ITMI20111161A1 - MCFC MULTI-STACK AND METHOD SYSTEM FOR SEPARATING CO2 FROM COMBUSTION FUMES CONTAINING NOX AND SOX - Google Patents

Description

DESCRIPTION

"MCFC MULTI-STACK SYSTEM AND METHOD FOR SEPARATING C02 FROM COMBUSTION FUMES CONTAINING NOX AND SOX"

The present invention relates to a multi-stack MCFC system for separating C02 from combustion fumes containing NOx and SOx and a method for separating C02 from combustion fumes containing NOx and SOx by means of a multi-stack MCFC system.

In particular, the invention is placed in the field of systems for the separation of C02 from combustion fumes and more specifically in the sector of processes and devices capable of selectively extracting C02 from the fumes in which it is diluted, to make it available concentrated in a flow gaseous from which it is easily separable. Even more specifically, the invention is inserted in the field of MCFC-CCS systems, that is to say systems in which, by means of molten carbonate fuel cells (MCFC), C02 is extracted from the fumes in which it is diluted and concentrated in a gaseous flow rich in H20 vapor and substantially free of N2 diluent, in order to facilitate its subsequent capture (CCS = "Carbon Capture and Storage").

The ability of molten carbonate fuel cell plants (MCFC) to operate the separation of C02 from combustion fumes fed to the cathode is known. Various system schemes have been proposed, with both pressurized and atmospheric pressure solutions.

The ability of the MCFC cells to extract C02 from the cathode gas and release it in the anode gas derives in fact from the operating principle of the cells; However, it is normally necessary, in order to create efficient CCS systems, to manipulate the anode outlet gas before the C02 separation.

Various ways of manipulating the exhausted anodic are known in order to obtain, in addition to the flow of C02 to be "sequestered" or used, also recovery H20 and residual fuels to be used, as well as a plurality of different ways with to recover energy and / or products obtained through such manipulations, within the MCFC-CCS system or for external uses.

It is also known to use both mono-stack MCFC systems and multi-stack MCFC systems for these purposes.

In almost all of the multi-stack MCFC systems made for distributed generation (currently an almost exclusive field of application of MCFC cells) all the batteries are in parallel for both anode and cathodic power supply and are in the same nominal working conditions .

However, in this context, MCFC systems have also been proposed where the batteries have cathodic power supply, anode power supply or both in series (for example, as shown in EP442352, US5413878, EP0947022), according to logic aimed at capturing specific purposes on a case by case basis. , usually relating to increased efficiency or improvements in thermal management. However, these are always solutions designed for systems in which the entire C02 accumulated in the anode outputs is sent to the cathodes because it is required for the cathodic supply within the MCFC system itself, a situation that in fact leaves no room for its extraction. and catch. In these systems, essentially, all the C02 in circulation is discharged into the atmosphere from one or more cathode outputs.

In addition to MCFC systems with two or more batteries fluidically in series, hybrid multi-stack systems are also known in the state of the art, in the sense that they incorporate fuel cells of different supply chains connected fluidly in series (as shown for example in US6033794, US6623880 , US5541014).

As regards the known MCFC-CCS systems, even when configured as multi-stacks (i.e. formed by several batteries of MCFC cells electrically connected to each other), they are described as consisting of identical batteries, or placed all fluidically in parallel, or organized in strings placed fluidically in parallel, with each string formed by two or more batteries in series, and are powered so that the batteries (if all in parallel) or, respectively, all the battery strings work in the same nominal process conditions. In the first case, the organs for handling the exhausted anode can be one for each of the individual batteries or a common one for several batteries; in the second case one for each single string, one common for several strings, or even one for single batteries of a string, as indicated in patent application MI2009A002259.

Therefore the manipulation organs of the anode exhausted can be one for each of the single batteries in parallel, one common for several batteries, of the same string or even one common to several strings.

Even when the solutions described are constituted by strings of two (or more) batteries in series each equipped with its own organ for handling the exhausted anode, there are no known solutions which provide for the H2-rich flows collected at the output of said organs of the differentiated recirculation paths for the different batteries of a string, so that, precisely through this differentiation, the enrichment effects in H2 and reduction of the use of H2 obtained from the recirculation itself are concentrated on the first of the batteries in series along the string .

It is also known that for MCFCs there are several critical contaminants and that each of them must remain under its own specific threshold, which translates into limits on their contents in the anode feeds and on their contents in the cathode ones.

These limits are also significantly different depending on the particular type of battery with direct internal reformer (DIR), internal indirect reformer (IIR), without internal reformer (with external reformer, powered by H2, syngas, biogas, etc.)

Combustion fumes can be very different in type and level of critical contaminants present, but they usually share some of them above the thresholds allowed by MCFCs (sometimes well beyond).

Therefore, almost all of the known MCFC-CCS systems, in order to be conveniently exploited, require that an adequate smoke clean up be placed upstream, with reference to the particular type of battery chosen.

