Relazione Arnesis En 20012008

Montevenda Engineering International Association www.montevenda.net – www.montevenda.eu

Arnèsis PROCESS AND PLANT FOR TREATING SOLID URBAN WASTE

Montevenda Engineering International Association Via Besso, 59 – 6906 Lugano (CH) – P.O. Box 406 phone: +41/91/966 33 66-966 80 86 – telefax +41/91/966 10 92 responsible of the project: Gualtiero A.N. Valeri, e-mail: [email protected] [email protected]

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Arnèsis process

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Arnèsis process and other pyrogasification processes

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Products

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Gaseous mixture

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Acetic solution

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Waxes

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Ash

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Brief description of Arnèsis process

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Arnèsis plant

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Prefeasibility and feasibility studies

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Plant, running and maintenance costs

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Input/Output

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Arnèsis® Process Introduction The Arnèsis process involves pyrolysis, gasification and inertization of waste, eliminating the negative aspects of traditional pyrogasification. It is not a truly new technology, but an optimized and patented set of technologies, consolidated in the western world until the Second World War and then perfected in the light of modern industrial chemistry. These technologies, of which pyrolysis and gasification are only the most important ones exploited in the Arnèsis process, were abandoned following the change-over from wood/coal to oil. The thinking behind the Arnèsis process The main characteristic behind the Arnèsis process is a different approach towards the problem of solid urban waste treatment: a process no longer addressed to the destruction of waste by the production of heat (which, from a thermodynamic viewpoint, is the most degraded form of energy), but one aiming at obtaining raw materials for the basic chemical industry, in which energy is stored, in the form of chemical energy, in valuable compounds yielded by the process itself. In other words, through the Arnèsis process, solid urban waste becomes an alternative and renewable source of carbon and hydrogen. If we consider the chemical industry over the last two centuries, we see that the only sources of carbon and hydrogen until the Second World War were wood and coal. Thereafter oil was used and, from the 1980s onwards, after the Middle East crises of the 1960s and 1970s had led the chemical industry to differentiate its sources of supply, natural gas was also exploited. The Arnèsis process of pyrolysis, gasification and inertization, aiming at producing raw materials, technologically

flanks not the traditional processes of thermodestruction of

waste, but processes aiming at obtaining raw materials for the chemical industry. With the Arnèsis process, these raw materials, instead of non-renewable fossil fuels like coal, oil and natural gas, come from a source which is renewable, independent of international markets, and inexhaustible: waste.

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The chemistry behind the Arnèsis® process Briefly, the Arnèsis process consists of the total thermochemical conversion of solid urban waste into basic chemical products, without the contemporary production of any solid, liquid or gaseous residues, harmful or innocuous, which must in turn be eliminated. No polychlorodioxins and/or chemically similar and in any case polluting products are formed. The products yielded by Arnèsis have the highest commercial value of all products of pyrolysis and gasification until now resulting from similar processes, mainly carbon with high contents of ash, liquid RDF and low-calorie gases. The Arnèsis process takes place by means of progressive pyrolysis in rigorously controlled conditions. Carbon residues are gasified by a stream of oxygen, carbon dioxide and water vapour, with the production of hydrogen and carbon monoxide, together with a quantity of heat sufficient to sustain pyrolysis reactions. These gases, produced by gasification, permeate the mass of waste in pyrolysis, supply heat, and create the necessary reducing environment in one or more thermodynamic sections, physically interconnected, which make up the reactor. From the operational viewpoint, the waste is suitably pre-treated, glass and metal being removed, sorted for size, and dried. Then the waste is progressively heated from environmental temperature to about 700°C. The residual carbon mass is then gasified at between 700 and 1,100°C. Heavy metals and halogenated compounds are blocked during the process by the joint action of heat and inertizing substances added to the waste. The main products of the conversion process leave the reactor in the form of gas and vapours, and may be condensed and fractionated, according to need, into pure chemical products (e.g., acetic acid, carbon dioxide) or mixtures (e.g., tarry oils, pyroligneous acid, or synthetic gases). The resulting products may be directly marketed or used for further working.

