Microwave Plasma Gasification for the Restoration of Urban Rivers and Lakes, and the Elimination of Oceanic Garbage Patches

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Proceedings of the ASME 2016 10th International Conference on Energy Sustainability ES2016 June 26-30, 2016, Charlotte, North Carolina

ES2016-59632

MICROWAVE PLASMA GASIFICATION FOR THE RESTORATION OF URBAN RIVERS AND LAKES, AND THE ELIMINATION OF OCEANIC GARBAGE PATCHES

Philip K. Panicker Amani Magid New York University in Abu Dhabi New York University in Abu Dhabi Abu Dhabi, United Arab Emirates Abu Dhabi, United Arab Emirates

the most widest range of waste materials, while consuming only ABSTRACT about a quarter of the energy released from the feedstock. MIPG systems can be scaled in size, power rating and waste- This review paper describes techniques proposed for treatment capacity to match financial needs and waste applying microwave-induced plasma gasification (MIPG) for processing requirements. MIPG systems can be set up in urban cleaning rivers, lakes and oceans of synthetic and organic waste locations and on the shores of the waterbody, to filter and pollutants by converting the waste materials into energy and remove debris and contaminants and clean the water, while useful raw materials. generating electric power to feed into the grid, and fuel or raw Rivers close to urban centers tend to get filled with man- materials for industrial use. made waste materials, such as plastics and paper, gradually For eliminating the pelagic debris fields, the proposed forming floating masses that further trap biological materials design is to have ships fitted with waste collector and filtration and animals. In addition, sewage from residences and systems that feeds the collected waste materials into a MIPG industries, as well as rainwater runoff pour into rivers and lakes reactor, which converts the carbonaceous materials into syngas carrying solid wastes into the water bodies. As a result, the (H2 + CO). Some of the syngas made will be used to produce water surfaces get covered with a stagnant, thick layer of the electric power needed for running the plasma generator and synthetic and biological refuse which kill the fish, harm animals onboard systems, while the remainder can be converted into and birds, and breed disease-carrying vectors. Such destruction methanol and other useful products through the Fischer-Tropsch of water bodies is especially common in developing countries process. This paper qualitatively describes the implementation which lack the technology or the means to clean up the rivers. schemes for the above processes, wherein MIPG technology A terrible consequence of plastic and synthetic waste being will be used to clean up major waste problems affecting the dumped irresponsibly into the oceans is the presence of several earth’s water bodies and to convert the waste into energy and large floating masses of garbage in the worlds’ oceans, formed raw materials in a sustainable and environmentally friendly by the action of gyres, or circulating ocean currents. In the manner, while reducing the dependence on fossil fuels and the Pacific Ocean, there are numerous debris fields that have been release of carbon dioxide and methane into the atmosphere. labeled the Great Pacific Garbage Patch. These patches contain whole plastic litters as well as smaller pieces of plastic, called NOMENCLATURE microplastics, which are tiny fragments that were broken down by the action of waves. These waste products are ingested by AC Alternating current animals, birds and fishes, causing death or harm. Some of the CVD Carbon vapor deposition waste get washed ashore on beaches along with dead marine life. DC Direct current The best solution for eliminating all of the above waste DDT dichloro-diphenyl-trichloroethane management problems is by the application of MIPG systems to EDC Endocrine disrupting chemicals convert solid waste materials and contaminated water into HDPE High density polyethylene syngas, organic fuels and raw materials. MIPG is the most efficient form of plasma gasification, which is able to process HHV Higher heating value

1 Copyright © 2016 by ASME IEEE Institute of Electrical and Electronics streams, lakes and other water bodies in or near cities. Such Engineers dwellings frequently lack proper sanitation and waste-disposal LDMOS Laterally-diffused metal oxide systems and the communities are not provided with waste semiconductor field effect transistor management services due to the absence of proper planning LDPE Low density polyethylene from the city administration. As a result, people discard their MIPG Microwave-Induced Plasma household wastes and empty the discharge from their toilets, Gasification bathrooms and kitchens into the water bodies, keeping with the maxim, “out of sight, out of mind”. The slums are an economic MSW Municipal Solid Waste necessity for the city, providing shelter to low-income workers, PAH Polycyclic aromatic hydrocarbons who provide the workforce for the industries in the cities. PCB Polychlorinated biphenyls Before long, traders providing services, sales, food production PET Polyethylene terephthalate and sales outlets, and even manufacturing start up and take root PP Polypropylene within the slums. All of these entities send ever larger amounts of waste into the water bodies. PS Polystyrene The accumulation of the waste in the water bodies causes PVC Polyvinyl chloride an overgrowth of algae, block up the flow, contaminate the RF Radio frequency ground water, breed vectors that cause and spread diseases, and WTE Waste to energy severely affect the environment and wildlife. There is often a noticeable and unpleasant stench that develops near the tpa Tonnes per annum contaminated rivers and lakes. As a result, the waterbodies turn tpd Tonnes per day into toxic waste pools. During rainy seasons, the precipitation carries more waste from the streets and surfaces into the rivers which eventually INTRODUCTION flow into the seas and oceans. However, waves and tides cause This paper is a review of existing literature on the topics of the waste to get deposited along the shores and beaches, waste accumulation in water bodies such as rivers, lakes, and creating another ecological crisis. Natural disasters, such as oceans; waste-to-energy (WTE) conversion; and gasification earthquakes, floods, hurricanes, etc. also cause wastes to enter technologies. The qualitative information gathered is then used the water bodies including the rivers, lakes and oceans from the to propose a viable solution to two major environmental land. problems affecting many countries today. The information Since the waste-filled waterbodies are very repulsive, presented here will be used to support a subsequent techno- people avoid dealing with them, and gradually the waste builds economic modeling study of the same subjects. up. But, if the cleaning up of the water bodies is delayed, the Firstly, in many developing countries, the rivers, streams, problems continue to grow until an environmental crisis occurs. lakes and other water bodies close to densely populated areas The main obstacle for the cleanup is a lack of money with the become filled with waste, turning them into dead or sewage city authorities. Therefore, the solution to this problem has to be streams [1,2]. Secondly, the waste on land gets carried away by economically viable and provide sufficient returns to the precipitation into the rivers and lakes, and much of it flows into stakeholders. the seas and oceans, further leading to the creation of large In order to provide a proper engineering solution to the garbage patches in the oceans. In this paper, microwave- problem, it is important to look at the composition of the waste. induced plasma gasification (MIPG) will be shown to be the Since the definitions are broad and tend to vary, waste items best candidate technology for converting all the wastes in the may be classified as below for the ease of practice [3]. water bodies mentioned above into energy through gasification, 1. Municipal Solid Waste (MSW): Commonly called while also providing an environmentally safe and sustainable garbage (US), rubbish (UK) or trash, this includes source of energy, fuels and raw materials. residential and commercial wastes generated in a community or municipality. It includes food and WASTE ACCUMULATION IN URBAN RIVERS, kitchen wastes, consumer items, containers and STREAMS, LAKES AND WATERBODIES wrapping made of paper, cardboard, wood, textiles, In many developing countries, the cities are experiencing a glass, plastics, metals, etc. MSW may also include rapid growth in populations as people migrate from the hazardous materials such as batteries, light bulbs, countryside, leaving their farms and villages, and move to the pesticides, cleaning chemicals, etc. Paper constitutes cities in search of jobs. This growth in urban populations about 15% by mass, while plastics which are non- creates a significant pressure on land and housing availability, biodegradable can be as high as 70%. Paper and leading to the formation of highly dense communities and plastics have significant carbon and hydrogen content. slums. Often these communities are located alongside rivers,

