released during burning and carbon monoxide. These problems lead to respiratory infections in children and complications during pregnancy;
  • Biomass is often bulky and may have a high water content.
  • Quantity of fuel is unpredictable and may be difficult to handle. Long-term fuel supply contracts;
  • Low energy density per unit of land, water, or per unit weight of raw product;
  • Energy crops and dedicated biomass requires a large amount of dedicated land area. Unfortunately, dedicated areas may reduce the soil fertility, biodiversity, water level, landscape, displace food, and affect the leaching of nutrients.

Business Traits:

Following is a brief description of the skills and relationships needed with contractors, suppliers, consultants and others in order to start a business using biomass. The purpose is to stimulate the entrepreneur to identify all of the business relationships that will be required to implement his or her core idea and begin to consider all of the pieces that must be woven together.

Biomass energy projects use organic matter -- plants, trees, agricultural residue, animal waste – as an input in an energy conversion process. This process may be simple, as in a closed container using anaerobic digestion to produce a gas for burning. The process may also be mechanical, as in the conversion of sugar cane waste – bagasse – into energy through simple combustion, or the same process might be sophisticated through the use of high pressure boilers.

The important relationships involved in a biomass project include:

  • Design – biomass varies greatly and there are numerous conversion processes. As a result an entrepreneur needs to build solid relationships with design experts.
  • Equipment suppliers – biomass projects tend to involve the integration of different components.
  • Knowledge of the nature of the biomass input – moisture, seasonality, an alternative use (which may eliminate their availability as a fuel source) is crucial.
  • Processing, Transport and Storage relationships with growers and truckers are crucial.
  • Compatible and back-up fuels need to be understood and relationships built in case the primary biomass stream is interrupted.
  • Relationships with providers of debt, equity and consumer finance.