IT201600108933A1 - A plant and a method to convert a carbonaceous raw material into electricity and a high purity carbon dioxide gas flow - Google Patents

Description

"A PLANT AND A METHOD TO CONVERT A CARBON RAW MATERIAL INTO ELECTRICITY AND A HIGH PURITY CARBON DIOXIDE GASEOUS FLOW"

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a plant for converting a carbonaceous raw material, be it a waste, a fossil fuel or a biomass, into electricity and a separate high purity carbon dioxide gaseous stream, ready for carbon dioxide capture and sequestration applications. or incremental oil recovery, as well as a method performed with such a facility.

STATE OF THE TECHNIQUE

Today, one of the main problems to be faced in the energy market is the conversion of carbonaceous raw materials into electrical energy, with a limited emission of carbon dioxide into the atmosphere.

This problem together with the need to find new waste disposal methods have led to the development of plants or methods for cogenerating electricity together with heat and including a carbonaceous raw material gasification unit or phase and a raw material utilization unit or phase. gasified, to generate electricity and useful heat, using conventional generators such as internal combustion engines.

AIMS OF THE INVENTION

An object of the present invention is to provide a new plant and a new method for converting a carbonaceous raw material into electricity with high efficiency, by feeding the synthesis gas (syngas) into a fuel cell, in particular a Solid Oxide Fuel Cell. .

Another object of the present invention is to provide a plant and a method as indicated above, which allow to obtain a combined production of electricity and heat, with no or minimized emission of CO2 into the atmosphere.

Another purpose of the present invention is to provide a plant and a method capable of being used in an application of capture and storage of carbon dioxide or of increased recovery of oil.

Another object of the present invention is to provide an economical plant and method for thermally treating waste, suitable for the cogeneration of electricity and heat.

According to a first aspect of the present invention, a plant according to claim 1 is proposed.

According to another aspect of the present invention, a method according to claim 11 is proposed.

The dependent claims refer to preferred and advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages can be better explained and understood by the following description and the attached drawing, given as a non-limiting example, in which:

Figures 1 to 3 illustrate respective examples of embodiment of a plant according to the present invention.

EXAMPLES OF REALIZATION OF THE INVENTION

With reference to the attached figures, a power island plant or system 1 for the conversion of carbonaceous raw material into electricity and into a separate gas stream of carbon dioxide (CO2) has been illustrated, ready for a capture and sequestration of carbon dioxide or increased recovery of petroleum, according to the present invention, which comprises at least a first unit or treatment system 2, designed to gasify carbonaceous raw materials, both in solid and liquid state, supplied for example at a temperature between 20 ° C and 60 ° C, preferably equal to about 40 ° C, so as to obtain a flow of syngas or synthesis gas containing carbon monoxide and hydrogen, at least one Solid Oxide Fuel Cell 4, comprising at least one anode section 4a and at least one cathode section 4b and adapted to receive, at the inlet, at the anode section 4a, the flow of syngas, for example supplied at a temperature of between 600 ° C and 800 ° C, preferably about 700 ° C and, at the cathode section 4b, a flow of air, supplied for example at a temperature between 550 ° C and 750 ° C, preferably equal to about 650-700 ° C , and (arranged) to produce, at the anode section 4a respective outlet gases, for example at a temperature ranging between 700 ° C and 850 ° C, preferably equal to about 750-800 ° C and, at the cathode section 4b, a mixture of O2 and N2.

Preferably, the syngas comprises a mixture of CH4, CO, CO2, H2 and H2O and possibly other contaminants as defined in the following table: Syngas component Min [% Vol] Max [% Vol]

CO 30.0 60.0

H 25.0 60.0

H2O 2.0 30.0

CO2 5.0 20.0

Inert gases 0.2 1.0

CH4 0.0 5.0

N2 0.5 4.0

H2S 0.1 ppm 1.0 ppm

COS 0.0 ppm 0.2 ppm

Others 0.0 0.3

The output gases may instead include a mixture of CO, CO2, H2 and H2O.

The amount of fuel that is converted from the Fuel Cell to Solid Oxide 4, i.e. the use of fuel, varies between 0.5 and 0.95 or, preferably, between 0.70 and 0.85.