2 Copyright © 2016 by ASME 2. Biomedical wastes: this may constitute medicines, TABLE 1 MASS FRACTIONS OF THE CONSTITUENT chemical waste from clinics, used medical wastes such ELEMENTS OF VARIOUS MSW SUBSTANCES AND THEIR as syringes, gloves, sanitary napkins, etc. The CALORIFIC VALUE IN HHV. [4,5] Volatile Fixed pharmaceuticals pose an under-recognized ecological Ash CHONS Cl HHV problem. Medicines that people consume that are not matter carbon (%mass) (%mass) (%mass) (%mass) (%mass) (%mass) (%mass) (%mass) (%mass) (MJ/kg) absorbed by the body get passed out through excretion. These pharmaceutical chemicals cannot be fully Newspaper 88.5 10.5 1 52.1 5.9 41.86 0.11 0.03 n.a. 19.3 removed by sewage treatment plants and contaminate Cardboard 84.7 6.9 8.4 48.6 6.2 44.96 0.11 0.13 n.a. 16.9 water reservoirs, rivers, lakes and underground water, Recycled 73.6 6.2 20.2 n.a. n.a. n.a. n.a. n.a. n.a. 13.6 and also affect wildlife. paper 3. Biological wastes: This constitutes human wastes, Glossy 67.3 4.7 28 45.6 4.8 49.41 0.14 0.05 n.a. 10.4 refuse from butcher shops that are disposed off paper Wood irresponsibly, dead organisms, etc. that attract pests, 89.6 10.2 0.2 47.4 6.3 46.2 0.07 n.a. n.a. 19.3 (Spruce) pathogens and vectors. They have high carbon content. Plastics 4. Biomass: This consist of waste vegetable matter, grass HDPE 100 0 0 86.1 13 0.9 n.a. n.a. n.a. 46.4 clippings, tree branches, sugarcane waste, rice husks, LDPE 100 0 0 85.7 14.2 0.05 0.05 0 n.a. 46.6 dead plants, algae in the water, etc. This also has high PP 100 0 0 86.1 13.7 0.2 n.a. n.a. n.a. 46.4 PS 99.8 0.2 0 92.7 7.9 0 n.a. n.a. n.a. 42.1 carbon content. PVC 94.8 4.8 0.4 41.4 5.3 5.83 0.04 0.03 47.7 22.8 5. Hazardous wastes: This consists of toxic substances, Juice carton such as mercury from laboratory instruments, batteries, (paper+met 86 6.1 7.9 n.a. n.a. n.a. n.a. n.a. n.a. 24.4 fluorescent lights, etc., corrosive chemicals, reactive al) chemicals, flammable and explosive substances, etc.

6. Electrical and electronic wastes: This include parts of Hydrogen 0 0 0 0 100 0 0 0 0 141.8 circuit boards and electrical or electronic appliances, which may have mixtures of plastics, glass, metals and Natural Gas 0 0 0 75.85 24.15 0 0 0 0 54 heavy metals. Diesel 0 0 0.6 83.8 12.1 0 0 3.5 0 44.9 7. Industrial and commercial wastes: Wastes from Gasoline 0 0 0 86.2 12.8 0 0 1 0 46.5 manufacturing industries, automotive wastes and some service industries may be derivatives of petroleum, but GARBAGE PATCHES IN OCEANS will also have heavy metals, common metals, textiles, Large amounts of floating waste materials, such as plastics, chemicals, plastics, paper, etc. get deposited in oceans from rivers and due to surface runoff [6- 8. Others: One recently recognized waste that is ending 13]. In addition, about 20% of the debris in the oceans come up in water bodies and hurting animals are from oil rigs and ships that discard or inadvertently drop microplastics in the form of plastic beads, 500 - 1000 materials into the water. These materials are then carried away micrometers in size, added to toothpastes, soaps and by oceanic currents called gyres. Gyres are caused by the shampoos. Coriolis effect of the earth. They course through large surface areas of the oceans, linking many continents together in their Table 1 is a small sampling of some constituent substances route. The gyres carry the marine debris and concentrate them that are part of wastes that end up in water bodies. Volatile in their centers where the flow velocities are small, forming matter includes all substances that evaporate away when the large patches of plastics, chemical waste and organic matter. substance is heated. Fixed carbon content of a solid material is Most of the floaters are made of plastic bottles, bottle caps, the amount of combustible solid carbon remaining after the plastic bags, Styrofoam cups, as well as pieces of rejected material is heated and all the volatile substances, moisture and fishing nets. The floaters may be seen on the surface or just ash have been removed. The percentage by mass of ash, carbon, below it and are spread out with a density of about 5 kg/km2. hydrogen, oxygen, nitrogen, sulfur and chlorine are shown. The plastics degrade over time due to the action of waves and Finally, the calorific values in terms of the higher heating value ultraviolet rays from the sunlight, creating small particles of (HHV) are indicated. Some common fuels are also shown for plastic about 5 mm wide or smaller, which are termed as comparison with the organic wastes. microplastics. The debris adsorb toxic chemicals such as pesticides, including DDT, PCBs, carcinogens such as polycyclic aromatic hydrocarbons (PAHs), endocrine disrupting chemicals (EDCs), and other organic pollutants [7]. Large plastic pieces and nets trap turtles, fishes and birds. When the

3 Copyright © 2016 by ASME plastic pieces and microplastics are ingested by fishes and birds, substances are released to the air and may get oxidized, and as a they kills the animals, and the adsorbed chemicals enters the result smoke, carbon monoxide, sulfur oxides (SO2 and SO3) food-chain and cause harm to other organisms. The plastics and other gases are also formed. If the temperatures reach as being non-biodegradable accumulate in the oceans and over high as 1,600 °C, then the nitrogen that may be present in the half end up sinking to the ocean floor. wastes as well as nitrogen from the air may form oxides of Garbage patches are present in all the oceans, with the most nitrogen, collectively called NOx (NO and NO2), in an well-known being the Great Pacific Garbage Patch in the North endothermic reaction. The sulfur oxides react with water in the Pacific Ocean. Debris fields in the North Atlantic, South atmosphere to form sulfuric acid (H2SO4) or sulfurous acid Atlantic, South Pacific, Indian Ocean and others have been (H2SO3), while NOx reacts with water to form nitric acid reported. Also, debris fields are found in the North Sea, English (HNO3), all of which will mix and come down with Channel and the Baltic Sea [8]. Garbage patches have been precipitation causing what is termed as acid rain. Acid rain is a known since the late 1980s and are a subject of intense highly destructive consequence of industrial pollution, that research. Several solutions have been proposed to clean up the attack vegetation, animal life and buildings. As a result, garbage patches. [12,13] incinerator plants that combust waste require the addition of multi-stage gas cleaning equipment, such as scrubbers, WASTE-TO-ENERGY PROCESSES cyclones, gas condensing and acid gas removal systems, to remove pollutants from flue gases, including fly ash, mercury, Most of the wastes end up in landfills. Some waste organic sulfur oxides and NOx, as well as more dangerous material such matter are used to produce biogas (methane) in anaerobic as dioxins, furans and polychlorinated biphenyls (PCBs). digesters. But, this is a slow process that still produces a lot of Dioxins, furans and PCBs are a broad class of toxic and solid waste which will eventually go into landfills. Here, the carcinogenic substances formed from the improper combustion processes involved in treating biomass or waste organic of certain organic compounds at temperatures of 400-700°C, substances to produce energy in a faster way with less land fill including waste incinerators. are considered, and they may be classified into three types: Nevertheless, today there are many waste incinerator plants Pyrolysis, combustion, and gasification [1,14-16]. Organic that convert municipal solid waste (MSW) to energy around the matter derived from biomass, such as paper, food waste, etc. world and it is currently the most common waste-to-energy can be considered a renewable energy source. conversion method wherein the MSW is used to produce Pyrolysis is thermochemical decomposition process in electricity, with the help of steam turbines, and the balance heat which biomass is heated in an anaerobic or low-oxygen is used for process heating or for district heating. These plants environment, typically at temperatures ranging from 100– are subject to strict emission standards imposed by the 650°C, whereby the complex hydrocarbons in the solid material environmental agencies. Incinerating the MSW causes a decompose into simpler components including gas, liquid and reduction in the volume of the solids by 95% or more, with the solid. The intensity and rate of heat addition affects the output remaining solid wastes going in to landfills or being used as raw of pyrolysis. Pyrolysis may conducted slowly over many days at materials in cement manufacture or for construction. The plants a low rate of heat addition reaching as high as 400°C such as in do release carbon dioxide into the atmosphere as a result of the the production of charcoal from wood or biochar from biomass combustion. However, if the MSW were to be sent to a landfill, in which the carbon content has been increased by breaking anaerobic decomposition of the biodegradable components in down the cellulose, hemicellulose and lignin into simpler the waste would produce methane which when released to the compounds, and the volatiles are driven out as gas, and some atmosphere has a far higher global warming potential (GW) liquids are obtained by distillation of the volatile substances. than the carbon dioxide. Pyrolysis may also be conducted at a fast rate when The drawback of combustion treatment is that the temperatures reach 450– 600°C within seconds, in which case incinerators can only process certain types of waste. The MSW much more condensable and non-condensable gases are has to be sorted to remove metals, glass, rocks, etc. Large produced. Pyrolysis is only useful for treating selective biomass objects, such as tires, appliances, furniture, tree stumps, etc. (wood or wood waste) or organic matter (e.g. coal and have to be broken down into smaller chunks that can be fed into petroleum) and not for a diverse, non-homogenous matter such the incinerator. Certain hazardous wastes such as batteries, as garbage. fluorescent light bulbs, etc. have to be removed and handled In combustion, the material undergoes an exothermic separately. oxidation in an oxygen rich environment producing Gasification [14-16] is a process of reacting organic matter temperatures of 700–1,400°C which allow for the processing of with controlled amounts of air and water vapor at high municipal solid wastes as well as biomass, such as the waste temperatures in excess of 700°C to produce a gaseous mixture from paper or wood industries. The combustion of organic consisting of carbon monoxide, carbon dioxide and hydrogen, matter produces carbon dioxide and water vapor. Solid fuels called synthesis gas (also known as syngas). Syngas can then be may leave behind a solid ash residue in the combustion converted into electricity and raw materials such as fuels, chamber. During the combustion of waste materials, volatile chemicals, fertilizers, etc. [14]. Within a gasification reactor,

