Excerpts from “Technological Regulations, initial data and recommendations for designing a plant-module for thermochemical processing of municipal waste”. Part2
According to the technological scheme, municipal waste is crushed, ferrous, non-ferrous metals and cullet are separated at special separators and the remainder is mixed with limestone sifting residue. The mixture is dried in a steam dryer which utilizes steam waste from heat boilers working on waste heat from flue and pyrolysis gases. If the incoming waste has high humidity level, after crushing, it is preliminary pressed in a screw press, In cold climate areas, part of hot dried waste is recirculated, to be mixed with the waste entering the dryer. Such a combined scheme of removing water from waste before its pyrolysis allows efficient processing of waste of any humidity, including frozen waste.
Pyrolysis process takes place in a rotating drum of the pyrolysis furnace heated by the outgoing flue gases of the firebox. Heat transfer takes place through the drum surface, i.e. without direct contact of the flue gases with the mass under pyrolysis. During the first stage of pyrolysis, halogen-containing components in the garbage, i.e. plastics containing chlorine (polyvinyl chloride, linoleum, etc.), get completely decomposed at a temperature of 200-250њу (390-480њF), releasing Hydrogen Chloride, which is neutralized by limestone to form Calcium Chloride (CaCl2). At the same time, sulfur compounds contained in municipal waste will be also neutralized with limestone. During the second stage of pyrolysis, the pre-treated waste is heated to a higher temperature of 500њC (930њF), sufficient to decompose other organic matter contained in the waste. Polychlorinated dioxins, furans and biphenyls are not formed during the process, because all the chlorine from the treated waste was removed at the previous stage of pyrolysis. Besides, absence of air and, consequently, free Oxygen, completely eliminates combustion in the furnace drum, which ensures the gas mixture composition to be practically insensitive to possible fluctuations in the composition of the initial solid waste (17 ). Thus, while all known processes of purification of pyrolysis gases produced in waste products processing are performed on special gas-cleaning equipment, the proposed process takes steps to ensure that highly toxic and dangerous products do not form in the furnace of pyrolysis space at all, i.e. conditions have been created to prevent formation of dioxins, which is much simpler than binding molecular chlorine and especially destroying dioxin.
Gases released during pyrolysis and vapors from the process equipment are condensed, the condensate is separated in the sump. Water after the source waste is pressed, together with water condensate formed during condensation of the pyrolytic gas are blown away from the light organic matter by air supplied then to the firebox as an air stream. The water purified from lightly volatile organic substances is used in the system of extraction from the solid residue of pyrolysis of water-soluble salts and heavy metal ions, and, at the same time, dissolves Calcium Chloride produced during the first stage of pyrolysis. Then the wash water is cleaned in a sorption filter loaded with activated carbon, and in a galvanocoagulator. This procedure removes heavy metals from the system as a concentrate (coal + heavy metals), instead of releasing them into the environment. The technology allows to separate 100% of Mercury and 90% of the remaining heavy metals compounds. Burial of activated carbon and sorbed heavy metals is excluded. Depending on local conditions, used activated Carbon is to be delivered, as a marketable product (additive to furnace mixture), to non-ferrous metallurgy enterprises or to a company engaged in production of activated Carbon and its usage in purifying various substances, for Carbon regeneration and reusage.
Then the water, purified from heavy metals and odors, filled with dissolved Calcium Chloride, is dried in a spray-drying unit (production of dry Calcium Chloride), heated with exhaust smoke gases from the pyrolysis furnace, which are then used for thermal - moisture treatment of slag products and production of liquid Carbon Dioxide by the standard method (12), applying Monoethanolamine and the steam from exhaust-steam boilers. This way, all the resulting technological condensate is used in the course of technological processes, which eliminates its discharge and, accordingly, there is no need for construction of a sewerage network and wastewater treatment plants.
Excess moisture, constantly coming from the original waste, is removed from the system during Calcium Chloride drying. Consumption of fresh industrial water from outside sources is also excluded. Hence, the environment water balance remains intact. Drinking water from the local water-supply line is used only for hot water supply, shower cabins, wash-stands, rest-rooms, the plant laundry and the plant canteen.