For this reason, the batteries with direct internal reformer (both in the basic version, DIR and in the one known as Advanced Internal Reformer, AIR), currently the best and most widely used in distributed generation, are not considered conveniently exploitable to create with them 1 'entire MCFC section of an MCFC-CCS plant, as they would require an almost prohibitive cleaning of the fumes (in particular, it is necessary to bring the SOx content back to the levels typically encountered in the air).

Moreover, the background art describes MCFC-CCS pluristack systems which have DIR batteries as a backbone for the capture of C02 from the fumes (and for the production of electrical power with high efficiency associated with it). entry higher SOx levels. In fact, in these pluristack systems there are also batteries without Direct Internal Reformer, whose cathodes are the exclusive way of entry of the fumes into the MCFC-CCS system itself. The DIR coils are enabled to operate on fumes that have entered dirty into the MCFC-CCS system by having the cathodic power supply downstream of a battery without DIR which, in addition to a complementary role in the capture of C02, carries out an action of filter (Italian patent application MI2009A002259).

For this system the limits on SOx are those (much milder) valid for batteries with indirect internal reformer or without internal reformer and not those, extremely restrictive, required by DIR batteries. In fact, the S present in the fumes (in the form of SOx) is almost completely captured by the electrolyte of the first battery it encounters in its path (and then released as H2S in the exhausted anodic of said battery). Since in the solution described in ΜΠ™ 2009Î ”002259 this first battery does not have a direct internal reformer, in it the thermal management and the availability of H2 are not affected by the release as H2S in the anodic compartment of the SOx entered on the cathode side. In the power supply of the cathodes of DIR batteries, SOx is absent and therefore the vitality of the catalysts, placed directly in the anodic compartment, is not threatened.

In batteries without DIR, those through which the fumes enter the MCFC-CCS system, the release of H2S in the anode gas flowing towards the outlet does not produce a drift towards irreversible degradation, as would happen if they were DIR batteries. So the SOx entered the cathode can be expelled as H2S without this having a destructive effect on the operation of the cell. Of course (if SOx exceeds the threshold valid for batteries of the specific type used) there is a performance penalty, which also entails a decrease in the current density which said first battery can operate with respect to operations with clean gas. However, it is possible to maintain a stable duty point, unless one expects to reach excessive exceedances of the threshold, in which case a degradation mechanism would also be triggered in this case.

Although MI2009A002259 exclusively concerns the placement in series of a battery without DIR and of a DIR, the teaching that can be obtained from it is broader: putting two batteries in series on the cathode side makes the one downstream work with cleaner oxidant and without SOx.

At the same level of SOx in the cathode, the amount of the penalty is very sensitive to the composition and use of the anodic gas: gases rich in H2 and low uses of H2 reduce it.

It is also known that recirculating at the anode inlet the flow with the H2-rich residue leaving the separator that removes H20 and extracts C02 from the anode exhaust allows to increase the efficiency of the MCFC-CCS system (as described for example in US7396603), as , without causing the cell voltage to drop, it allows the percentage of hydrogen introduced from the outside (or obtained from fuel supplied from the outside) that is exploited to generate current to be brought to the limit up to 100%. In fact, in order to appropriately increase the flow rate of this recirculation, it is possible to contain the so-called "use of H2 at battery level" within the desired limits, i.e. the one calculated as the ratio between the flow rate of H2 consumed to produce current and the flow rate of H2 which it enters the anode as a whole, including recirculation.

In general, the known system configurations (in particular, the monostack or pluristack ones with only coils in parallel and without anodic recirculation) inevitably require an additional strong clean up.

In particular, the SOx content must be brought below the valid threshold when the specific type of battery used operates with lean anode gas.

In fact, these systems can only entrust the entire generation of current, which is associated with the capture of C02, to batteries in which the fumes enter directly. Furthermore, it is not possible to achieve high electrical efficiency without a high use of fuel and in such systems a high use of H2 automatically entails a depletion of the gas in the whole portion of the cell close to the anodic outlet. Therefore the sensitivity to SOx, for such batteries is high and the additional clean up can only be adequately pushed.

The solutions which add the simple recirculation at the anode inlet of a portion of the exhausted anode as such (such as for example some solutions shown in EP0418064) accentuate the problem.

Ultimately, most of the known MCFC-CCS systems, to produce power with high efficiency, must deplete the anode gas, at least in the portion of the cell close to the outlet, and therefore require very strict thresholds on the levels of SOx and NOx in the fumes. powered up.

The correction of the defect through the recirculation at the anode inlet of the H2-rich flux exiting the device that extracts C02 from the anodic exhaust generates accumulation mechanisms that accentuate the dynamics of SOx and, respectively, NOx poisoning. If the accumulation of H2S deriving from SOx can be avoided with an appropriate choice of the C02 separator device installed on the anode exhaust, the only defense against NOx (apart from their removal from the fumes) is to change the approach to enrich the anode gas .

The NOx present in the cathode gas tend to react with the electrolyte, forming alkaline nitrites and nitrates which diffuse into the matrix. The removal of the anode side due to the effect of the anode gas, the more effective the richer in H2 the anode gas is, occurs almost entirely by generating N2 and minimally NH3 (ratio of the order of 100: 1).