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Arnèsis® plant The plant is composed of three sections: • pretreatment • Arnèsis reactor • post-treatment Pre tr e atm e nt The aims of pre-treatment are as follows: 1)

Optimization of the characteristics of the waste, according to the maximum yield of the reactor. Waste must therefore be ground and dried to eliminate excess water.

2)

Initial profit from the sale of some materials present in the waste. Urban waste generally contains considerable quantities of glass and metals, which may easily be separated.

Pretreatment is thus subdivided into the following operations: • grinding; • drying; • removal of glass (not necessary with waste coming from differentiated collection); • removal of metals (not necessary with waste coming from differentiated collection). The thermal and electrical energy needed to work the pre-treatment equipment may be supplied, entirely or partially, by the Arnèsis reactor and the gases produced. These are in any case already well-known and consolidated technologies. Ar nè s is Re a c t o r The Arnèsis reactor is a cylinder, sized in proportion to the daily quantity of waste to be treated. Pretreated waste is loaded into the top of the reactor by a screw feeder.

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Inside the reactor, the waste begins its passage towards the bottom of the reactor itself, encountering steadily increasing temperatures ranging from about 150°C to about 1,100°C. Towards the bottom, it is reduced to a carbon mass, and meets a flow of oxygen, water vapour and carbon dioxide. Pyrolysis occurs as far as the zone at about 700°C, and produces gases, liquids and waxes. Gasification occurs at between about 700°C and 1,100°C, and it is in this phase that most of the gases are produced to yield mineral solids. Inertization occurs throughout the temperature range of the reactor, and transforms polluting substances into harmless products; inorganic pollutants (heavy metals) in the mineral solids, now rendered harmless. Inertization may require the addition to the waste, after grinding, of small quantities of easily obtained and inexpensive substances. The temperature at the bottom of the reactor (about 1,100°C) is ensured by the exothermic reactions of gasification. Carbon dioxide is produced in the top part of the Arnèsis reactor and partly re-injected into the lower part. Water vapour is obtained thanks to residual heat deriving from heat recovery. Oxygen is obtained from the air by means of traditional fractionation or adsorption plant installed in the same area. The reactor is equipped with condensation plant (formed of a series of condensers and heat exchangers) required for the recovery and initial separation of products resulting from the process. Pos t-tre a t m e nt The raw materials leaving the condensation section must be initially fractionated or purified before use. In some cases, this treatment is preferably carried out directly on site (e.g., gases, difficult to transport); in other cases, they can be worked elsewhere. Briefly, it is recommended that the following working phases be carried out at the Arnèsis plant:

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Mixtures of gases: the following phases of separation and storage are required: ●

carbon dioxide, of which part is re-used in the process;

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hydrogen (if produced);

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mixture of hydrocarbons and carbon monoxide (hydrogen, if produced); this mixture (high heat value: with hydrogen, 5,270÷5,990 Kcal/Nm3; without hydrogen, 5,670÷6,710 Kcal/Nm3) is sent to the electricity generating plant.

Acetic solutions: oil extracting equipment. Waxes: dewatering equipment. Ash: grinding, sorting and washing equipment.

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The Arnèsis® process and other pyrogasification processes The differences between the Arnèsis process and other pyrogasification processes are listed below. In the Arnèsis plant: • Pyrolysis occurs in a highly reducing environment, thus preventing the oxidation and saturation of resulting compounds, which would reduce their commercial value. • Pyrolysis is slow, thus preventing the formation of halogenated compounds like polychlorodioxins. • The maximum processing temperature does not exceed 1,100°C, thus allowing the use of long-lasting and relatively inexpensive refractory materials. • Waste is entirely converted into basic chemical products, for sale on the market; • There are no polluting emissions of any kind, neither polluting, neither harmless, and the carbon residue is completely converted into gas.

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Products of the Arnèsis® process The products of the Arnèsis process may be classified as follows: •

Gases: mixtures of carbon dioxide, carbon monoxide, hydrogen, methane, and other light hydrocarbons.