The non-condensable part of the pyrolysis gas, together with part of condensed liquid organic products, are sent to the furnace for co-combustion with solid pyrolysis residue of washed out of heavy metals (coal-mineral composition). Combustion takes place in three stages, which significantly reduces the emission of Nitrogen oxides into the atmosphere (9, 10, 11). Ventilation air from the premises and air from the processing equipment is fed to blow-off the condensate from the volatile organic matter, then it is heated at the expense of slag being dry cooled while coming out of the furnace, and enters the same furnace in a forced blast. Air consumption equals the needs of the combustion process in the furnace, which ensures its full use, completely eliminating the release of contaminated blast air into the environment. The cooled slag, purified from glass, heavy metals and sulfuric compounds, and water filled with dissolved Calcium Chloride (an accelerator of concrete hardening) are used for manufacturing slag-concrete products. The remaining liquid organic products (pyrolysis resin) are removed from the system as commercial synthetic liquid fuel. Multistep utilization of the heat of flue gases coming out of the firebox, together with the heat generated during condensation of some of water vapor generated in combustion of Hydrocarbon fuels, by sequential cooling and release into the smoke stack at 85њC (185њF) provides a high fuel utilization rate (> 100%), and, respectively, its output to the market. Previously produced liquid fuel or fuel from foreign sources are to be used only during the plant start-up.
Electronic, electrical and cable scrap recycling is carried out without prior disassembly of the products to be recycled, because of its crushing, magnetic and explosion-proof electrostatic separation into fractions. Non-metals (polymers, textolite, silicones, organic resins, rubber and other components) are sent to the pyrolysis furnace for production of liquid fuels, ferrous metals are sent to the warehouse and then to metal scrap collection points. Non-ferrous metals, enriched with platinoids, gold and silver are sent to refining plants where chemically pure metals are released. This enrichment method is not refining; however, it is used as a preliminary stage in the recycling of electronic scrap. The advantage of such treatment is the ease with which significant amounts of electronic waste can be recycled (16). The major purpose of the electronics waste processing facility chosen for this project is increasing purity of released metals (enrichment) to a level allowing the minimum amount of pollutant emissions into the atmosphere during subsequent smelting at the refining plant, and to ensure production of additional fuel from the nonmetal fraction.
Depending on local conditions, if it is necessary or if there are consumers, it is possible to use the heat from technological condensates for cleaning garbage trucks and returning polluted warm water back to the plant, for subsoil heating of the ground in greenhouses and conservatories, for heating water in artificial reservoirs for year-round cultivation of fish at fish farms, for hot water supply in residential areas of the city or the town, etc. It is also possible to generate electricity, for example, on a diesel generator or gas-turbine installations, for their own consumption and for outside consumers.
2.6. Products obtained as a result of recycling solid municipal waste
and recommendations for their use.
Produced commercial products are: liquid fuels, ferrous and non-ferrous scrap, a mixture of various types of cullet, slag-concrete peeled from heavy metals, Sulfur and glass, dry Calcium Chloride, liquid Carbon Dioxide, a concentrate of non-ferrous and noble metals obtained from electronic, electrical and cable scrap. After purification of water condensates in sorption filters, activated carbon with sorbed heavy metals becomes a valuable commodity product to be sent to plants producing non-ferrous metals; it is an expensive additive for furnace charge during reconstructive combustion in production furnaces, as a result of which a concentrate of a mixture of these metals is produced. If such sales cannot be organized, the spent activated Carbon is to be sent for regeneration to a supplier of activated Carbon, which also deals with maintenance of installations for purifying various substances with these coals, for their regeneration and multi-rate reusage. Today, these companies activities cover practically all the countries in the world (20). In any case, burial of spent activated Carbon is excluded and, accordingly, the land is released and the costs of maintaining a special landfill are saved.
