Methods Of Recovering Energy From Waste

Methods Of Recovering animation From ragingBiomass ( bumble) life force is more and more attracting attention worldwide because it is a re new-sprung(prenominal)able source of efficiency and potentially carbon dioxide neutral. At present, well-nigh ingest materials be converted into electricity often by conflagration. barren combustion is widely utilize for district stir upinging and combined heat and force for electricity generation. This report describes shove off, licentiousness reduction and discussion regulations in Europe as well as contrastive types of fellate generated, an overview of blow to button technologies employ finishedout the world today. qualification from risky has been evaluated base on their ability to reduce the emission of pollutant into the atmosphere. In gear up to mitigate climate change which is gaining increasing awareness, recent developments of different technologies that have been able to bear on bungle to generate heat and power with in high spirits efficiencies substructure be considered to be the most workable option to replace fogey fuels.2 INTRODUCTIONDue to the rising cost and the ecological disadvantages of fossil fuels, there as been concerns about the future of heftiness supply in the world. According to the World Energy Council, fossil fuel covers about 82% of the worlds energy. And this has caused severe damages for the environment in terms of nursery emissions, sea level rising, air pollution, etc. Moreover, as the World continues to experience globalization, rapid industrialization and technological advancement, it will certainly get to a point, where supply of these fossil fuels will non pile up demand. Therefore, it is clamant to find an alternative source of energy (Soetaert and Vandamme, 2006).Research and development of renewable sources of energy and energy from biomass is pass judgment to be of immense benefit to the society as it reduces the concentration of carbon dioxide in the atmosphere and it is not exhaustible. Biomass is a major source of biologically derived bio fuels (bio-ethanol) and bio liquid. This is considerably becoming a reality in energy/electricity generation. Biomass pot be burnt directly to produce heat or electricity, or it can be converted into full-blooded, liquid or gaseous fuel through fermentation process into intoxicant and anaerobic digestion into biogas. There are mevery environmental and social benefits associated with biomass energy. These imply reduction in CO2 levels, energy carriers to rural communities, waste control, etc. (Calbe, Bajay, Rothman and Harry, 2000).Biomass raw materials for energy generation includes the first generation feedstocks i.e. energy crops (corn, sugarcane, wheat, etc) and the second generation feedstock main(prenominal)ly lignocellulosic materials (wood and boorish residues). Hence, using biomass as a substitute for fossil fuels is sustainable and in effect(p). However, there have be en topicions on the use of human food (energy crop) for energy generation especially in developing countries where there is shortage of food. Hoffert et al. (2002), Dismiss the use of biomass for energy, others take the opposite view (Dewulf and Langenhove 2006). To this effect, energy recuperation from waste can be an economical viable option.3 eat upS3.1 DefinitionWaste arises as a result of human technological development and social activities. The Uks Environmental Protection Act 1990 indicated waste includes whatever substance which constitutes a scrap material, an effluent or other unwanted surplus arising from the application of any process or any substance or article which requires to be disposed of which as been broken, worn out out, contaminated or otherwise spoiled, this is supplemented with anything which is discarded otherwise dealt with as if it were waste shall be presumed to be waste unless the contrary is proved. Murphy et al. (2002) defined waste as a material with no further beneficial use. The figure below shows the Schematic illustration of the EU Legal definition of waste3.2 EU WASTE FRAMEWORK DIRECTIVEThe Directive requires all Member States to take the necessary measures to ensure that waste is acquire or disposed of without endangering human health or causing harm to the environment and includes permitting, registration and follow-up requirements. The Directive also requires Member States to take appropriate measures to encourage firstly, the prevention or reduction of waste production and its harmfulness and secondly the recuperation of waste by means of recycle, re-use or reclamation or any other process with a view to extracting secondary raw materials, or the use of waste as a source of energy (Department for Environment, Food and Rural Affairs, 2009).3.3 UK WASTE MANAGEMENT POLICYThe UK Waste Policy is essential from the idea of sustainable development. This policy encourage diversion from footingfills by imposing high t ax levies on landfill site, reduce the amount of waste produced by the commercial sector, and ultimately encourage re-use and recycling of materials.3.4 WASTE HIERARCHYFigure 3.1 Waste hierarchy3.5 TYPES OF WASTEMunicipal self-coloured Wastefurious/Radioactive WasteSewage SludgeMedical/Clinical WasteAgricultural Wasteindustrial and Commercial WasteOther Waste e.g. construction and demolition industry waste, mines and quarry waste and power station ash, iron and steel slags (Williams, 1999).There