Mechanical Engineering: Energy Processes for Biomass

These days, increasing stress is being placed upon renewable energy sources. Here, find out what biomass energy is used for and what various biomass energy processes are in place.

Introduction to Biomass Energy Processes

With rapid depletion in renewable resources and added pressure on the natural resources, it is imperative to find an alternative source of energy for sustainable development. Let's find out: "What is biomass used for?"

Biomass, a renewable energy resource, is biological material from living as well as other microorganisms. Biomass can be used to generate electricity or produce heat. It can be made from both plant or animal matter and biodegradable wastes. If fully tapped, biomass can help meet the energy requirements. Some 10^11 metric tons of biomass is produced in our planet that is capable of producing an energy content of 2.425*1018 kJ (Mateos & Gonzalez).

Some of the main sources of biomass energy are listed as follows:

• Garbage
• Wood
• Landfill gases
• Alcohol fuels

Other than electricity, it can also be converted into other energy forms such as methane, or fuels such as ethanol. There are numerous technologies to convert biomass into another form, such as liquid biofuel or combustible gas. The processes in which heat is the dominant mechanism to convert biomass into other liquid forms are combustion (process of oxidation), gasification (mixing of gases under gasification parameters), and pyrolysis (use of gas, liquid, and solid char depending upon parameters of the process). These are also called thermal conversion techniques. Biochemical conversion is a chemical process where biomass is used to produce fuel. Mostly, microorganisms are used to perform the conversion process through anaerobic digestion (breaking of organic matter by bacteria in absence of air) , fermentation (conversion of sugar into alcohol), and composting (aerobic decomposition of organic matter by microorganisms).

Other lesser known thermal conversion techniques consist of Hydrothermal upgrading (HTU) and Hydroprocessing. The former is a liquefaction process developed to convert high moisture content biomass into a product with high energy density while the latter consists of hydrogenation of vegetable oils to remove unsaturated bonds and a glycerol ester component to yield a range of paraffins.
Biomass is capable of producing high amounts of energy. Wood-to-energy systems are capable of producing anywhere from less than one MW to more than 100 MW of power. This energy can be used for the production of electric power, produce steam for industrial processes or power vehicles. Analysis shows (IATA) that gasification can produce approximately 0 .62 kg of carbon monoxide and hydrogen synthesis gas from one kg of biomass, with a conversion efficiency of 62 percent. To convert biomass into biofuel, analysis of energy input is needed at each processing step that determines the overall efficiency of gasification and fuel synthesis.

The overall efficiencies for different fuels produced via thermo-chemical processing technologies can also be calculated. Ethanol has an energy efficiency of 61.42 percent and Methanol has an energy efficiency of 79.99 percent. A high starch biomass-like corn can be changed to ethanol at a mass ratio of 0.35 kg of ethanol per kg of corn. Butanol and Acetone have energy efficiency 17.62 percent and 7.55 percent, respectively from biochemical conversion.

Energy produced from biomass can be used as a source to produce energy. However, this comes at a cost. The cost of producing Biomass energy comes between five to ten cents per kilowatt hour, which equates to somewhere above $1,500 per kilowatt peak. Electricity is another important cost. It varies depending on factors like type of bio-fuel used, production method, plant size and system design. If these costs are minimized, biomass can be used as an effective source of energy generation. The best thing about this technique is its ability to create energy through the utilization of waste materials. The biomass is easily available and at a relatively cheaper cost. It can, not only produce electricity, but at the same time heat homes and offices. Combustion also generates air emissions like carbon dioxide, nitrogen oxide, and sulfur dioxide.
These emissions can have an adverse impact on the environment. Wood is extensively used as a biomass ingredient. Wood from forests is removed with non-constructive techniques, the renewal of lost wood could take years to replenish. These factors need to be kept in mind.
Biomass has the potential to become the next big thing. This source can be used as an alternative source for generating energy. Sophisticated plant designs and efficient conversion techniques will yield better results and make it the preferred mode of energy generation.