CN113711401B

CN113711401B - Fuel cell classification for molten carbonate fuel cells

Info

Publication number: CN113711401B
Application number: CN201980090518.XA
Authority: CN
Inventors: R·F·布兰科·古铁雷斯; E·B·沈; C·S·佩雷拉; K·E·戴维斯; H·盖泽尔-阿亚
Original assignee: Fuelcell Energy Inc
Current assignee: Fuelcell Energy Inc
Priority date: 2018-11-30
Filing date: 2019-11-26
Publication date: 2023-09-01
Anticipated expiration: 2039-11-26
Also published as: CN113711401A; CN116885241A

Abstract

Is provided for when in CO ₂ Systems and methods for reducing or minimizing current density variation using fuel cell staging when operating molten carbonate fuel cells with increased utilization. The fuel cell classification can reduce the CO content ₂ The amount of alternative ion transport that occurs when a molten carbonate fuel cell is operated with increased utilization.

Description

Fuel cell classification for molten carbonate fuel cells

Technical Field

Is provided for when in CO ₂ A method of classifying a molten carbonate fuel cell using the fuel cell is provided.

Background

The present application discloses and claims the subject matter of activity efforts within the scope of a joint research agreement between the exxon mobil research and engineering company (ExxonMobil Research and Engineering Company) and the fuel cell Energy company (inc.) that was validated on or before the date of the effective application of the present application.

Molten carbonate fuel cells utilize hydrogen and/or other fuels to generate electricity. The hydrogen may be provided by reforming methane or other reformable fuel in a steam reformer, such as a steam reformer located upstream of or integrated within the fuel cell. The fuel may also be reformed in an anode cell in a molten carbonate fuel cell, which may be operated to create conditions suitable for reforming the fuel in the anode. Yet another option is to perform some reforming both outside and inside the fuel cell. The reformable fuel can encompass hydrocarbonaceous materials that can react with steam and/or oxygen at elevated temperature and/or pressure to produce gaseous products comprising hydrogen.

The basic structure of a molten carbonate fuel cell comprises a cathode, an anode, and a matrix between the cathode and the anode, the matrix comprising one or more molten carbonates serving as an electrolyte. During normal operation of the molten carbonate fuel cell, molten carbonate partially diffuses into the pores of the cathode. This diffusion of molten carbonate into the cathode pores provides an interface region where CO ₂ Can be converted into CO ₃ ^2- To be transported across the electrolyte to the anode.

Conventionally, cathodes for molten carbonate fuel cells are typically constructed to have a single layer. The properties of the single layer cathode are selected based on several types of properties. First, the cathode needs to have sufficient structural stability to maintain the integrity of the cathode layer, while also providing sufficient electrical conductivity to allow fuel cell operation. This typically results in the use of materials such as nickel for the electrodes that are oxidized and (optionally) lithiated during initial operation of the fuel cell. Regarding other properties, it is desirable to have a pore size that is small enough to provide adequate wetting of the cathode by the electrolyte to again provide suitable conductivity.

One difficulty with conventional electrode materials, such as (optionally lithiated) nickel oxide, is that nickel oxide is susceptible to polarization under fuel cell operating conditions. During fuel cell operation, polarization of the cathode can result in additional voltage loss across the cathode. The effect of polarization can be mitigated by increasing the operating temperature of the fuel cell, but this results in a shortened operating life. It is therefore desirable to have a molten carbonate cathode structure that can reduce polarization, as this can provide reduced voltage loss and/or can allow for reduced operating temperatures.

Us patent 9,077,007 describes a method for operating a molten carbonate fuel cell for integrated power generation and chemical production. The method includes operating the fuel cell at a reduced fuel utilization level. Configurations are also described that include fuel cells that operate in parallel or that pass an anode stream and a cathode stream through a series of fuel cells.

Disclosure of Invention

In one aspect, a method for generating electrical power is provided. The method comprises the steps of ₂ An anode input stream of reformable fuel, or a combination thereof, is introduced into a first anode stage of the plurality of molten carbonate fuel cell stages. The method further comprises the steps of ₂ And CO ₂ Is introduced into a first cathode stage of the plurality of molten carbonate fuel cell stages. The method further includes passing a second anode input stream into a second anode stage of the plurality of molten carbonate fuel cell stages. The method further includes passing the intermediate cathode output into a second cathode stage of the plurality of molten carbonate fuel cell stages. The method further comprises operating the plurality of molten carbonatesFuel cell stage to produce: i) Average current density of 60mA/cm ² Or greater power; ii) anode exhaust from the plurality of molten carbonate fuel cell stages, the anode exhaust comprising H ₂ CO and CO ₂ The method comprises the steps of carrying out a first treatment on the surface of the And iii) cathode exhaust from the plurality of molten carbonate fuel cell stages, the cathode exhaust comprising CO in an amount of 2.0vol% or less ₂ H in an amount of 1.0vol% or more ₂ O and O in an amount of 1.0vol% or more ₂ At least one of the first cathode stage and the second cathode stage operates at a transfer rate of 0.97 or less.

Drawings

FIG. 1 shows an example of fuel cell classification in a co-current cross-flow configuration (co-current cross-flow configuration).

Fig. 2 shows an example of fuel cell classification in a counter-current cross-flow configuration (counter-current cross-flow configuration).

Fig. 3 shows an example of a portion of a molten carbonate fuel cell stack.

Fig. 4 shows an example of flow patterns of a molten carbonate fuel cell in which the anode flow direction is aligned approximately perpendicular to the cathode flow direction.

FIG. 5 shows the process in CO ₂ CO in the cathode of a fuel cell operating as a single stage with increased utilization ₂ Concentration pattern.

FIG. 6 shows the process at CO ₂ CO in cathodes of two fuel cell stages operating with increased utilization ₂ Concentration pattern.

Detailed Description

SUMMARY

In various aspects, a method for producing a catalyst for use in a CO ₂ Systems and methods for reducing or minimizing current density variation using fuel cell staging when operating molten carbonate fuel cells with increased utilization. In some aspects, in CO ₂ Operating the fuel cell or series of fuel cell stages with increased utilization corresponds to operating to a transfer rate of 0.97 or less, or 0.95 or less, or 0.90 or lessOne less fuel cell stage. Additionally or alternatively, in CO ₂ During operation with increased utilization, CO from the output stream of the last cathode stage ₂ The content may contain 2.0vol% or less, or 1.0vol% or less, or 0.8vol% or less of CO ₂ 。

When operating a molten carbonate fuel cell stack as a single stage to increase CO ₂ With utilization, it has been found that a large number of alternative ion transport can occur. Alternative ion transport refers to removal of carbonate ions (CO ₃ ^2- ) Transmission of other ions across the molten carbonate electrolyte.

The normal operating conditions of a molten carbonate fuel cell generally correspond to conditions where the amount of alternative ion transport is reduced, minimized or absent. The amount of transport of the surrogate ions may be quantified based on the transfer rate of the fuel cell. The transfer rate is defined as the fraction of ions transported across the molten carbonate electrolyte that correspond to carbonate ions, but not hydroxide ions and/or other ions. A convenient method of determining the transfer rate may be based on measuring a) the CO at the cathode inlet ₂ The change in concentration compared to the cathode outlet is compared to b) the amount of carbonate ion transport required to achieve the current density produced by the fuel cell. Notably, this definition of the transfer rate assumes CO ₂ The return transport from anode to cathode is minimal. It is believed that such return transmissions are minimal for the operating conditions described herein. For CO ₂ Concentration, the cathode input stream and/or the cathode output stream may be sampled, wherein the sample is transferred to a gas chromatograph to determine CO ₂ The content is as follows. The average current density of the fuel cell may be measured in any convenient manner.

Under normal operating conditions, the transfer rate may be relatively close to 1.0, such as 0.98 or higher, and/or such as substantially no surrogate ion transport. A transfer rate of 0.98 or higher means that 98% or more of the ionic charge transferred across the electrolyte corresponds to carbonate ions. Notably, the charge of the hydroxide ion is-1 and the charge of the carbonate ion is-2, so that two hydroxide ions need to be transported across the electrolyte to produce the same charge transfer as one carbonate ion.