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Acetic solution: a water-based solution of acetic acid, methanol, acetone, aldehydes, esters, ethers and light oils;

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Waxes: Mixtures of heavy hydrocarbons (mainly long-chain paraffins and olefins), aromatic compounds such as naphthaline, and phthalic esters.

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Ash: A whitish powdery mass, mainly composed of salts (silicates and traces of chlorides and sulphates) of calcium, magnesium, sodium, potassium, heavy metal silicates and oxides.

These products are obtained in the following proportions (percentages refer to pretreated waste, i.e., dried, without glass or metals, 66% of the original quantity: - Gases - Acetic solution - Waxes - Ash

70÷80 % 9÷16 % 8.5÷9 % 4÷7 %

The main characteristics of Arnèsis products are as follows: •

Almost complete absence of oxygenated compounds in waxes: the waxy fraction is the homologue of the tarry fraction, of little market value, resulting from other pyrogasification processes; instead, the waxes deriving from the Arnèsis process are of high commercial value. Oxygenated compounds, also of commercial interest, are concentrated in the acetic solution.

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Very low occurrence of double bonds in waxes: this makes them very dissimilar to the tars produced in other pyrogasification processes, and of much greater value.

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Absence of organic and inorganic micropollutants: sulphur and chlorine occur as chlorides and sulphates in mineral solids, as acids (in trace amounts) in gases, or as sulphurated compounds in waxes, where they are incorporated and thus rendered harmless.

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Possible use of products: •

Acetic solution: refining for production of acetic acid and other chemicals, with membranes technologies, or directly uses how acidifing agent in industrial processes, or for pickling of metals, or production of water-soluble paints.

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Waxes: refining for production of chemicals, how ftalic acid, artificial waxes, and so on. Directly it can used in formulation of bitumen, as a plastifier.

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Gas: use in Fischer-Tropsh synthesis, hydrogen separation and production, ammonia synthesis, methanation, and so on. With the possibility, naturally, of production of electricity. Very interesting is possibility of carbon dioxide recovery for industrial uses.

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Ash: Arnèsis ash may be used either as they are or after suitable treatment, as inert substances; previous washing to get further chlorides and sulphates in the formulation of cement conglomerates; or – even more interestingly – as raw materials for cement manufacture, according to the latest technological developments.

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Results of qualitative and quantitative analyses on products:

Gaseous mixture Carbon monoxide Methane Carbon dioxide1 C2÷C4 mixture Hydrogen Sulphur dioxide Formaldehyde Nitrogen Oxygen Hydrochloric acid

34÷64 % 5÷6 % 9÷30 % 8÷10 % 12÷30 % 0÷0.4 % Traces Traces Traces Traces

As may be seen, the Arnèsis reactor is flexible: it can be calibrated according to increased production of certain gases instead of others2. The same applies to other products.

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A variable quantity of carbon dioxide (maximum 95 Nm3/t of pre-treated transformed waste) is re-used in the process.

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For example, in the case of carbon dioxide, calibration ranges from a minimum production of 9% to a maximum of 30%, again with

respect to the total quantity of gases produced (890-1,110 Nm 3/t of pre-treated transformed waste). In this case, the range mainly involves carbon monoxide.

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Acetic solution Acetic acid Furfurol Methanol Phenol Acetone Furans Phenols and polyphenols Alkylbenzenes Formic acid Propionic acid Ethanol Heavy hydrocarbons Water

≤ 7.5 % ≤5% ≤ 2.8 % 2÷7 % <1% Present Present Present Present Present Present Traces to 100 %

As may be seen, this mixture is very unlike the classic “pyroligneous acid” resulting from pyrolysis of wood.

