WO2013088391A1

WO2013088391A1 - Electrochemical plant for the treatment of fumes

Info

Publication number: WO2013088391A1
Application number: PCT/IB2012/057291
Authority: WO
Inventors: Achille DE BATTISTA; Tullio Caselli; Marco CALCOPIETRO; Francesco Repetto
Original assignee: WWEELAB Srl
Current assignee: WWEELAB Srl
Priority date: 2011-12-13
Filing date: 2012-12-13
Publication date: 2013-06-20
Anticipated expiration: 2014-06-13
Also published as: ITRM20110665A1

Abstract

An electrochemical plant (1) for the treatment of fumes, comprising a condensing boiler (2), a fluidized bed electrolysis chamber (3) and a transfer line (18) for transferring the fumes from the condensing boiler (2) to the fluidized bed electrolysis chamber (3). The fluidized bed electrolysis chamber (3) is filled with an electrolytic solution and comprises a fluidization portion (6) adapted to constitute a first electrode and an upper portion (7) for housing a second electrode (8). The first electrode defined by the fluidization portion (6) comprises a portion (13) of retaining wall of the fluidized bed electrolysis chamber (3), grains with a diameter ranging from 0.8 to 1.2 mm and free to fluidize inside the electrolytic solution, a retaining net (9) adapted to retain the granules from above and a plurality of cavitation Venturi injectors (12), which are fed with the fumes from the fume transfer line (18) and with the electrolytic solution coming from the expansion chamber (4) and/or with an electrolytic solution/granule complex coming from the same fluidization portion (6). The second electrode (8) comprises grains with a diameter ranging from 2 to 3 cm and enclosed in a net (14). The plurality of cavitation Venturi injectors (12) is adapted to produce inside the fluidization portion a plurality of microbubbles.

Description

ELECTROCHEMICAL PLANT FOR THE TREATMENT OF FUMES

TECHNICAL FIELD

The present invention relates to an electrochemical method plant for the treatment of combustion fumes, in particular fumes deriving from endothermic motors, gas and liquid fuel turbines of any nature, combustion and pyrogasification processes fed with fossil fuels or derivatives, with biomasses and organic waste in general .

The present invention provides for separation of pollutants from the gaseous flow through electrochemical reduction oxidation processes. In particular, the invention is principally, but not exclusively, directed at particulate matter of any form or composition, at heavy metals present in the fumes both in gaseous and in particulate form, and at all organic and inorganic pollutants typical of combustion processes, such as Ox, SOx, HCL, dioxins and furans .

BACKGROUND ART

The exhaust gases deriving from combustion and gasification processes are characterized by the presence of solid and gaseous contaminants of various chemical species at different concentrations and with many chemical-physical properties. The presence of pollutants in exhaust gases varies in relation to variations in the type of fuels used and in the specific combustion conditions. In general, pollutants come within the following groups: particulate and fine particles of various nature and chemical-physical properties; chemical compounds, such as HCL, dioxins and Furans, SOx, HF, NH₃, NOx, VOC, CO, unburned aromatic hydrocarbons and heavy metals present both in gaseous and solid form. Metals in combustion fumes are mainly: Cadmium, Thallium, Mercury, Arsenic, Cobalt, Chrome, Copper, Manganese, Nickel, Lead, Antimony and Vanadium.

The production of thermoelectric, mechanical, thermal and thermochemical energy has characterized the development of industrial economy. The fuels involved in these production processes have been used in succession in history. The initial use of only lignocellulosic biomass was subsequently replaced by coal, oil and its derivatives and natural gas. In addition to reasons of greater operating efficiency, as is the case in the passage from coal (solid fuel) to gas (liquid fuel) , especially in the last 60 years this succession has been dictated by a growing awareness of the consequences, in terms of environmental damage and human health, that can derive from releasing pollutants produced by combustion into the atmosphere .

Combustion residues from the two most widely used types of fuel, coal and oil derivatives, have generated serious pollution phenomena on the planet, caused not only by the release of fossil carbon dioxide into the atmosphere, but also by the dispersion into the environment of very high quantities of polluting products, such as coarse particulate matter, sulphur and nitrogen oxides and aromatic hydrocarbons.

Technological progress of recent years (pre- treatment of fuel, particulate reduction, desulphurization, etc.) has enabled a significant reduction in the presence of these pollutants in atmospheric emissions.