Operating a molten carbonate fuel cell at a transfer rate of 0.95 or less (or 0.97 in at least one stage of a multi-stage configuration) can increase the effective amount of carbonate ion transport that is achieved compared to conventional operating conditions, even though a portion of the current density produced by the fuel cell is due to transport of ions other than carbonate ions. In order to operate a fuel cell at a transfer rate of 0.97 or less, or 0.95 or less, it is necessary to consume CO within the fuel cell cathode ₂ . It has been found that such CO within the cathode ₂ Consumption tends to be local. Many areas within the fuel cell cathode can still have sufficient CO ₂ For normal operation. These regions contain additional CO that is desired to be transported across the electrolyte (e.g., for carbon capture) ₂ . However, CO in such areas when operated under conventional conditions ₂ And typically will not be transported across the electrolyte. By selecting the operating conditions with a transfer rate of 0.97 or less, or 0.95 or less, sufficient CO is obtained ₂ May be used to transport additional CO ₂ While the consumed region may be based on a surrogate ion transport operation. This may increase the capture of CO from the cathode input stream ₂ Practical limits of the amount.

Use of MCFC to boost CO ₂ One difficulty with the capture rate is that if one or more of the reactants required for fuel cell operation are present in small amounts, fuel cell operation may be kinetically limited. For example, when CO is used ₂ At a cathode input stream content of 4.0vol% or less, a CO of 75% or more is achieved ₂ The utilization corresponds to a cathode outlet concentration of 1.0vol% or less. However, a cathode outlet concentration of 1.0vol% or less does not necessarily mean CO ₂ Evenly distributed throughout the cathode. In contrast, the concentration within the cathode typically varies due to a variety of factors, such as the flow patterns in the anode and cathode. CO ₂ The concentration variation may cause CO in some parts of the cathode ₂ The concentration is significantly lower than 1.0vol%.

Conventionally, intra-cathode CO is expected ₂ Is effective in eliminating (1)The drain will result in a reduced voltage and reduced current density. However, it has been found that due to CO removal ₃ ^2- Other ions are transported across the electrolyte and the current density can be at CO ₂ Is maintained during consumption. For example, a portion of the ions transported across the electrolyte may correspond to hydroxide ions (OH ^- ). The transport of the surrogate ions across the electrolyte may allow the fuel cell to maintain a target current density even at CO transported across the electrolyte ₂ This is also the case in insufficient amounts.

One of the advantages of transporting the surrogate ion across the electrolyte is that even in the absence of sufficient amounts of CO ₂ Where the molecules are available kinetically, the fuel cell can also continue to operate. This may allow for additional CO ₂ Transferring from cathode to anode, even if CO is present in the cathode ₂ The amount is generally considered to be insufficient for normal fuel cell operation. This may allow the fuel cell to measure CO ₂ Operating at a utilization close to 100%, whereas the calculated CO ₂ Utilization (based on current density) can be compared to measured CO ₂ The utilization is at least 3% higher, or at least 5% higher, or at least 10% higher, or at least 20% higher. Notably, alternative ion transport may allow the fuel cell to operate with more than 100% calculated CO ₂ The current density corresponding to the utilization ratio operates.

While transport of the surrogate ions may allow the fuel cell to maintain a target current density, it has further been found that transport of the surrogate ions across the electrolyte may also reduce or minimize the life of the molten carbonate fuel cell. Thus, it is desirable to mitigate such loss of fuel cell life. Unexpectedly, it has been found that the use of multiple fuel cell stages can allow for increased CO ₂ The trapping rate while reducing or minimizing the amount of surrogate ion transport.

In some aspects, the enhanced CO ₂ The capture rate may be defined based on the amount of transfer rate, such as a transfer rate of 0.97 or less, or 0.95 or less, or 0.93 or less, or 0.91 or less. Maintaining an operating condition with a transfer rate of 0.97 or less, or 0.95 or less, may also generally result in CO in the cathode output stream ₂ The concentration is 2.0vol% or less, or 1.5vol% or less, or 1.0vol% or less. Higher CO in the cathode output stream ₂ At concentrations, there is generally not enough CO to result in lower transfer values ₂ Local consumption.

The presence of CO can also be indicated by other factors ₂ The increase in capture rate, but such other factors are not, in and of themselves, generally indicative of CO ₂ Sufficient conditions for improving the capturing rate. For example, when using lower CO ₂ Increased CO upon concentration of the cathode input stream ₂ CO for which the capture rate may correspond in some aspects ₂ The utilization is 70% or higher, or 75% or higher, or 80% or higher, such as up to 95% or possibly even higher. CO ₂ Examples of sources of lower concentration of (c) may correspond to CO resulting in the cathode input stream containing ₂ CO of 5.0vol% or less, or 4.0vol% or less (e.g., as low as 1.5vol% or possibly less) ₂ A source. The exhaust gas from a natural gas turbine is CO-containing ₂ Examples of streams, CO thereof ₂ CO content of 5.0vol% or less ₂ Or 4.0vol% or less. Additionally or alternatively, enhanced CO ₂ The capture rate may correspond to operating conditions that produce a substantial current density, such as 60mA/cm, using a molten carbonate fuel cell ² Or greater, or 80mA/cm ² Or greater, or 100mA/cm ² Or greater, or 120mA/cm ² Or greater, or 150mA/cm ² Or greater, or 200mA/cm ² Or greater, e.g. up to 300mA/cm ² Or may be higher. It is noted that alternative ion transport may also be indicated by a decrease in the operating voltage of the fuel cell, since the alternative ion transport reaction pathway has a lower theoretical voltage than the reaction pathway using carbonate ions.

Conventionally, CO in cathode exhaust of molten carbonate fuel cells ₂ The concentration is kept at a relatively high value, e.g. 5vol% CO ₂ Or greater, or 10vol% CO ₂ Or larger, or possibly also higher. In addition, molten carbonate fuel cells typically have a CO of 70% or less ₂ The utilization value operates. When storedAt any of these conditions, the primary mechanism of charge transport across the molten carbonate electrolyte is the transport of carbonate ions. Although transport of the surrogate ion (e.g., hydroxide ion) across the electrolyte may occur under such conventional conditions, the amount of transport of the surrogate ion is very small, which corresponds to a current density of 2% or less (or equivalently, a transfer rate of 0.98 or higher).

As an alternative to describing the operating conditions in terms of transfer rate, the operating conditions may be based on measured CO ₂ Utilization and "calculated" CO based on average current density ₂ Utilization is described. In this discussion, measured CO ₂ Utilization corresponds to the removal of CO from the cathode input stream ₂ Is a combination of the amounts of (a) and (b). This may be done, for example, by using gas chromatography to determine the CO in the cathode input stream and the cathode output stream ₂ Concentration is determined. This may also be referred to as actual CO ₂ Utilization, or simply CO ₂ Utilization rate. In this discussion, calculated CO ₂ Utilization is defined as all current densities produced in a fuel cell based on CO ₃ ^2- Ion transport across electrolytes (i.e., based on CO ₂ Ion transport of (c) and the CO occurring in the case of production ₂ Utilization rate. Measured CO ₂ Utilization and calculated CO ₂ The difference between the utilizations may be used alone to characterize the amount of surrogate ion transport and/or these values may be used to calculate the transfer rate, as described above.

It has been found that in the presence of increased CO ₂ The amount of surrogate ion transport generated when operating molten carbonate fuel cells with utilization may be increased by performing increased CO using more than one fuel cell stage ₂ Utilization is reduced or minimized. Operating multiple fuel cell stages to achieve increased CO even with the same (or preferably smaller) fuel cell area ₂ Utilization may reduce or minimize CO in cathode flow mode ₂ The amount of change in concentration. This can allow the amount of transport of the substitute ions to be correspondingly reduced. For example, when operating a fuel cell stage in a cross-flow configuration of anode and cathode gas flows, fuel corresponding to anode inlet and cathode outletThe amount of alternate ion transport in the cell corners can be reduced or minimized. Such a reduction in alternative ion transport may be beneficial, for example, to increase the operational life of one or more fuel cells.

When multiple fuel cell stages are used in series, the anode and cathode flows through the cells may be arranged in a variety of ways (e.g., with co-current or counter-current). In co-current flow, the fuel cell corresponding to the first stage of the anode flow is also the first stage of the cathode. In counter-current flow, the fuel cell corresponding to the first stage of the anode (or cathode) corresponds to the last stage and/or a different stage than the first stage of the cathode (or anode). In addition, flow within a single fuel cell may be characterized. For example, in a cross-flow configuration, the flow direction in the anode of a given fuel cell may be oriented substantially perpendicular to the flow direction in the anode. The cross-flow configuration is opposite to an aligned flow configuration in which the flow direction in the anode may be oriented along a flow axis that is substantially the same as the flow direction in the cathode. According to the aspects, various combinations of fuel cells (e.g., combinations of fuel cell stacks) may be arranged in series and/or in parallel. In such aspects, any convenient combination of co-current, counter-current, cross-current, and/or aligned flow may be used for fuel cells arranged in series.