Like SOx, NOx also entails a performance penalty, so that also in this case a stable operating point can only be obtained at a reduced current density and with a voltage lower than that which would occur under the same conditions with clean gases.

Trapping N2 in the anode loop would inexorably inhibit the washing, on the anode side, of the nitrites and nitrates formed in the electrolyte due to the reaction at the cathode with NOx. This would oblige to demand that the NOx in the fumes are a few ppm, in order not to jeopardize the operation of the battery.

Furthermore, as a side effect, by interrupting the drainage of NOx by the electrolyte, the accumulation of N2 would prevent the batteries themselves from being used as a tool to further reduce the NOx emissions into the atmosphere by the host plant, making the capacity useless. , intrinsic to MCFC but closely linked to the establishment and persistence of washing conditions on the anode side, to convert a conspicuous portion of the NOx entered on the cathode side into N2.

It is an object of the present invention to provide a system and a method for separating C02 from combustion fumes by means of multi-stack molten carbonate fuel cells (MCFC) which is free from the drawbacks highlighted herein of the known art; in particular, it is an object of the invention to provide a system of the MCFC-CCS type which operates, with respect to known systems, with high electrical efficiency and at the same time with higher thresholds on SOx and NOx in the cathode gas.

The present invention therefore relates to a system and a method for separating C02 from combustion fumes by means of multi-stack molten carbonate fuel cells (MCFC) as defined in essential terms in the annexed claims 1 and 12, respectively, as well as , for the additional preferred characters, in the dependent claims.

Basically, the main features of the invention are the following:

- the MCFC-CCS system is organized in two or more battery blocks, blocks having their respective cathode lines connected in series;

the fumes to be treated, containing contaminants, only enter the cathodes of the batteries of the first block;

- the anodes of the batteries of the first block are made to work as much as possible in excess of H2, making them pass through as much H2 as possible of that globally needed to power the entire MCFC-CCS system as a whole, possibly adding other usable H2 from the host system or from other users;

- in this way the coils of the first block can operate with rich anode gas at the inlet and with low H2 use, and therefore with (anodic exhausted) gas rich also at the outlet; this condition, for a given level of SOx and, respectively, NOx in input, minimizes the performance penalty of the coils of the first block compared to those obtainable in the same working points with clean gases and at the same time maximizes the capacity to drain SOx and NOX from the fumes fed to the cathodes;

this allows to transfer in the anode exhausted of the batteries of the first block: in the form of H2S, almost all of the sulfur entered as SOx on the cathode side and, in the form of N2, most of the NOx entered on the cathode side;

- the separation devices for the recovery of C02, placed on the anode outputs of the batteries of the different blocks, and the lines that handle the exhausted anode are organized in such a way that said H2S and N2 can be expelled from the MCFC-CCS system without passing through from the anodes of the batteries of the second (and subsequent) H2S block generated by the SOx present in the fumes;

as a result of the aforementioned measures, the batteries of the blocks following the first work on substantially clean oxidants, containing at most NOx residues brought back below the thresholds that cause effects on performance.

The main constituent elements of the inventive idea are therefore:

a} an MCFC-CCS system comprising at least two blocks of MCFC batteries (there are no preclusions for the type of batteries, which can be for example of the DIR, IIR type, without internal reformer, etc.);

b) a connection system configured so that:

- the fumes to be treated with the MCFC-CCS system only feed the cathodes of the coils of the first block (with or without added air); in the subsequent blocks no fumes enter that have not passed through the cathodes of the batteries of the first block;

- the different blocks are fluidically connected in series on the cathode side, that is to say that the cathode outputs of the batteries of the first block supply the cathodes of the batteries of the second block (with or without added air) and, if the blocks are more than two, the outputs of the cathodes of the batteries of the second block supply (with or without adding air) the cathodes of the batteries of the third block and so on for any subsequent blocks;

c) separator devices, connected to the anode outputs of all battery cells of all blocks and which remove H20 and separate a flow with the C02 destined for sequestration from a flow rich in H2; said separator devices are organized in such a way:

- to process the exhausted anode of the batteries of the first block by removing H20, extracting C02 and at the same time also removing H2S, in particular until there is a residual H2S below 10% of the H2S level present at the anode output; in this way, the H2-rich stream remains substantially H2S-free (or in any case has a sufficiently low H2S content); And

- that at least a portion of the H2-rich flow outgoing from the separator device connected to the anode outputs of the batteries of the first block is sent, directly or after passing through the battery anodes of one or more of the other blocks, to a burner, which can be internal o external to the MCFC-CCS system; in this way, N2 accumulation phenomena are avoided;

- that at least a portion of the fuel required by other blocks, by the host plant or by other external users, transits, in the form of H2, from the anodes of the batteries of the first block or that, alternatively, at least a portion of the outgoing H2-rich flow from separator devices connected to the anode outputs of the batteries of other blocks transits from the anodes of the batteries of the first block (and therefore from the separator connected to the anode outputs of the batteries of the first block) before reaching the burner inside or outside the system.

The system as a whole is thus configured in such a way as to raise the H2 content in the anode gas of the coils of the first block (at the inlet, but also at the outlet), without wasting fuel.

