Tool Presentation

C H A P T E R 12

Waste-to-Energy Model/Tool Presentation Sunil Kumar1, Snehalata Ankaram2 Solid and Hazardous Waste Management Division, CSIR e National Environmental Engineering Research Institute, Nagpur, India; 2Department of Zoology, Vasantrao Naik Mahavidyalaya, Aurangabad, India 1

1. Introduction Competition among industrial and urban areas and increased demand for energy and fuel have created a threat to energy security. In addition, fossil fuels are declining toward extinction. To compensate for humankind’s needs, innovative and best practices are needed to be implemented for a viable future, one that includes energy recovery from human refuse and renewable biomasses. There is an increasing burden on the earth due to the continuous generation and deposition of waste through human activities, causing a huge environmental impact posing a threat to ecosystems and living creatures. Waste and biomass are very diverse by nature, constituting degradable and nondegradable components. The methodological tools designed for energy recovery from waste should have global applications. Energy recovery in the forms of electricity, heat, steam, ash, and transport fuel processed from waste through various technological approaches is called waste to energy (WTE). WTE keeps waste management and energy security in balance with waste treatment policies and environmentally safe energy production.

1.1 Waste Designation According to Source The key ingredients needed for these technologies are merely humans’ dismissed materials put back into the process for energy recovery are shown in Table 12.1. Nonrecyclable waste can be diverted either for disposal and burying at the landfill or for the thermal and nonthermal conversion of waste. The approaches for recovering energy through thermal and nonthermal conversion include the combustion of waste in gigantic designed chambers operated at high temperature, readily reducing the volume of waste to one-tenth of its parent volume. Heat recovered from burning the waste is converted into steam released through a turbine to produce electricity. The mechanism of recovering the Current Developments in Biotechnology and Bioengineering. https://doi.org/10.1016/B978-0-444-64083-3.00012-9 Copyright © 2019 Elsevier B.V. All rights reserved.

239

240 Chapter 12 Table 12.1: Sources of Biomass for Energy Conversion Residential

Industrial

Agricultural

Kitchen waste Paper and cardboard Electronic waste Glass Plastic Metal Vegetable waste Temple waste Laundry and sanitary waste

Bagasse Paper and pulp Fly ash Textile waste Distillery waste Sludge waste Slurry Sludge from oil and dyes Sugarcane thrash from juice centers

Farmyard waste Animal and dairy waste Forest waste

energy from nonbiodegradable waste through thermal processes is called WTE. Considering the material feedstock required for WTE, the United States generates 25 million tons of plastic from which 1.5 million is diverted for recycling, 3.5 million is utilized for mass burning, and 20 million is dumped, thus following the joint process of recycling and WTE for waste reduction.

1.2 Preferential Role of Waste to Energy WTE plants are a substitute for fossil fuels with the least dependence on coal, oil, natural gas, etc., by generating electricity. An example is the Huntsville, Alabama, WTE facility, a single WTE plant that eliminates the use of 200,000 barrels of oil per year [1]. Mass burning of 1 ton of municipal solid waste (MSW) cuts over the use of one barrel or 0.25 ton of coal. WTE offers an opportunity for “zero waste” by reducing 90% of the MSW and yielding ash as a by-product, which if reused claims 100% recovery from waste. It guarantees the minimum emission of pollutants into the environment. It also overcomes the problem of solid waste disposal and landfilling, thereby relieving the need for more and more land. WTE plays an important role in minimizing methane and CO2 emissions from landfills, deferring the global warming issue. A case study was conducted on a landfill, Taman Beringin in Malaysia, comparing it with various methods like incineration, landfill gas recovery, and anaerobic digestion to assess the economic and environmental effects of MSW. The results suggested incineration as a useful aid for the energy recovery of 1430 MWh/day of heat and 480 MWh/day of electricity from 1000 tons/day of MSW feed [2].