Fig. 1 shows an example of a series of fuel cells (e.g., a series of fuel cell stacks) arranged in a parallel flow cross-flow configuration. In the example shown in fig. 1, the fuel cell 120, the fuel cell 130, and the fuel cell 140 are arranged to operate in series. Both the cathode input stream 119 and the anode input stream 115 enter the fuel cell 120 as a first fuel cell stage. The first stage cathode intermediate output 129 and the first stage anode intermediate output 125 then enter the second fuel cell 130. The second stage cathode intermediate output 139 and the second stage anode intermediate output 135 then enter the third fuel cell stage 140. In the example shown in fig. 1, the third fuel cell 140 corresponds to the last stage, and thus the output from the third fuel cell 140 corresponds to the cathode output 149 and the anode output 145. As shown in fig. 1, in each of the fuel cells 120, 130, and 140, the flow direction of the anode flow is substantially orthogonal to the flow direction of the cathode flow. Thus, the flow in fuel cell 120, fuel cell 130, and fuel cell 140 corresponds to the cross-flow orientation.

Fig. 2 shows an example of a series of fuel cells (e.g., a series of fuel cell stacks) arranged in a counter-current cross-flow configuration. In the example shown in fig. 2, the fuel cell 220, the fuel cell 230, and the fuel cell 240 are arranged to operate in series. The cathode input stream 219 enters the fuel cell 220 as a first cathode fuel cell stage. The first stage cathode intermediate output 229 enters the fuel cell 230 as a second cathode fuel cell stage. The second stage cathode intermediate output 239 enters the fuel cell 240 as a third cathode fuel cell stage. In the example shown in fig. 2, the fuel cell 240 corresponds to the last cathode fuel cell stage, and thus the output from the cathode of the fuel cell 240 corresponds to the cathode output 249. In contrast to fig. 1, the anode input 215 enters the fuel cell 240 as a first anode fuel cell stage. This produces a first stage anode intermediate output 255 that enters the fuel cell 230 as a second anode fuel cell stage. The second stage anode intermediate output 265 enters the fuel cell 220, which corresponds to the third (last) fuel cell stage of the anode stream. The output from the anode of fuel cell 220 corresponds to anode output 245. As shown in fig. 2, in each of the fuel cells 220, 230, and 240, the flow direction of the anode flow is substantially orthogonal to the flow direction of the cathode flow. Thus, the flow in fuel cell 220, fuel cell 230, and fuel cell 240 corresponds to the cross-flow orientation.

In some aspects, any convenient type of electrolyte suitable for operating a molten carbonate fuel cell may be used. Many conventional MCFCs use eutectic carbonate mixtures as carbonate electrolytes, such as 62mol% lithium carbonate and 38mol% potassium carbonate (62% li) ₂ CO ₃ /38％K ₂ CO ₃ ) Or 52mol% lithium carbonate and 48mol% sodium carbonate (52% Li) ₂ CO ₃ /48％Na ₂ CO ₃ ) Is a eutectic mixture of (a) and (b). Other eutectic mixtures may also be used, such as 40mol% lithium carbonate and 60mol% carbonPotassium acid (40% Li) ₂ CO ₃ /60％K ₂ CO ₃ ) Is a eutectic mixture of (a) and (b). Although eutectic mixtures of carbonates may be conveniently used as the electrolyte for various reasons, non-eutectic mixtures of carbonates may also be suitable. Typically, such off-eutectic mixtures may comprise various combinations of lithium carbonate, sodium carbonate, and/or potassium carbonate. Optionally, smaller amounts of other metal carbonates may be included in the electrolyte as additives, such as other alkali metal carbonates (rubidium carbonate, cesium carbonate) or other types of metal carbonates, such as barium carbonate, bismuth carbonate, lanthanum carbonate or tantalum carbonate.

Notably, the structure of the molten carbonate fuel cell may also have an effect on the rate at which degradation occurs. For example, the open area of the cathode surface available for receiving cathode gas may affect the rate at which degradation occurs. For electrical contact, at least a portion of the cathode current collector is typically in contact with the cathode surface in a molten carbonate fuel cell. The open area of the cathode surface (adjacent to the cathode current collector) is defined as the percentage of the cathode surface that is not in contact with the cathode current collector. For conventional molten carbonate fuel cell designs, a typical value for open area is about 33%. This is due to the nature of conventional cathode current collector arrangements, which correspond to plate-like structures resting on the cathode surface, wherein a portion of the plate-like structures has openings allowing the cathode gas to diffuse into the cathode. In various aspects, additional benefits may be obtained by using a cathode current collector that provides a greater open area (e.g., 45% or greater, or 50% or greater, or 60% or greater, such as up to 90% or possibly also a higher open area) at the cathode surface.

Conditions for molten carbonate fuel cell operation with alternative ion transport

In various aspects, the operating conditions of a molten carbonate fuel cell (e.g., a cell that is part of a fuel cell stack) can be selected to correspond to a transfer rate of 0.97 or less, or 0.95 or less, such that the cell transmits carbonate ions and at least one type of surrogate ion across the electrolyte simultaneously. In addition to the transfer rateIn addition, operating conditions that may dictate that a molten carbonate fuel cell operate with transport of surrogate ions include, but are not limited to, CO of the cathode input stream ₂ Concentration of CO in cathode ₂ Utilization, current density of fuel cell, voltage drop across cathode, voltage drop across anode, O in cathode input stream ₂ Concentration. In addition, the anode input stream and fuel utilization in the anode may generally be selected to provide a desired current density.

In general, to cause alternative ion transport, it is necessary to have CO in at least a portion of the cathode while operating the fuel cell to provide a sufficiently high current density ₂ The concentration is sufficiently low. CO in cathode ₂ A sufficiently low concentration generally corresponds to a low CO in the cathode input stream ₂ Concentration, high CO ₂ Utilization and/or a certain combination of high average current densities. However, such conditions alone are not sufficient to indicate a transfer rate of 0.97 or less, or 0.95 or less.

For example, a molten carbonate fuel cell with a cathode open area of about 33% CO at 19vol% ₂ Cathode inlet concentration, 75% CO ₂ The utilization and the average current density of 160mA/cm 2. These conditions correspond to the calculated CO ₂ Utilization and measured CO ₂ The difference between the utilization rates is less than 1%. Therefore, it is not easy to remove the high CO ₂ The availability and presence of high average current densities infer that there is a significant amount of alternative ion transport/transfer rates of 0.97 or less, or 0.95 or less.

As another example, a molten carbonate fuel cell with a cathode open area between 50% and 60% CO at 4.0vol% ₂ Cathode inlet concentration, 89% CO ₂ Utilization and 100mA/cm ² Is controlled by the current density of the current source. These conditions correspond to a transfer rate of at least 0.97. Therefore, it is not easy to remove the high CO ₂ Utilization and low CO in cathode input stream ₂ The presence of a combination of concentrations concludes that there is a transfer rate/mass transport of the surrogate ion of 0.95 or less.

As yet another example, the cathode has an open area of between 50% and 60% molten carbonic acidSalt fuel cell with 13vol% CO ₂ Cathode inlet concentration, 68% CO ₂ The utilization and the current density of 100mA/cm 2. These conditions correspond to a transfer rate of at least 0.98.

In this discussion, operating the MCFC to transport the surrogate ion across the electrolyte is defined as operating the MCFC such that the surrogate ion is transported beyond a minimum limit amount. Under various conventional conditions, small amounts of surrogate ions may be transported across the MCFC electrolyte. Such alternative ion transport under conventional conditions may correspond to a transfer rate of 0.98 or higher, which corresponds to an alternative ion transport corresponding to a fuel cell current density of less than 2.0%. In contrast, in this discussion, operating the MCFC to cause alternative ion transport is defined as operating the MCFC at a transfer rate of 0.95 or less such that a current density of 5.0% or more (or calculated CO of 5.0% or more) ₂ Utilization) corresponds to a current density based on the transport of the surrogate ions, or 10% or higher, or 20% or higher, such as up to 35% or possibly higher as well. Notably, in some aspects, operating at multiple fuel cell stages may reduce the CO that would otherwise be achieved in any single fuel cell stage ₂ The severity of the conditions required for capture rate. Thus, by operating in multiple stages, some have increased CO ₂ The operating conditions of the capture rate may correspond to a transfer rate of 0.97 or less.

