The term “waste to energy” has traditionally referred to the practice of incineration of garbage. Today, a new generation of waste-to-energy technologies is emerging which hold the potential to create renewable energy from waste matter, including municipal solid waste, industrial waste, agricultural waste, and waste byproducts.
The main categories of waste-to-energy technologies are physical technologies, which process waste to make it more useful as fuel; thermal technologies, which can yield heat, fuel oil, or syngas from both organic and inorganic wastes; and biological technologies, in which bacterial fermentation is used to digest organic wastes to yield fuel. Waste-to-energy technologies convert waste matter into various forms of fuel that can be used to supply energy.
Waste feedstocks can include municipal solid waste (MSW); construction and demolition (C&D) debris; agricultural waste, such as crop silage and livestock manure; industrial waste from coal mining, lumber mills, or other facilities; and even the gases that are naturally produced within landfills. Energy can be derived from waste that has been treated and pressed into solid fuel, waste that has been converted into biogas or syngas, or heat and steam from waste that has been incinerated. Waste-to-energy technologies that produce fuels are referred to as waste-to-fuel technologies.
Advanced waste-to-energy technologies can be used to produce biogas (methane and carbon dioxide), syngas (hydrogen and carbon monoxide), liquid biofuels (ethanol and biodiesel), or pure hydrogen; these fuels can then be converted into electricity. (For further information on the conversion of waste biomass into biofuels like ethanol and biodiesel, please see Technology Profile 3. 1. 2, “Biofuels. ”) The primary categories of technology used for waste-to-energy conversion are physical methods, thermal Methods, and biological methods.
This paper is the second in a series of two on the slagging and fouling behavior of rice husk when fired alone or in combination with other fuels in a fluidized-bed boiler. The first paper involved the fuel properties of rice husk, as investigated by a variety of laboratory methods. In this second paper, we report the results of fireside fouling measurements when burning rice husk alone and together with eucalyptus bark in various ratios.
This study is based on short-term (3? 0 h) deposit samples taken with air-cooled deposit probes in the super heater region of a large-scale (157 MWth) bubbling fluidized-bed (BFB) boiler burning rice husk and eucalyptus bark. Using an entrained-flow type of pilot furnace, we further made more, systematic measurements of the influence of the fuel mixture ratio on the fouling tendency of the fly ash formed. Burning of rice husk alone did not result in any detectable fouling, neither in the pilot furnace nor on the deposit probes in the super heater area of the fluidized-bed boiler.
After deposit samplings with durations of up to 10 h during 100% rice husk firing, the deposit sampling probe had not collected more than 95 mg (app) of deposit material. The combustion of eucalyptus bark alone caused significant fouling. Here, the corresponding amount of deposit was approximately 90 mg after 10 h of sampling. The fouling tendency of mixtures of rice husk and bark showed a nonlinear dependence on the fuel mixture ratio. The results suggest that the rice husk ash acted as an erosive, cleaning agent in the fly ash mix.
“From everyday collection to environmental protection, Think Green. Think Waste Management. ” Governments, businesses and the public are increasingly concerned about the security of supply. The sustainability and the environmental impact of our energy sources. Is responding to the demand for alternatives to fossil fuels through the development of waste based energy from the waste we all generate. About Waste Management: As the leading provider of comprehensive waste management and environmental services in North America, Waste Management serves municipal, commercial, industrial and residential customers throughout the United States, Canada and Puerto Rico.
Headquartered in Houston, Texas, the company serves more than 20 million residential and two million commercial customers through its network of collection operations, transfer stations, landfill disposal sites, waste-to-energy plants, recycling plants, landfill gas to energy projects and other related services. Waste-to-energy (WtE) : Energy-from-waste (EfW) is the process of creating energy in the form of electricity or heat from the incineration of waste source. WtE is a form of energy recovery.
Most WtE processes produce electricity directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels. Traditionally, waste is viewed as an unnecessary element arising from the activities of any industry. In reality, waste is a misplaced resource, existing at a wrong place at a wrong time. Waste is also the inefficient use of utilities such as electricity, water, and fuel, which are often considered unavoidable overheads. The costs of these wastes are generally underestimated by managers.
- Prevention and reduction of waste generated
- Efficient use of raw materials and packaging
- Efficient use of fuel, electricity and water
- Improving the quality of waste generated to facilitate recycling and/or reduce hazard
- Encouraging re-use, recycling and recovery.
Waste minimization is also known by other terms such as waste reduction, pollution prevention, source reduction and cleaner technology. It makes use of managerial and technical interventions to make industrial operations inherently pollution free .