2. Advantages of Incineration Incineration is a value-added process for health care sectors, where the waste developed is potentially hazardous and infectious for humans and has an environmental impact. Clinical

Waste-to-Energy Model/Tool Presentation 241 Minimized waste transportation

Substitute for fossil fuel combustion

Waste Volume Reduction

Less land required as compared to landfill site

Advantages of Incineration

Heat and Power recovery

Eliminate methane gas emissions

Reducing landfilling burden

Ash for construction

Figure 12.1 Advantages of incineration.

waste, like pathological waste, pharmaceutical waste, surgical waste, and radioactive waste, would pose a threat if disposed of or landfilled. Transforming this waste into the form of energy is one best practice [3]. Most of the WTE facilities, such as those in the United States, offer the recovery of material from the by-product ash after processing of the waste, ranging around 702,727 tons of ferrous metal per year. Around 43% of plant facilities recover other source types, like plastic, glass, white goods, etc., which are diverted for road construction. The total recovery of materials from 82% of WTE plants is 1,479,091 tons [4]. The Sheffield, UK facility is equipped with a capacity of 225,000 tons of MSW per year, recovers 17 MWe of electrical energy and 39 MWth of thermal energy. In Nottingham, UK, the WTE plant extracts 14.4 MWe of electrical energy and 44.2 MWth of thermal energy from 160,000 tons of MSW per year [5]. Mass-burning plants lower the waste volume to 95%, with 80% reduction in pile accumulation [6]. The advantages of incineration are shown in (Fig 12.1).

3. Waste-to-Energy Tools WTE techniques operate with minimum emissions and maximum yield of energy. Modern and looming WTE technologies have been reviewed, highlighting diversified methods, like incineration, pyrolysis, gasification, anaerobic digestion, ethanol fermentation, landfill, microbial fuel cells, and microbial electrolysis cells. They have suggested, in the context of future perspectives, the microbial fuel cell and microbial electrolysis cell as impending and eco-friendly safe methods to be studied and implemented [7]. Life-cycle assessment of landfill gas, environmental impact, and greenhouse gas (GHG) emissions in terms of the landfill as a WTE practice have been studied and reviewed by many authors. According to the European Commission, the performance of WTE should enact the growth of a circular economy with a foundation in the EU waste hierarchy,

242 Chapter 12 which should not hamper the other aspects, such as prevention, reuse, and recycling. It also put forth the design and recommendations for technological applications, such as: • •

•

coincineration of solid recovered fuel and syngas in cement kilns; enhancement of incinerative skills by using super heaters and heat pumps and extracting energy from by-product flue gas, and the use of the cooling process for district heat networks; use of anaerobic digestion plants with advanced tools for biomethane production.

Combustion plants should work efficiently under minimum temperature conditions with significant energy output surpassing the accessory energy required. State-of-the-art WTE technology is equipped with fundamentals like a combusting unit and a restored boiler with a significant yield of steam directed forward to the turbines for electricity generation. Also, the resulting emissions of flue gas are cleared by means of sorption and filtration through a flue treatment system [8]. Mass burning relies on heating with an excess supply of oxygen at high temperature. The unique property of incineration is its low dependency on pretreatment of waste; solid waste management is an ideal feedstock for combustion. Combustion of waste in furnaces involves injecting air through it, forming a fuel layer on the grate, followed by decomposition of the waste at increased temperature, converting the carbon-oriented material into gases and heat energy. Hot gases from the combustor are trapped by the recovery boiler, and may be diverted to a steam turbine for electricity generation [9]. Thermal treatment technology comprises combustion, gasification, and pyrolysis, based on the controlled supply of oxygen and temperature. The combustion process relies on the supply of elevated oxygen; a limited amount of oxygen works for gasification, while pyrolysis takes place in the absence of oxygen. Thermal conversion technologies depend on a lower oxygen supply and emit fewer gases with minimum waste residue that is to be landfilled.

3.1 Thermal Treatment Through Incineration The incineration process is done via a grate system that combusts the waste, which is not refined and is crude. The boilers are equipped with hydraulic rams, which load the waste into an ignition cubicle. The grate method monitors the passage of waste into the burning chamber in a disciplined way. Drying of the waste facilitates its volatile property, and it is further burned on the abrade, yielding the by-product ash. The resulting flue gases from the furnaces are transported further for energy recovery in the form of steam. Combustion plants produce steam from hot flue gases emitted from the furnace at a temperature of 850
C. This hot steam is deported to the district for heating or electricity or is utilized for running the plant itself on site or for industrial use.

