POWER PLANT ENGINEERING 7th SEMESTER B.TECH DEPARTMENT OF MECHANICAL ENGINEERING VSSUT BURLA
MODULE-I SOURCES OF ENERGY There are mainly two types of sources of energy 1. Conventional Sources of Energy (Non-Renewable Sources of Energy) 2. Non-conventional Sources of Energy (Renewable Sources of Energy). 1. CONVENTIONAL SOURCES OF ENERGY These resources are finite and exhaustible. Once consumed, these sources cannot be replaced by others. Examples include coal, timber, petroleum, lignite, natural gas, fossil fuels, nuclear fuels etc. The examples are (i) fossil fuel (ii) nuclear energy (iii) hydro energy Have you not seen the filling of fuel in automobiles? What are the fuels that are being used in automobiles? What type of sources of energy are they? Are they non-conventional? Fossil fuel is an invaluable source of energy produced due to chemical changes taking place in the absence of oxygen, in plants and animals that have been buried deep in the earth’s crust for many million years. Fossil fuels like coal, petroleum and natural gas are formed in this manner. These are conventional sources of energy. For example, energy from, Petroleum, natural gas, coal, nuclear energy, etc THERMAL POWER Thermal generation accounts for about 70% of power generation in India. Thermal energy generation is based on coal, furnace oil and natural gas. Steam cycle, rankin cycle or sterling cycle can be used for energy production. Now clean coal technologies (with 10% ash content) have been used in thermal power plants on commercial scale. NATIONAL THERMAL POWER CORPORATION (NTPC) It was incorporated in November 1975 as a public sector undertaking with the main objectives of planning, promoting and organising integrated development of thermal power. Installed capacity of NTPC projects stands at 16000 MW. 2. NON-CONVENTIONAL SOURCES OF ENERGY These sources are being continuously produced in nature and are not exhaustible. Examples include wood, geothermal energy, wind energy, tidal energy, nuclear fusion, gobar gas, biomass, solar energy etc. The examples are (i) Solar energy (ii) wind energy (iii) geothermal energy (iv) ocean energy such as tidal energy, wave energy (v) biomass energy such as gobar gas. It is evident that all energy resources based on fossil fuels has limitations in availability and will soon exhaust. Hence the long term option for energy supply lies only with non-conventional energy sources. These resources are in exhaustible for the next hundreds of thousands of years. 52 POWER PLANT ENGINEERING The sources which are perennial and give energy continuously and which do not deplete with use are the Non conventional sources of energy. For example, energy from, solar energy, bio-energy, wind energy, geothermal energy, wave, tidal and OTEC. INTRODUCTION TO VARIOUS NON CONVENTIONAL (RENEWABLE) SOURCES OF ENERGY Renewable energy development programme is gaining momentum in India. It has emerged as a viable option to achieve the goal of sustainable development. However, Indian renewable energy programme need more thrust at this stage. India has now the world’s largest programme for deployment of renewable energy products and systems, the spread of various renewable energy technologies in the country has been
supported by a variety of incentives and policy measures. Power generation from non-conventional renewable sources has assumed significance in the context of environmental hazards posed by the excessive use of conventional fossil fuels. Renewable energy technologies have provied viable for power generation not so much as a substitute, but as supplement to conventional power generation. Currently renewables contribute over 3500 MW, which represents almost 3.5 percent of the total installed generating capacity of one lakh MW from all sources. Of this, wind power alone accounts for 1617 MW, while biomass power accounts for 450 MW and small hydros 1438 MW. An additional 4000 MW of power from renewable sources is to be added during the Tenth Five Year Plan period (2002–07) mainly through wind, biomass, small hydros, waste energy and solar energy system. Further, India has set a goal elevating the share of renewable energy sources in power generation up to 10 percent share of new capacity addition or 10,000 MW to come from renewable by 2012. Today, India has the largest decentralised solar energy programme, the second largest biogas and improved stove programmes and the fifth largest wind energy programme in the world. A substantial manufacturing base, has been created in a variety of renewable energy technologies placing India in a position not only to export technologies; but also offer technical expertise to other countries. BIO-GAS Biogas is a good fuel. Have you thought how this is fomed? Biomass like animal excreta, vegetable wastes and weeds undergo decomposition in the absence of oxygen in a biogas plant and form a mixture of gases. This mixture is the biogas. Its main constituent is methane. This is used as a fuel for cooking and Lighting. AEROBIC AND ANAEROBIC BIO-CONVERSION PROCESS There are mainly three aerobic and anaerobic bio-conversion process for the biomass energy applications: There are: Bioproducts: Converting biomass into chemicals for making products that typically are made from petroleum. Biofuels: Converting biomass into liquid fuels for transportation. Biopower: Burning biomass directly, or converting it into a gaseous fuel or oil, to generate electricity. Bioproducts. Whatever products we can make from fossil fuels, we can make using biomass. These bioproducts, or biobased products, are not only made from renewable sources, they also often require less energy to produce than petroleum-based products. Researchers