It should be also clearly understood that waste minimization, however attractive, is not a panacea for all environmental problems and may have to be supported by conventional treatment disposal solutions. Waste minimization is best practiced by reducing the generation of waste at the source itself. After exhausting the source reduction opportunities, attempts should be made to recycle the waste within the unit. Finally, modification or reformulation of products so as to manufacture it with least waste generation should be considered.
Under this category, four techniques of WM are briefly discussed below: Good Housekeeping- Systems to prevent leakages & spillages through preventive maintenance schedules and routine equipment inspections. Also, well-written working instructions, supervision, awareness and regular training of workforce would facilitate good housekeeping.
Process Change: Under this head, four CP techniques are covered:
- Input Material Change – Substitution of input materials by eco-friendly (nontoxic or less toxic than existing and renewable) material preferably having longer service time.
- Better Process Control – Modifications of the working procedures, machine-operating instructions and process record keeping in order to run the processes at higher efficiency and with lower waste generation and emissions.
- Equipment Modification – Modification of existing production equipment and utilities, for instance, by the addition of measuring and controlling devices, in order to run the processes at higher efficiency and lower waste and emission generation rates.
- Technology change – Replacement of the technology, processing sequence and synthesis route, in order to minimise waste and emission generation during production.
A flow chart should list, and characterize the input and output streams, as well as recycle streams. Even the so called free or less costly inputs like water, air, sand, etc should be taken into account as these often end up in being the major cause of wastes. Wherever required, the process flow diagram should be supplemented with chemical equations to facilitate understanding of the process. Also the materials which are used occasionally and / or which do not appear in output streams (for example catalysts, coolant oil) should be specified.
The periodic / batch / continuous steps should also be appropriately highlighted. Preparation of a detailed and correct process flow diagram is a key step in the entire analysis and forms the basis for compilation of materials and energy balance. Make material and Energy Balances Material and Energy balances are important for any Waste minimization programme since they make it possible to identify and quantify, previously unknown losses or emissions. These balances are also useful for monitoring the progress achieved in a prevention programme, and evaluating the costs and benefits.
Typical components of a material balance and energy balance are given below (see Figures 13. 1 & 13. 2): Identify and Select Wasteful Process Steps In multi-process type industries, it may be difficult to start detailed Waste minimization activities covering the complete unit. In such cases, it is advisable to start with fewer process steps to begin with. The selected step(s) could be the most wasteful and / or one with very high waste minimization potential. This activity could also be considered a preliminary prioritization activity.
All the various wasteful steps identified in 1. 2 should be broadly assessed in terms of volume of waste, severity of impact on the environment, Waste minimization opportunities, estimated benefits (specially cost savings), cost of implementation etc. Such assessment would help in focusing on the process steps areas for detailed analysis. It is not advisable to spent more time and money to make a perfect material balance. Even a rough preliminary material balance throws open Waste Minimization opportunities which can be profitably exploited.
On the other hand, the precision of analytical data and flow measurements is important as it is not possible to obtain a reliable estimate of the waste stream by subtracting the materials in the product from those in the raw materials. In such cases, a direct monitoring and analysis of waste streams should be carried out. Assign Costs To Waste Stream In order to assess the profit potential of waste streams, a basic requirement would be to assign costs to them. This cost essentially reflects the monetary loss arising from waste.
The options for Waste Minimization with respect to their impact on the environment should be assessed. In many cases the environmental advantage will be obvious if there is a net reduction in the toxicity and / or quantity of waste. Other impacts could be changes in treatment of the wastes. In the initial stages, environmental aspects may not appear to be as compelling as economic aspects. In future as in developed countries, environmental aspects would become the most important criteria irrespective of the economic viability. Implement Solutions:
In addition to installing the cullet crusher, the company had initiated a number of other associated waste minimization measures such as segregation by source of inhouse cullet, segregating stones from cullet, lead recovery from reject cullet, crusher fines and waste glass prior to disposal. Global warming: It has been suggested that emissions of pollutants and greenhouse gases from electricity generation account for a significant portion of world greenhouse gasemissions; In the United States, electricity generation accounts for nearly 40 percent of emissions, the largest of any source.
Transportation emissions are close behind, contributing about one-third of U. S. production of carbon dioxide. As per conditions/ guidelines of MNES administrative sanction for CBP/IBP/NBPs programme , the installation of bio-gas plant of 15, 25, 35, 45, 60 and 85 m3/day are considered and the above capacity is decided based on the Technical feasibility study of the plant site focussing on the bio-gas generation potential and gas utilisation aspects.