4 Copyright © 2016 by ASME many processes may be occurring at different stages. entrained-bed and molten salt gasifiers. Even these four Dehydration occurs at temperatures of 100–200°C, where water classifications have many sub-categories, depending on the is released from the reactants and turned into steam. In some form factor of the reactors and various aspects of the feedstock, gasifiers, liquid water may be added to the reactants, while in such as type, energy content, moisture content, volatile matter most cases, the materials may have significant amounts of water content, mineral content, ash composition, reactivity, size, within them, such as wood and food waste. Pyrolysis occur at density, etc. Plasma gasifiers will be discussed in more detail temperatures of 200–400°C, where the volatile substances are below. released and carbon content of the solids are increased. Partial Thermochemical gasification has been known for over 350 combustion of some of the reactants occurs at higher years [1]. In 1659, Thomas Shirley, in the United Kingdom, temperatures, as the carbon reacts with oxygen to form carbon performed experiments on coal gas derived from coal mines. monoxide and carbon dioxide. Finally, all the reactants and Various individuals since then have used gasification for town intermediate products combine to form syngas since the lighting, heating and in factories. During the Second World residence time can range from a few minutes to an hour. The War, a shortage of petroleum led to many cars and trucks being various reactions are listed below with the heat of reaction retrofitted with an onboard gasifier that allowed the vehicles to indicated alongside. Note that the carbon is released from the operate on coal or biomass. Although, the availability of organic matter [14]. The last equation below is known as the petroleum and natural gas caused gasification to become water-gas shift reaction [17]. dormant, the lack of petroleum availability in the early 1970s due to the oil embargo imposed by the members of the C + O2 → CO2 ; ∆Hr = -393.4 MJ/kmol (exothermic) (1) Organization of Petroleum Exporting Countries (OPEC) revived an interest in gasification technologies. In the 21st C + CO2 → 2CO ; ∆Hr = 170.7 MJ/kmol (endothermic) (2) Century, the dread of pollution and climate change has given a new impetus to using gasification technologies in converting C + H2O → CO + H2 ; ∆Hr = 130.5 MJ/kmol coal into “clean coal”. Gasification is also being considered for (endothermic) (3) making use of oil sands, tar, fossil fuel waste and municipal solid waste as fuel in an environmentally safe and sustainable CO + H2O ↔ CO2 + H2 ; ∆Hr = -40.2 MJ/kmol manner. (exothermic) [water-gas shift reaction] (4) ADVANTAGES OF GASIFICATION OVER The residue of the gasification process collects at the COMBUSTION bottom of the gasifier. The composition of the residue is Although there are numerous MSW incineration power dependent on the feedstock material and the type of gasifier, plants around the world, gasification plants offer many and can consist of ash, char, or a slag that is a mixture of metals, advantages [18,19]. silica and ash which solidifies into a dark, glassy substance that Gasification is a much more versatile method of converting has found many industrial uses, including as a building material. organic matter to energy because it can process feedstocks of In addition to syngas, there are other gases of lesser any phase, including gaseous (natural gas), liquid (petroleum, calorific value produced in gasifiers operated at lower vegetable oils, sewage) or solid (coal, sewage sludge, etc.) or temperatures and pressures. Producer gas is composed of combinations of the above. The flue-gas from a gasifier plant carbon monoxide and is produced by passing air over heated has far less harmful products, such as SO2 or NOx. Sulfur in a coal, coke or wood. Coal gas, also known as town gas, was gasifier forms H2S or COS, which can be converted to H2SO4 or produced from the partial combustion of coal and it contains a elemental sulfur easily. Nitrogen forms NH3 which can be mixture of carbon monoxide, hydrogen, methane, as well as removed with water. Since oxygen required for partial volatile gases produced from the coal and carbon dioxide. Coal combustion is much less in a gasifier than in an incinerator, the gas has higher calorific value than producer gas, but it is has volume of process gas is lower, the partial pressures of the significant amounts of impurities. Water gas is a syngas formed contaminants is higher in the off-gas, which is favorable for by passing steam over red hot coke, formed by the water-gas removal of contaminants by adsorption and gas cleaners. The shift reaction. It also contains impurities picked up from the syngas leaves the plant at a higher temperatures which prohibit coke. tar formation. Present day gasifiers may be divided into two main kinds The syngas from a gasifier is a pure, clean burning fuel, depending on how their energy is generated as thermochemical which can be used in fuel cells, internal combustion engines or gasifiers and plasma gasifiers. Thermochemical gasifiers derive converted into useful products such as methanol, gasoline, their heat from direct combustion (or partial combustion) of the diesel, other fuels, chemicals, fertilizers, etc. The end products feedstock and the heat generated drive the chemical reactions from a gasifier containing sulfur and nitrogen are valuable within the reactor sections. Their operating temperatures can go commodities. The solid waste generated in a gasifier has lower up to about 1,400°C. Of these there are four types of gasifiers volume than an incinerator plant and exits in a molten state available commercially, namely fixed-bed, fluidized-bed,

5 Copyright © 2016 by ASME which can be cooled and formed into desirable shapes, making petroleum, tars, plastics, biomass, tire waste, MSW, commercial it a useful raw material. These benefits are simply not available and industrial waste, and sewage sludge [23,24, 25]. Moreover, with incinerators. plasma gasifiers can also pyrolyze discarded electronic gadgets Syngas can also be used directly in an internal combustion and appliances that use metals, glass, plastics and other organic engine or a gas turbine, without the need for boilers. Thus, and inorganic materials in their construction. Thus, sorting of gasifiers can be made smaller and modular, for easy application MSW is not required for a plasma gasifier. Moreover, waste in a rural or sub-urban location. The water usage in a materials from electrical appliances, food packaging, and many gasification plant is much lower than that of an incinerator household and commercial items have plastics, paper or plant. cardboard and metals that are fused together, e.g., chewing gum Gasifiers can be used in combined cycle systems as well, wrappers, which cannot be mechanically separated. Plasma known as the integrated gasification combined cycle (IGCC) gasifiers can take in all such waste and gasify them. power plants. Thus, the production of CO2 per MWh as well as Materials that are wet or contain small amounts of water the production of pollution in gasifier combined cycle power can also be gasified in a plasma gasifier, as water vapor is one plants is significantly less than incinerator plants. of the reactants for the formation of syngas, as understood from the chemical reactions shown earlier. Thus, plasma gasifiers can PLASMA GASIFICATION directly turn sewage sludge and waste, with minimal drying, into syngas, eliminating the need for dumping them into rivers, Plasma gasification is a process in which the organic oceans or landfills. Plasma gasifiers can also take in materials feedstock, including MSW, coal, and other organic material, is that are classified as biomedical wastes and substances pyrolyzed in a plasma medium, causing them to be decomposed classified as hazardous materials, such as those that are into syngas. A schematic of the plasma arc gasifier is shown in corrosive, poisonous, or toxic. Fig. 1. The plasma temperature can be higher than 5,000°C and Plasma gasification can neutralize biohazard wastes, can theoretically exceed 13,000°C. However, the temperature at including infectious substances, refuse from hospitals and the region where the feedstock is in contact with the plasma can medical facilities, toxins, poisons, etc. All such matter are be 2,700–4,500°C. Plasma gasifiers have high thermal decomposed into their elemental stage or converted into clean efficiencies compared to conventional gasifiers. The syngas, thereby eliminating the need for specialized handling, temperature of the products downstream of the core plasma storing or dumping grounds. Pharmaceutical compounds that reaction zone is still high enough for secondary and tertiary are washed down into the sewage systems pose a major problem reactions to occur. Oxygen (from air) and/or steam can be by contaminating rivers, lakes and underground aquifers. The introduced at specific locations as required to achieve the pharmaceutical compounds cannot be completely eliminated by required mixture and form the desired products. At such high sewage treatment plants and end up in the fresh water sources temperatures, all organic compounds break down into simple and even the oceans. Plasma gasification is the best solution for gases, such as CO and H2. Inorganic components such as eliminating these compounds by gasifying the sewage sludge. metals, silicates, glass, etc. melt and collect together as a slag at The carbon dioxide emissions are much lower for a plasma the bottom of the reactor. The molten slag is piped off from the gasifier than conventional thermochemical gasifiers. Plasma bottom and it cools into a glassy, hard, vitrified substance which gasifiers take in air at the stoichiometric amount for aiding the is used for manufacturing architectural tiles, construction reactions and do not require oxygen, thus eliminating the need materials and for fillers in road building. for an oxygen plant. All contaminant gases such as fluorine, chlorine, etc. are reduced to elemental stage and can be easily ADVANTAGE OF PLASMA GASIFICATION OVER removed. Similarly, mercury is also removable from the reactor, CONVENTIONAL THERMOCHEMICAL GASIFICATION without contaminating the syngas. Harmful products such as Plasma gasification [1,20,21,22] has all the benefits of dioxins, furans and PCBs are eliminated by the plasma reactor. thermochemical gasification with many other added advantages. The syngas produced by plasma gasification can be directly The syngas leaves the gasifier at temperatures in excess of 1 burned in a gas turbine, internal combustion engine or 000 °C, which has a high heating value and can be used to run a combined cycle systems [25], without further purification combustion-turbine system to generate electricity. Such high processes. It can also be used in hydrogen fuel cells that can temperatures allow multi-stage cogeneration as well. The accept carbon monoxide admixture. The fuel product can be syngas produced is very clean, and can be used for feeding into used in a steam cycle or cogeneration system. The syngas can a fuel cell or for combustion in a clean burner. Upwards of 99% be further processed into hydrogen, liquid fuels or chemicals of the carbonaceous mater is converted to syngas. No tar is without extra cleaning. The efficiency of syngas production produced because at the high temperatures, all tars are gasified. from biomass is much higher for plasma gasification than No ash, char or residual carbon are produced as well for the conventional thermochemical gasification [25]. same reason. Plasma gasification can help bring about a nearly 0% waste A big advantage of plasma gasifiers is that it can process a to landfill solution. The solid residue from the decomposition is wide variety of materials, including coal, coke, lignite, a useful raw material for industry. The carbonaceous matter is