The plant 1 also comprises at least one oxygen combustion unit 5, designed to combine the output gases with a flow of O2, for example fed at a variable temperature between 10 ° C and 40 ° C, preferably equal to about 25 ° C, in order to generate respective exhaust gases, for example comprising a mixture of CO2 and H2O, and optionally, at least one heat exchanger unit 6 arranged to receive the exhaust gases at the inlet and cool them for recovery of energy.

The oxygen combustion unit 5 is or can be placed in fluid communication with a suitable source of O2 (SO). The oxygen combustion unit 5 is mainly designed to complete the combustion of exhaust gases, such as electro-chemically unreacted hydrogen and carbon monoxide, coming from the anode section 4a.

The heat obtained from the anode section 4a and the oxygen combustion system could, if desired, be used by an electricity generation cycle comprising a heat recovery steam generator and a steam turbine or a Rankine cycle generator. Organic, which is a system for the production of additional electrical power from recovery heat sources.

The thermal power obtainable with a plant according to the present invention can vary between 50 and 2000 MWth (thermal megawatt), or preferably from 50 to 500-800 MWth of chemical energy transported by the syngas.

The power island is probably made up of a set of SOFC modules, each including the elements within the dotted line. This set could be enclosed in a thermally insulated enclosure called ("Hot Box"), while the oxygen combustor can be outside the Hot Box and serve multiple SOFCs. The single SOFC module can have a capacity of 50-200 kWe A.D.

As regards the connections of the components or units of the plant, the plant 1 comprises at least a first duct or line 7 to convey carbonaceous raw material to the first treatment unit 2, a second duct or line 8 to supply steam, for for example at a temperature between 600 ° C and 800 ° C, preferably from about 650 ° C to 700 ° C, towards the first treatment unit 2, to be used as a fluidifying agent in the gasification system, a third duct or line 9, to transfer syngas from the first treatment unit 2 to the Solid Oxide Fuel Cell 4, and a fourth duct or line 10, to transport the output gases from the Solid Oxide Fuel Cell 4 to the oxygen combustion unit 5.

The Solid Oxide Fuel Cell 4 is structured so that the gas flows leaving the anode and the cathode are kept separate.

Optionally, the plant 1 comprises a fifth duct or line 11 to transmit the exhaust gases to the heat exchanger unit 6, and / or a sixth duct or line 12 to convey a flow of O2 from the source of O2 (SO) to the Oxygen combustion unit 5. The O2 flow is also used to feed the gasification system or device, as an oxidizing agent through a respective conduit 12a. The O2 can be produced by an air separation unit or ASU.

Clearly, the first duct or line 7 is or can be placed in fluid communication with or connected to a suitable source W of carbonaceous raw material, while the second duct or line 8 is or can be placed in fluid communication with or connected to a suitable source S of steam (see in particular Figure 3). The steam can also be obtained by means of the heat recovery steam generator unit 28 (see in particular Figures 1 or 2).

The second duct or line 8 could also branch into two respective ducts 8a, 8b, one 8a which enters the first treatment unit 2 and the other 8b which flows into the third duct 9 or the anode section 4a.

The material to be treated in a plant and in a method according to the present invention comprises a number of carbonaceous raw materials, including but not limited to both virgin and waste biomass, municipal and industrial solid waste, petrochemical or industrial waste and solid fossil fuels. .

With reference now more particularly to the first treatment unit 2, it comprises at least one gasification device (not illustrated in detail) suitable for treating the carbonaceous raw material, in the presence of oxygen and steam, to produce raw syngas or raw synthesis gas and a char (i.e. unburned components of the gas phase) and / or at least one pyrolysis device adapted to treat the carbonaceous raw material, to produce crude syngas or crude synthesis gas and a char.

The first treatment unit 2 further comprises a syngas cleaning unit (not shown in detail), designed to treat the raw syngas and char at a high temperature, in order to destroy or reduce (preferably below 5 ppm or more preferably below 1 ppm) the tar (tar) contained in it, so as to make it suitable for feeding the Solid Oxide Fuel Cell 4.