The use of methane in combined cycle plants was welcomed as a final solution for the elimination of the principal pollutants: natural gas does not contain sulphur, does not produce coarse particulate, control of the combustion temperature reduces the formation of Ox, combustion in gaseous phase enables complete oxidation of hydrocarbon molecules .

However, it was discovered that natural gas plants emit fine particulate matter (PM₂.₅ and PMi) , transparent to the most modern collection systems and extremely dangerous because they deposit in tissues of living organisms as their immune systems are unable to intercept them.

The rapid increase in the temperature on the planet is generally acknowledged as the consequence of the greenhouse effect generated by a series of gases released into the atmosphere by industrial processes, in particular C0₂, which is produced by all combustion processes. The strategies implemented by international protocols to diminish this phenomenon are aimed both at technologies for the capture and geological sequestration of the C0₂ present in the combustion fumes of fossil fuels, and through recourse to the alternative use of biomasses in small and medium sized plants, for distributed production of electricity and heat.

The combustion of biomass or derivatives, such as biodegradable waste in general, does not influence the greenhouse effect as the C0₂ produced by their combustion is the same as the quantity absorbed by the process for formation of the biomass through chlorophyll synthesis. Moreover, recourse to biomass combustion diminishes the greenhouse effect, as it prevents release into the atmosphere of biogas and C0₂ deriving from anaerobic and aerobic oxidative processes, resulting from their use as agricultural amendment or being placed in landfills.

However, biomass combustion causes environmental problems that are no less serious than those generated by fossil fuels. These problems are related to particulate matter, to the emission of heavy metals, of HCL, of SOx, of dioxins and furans, of NOx and of unburned and volatile hydrocarbons.

The prospect of a generalized use of biomass to produce thermal and electrical energy in small and medium sized plants leads to the need for efficient and low cost technologies for the treatment of fumes, also for these sizes of plants.

In this regard, various technologies have been developed to date, generally specialized in the reduction of specific groups of pollutants. The logic of functional specialization has led to the concept of treatment of emissions through plant lines arranged in series.

Dust collectors for ash and coarse particulate are always at the beginning of the fume treatment lines, generally followed by wet and/or dry scrubber systems, adapted to absorb HCL, SOx, NH₃, dioxins and other organic molecules.

Catalytic systems, which operate at relatively high temperatures, are used for NOx.

Both bag filters and electrostatic precipitators are used in the end sections . The former are capable of stopping PM₁₀ particulate, with an efficiency of 98%, but do not see PM₂.s and PMi particulate.

To date, the fume treatment lines currently used, whether dry lines or wet lines, suffer from the problem of still releasing a number and type of pollutants which, although satisfying the concentrations established by the regulations, still constitute an extremely dangerous source of pollution for public health.

One solution could be to arrange, downstream of the fume treatment line, a plant for the electrostatic removal of pollutants .

Electrostatic filters, which are able to electrically charge even fine particles, require very high dwell times of the fumes and therefore become extremely costly applications, above all for small plants. In order to obtain emissions compatible with the most restrictive regulations, such as the EC regulations, it is necessary to design plants with a combination of different types of treatment, which is generally very difficult to achieve.

Solutions are known which use electrolytic processes of various form and nature, aimed at reducing the pollutants present in the exhaust combustion gases.

Starting from the 1970s, numerous patents were filed proposing the use of the fluidized bed as electrolytic cell, such as US 3,977,951; US 4,202,752; US 4,824,541; US 5,096,054; US 2008/02772787.

The devices relating to this technology are based on the efficacy both of the electrochemical process for the reduction oxidation of contaminants in low dilution in the combustion fumes or fumes of other industrial processes, and of the fluidized bed in the exposure to ionization, generated by the electrical field, of the particles of contaminants present in non-conductive gases, with respect to the electrostatic filter.

However, the solutions proposed have not met with adequate industrial success, above all due to their complexity and to their high cost. The need was therefore felt to provide a plant for ^"the treatment of fumes that uses fluidized bed electrolysis technology and whose technical characteristics are such as to overcome the problems of prior art .

DISCLOSURE OF THE INVENTION

The subject matter of the present invention is a plant for the treatment of fumes, the basic characteristics of which are specified in claim 1, and preferred and/or auxiliary characteristics of which are specified in claims 2-7.