Waste-to-Energy Model/Tool Presentation 243 A wide spectrum of grates is seen in practice, such as forward reciprocating, reverse reciprocating, roller system, and horizontal pattern. The final cleared gases to be released into the atmosphere through the chimneys are released passing through air pollution control system, detoxifying pollutants like nitrogen, heavy metals, dioxins and furans, etc. Solid by-products like bottom ash and fly ash resulting from the incineration process may be further treated to remove pollutants or else utilized for road making or diverted to landfills. Another aspect of incineration is the fluidized-bed system, based on the conversion of solids to liquid form in the presence of air. Types of applicable waste are sewage sludge, organic constituents, and solid waste. Furnaces of the fluidized-bed system consist of rectangular or cylindrical heating grids working efficiently on waste of minute particle size, which is burned in the fluidized sand berth. The incineration process can be enhanced by the addition of dolomite for controlling acid gas emissions. Waste with high calorific value is suitable for this process. In Japan, MSW is diverted to fluidized-bed plants. The fluidized-bed system has benefits over the grate system because it works on minimum floor area utilizing less space. Fluidized-bed systems consist of bubbling type, circulating reactor, and revolving activator for efficient conversion of waste into fuel [10e12].

3.2 Thermal Treatment at Elevated Temperature: Pyrolysis Waste such as plastics, polymers, medical, and hazardous waste can be managed through plasma pyrolysis. The plasma torch is the leading component of plasma pyrolysis, based on skilled energetic heat production capability and shredding of organic content at the molecular level. Emissions of dioxins and furans through the plasma pyrolysis process are within the range of US Environmental Protection Agency guidelines. The plasma torch is composed of graphite electrodes that transform electric energy into thermal energy, producing arc plasma. The high-voltage electricity generated by the plasma torch breaks the molecular structure of the waste, yielding the final product gases and a solid residue. Syngas shows a high calorific value that can be altered into steam, electricity, or a feedstock in the petrochemical and refining industries. The process of pyrolysis involves combusting the waste in starved oxygen, forming gas, oils, or char, eradicating the particulates, hydrocarbons, and dissolved elements through cleaning of the gas. The purified gas is then applied to create electricity through steam turbines, gas engines, or hydrogen fuel cells [11,12].

3.3 Waste Into Syngas: Gasification Gasification transforms organic waste into gaseous form in the presence of minimum oxygen by the shredding of carbon material through chemical reactions into simple

244 Chapter 12 molecules used for value-added electricity, fuels, chemicals, or fertilizers. One ton of MSW generates 1000 kWh of electricity through the gasification method [13]. The production of hydrogen-rich syngas was studied by the authors. The different types of bio-char generated by the steam gasification of rapeseed, wood, sewage sludge, and Miscanthus waste were subjected to average pyrolysis and transferred in a quartz tubular activator for gasification aided by steam. The interactive properties such as temperature factor, steam, and role particle size were investigated. It was reported that hydrogen yield was increased from gasification of rapeseed bio-char up to 58.7% at 750
C [14]. A steam gasification plant consists of two fluidized beds attached to each other in which the dried biomass is gasified in the presence of steam replacing the use of air. It functions best at a temperature of 850
C, yielding high-calorific syngas with a minimum amount of tar and nitrogen [15]. A Westinghouse energy plant converts solid waste into syngas, electricity, biofuels, and petrochemicals by plasma gasification technology. These plasma torches are designed so as to produce the highest heating capacity power of more than 3000
C, processing 330,000 tons of garbage per year, producing 3.5 million BTU of syngas per year [16]. Advancements in the competence of the boiler performance of WTE plants, which is affected by the varied moisture contents of the waste, are also to be considered. Asian WTE plants yield steam with a limit of 40 bars, 400
C, while in developed countries it is 60 bars with enhanced thermal properties. These advanced techniques are being developed round the clock to compensate for and replace errors faced by WTE plants, and include the introduction of advanced combustion control, high steam pressure, reduced steam condenser pressure and boiler vent temperature, combined heat and power operating systems, and provision of elevated temperature systems with increased energy yield. Another concerning factor is the WTE plant’s efficiency at reducing the emission of pollutants such as dioxins. Certain filters are designed according to the type of pollutant emitted. Fabric, wet, and semiscrubbers are employed for cleaning acid gases like sulfur dioxide, hydrogen chloride, and hydrogen fluoride. Fabric filters and activated carbon injections remove heavy metals like mercury, cadmium, lead, and copper, while electrostatic charges precipitate and cyclones eradicate crude material from flue gases. All these systems are sorted out for cleaning the dioxins and furans. Partial provision of oxygen during gasification maintains control of carbon and hydrogen production from waste during conversion into syngas, extracting about 80% of energy. The temperature range may vary from 900 to 1000
C with air and from 1000 to 1400
C in the presence of oxygen. Oxygen-aided gasification results in 10e18 MJ/Nm3 heating value [17].