are also twain different kinds of component share in a waste stream The Organic fraction i.e. Biodegradable and the Inorganic fraction.3.5.1Municipal Solid WasteThis is composed of/includes mainly household waste, with commercial and trade waste which is collected or disposed of by a municipality within an area. The composition of MSW streams varies, depending upon socio-economic factors, geographical locations, climate, population density and level of industrialization etc. for utilisat ion in US and other industrialized countries where value is placed on time, consumers have adapted to the lookout of using disposable at all times, thereby driving packaging and wrapping technologies to a new level, in addition with the putrescible waste from food stuffs. The energy fraction contained in materials of this type of waste stream can be between 75 to 90%. Whereas in less developed countries where the waste stream is composed dominantly of putrescible fraction i.e. foodstuffs, vegetable and organic materials with minute packaging materials, the energy content will be much glower (Murphy, 2002).3.5.2 Hazardous WasteHazardous Waste is waste which contains substances that are considered to be dangerous to health and society. This includes substances which are reactive, infectious, harmful, toxic and corrosive etc. examples are chemicals much(prenominal) as, atomic number 1 cyanide, sulphuric acid, hydrofluoric acid etc. explosives such as dynamite, ammunition etc. weew ee reactive chemicals such as potassium, phosphorous, sodium hydride etc. In USA, estimate arisings of hazard waste is 275 million tonnes, UK 4.5 million tonnes, Germany 6 million tonnes, Spain 1.7 million tonnes (Williams, 1999).3.5.3 SEWAGE SLUDGESewage Sludge is usually generated at the waste water intervention facility. It is a by-product of the treatment of raw sewage from domestic households, which may also include commercial and industrial waste. The sewage is composed mainly of water, but after treatment, the moisture material is concentrate to form sewage seepage (Williams, 1999). They are solid, semi-solid or bio solid in nature. Harper-Collins Dictionary of Environmental accomplishment defines Sewage Sludge as a semi-solid mixture of bacteria, virus-laden organic matter, toxic metallic elements, synthetic organic chemicals, and settled solids removed from domestic and industrial waste at sewage treatment jells. (Renewable Energy Institute) The sewage sludge treatme nt chthonicgoes some(prenominal) aerobic and anaerobic digestion and the final treated sewage sludge is either land filled, spread on land as fertilizers or incinerated. Recent developments have shown that biogas can be produced during anaerobic digestion.3.5.4 CLINICAL WASTEClinical Waste is mainly produced/waste arising from health centres, hospitals and nursing homes etc. Examples include drugs, syringes, needles, blood, human or fauna tissue etc. Approximately 0.3 millions tonnes of clinical waste arises in the UK annually. majority of clinical waste are incinerated (Williams, 1999).3.5.5 AGRICULTURAL WASTEAgricultural waste is waste streams generally produced from agricultural activities. They are produced within agricultural premises and they include organic materials such as slurry, manure from livestock, ensilage effluent and crop residues. It is estimated that approximately 700 million tonnes of agricultural waste is produced in OECD countries. UK also produces large to nnage, 80 million tonnes estimated from housed livestock alone (Williams 1999).3.5.6 INDUSTRIAL AND COMMERCIAL WASTEThese are types of waste stream that arises from both industrial and commercial sectors such as hotels and catering, food, drink and tobacco manufacturing industries, metal manufacturing industries, timber and wooden article of furniture industries, mechanical and electrical industries, transport and communication industries etc. The typical composition of this waste streams differs and very wide. A survey carried out by Environmental Agency of some 4,500 commercial and industrial businesses in England in 2002/2003 showed that commercial waste amounted to 30 million tonnes and industrial waste 38 million tonnes (mt). In that survey, the main sectors producing CI wastes were retail (12.7mt), food, drink and tobacco (7.2mt), professional services and other (7.1mt), utilities (6.2mt), the chemicals industries (including fibre, rubber and plastics) (5.3mt), basic metal man ufacture (4.8mt) and hotels/catering (3.4mt) (Defra, commercial and industrial waste in England, 2009).4 ENERGY RECOVERIES FROM WASTE TECHNOLOGIESEnergy is recovered from waste either through thermal combustion or biological/chemical reactions. The energy recovery process produces electricity directly through combustion, or produces synthetic and combustible fuel i.e. methane.4.1 INCINERATIONIncineration with energy recovery is the controlled combustion of waste and it is the most wide spread waste to energy implementation. It involves the combustion of waste streams at high temperatures and the heat produced can be used to drive a turbine in order to produce electricity and district heating. Waste materials or fuel are fed into incinerators in two ways, the mass fired/burning systems and refuse derived fuel (RDF) fired systems. The mass burning involves minimal process the entire mixed municipal solid waste is fed into a furnace without any removal/ time interval of recyclable and non combustible