In this discussion, operating the MCFC to cause a significant amount of alternative ion transport (i.e., operating at a transfer rate of 0.95 or less, or 0.97 or less, within one or more stages of a multi-stage configuration) is further defined as corresponding to operating the MCFC with a voltage drop across the anode and cathode suitable for generating electricity. The total electrochemical potential difference of the reaction in the molten carbonate fuel cell was-1.04V. For practical reasons, MCFCs typically operate at voltages near 0.7V or about 0.8V to produce current. This corresponds to a combined voltage drop across the cathode, electrolyte and anode of about 0.34V. To maintain stable operation, the combined voltage drop across the cathode, electrolyte and anode may be less than 0.5V, such that the current produced by the fuel cell is at a voltage of 0.55V or more, or 0.6V or more.

Regarding the anode, in a large number ofOne condition for operation in the case of substitution ion transport of (C) may be that 8.0vol% or more, or 10vol% or more of H is present in the region where a large amount of substitution ion transport occurs ₂ Concentration. According to the aspect, this may correspond to a region near the anode inlet, a region near the cathode outlet, or a combination thereof. In general, if H in the anode region ₂ Too low a concentration, there will be insufficient driving force to produce a large number of alternative ion transports.

Conditions suitable for the anode may also include providing H to the anode ₂ A reformable fuel, or a combination thereof; and any convenient fuel utilization to produce the desired current density, including fuel utilization in the range of 20% to 80%. In some aspects, this may correspond to conventional fuel utilization, such as 60% or more, or 70% or more, such as up to 85% or possibly even higher fuel utilization. In other aspects, this may correspond to being selected to provide a signal with enhanced H ₂ Content and/or enhanced H ₂ And CO (i.e., syngas), such as 55% or less, 50% or less, or 40% or less, such as low as 20% or possibly also lower. H in anode output stream ₂ Content and/or H in the anode output stream ₂ And CO may be present in an amount sufficient to allow the desired current density to be produced. In some aspects, H in the anode output stream ₂ The content may be 3.0vol% or more, or 5.0vol% or more, or 8.0vol% or more, such as up to 15vol% or possibly even higher. Additionally or alternatively, H in the anode output stream ₂ And CO may be 4.0vol% or more, or 6.0vol% or more, or 10vol% or more, such as up to 20vol% or possibly even higher. Optionally, when the fuel cell is operating at low fuel utilization, H in the anode output stream ₂ The content may be in a higher range, such as 10 to 25vol% of H ₂ The content is as follows. In such aspects, the synthesis gas content of the anode output stream may be correspondingly higher, such as 15vol% to 35vol% H ₂ And the combined content of CO. According to the aspect, the anode can be operatedTo increase the amount of electrical energy produced, to increase the chemical energy produced (i.e., H produced by reforming available in the anode output stream) ₂ ) Or the anode may be operated using any other convenient strategy compatible with operating the fuel cell to cause alternative ion transport.

Except that there is sufficient H in the anode ₂ In addition to the concentration, one or more locations within the cathode need to have sufficiently low CO ₂ Concentration such that a more favorable carbonate ion transport pathway is not readily available. In some aspects, this may correspond to CO in the cathode outlet stream (i.e., cathode exhaust gas) ₂ The concentration is 2.0vol% or less, or 1.0vol% or less, or 0.8vol% or less. Notably, due to variations within the cathode, an average concentration of 2.0vol% or less (or 1.0vol% or less, or 0.8vol% or less) in the cathode exhaust may correspond to still lower CO in localized areas of the cathode ₂ Concentration. For example, in a cross-flow configuration, CO is present at the corners of the fuel cell adjacent the anode inlet and the cathode outlet ₂ The concentration may be lower than at the corners of the same fuel cell adjacent the anode outlet and the cathode outlet. Similar CO ₂ Local variations in concentration may also occur in fuel cells having co-current or counter-current configurations.

Removal of CO with low concentration ₂ In addition, the partial region of the cathode may also have 1.0vol% or more, or 2.0vol% or more of O ₂ . In a fuel cell, O ₂ For forming hydroxide ions that allow for alternate ion transport. If there is not enough O ₂ The fuel cell will not operate because both carbonate ion transport and alternate ion transport mechanisms are dependent on O ₂ Availability of (c). With respect to O in the cathode input stream ₂ In some aspects, this may correspond to an oxygen content of 4.0vol% to 15vol% or 6.0vol% to 10 vol%.

It has been observed that sufficient amounts of water (e.g., 1.0vol% or more, or 2.0vol% or more) should also be present for alternate ion transport. Without being bound by any particular theory, if one were to attempt to transport in a large number of alternative ionsThe rate of degradation of the fuel cell appears to be much faster than the deactivation rate observed with sufficient available water due to alternative ion transport when operated with no water available in the cathode. Notably, since air is commonly used as O ₂ From and due to H ₂ O is one of the products produced during combustion and therefore a sufficient amount of water is typically available in the cathode.

Due to operation in molten carbonate fuel cells to increase CO ₂ During the capture rate, the non-uniform distribution of cathode gas and/or anode gas, it is believed that one or more of the corners and/or edges of the molten carbonate fuel cell will typically have a significantly higher density of alternative ion transport. One or more corners may correspond to CO in the cathode ₂ Locations with concentration lower than average, or H in anode ₂ Locations where the concentration is higher than the average, or a combination thereof.

In this discussion, a fuel cell may correspond to a single cell in which the anode and cathode are separated by an electrolyte. The anode and cathode may receive an input gas stream to facilitate respective anode and cathode reactions to transfer charge across the electrolyte and generate electricity. The fuel cell stack may represent a plurality of cells in an integrated unit. While a fuel cell stack may contain multiple fuel cells, the fuel cells may typically be connected in parallel and may function (substantially) as if they collectively represent a single fuel cell of larger size. When the input stream is delivered to the anode or cathode of the fuel cell stack, the fuel cell stack may contain flow channels for distributing the input stream between each of the cells in the stack and flow channels for combining the output streams from the individual cells. In this discussion, a fuel cell array may be used to refer to a plurality of fuel cells (e.g., a plurality of fuel cell stacks) arranged in series, parallel, or any other convenient manner (e.g., in a combination of series and parallel). The fuel cell array may comprise one or more stages of fuel cells and/or fuel cell stacks, wherein the anode/cathode output from a first stage may be used as the anode/cathode input for a second stage. It is noted that the anodes in a fuel cell array do not have to be connected in the same way as the cathodes in the array. For convenience, the input of the first anode stage of the fuel cell array may be referred to as the anode input of the array, and the input of the first cathode stage of the fuel cell array may be referred to as the cathode input of the array. Similarly, the output from the last anode/cathode stage may be referred to as the anode/cathode output from the array. In aspects where the fuel cell stack comprises a separate reforming element, it is noted that the anode input stream may first pass through the reforming element before entering the one or more anodes associated with the reforming element.

It should be understood that references to the use of fuel cells herein generally refer to a "fuel cell stack" that is made up of individual fuel cells, and more generally refer to the use of one or more fuel cell stacks in fluid communication. Individual fuel cell elements (plates) may be "stacked" together, typically in a rectangular array known as a "fuel cell stack". Other types of elements, such as reforming elements, may also be included in the fuel cell stack. Such a fuel cell stack may typically employ a feed stream and distribute reactants into all of the individual fuel cell elements, and then the product may be collected from each of these elements. When considered as a unit, the fuel cell stack in operation can be considered as a whole even if it is made up of many (typically tens or hundreds) individual fuel cell elements. These individual fuel cell elements may typically have similar voltages (because of similar reactant and product concentrations), and when the elements are electrically connected in series, the total power output may be from the sum of all the currents in all the cell elements. The stacks may also be arranged in a series arrangement to generate a high voltage. The parallel arrangement may increase the current. The systems and methods described herein may be used with a single molten carbonate fuel cell stack if a sufficiently large volume fuel cell stack is available to handle a given exhaust stream. In other aspects of the invention, multiple fuel cell stacks may be desired or required for a variety of reasons.