In addition to the general advantage, common to C02 separator systems operating with MCFC cells, of separating C02 by producing energy instead of consuming it (as conventional separator systems do, all of the passive type), the invention achieves the following specific advantages with respect to systems MCFC-CCS manufactured in accordance with known techniques.

In the first place, the present invention is able to keep the current generation mechanism active in the MCFC system, which determines the removal of C02 from the combustion fumes, in spite of SOx and NOx inlet levels higher than those set as thresholds for known solutions.

It is important to note that the measures adopted in accordance with the invention are simultaneously effective against NOx and SOx.

At the same time, the present invention makes it possible to concretely exploit the potential of the MCFC cells to act themselves as an instrument to reduce the emissions of residues not only of CO and SOx, but also of NOx present in the fumes.

Therefore :

- compared to known solutions consisting of a single battery or of several batteries all in parallel, without anodic recirculation or with recirculation at the anode inlet of a portion of the exhausted anode taken upstream of the separator, the invention follows: with equal efficiency, higher thresholds on both SOx and NOx levels in the fumes; and with the same levels of SOx and NOx, higher efficiency;

- compared to known solutions consisting of a single battery or several batteries all in parallel, with recirculation of the H2-rich flow at the anode inlet coming out of the separator, the invention achieves much higher thresholds on NOx and the ability to use the battery itself as additional NOx removal tool;

- compared to the solution with batteries fluidically in series along the cathode lines (such as the one described in ΜΠ™ 2009A002259), the invention achieves higher thresholds for both SOx and NOx, together with a wide freedom in the choice of the types of batteries with which create the blocks of the MCFC-CCS system.

Room for maneuver in the choice of the type of batteries allows adequate responses to changes in priority between the need for higher performance over shorter life spans or longer life spans.

Further characteristics and advantages of the present invention will appear clear from the following description of a non-limiting example of its implementation, with reference to the figures of the annexed drawings, in which:

Figure 1 is a schematic view of a system for separating C02 from combustion fumes by means of molten carbonate fuel cells (MCFC) made in accordance with a first embodiment of the invention;

Figure 2 is a schematic view of a second embodiment of the invention;

Figures 3 and 4 are partial schematic views of further variants of the system of the invention.

With reference to Figure 1, a system 1 comprises: a first block 11 MCFC-CCS of MCFC batteries, at least a second block 12 MCFC-CCS of MCFC batteries, at least one burner 13 equipped with a reformer 14, and a connection system 15 which connects blocks 11, 12 and burner 13.

Although here and in the following reference is made to only one second block 12, it is understood that system 1 can include a series of second blocks 12.

The blocks 11, 12 comprise respective groups of batteries 21, 22 of MCFC cells, having respective cathodes 23, 24 (or cathode compartments) and anodes 25, 26 (or anode compartments), and respective separators 27, 28 acting on the anode exhaust of the batteries 21, 22. The cathodes 23, 24 of the two blocks 11, 12 are connected in series; if more than 12 second blocks are present, they have the cathodes of the respective batteries connected in series.

Preferably, the batteries 21, 22 of both blocks are provided with an internal reformer 31, 32, for example an indirect (IIR) or direct (DIR) reformer.

System 1 has a smoke inlet 33, through which the combustion fumes to be processed, coming from a host plant and generally containing SOx and NOx, enter system 1.

In the example shown in figure 1, the smoke inlet 33 is located upstream of the burner 13 and is connected to the burner 13, which is for example a catalytic burner, by a flue gas supply line 34, through which the fumes enter the burner 13; the reformer 14 is for example a reformer of the type MIR ("modular integrated reformer").

Optionally, air is added to the fumes fed to system 1 by means of an air supply line 35 which connects to the fumes supply line 34.

The burner 13 has an output connected to the cathodes 23 of the batteries 21 of the first block 11, through a cathode input line 36; the cathodes 23 are then fed with oxidizing gas consisting of the fumes coming from the host plant, possibly enriched with air and the products of the combustion that occurs in the burner 13.

The output of the cathodes 23 is connected via a cathode line 37 to the input of the cathodes 24 of the batteries 22 of the second block 12. Optionally, an air supply line 38 is connected to the cathode line 37 to add air to the flow fed to the cathodes 24. The outgoing flux from cathodes 24 is collected by a vent line 39 which leads to a vent 40.

The anodes 25 of the first block 11 are fed with a flow coming from the reformer 14 through an anode inlet line 41; the reformer 14 is fed, through a fuel supply line 42, with fuel, for example CH4, and with a flow rate of H20 (steam) needed to convert the fuel into H2. Advantageously, the fuel flow fed to the reformer 14 serves to cover all the consumptions of the blocks 11, 12 (if only batteries without internal reformer are used) or the part exceeding that already covered by the hydrogen produced inside the batteries (if there are internal reformer batteries) and also to supply a fraction of the energy of the host plant.

The flows outgoing from the anodes 25 of the batteries 21 of the first block 11 are sent, through an anode line 43, to the separator 27 (of known type), configured so as to remove H20 and extract C02 and H2S, in sequence or jointly.

