Biomass

Biomass, a renewable energy source, is biological material from living, or recently living organisms,^[1] such as wood, waste, (hydrogen) gas, and alcohol fuels. Biomass is commonly plant matter grown to generate electricity or produce heat. In this sense, living biomass can also be included, as plants can also generate electricity while still alive.^[2] The most conventional way on how biomass is used however, still relies on direct incineration. Forest residues for example (such as dead trees, branches and tree stumps), yard clippings, wood chips and garbage are often used for this. However, biomass also includes plant or animal matter used for production of fibers or chemicals. Biomass may also include biodegradable wastes that can be burnt as fuel. It excludes organic materials such as fossil fuels which have been transformed by geological processes into substances such as coal or petroleum.

Industrial biomass can be grown from numerous types of plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane^[3], and a variety of tree species, ranging from eucalyptus to oil palm (palm oil). The particular plant used is usually not important to the end products, but it does affect the processing of the raw material.

Although fossil fuels have their origin in ancient biomass, they are not considered biomass by the generally accepted definition because they contain carbon that has been "out" of the carbon cycle for a very long time. Their combustion therefore disturbs the carbon dioxide content in the atmosphere.

Plastics from biomass, like some recently developed to dissolve in seawater, are made the same way as petroleum-based plastics. These plastics are actually cheaper to manufacture and meet or exceed most performance standards, but they lack the same water resistance or longevity as conventional plastics.^[4]

Chemical composition

Biomass is carbon based and is composed of a mixture of organic molecules containing hydrogen, usually including atoms of oxygen, often nitrogen and also small quantities of other atoms, including alkali, alkaline earth and heavy metals. These metals are often found in functional molecules such as the porphyrins which include chlorophyll which contains magnesium.

Biomass sources

Biomass energy is derived from five distinct energy sources: garbage, wood, waste, landfill gases, and alcohol fuels. Wood energy is derived both from direct use of harvested wood as a fuel and from wood waste streams. The largest source of energy from wood is pulping liquor or “black liquor,” a waste product from processes of the pulp, paper and paperboard industry. Waste energy is the second-largest source of biomass energy. The main contributors of waste energy are municipal solid waste (MSW), manufacturing waste, and landfill gas. Biomass alcohol fuel, or ethanol, is derived mostly from sugarcane, although corn is also a common source. It can be used directly as a fuel or as an additive to gasoline.^[5]

Biomass can be converted to other usable forms of energy like methane gas or transportation fuels like ethanol and biodiesel. Methane gas is the main ingredient of natural gas. Smelly stuff, like rotting garbage, and agricultural and human waste, release methane gas - also called "landfill gas" or "biogas." Crops like corn and sugar cane can be fermented to produce the transportation fuel, ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products like vegetable oils and animal fats.^[6] Also, Biomass to liquids (BTLs) and cellulosic ethanol are still under research.^[7][8]

Biomass conversion process to useful energy

There are a number of technological options available to make use of a wide variety of biomass types as a renewable energy source. Conversion technologies may release the energy directly, in the form of heat or electricity, or may convert it to another form, such as liquid biofuel or combustible biogas. While for some classes of biomass resource there may be a number of usage options, for others there may be only one appropriate technology.

Thermal conversion

These are processes in which heat is the dominant mechanism to convert the biomass into another chemical form. The basic alternatives are separated principally by the extent to which the chemical reactions involved are allowed to proceed (mainly controlled by the availability of oxygen and conversion temperature):Combustion, Torrefaction, Pyrolysis, Gasification.

There are a number of other less common, more experimental or proprietary thermal processes that may offer benefits such as hydrothermal upgrading (HTU) and hydroprocessing. Some have been developed for use on high moisture content biomass, including aqueous slurries, and allow them to be converted into more convenient forms. Some of the Applications of thermal conversion are Combined heat and power (CHP) and Co-firing. In a typical biomass power plant, efficiencies range from 20-27%.^[9]

Chemical conversion

A range of chemical processes may be used to convert biomass into other forms, such as to produce a fuel that is more conveniently used, transported or stored, or to exploit some property of the process itself.

Biochemical conversion

A microbial electrolysis cell can be used to directly make hydrogen gas from plant matter

As biomass is a natural material, many highly efficient biochemical processes have developed in nature to break down the molecules of which biomass is composed, and many of these biochemical conversion processes can be harnessed.