6 Copyright © 2016 by ASME completely converted into syngas. All other substances are decomposed into their elemental stages and can be removed to be used as raw materials. The syngas can be used for generating electricity and for producing other fuels and chemicals. Thus, nearly all the waste is converted to energy and useful raw materials, making this process environmentally friendly and sustainable.

TYPES OF PLASMA GASIFICATION The plasma gasifiers in usage today can be classified into two types based on the mechanism used for generating the plasma. The first type utilizes a plasma torch, similar in operation to that used for cutting metals in industrial workshops. This type of gasification is called plasma arc gasification or simply plasma gasification. The torch uses electrodes made out of copper, tungsten, graphite or alloys. The torch also uses a working fluid which is pumped through the gap in between electrodes, such as argon, nitrogen, air, oxygen FIGURE 1 SCHEMATIC OF THE PLASMA TORCH and others as per the conditions required within the reactor, and GASIFICATION SYSTEM. [24] the working fluid also performs the task of cooling the electrodes and the active regions of the torch. The torch may be The second type of plasma generator used for gasification powered by direct current or alternating current which may also is the microwave-induced plasma generator (MIPG) or simply extend into the radio frequency band. For waste-to-energy microwave plasma gasification, which will be described more in gasification, plasma torches rated at tens of MWs have been a subsequent section [26]. MPIG is a relatively new concept developed and alternating current power would be preferable as with many interesting research programs in progress around the they can be supplied from the electric grid through the world, and is the technology being promoted in this paper. At appropriate transformers and switchgear. Radio-frequency (RF) this time, there do not seem to be a commercial microwave plasma torches have been developed that use inductive coupling plasma gasifier in operation but several are proposed or in the or capacitive coupling to transmit the power to the torch construction phase. electrodes, but the current units have been rated at a few kilowatts (kW) mainly used for material synthesis applications MICROWAVE RADIATION such as plasma-enhanced thin-film deposition, material surface treatments, etc. and also in research of gasification, such as Microwave radiation [27] lies on the electromagnetic biomass pyrolysis [23]. The Westinghouse Plasma Corporation spectrum ranging from 300 MHz (1m wavelength) up to 300 (WPC), a subsidiary of the Alter NRG Corp., a Canadian GHz (1 mm wavelength), as shown in Table 2. On the lower end alternative energy company, has built many waste-to-energy of the frequency band, it overlaps with the higher radio (WTE) plants around the world, including three plants in Japan. frequency (RF) band, while on the upper end, it overlaps with One plant in Yoshii city rated at converting 166 short tonnes per the terahertz radiation band as well as the (lower) far infrared day (tpd) of MSW to energy has been in operation since 1999 band. Microwave frequencies are used for communication, [24]. WPC is one of the leading companies in plasma torch radar and heating in microwave ovens [27-29]. On the lower technologies. The torch is reported to consume about 2 % of the end of the microwave band, the RF signals can be transmitted energy generated by the plant. While the thermal efficiency on open parallel wires or coaxial cables, but they can also be (energy content of reactants going in to total energy content of transmitted in waveguides (resembling hollow metallic pipes, products) of a conventional WTE plant based on with circular or rectangular cross section, whose diameter is thermochemical gasification or incineration is rated to be equal to one-half the wavelength of the signal) or striplines, between 18-22%, the WPC’s integrated gasification combined which are flat metallic strip conductors sandwiched between cycle (IGCC) plant can deliver over 80% thermal conversion two flat conductors acting as electrical grounds, separated by a efficiency. In comparison, fluidized bed gasifier/combustor dielectric medium. plants that only produce electricity from the waste can reach The various bands of the electromagnetic spectrum are only about 62% thermal efficiency [24]. regulated by professional societies, such as the Institute of Electrical and Electronics Engineers (IEEE), national communication agencies, such as the Federal Communications Commission (FCC) in the US, and by international agreements, such as the International Telecommunications Union- Radio

7 Copyright © 2016 by ASME Regulations (ITU-R). These agencies have designated bands 150 MW), gyrotrons (8 GHz to 800 GHz), travelling wave and allocated them or specific uses. Certain bands have been tubes (300 MHz to 50 GHz, 100W to 100 MW), and others. labeled as industrial, scientific and medical (ISM) radio bands, These devices have been developed primarily for radar and for which are used for applications such as RF process heating, plasma heating purposes used in fusion research, and various microwave heating and medical diathermy machines used for versions of the above devices have been developed that are radiotherapy and chemotherapy. The ISM bands used for capable of generating microwave radiation at power ratings microwave heating applications are also shared with amateur from a few kW to 100s of MW. High powered microwave radio, communication systems such as Wi-Fi, Bluetooth, etc. as sources which are later versions of the above devices use pulsed well as radar, as shown in Table 2. Microwave heaters are power sources and can output microwave power for short available that operate at 915 MHz (for commercial and durations, lasting as long as a few nano-seconds, repeating at up industrial heating applications), 2.45 GHz (most home to a few kilo-hertz, thus achieving power ratings well into the microwave ovens as well as commercial and industrial heating giga-watts range [29]. However, these high powered microwave applications) and 5.8 GHz (industrial heating applications). Of devices. However, these can only run for short periods of time, these, 2.45 GHz is most commonly used for microwave ovens, lasting from a few seconds to a few minutes. The power both for home use and industrial or commercial use, as well as conversion efficiency is the ratio of the power of the radio for microwave plasma applications, such as for gasification frequency output of the device to the electrical power input. purposes, while 5.8 GHz is less commonly used and costs are Magnetrons have been reported to have about 65 % efficiency, therefore higher. while klystrons run at between 45-55% efficiency. Due to the popularity of microwave ovens, magnetrons are TABLE 2 THE VARIOUS BANDS OF THE MICROWAVE very easily available in many power ratings, and various RADIATION, SHOWING THE FREQUENCY RANGES, frequencies, and they have become highly efficient, over 65% WAVELENGTHS, AND PHOTON ENERGIES. ALSO, A efficiency reported at optimum operating frequencies. SHORT LIST OF APPLICATIONS WITHIN EACH BAND IS Magnetrons in the 1 kW range can be bought for as low as SHOWN. US$10 [28]. Magnetrons are the most widely used microwave