For the purposes of the present invention, unless otherwise specified, the term "fuel cell" shall be understood to also refer to and/or be defined to encompass reference to a fuel cell stack that is made up of a set of one or more individual fuel cell elements having a single input and output, which is also the manner in which fuel cells are commonly employed in practice. Similarly, unless otherwise specified, the term one or more fuel cells should be understood to also refer to and/or be defined to encompass a plurality of individual fuel cell stacks. In other words, unless specifically indicated otherwise, all references in this document may interchangeably refer to "operation of a fuel cell stack" as "fuel cell". For example, the volume of exhaust gas produced by a commercial-scale combustion generator may be too large to be handled by a conventionally sized fuel cell (i.e., a single stack). To treat the entire exhaust gas, a plurality of fuel cells (i.e., two or more individual fuel cells or fuel cell stacks) may be arranged in parallel such that each fuel cell can treat (approximately) equal amounts of combustion exhaust gas. Although a plurality of fuel cells may be used, each fuel cell may generally operate in a substantially similar manner, given that the amount of combustion exhaust of each fuel cell is (substantially) equal.

Examples of molten carbonate fuel cell operation: cross-flow orientation of cathode and anode

Fig. 3 shows a general example of a portion of a molten carbonate fuel cell stack. The portion of the stack shown in fig. 3 corresponds to the fuel cell 301. To isolate the fuel cell from adjacent fuel cells in the stack and/or other elements in the stack, the fuel cell includes separators 310 and 311. In fig. 3, a fuel cell 301 comprises an anode 330 and a cathode 350 separated by an electrolyte matrix 340 containing an electrolyte 342. In various aspects, the cathode 350 may correspond to a bilayer (or multilayer) cathode. Anode current collector 320 provides electrical contact between anode 330 and other anodes in the fuel cell stack, while cathode current collector 360 provides similar electrical contact between cathode 350 and other cathodes in the fuel cell stack. In addition, the anode current collector 320 allows gas to be introduced and discharged from the anode 330, and the cathode current collector 360 allows gas to be introduced and discharged from the cathode 350.

During operation, CO ₂ With O ₂ Together into cathode current collector 360.CO ₂ And O ₂ Diffuses into the porous cathode 350 and travels to the cathode interface region near the boundary of the cathode 350 and electrolyte matrix 340. In the cathode interface region, a portion of the electrolyte 342 may be present in the pores of the cathode 350. CO ₂ And O ₂ Can be converted to carbonate ions (CO) near/at the interface region of the cathode ₃ ^2- ) The carbonate ions may then be transported across the electrolyte 342 (and thus across the electrolyte matrix 340) to facilitate the generation of an electrical current. In aspects in which transport of the surrogate ion occurs, a portion of O ₂ May be converted to a substitute ion (e.g., hydroxide ion or peroxide ion) for transport in electrolyte 342. After transport across electrolyte 342, carbonate ions (or substitute ions) may reach the anode interface region near the boundary of electrolyte matrix 340 and anode 330. In the presence of H ₂ In the case of (2) carbonate ions can be converted back into CO ₂ And H ₂ O, thereby releasing electrons for forming the current generated by the fuel cell. H ₂ And/or is suitable for forming H ₂ Is introduced into the anode 330 through the anode current collector 320.

The flow direction within the anode of the molten carbonate fuel cell may have any convenient orientation relative to the flow direction within the cathode. One option is to use a cross-flow configuration such that the flow direction in the anode is at an angle of substantially 90 ° with respect to the flow direction in the cathode. This type of flow configuration may have practical benefits because the use of a cross-flow configuration may allow the anode inlet/outlet manifolds and/or tubes to be located on a different side than the cathode inlet/outlet manifolds and/or tubes of the fuel cell stack.

Fig. 4 schematically shows an example of a top view of a fuel cell cathode, while arrows indicate the flow direction within the fuel cell cathode and the corresponding fuel cell anode. In fig. 4, arrow 405 indicates the direction of flow within cathode 450, while arrow 425 indicates the direction of flow within the anode (not shown).

Since the anode and cathode streams are oriented at about 90 ° relative to each otherThe anode and cathode flow patterns may thus help to have different reaction conditions at various portions of the cathode. The different conditions can be illustrated by considering the reaction conditions in the four corners of the cathode. In the illustration of FIG. 4, the reaction conditions described herein are similar in nature to CO at 70% or higher (or 80% or higher) ₂ Reaction conditions of fuel cells operated with the use of the efficiency.

Corner 482 corresponds to a portion of the fuel cell near the entry point of the cathode and anode input streams. Thus, CO in corner 482 ₂ (in cathode) and H ₂ The concentration (in the anode) is relatively high. Based on the high concentration, it is contemplated that portions of the fuel cell near the corners 482 may operate under expected conditions wherein substantially no ions other than carbonate ions are transported across the electrolyte.

Corner 484 corresponds to a portion of the fuel cell near the entry point of the cathode input stream and near the exit point of the anode output stream. In locations near corners 484, the amount of current density may be due to H in the anode ₂ The decrease in concentration is limited depending on the fuel utilization. However, sufficient CO should be present ₂ Such that any ions transported across the electrolyte substantially correspond to carbonate ions.

Corner 486 corresponds to a portion of the fuel cell that is near the exit point of the anode output stream and near the exit point of the cathode output stream. In a position near corner 486, due to H ₂ (in the anode) and CO ₂ The concentration (in the cathode) is low and the current is expected to be small or nonexistent due to the low driving force of the fuel cell reaction.

Corner 488 corresponds to a portion of the fuel cell near the entry point of the anode input stream and near the exit point of the cathode output stream. It is expected that the relatively high availability of hydrogen at locations near corners 488 will produce a substantial current density. However, due to CO ₂ The concentration is relatively low and the transport of large amounts of hydroxide ions and/or other substitute ions may occur. According to the aspect, a large number of alternative ion transport can transport the calculated CO ₂ The utilization rate is improved by 5% or more, or 10% or moreMore, or 15% or more, or 20% or more. Additionally or alternatively, the transfer rate may be 0.95 or less, or 0.90 or less, or 0.85 or less, or 0.80 or less. The transport of a large number of surrogate ions across the electrolyte may temporarily allow for higher current densities to be maintained at locations near corners 488. However, transport of the substitute ions also degrades the cathode and/or anode structure, resulting in a decrease in current density (and possibly an absence) over time at locations near corners 488. Notably, the amount of lifetime degradation is less severe at lower amounts of surrogate ion transport (e.g., 0.96 or higher, or 0.98 or higher transfer rates).

It has been found that when transport of surrogate ions becomes significant at one or more locations within the fuel cell, the fuel cell will begin to degrade rapidly. This is believed to be due to one or more locations deteriorating and not providing any further current density. Since one or more zones stop contributing to the required current density, the rest of the locations in the fuel cell must be operated at a higher current density in order to maintain a constant total (average) current density for the fuel cell. This may cause the region for the transport of the substitute ions to grow, resulting in degradation of the expanded portion of the fuel cell and eventual shutdown. Alternatively, degradation of a portion of the fuel cell may result in a decrease in the total current density from the cell, which is also undesirable. Operating multiple fuel levels can reduce CO ₂ The amount of surrogate ion transport that occurs within the fuel cell stage during the increase in capture rate, thereby extending the service life of the fuel cell.

Anode input and output

In various aspects, the anode input stream of the MCFC can comprise hydrogen, a hydrocarbon (e.g., methane), a hydrocarbon-containing or hydrocarbon-like compound that can contain heteroatoms other than C and H, or a combination thereof. The source of hydrogen/hydrocarbon-like compounds may be referred to as a fuel source. In some aspects, the majority of the methane (or other hydrocarbon, hydrocarbonaceous or hydrocarbon-like compounds) fed to the anode may typically be fresh methane. In this description, fresh fuel (e.g., fresh methane) refers to fuel that is not recycled from another fuel cell process. For example, methane recycled back to the anode inlet from the anode outlet stream may not be considered "fresh" methane, but may be described as recovered methane.