The flow rich in H2 and containing residual fuels leaving the separator 27 is sent in part to the anodes 26 of the batteries 22 of the second block 12, through a further anodic line 44 (directly or passing through the reformer 32), and in part to the host plant, via an anode output line 45, to be consumed there.

The flows outgoing from the anodes 26 of the batteries 22 of the second block 12 are sent, through an anode line 46, to the separator 28 (of known type) which removes H20 and extracts C02. The stream rich in H2 and containing residual fuels exiting the separator 28 is sent via a recirculation line 47 to the burner 13, where the residual fuels contained in this stream are burned and the heat is recovered to support the reactions in the reformer 14 and to heat the oxidizing gas containing the combustion fumes fed to the first block 11 (optionally, the fumes are preheated by heat exchange with the flow outgoing from the cathodes 24 of the second block 12). The conversion into H2 of a fuel flow rate exceeding the requirement of the first block takes place in the reformer 14, that is, upstream of the anodes 25 of the first block 11.

In this way an additional flow rate of H2 is generated which can pass intact from the anodes 25 of the first block 11, helping to reduce the use of H2 and therefore to raise the percentage of H2 also at the outlet. This helps to create more favorable conditions for the removal of sulfur and nitrites / nitrates from the electrolyte. It is important to note that this happens without the need for additional fuel, because part of the fuel used by the host plant is used without consuming it.

The internal reformers 31, 32 of the batteries 21, 22 are fed through respective fuel supply lines 48, 49 with fuel (CH4) and steam flow rates necessary to allow the thermal management of the respective batteries 21, 22, through the absorption of heat associated with the endothermic H2 production reaction from the fuel reform. The H2 streams produced in the reformers 31, 32 are fed to the anodes 25, 26 of the respective batteries 21, 22.

The remaining portion of H2 required to complete the overall H2 requirement of the batteries 21, 22 is produced in the reformer 14, starting from fuel (CH4) and steam introduced through line 42.

The H2 flow rate generated in the reformer 14 from the conversion of the fuel introduced through the line 42, adding to the H2 flow rates generated in the reformers 31, 32 inside the batteries 21 of the first block 11 and the batteries 22 of the second block 12, covers the H2 requirement required so that the batteries 22 of the second block 12 can operate at the desired current with the use of the desired H2, once the quantity of H2 consumed in the batteries 21 of the first block 11 has been subtracted to generate the desired current and that sent to the host plant via line 45.

Since the reformer 14 is placed upstream of the anodes 25 of the first block 11, all the hydrogen generated in the system 1, with the exception of what is absolutely necessary to generate in the internal reformer 32 of the batteries 22 of the second block 12 to ensure its thermal management , enters the anodes 25 of the batteries 21 of the first block 11. This is essential to enrich the anode gases of the batteries 21 of the first block 11 in H2, both in input and output, to the maximum extent allowed, with the same fuel flow rate supplied to system 1. In this way, it contributes to creating the most favorable conditions for the removal of sulfur and nitrites / nitrates from the electrolyte in the batteries 21 of the first block 11, while minimizing the impact of SOx and NOx on performance, and to enabling the batteries 22 of the second block 12 to work with drastically reduced levels of SOx but also NOx.

The measures used to enrich the anode gas of the batteries 21 of the first block 11 are effective because they do not trigger accumulation mechanisms, neither of H2S (which is removed from the separator 27) nor of N2 (which is partly eliminated through the line 45 of anode outlet, and partly through the vent line 39).

It is clear that numerous modifications and variations can be made to the general scheme described here, especially regarding the ways to enrich the anode gas in H2.

For example, according to a variant, the entire H2-rich flow outgoing from the separator 27 of the first block 11 is sent to the anodes 26 of the batteries 22 of the second block 12, via the anode line 44 (while the line 45 is not used). of anode output shown in Figure 1).

According to a further variant, the H2-rich flow outgoing from the separator 27 is not sent to the anodes 26 of the batteries 22 of the second block 12, but is sent in part to the host plant, via the anode output line 45, to be there. consumed, and in part is recirculated, by means of an anodic recirculation line 51 (shown in broken line in figure 1) which is inserted on the anode input line 41, to the anodes 25 of the batteries 21 of the first block 11 (while it is not used the anodic line 44).

According to further variants, the H2-rich flux exiting the separator 27 is recirculated for a part to the anodes 25 of the batteries 21 of the first block 11, through the anodic recirculation line 51, and for the remaining part to the burner 13, arriving there or through the recirculation line 47, after passing through the anodes 26 of the battery 22 and the separator 28 of the second block 12, or directly through a further recirculation line 52 (also shown in broken lines in figure 1) which is inserted on said line 47, and / or to an external user (for example the host plant), directly or after passing through the anodes 26 of the battery 22 of the second block 12 (or subsequent blocks if present).

According to a further variant, the H2-rich flows outgoing from the separators 28 of the second block 12 are entirely or partially sent (instead of or in addition to the burner 13) to the anodes 25 of the batteries 21 of the first block 11, via an auxiliary line 53 which it branches off from the recirculation line 47 and connects to the anode input line 41, before being sent to the burner 13 (or to another burner, internal or external to the blocks 11, 12 MCFC-CCS), or to an external user.