Name Photon energy (eV) Wavelength Frequency (Hz) sources for heating applications and are also used in microwave -3 -18 Radio 1.24x10 – 12.4x10 1 mm – 100,000 km 300x109 – 3 induced plasma gasification reactors. One advantage of using -3 -6 Microwave 1.24x10 – 1.24x10 1 mm – 1 m 300x109 – 300x106 -3 microwave sources for generating plasma is that it is not Infrared 1.7 – 1.24x10 750 nm – 1 mm 400x1012 – 300x109 12 12 imperative to have a large microwave source capable of a very Visible light 3.2 – 1.7 390 nm – 750 nm 770x10 – 400x10 Ultraviolet 124 – 3 10 nm – 400 nm 30x1015 – 750x1012 high power output in the MW or GW range. Microwaves make 12 15 X-ray 124 000 – 124 0.01 nm – 10 nm 30x10 – 30x10 it possible to build a reactor with multiple low-powered 18 Gamma ray > 62 100 < 0.02 nm > 15x10 magnetrons operating in parallel which can give a combined Name IEEE Classification Band Name Frequency high power rating. Radio/Micro- UHF 0.3 – 1 GHz (109 Hz) Recently, solid-state microwave sources have made the wave Ultra High Frequency L Long wave 1 – 2 GHz transition from cellphones and low-powered communications S Short wave 2 – 4 GHz systems to heating applications. One of the first entrants to the Compromise between C 4 – 8 GHz S and X market with a solid state microwave source was Freescale Microwave X Exotic, used in WW II 8 – 12 GHz Semiconductor, Inc. a US semiconductor company that was

Band spun out of Motorola in 2004 and was acquired in December Wavelength Photon energy (eV) Applications frequency 2015 by NXP Semiconductors, formerly a division of Philips, -6 ISM band; amateur radio (33 902 – 3.73x10 – 33.24 cm – 32.31 cm cm band); cordless phones the Dutch technology company [30]. Their RF transistor models 928 MHz (915 3.838x10-6 (32.76 cm center) and stereo; radio-frequency MHz center) -6 are based on the laterally-diffused metal oxide semiconductor (3.784x10 center) identification (RFID); datalinks ISM band; IEEE 802.11, field effect transistor (LDMOS) technology [31]. Solid-state RF 802.11b, 802.11g, 802.11n 2400 – -6 transistors offer many advantages over magnetrons. Magnetrons 9.926x10 – wireless LAN; IEEE 802.15.4- 2483.5 MHz 12.49 cm – 12.07cm 1.03x10-5 2006; Bluetooth; radio- use a supply voltage of about 2 kV or higher, have a life time of (2.45 GHz (12.24 cm center) -5 controlled aircraft; microwave center) (1.013x10 center) ovens; ZigBee; 2-way radios about 500 hours and performance degrades over time. The RF incl. FRS, GMRS; GPS transistors use a DC supply voltage of 28-50 V and can last up 5.725 – ISM band; Amateur radio; 5.875 GHz 5.24 cm – 5.1cm 2.37x10-5 – 2.43x10- to 20 years with no performance degradation. The DC operation radar; earth stations (5.8 GHz (5.17 cm center) 5 -5 enables the transistors to be operated from low voltage power (2.399x10 center) (satellite links) center) supplies, such as solar photo-voltaic systems, battery packs and vehicular power generator systems (e.g., buses, airplanes, ships, MICROWAVE GENERATORS etc.), and eliminates the necessity for heavy and bulky power Microwaves [26-29] are most commonly generated using a conversion systems such as transformers, and the associated vacuum tube devices known as the magnetron. Other vacuum switching gear. Unlike magnetrons, the properties of the RF tube sources include klystrons (300 MHz to 40 GHz, 100 W to generated by solid-state devices can be controlled for phase, amplitude, and frequency and their smaller size makes it

8 Copyright © 2016 by ASME possible to more finely direct the energy towards the target. The that these materials can be selectively used for construction or MHT1003N model is rated at 250 W, 32 V operating voltage thermal insulation in a reactor. outputting 2.45 GHz at up to 58% overall efficiency and the MHT1002N is rated at 350 W, 50 V supply voltage outputting MICROWAVE HEATING 915 MHz radiation at 63% power-added efficiency (PAE), In conduction or convection, heat travels very slowly and which is defined as shown in the equation below, where the depends on the conductivity of the material or the convection numerator is the difference between the RF power output by the coefficients. The container of the material being heated has to source and the RF power input to the source from an oscillator be heated to a higher temperature to create a differential for the and the denominator is the DC power supplied to the source. heat to flow to the material inside, which creates losses of

energy. Microwave radiation passes through transparent (5) materials such as quartz or ceramic and penetrates the material within, direct coupling its energy with the molecules of the The Chinese electrical appliance manufacturer, Midea material causing the bulk of the material to be heated Group, has several patents for microwave ovens using the simultaneously. Thus, heat transfer happens very quickly with LDMOS RF transistors and have demonstrated some working much less loss of energy to the surroundings. prototypes [32]. It is likely that the price of solid-state Microwaves interact with materials in four different ways microwave sources will drop considerably as more and more [26,28,29,33]. Conductive materials, such as metals, reflect the models enter the market, making them cheap and viable for waves, and appear to be opaque to the microwave radiation. building small or modular microwave-induced plasma Insulating materials, such as ceramics, Teflon, air and gases gasification units. Similar to the magnetrons, many RF only absorb a tiny amount of the energy and appear as transistors can be used in parallel within a reactor to increase transparent materials to the radiation. Many materials absorb the power input to the gasification process. much of the wave energy, such as water, food, certain biomass, The electron density within the plasma generated by the etc. and convert the wave energy to heat. Magnetic materials, microwave source increases with the frequency of the such as ferrites, interact with the magnetic field of the wave and microwave radiation. Higher frequencies also allow heating to convert it into heat. occur faster as the electron energy is higher [33]. The Microwaves heat materials in four different ways due to the waveguides get smaller with increasing frequency. Thus, the polarizing effects of the alternating electric and magnetic fields 2.45 GHz frequency is more preferable than the 915 MHz. Cost of the wave acting on the molecular or atomic structure of the of 2.45 GHz magnetrons are lower due to economy of scale of materials, creating kinetic energy to be generated which is then production, as compared to 915 MHz and the 5.8 GHz sources. converted to heat. Electronic polarization occurs in covalent Another reason for choosing the 2.45 GHz frequency over solids with valence electrons whereby the valence electrons are the 915 GHz is the penetration depth which is defined as the cyclically shifted from equilibrium by the alternating electric distance from the surface of the material at which the irradiated field of the wave. This cyclic polarization of the electrons microwave power reduces to 36.8 % or 1/e of the value at the causes heating to occur. Silicon and germanium crystals exhibit surface [28,33]. Generally, shorter penetration depths mean that this effect. more energy is being absorbed by the material. For water at Dipolar polarization is the most important means of heating 25°C, the penetration depth is 38.26 cm for a 915 MHz wave that occurs in microwave ovens. Atoms or molecules of most 1.44 cm for a 2.45 GHz wave. However, at 95°C, it is 5.7 cm dielectric (insulating) materials possess a permanent dipole making it more difficult to heat water at higher temperatures. At moment and they are randomly aligned in the normal state. temperatures above 374°C, supercritical water is transparent to When the microwave radiation, which has an alternating electric microwave irradiation. Also, ice at -12°C has a value of 1,100 and magnetic field, strikes the material, the dipoles are caused cm, showing why it is difficult to heat frozen food in the to oscillate by the varying electric field. This causes the microwave. material to heat up rapidly. For paper, the penetration depths are 43.66 cm for 915 Interfacial polarization occurs in materials with free MHz and 16.01 for 2.45 GHz. The penetration depths for electrons that accumulate at interfaces within the material, grain metals compared to dielectrics are much lower, e.g., the values boundaries, or between the free surfaces of mixtures of for waves of 915 MHz and 2.45 GHz for aluminum are 2.7 µm materials. In the presence of the alternating electric field, the and 1.7 µm, and for iron, they are 5.2 µm and 3.2 µm free electrons and charges are caused to oscillate at the respectively. interfacial boundaries, causing heat to be generated. Certain inorganic materials are have large values of Ionic polarization occurs in ionic substances such as penetration depths. At 25°C, glass has a penetration depth of 35 crystals of potassium fluoride, sodium chloride, and other alkali cm, alumina ceramic has 633 cm, Teflon has 9,200 cm, and halides, or ionic liquids such as tap water, in which the ions are quartz glass has 16,000 cm, all for 2.45 GHz wave. It means oscillated by the alternating electric field, causing them to move, collide and to generate heat.