3.4 Biological Breakdown of Waste: Anaerobic Digestion Anaerobic digestion involves the degradation of organic matter biologically in an oxygenfree environment, releasing the product in the form of biogas composed mainly of

Waste-to-Energy Model/Tool Presentation 245 methane. The digestion is aided by microorganisms, involving a series of steps such as hydrolysis, acidogenesis, and methanogenesis. The ideal feedstock for anaerobic digestion is livestock excreta, farmyard manure, pulp and food industrial waste, etc. [18]. A study was based on a combined experiment on anaerobic digestion of corn straw for methane production and the formation of biobriquettes from corn stover and the resulting digestate. The digestor included a leach-bed reactor and corn straw as feedstock, the fermentation of which produced methane at 179.6 mL/g VS (parallel to 5.55 MJ/kg corn straw). A comparison was also performed on the calorific value of biobriquettes made from corn stover and from digestate. The results showed the highest calorific value (20.21 MJ/kg) in biobriquettes made from digestate [19]. Anaerobic digestion is applicable to feedstocks of more than one type mixed as polyfeedstocks. An experiment conducted by the authors [20] focused on the methane yield from both mono- and polyfeedstocks in different combinations. The results revealed the highest methane yield (1.27e3.46 times) from cucumber waste:pig manure:corn stover in the ratio of 5:2:3, an ideal blend for methane production. This mixture not only enhanced methane yield but also facilitated the microbial growth of Firmicutes (44.6%), Bacteroidetes (32.5%), Synergistetes (3.8%), Methanosaeta (37.1%), and Methanospirillum (18.2%).

3.5 Fuel Cells Fuel cells have an array of applications, viz., treatment of brewery waste and domestic effluent, hydrogen genesis, remote sensing, etc., facilitating the reclamation of waste. Molten carbonate fuel cells operate at a temperature around 650
C, converting waste into vital power and heat from biogas with minimum carbon monoxide emissions, and work without catalysts, a suitable WTE technology involved in waste management. Compared with traditional incineration and combustion methods, conversion technologies such as pyrolysis, gasification, etc., produce synthesis gas composed of hydrogen and carbon monoxide, which can be redirected to make electricity. Plasma gasification, a modern technique, works via a plasma torch that provides heat up to 5000e20,000
F during the gasification process. Although an expensive technology, it provides benefits in lowering solid waste, and the postprocess residue is environmentally safe, with a lower quantity of byproduct yield. Reclamation of metals and the inert residue is feasible before disposal [21,22].

3.6 Hydrothermal Carbonization Hydrothermal carbonization (HTC) is another looming WTE technology specially designed for conversion of wet biomass feedstock with no dependency on energy input, which

246 Chapter 12 otherwise is needed for drying of the feedstock in other techniques. Pretreatment for drying of biomass is not needed in HTC. The resulting by-product ash can be applied as a plant nutrient enhancer because of its phosphorus content, and also a liquid by-product produced by the HTC plant can be used for watering plants as it is loaded with potassium content [23]. Thermochemical means of conversion through HTC transformed unprocessed waste into a hydro-char bearing a high calorific content and complemented with elevated levels of carbon content. A feedstock with 75%e90% moisture content is considered ideal for this process. HTC comprises three processes, namely, dehydration, decarboxylation, and decarbonylation, for which pretreatment or drying of the feedstock waste is not needed. The hydro-char, rich in carbon, can be utilized as fuel, as an alternative for coal thus replacing a fossil fuel, as feedstock for gasification, as a soil additive for nutrient enrichment, or as an adsorbent or precursor for activated carbon [24e27]. In the study conducted by Fabio et al., the methane yield was assessed by employing spent coffee grounds as the feed material subjected to a codigestion process combined with HTC. The hydro-char produced was studied for heating value and methane yield of 46 mL CH4/g VS day [28]. Fig 12.2 shows energy creation from waste through ecologically safe and economically sound techniques by combustion of waste at elevated temperatures, yielding steam, which is later converted to electricity through turbines, and a by-product ash, which is collected at the end.