The fuel source used may be shared with other components, such as providing CO-containing fuel to the cathode input using a portion of the fuel source ₂ Is a turbine of the stream of (a). The fuel source input may comprise water proportional to the fuel, which is suitable for reforming hydrocarbon (or hydrocarbon-like) compounds in a reforming section that generates hydrogen. For example, if methane is used for reforming to produce H ₂ The molar ratio of water to fuel may be from about one to about ten to one, such as at least about two to one. Typical ratios for external reforming are four to one or more, but typical values for internal reforming may be lower. H is just ₂ For part of the fuel source, in certain optional aspects, additional water may not be required in the fuel because of H ₂ Oxidation at the anode tends to produce H that can be used to reform the fuel ₂ O. The fuel source may also optionally contain components that are incidental to the fuel source (e.g., the natural gas feed may contain some level of CO as an additional component) ₂ ). For example, the natural gas feed may contain CO ₂ 、N ₂ And/or other inert (noble) gases as further components. Optionally, in some aspects, the fuel source may also contain CO, such as CO from a recycle portion of the anode exhaust. An additional or alternative potential source of CO in the fuel entering the fuel cell assembly may be CO produced by steam reforming of hydrocarbon fuel from the fuel prior to entering the fuel cell assembly.

More generally, multiple types of fuel streams may be suitable for use as an anode input stream for an anode of a molten carbonate fuel cell. Some fuel streams may correspond to streams containing hydrocarbons and/or hydrocarbon-like compounds that may also contain heteroatoms other than C and H. In this discussion, unless otherwise indicated, references to hydrocarbon-containing fuel streams for MCFC anodes are defined to include fuel streams containing such hydrocarbon-like compounds. Examples of hydrocarbon (including hydrocarbon-like) fuel streams include natural gas, streams containing C1-C4 carbon compounds (such as methane or ethane), and streams containing heavier c5+ hydrocarbons (including hydrocarbon-like compounds), and combinations thereof. Still other additional or alternative examples of potential fuel streams for anode input may include biogas-type streams, such as methane produced by natural (bio) decomposition of organic materials.

In some aspects, molten carbonate fuel cells may be used to process an input fuel stream, such as a natural gas and/or hydrocarbon stream, that has a low energy content due to the presence of diluent compounds. For example, some sources of methane and/or natural gas are those that may contain significant amounts of CO ₂ Or other sources of inert molecules such as nitrogen, argon, or helium. Due to the presence of increased amounts of CO ₂ And/or inert materials, may reduce the energy content of the fuel stream based on the source. The use of low energy content fuels to perform combustion reactions (e.g., to power combustion power turbines) can present difficulties. However, molten carbonate fuel cells can produce electricity based on low energy content fuel sources with reduced or minimal impact on fuel cell efficiency. The presence of additional gas volumes may require additional heat to raise the temperature of the fuel to the temperature required for reforming and/or anode reactions. In addition, due to the equilibrium nature of the water gas shift reaction within the fuel cell anode, additional CO ₂ The presence of (2) will be relative to the presence of H in the anode output ₂ And the relative amount of CO. However, inert compounds may otherwise have only minimal direct impact on reforming and anode reactions. CO in a fuel stream for molten carbonate fuel cells ₂ And/or the amount of inert compound(s), when present, may be at least about 1vol%, such as at least about 2vol%, or at least about 5vol%, or at least about 10vol%, or at least about 15vol%, or at least about 20vol%, or at least about 25vol%, or at least about 30vol%, or at least about 35vol%, or at least about 40vol%, or at least about 45vol%, or at least about 50vol%, or at least about 75vol%. Additionally or alternatively, CO in a fuel stream for a molten carbonate fuel cell ₂ And/or the amount of inert compoundMay be about 90vol% or less, such as about 75vol% or less, or about 60vol% or less, or about 50vol% or less, or about 40vol% or less, or about 35vol% or less.

Still other examples of potential sources of anode input streams may correspond to refinery and/or other industrial process output streams. For example, coking is a common process used in many refineries to convert heavier compounds to a lower boiling range. Coking typically produces exhaust gases containing a variety of compounds that are gaseous at room temperature, including CO and various C' s ₁ –C ₄ And (3) hydrocarbons. Such exhaust gas may be used as at least a portion of the anode input stream. Other refinery off gas streams may additionally or alternatively be suitable for inclusion in the anode input stream, such as light ends (C ₁ –C ₄ ). Still other suitable refinery streams may additionally or alternatively comprise CO or CO-containing streams ₂ Which also contains H ₂ And/or reformable fuel compounds.

Still other potential sources for anode input may additionally or alternatively comprise streams with increased water content. For example, an ethanol output stream from an ethanol plant (or another type of fermentation process) may contain a substantial portion of H prior to final distillation ₂ O. This H ₂ O generally has only a minimal impact on the operation of the fuel cell. Thus, a fermentation mixture of alcohol (or other fermentation product) and water may be used as at least a portion of the anode input stream.

Biogas or biogas is another additional or alternative potential source of anode input. Biogas may consist essentially of methane and CO ₂ And are typically produced by decomposing or digesting organic matter. Anaerobic bacteria can be used to digest organic matter and produce biogas. Impurities, such as sulfur-containing compounds, may be removed from the biogas prior to use as anode input.

The output stream from the MCFC anode may comprise H ₂ O、CO ₂ CO and H ₂ . Optionally, the anode output stream may also contain unreacted fuel in the feed (e.g H ₂ Or CH (CH) ₄ ) Or inert compounds as additional output components. The anode output stream may be subjected to one or more separations to convert CO ₂ With potentially valuable components (e.g. H) as inputs to another process ₂ Or CO) separation, rather than using such output streams as a source of fuel for providing heat for the reforming reaction or as a combustion fuel for heating the cell. H ₂ And/or CO may be used as a source of chemically synthesized synthesis gas, chemically reacted hydrogen, and/or as a fuel to reduce greenhouse gas emissions.

Cathode input and output

Conventionally, molten carbonate fuel cells may operate based on drawing a desired load while consuming a portion of the fuel in a fuel stream delivered to the anode. The voltage of the fuel cell may then be determined by the load, the fuel input to the anode, the air supplied to the cathode, and the CO ₂ And the internal resistance of the fuel cell. CO may be conventionally provided to the cathode in part by using anode exhaust as at least a portion of the cathode input stream ₂ . In contrast, the present invention may use separate/distinct sources for the anode input and the cathode input. By removing any direct link between the compositions of the anode input stream and the cathode input stream, additional options become available for operating the fuel cell, such as generating excess syngas, increasing the capture rate of carbon dioxide, and/or increasing the overall efficiency (electrical energy plus chemical energy) of the fuel cell, etc.

In various aspects, MCFCs can be operated to cause alternative ion transport across the electrolyte of the fuel cell. To induce alternative ion transport, CO of the cathode input stream ₂ The content may be 5.0vol% or less, or 4.0vol% or less, such as 1.5vol% to 5.0vol%, or 1.5vol% to 4.0vol%, or 2.0vol% to 5.0vol%, or 2.0vol% to 4.0vol%.

CO-containing suitable for use as cathode input stream ₂ An example of a stream of (c) may be an output stream from a combustion source or an exhaust stream. Examples of combustion sources include, but are not limited to, those based on natural gas combustion, coal combustion, and/or other hydrocarbon-type fuels (includingBiologically derived fuel) combustion source. Additional or alternative sources may include other types of boilers, fired heaters, furnaces, and/or other types of devices that burn a carbonaceous fuel to heat another substance, such as water or air.

Other potential sources of the cathode input stream may additionally or alternatively comprise biologically produced CO ₂ Is a source of (a). This may comprise, for example, CO generated during the treatment of the biologically derived compounds ₂ Such as CO generated during ethanol production ₂ . Additional or alternative examples may include CO produced by combustion of a biologically produced fuel (e.g., combustion of lignocellulose) ₂ . Still other additional or alternative potential CO ₂ The source may correspond to an output stream or an exhaust stream from various industrial processes, such as factory-generated CO-containing for the manufacture of steel, cement and/or paper ₂ Is a stream of (a) a stream of (b).

Yet another additional or alternative potential CO ₂ The source may be CO-containing from a fuel cell ₂ Is a stream of (a) a stream of (b). CO-containing from fuel cells ₂ The streams of (a) may correspond to cathode output streams from different fuel cells, anode output streams from different fuel cells, recycle streams from cathode outputs to cathode inputs of the fuel cells, and/or recycle streams from anode outputs to cathode inputs of the fuel cells. For example, an MCFC operating in stand alone mode under conventional conditions may produce CO ₂ A cathode exhaust gas concentration of at least about 5 vol%. Such a CO-containing product ₂ Can be used as the cathode input to an MCFC operating in accordance with one aspect of the invention. More generally, the production of CO from the cathode exhaust may additionally or alternatively be used ₂ Other types of fuel cells for output, and other types of CO-containing not produced by "combustion" reactions and/or combustion-powered generators ₂ Is a stream of (a) a stream of (b). Optionally but preferably CO-containing from another fuel cell ₂ May be from another molten carbonate fuel cell. For example, for cathodes of molten carbonate fuel cells connected in series, the output from the cathode of a first molten carbonate fuel cell may be used as a secondThe cathode of a molten carbonate fuel cell.