In general, the burner 13 can be inside or outside the blocks 11, 12 MCFC-CCS.

Further combinations of the described configurations may of course also be employed.

In all cases, the passage of the fumes into the burner 13 favors the heating of the oxidizing gas to the inlet temperature in the coils.

Naturally, the heating of the fumes can also be provided in another way, for example by recovering heat, with suitable exchangers, from one or more of the hot flows circulating in system 1 and which must be cooled (such as for example the flow outgoing from the cathodes 24 of the second block 12 and collected by the vent line 39, or the anodic discharges coming out of the anodes 25, 26 through the anodic lines 43, 46).

In the examples described so far, the output of the burner 13 in which the combustion of the residual fuels not used by the batteries 21, 22 of the blocks 11, 12 takes place is connected to the cathodes 23 of the batteries 21 of the first block 11, which are therefore fed with the gaseous flow exiting the burner 13.

Alternatively, as shown in Figure 2, in order to increase the capture of C02, the system 1 comprises an additional group 55 MCFC, formed by one or more batteries 56 of MCFC cells having respective cathodes 57 and anodes 58, and the output of the burner 13 is connected to the cathodes 57 of the group 55, so that the gaseous flow exiting the burner 13 feeds the cathodes 57 (optionally enriched with air).

The group 55 has an anode output connected, via an anode line 60, to a separator 59 which removes H20 and C02 from a residual flow containing H2.

In this case, the combustion fumes coming from the host plant are fed, instead of the burner 13 as described above, to the cathodes 23 of the batteries 21 of the first block 11 (optionally, after adding air through the air supply line 35 ). The fumes inlet 33 is located upstream of the cathodes 23 and the fumes supply line 34 enters directly into the first block 11 and feeds the cathodes 23.

In addition to the reformer 14 as previously described, the fuel feed line 42 also supplies the anodes 58 of the supplementary group 55.

For the rest, the system 1 still has the general configuration described above, and the variants already highlighted with reference to Figure 1 are possible, especially with regard to the management of the flow rich in H2 and containing residual fuels leaving the separator 27 of the first block 11 , which can be sent to one or more of:

- the anodes 26 of the batteries 22 of the second block 12, through the anodic line 44 (directly or passing through the reformer 32);

- the host plant, via the anode output line 45;

- to the anodes 25 of the batteries 21 of the first block 11, through the anode recirculation line 51;

- to the burner 13, through the recirculation line 52 which departs from the anode output line 45 and connects to the recirculation line 47 coming from the anodes 26, after passing through the separator 28 of the second block 12.

According to a further variant, the flow rich in H2 (and containing residual fuels) leaving the separator 28 of the second block 12 is sent in part directly to the burner 13 through the recirculation line 47, and in part also to the anodes 25 of the batteries 21 of the first block 11, through an auxiliary line 53 which departs from the line 47 and connects to the anode inlet line 41 (which connects the reformer 14 to the anodes 25) before being sent to the burner 13 (or to another burner, internal or to blocks 11, 12 MCFC-CCS), or to an external user.

According to a further variant (not shown) based on the general scheme of figure 2, the flux exiting the burner 13 is also sent to the cathodes 24 inlet of the batteries 22 of the second block 12, and / or, in the case of more blocks 12 in series, of the cathodes of the batteries of one of the following blocks.

Further variants capable of further enriching the anode gas of the batteries 21 of the first block 11 in H2 are illustrated, partially and schematically, in Figures 3 and 4; although inserted by way of example in the general configuration of Figure 1, these variants can also be applied to both the general schemes of Figures 1 and 2.

In the variant of Figure 3, the separator 27 is configured in such a way as to separate a flow of H20 and, separately, a flow substantially of H2 only from the anode exhaust coming out from the anodes 25 of the batteries 21 of the first block 11; this "pure" H2 flow is recirculated to the anodes 25 themselves, through the anodic recirculation line 51; the residual flow of the separator 27, containing C02, H2, residual fuels, H2S, etc., is sent via a treatment line 62 to the burner 13 (or to another burner), where the residual fuels left with the C02 are eliminated to be sent for seizure, by combustion in 02 or in 02 / C02 mixtures; a further final C02 separator 63 follows.

In the example of Figure 3, the battery 22 of the second block 12 also includes MCFC cells with an indirect internal reformer, with recirculation on the anodes 26 of the H2-rich flow leaving the separator 28.

In the variant of figure 4, the system comprises a further auxiliary separator 64 arranged between the outlet of the reformer 14 and the anodes 25 of the battery 21 of the first block 11 and therefore along the anode inlet line 41. The auxiliary separator 64 removes C02 and H2o from the flow fed to the anodes 25.

The innovation also allows a wide freedom of choice regarding the type of batteries to be used for the different blocks.

Use for the first block with internal indirect reformer IIR or without internal reformer and for the second block (and any subsequent ones) internal reformer batteries (direct DIR or indirect IIR) is the preferable choice in most cases, where it is advisable to operate at atmospheric pressure. But also different combinations can be conveniently exploited in particular situations. The use of cells with DIR reformer can even be used in the first block where it, while removing C02, mainly plays the role of reducing NOx to the benefit of the following blocks, in the case of sulfur-free fumes.