9 Copyright © 2016 by ASME In addition to the polarization mechanism, yet another oxygen is supplied to the microwave induced plasma according effect occurs in metals and semiconductor. The oscillating to the stoichiometric ratio of the reactants. [39-46] magnetic field of the wave induces oscillating eddy currents to The electrodes of the torch experience wear during flow on the surface, which creates heat in the material through operation, giving it a short lifespan. The reactor has to be shut ohmic (or resistance) heating. This flow of eddy currents on the down periodically to remove and upgrade the torch surface is known as skin effect. Thin metal films heat up rapidly components. due to skin effect ohmic heating, as a result of which they can The plasma torch cannot be controlled for varying its be seen to spark within microwave ovens. Graphite and silicon power consumption, energy output or temperature. The carbide absorb microwave energy in this way, and these microwave generator, which may be a magnetron, can be substances can be added to the microwave reactor as passive controlled easily to modulate the power output and thereby the heating elements called suscepters. energy input into the reactants and the temperature of the In a microwave reactor, all the above forms of heating can plasma. Solid-state microwave generators can be controlled for happen within the reactants, causing heat to build up inside the varying the power, phase and frequency. Microwave sources are bulk of the materials. Materials will conduct or convect heat to much more compact and easy to operate in comparison to the the surroundings as they are internally heated by the radiation. plasma torch, or arc discharge unit, which require massive Since the matter is confined within the reactor, temperatures power transformers and switching gear, all of which add to the shoot up rapidly and ionization occurs thereby initiating the costs. formation of a thermal plasma which is then sustained by the Many microwave generators can be added in parallel to a energy of the microwave radiation. reactor to get the required power rating, with only a minimal Microwaves generated by high powered gyrotrons are used increase in complexity of the overall system. Thus, microwave to create plasmas of very high temperatures in nuclear fusion plasma gasifiers can be made smaller and modular and give research. Low powered microwave induced plasmas (100s to a much better cost savings. few 1000s of watts) are used as sources of excitation for optical The initial investment costs of the plasma torch gasifying emission spectrometry and mass spectrometry. Spectrometry system is very high, running into the hundreds of millions of US being an established science can be directly applied for dollars. This is the biggest setback for investors and public diagnostics within the plasma reactor. Reactants and products utility management organizations. As a result, the plasma can be identified through spectroscopy. It can be used to gasifier plants tend to be large in size to match an economy of determine whether more or less oxygen or steam is required for scale and return on investment. The plant cannot be easily the reaction. Or some materials can be directed for further scaled up or down. On the other hand, microwave sources are processing or removed out of the reactor through ports when very cheap, and many brands and models with high efficiencies they are determined to be in the proper chemical constituency. are available now. The gasifier plant can be scaled to whatever Other lower temperature, non-plasma microwave size is required and costs can be kept low. applications [26,28] include sintering and processing of metals, Microwave sources allow multiple frequencies to be used, ceramics, woods, making of steel and synthesis of organic allowing the reactor to be tuned for particular reactants and chemicals [20]. Microwave heating is used for lower products. Also, different stages of the reactor can be designed to temperature pyrolysis of biomass, such as wood, plastics and operate at different temperatures and pressures. For example, a other wastes [34-36]. lower temperature primary stage can be set up where some useful volatile gases can be removed or the material can be ADVANTAGE OF MICROWAVE PLASMA SOURCES partially processed and removed before the rest of the matter is OVER PLASMA TORCH SOURCES fully pyrolyzed to syngas. Thus, microwave induced plasma systems enable much more versatility in the design of the In a plasma torch generator, a significant amount of reactor and plant all at a much lower cost. parasitic heat is lost to the body and housing of the torch, as well as to the cooling system. A working fluid is converted to plasma which then transfers the heat to the reactant materials. Thus, there is loss of heat at every stage. The working fluid in some cases may be a gas such as argon, which can add to the running costs. The heat is transferred to the working fluid right outside the mouth of the torch where the plasma is created. Thus, the effective work area is limited in size by the size of the torch. Microwave sources irradiate the reactant materials directly, which is heated inside out, without any initial loss of heat by convection or conduction. Expensive working fluids such as argon or nitrogen are not required. Limited amounts of

10 Copyright © 2016 by ASME into the river. A pay-per-use or periodic subscription fee can be charged for users of this waste disposal service. For people who have residences along the sides of the river or lake who dump their kitchen, toilet and other sewage wastes into the river, a vacuum tank truck service could be started with periodic subscription programs so that sewage is collected from a septic tank at the residences [46,47]. Gradually, the sewage collection system could be extended into a drainage system that pipes the sewage directly into the gasification plants. Thus, the gasifier will have a steady inflow of feedstock material from the community that it serves. As the gasifier system scales up to meet the waste processing demand, more gasification reactors can be added to the plant, and the gasifier could handle MSW and industrial or commercial waste materials from the community. Microplastics present in the river water will have to be strained out and gasified. Larger sizes of garbage can be shredded to the appropriate particle size before gasification. Wet sewage sludge collected can be directly fed into the

FIGURE 2 A SCHEMATIC OF A MICROWAVE-INDUCED gasifier, since water is a part of the hydrogen production PLASMA GASIFIER. reaction (water shift reaction) [42]. The quality of the syngas will need to be analyzed or modelled to study the effects of MICROWAVE PLASMA SOLUTIONS FOR CLEANING various feedstock. But, based on pyrolysis studies, the syngas RIVERS, LAKES, BEACHES AND INLAND WATER product can power a cogeneration system, with some of the BODIES electricity being used to power the plant. The plant will have to For polluted water bodies with flowing water, such as be connected to the electricity grid to power up the gasifier and rivers, streams and navigable water ways, the solution is to set to operate it during down times. The excess electricity up a microwave-induced plasma gasifier station with a collector generated by the plant can be fed into the grid. The solid wastes system which strains the water and removes solid particles and can be sold to industries that can convert them into useful raw contaminants. The collector could be in the form of a motorized materials. Substance such as chlorine, fluorine, Sulphur, etc. water wheel that dumps the solids onto a conveyor system while need to be collected and sold to appropriate industrial also aerating the water. A boat with a comb and boom could customers [44]. Thus, all the waste can be converted to energy drive the refuse towards the collector station. A mechanized hoe and raw materials. It is also possible to feed the carbon dioxide will be required to remove heavy or immobile material, such as back into the gasifier in regulated quantities to be converted tree trunks and matter caught in brushes to clear the flow path. back into syngas [45]. The gasifier reactor is fed from a conveyor system that feeds Lakes and placid water bodies with heavy pollution can into a shredder to reduce the particle size of the materials. have one or more microwave gasifiers situated at the periphery Smaller particles will gasify faster due to their larger surface of the body. Beaches and shores of lakes, rivers, etc. will need area and is able to absorb heat from its surroundings the use of street sweeper trucks and crews to collect and deliver conventionally in the reactor. the waste from these locations. Microwave gasification can The operating frequency of the microwave source can be neutralize the pharmaceuticals, insecticides, toxins and other set at 2.45 GHz for lower costs and ease of availability of chemicals contained in the sewage sludge. Since the products of sources. A solid-state microwave source would be preferable for the gasifier are all clean, this plant can be placed close to a ship-based microwave gasifier due to their lower operating heavily inhabited locations and will act as a waste disposal and voltages, low energy consumption, lower size and mass, better cleansing station for the community while providing it with controllability and absence of high voltage transformers and power, sanitation services, useful materials and a source of switching gear, both of which would have added costs and employment. weight. However, magnetrons are cheaper, highly efficient, easily available and serviceable. It would be advisable to use several magnetrons of about 10 kW to bring the power up to MICROWAVE PLASMA SOLUTIONS FOR CLEANING required levels, thus saving initial costs. Several such GARBAGE PATCHES IN OCEANS AND TO ELIMINATE microwave gasifier stations could be set up along rivers at, say, OIL AND CHEMICAL SPILLS 2 to 3 km intervals. Many suggestions have been made to clear the garbage Such a gasifier station could also accept trash from local patches in the oceans, including pyrolysis of the plastics and inhabitants so that they do not continue to discard their garbage