CO removal ₂ In addition, the cathode input stream may also contain O ₂ To provide the components required for the cathodic reaction. Some cathode input streams may be based on air as a component. For example, the combustion exhaust stream may be formed by combusting a hydrocarbon fuel in the presence of air. This combustion exhaust stream, or another type of cathode input stream having an oxygen content based on comprising air, may have an oxygen content of about 20vol% or less, such as about 15vol% or less, or about 10vol% or less. Additionally or alternatively, the oxygen content of the cathode input stream may be at least about 4vol%, such as at least about 6vol% or at least about 8vol%. More generally, the cathode input stream may have a suitable oxygen content for performing the cathode reaction. In some aspects, this may correspond to an oxygen content of about 5vol% to about 15vol%, such as about 7vol% to about 9 vol%. For many types of cathode input streams, CO ₂ And O ₂ The combined amount of (a) may correspond to less than about 21vol% of the input stream, such as less than about 15vol% of the stream or less than about 10vol% of the stream. The air stream containing oxygen may be CO with low oxygen content ₂ Source combination. For example, the exhaust stream produced by burning coal may contain a low content of oxygen, which may be mixed with air to form the cathode inlet stream.

In addition to CO ₂ And O ₂ In addition, the cathode input stream may be composed of inert/non-reactive materials (e.g., N ₂ 、H ₂ O and other typical oxidant (air) components). For example, for a cathode input from a combustion reaction exhaust, if air is used as part of the oxidant source for the combustion reaction, the exhaust may contain typical components of air, such as N ₂ 、H ₂ O and other small amounts of compounds present in air. Depending on the nature of the fuel source used for the combustion reaction, additional substances present after combustion based on the fuel source may contain H ₂ One or more of O, oxides of nitrogen (NOx) and/or oxides of sulfur (SOx) and other compounds present in the fuel and/orPartial or complete combustion products of compounds present in the fuel, such as CO. These materials may be present in amounts that do not poison the cathode catalyst surface but they may reduce the overall cathode activity. This reduction in performance is acceptable or the species that interact with the cathode catalyst can be reduced to acceptable levels by known contaminant removal techniques.

O present in the cathode input stream (e.g., combustion exhaust-based input cathode stream) ₂ May be in an amount sufficient to advantageously provide the oxygen required for the cathode reaction in the fuel cell. Thus, O ₂ May advantageously be the volume percentage of CO in the exhaust gas ₂ At least 0.5 times the amount of (c). Optionally, additional air may be added to the cathode input as needed to provide sufficient oxidant for the cathode reaction. When using some form of air as the oxidant, N in the cathode exhaust ₂ May be present in an amount of at least about 78vol%, such as at least about 88vol% and/or about 95vol% or less. In some aspects, the cathode input stream may additionally or alternatively contain compounds commonly regarded as contaminants, such as H ₂ S or NH ₃ . In other aspects, the cathode input stream may be purified to reduce or minimize the content of such contaminants.

Suitable temperatures for MCFC operation may be between about 450 ℃ and about 750 ℃, such as at least about 500 ℃, e.g., an inlet temperature of about 550 ℃ and an outlet temperature of about 625 ℃. Heat may be added to or removed from the cathode input stream, if desired, prior to entering the cathode, for example, to provide heat for other processes, such as reforming the fuel input to the anode. For example, if the source of the cathode input stream is a combustion exhaust stream, the temperature of the combustion exhaust stream may be higher than the desired temperature of the Yu Yinji inlet. In such aspects, heat may be removed from the combustion exhaust prior to its use as a cathode input stream. Alternatively, the combustion exhaust gas may be at a very low temperature, for example after a wet gas scrubber on a coal-fired boiler, in which case the combustion exhaust gas may be below about 100 ℃. Alternatively, the combustion exhaust may be from the exhaust of a gas turbine operating in a combined cycle mode, wherein the gas may be cooled by generating steam to operate the steam turbine for additional power generation. In this case, the gas may be below about 50 ℃. Heat may be added to the combustion exhaust gas at a temperature lower than desired.

Additional molten carbonate fuel cell operating strategies

In some aspects, the anode of the fuel cell may be operated at a conventional fuel utilization value of about 60% to 80% when the MCFC is operated to cause transport of the surrogate ions. Operating the anode of a fuel cell at a relatively high fuel utilization may be advantageous to improve electrical efficiency (i.e., the electrical energy produced per unit of chemical energy consumed by the fuel cell) when attempting to generate electricity.

In some aspects, the electrical efficiency of the fuel cell is reduced to provide other benefits (e.g., increasing the H provided in the anode output stream ₂ The amount of (c) may be beneficial. This may be beneficial, for example, if it is desired to consume excess heat generated in the fuel cell (or fuel cell stack) by performing additional reforming and/or performing another endothermic reaction. For example, molten carbonate fuel cells may be operated to increase the production of synthesis gas and/or hydrogen. The heat required to perform the endothermic reforming reaction may be provided by an exothermic electrochemical reaction in the anode for generating electricity. This excess heat may be used in situ as a heat source for reforming and/or another endothermic reaction, rather than attempting to transfer heat generated by one or more exothermic fuel cell reactions away from the fuel cell. As a result, thermal energy may be used more efficiently and/or the need for additional external or internal heat exchange may be reduced. The efficient generation and use of such thermal energy (substantially in situ) may reduce system complexity and reduce components while maintaining favorable operating conditions. In some aspects, the amount of reforming or other endothermic reaction may be selected to have an endothermic heat demand comparable to or even greater than the excess heat generated by the exothermic reaction or reactions, rather than significantly lower than that typically described in the prior art.

Additionally or alternatively, the fuel cell may be operated such that the temperature difference between the anode inlet and the anode outlet may be negative rather than positive. Thus, a sufficient amount of reforming and/or other endothermic reactions may be performed such that the output stream from the anode outlet is at a lower temperature than the anode inlet, rather than increasing the temperature between the anode inlet and the anode outlet. Further additionally or alternatively, additional fuel may be supplied to the heater and/or internal reforming stage (or other internal endothermic reaction stage) of the fuel cell such that the temperature difference between the anode input and the anode output may be less than a desired temperature difference based on the relative requirements of one or more endothermic reactions and the combined exothermic heat generation of the cathode combustion reaction and the anode reaction for generating electricity. In aspects where reforming is used as the endothermic reaction, operating the fuel cell to reform excess fuel may allow for increased synthesis gas and/or increased hydrogen production relative to conventional fuel cell operation while minimizing heat exchange and reforming system complexity. The additional synthesis gas and/or additional hydrogen may then be used in a variety of applications, including chemical synthesis processes and/or collection/reuse of hydrogen for use as a "clean" fuel.

The amount of heat generated per mole of hydrogen oxidized by the exothermic reaction at the anode may be significantly greater than the amount of heat consumed per mole of hydrogen generated by the reforming reaction. Net reaction of hydrogen in molten carbonate fuel cells (H ₂ +1/2O ₂ ＝>H ₂ The reaction enthalpy of O) may be about-285 kJ/mol hydrogen molecules. At least a portion of this energy may be converted to electrical energy in the fuel cell. However, the difference between the reaction enthalpy and the electrical energy produced by the fuel cell may become (approximately) heat within the fuel cell. This energy can alternatively be expressed as the current density (current per unit area) of the cell multiplied by the difference between the theoretical maximum voltage and the actual voltage of the fuel cell, or<Current density>* (Vmax-Vact). This energy is defined as the "waste heat" of the fuel cell. As an example of reforming, the reforming enthalpy (CH ₄ +2H ₂ O＝>4H ₂ +CO ₂ ) May be about 250kJ/mol methane or about 62kJ/mol hydrogen molecules. From the viewpoint of heat balance, each isThe electrochemically oxidized hydrogen molecules can generate sufficient heat to produce more than one hydrogen molecule by reforming. In conventional arrangements, this excess heat may result in a significant temperature difference from the anode inlet to the anode outlet. Instead of using this excess heat to increase the temperature in the fuel cell, the excess heat may be consumed by performing a matching amount of reforming reaction. The excess heat generated in the anode may be supplemented with the excess heat generated by the combustion reaction in the fuel cell. More generally, excess heat may be consumed by performing an endothermic reaction at the fuel cell anode and/or in an endothermic reaction stage thermally integrated with the fuel cell.