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Waxes Concentration range > 10%: • Aliphatic hydrocarbons; •

Esters of phthalic acid (minimum 5÷15%)

Concentration range 1÷10%: • Naphthalene (abundant); • Anthracene; • Phenantrene; • Cycloparaffin and derivates (alkylcyclopentanes and alkylcyclohexanes); • Alkylnaphthalene; • Alkylbenzenes. Concentration range < 1 %: • Phenol; • Cresols. Occasional appearance in concentration range 0÷10%: • High molecular weight aldehydes; • High molecular weight organic acids; • Esters of organic acids. This mixture is a dark brown to blackish waxy mass, with red reflections, with a melting point of 100÷110°C. Both its aspect and chemical analyses have shown that the word “tars” cannot be applied to this mixture, which is very similar to a mineral wax. Of note is the very low occurrence of oxygenated compounds and double bonds, mainly at the ends of the hydrocarbon chains.

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Ash These white or pale powders, with no traces or organic substances or carbon, are composed of: • Silicates; • Inorganic oxides; • Alkaline alides; • Chlorides and sulfates: traces. They are introduced in the form of white or clear color dusts, loose, deprived of whatever trace of organic substance or carbon.

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Brief description of the Arnèsis® process Before processing, the waste undergoes pretreatment, which involves the following operations: 1) grinding; 2) removal of glass; 3) removal of metals; 4) drying; 5) addition, if necessary, of inertizing substances. Operations 2), 3) and 4) may be scaled down or even eliminated if the waste in question is the dry fraction from differentiated collection, and is stored under cover or protected from humidity. The waste is then subjected to the Arnèsis process, which begins with slow pre-heating, from room temperature to about 150°C, to eliminate residual humidity. At this point, slow, progressive pyrolysis begins, ending at about 700°C. The temperature continues to rise to 800÷1,000°C, during which the residues of pyrolysis are gasified. Gasification converts carbon residues into gases (carbon dioxide, carbon monoxide, hydrogen), supplies the heat necessary to sustain all the other reactions of the process (inertization, pyrolysis, preheating of materials) and removes pyrolysis products from the reactor in a gaseous state (latent heat due to evaporation of liquid products and the sensible heat of the gaseous mixture). Gasification gives rise mainly to carbon monoxide and hydrogen, which is why pyrolysis occurs in a reducing atmosphere. The resulting products are less oxidized and unsaturated, and thus of greater chemical and commercial interest. Gasification and combustion reactions take place in the presence of oxygen, carbon dioxide, and saturated water vapour. Pyrolysis is accompanied by inertization of halogens and heavy metals, which normally produce polluting substances in ordinary processes of waste destruction. Since in the Arnèsis case pyrolysis is very slow (minimum 20 minutes), takes place in a highly reducing envir-

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onment with respect to other pyrolysis processes, and in the presence of inertizing substances, conditions favourable to the formation of polychlorodioxins and other aromatic chlorine derivates do not arise. Halogens, such as chlorine, in the Arnèsis environment tend to develop in the form of hydrochloric acid and, in the presence of inertizing substances, form salts such as sodium chloride. Heavy metals are rendered inert as silicates. The process concludes when the hot calcined residues come into contact with a flow of pure oxygen, which completely and rapidly transforms carbon and residual organic compounds into carbon dioxide. All the reactions of pyrolysis, gasification and inertization, including combustion and pre-heating, take place in the same environment. This process is followed by post-treatment, primary or complete, which refines one or more of the products resulting from the Arnèsis process.

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Arnèsis® plant Plant potential The minimum potential of the Arnèsis plant is linked to its low running costs, its breakeven point, i.e., the minimum threshold value under which plant running would not be economical. This threshold is estimated at a potential of about 150 t/day. The considerations made above, and assessments based on waste cycle management in the territory in question, identify the mean optimal potential of a Arnèsis plant at 200÷250 t/ day of waste. The maximum potential of a Arnèsis plant (fluidized bed) is about 1,000 t/day. A first example of plant use The best use of a Arnèsis plant is for production of chemicals, width refinement of waxes and acetic solution, and conversion of gases in hydrocarbons and alcools (width Fischer-Tropsh syntesis), so much as chemicals, how much as biofuels of second generation. Plant with a potential of 200 t/day: Materials entering:

Quantity

Pretreated waste

200 t/day

Oxygen

65÷75 t/day

Carbon dioxide

Max. 37 t/day3

Water vapour

Max. 100 t/day4

Total

275÷312 t/day

Products leaving plant: Gas mixture

Quantity 178,000÷220,000 Nm3/day (or: 215÷242 t/day) 50÷70 t/day

Acetic solution, waxes, ash

3

Theoretical upper limit.