BRIEF DESCRIPTION OF THE DRAWING

For a better understanding of the invention, an embodiment is provided below purely by way of illustrative and non-limiting example with the aid of the figure of the accompanying drawing, which illustrates in schematic form a plant according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the figure, the plant for the treatment of fumes forming the subject matter of the present invention is indicated as a whole with the numeral 1. The plant 1 is introduced downstream of a known treatment line for exhaust gases, for example comprising polycyclones , scrubbers, bag filters or electrostatic filters known in the art. In other words, the plant 1 treats the exhaust gases before they are fed to the chimney.

The plant 1 substantially comprises a condensing boiler 2, a fluidized bed electrolysis chamber 3 in which the pollutants are reduced electrochemically and an expansion chamber 4 in which the electrolytic liquid is regenerated.

The condensing boiler 2 has the function of lowering the temperature of the fumes from a temperature typically around 180/200°C to temperatures in the order of 45/55°C, with consequent thermal recovery of the heat from the fumes destined for cogeneration uses. As is known, the condensing boiler 2 comprises means for reducing the acidity of the condensate water.

The fluidized bed electrolysis chamber 3 is without physical separation between the cathode compartment and the anode compartment and is made of titanium coated with oxides with a metallic or semi-metallic conductivity, chosen among oxides of Sn, Ti, Zr, Nb, Ta, Ru, Ir, Os, Pt, Rh, or mixtures thereof, of dimensions proportional to the volumes of air to be treated and to the predetermined dwell time. The walls of the anode compartment and the walls of the cathode compartment are electrically isolated from each other for reasons that will be clear in the description below. The electrolysis chamber 3 is closed by a suction hood 5 which is adapted to convey the treated fumes to a chimney.

The fluidized bed electrolysis chamber 3 is filled with an electrolytic solution, such as an aqueous solution of sodium sulphate with a molar concentration ranging from 0.01 to 1, and is divided into a fluidization portion (6) , adapted to constitute a first electrode and an upper portion 7 for housing a second electrode 8. In the example described here, the fluidization portion 6 defines a cathode, while the upper portion 7 houses an anode 8.

The fluidization portion 6 houses grains of appropriate material free to fluidize inside the electrolytic solution and retained above by a retaining net 9 made of titanium coated with conductor metal oxides chosen among oxides of Sn, Ti , Zr, Nb, Ta, Ru, Ir, Os, Pt, Rh, or mixtures thereof.

The aforesaid grains are made of material selected in the group constituted by carbon, hematite, magnetite, ruthenium dioxide, iridium dioxide, manganese dioxide, titanium dioxide and mixtures thereof and have a diameter ranging from 0.8 to 1.2 mm . The fluidization portion 6 also comprises an emptying valve 10 and a fume distribution assembly 11, which has the function of sucking in the fumes, distributing them in the electrolyte in the form of microbubbles with dimensions that enable the grains constituting a fluidization bed to absorb them, performing complete ionization and/or reduction oxidation of the molecules and particles of contaminants present in the gaseous mass. The micrometric dimension of the bubbles minimizes the effect of dilution of the contaminants in the gaseous flow, prevalently composed of N₂ and C0₂. The fume distribution assembly 11 comprises a plurality of cavitation Venturi injectors 12, which are fed with the fumes coming from the condensing boiler 2 and with an electrolytic solution coming from the expansion chamber 4, as will be described hereunder. Alternatively, in place of the electrolytic solution or in combination therewith, the cavitation Venturi injectors can be fed with the electrolytic solution/granule complex coming from the emptying valve 10.

The cavitation Venturi injectors, just as part of the pipes connected thereto and housed inside the fluidization portion 6, are made of titanium coated with conductor metal oxides chosen among oxides of Sn, Ti, Zr, Nb, Ta, Ru, Ir, Os, Pt , Rh, or mixtures thereof . As mentioned above, the fluidization portion 6 defines as a whole a cathode that is, therefore, constituted by a fluidizing element made of granules immersed in the electrolytic solution and by a metallic structural element made by the walls 13 of the fluidizing portion 6, by the retaining net 9 and by the cavitation Venturi injectors 12. The cavitation Venturi injectors are, therefore, an integral part of the cathode electrode and, thus, already when the fumes are fed into the injector, the grains recover the electrical charge through contact with the walls of the injectors.