The first treatment unit 2 preferably comprises a thermal gasification system to convert the raw material into raw syngas, in the presence of steam and oxygen, and a plasma treatment unit, separated from the gasification unit, of this raw syngas. The plasma treatment unit conditions the raw syngas, optionally in the presence of oxygen and at a temperature of 1200 - 1500 ° C, preferably 1350 ° C, in the presence of intense ultraviolet light, so that the long chains of the carbon are reduced to simple molecules of carbon monoxide and hydrogen and that the bottom ash of the gasifier is melted into a slag. The plasma-treated syngas cooling and cleaning unit may comprise a combination of a heat exchanger, designed to cool the syngas stream to 200-100 ° C, preferably 150 ° C, and thermochemical cleaning devices, in in such a way as to obtain purified syngas.

A first treatment unit according to the present invention can be as taught by the international application published under number WO2007000607A1.

The first treatment unit 2 may, for example, include a series of components, such as a gas cooling system, a particulate removal system, a wet gas cleaning system and / or a heater.

The gas cooling system or waste heat exchanger preferably comprises a heat recovery exchanger, designed to reduce the temperatures of the syngas, from about 1150 ° C to 150 ° C, and transfer this sensitive heat to a heat transfer oil to be about 150 ° C to 320 ° C. Diathermic oil is used by an organic Rankine cycle to generate electrical energy, starting from waste heat.

This gas cooling system mainly includes a shell and tube exchanger traversed by oil, with the specific characteristics used in the waste industry and with particular attention paid to construction materials for a long service life and to minimize the time of inactivity caused by the accumulation of deposits and corrosion. A portion of the heat transferred to the diathermic oil can be used for the generation of steam, by means of a recovery heat boiler. This steam can be used as a gasification medium together with oxygen, to fluidify the gasifier bed.

The gas cooling system can further comprise a hopper or hoppers for removing the powders from the heat exchanger.

The oil-flowed shell and tube exchanger may include cleaning systems, such as pulse cleaning systems. Regarding the particulate removal system, it should be considered that this gas cleaning system, operating at 150-170 ° C, in addition to removing fine particles from the gas stream, neutralizes acid gases such as hydrochloric acid ( HCl) and sulfur dioxide (SO2) and removes heavy metal vapors.

The syngas can then be passed through a ceramic particulate filter, through an insulated duct into which sodium bicarbonate and activated carbon are injected. The conduit allows sufficient residence time and turbulence to allow for good reaction and collection, providing high capture rates for acidic components. Particulate matter is retained on the ceramic filter elements and periodically removed using a reverse pulse system by means of a nitrogen jet.

The syngas at 150 ° C will then enter a ceramic filter, which is designed to remove solids and to allow the reaction between sodium bicarbonate and hydrochloric acid and sulfur dioxide in the dispersed gas phase to take place. Activated carbon can also be added to the incoming gas stream to adsorb vaporized heavy metals from the feedstock in upstream processes.

With reference now to the wet gas cleaning system, it can comprise a first gas cooling stage, in which the gas is cooled from 170 ° C to 30 ° C, capable of condensing most of the moisture contained in the flow. of gas. In its second stage, a wet scrubbing system using a conventional alkaline oxidizer can be used to remove H2S from the gas flow.

The wet gas cleaning system may include a cooling and desulfurization package and / or an activated carbon bed.

As for cooling in the first place, the syngas from the dry filter containing a residual amount of hydrochloric acid, hydrogen sulphide and sulfur dioxide, can be passed into a scrubber, where it is cooled by direct contact with cold water.

Regarding the activated carbon bed filter, a carbon bed container can be included to capture any residual volatile metals and sulfur in the syngas.

With reference now to heating, the saturated syngas leaving the desulfurization column can be passed through a heating unit to raise the syngas temperature beyond the saturation point. The heating unit may include a water / gas heat exchanger, with hot water from the process used to provide the heat source.

The temperature of the syngas leaving the heating unit will depend on the solution used for the power island.

The syngas cooling and cleaning system can be equipped with one or more fans, for example two induced draft fans or ID fans. The first fan ID can be placed between the particulate filter and the wet gas cleaning system, while the second fan ID (can be arranged) between the heater and the power island.