ENERGY FROM AGRICULTURAL WASTE
A vast majority of the Indian population lives in villages and agriculture is the main work of the people living there. Thus agricultural waste products are available in huge amounts and do not cost any thing to produce,only the collection cost is there, so the electricity produced will be of very low cost and most appropriate for domestic purpose and for running of small scale industries. In India, about 17million tons of rice husk and about 5 million tons of rice bran are produced annually,along with about 52 million tons of clean rice. Farm income can be increased both directly and indirectly if these large quantities of rice husk are utilized in an economically profitable manner. Agricultural wastes, like paddy and wheat straw, have significant long term potential due to their abundant availability.
AGRO THERMAL POWER PLANTS
The Department of Non-Conventional Energy in collaboration with Punjab has set up to 10MW agro-thermal power plant based on rice husk at Jalkheri near Patiala. This project envisages de-husking of large quantities of rice and utilization of husk in the first stage, to extract furfural and then to fire husk in a fluidized boiler linked wit cogeneration plant to generate plant to generate 10MW of electricity. This plant will have about 5MW of surplus electricity to be connected to the grid.
It has been estimated that the sugar industry in India can generate almost 2,000MW as surplus electricity during the crushing season. It has been estimated that a sugar plant requiring 4MW can produce with its bagasse 10 MV of electricity. Hence after meeting the factory’s requirement, about 6 MV can be surplus to be fed to the grid. Since sugar factories are normally in the rural areas, this surplus electricity could be used for irrigating sugarcane fields or industrialization of rural areas. It has been estimated that power requirement to the extent of 12000MV can be met within India by utilization of paddy and wheat straw.
Rice and sugarcane is harvested in the month of November. Since the rice straw and bagasse has moisture contents from (4 to 50%), we have to dry them in the open air for two or three months. Then some of these wastes can be utilized for generating energy and supplying it to irrigation pumps for irrigating the wheat Crop in the months of july to august. In addition to the major advantages of rural energy, there are lots of other advantages. The coal generally used in a thermal power plant contains 26 to 55% of ash. But in case of agricultural wastes ( husk, straw, bagasse) the ash percentage is 1-17%.
Thus the area required to dump this ash is less. Also, the ash handling cost is less. So, while for coal based thermal plants very efficient filters are required to reduce dust pollution, it is almost negligible in the case of agricultural wastes.
FLUIDIZED BED COMBUSTION
The fuel such as rice husk , bagasse and saw dust can be utilized by using fluidized bed combustion (FBC) in an economically viable and environmentally acceptable manner. More than any other type of combustion system, FBC system are flexible in their ability to burn a wide range of fuels.
Fluidized bed energy technology offers several unique characteristics for using biomass in small scale energy conversion operations. A fluidized bed consists of a chamber in which solid particles are suspended by high velocity air that is forced upwards through the particles. The turbulent mass of solid particles stores heat and rapidly transfers this heat to any fuel introduced into the bed. Before rice husk is burnt in the fluidized bed it is necessary to heat the inert bed of solids to about 5000 C using an auxiliary heating system. Normally about 2 to 3 hours of time is required for pre-heating the bed.
Initial combustion tests reveled that 30 to 45 minutes were required to reach stable bed operating temperature after initiating the fuel bed. The units could be shut down for periods of 8-10 hours and can be restarted without pre-heating of the bed. Until a bed temp of 600 to 6500 C is reached considerable amount of visible smoke and emissions were observed after initiating the fuel feed. According to the Institute of Solid Waste Research & Ecological Balance (INSWAREB), rice husk is the cheap by-product of paddy milling, and has the potential to galvanize the electricity starved rural India.
With a gross calorific value of 3000 kcal/kg, it is capable of high efficiency combustion, and could serve as the fuel for mini power plants of 1 to 2 MW capacity that can be set up in rural areas. The rural electrification programme is one of the important components in rural development and as important as rural drinking water supply, health, nutrition, primary education, shelter and rural connectivity. The availability of power in rural areas will lead to economic development and its attendant spin-off benefits like food security, better health, literacy, etc.
As a vast majority of India’s population live in villages, therefore efforts are being made to accelerate the process of rural electrification. The primary objective of rural electrification is to ensure increased agricultural output by providing reliable and economical power for irrigation pumps. The secondary objective is the provision of electricity for domestic, commercial and small industrial consumers in the villages. At the commencement of the First Five Year Plan (1st April, 1951), only 3061 villages were electrified and about 21,000 pump sets were energized, and up to 31st March, 1986,51. 1% of villages have been electrified.