Drop Off Center

Combustion Unit

Trash Repository Unit

Steam through Turbine Generator

Electricity

Vented Gases Through chimneys

Water vapor and cleaned gases

Ash Conveyer Belt

Recovered Ash

As by-product for road construction, landfilling

Figure 12.2 Waste to energy processes.

Waste-to-Energy Model/Tool Presentation 247

4. Feedstock and Processes of Waste to Energy In the WTE strategy, the action of anaerobic digestion was found to be effective at providing energy from biodegradable biomass and trapping landfill gases, reducing GHG emissions and thus limiting environmental pollution [29]. Recycling of MSW through composting aids in reducing the landfill burden, and the surplus resulting from recycling can be diverted for incineration and other combustible processes, yielding a diversity of fuels offering a wide array of utilization [30]. Globally, the rate of increase in municipal waste is higher than the rate of urbanization. A review article reported the generated amount of MSW at 1.3 billion tons every year, suggesting 1.2 kg/capita/day, and this volume is likely to increase by 2.2 billion tons by 2025 [31]. Living standards of the population are influenced by a hike in economy, contributing to an enhanced municipal waste generation. The overcrowding of communities in India was 1252 million in 2013 compared with 1028 million in 2001. Population growth is a major contributor to increasing MSW in India. MSW production in India is approximately 133, 760 tons/day, at an individual level of 0.17 kg per person per day in small towns to approximately 0.62 kg per person per day in urban regions (Fig. 12.3). Of the total waste production of 133,760 tons/day, 25,884 tons is treated by various techniques [32e34]. India shows agriculture as the giant industry in the country, subsidizing the socioeconomic growth of the country. The shift of metro cities toward smart cities shows the diversity in infrastructure and size of the city, innovated commodities, intensified living standards of citizens, etc., with changing consequences on countries’ economic status. Inflated prosperity increases the utilization of inorganic materials like plastics, paper, fuel, etc. [35]. 45% 40% 35% 30% 25% 20% 15% 10% 5% 0%

compostable inert paper plastic glass metals textile

le

at

he

r

ile xt te

m

et

al

s

s as gl

tic as pl

r pe pa

t er in

co

m

po

st

ab

le

leather

Figure 12.3 Municipal waste composition in India [37].

248 Chapter 12 Municipal waste in Beijing, Xiamen, Shenzhen, and Hangzhou is categorized as kitchen waste, recyclables, hazardous waste, and other waste. Shanghai grades its waste in a fourcategory classification, i.e., recyclables, hazardous waste, wet waste, and dry waste [36]. Table 12.2 illustrates the amount of waste created per capita in various regions. The table also depicts the projected population and waste generated for the year 2025. The amount of energy as an end product resulting from the incineration process depends on factors of waste quality, like density, ingredient type and structure, displaying the waste, percentage of moisture, etc. Waste composed of organic matter generates around 65%e80% of energy [39]. Combusting pyres are introduced with updated technology to eliminate the total emissions by furnishing digital pollution control devices, suitable furnaces with controlled temperature, and thermogenic processes. Inappropriate waste management in India has led to the discontinuation and failure of working WTE plants and continued with other causes such as lack of scientific planning, untrained professionals, untimely and insufficient funds, poor waste segregation, waste characteristics changing during seasons and festivals, mixing of inert materials, etc. A comparative study on WTE key issues in India with those of European waste incinerators was performed, along with additional interactions with authorized officers, industry practitioners, and academics extensively engaged in waste management practices. The conclusions revealed that the failures of WTE plants were due to the challenges posed by improper waste segregation, mixing of waste during transport, and storage facilities, with improvements to be made in shipment tasks, funding provisions, designing and implementation of dumping regulations, ash management, and emission controls [40]. The modified form of components such as stoker, fluidized, and modernized furnaces with a water wall have proven potential and were launched along with a twin interchanging fluidized-bed combustor invented by a Japanese company. These furnaces rely significantly on burning of wastes with low and high calorific values. Energy recovery from the MSW of Belo Horizonte, Brazil, was analyzed based on two processes, landfill and WTE, with a supplementary life-cycle assessment resulting in an efficient vital recovery from WTE methodology compared with the landfill technique. The energy content of MSW and methane generation by landfill were studied, which adds higher emissions to the environment [41]. A case study on green gas emissions at landfill sites from three different regions of Delhi, Ghazipur, Bhalswa, and Okhla, based on distinct patterns like default, modified triangular, first-order decay, and in situ closed chamber, established first-order decay as a potential method with a scope of 1.5e3.00 MW electricity generation [42]. The evaluative study on the “3E’s”, viz., energy, economics, and environment, of WTE was conducted on different