Furthermore, the use of a thermal oxidizer 29 is also envisaged, which is designed to treat all the combustion gases and syngas during plant start-up and to control (through a suitable control unit) the interruption of communication. of fluid between the first treatment unit 2 and the Solid Oxide Fuel Cell 4, in the case in which the syngas is not suitable, that is, if it has an unsatisfactory composition predetermined requirements, necessary to power the generator of the fuel cell. Thermal oxidizer 29 is specified to ensure compliance with the residence time criteria imposed by the Industrial Emissions Directive (IED) requiring at least 850 ° C, for a time of at least 2 seconds. The thermal oxidizer is able to treat 100% of the syngas flow.

The fluid treated by the thermal oxidizer 29 can be sent to a vent VE.

The syngas passes to the thermal oxidizer before passing through the burner head and into the combustion chamber of the thermal oxidizer. Combustion and dilution air is added by the burner fan. The geometry of the system creates turbulent flow conditions causing effective mixing of the air with the fuel, resulting in a rapid achievement of a uniform temperature inside the combustion chamber.

When the thermal oxidizer is not in use, to treat the flue gas or syngas, a backup burner will operate, which maintains the temperature of the primary zone of the thermal oxidizer at 850 ° C.

The fuel for the thermal oxidizer can be liquefied petroleum gas (LPG), natural gas or oil.

Preferably, the plant comprises a seventh duct or line 13 for recirculating the outlet gases towards the duct 9. The percentage of the outlet gases recirculated towards the inlet depends on the particular composition of the syngas.

As regards the Solid Oxide Fuel Cell 4, it advantageously comprises a battery of several SOFC stack modules, each integrating one or more stacks, typically from 1 to 20, preferably from 1 to 8, each stack being made up of a number of cells between 20 and 200, preferably between 50 and 100 electrically connected in series, which work in the fuel conversion range (Use of Fuel or FU) between 50% and 95%, preferably between 70% and 85%.

To optimize thermal integration and electrical efficiency, several stacks can also be connected in a cascade configuration, i.e. one in series with the other, with respect to the syngas flow.

Furthermore, in order to optimize thermal integration and electrical efficiency, the batteries can also be connected in a cascade configuration with respect to the cathodic air flow.

To optimize electrical integration, the batteries can be connected both in series and in parallel.

Furthermore, the plant 1 can be equipped with at least an air recovery or separation unit 14, fed with a flow of air, for example with a variable temperature from 10 ° C to 40 ° C, preferably equal to about 25 ° C, possibly by means of an eighth duct or line 15, which is in fluid communication or connected or connectable to a suitable source of air A. The air recovery unit 14 is designed to generate the flow of air from feed through a ninth duct or line 16, at the inlet to the cathode section 4b. If desired, a return duct or line 17a, 17b is provided for the distribution of O2 and N2 from the cathode section 4b to the air recovery unit 14 and optionally from the air recovery unit 14 to a vent V.

The plant 1 can also include a start burner 18 arranged to start the operation of the Solid Oxide Fuel Cell 4.

The start-up burner 18 can be fed by a suitable flow, such as a mixture of natural gas and air 19, for example supplied at a temperature ranging from 10 ° C to 40 ° C, preferably equal to about 25 ° C, and is designed to send a suitable heating flow 20, for example at a temperature between 600 ° C and 900 ° C, preferably equal to about 780 ° C-800 ° C, or electrical heating signals to the air recovery unit 14 or to the section cathode 4b. The starting burner 18 is or can be placed in fluid communication or connected to a suitable source NG of natural gas and air.

Typically, a natural gas pre-mix burner operates with a Lambda, i.e. the excess air between 1 and 1.3, preferably between 1.1 and 1.2.

Oxygen and nitrogen can be obtained by means of oxygen and nitrogen generation plants.

As regards the heat exchanger unit 6, it is designed to heat exchange a first flow of H2O and CO2 coming from the exhaust of the oxygen combustor 5 and a second flow of diathermic oil (see figures 1 and 2) . The plant may further comprise an Organic Rankine Cycle unit 21 and a heat recovery steam generator 28.