Liquid fuel (its calorific value, in accordance with the accepted morphological composition of waste, is determined to be 5880 kcal / kg (24618kJ/kg,10600 Btu/lb) is sent to be used as additives to naphtha residual fuel (mazut) to thermal power plants, industrial and heating boilers, plants in various industries. Mixing of these fuels (homogenization) immediately before burning reduces naphtha residual fuel viscosity, reduces heat consumption for its warming-up and storage, reduces energy consumption for pumping, saves naphtha fuel discharge, improves conditions of burners operation. This improves the quality of combustion and, accordingly, reduces air excess factor and increases the boiler efficiency, reduces the content of Sulfur Oxides in the flue gases (pyrolysis fuel does not contain sulfuric compounds because they are neutralized with limestone in the pyrolysis furnace). At the same time, the general plan of the plant provides space for possible additional assembling an installation for gasoline and oven fuel production unit, that meets all the requirements of the standard and is economically feasible (19). It should be noted that the calorific value of pyrolysis liquid fuel can reach 9000 kcal/kg (37680 kJ/kg) (41, section “Pyrolysis Products”). Thus, a different composition of waste, for example, with a high content of plastics, rubber, fabrics, etc., the calorific value of liquid fuel increases respectively, which has a positive effect on the technical and economic features of the project.
If all the produced commercial fuel is to be used for generating electricity directly at the plant, for example, on a diesel generator or gas-turbine installation, the plants own needs and the supply of electricity to district electric networks are provided for. In this case production cost of power generated by the plant with its own fuel produced there, will be 60% lower than the production cost of electricity produced by heat power plant (TPS) (see 9. Electric capacity used by a plant. Major equipment for electricity supply to the consumers). This option of fuel consumption depends on local conditions and must be coordinated with the local administration.
Calcium Chloride, purified of heavy metals, is used to accelerate the setting and the hardening of concretes, as an anti-icer for roads and railroad switches, against freeze-up of coal and ores, in the preparation of refrigerants and medications, as a desiccant preventing rapid absorption of moisture from the environment.
Liquid Carbon Dioxide has a purity of no less than 99.998% (vol.) With a residual Oxygen content of <5 ppm (vol.), which fully complies with the standards used in the brewing industry (12), it is also used in the food industry as a baking powder for dough, for saturation of soft drinks, mineral water and sparkling wines, for production of dry ice, as a preservative in packaging food in a modified atmosphere, in order to increase its shelf life, for extracting aromatic raw materials. It is used in the chemical industry and pharmaceuticals for production of synthetic chemicals, for neutralizing alkaline wastewater, in the processes of purification and drying of polymers, of fibers of animal or vegetable origin. In metallurgy, it is used to precipitate brown smoke in the processes of filling scrap and injecting carbon, to reduce the amount of Nitrogen absorption in the process of opening electric arc furnaces; in processing non-ferrous metals for deposition of smoke during bucket transportation of matte (Cu/Ni production) or ingots (Zn/Pb production); in the pulp-and-paper industry, to regulate the pH level in processed raw materials after alkaline bleaching of wood-pulp or paper pulp, in the welding industry – as in an inert medium in wire welding. Cylinders with liquid Carbon Dioxide are widely used as fire extinguishers and in pneumatic weapons.
Slag cleared of heavy metals, Sulfur and glass is used as a filler in production of slag concrete products directly at the plant (13), and or sent to the consumer.
Broken glass (crushed window and container glass, stained glass, mirrors, glass furniture, bottles and other products) is sent to manufacturing paving slabs, curb stone, bricks, slabs for plinth lining, floor slabs for industrial, agricultural buildings and structures with increased aggressive environments, concrete for radiation protection, and non-combustible heat-insulating coatings in nuclear industry; it is used as an additive to Portland cement and polymers, as a rubber filler, increasing its abrasive resistance and hardness. Contaminated broken glass (containing some small stuff, paper and organic residues stuck to it) are used as an additive in the manufacture of bricks without special requirements for its quality. When replacing 50% of clay with contaminated broken glass, the temperature of brick firing can be lowered from 1,170њу to 900њу. At the same time, productivity of the furnace increases by approximately 30%. Quality bricks are obtained from the following mixture: cullet - 30%, brick waste - 60% and clay - 10%. Such bricks have high resistance to weathering and are suitable for use as facing materials (14). At the same time, the project demonstrates a possibility and economic efficiency, after the construction of the plant, of additional installation of equipment for washing and grinding cullet and sending it to concrete production, which ensures an anomalous increase in the strength of concrete, significantly exceeding the strength of compositions on a standard Silica sand filler (15).