Table 12.2: Waste Generation in Various Countries [38] Current Available Data (2012) Urban Waste Generation

Region

Per Capita (kg/capita/ day)

Total (tons/day)

Projected Population Total Population (Millions)

Urban Population (Millions)

Projected Urban Waste Per Capita (kg/capita/ day)

Total (tons/ day)

260 777

0.65 0.95

169,119 738,958

1152 2124

518 1229

0.85 1.5

441,840 1,865,379

227

1.1

254,389

339

239

1.5

354,810

399

1.1

437,545

681

466

1.6

728,392

162

1.1

173,545

379

257

1.43

369,320

729 426

2.2 0.45

1,566,286 192,410

1031 1938

842 734

2.1 0.77

1,742,417 567,545

2980

1.2

3,532,252

7644

4285

1.4

6,069,703

OECD, Organization for Economic Cooperation and Development.

Waste-to-Energy Model/Tool Presentation 249

African Region East Asia and Pacific Region Eastern and Central Asia Region Latin America and Caribbean Region Middle East and North Africa OECD South African Region Total

Total Urban Population (Millions)

Projections for 2025

250 Chapter 12 methods, including landfill gas recovery system, incineration, anaerobic digestion, and gasification, with output recommendations of effective energy creation likely from anaerobic digestion and incineration methods [43]. In the United States, WTE plants have proven to be an intensified medium to tackle the debated issue of waste management along with energy recovery. The United States operates around 86 facility centers for WTE, potentially generating 2720 MW/year. MSW is the source feedstock tackled readily, with 28 million tons of waste processed per year and a 10% ash yield as a by-product [44]. MSW management includes a detailed pretreatment study to determine the heating value and composition of MSW in the area before investing in and financing giant processing plants, which are capital-intensive and require high maintenance costs. Waste arising from municipalities and industry can be diverted to combustion plants that are equipped with boilers to burn the waste with the release of heat that can be converted into electrical power or steam. They are also installed with air pollution control systems that clear the pollutants from combustion gases that are released into the open through the chimney. Bottom ash and fly ash are the by-products of this combustion process. In the context of landfill versus incineration, a study focused on data collected from the city of Toronto, Ontario, identified an increased net electricity yield by incineration with significantly reduced GHG emissions [45]. Curtailing the quantity and limiting the landfilling of waste can be achieved by incineration with plants operating near the generation sites of waste, reducing the transportation cost. In Caifornia, WTE plant based on fuel cell energy supplemented with an anaerobic digestion gas system is generating and supplying power, hydrogen, and heat to a treatment facility and hydrogen refueling center (around 10 refueling stations), and heat is utilized for biogas conversion to carbon dioxide and hydrogen [46]. Energy recovery from refuse and the recycling of waste to reduce it are practiced in almost all countries; the maximum source of this waste is MSW (Table 12.3). In a developed country, the United States, an American Ref-Fuel-operated SEMASS WTE plant facility in Rochester, Massachusetts, works with emphasis on waste management by lessening the MSW disposal and limiting emissions, devoid of a prerequisite for preprocessing of waste for mass burning. Notably, both wet and dry waste is suitable for the plant, which consists of three units designed to process 910,000 metric tons/year, yielding 720 kWh of electricity per ton. Of this total yield, around 100 kWh/ton of waste is consumed to operate the facility [54]. Mass burning in Japan is practiced in advanced fluidized-bed WTE plants, starting with reduction of feedstock and sorting of the inert materials from mass laid on limestone, maintaining a constant temperature at a range of 830e910
C with enhanced combustion, yielding better energy as an end product.