More particularly, the plant includes a tenth duct or line 22 to supply the first flow, for example at a temperature between 250 ° C and 400 ° C, preferably equal to about 320 ° C, to the Organic Rankine Cycle unit. 21, after which, the first flow can be further cooled through a heat recovery steam generator 28 (see figure 1) before being returned to the heat exchanger unit 6, via the eleventh duct or line 23, for example at a temperature between 100 ° C and 300 ° C, preferably equal to about 150 ° C. A twelfth duct or line 24 is also provided for supplying the second flow, for example at a temperature between 200 ° C and 400 ° C, from the heat exchanger unit 6 to the next plant unit. In this regard, the plant 1 can also include a condenser 25, enslaved by the twelfth duct or line 24 and arranged to treat the second flow, after having passed it through the heat exchanger unit 6 and to separate respective mixed or contained components. in it, for example CO <2> and H2O, to be transported to respective lines or ducts 26, 27.

The heat recovery steam generator 28 can also be arranged in such a way as to intercept the twelfth duct or line 24 (see Figure 2).

In both cases described (Figures 1 or 2), the heat recovery steam generator 28 can produce the steam S to be fed to the first treatment unit 2.

Alternatively, the plant is not equipped with this evaporator and the steam for the first treatment unit 2 is supplied by an external source. In this case, the heat exchanger 6 is used for a different type of energy recovery.

The plant can be further equipped with a master (system) and many local control and monitoring systems intended to receive signals from the plant sensors and / or to control the units or components or valves of the plant itself. , on the basis of these signals and / or settings predetermined by an operator.

Certainly, a system according to the present invention may include other components, although not shown in the attached figures, such as an expander / generator, for example intercepting the third duct or line 9, which generates part of the electricity produced by the system.

According to the present invention, a method is also provided for the conversion of carbonaceous raw materials, which can be carried out with the aforementioned plant 1.

This method includes:

- a gasification step carried out in the first treatment unit 2, thus obtaining a flow of syngas,

- a phase of treatment of the syngas flow, in the Solid Oxide Fuel Cell 4, in such a way as to produce respective outlet gases at the anode section 4a, and a mixture of O2 and N2, at the cathode section 4b,

- a step of combining the output gas with a flow of O2 in the oxygen combustion unit 5, in order to generate respective exhaust gases.

Optionally, the method can include a step in which the exhaust gases are subjected to heat exchange, in the heat exchanger unit 6, in order to cool the gases themselves.

The gasification step may include a raw material treatment step in the presence of oxygen and steam, to produce exhaust gas and a char, or a pyrolysis step, intended to treat the raw material, to produce exhaust gas and a char. , and a phase of treatment of the exhaust gases and char, in a plasma treatment unit, in the presence of oxygen.

Furthermore, the gasification step can include a step of thermal gasification of the carbonaceous raw material in the presence of oxygen and steam, to produce crude syngas comprising mainly carbon monoxide and hydrogen and the method further comprises a plasma treatment step, separated from the phase. of gasification, of this raw syngas.

The method could also include a step of combining the output gases with a flow of O2 in the oxygen combustion unit 5.

The present invention has been described according to a preferred embodiment but equivalent variants can be conceived without departing from the scope of protection offered by the following claims.

Claims (16)