4

Theoretical upper limit, as for carbon dioxide.

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A second example of plant use: for production of maximum quantity of combustible gases and thus electrical energy (minimal application) As already mentioned, the Arnèsis plant is flexible, i.e., it can be calibrated according to the need for increased production of certain gases rather than others. By varying process conditions, e.g., working at a maximum temperature of 700°C (instead of 1,100°C), combustible gases with high thermal potential and, consequently, electricity, can be produced in large quantities. Maximum process temperature: 700°C Yield of combustible gases: 124,400 Nm3/day Thermal potential of mixture: 5,990 kcal/Nm3 (including hydrogen) Composition of gases:

Quantity

H.H.V. (kcal/Nm3)

Carbon monoxide

61 %

3,018

Hydrogen

18 %

3,048

Methane

7%

9,494

C2÷C4 hydrocarbons

14 %

20,900

124,400 Nm3/day

5,990 Kcal/Nm3

Gas

Total Electric power obtainable:

11,070 kWe

Cogenerated thermal potential:

21,080 kWt

These results refer to the employment of cogenerators of Italian production of series and of contained power. You give the powers in game it results however more opportune to use groups of great power.

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Plant self-consumption: ~ 630 kWe, for gas separation alone. The power required to feed the entire plant is also quite low. The units which absorb the greatest electric load are definitely those for working gases (for compressors) and the pre-treatment section (grinders, etc.). Some residual heat is absorbed by the dryer during pre-treatment. More detailed and exact estimates require special feasibility studies.

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Prefeasibility studies Montevenda Engineering International Association can carry out prefeasibility studies of Arnèsis plants, showing essential data and guide-lines for proposed solutions.

Feasibility studies A feasibility study is the first phase of overall planning of a Arnèsis plant. Within the standard precision limits of this phase, such a study indicates: • time required for plant planning and construction; • surface areas required; • costs for construction, management and maintenance; • if desired, assistance by Montevenda Engineering International Association in managing and maintaining plant.

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Plant costs The costs of a Arnèsis plant may vary greatly, due to the following factors: • Plant potential: the best cost/benefit ratio is reached when the plant works at a rate of 200÷250 t/day. • Plant siting: the greater or lesser expense involved in siting the plant is due to soil characteristics and thus to the necessary type of foundations, and to transport costs of waste and products. It refers to a centrally located site with respect to urban waste collection points and the industrial areas of working and/or use of resulting products. • Type of waste: the degree of differentiation of waste collection in the area in question affects the greater or lesser expense for the pre-treatment plant, but does not significantly influence the cost of the Arnèsis reactor and connected services.

Running costs Two main items are involved here: • personnel: 10÷15 specialized workers, as well as secretarial and management staff; • purchase of oxygen: about 50,000 Nm3/day for a plant of the potential described above.

Maintenance costs Plant maintenance costs, referring to spare parts necessary for the ordinary maintenance of a normal chemical plant, are 5÷10% annually of the initial invested capital (the maintenance costs of a chemical plant are unlike those of other types of plant and, in some cases, may reach 20% of the invested capital). Naturally, these costs are highest at the beginning and end of the life of the plant and minimal at the end of its running-in period (about one year).

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Input/Output Materials entering plant Mean quantities Pretreated urban wast

200 t/day

Oxygen

50,000 Nm3/day

Carbon dioxide

15,000 Nm3/day

Water vapour

16 t/day Materials leaving plant Mean quantities

Carbon dioxide

45,000 Nm3/day

Other gases

175,000 Nm3/day

Acetic solution

24 t/day

Waxes

18 t/day

Ash

10 t/day

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