The anode electrode 8 is constituted by a volumetric electrode made of grains with a diameter ranging from 2 to 3 cm and enclosed in a fine net 14 made of titanium coated with conductor metal oxides chosen among oxides of Sn, Ti, Zr, Nb, Ta, Ru, Ir, Os, Pt, Rh, or mixtures thereof. Just as for the cathode electrode defined by the fluidizing portion 6, also for the anode electrode 8 the grains are made of a material selected in the group constituted by carbon, hematite, magnetite, ruthenium dioxide, iridium dioxide, manganese dioxide, titanium dioxide and mixtures thereof.

The expansion chamber 4 is adapted to regenerate the electrolyte and is fed by a first feed line 15 coming from an overflow system arranged in the electrolysis chamber 3 above the anode electrode 8, and by a second feed line 16 responsible for feeding new electrolyte solution.

Said first feed line is constituted by pipes made of titanium and stainless steel.

The expansion chamber 4 is provided with a discharge assembly 17, from which a part of the electrolytic solution comprising the pollutants in legally permitted concentrations, and identified also as water in Class A, is discharged.

The plant 1 comprises a transfer line 18 for transferring the fumes from the boiler 2 to the distribution assembly 13. The line 16 comprises, in turn, a fan 19 required for movement of the f mes. In fact, after being cooled in the condensing boiler 2, the fumes lose their tendency to move spontaneously and therefore the action of a fan is necessary.

The plant 1 comprises a transfer line 20 for transferring the electrolytic solution from the expansion chamber to the distribution assembly 11 and a further transfer line 21 for transferring the electrolytic solution/granule complex from the emptying valve 10 to the distribution assembly 11. The transfer lines 20 and 21 are made with titanium and stainless steel pipes and provide for the insertion of an appropriate pump 19a arranged downstream of the connection of the two transfer lines 20 and 21. In particular, the connection of the transfer lines 20 and 21 is regulated by a valve, known and not illustrated for simplicity, such as to regulate the related flow.

Feed of the cavitation Venturi injectors 12 with the electrolytic solution/granule complex enables the granules to come into direct contact with the polluting compounds to be absorbed starting from the cavitation area.

The flow rate, the velocity and the pressure of the electrolyte containing the microbubbles of fumes at the exit of the injectors and the geometric distribution of these injectors are all parameters that must be set in such a manner as to ensure fluidization of the cathode bed and simultaneous maintenance of the electrical contact. The correct fluidization of the bed plays a fundamental role in the ratio between microbubbles and carbon particles of the cathode, producing a uniform contact surface between the microbubbles and the cathode particles, which due to the movement induced by fluidization constantly modify their geometry, promoting exposure to the electrical field of the particles or molecules of pollutants located in the central part of the microbubbles.

A relaxation of the electrolyzed element accompanied by completion of the reactions between the oxidizers produced by the anode and the electroactive pollutants takes place inside the expansion chamber 4.

The plant of the present invention enables the particulate and gaseous contaminants diluted in the gaseous mass to be subjected to electrolysis, without passing through a complete dissolution in the electrolytic solution. In this regard, it must be considered that dissolution in water of gaseous solutes causes a great waste of energies due to a necessary increase of the pressure of the solute in the solvent. Due to the use of cavitation Venturi injectors it is possible to feed fumes into the electrolytic solution in the form of microbubbles of adequate dimensions. In this way it is possible to subject the polluting compounds present in the gaseous flow to electrolysis, overcoming the limits deriving from the sole dissolution of the gas in a liquid.

With the plant of the present invention, it is possible to obtain the removal of exhaust fumes of compounds such as: Ox, SOx, PMio, PM .5, PMi particulate, and ultrafine particulate, HCL, Dioxins and Furans, HF, NH₃, VOC, CO and heavy metals present both in solid and gaseous form. As will be apparent to those skilled in the art, the plant 1 comprises an electrical system such as to give power to the electrodes and constituted by inverter and capacitor and other apparatus capable of controlling both the voltage and the current amperage and, at the same time, to invert the polarity of the electrodes, as required.

Finally, the plant 1 comprises a control unit, known and not illustrated for simplicity, adapted to operate according to logics that automatically adapt activity to the data received from a plant sensor system.