Finally, it is understood that further modifications and variations may be made to the system and method described and illustrated here, which do not depart from the scope of the attached claims.

Claims (21)

CLAIMS 1. Multi-stack MCFC system (1) for separating CO2 from combustion fumes containing NOx and SOx, comprising a first block (11) MCFC-CCS of MCFC batteries and at least one second block (12) MCFC-CCS of MCFC batteries, at least one burner (13), and a connection system (15) which connects the blocks (11, 12) and the burner (13); the blocks (11, 12) comprising respective batteries (21, 22) of MCFC cells, having respective cathodes (23, 24) and anodes (25, 26), and respective separators (27, 28) acting on the exhausted anode of the batteries ( 21, 22); the system being characterized by the fact that the connection system (15) is configured so that: - the cathodes (23, 24) of the batteries (21, 22) of the two blocks (11, 12) are connected in series; - the fumes to be treated only enter the cathodes (23) of the coils (21) of the first block (11), with or without the addition of air; in the second block (12), and in any subsequent blocks, no fumes enter that have not passed through the cathodes (23) of the batteries (21) of the first block (11); - the anodes (25, 26) of the batteries (21, 22) of each block (11, 12) are connected to respective separators (27, 28), which remove H2O and separate a flow with CO2 destined for sequestration from a rich flow in H2; - the separators (27, 28) and the lines that handle the anodic exhaust are organized in such a way that H2S and N2 are expelled from the system. System according to claim 1, wherein the burner (13) is associated with a reformer (14). 3. System according to claim 1 or 2, in which the separators (27, 28) are organized in such a way as to process the anode exhausts of the batteries (21) of the first block (11) by removing H2O, extracting CO2 and at the same time also removing H2S, up to having an H2S residue below a predetermined threshold; and so that at least a portion of the H2-rich flow outgoing from the separator (27) connected to the anode outputs of the batteries (21) of the first block (11) is sent, directly or after passing through the anodes (26) of the batteries (22) of one or more of the other blocks (12), to the burner (13), or to another external burner or to an external user in such a way as to avoid N2 accumulation phenomena. 4. System according to claim 3, in which the flow rich in H2 and containing residual fuels leaving the separator (27) of the first block (11) is sent: to the anodes (26) of the batteries (22) of the second block (12 ), through an anodic line (44), directly or passing through a reformer (32) associated with said batteries (22) of the second block (12); and / or to the plant hosting the system (1), through an anodic output line (45), to be consumed there; and / or to the anodes (25) of the batteries (21) of the first block (11), by means of an anode recirculation line (51) which engages on the anode input line (41); and / or to the burner (13), by means of a further recirculation line (52) which connects to a recirculation line (47) coming, after passing through the separator (28) of the second block (12), from the anodes (26) of the second block (12). 5. System according to claim 3 or 4, in which the stream rich in H2 and containing residual fuels leaving the separator (28) of the second block (12) is sent: via a recirculation line (47) to the burner (13) , where the residual fuels contained in this stream are burned and the heat is recovered to support the reactions in the reformer (14) associated with the burner (13) and to heat the oxidizing gas containing the combustion fumes fed to the first block (11) ; and / or to the anodes (25) of the batteries (21) of the first block (11), through an auxiliary line (53) which branches off from the recirculation line (47) and connects to the anode input line (41), before to be sent to the burner (13) or to another burner, inside or outside the blocks (11, 12), or to an external user. System according to one of claims 3 to 5, having a flue gas inlet (33) which is located upstream of the burner (13) and is connected to the burner (13) by a flue gas supply line (34), through which the fumes enter the burner (13); and the burner (13) has an output connected to the cathodes (23) of the batteries (21) of the first block (11), through a cathode input line (36). System according to one of claims 3 to 5, in which the combustion fumes are fed to the cathodes (23) of the coils (21) of the first block (11) by means of a fumes supply line (34) which connects a fumes inlet (33) to the cathodes (23) of the first block (11); and the system (1) comprises an additional MCFC group (55), formed by one or more batteries (56) of MCFC cells having respective cathodes (57) and anodes (58); the burner (13) having an output connected to the cathodes (57) of the additional group (55), so that the gaseous flow leaving the burner (13) feeds said cathodes (57) of the additional group (55). System according to claim 7, wherein the supplementary assembly (55) has an anode output connected, via an anode line (60), to a separator (59) which removes H2O and CO2 from a residual H2 containing stream. System according to claim 7 or 8, in which a fuel feed line (42) supplies, in addition to the reformer (14) associated with the burner (13), also the anodes (58) of the supplementary group (55). 10. System according to one of the preceding claims, in which the separator (27) of the first block is configured in such a way as to separate a flow from the anode exhaust coming out from the anodes (25) of the batteries (21) of the first block (11) of H20 and, separately, a flow substantially of H2 only which is recirculated to the same anodes (25) of the first block (11); the residual flow of the separator (27) of the first block (11) being sent via a treatment line (62) to the burner (13), where the residual fuels left with the CO2 to be sequestered are eliminated by combustion in O2 or in O2 / CO2 mixtures, and then to a further final CO2 separator (63). 