CLAIMS 1. A plant for converting a carbonaceous raw material into electricity and a separate carbon dioxide (CO2) gas stream, comprising: - at least one first heat treatment unit (2) designed to gasify the carbonaceous raw material, so as to obtain a flow of syngas, comprising carbon monoxide and hydrogen, - at least one Solid Oxide Fuel Cell (4) comprising at least one anode section (4a) and at least one cathode section (4b) and designed to receive said flow of syngas in correspondence with said anode section (4a), and a flow of air at said cathode section (4b), and to produce respective output gases at said anode section (4a) and a mixture of O2 and N2 at said cathode section (4b), - at least one oxygen combustion unit (5) designed to combine said output gases with an O2 flow, in order to generate respective exhaust gases, - a first duct or line (7) to convey carbonaceous raw material to said first treatment unit (2), - a second duct or line (8) for supplying steam to said first treatment unit (2), - a third duct or line (9) to transfer syngas from said first treatment unit (2) to said Solid Oxide Fuel Cell (4), - a fourth duct or line (10) for transporting the output gases from said Solid Oxide Fuel Cell (4) to said oxygen combustion unit (5), wherein said first treatment unit (2) comprises at least one gasification device adapted to treat carbonaceous raw material in the presence of oxygen and steam to produce crude syngas and a char and / or at least one pyrolysis device adapted to treat carbonaceous raw material, to produce crude syngas or crude synthetic gas and a char, said first treatment unit (2) further comprising a syngas cleaning unit designed to treat crude syngas and char at a high temperature, in order to destroy or reduce the tar contained in it, so as to make it suitable for feeding the Solid Oxide Fuel Cell (4). A system according to claim 1, wherein said first conversion unit (2) includes one or more of the following components: a gas cooling system, a particulate removal system, a wet gas cleaning system and a heater. 3. Plant according to claim 1 or 2, wherein said syngas cleaning system comprises at least one plasma treatment unit. 4. Plant according to claim 2 or according to claim 3 when dependent on claim 2, wherein said gas cooling system or said heater comprises a heat recovery exchanger designed to reduce the temperatures of the syngas from about 1150 ° C to 150 ° C and transfer the heat thus obtained to a diathermic oil to heat it from about 150 ° C to 320 ° C. Plant according to any one of the preceding claims, comprising a thermal oxidizer (29) designed to treat combustion gas and syngas during plant start-up and to control the interruption of fluid communication between the first treatment unit (2 ) and the Solid Oxide Fuel Cell (4) if the syngas is not suitable for feeding said Solid Oxide Fuel Cell (4). 6. Plant according to any one of the preceding claims, wherein said at least one Solid Oxide Fuel Cell (4) includes a battery of different SOFC modules, each integrating one or more stacks, each stack being constituted by a number of cells between 20 and 200, preferably between 50 and 100 electrically connected in series. 7. Plant according to any one of the preceding claims, comprising at least an air recovery unit (14) fed with a flow of air and designed to generate said flow of air to be fed into said at least one cathode section (4a ). 8. Plant according to any one of the preceding claims, including a starting burner (18) designed to start the operation of said Solid Oxide Fuel Cell (4). 9. Plant according to any one of the preceding claims, comprising at least one heat exchanger unit (6) designed to receive said exhaust gases at the inlet and cool them for energy recovery. 10. Plant according to claim 9, wherein said heat exchange unit (6) is designed to heat exchange a first flow of H2O and CO2, coming from the exhaust of said oxygen combustor (5), and a second flow. 11. Plant according to any one of the preceding claims, comprising an Organic Rankine Cycle unit (21) and a heat recovery steam generator (28). Plant according to claims 10 and 11, comprising a tenth duct or line (22) for transporting said first flow to said Organic Rankine Cycle unit (21), after which the first flow can be further cooled through said steam generator to heat recovery (28) before being returned to the heat exchanger unit (6) via an eleventh duct or line (23). 13. Plant according to claim 10 to 12 when dependent on claim 10, comprising a condenser (25) designed to treat said second flow after having been passed through said heat exchange unit (6) and to separate respective mixed or mixed components it contained. 14. Plant according to any one of the preceding claims, comprising a seventh duct or line (13) for recirculating the outlet gases towards said third duct or line (9). A method of converting a carbonaceous raw material into electricity and a carbon dioxide gas stream with a plant according to any one of the preceding claims, comprising: - a gasification step in said first treatment unit (2), thus obtaining a flow of syngas, - a treatment step of said syngas flow in said Solid Oxide Fuel Cell (4), in such a way as to produce respective outlet gases at said anode section (4a), and a mixture of O2 and N2, in correspondence of said cathode section (4b), ed - a step of combining said output gases with a flow of O2 in said oxygen combustion unit (5) in order to generate respective exhaust gases. The method of claim 15, wherein said gasification step includes a step of thermal gasification of said carbonaceous raw material in the presence of oxygen and steam to produce crude syngas comprising mainly carbon monoxide and hydrogen, and the method further comprises a step of plasma treatment, separated from the gasification phase, of this raw syngas.