11 Copyright © 2016 by ASME turning them into oil or diesel onboard ships [12,13]. However, Methanol is formed by a one-step synthesis from syngas, or these solutions are not clean because they fail to account for from methane (syngas to methane to methanol is also possible). contaminants that are adsorbed by the plastics, including heavy Methanol can be further converted by the Fischer-Tropsch metals, pesticides such as DDT, PCBs, carcinogens, etc. [7]. In process in gasoline and diesel [1]. Thus, it is proposed that the addition, pyrolysis of the plastics and biomass from the oceans syngas derived by the microwave gasification of ocean garbage can release dioxins, furans and other toxins. Also, pyrolysis or patches be turned into methanol, which can also be used to run combustion processes cannot handle the large content of the engines on board the reactor ship. moisture and salt that come with the waste material, which One profitable option available for using the energy and would require preprocessing prior to the waste-to-energy carbon produced by the microwave plasma reactor would be conversion process. diamond synthesis from the carbon plasma [58]. An additional Therefore, the best option for eliminating the garbage diamond synthesis reactor could be added to the microwave patches while also neutralizing hazardous wastes associated gasifier so that some of the carbon in gaseous state could be with them is microwave-induced plasma gasification (MIPG) bled off to coat materials with thin layers of diamonds or to reactors placed on ships. The ships can have systems of booms produce artificial diamonds using the well-known carbon vapor and combs to collect the debris from the water and convey them deposition process (CVD). The applications of CVD include the into a shredder prior to gasification. This system should be manufacture of cutting tools, thermal conductors for laser capable of drawing in the microplastics while at the same time diodes and high powered semiconductors, electronic preventing fish and aquatic creatures from being sucked into the components and optical materials. Thus, the gasifier ship could conveyor system. The sea water can be used for cooling the be an ocean going factory producing valuable commodities out reactor. Some amount of desalination will have to be done, to of the ocean garbage patches. get clean water for processes, and the waste heat from the The waste generated on board the ship, including kitchen reactor could be used for this purpose. and toilet wastes [46,47], as well as other solid wastes could Once the waste is in the gasifier, the syngas produced can also be fed right into the gasifier. Some of the products could be used to power a gas turbine and steam cycle-cogeneration then be applied for the CVD diamond synthesis as well. system to provide power to the onboard systems [25]. The ship The microwave gasifier ships can also be used to clean up will need a small generator running on methanol or diesel to oil spills. The oil floating on the sea can be collected with provide initial power. The salt can be converted to sodium or booms, while beach sand contaminated with oil will have to be turned into sodium nitrates for use in molten salt energy storage scooped up. All these can then be directly input into the gasifier systems. Ocean water contains trace elements, including gold, and converted to syngas and useful raw materials. selenium, silver, antimony, cobalt, nickel, manganese, etc. All of the above suggestions would mean that the [49,50] There are also small quantities of rare earths [51 - 54,] application of microwave plasma gasification for the such as scandium, yttrium, lanthanum, cerium, neodymium, and elimination of the ocean garbage patches could be a very other lanthanides. MIPG reduces all dissolved substances into profitable, environmentally conscious and sustainable their elemental states. It may be profitable to extract trace enterprise. elements and rare earths out of the sea water that is used for cooling the reactor on board. CONCLUSION A portion of the syngas can be fed into a Fischer-Tropsch A vast literature survey was done to identify the problems reactor [55] to convert to methanol using a well-established associated with the contamination of rivers, lakes and water method of synthesis that has been in use since the 1920s. The bodies located near densely populated centers in developing syngas to methanol synthesis is exothermic and is shown below. countries, by sewage, household wastes, biological wastes and

synthetic wastes. The waste accumulation creates pollution, 2 H2 + CO → CH3OH ; ΔHr = -92 kJ/mol (6) breed disease-carrying vectors, and harm wildlife and humans.

Plastics and floating synthetic wastes originating on land are Even though methanol only has a calorific value of 20 carried off by rivers into oceans. Ocean currents, called gyres, MJ/kg (HHV), compared to diesel (44.8 MJ/kg HHV) and carry the waste and accumulate them in specific regions in the gasoline (47 MJ/kg HHV), methanol has been gaining much oceans. In addition, trash and refuse discarded from ships along attention as a marine fuel [50,51]. Methanol has been shipping lanes are also transported by the gyres. The plastic transported by truck and sea for over a hundred years. Thus, the trash form a wide field of floating plastic and debris that harm modification needed for storage and handling is minimal or or kill the fish, birds and animals. The debris are predominantly none in many cases. The conversion on the engines, such as visible just below the surface of the water. The plastics larger fuel ports on the injectors, are also minimal and cost disintegrate into tiny particles called microplastics, due to the effective. It is not derived from crops that may hurt the food action of the sun and waves. The plastics also adsorb pesticides supply, such as corn, sugar cane or sugar beet. It is easily and and toxins which can kill fishes and enter the food chain. Many safely storable, and biodegradable. It is a very clean burning fuel on which engines have been known to perform well.

12 Copyright © 2016 by ASME studies have been done and proposals made to clean up the [12] Tremblay, J. F., 2009, "Mining the sea of plastic," garbage patches but most are not feasible. Chemical and Engineering News, 87(33). Gasification is looked at as a better method of turning [13] Sigler, M., 2014, "The effects of plastic pollution on MSW and other waste to energy in the form of syngas. aquatic wildlife: Current situations and future solutions," Water, Microwave-induced plasma gasification is presented as the most Air, and Soil Pollution, 225(11). cost-effective, versatile, modular and efficient method of [14] Luque, R., and Speight, J., 2014, Gasification for Synthetic turning waste to energy and raw materials. It is also able to take Fuel Production: Fundamentals, Processes and Applications, in all kinds of waste without pre-sorting or pre-treatment, Elsevier. including waste with high moisture content, as well as [15] Brar, S. K., Dhillon, G. S., and Soccol, C. R., 2014, hazardous and biomedical wastes. A microwave plasma Biotransformation of waste biomass into high value gasification system is presented as the best solution for cleaning biochemicals, Springer. up the waste contamination in rivers, lakes and urban water [16] Young, G. C., 2010, Municipal solid waste to energy bodies, as well as beaches and seas. Finally, a ship based conversion processes: economic, technical, and renewable microwave plasma gasification system coupled with a Fischer- comparisons, John Wiley & Sons. Tropsch processor is presented as the best solution for cleaning [17] Shah, Y. T., 2014, Water for energy and fuel production, up the garbage patches accumulating in oceans. CRC Press. [18] Ouda, O. K. M., and Raza, S. A., "Waste-to-energy: REFERENCES Solution for Municipal Solid Waste challenges- global perspective," Proc. ISTMET 2014 - 1st International [1] Basu, P., 2013, Biomass gasification, pyrolysis and Symposium on Technology Management and Emerging torrefaction: practical design and theory, Academic press. Technologies, Proceedings, pp. 270-274. [2] Chandrappa, R., and Das, D. B., 2014, Sustainable water [19] Arafat, H. A., and Jijakli, K., 2013, "Modeling and engineering: theory and practice, John Wiley & Sons. comparative assessment of municipal solid waste gasification [3] Chandrappa, R., and Brown, J., 2012, Solid waste for energy production," Waste management, 33(8), pp. 1704- management: principles and practice, Springer Science & 1713. Business Media. [20] Kappe, C. O., Dallinger, D., and Murphree, S. S., 2009, [4] Sørum, L., Grønli, M. G., and Hustad, J. E., 2001, Practical Microwave Sythesis for Organic Chemists - Strategies, "Pyrolysis characteristics and kinetics of municipal solid Instruments, and Protocols, Wiley-VCH, Weinheim. wastes," Fuel, 80(9), pp. 1217-1227. [21] Dias, F., Bundaleska, N., Henriques, J., Tatarova, E., and [5] Panda, A. K., Singh, R. K., and Mishra, D. K., 2010, Ferreira, C., "Microwave plasma torches used for hydrogen "Thermolysis of waste plastics to liquid fuel: A suitable method production," Proc. Journal of Physics: Conference Series, IOP for plastic waste management and manufacture of value added Publishing, p. 012002. products—A world prospective," Renewable and Sustainable [22] Janajreh, I., Raza, S. S., and Valmundsson, A. S., 2013, Energy Reviews, 14(1), pp. 233-248. "Plasma gasification process: Modeling, simulation and [6] Kaiser, J., 2010, "The Dirt on Ocean Garbage Patches," comparison with conventional air gasification," Energy Science, 328(5985), p. 1506. Conversion and Management, 65, pp. 801-809. [7] Rios, L. M., Jones, P. R., Moore, C., and Narayan, U. V., [23] Tang, L., and Huang, H., 2005, "Biomass gasification 2010, "Quantitation of persistent organic pollutants adsorbed on using capacitively coupled RF plasma technology," Fuel, plastic debris from the Northern Pacific Gyre's “eastern garbage 84(16), pp. 2055-2063. patch”," Journal of Environmental Monitoring, 12(12), pp. [24] Juniper Consultancy Sevice, 2008, "Independent Waste 2226-2236. Technology Report: The Alter NRG/Westinghouse Plasma [8] Foekema, E. M., De Gruijter, C., Mergia, M. T., van Gasification Report," Bathurst House, Bisley, GL6 7NH, Franeker, J. A., Murk, A. J., and Koelmans, A. A., 2013, England. "Plastic in North Sea Fish," Environmental Science & [25] Rutberg, P. G., Bratsev, A. N., Kuznetsov, V. A., Popov, V. Technology, 47(15), pp. 8818-8824. E., Ufimtsev, A. A., and Shtengel, S. V., 2011, "On Efficiency of [9] Van Sebille, E., England, M. H., and Froyland, G., 2012, Plasma Gasification of Wood Residues," Biomass and "Origin, dynamics and evolution of ocean garbage patches from Bioenergy, 35(1), pp. 495-504. observed surface drifters," Environmental Research Letters, [26] Shuttleworth, P., Budarin, V., and Gronnow, M., 2013, 7(4). "The Thermochemical Conversion of Biomass into High-Value [10] Ryan, P. G., 2015, "A brief history of marine litter Products: Microwave Pyrolysis," The economic utilisation of research," Marine Anthropogenic Litter, pp. 1-25. food co-products, A. Kazmi, and P. Shuttleworth, eds., RSC [11] Gerlach, D. W., "A modest proposal1 for the removal of Publishing, Cambridge, UK. floating rubbish from the north pacific central gyre," Proc. [27] "Microwave," https://en.wikipedia.org/wiki/Microwave. ASME 2011 International Mechanical Engineering Congress [28] Gupta, M., and Wong Wai Leong, E., 2007, "Microwaves and Exposition, IMECE 2011, pp. 1101-1103. and Metals," John Wiley & Sons (Asia), Singapore.

