THE GRASS TURNS GREENER

Bio-mass has emerged as a promising environment friendly source of energy. The term bio-mass means anything that is of biological or botanical origin. It is material from living, or organisms which have been living till recently, like wood, waste, gas, and alcohol. Usually biomass refers to vegetation grown to generate energy. In this sense, living plants can also be included, as they can generate electricity.

Before the industrial revolution bio-fuels used to be the principal source of energy all over the world, and even today on an average it supplies around five percent of the energy consumed worldwide, with most of it accounted for by the Third World household sector. In the US, bio-fuels account for three percent of the energy consumed.

Biomass energy is derived from five sources. They are garbage, wood, waste, landfill gases and alcohol. In the case of wood, energy is derived from directly harvested wood as well as wood waste. The largest source of energy from wood is pulping liquor or “black liquor,” a waste product from the manufacturing processes of the pulp, paper and paperboard industry.

Waste is the second largest source of biomass energy. The main sources of waste energy are municipal solid waste (MSW), manufacturing waste, and landfill gas. Biomass alcohol or ethanol is produced mainly from sugarcane and corn. It can be used directly as a fuel or as an additive to gasoline.

Plants like miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane and many kinds of trees, ranging from eucalyptus to oil palms are the principal sources of commercial bio-fuel mass. The plant used has no effect on the end products, but the processing of the raw material changes with the type of bio-mass used like crop or livestock waste

Crop and livestock waste can be used as biomass. Process residues, dung and bagasse (sugarcane waste) can be used for producing bio-energy. Methane is commonly produced bio-energy source and it is considered a very efficient fuel.

Another source of bio-energy is fast-growing trees and grasses. Many biological material like stalks, straws, treetops, branches, perennial crops and forest waste can be used as biomass. Using this, it is possible to manufacture fuels like ethanol, hydrogen and methane.

In fact, bio-fuels can be made from many kinds of materials. For example, byproducts from the manufacture of fibers can be used as bio-fuel. The manufacture of pulp, paper, lumber, plywood and cotton yields residues like black liquor, sawdust and bark which can also be used as biomass.

The wood waste generated by the construction industry, yard trimmings and non-recyclable organic material can also be used to produce energy. In fact, it is possible to manufacture your own alcohol, methane or bio-diesel from many waste products.

Biomass includes plant or animal matter used for the production of fibers and chemicals and biodegradable wastes that can be burnt as fuel.

However, bio-fuels does not include fossil fuels, although they are organic material transformed by geological processes into coal or petroleum. Although fossil fuels have their origin in ancient biomass, they are not considered biomass as their carbon has been "out" of the carbon cycle for a very long time. In fact their combustion disturbs the carbon dioxide levels in the atmosphere.

Bio-energy producers use bio-mass to produce electricity, gas, liquids, chemicals and other materials which can be converted into energy.

Bio-energy ranks second to hydropower in renewable energy sources and in many advanced countries it provides almost five percent of the total energy mix.

Chemical composition:
Biomass is essentially made up of carbon, hydrogen and oxygen. It also contains some nitrogen and small quantities of alkalis, alkaline earth and heavy metals. Metals are often found in molecules like Porphyrins which include chlorophyll. Incidentally chlorophyll contains magnesium.

Plants combine water and carbon dioxide to make sugar building blocks. The energy required for this is produced from sunlight via photosynthesis using chlorophyll. On an average, between 0.1 and one percent of the sunlight is stored as chemical energy in plants. The sugar building blocks are the basic constituents of the major fractions found in all terrestrial plants, that is lignin, hemicellulose and cellulose.

The most common way in which biomass is used is still direct incineration. Forest residues (dead trees, branches and tree stumps), yard clippings, wood chips and garbage are often directly burnt.

Biomass can be converted to methane or fuels like ethanol and biodiesel. Rotting garbage, agricultural and human waste release methane, the so called "landfill gas" or "biogas." Crops like corn and sugarcane can be fermented to produce ethanol. Biodiesel is produced from left-over food products like vegetable oils and animal fats. The production of liquid fuels from biomass (BTLs) and cellulosic ethanol is still under research.