Waste-to-Energy Model/Tool Presentation 251 Table 12.3: Energy Recovery Through Waste-to-Energy Conversion in Various Countries [47e53] WTE Methodology Incineration Incineration Incineration Gasification and pyrolysis Gasification plant Incineration: circulating fluidized bed Mass-burn combustion

Country Beijing (Lujiashan incineration plant) Taiwan Naples, Italy Turkey Manchester, UK China

Incineration

Covanta Energy, Lorton, VA, USA Tampa Bay area, FL, USA Thun, Switzerland

Incineration

Isseane, France

WTE

Italy

Combustion

Energy Recovery

Waste Handling Capacity

320 million kWh 2967 GWh 100 kWe 300 kWth and 50 kWe

650,000 tons/year 78,000 tons/year 800 tons/day

80 MW

3000 tons/day

150 MW

5 million tons of MSW per year 100,000 tons/year

Electricity, 12 MW; heat, 25 MW Electricity, 52 MW; heat, 150 MW 2.4 million MWh electrical energy 0.575 million MWh thermal energy

460,000 tons/year 4.1 million tons

WTE, waste to energy.

The increasing pressure of used tires on the global environment and its management has been always a center of debate. An emphasis has been put on energy recovery from used tires by employing WTE techniques such as incineration, pyrolysis, and gasification, which have proven to be very beneficial and fair methods [55]. In Denmark, a successful approach to substituting for fossil fuels by installing incineration WTE plants was taken by extracting energy from MSW and providing this 20% heat energy to 400 district heating networks in Denmark. Two heating grids were monitored for successful replacement by waste-generated heat, among which one grid showed a CO2 savings of 48 kg CO2/GJ energy and another grid displayed savings of 43 kg CO2/GJ [56]. WTE plants in the United States, with 70 mass-burning facilities, participate in MSW management and energy recovery by converting 13% of refuse into a potential 2.5 GW of energy with minimal emissions [57e61]. The WTE plant based in Lee County, Florida, widely relieves the pressure of different types of waste management by combusting all horticulture waste, yard waste, construction debris, and MSW, with the value-added product of electricity and the ash residue reduced

252 Chapter 12 up to 10% to its parent volume. This WTE facility provides a metal recovery system, totally removing the metal contaminants from ash residue, like ferrous and nonferrous metals, postrecovery discarded at landfills in Hendry County. This mass-burning plant is well equipped with large-scale pollution control panels and a permanently activated carbon injection system for monitoring and restricting mercury emissions. It is also designed to manage horticultural and yard waste by segregating and sorting it into processed and unprocessed reserves that are grated and converted into mulch to be distributed free of cost to residents [62]. The resulting ash by-product from WTE plants was used in an innovative and sustainable method as a structural base cover below the pavement in road construction and as an additive in asphalt and concrete pavement in a project of road construction in Pasco County, Florida [63]. In Bermuda, WTE-generated ash is used as an additive for concrete products for artificial reefs or shore abatements. A promising application of WTE over landfilling is preventing GHG sinks and energy generation along with waste reduction, with 1 ton CO2/ton of MSW lessening the burden and contamination of the earth [64]. WTE is a key consideration for replacing landfilling, an expensive option working via different techniques such as anaerobic digestion, pyrolysis, incineration, gasification, etc. Waste is processed by different methods of WTE conversion utilizing an array of biomass refuse, generating energy (Table 12.4).

4.1 Municipal Solid Waste Management Through Waste to Energy Along with the lack of appropriate technologies in municipal waste management, disposal is the burning issue in most cities in developing countries like India. Some cities have facilities for recycling and incineration to tackle waste, while some show dependency on landfills alone with no other management policies. In such cases, excess landfilling of waste impacts the residential areas with emissions from the landfill, rising odor, living creatures growing and dwelling on the waste, and diseases. Eventually, to some extent the MSW seems to be scattered within the vicinity of city localities. The matter of proper management is a demanding priority, along with transport facilities, decision-making, and fund provision, but also policies to be designed and implemented at the municipal level, action plans needed for the waste management, and incineration facilities to be installed. Energy from feedstock waste in developing countries minimizes disposal problems, ensuring a safer shift toward energy supply, a role to be played at all levels of national and local policy and decision makers, investors, and WTE facility providers, with an emerging demand for implementation of source segregation, collection, transport, and knowledge regarding which waste needs what technology protocol and disposal.

Waste-to-Energy Model/Tool Presentation 253 Table 12.4: Waste-to-Energy Facility Outputs [65e72] US State

Process Type

Energy Form

Minnesota

Biomass

Electricity

CHP

Electricity, heat

Fuel cell

Electricity

Gas turbines

Electricity

Natural gas

Anaerobic digestion

Electricity, heat, and compressed natural gas Electricity

Swine waste

Hugoton, Kansas Wisconsin, Gundersen Health System University of Texas, Austin Boston and Cambridge, Massachusetts California, Connecticut, and New York Walmart, Delaware Towantic Energy, Oxford, Connecticut Rock Falls, Illinois Ashley, Ohio,

Orlando, Florida

Feedstock Agricultural by-products Cellulosic material Landfill gas

Energy Generation 23 MW CHP 21 MW 75%e85%

250 MW 30 MW 61%

Food waste

CHP, combined heat and power.