Concentrate of non-ferrous and noble metals, obtained by processing and sorting electronic and electrical and cable scrap, contains Copper, Aluminum, Stannic, Chromium, Nickel and other metals. Of particular value are precious metals that can be used in the following industries (16):
Gold - jewelry production, electronic and electrotechnical industry, art and decorative field, dentistry;
Iridium - often used as a reinforcing element in alloys with Platinum and Palladium, in chemical industry, electrical engineering, manufacturing of instruments for heart operations, jewelry industry, laser technology, medicine;
Rhodium - automobile industry, glass production, alloys for dental prosthetics and jewelry, chemistry, petrochemistry.
Utilization of heat supplied by secondary energy sources provides hot water for heating and hot water supply to the plant. Depending on local conditions, it is also possible to use process condensate for cleaning garbage trucks, returning polluted warm water back to production cycles, subsoil heating of land in greenhouses and conservatories, heating water in artificial reservoirs for year-round fish farming, hot water supply for residential areas of a city or villages, and more (the technical and economic features of the project do not include this option of heat utilization, as it is possible only if there are permanent outside heat consumers).
13. Conclusion.
It only pictures a possibility, environmental safety and economic feasibility of building a plant-module for thermochemical processing of municipal waste, which may provide garbage recycling for a statistically average US population cluster with population of 112,000 persons (in Israel – with 126,000 persons, in Australia – with 137,000 persons, in Germany – with 142,000 persons, in Italy – with 154,500 persons, in Russia – with 191,000 persons, in Japan – with 207,000 persons, in Brazil – with 218,000 persons, in Kazakhstan – with 266,000 persons, and in the Ukraine – with 283,000 persons). The capacity of the proposed enterprise and, accordingly, the number of the population serviced can vary widely, since production consists of individual autonomous technological lines (modules). Depending on local conditions, it is possible to build factories of low productivity (mini-factories), which number and geographical location for a given area is determined by a technical and economic calculation. This will reduce the amounts of long-distance waste transportation by trucks and heavy trailers, and, accordingly, reduce the costs and the additional burden on the environmental situation caused in vehicles. The “Technological Regulation” is especially important for countries experiencing a shortage of fuel, for hot and arid regions with water deficit and for cold regions where it is possible to deliver frozen waste to the plant.
The “Technological Regulations” ensure creating a new direction in processing unsorted municipal solid waste, which, due to its multicomponent nature and instability of its morphological composition, is a most difficult product to process. The proposed module with rated capacity of 10 tons/hour (85,000 tons/year) and an expected cost of USD 5,575,000 is self-sustained, at the expense of manufactured environmentally friendly products, and, even without estimating prevented damage to the environment, provides an extremely fast return on investment – 7 months, and with free admission of municipal waste – in 10 months, i.e. less than in a year. In this regard, it can be assumed that the actual payback period for the construction of the plant, taking into account environmental protection, will be even lower than expected. Such a short payback period for such industries has not yet been found in the available literature. A full calculation of economic efficiency can be made only after the development of a feasibility study for the construction of a plant tied to a particular locality.
Thus, the proposed plant will ensure production of liquid fuel (and, if necessary, electricity) from waste materials and will resist the tendencies of dangerous accumulation of garbage, its uncontrolled burning, auto-ignition, enormous quantities of formed toxic substances getting into the atmosphere, soil and water bodies, it not only provides for environmentally friendly waste processing, but also significantly reduces environmental pollution in places of consumption of environmentally friendly products of the plant. In addition, the proposed technical solution ensures significant profit to companies that will work in this area.
Recycling plastics waste
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