have discovered that the process for making biofuels releasing the sugars that make up starch and cellulose in plants also can be used to make antifreeze, plastics, glues, artificial sweeteners, and gel for toothpaste. Other important building blocks for bioproducts include carbon monoxide and hydrogen. When biomass is heated with a small amount of oxygen present, these two gases are produced in abundance. Scientists call this mixture biosynthesis gas. Biosynthesis gas can be used to make plastics and acids, which can be used in making photographic films, textiles, and synthetic fabrics. When biomass is heated in the absence of oxygen, it forms pyrolysis oil. A chemical called phenol can be extracted from pyrolysis oil. Phenol is used to make wood adhesives, molded plastic, and foam insulation. Biofuels. Unlike other renewable energy sources, biomass can be converted directly into Liquid fuels, biofuels. For our transportation needs (cars, trucks, buses, airplanes, and trains). The two most common types of biofuels are ethanol and biodiesel. Ethanol is an alcohol, the same found in beer and wine. It is made by fermenting any biomass
high in carbohydrates (starches, sugars, or celluloses) through a process similar to brewing beer. Ethanol is mostly used as a fuel additive to cut down a vehicle's carbon monoxide and other smog-causing emissions. But flexible fuel vehicles, which run on mixtures of gasoline and up to 85% ethanol, are now available. Biodiesel is made by combining alcohol (usually methanol) with vegetable oil, animal fat, or recycled cooking greases. It can be used as an additive to reduce vehicle emissions (typically 20%) or in its pure form as a renewable alternative fuel for diesel engines. Other biofuels include methanol and reformulated gasoline components. Methanol, commonly called wood alcohol, is currently produced from natural gas, but could also be produced from biomass. There are a number of ways to convert biomass to methanol, but the most likely approach is gasification. Gasification involves vaporizing the biomass at high temperatures, then removing impurities from the hot gas and passing it through a catalyst, which converts it into methanol. Most reformulated gasoline components produced from biomass are pollution reducing fuel additives, such as methyl tertiary butyl ether (MTBE) and ethyl tertiary butyl ether (ETBE). Biopower. Biopower, or biomass power, is the use of biomass to generate electricity. There are six major types of biopower systems: direct fired, cofiring, gasification, anaerobic digestion, pyrolysis, and small, modular. Most of the biopower plants in the world use direct fired systems. They burn bioenergy feedstocks directly to produce steam. This steam is usually captured by a turbine, and a generator then converts it into electricity. In some industries, the steam from the power plant is also used for manufacturing processes or to heat buildings. These are known as combined heat and power facilities. For instance, wood waste is often used to produce both electricity and steam at paper mills. Many coal fired power plants can use cofiring systems to significantly reduce emissions, especially sulfur dioxide emissions. Coal firing involves using bioenergy feedstocks as a supplementary energy source in high efficiency boilers. Gasification systems use high temperatures and an oxygen starved environment to convert biomass into a gas (a mixture of hydrogen, carbon monoxide, and methane). The gas fuels what's called a gas turbine, which is very much like a jet engine, only it turns an electric generator instead of propelling a jet. The decay of biomass produces a gas methane that can be used as an energy source. In landfills, wells can be drilled to release the methane from the decaying organic matter. Then pipes from each well carry the gas to a central point where it is filtered and cleaned before burning. Methane also can be produced from biomass through a process called anaerobic digestion. Anaerobic digestion involves using bacteria to decompose organic matter in the absence of oxygen. Methane can be used as an energy source in many ways. Most facilities burn it in a boiler to produce steam for electricity generation or for industrial processes. Two new ways include the use of microturbines and fuel cells. Microturbines have outputs of 25 to 500 kilowatts. About the size of a refrigerator, they can be used where there are space limitations for power production. Methane can also be used as the “fuel” in a fuel cell. Fuel cells work much like batteries but never need recharging, producing electricity as long as there’s fuel. In addition to gas, liquid fuels can be produced from biomass through a process called pyrolysis. Pyrolysis occurs when biomass is heated in the absence of oxygen. The biomass then turns into a liquid called pyrolysis oil, which can be burned like petroleum to generate electricity. A biopower system that uses pyrolysis oil is being commercialized. Several biopower technologies can be used in small, modular systems. A small, modular system generates electricity at a capacity of 5 megawatts or less. This system is designed for use at the small town level or even at the consumer level. For example, some farmers use the waste from their livestock to provide their farms with electricity. Not only do these systems provide renewable energy, they also help farmers and ranchers meet environmental regulations. Small, modular systems also have potential as distributed energy resources. Distributed energy resources refer to a variety of small, modular power generating technologies that can be combined to improve the operation of the electricity delivery system.