The debate over the issue of the inflation rate of municipal waste generation to 2.2 billion tons per year by 2025 was addressed by Moya et al. [73], also focusing on the waste management status in developed and developing countries. They also reviewed issues like collection, storage, transport, and disposal in expanding countries and the advancement in WTE technologies with value-added end products like heat, electric power, compost, and biofuels and their implementation in developed countries. Municipal waste as a feedstock for WTE plants poses a great challenge due to some issues such as: • • • • • • •

variations in the elusive contents of the waste; changes in waste composition types due to customary festivities and seasonal harvesting of crops; improper waste practices; lack of technologies and skilled staff; insufficient funding; the absence of protective measures for waste sorters, rag pickers, kabadiwalas, and other communal workers who deal with waste; weak environmental standards and public health issues.

254 Chapter 12 Uncontrolled and open dumping can be converted into sanitary landfills where waste treatment is operated in a controlled and environmentally safe method. It facilitates the capture and trapping of landfill gas, reducing GHG sinks, since landfill gas consists of 45%e55% methane gas that can be diverted for energy recovery. Landfill gas is collected by installing pipes with holes placed either vertically or horizontally within the dumped waste. A central gas-collecting storage tank is mounted near the site. The landfill gas harvesting depends on the composition of waste, physical and chemical properties, moisture content, etc. Even sanitary landfills pose threats of ground leaching, groundwater pollution, odor, etc. Hence it finds its position hard in the WTE treatment technology [74]. The United Kingdom generates 7.4% of its electrical energy from renewable sources and one-third of that energy is derived from landfill gases. Of 32 million tons of municipal waste generated by the United Kingdom, 39% was recycled and 48% was diverted for dumping at landfills, while WTE plants processed the remaining waste, accommodating 13% vital energy. During the same period of time, commercial and industrial waste developed about 58 million tons of garbage. A recycling policy for 50% of refuse was implemented, while a fraction of the waste, i.e., 25%, was landfilled [75].

5. Conclusions and Perspectives Material and energy recovery through WTE is raising hope for a sustainable environment in the context of reducing the need for fossil fuels. The initial act is that of avoiding waste, designing any material to yield minimum refuse after the lifespan of product, later opting for recycling with least energy input. Also, during the journey of waste collection to disposal, an array of processes including separation on site at the plant into batches such as paper, glass, metal, biodegradable waste, etc., should be highlighted for successful conversion at WTE facilities. Data need to be collected on recycling strategies, the ratio of input energy needed and end product energy, landfilling emissions, land used for dump yards, and postrecycling recovery through WTE. Developed countries have ameliorated contents like waste composition, waste transport, segregation facilities, and least dependence on economic funds. Among WTE technologies, incineration is the dominant form of energy recovery largely practiced by several countries despite the issues of emissions, with plants being highly modified and installed with pollution control devices and water wall furnaces thereby enhancing the mass-burning process. A precise survey needs to be made in developing countries on successful WTE operations and continued with data on the waste source, composition, segregation, and technological aspects. WTE technologies are dependent on the type of waste and amount of refuse generated; the type of energy to be recovered and the physicochemical properties of the waste feedstock determine the method to be employed. Most WTE facilities rely on thermochemical methods for energy processing.

Waste-to-Energy Model/Tool Presentation 255 WTE encompasses a broad spectrum of scientific and technological arrays functioning on different principles and resulting in various end products. It exhibits production of biogas from domestic garbage and farmyard manure through anaerobic digestion at small scale, mostly practiced in rural areas; capturing methane gas from landfills; incineration plants based on thermochemical treatments converting waste into electricity, heat, and steam with added by-products applied; and recycling of refuse-derived fuels generated from cement plants through an array of thermal, thermochemical, and biological processes. Coordinated work needs to be established between various municipal bodies aiming for socioeconomy of integrated waste management, long-term sustainable management plans, categorization of waste stream and its characteristics, and treatment options based on type and amount of waste generated with minimum energy input.

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