materials. For RDF fired technologies, MSW undergoes pre-treatment, separation of non-combustible and recyclable material which is known as RDF. RDF fired systems has a higher energy content compared to unprocessed MSW because of its homogeneity (Tchobanoglous, Thiesen and Vigil, 1993).There are various types of incinerator plant traffic pattern moving grate, fixed grate, rotary-kiln, and fluidized bed incinerator.4.1.1 Moving GrateThis can also be called Municipal Solid Waste incinerators. The moving grate enables the movement of waste by a waste crane at one end of the grate through the combustion chamber to the ash pit at the lower end. The combustion air is supplied through the grate lying below. Cooling of the grate itself is essential for the mechanical susceptibility of the grate. One single moving grate boiler can handle 35 metric tonnes of waste per hour, and 8,000 hours per year.4.1.2 Fixed GrateThis is a simpler type of incinerator. It is made of a brick lined compartment with a fixed metal grate above the lower ash pit, with one opening for loading and another opening in the side for removing incombustible solids known as clinkers.4.1.3 Rotary kilnIt is mostly used by municipalities and large industrial plants. Rotary kiln incinerators have 2 chambers, primary and secondary chamber. In the primary chamber, movement and conversion of solid fraction of the waste to gases and partial combustion occurs while the secondary chamber completes the gas phase combustion reactions.4.1.4 Fluidized BedFluidized Bed Combustion (FBC) is a combustion technology used in power plants. FBC developed from efforts to find a combustion process that is able to control pollutant emissions. Advanced fluidized bed combustion offers a viable power generation technique. In fluidized bed combustion, a strong airflow is forced through a sand bed, which keeps the waste suspended on pumped air currents and takes on fluid the like character. Due to the turbulent mixing, the waste and sand are fully circulated through the furnace.4.2 BALDOVIE WASTE TO ENERGY installThe Baldovie waste to energy plant is a state of the art facility commissioned in Dundee in 1999, to replace a waste disposal incinerator due to its inability to meet EU requirements on emissions. The plant is run by a conjunction venture between Dundee city council and private sector partners. The joint venture is collectively called Dundee energy recycling limited (DERL). The plant processes 120,000 tonnes of waste annually and generates electricity to meet its own demand (about 2.2MW) and also supply to the public (about 8.8MW). Separation techniques carried out before combustion removes and recovers ferric metals which can be resold (Gazetteer for Scotland, 2010).4.3 LANDFILL GAS CAPTURELandfill is a waste disposal site where waste is deposited onto or into the land. When waste is deposited, it undergoes various degradation process which produces gas mainly methane. Modern landfills have gas recovery systems, where the landfill gas is extracted and can be used for production of steam, heat and electricity (Dewulf and Langenhove 2006, p.248)4.4 ANAEROBIC DIGESTIONAnaerobic treatment technologies are used throughout the world for effective treatment of organic waste. This technology is particularly showy because the energy required for operating the process is minimal compared to energy required for aerobic process. Anaerobic digestion is a complex biogenic process which involves the microbial degradation or conversion of organic waste in a closed reactor vessel (absence of air) to produce gas chiefly methane (55-65%), CO2 (35-45%), and trace amounts of N2, H2 and H2S, depending on factors such as the composition of waste, organic loadings applied to the digester, time and temperature. The methane-rich biogas which can be combusted to generate heat and electricityIn general anaerobic digestion is considered to occur in three stagesA Liquefaction or po lymer breakdownB sour formation andC Methane formationSubstrates for anaerobic digestion includes waste water from food processing, breweries, distilleries etc. sewage sludge, animal waste, farm residues.4.5 GASIFICATION AND PYROLYSISGasification is defined as a partial oxidation/combustion of biomass and various combustible waste/carbonaceous fuels to produce gas. This gas can be used in internal combustion engines and gas turbines to generate electric power.Pyrolysis is a thermal process which involves the breakdown of organic materials in waste under pressure in the absence of oxygen. The pyrolysis process produces a liquid residue and gas which can be combusted to generate electricity.The principal difference between the two systems is that, pyrolysis system use an external source of heat to drive the endothermic pyrolysis reaction in an oxygen free environment, whereas gasification systems are self-sustainable and use air or oxygen for partial combustion of solid state (Tchoba noglous, Thiesen and vigil 1993).5 CONCLUSIONSEnergy from waste has been evaluated based on their ability to reduce the emission of pollutant into the atmosphere, minimise waste, and generate heat and power.With the recent development of different technologies that have been able to process waste to generate energy with high efficiencies, waste to energy technologies can be considered to be viable substitute/option for fossil fuels for electricity generation and also in minimizing of waste accumulation.