But the 10th Five Year Plan resulted in the electrification of around 86 per cent of the country’s villages i. e. according to the 1991 Census, there are 5,87,000 villages of which 5,00,000 (86%) are declared to be electrified. Thirteen states have declared 100% electrification of their villages. The villages yet to be electrified are mostly in Assam, Raunchily pradesh, Bihar, Jharkhand, Madhya pradesh, Meghayala, Orissa, Rajasthan, Uttar pradesh, Uttaranchal and West Bengal.
Solid waste management deals with the way disposal of municipal solid waste (MSW) material for generation of energy in an economical and environmentally friendly manner. Waste disposal is one of the major problems being faced by all nations across the globe. The main difficulty for waste disposal is collection and separation of waste material. It takes anywhere between three and seven days for the waste to be displaced from the time of its generation. A major portion of collected waste is dumped in landfill sites. The recyclable contents of waste ranges from about 13% to 20%. A study of U. K.
Department of Energy’s technology support unit (ETSU) at Harwell revealed that about 60 million tones of coal equivalent of energy 18% of total energy consumption was thrown away every year as waste, which is made of organic residues. According to Technology Information Forecasting Council (TIFAC), Delhi, Mumbai, and Calcutta would be generating 5000 tones of garbage everyday, in about a decade, and disposal would be difficult. The existing dumping years would create enormous pollution and health hazards. Municipal authorities would find it expensive to transport garbage and dispose it off scientifically.
As part of pilot project for integrated waste management, the Department of Science & Technology had established a prototype fuel pelletization plant at Deonar-Mumbai, in the early 1990s. The plant was designed to process garbage. The garbage was first dried to bring down the high moisture levels. Sand, grit and other incombustible matters were than mechanically separated before the garbage was compacted and converted into pellets. Fuel pellets have several advantages over coal and wood. It is cleaner, free from incombustibles, has lower ash and moisture contents, is of uniform size, cost effective, and eco-friendly.
It is planned to establish a 10MW power plant, which convert the city’s garbage into fuel pellets. In addition to MSW, a large quantity of waste, in both solid and liquid forms, is generated by the industrial sector like breweries, sugar mills, distillers, food processing industries, tanneries, and paper and pulp industries. Out of the total pollution contributed by industrial sub sectors , 40 to 45% of the total pollutants can be traced to the processing of industrial chemicals and nearly 40% of the total organic pollution to the food products industry alone.
Food products and agro based industries together contributes 65-70% of the total industrial waster water in terms of organic load. Table below gives an estimate of waste generated in India by various sectors and industries. In addition, the manufacturing sector also contributes a significant quantity to the country’s waste. From the estimated availability of garbage , there is a potential to generate 1,700 MW of electricity (1,000 MW from urban and municipal waste and 700 MW from industrial waste). In addition, the daily per capita sewage generation is about 150 liters. The total sewage generated in India, about 5 billion liters/day in 1947,grew to 30 billion liters/day in 1997.
However, the total treatment capacity available is only about 10% of the quantum generated. It is estimated that under the Gangs action plan, 46000Nm3 (Normal cubic meter) of biogas can be produced daily from the sewage treatment plants in 21 Indians cities by treating about 339 millions liters/day of municipal waste water. This, with appropriate biogas power plants, will generate total electrical energy of 99,450 kwh/day. By purifying biogas produced from distillery wastes, scienties claimed to have generated huge quantities of compressed methae-a gas with immense potential as an alternative source of vehicular fuel.
Experimenting with bulk distillery wastes from alcohol manufacturing breweries, researchers from the Chemical Engineering Department of the Jadavpur University produced the gas by a process called biomethanation of the effluents. The process, which also cuts down on environment pollution, has proved to be and eco-friendly energy production method. It is estimated that about 30 millions tons of solid waste and 4,400 million cubic meters of liquid waste are generated every year in urban areas from households and commercial nterprises. Technologies are now available to treat the garbage to meet the required pollution control standards, besides generating power. A national program under the ministry of Non-Conventional energy sources seeks to promote such projects with suitable financial and social incentives to encourage private sector participation. International financial institutions also take keen interest in these types of projects and come forward to support them.
This paper has presented management of energy from MSW and agricultural waste by converting this energy into electrical energy with the help of small thermal plants which may be utilized to provide electricity for irrigation pumps in rural area. For small scale industries, for recycling and for producing gaseous fuels. In this way, the waste can utilize as renewable sources of energy. The additional advantage is economics in production, reduction in pollution and avoiding land filling is also obtained in this process of energy management.