Biochemical conversion makes use of the enzymes of bacteria and other micro-organisms to break down biomass. In most cases micro-organisms are used to perform the conversion process: anaerobic digestion, fermentation and composting. Other chemical processes such as converting straight and waste vegetable oils into biodiesel is transesterification.^[10] Another way of breaking down biomass is by breaking down the carbohydrates and simple sugars to make alcohol. However, this process has not been perfected yet. Scientists are still researching the effects of converting biomass.

Environmental impact

On combustion, the carbon from biomass is released into the atmosphere as carbon dioxide (CO₂). The amount of carbon stored in dry wood is approximately 50% by weight.^[11] When from agricultural sources, plant matter used as a fuel can be replaced by planting for new growth. When the biomass is from forests, the time to recapture the carbon stored is generally longer, and the carbon storage capacity of the forest may be reduced overall if destructive forestry techniques are employed.^{[12][13][14][15]}

The existing biomass power generating industry in the United States, which consists of approximately 11,000 MW of summer operating capacity actively supplying power to the grid, produces about 1.4 percent of the U.S. electricity supply.^[16]

Currently, the New Hope Power Partnership is the largest biomass power plant in North America. The 140 MW facility uses sugar cane fiber (bagasse) and recycled urban wood as fuel to generate enough power for its large milling and refining operations as well as to supply renewable electricity for nearly 60,000 homes. The facility reduces dependence on oil by more than one million barrels per year, and by recycling sugar cane and wood waste, preserves landfill space in urban communities in Florida.^[17][18]

Biomass power plant size is often driven by biomass availability in close proximity as transport costs of the (bulky) fuel play a key factor in the plant's economics. It has to be noted, however, that rail and especially shipping on waterways can reduce transport costs significantly, which has led to a global biomass market ^[19]. To make small plants of 1 MW_el economically profitable those power plants have need to be equipped with technology that is able to convert biomass to useful electricity with high efficiency such as ORC technology, a cycle similar to the water steam power process just with an organic working medium. Such small power plants can be found in Europe.^{[20] [21][22][23]}

Despite harvesting, biomass crops may sequester carbon. So for example soil organic carbon has been observed to be greater in switchgrass stands than in cultivated cropland soil, especially at depths below 12 inches.^[24] The grass sequesters the carbon in its increased root biomass. Typically, perennial crops sequester much more carbon than annual crops due to much greater non-harvested living biomass, both living and dead, built up over years, and much less soil disruption in cultivation.

The biomass-is-carbon-neutral proposal put forward in the early 1990s has been superseded by more recent science that recognizes that mature, intact forests sequester carbon more effectively than cut-over areas. When a tree’s carbon is released into the atmosphere in a single pulse, it contributes to climate change much more than woodland timber rotting slowly over decades. Current studies indicate that "even after 50 years the forest has not recovered to its initial carbon storage" and "the optimal strategy is likely to be protection of the standing forest".^[25][26]

Using biomass as a fuel produces the same air-pollution challenges as other fuels. Black carbon - a pollutant created by incomplete combustion of fossil fuels, biofuels, and biomass - is possibly the second largest contributor to global warming.^[27] In 2009 a Swedish study of the giant brown haze that periodically covers large areas in South Asia determined that it had been principally produced by biomass burning, and to a lesser extent by fossil-fuel burning.^[28] Researchers measured a significant concentration of ¹⁴C, which is associated with recent plant life rather than with fossil fuels.^[29]

See also

References

External links

• Biomass Incineration
• Nordic Energy Solutions Advanced Bioheat Solutions from the Nordic Region
• INBIOX Biomass News
• Biomass as an Energy Source - Växjö University
• Biomass Thermal Energy Council
• Everything Biomass
• What is Biomass? - Växjö University
• Biomass program
• European Biomass Conference & Exhibition.
• European Biomass Industry Association (EUBIA)
• Forest Bioenergy
• Pellet Fuels Institute
• Renewable Products Development Laboratories (RPDL)
• RES LEGAL - database on the promotion and the access to the grid of electricity generated from renewable energy sources (including biomass) in Europe

Further reading

• Greater Caution Needed Before Supporting Thinning, Biomass Projects by George Wuerthner, 2-08-10 New West.

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