There are many technological means available to use the wide variety of biomass available. Conversion technologies can release the energy directly, in the form of heat or electricity, or may convert it to another form, like liquid bio-fuel or combustible biogas. While some types of biomass offer many usage options, for some we have to use appropriate technology.

These are processes in which heat is the dominant mechanism to convert the biomass into another chemical form. The basic alternatives of combustion, torrefaction, pyrolysis, and gasification 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).

There are other less common, experimental thermal processes that may offer benefits such as hydrothermal upgrading (HTU) and hydro processing. 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. The efficiency of a biomass power plant can range from 20 to 27 percent.

There are many chemical processes available to convert biomass into other forms, so as to produce a fuel that can be conveniently used, transported or stored, or to exploit some property of the process itself.

Biomass can also be converted directly into liquid fuels. The two most common liquid bio fuels are ethanol and biodiesel. Ethanol, an alcohol, is made by fermenting any biomass rich in carbohydrates. Although 100 percent alcohol is combustible and can be used as a fuel generally it is used as an additive to cut down a vehicle's carbon monoxide and other harmful emissions.

Biodiesel, an ester, is made from vegetable oils, animal fats, algae or even recycled cooking oils. It can also be used as a diesel additive to reduce vehicle pollution.

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 exist in nature to break down its molecules, and many of these biochemical conversion processes can be harnessed industrially.

Biochemical conversion processes use the enzymes produced by bacteria and other micro-organisms to break down biomass. In most cases micro-organisms are used to carry out conversion processes like anaerobic digestion, fermentation and composting.

Another chemical process used to convert straight and waste vegetable oils into biodiesel is transesterification. Biomass is also broken down into carbohydrates and simple sugars to make alcohol. However, this process has not been perfected yet.

Heat can be used to chemically convert biomass into fuel oil, which can be burnt to generate electricity. Biomass can also be burnt directly to produce steam for electricity generation.

Environmental impact:
Burning biomass produces carbon monoxide, NOx (nitrogen oxides), VOCs (volatile organic compounds), particulates and other pollutants, in some cases at levels above those from fuels coal and natural gas. Black carbon - a pollutant created by the incomplete combustion of fossil fuels, bio-fuels and biomass, is the second largest contributor to global warming.

In 2009, a Swedish study of the giant brown haze that periodically covers large areas in South Asia concluded that it was mainly produced by the burning of biomass, and fossil fuels. Researchers found a significant concentration of 14C in the haze, which is associated with recent plant life rather than fossil fuels.

When bio-mass is burnt, the carbon in it is released into the atmosphere as carbon dioxide (CO2). The amount of carbon stored in dry wood is approximately 50 percent of weight. If the biomass is from quick growing agricultural sources, it can be replaced by planting anew. But if it from forests, recapturing the carbon will take a long time.

The size of a bio-mass power plant is often determined by the availability of biomass as transport costs play a key role. However, rail and inland shipping can cut transport costs significantly.

Biomass crops can sequester carbon even after harvesting. For example soil organic carbon is greater in switchgrass stands than in cultivated cropland soil, especially at depths below 12 inches. The grass sequesters the carbon in its root mass. Perennial crops sequester much more carbon than annual crops due to their much greater non-harvested living biomass, both living and dead, built up over years, and lesser soil disruption.

The biomass-is-carbon-neutral theory which was floated in the early 1990s has now been replaced by recent discoveries that mature 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.

Advantages:
With the prices of fossil fuels rising bio-fuels are once again becoming popular, and one of its great plus points is that it is possible to grow fuel in our backyards and thus reduce dependence on foreign sources.

Another great plus point of bio-energy is that it helps to control carbon dioxide emissions (plants absorb CO2 and this offsets emissions). The use of biomass to generate energy opens a new source of income to farmers.

Bio-mass has some negative points too. The burning of biomass produces greenhouse emissions. The biggest drawback of biomass is that it produces carbon dioxide and other greenhouse gases. It takes more energy to plant, cultivate and harvest the crops than the energy they yield. It also uses up more water and fossil fuels to make the fertilizers and the fuels for planting and harvesting.

Biomass collection is difficult and they are not available throughout the year. Corn, wheat, barley etc used to produce ethanol are seasonal. Trees are slow growing even though they are renewable.

<< BACK >>