13 Copyright © 2016 by ASME [29] Benford, J., Swegle, J. A., and Schamiloglu, E., 2007, High sustainability analysis for upgrading human waste to power," power microwaves, CRC Press. Energy, 68, pp. 377-384. [30] "NXP Semiconductors," http://www.nxp.com/. [47] Shinogi, Y., and Kanri, Y., 2003, "Pyrolysis of plant, [31] Sechi, F., and Bujatti, M., 2014, Solid-state microwave animal and human waste: physical and chemical high-power amplifiers, Artech House. characterization of the pyrolytic products," Bioresource [32] Tang, X., Ou, J., and Liang, C., 2012, "Semiconductor Technology, 90(3), pp. 241-247. microwave oven and microwave feeding structure thereof," [48] Westphal, G., Kristen, G., Wegener, W., Ambatiello, P., Google Patents. Geyer, H., Epron, B., Bonal, C., Steinhauser, G., and Götzfried, [33] Moisan, M., Barbeau, C., Claude, R., Ferreira, C. M., F., 2000, "Sodium Chloride," Ullmann's Encyclopedia of Margot, J., Paraszczak, J., Sá, A. B., Sauvé, G., and Wertheimer, Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA. M. R., 1991, "Radio frequency or microwave plasma reactors? [49] Schutz, D. F., and Turekian, K. K., 1965, "The Factors determining the optimum frequency of operation," investigation of the geographical and vertical distribution of Journal of Vacuum Science & Technology B, 9(1), pp. 8-25. several trace elements in sea water using neutron activation [34] Appleton, T. J., Colder, R. I., Kingman, S. W., Lowndes, I. analysis," Geochimica et Cosmochimica Acta, 29(4), pp. 259- S., and Read, A. G., 2005, "Microwave technology for energy- 313. efficient processing of waste," Applied Energy, 81(1), pp. 85- [50] Nozaki, Y., 1997, "A fresh look at element distribution in 113. the North Pacific Ocean," EOS Transactions, 78, pp. 221-221. [35] Beneroso, D., Bermúdez, J. M., Arenillas, A., de la Peña, [51] Alibo, D. S., and Nozaki, Y., 1999, "Rare earth elements in F., García, J. L., Prieto, M. A., and Menéndez, J. A., 2015, "Oil seawater: particle association, shale-normalization, and Ce fractions from the pyrolysis of diverse organic wastes: The oxidation," Geochimica et Cosmochimica Acta, 63(3), pp. 363- different effects of conventional and microwave induced 372. pyrolysis," Journal of Analytical and Applied Pyrolysis, 114, pp. [52] De Baar, H. J. W., Bacon, M. P., Brewer, P. G., and 256-264. Bruland, K. W., 1985, "Rare earth elements in the Pacific and [36] Ludlow-Palafox, C., and Chase, H. A., 2001, "Microwave- Atlantic Oceans," Geochimica et Cosmochimica Acta, 49(9), Induced Pyrolysis of Plastic Wastes," Industrial & Engineering pp. 1943-1959. Chemistry Research, 40(22), pp. 4749-4756. [53] Elderfield, H., Upstill-Goddard, R., and Sholkovitz, E. R., [39] Lupa, C. J., Wylie, S. R., Shaw, A., Al-Shamma'a, A., 1990, "The rare earth elements in rivers, estuaries, and coastal Sweetman, A. J., and Herbert, B. M., 2012, "Experimental seas and their significance to the composition of ocean waters," analysis of biomass pyrolysis using microwave-induced Geochimica et Cosmochimica Acta, 54(4), pp. 971-991. plasma," Fuel Processing Technology, 97, pp. 79-84. [54] Elderﬁeld, H., and Greaves, M. J., 1982, "The rare earth [40] Lupa, C. J., Wylie, S. R., Shaw, A., Al-Shamma'a, A., elements in seawater," Nature, 296(5854), pp. 214-219. Sweetman, A. J., and Herbert, B. M., 2013, "Gas evolution and [55] Psarras, P. C., 2015, "Toward an Understanding of syngas heating value from advanced thermal treatment of waste Methane Selectivity in the Fischer-Tropsch Process," Cleveland using microwave-induced plasma," Renewable Energy, 50, pp. State University. 1065-1072. [56] Andersson, K., and Salazar, C. M., 2015, "Methanol as a [41] Chaichumporn, C., Ngamsirijit, P., Boonklin, N., Marine Fuel Report," Report, Methanol Institute, FCBI Energy. Eaiprasetsak, K., and Fuangfoong, M., 2011, "Design and [57] Chudnovsky, B., Reshef, M., Keren, M., and Baitel, S., Construction of 2.45 GHz Microwave Plasma Source at "Successful Implementation of Methanol Firing at 50 MW Gas Atmospheric Pressure," Procedia Engineering, 8, pp. 94-100. Turbine for Long Term Operation," Proc. ASME 2015 Power [42] Djebabra, D., Dessaux, O., and Goudmand, P., 1991, Conference collocated with the ASME 2015 9th International "Coal gasification by microwave plasma in water vapour," Fuel, Conference on Energy Sustainability, the ASME 2015 13th 70(12), pp. 1473-1475. International Conference on Fuel Cell Science, Engineering and [43] Gadonna, K., Leroy, O., Leprince, P., Boisse-Laporte, C., Technology, and the ASME 2015 Nuclear Forum, American and Alves, L. L., 2012, "Study of gas heating by a microwave Society of Mechanical Engineers, pp. V001T003A015- plasma torch," Journal of Modern Physics, 3(10), p. 1603. V001T003A015. [44] Kim, J. H., Cho, C. H., Shin, D. H., Hong, Y. C., and Shin, [58] Kamo, M., Sato, Y., Matsumoto, S., and Setaka, N., 1983, Y. W., 2015, "Abatement of fluorinated compounds using a 2.45 "Diamond synthesis from gas phase in microwave plasma," GHz microwave plasma torch with a reverse vortex plasma Journal of Crystal Growth, 62(3), pp. 642-644. reactor," Journal of Hazardous Materials, 294, pp. 41-46. [45] Kwak, H. S., Uhm, H. S., Hong, Y. C., and Choi, E. H., 2015, "Disintegration of Carbon Dioxide Molecules in a Microwave Plasma Torch," Scientific Reports, 5, p. 18436. [46] Liu, M., Woudstra, T., Promes, E. J. O., Restrepo, S. Y. G., and Aravind, P. V., 2014, "System development and self-