11. System according to one of the preceding claims, comprising a further auxiliary separator (64) arranged between the outlet of the reformer (14) associated with the burner (13) and the anodes (25) of the batteries (21) of the first block (11 ), along an anode inlet line (41); said auxiliary separator (64) being configured to remove CO2 and H2O from the flow fed to the anodes (25) of the first block (11). 12. Method for separating CO2 from combustion fumes containing NOx and SOx by means of a multistack (1) MCFC system, comprising the steps of: - preparing a multi-stack MCFC system (1) comprising a first block (11) MCFC-CCS of MCFC batteries and at least a second block (12) MCFC-CCS of MCFC batteries; the blocks (11, 12) comprising respective batteries (21, 22) of MCFC cells, having respective cathodes (23, 24) and anodes (25, 26), and respective separators (27, 28) acting on the exhausted anode of the batteries ( 21, 22); the cathodes (23, 24) of the batteries (21, 22) of the two blocks (11, 12) being connected in series; - feed the fumes to be treated only in the cathodes (23) of the coils (21) of the first block (11), with or without adding air; while in the second block (12), and in any subsequent blocks, no fumes enter which have not passed through the cathodes (23) of the batteries (21) of the first block (11); - process the exhausted anodes of the anodes (25, 26) of the batteries (21, 22) of each block (11, 12) with respective separators (27, 28) to remove H2O and separate a flow with CO2 destined for sequestration from a flow rich in H2, and so as to eliminate H2S and N2 from the system (1). 13. Method according to claim 12, comprising the step of processing the exhausted anode of the batteries (21) of the first block (11) by removing H2O, extracting CO2 and at the same time also removing H2S, until there is a residue of H2S below a predetermined threshold ; and so that at least a portion of the H2-rich flow outgoing from the separator (27) connected to the anode outputs of the batteries (21) of the first block (11) is sent, directly or after passing through the anodes (26) of the batteries (22) of one or more of the other blocks (12), to a burner (13), or to another external burner or to an external user in such a way as to avoid N2 accumulation phenomena. 14. Method according to claim 13, wherein the stream rich in H2 and containing residual fuels leaving the separator (27) of the first block (11) is sent: to the anodes (26) of the batteries (22) of the second block (12 ), through an anodic line (44), directly or passing through a reformer (32) associated with said batteries (22) of the second block (12); and / or to the plant hosting the system (1), through an anodic output line (45), to be consumed there; and / or to the anodes (25) of the batteries (21) of the first block (11), through an anode recirculation line (51) which engages on the anode input line (41); and / or to the burner (13), by means of a further recirculation line (52) which connects to a recirculation line (47) coming, after passing through the separator (28) of the second block (12), from the anodes (26) of the second block (12). 15. Method according to claim 13 or 14, in which the stream rich in H2 and containing residual fuels leaving the separator (28) of the second block (12) is sent: via a recirculation line (47) to the burner (13) , where the residual fuels contained in this stream are burned and the heat is recovered to support the reactions in the reformer (14) associated with the burner (13) and to heat the oxidizing gas containing the combustion fumes fed to the first block (11) ; and / or to the anodes (25) of the batteries (21) of the first block (11), through an auxiliary line (53) which branches off from the recirculation line (47) and connects to the anode input line (41), before to be sent to the burner (13) or to another burner, inside or outside the blocks (11, 12), or to an external user. Method according to one of claims 13 to 15, wherein the combustion fumes are fed to the burner (13) and are then sent to the cathodes (23) of the batteries (21) of the first block (11). Method according to one of claims 13 to 15, wherein the combustion fumes are fed to the cathodes (23) of the batteries (21) of the first block (11); and the method comprises the step of sending the gaseous flow outgoing from the burner (13) to the cathodes (57) of an additional MCFC group (55), formed by one or more batteries (56) of MCFC cells having respective cathodes (57) and anodes (58). A method according to claim 17, comprising the step of sending the outgoing flow from the anodes (58) of the group (55) to a separator (59) which removes H2O and CO2 from a residual flow containing H2. 19. Method according to one of claims 12 to 18, comprising the step of separating a flow of H20 from the anodes (25) of the batteries (21) of the first block (11) and, separately, a substantially of H2 only which is recirculated to the same anodes (25) of the first block (11), obtaining a residual flow, containing residual fuels, which is sent to the burner (13), where the remaining residual fuels are eliminated with the CO2 to be sent for sequestration, by combustion in O2 or in O2 / CO2 mixtures, and subsequently to a final phase of CO2 separation. Method according to one of claims 12 to 19, comprising a step of removing CO2 and H2O from the flow fed to the anodes (25) of the first block (11). Method according to one of claims 12 to 20, comprising the step of making at least a portion of the fuel required by the second block (12) pass in the form of H2 from the anodes (25) of the batteries (21) of the first block (11) and / or any other battery blocks, the host system and / or other users.