The advantages of the plant of the present invention can therefore be summarized in the fact of making electrolysis of the pollutants possible inside an electrolytic solution in an economically sustainable and effective manner. With the plant of the present invention it will therefore be possible to reduce the fumes delivered from cogeneration plants of pollutants such as NOx, SOx, PM₁₀, PM₂.₅, M_X particulate, and ultrafine particulate of any nature, HCL, dioxins and furans, HF, NH₃, VOC, CO and heavy metals present both in gaseous and in solid form. As will be immediately apparent to those skilled in the art, an advantage of this kind has an immediate effect on cogeneration plants, also of small size, which will thus increase their overall advantageousness and environmental and social acceptability.

Moreover, i is important to stress that the plant of the present invention facilitates the use in a line for the treatment of fumes of a condensing boiler and, therefore, the possibility of recovering heat by cooling these fumes, and this is due to the fact that the cold fumes are appropriately treated in the electrolytic system and eliminate the risk posed by potentially toxic fumes, due to the considerable presence of CO, falling to the ground, a danger that is always present where fumes are cooled, thereby increasing their density and decreasing the speed at which they rise.

Claims

1. An electrochemical plant (1) for the treatment of fumes, characterised in that it comprises a condensing boiler (2) , a

5 fluidized bed electrolysis chamber (3) and a transfer line (18) for transferring the fumes from said condensing boiler (2) to said fluidized bed electrolysis chamber (3) ; said fluidized bed electrolysis chamber (3) being filled with an electrolytic solution and comprising a fluidization portion

10 (6) adapted to constitute a first electrode and an upper portion (7) for housing a second electrode (8) ; said first electrode defined by said fluidization portion (6) comprising a portion (13) of retaining wall of said fluidized bed electrolysis chamber (3), grains with a diameter ranging from

15 0.8 to 1.2 mm and free to fluidize inside the electrolytic solution, a retaining net (9) adapted to retain said granules from above and a plurality of cavitation Venturi injectors (12) , which are fed with the fumes from said fume transfer line (18) and with the electrolytic solution coming from an

20 expansion chamber (4) and/or with a electrolytic solution/granule complex coming from the same fluidization portion (6); said second electrode (8) comprising grains with a diameter ranging from 2 to 3 cm and enclosed in a net (14) ; said plurality of cavitation Venturi injectors (12) being

25 adapted to produce inside the fluidization portion a plurality of microbubbles ; the grains comprised in said first electrode (6) and in said second electrode (8) being made of a material selected in the group constituted by carbon, hematite, magnetite, ruthenium dioxide, iridium dioxide, manganese -30 dioxide, titanium dioxide and mixtures thereof.

2. An electrochemical plant (1) according to claim 1, characterized in that said first electrode (6) is a cathode electrode and said second electrode (8) is an anode electrode.

35

3. An electrochemical plant (1) according to claim 1 or 2, characterized in that said cavitation Venturi injectors (12), said retaining nets (9, 14) and said portion (13) of wall are made of titanium coated with metal oxides comprised in group consisting of oxides of Sn, Ti , Zr, Nb, Ta, Ru, Ir, Os , Pt, Rh, or mixtures thereof.

4. An electrochemical plant (1) according to one of the preceding claims, characterised in that it comprises an expansion chamber (4) adapted to receive the electrolyte from said fluidized bed electrolysis chamber (3); a relaxation of the electrolyzed element accompanied by completion of the reactions between the oxidizers produced by the anode and the electroactive pollutants takes place inside said expansion chamber (4) .

5. An electrochemical plant (1) according to claim 4, characterised in that said expansion chamber (4) is provided with a discharge assembly (17) , from which part of the electrolytic solution comprising the pollutants is discharged.

6. An electrochemical plant (1) according to claim 4 or 5, characterised in that it comprises a transfer line (20) for transferring the electrolytic solution from the expansion chamber (4) to the plurality of cavitation Venturi injectors (12) and a further transfer line (21) for transferring the electrolytic solution/granule complex from an emptying valve (10) of the fluidized bed electrolysis chamber (3) to the plurality of cavitation Venturi injectors (12) .

7. An electrochemical plant (1) according to any one of the preceding claims, characterised in that it comprises a suction hood (5) arranged to close the top of the fluidized bed electrolysis chamber (3) and adapted to convey the treated fumes to a, chimney.