According to the aspects, the amount of reforming and/or other endothermic reactions can be selected relative to the amount of hydrogen reacted in the anode to achieve a desired heat ratio of the fuel cell. As used herein, a "heat ratio" is defined as the amount of heat generated by the exothermic reaction in the fuel cell assembly (including the exothermic reaction in both the anode and cathode) divided by the endothermic demand of the reforming reaction occurring within the fuel cell assembly. Expressed mathematically, the heat ratio (TH) =q _EX /Q _EN Wherein Q is _EX Is the sum of the heat generated by the exothermic reaction, and Q _EN Is the sum of the heat consumed by the endothermic reactions occurring within the fuel cell. It should be noted that the heat generated by the exothermic reaction may correspond to any heat generated due to reforming reactions in the cathode, water gas shift reactions, combustion reactions (i.e., oxidation of fuel compounds), and/or electrochemical reactions in the cell. The amount of heat generated by the electrochemical reaction can be calculated based on the ideal electrochemical potential of the fuel cell reaction on the electrolyte minus the actual output voltage of the fuel cell. For example, the ideal electrochemical potential for the reaction in MCFCs is considered to be about 1.04V based on the net reaction occurring in the cell. During MCFC operation, the output voltage of the battery is typically below 1.04V due to various losses. For example, a typical output/operating voltage may be about 0.7V. The heat generated may be equal to the electrochemical potential of the cell (i.e., -1.04V) minus the operating voltage. For example, when the output voltage in the fuel cell reaches 0.7V, the heat generated by the electrochemical reaction in the cell may be 0.34V . Thus, in this case, the electrochemical reaction will produce 0.7V of electrical energy and 0.34V of thermal energy. In such examples, 0.7V of electrical energy is not taken as Q _EX Is included. In other words, the thermal energy is not electrical energy.

In various aspects, the thermal ratio of any convenient fuel cell structure may be determined, such as a fuel cell stack, individual fuel cells within a fuel cell stack, a fuel cell stack with integrated reforming stages, a fuel cell stack with integrated endothermic reaction stages, or a combination thereof. The heat ratio may also be calculated for different units within the fuel cell stack, such as the fuel cells or an assembly of fuel cell stacks. For example, the heat ratio may be calculated for the fuel cell(s) within the fuel cell stack along with integrated reforming stage and/or integrated endothermic reaction stage elements that are sufficiently close to the one or more fuel cells to be integrated from a thermal integration perspective.

From a thermal integration perspective, the feature width in a fuel cell stack may be the height of an individual fuel cell stack element. It is noted that the individual reforming stages and/or the individual endothermic reaction stages may have different heights in the stack than the fuel cell. In such cases, the height of the fuel cell element may be used as the feature height. In this discussion, an integrated endothermic reaction stage may be defined as a stage thermally integrated with one or more fuel cells such that the integrated endothermic reaction stage may use heat from the fuel cells as a source of heat for reforming. Such an integrated endothermic reaction stage may be defined as positioning the height 10 times smaller than the height of the stack elements of the fuel cells that provide heat to the integrated stage. For example, the positioning height of an integrated endothermic reaction stage (e.g., reforming stage) may be 10 times less than the height of a stack element from any thermally integrated fuel cell, or may be 8 times less than the height of a stack element, or may be 5 times less than the height of a stack element, or may be 3 times less than the height of a stack element. In this discussion, an integrated reforming stage and/or an integrated endothermic reaction stage representing a stack element adjacent to a fuel cell element may be defined as a height of about one stack element height or less from the adjacent fuel cell element.

A thermal ratio of about 1.3 or less, or about 1.15 or less, or about 1.0 or less, or about 0.95 or less, or about 0.90 or less, or about 0.85 or less, or about 0.80 or less, or about 0.75 or less, may be lower than that typically sought when using MCFC fuel cells. In aspects of the invention, the heat ratio may be reduced to increase and/or optimize the production of synthesis gas, the production of hydrogen, the production of another product by an endothermic reaction, or a combination thereof.

In various aspects of the invention, operation of the fuel cell may be characterized based on the thermal ratio. When the fuel cell is operated to have a desired heat ratio, the molten carbonate fuel cell may be operated to have a heat ratio of about 1.5 or less, for example about 1.3 or less, or about 1.15 or less, or about 1.0 or less, or about 0.95 or less, or about 0.90 or less, or about 0.85 or less, or about 0.80 or less, or about 0.75 or less. Additionally or alternatively, the thermal ratio may be at least about 0.25, or at least about 0.35, or at least about 0.45, or at least about 0.50. Further additionally or alternatively, in some aspects, the fuel cell may be operated to have a temperature rise between the anode input and the anode output of about 40 ℃ or less, such as about 20 ℃ or less, or about 10 ℃ or less. Still further additionally or alternatively, the fuel cell may be operated to have an anode outlet temperature that is about 10 ℃ lower to about 10 ℃ higher than the temperature of the anode inlet. Still further additionally or alternatively, the fuel cell may be operated such that its anode inlet temperature is higher than the anode outlet temperature, such as at least about 5 ℃ higher, or at least about 10 ℃ higher, or at least about 20 ℃ higher, or at least about 25 ℃ higher. Still further additionally or alternatively, the fuel cell may be operated such that its anode inlet temperature is about 100 ℃ or less, or about 80 ℃ or less, or about 60 ℃ or less, or about 50 ℃ or less, or about 40 ℃ or less, or about 30 ℃ or less, or about 20 ℃ or less, higher than the anode outlet temperature.

Operating the fuel cell at a thermal ratio of less than 1 may cause the temperature of the entire fuel cell to drop. In some aspects, the amount of reforming and/or other endothermic reactions may be limited such that the temperature drop from the anode inlet to the anode outlet may be about 100 ℃ or less, such as about 80 ℃ or less, or about 60 ℃ or less, or about 50 ℃ or less, or about 40 ℃ or less, or about 30 ℃ or less, or about 20 ℃ or less. The limitation of the temperature drop from the anode inlet to the anode outlet may be beneficial, for example, to maintain a sufficient temperature to allow complete or substantially complete conversion (by reforming) of the fuel in the anode. In other aspects, due to the balance between the heat consumed by the endothermic reaction and additional external heat supplied to the fuel cell, additional heat may be supplied to the fuel cell (e.g., by heat exchange or combustion of additional fuel) such that the anode inlet temperature is about 100 ℃ or less, such as about 80 ℃ or less, or about 60 ℃ or less, or about 50 ℃ or less, or about 40 ℃ or less, or about 30 ℃ or less, or about 20 ℃ or less, higher than the anode outlet temperature.

The amount of reforming may additionally or alternatively depend on the availability of reformable fuel. For example, if the fuel includes only H ₂ No reforming occurs because of H ₂ Has been reformed and cannot be further reformed. The amount of "syngas produced" by a fuel cell may be defined as the difference between the Lower Heating Value (LHV) value of the syngas in the anode input and the LHV value of the syngas in the anode output. The resulting synthesis gas LHV (sg net) = (LHV (sg out) -LHV (sg in)), where LHV (sg in) and LHV (sg out) refer to the LHV of the synthesis gas in the anode inlet stream or stream and the LHV of the synthesis gas in the anode outlet stream or stream, respectively. Is provided with a large amount of H ₂ Fuel cells for fuels of (2) may be limited in terms of potential syngas production because the fuel contains a significant amount of already reformed H ₂ Rather than containing additional reformable fuel. The lower heating value is defined as the conversion of the fuel components to the gas phase, complete oxidation products (i.e., gas phase CO ₂ And H ₂ O product). For example, any CO present in the anode input stream ₂ Will not contribute to the fuel content of the anode input because of the CO ₂ Has been fully oxidized. For this definition, the amount of oxidation occurring in the anode as a result of the anode fuel cell reaction is defined as in the anode as part of the electrochemical reaction in the anodeH of (2) ₂ Is a metal oxide semiconductor device.

An example of a method for operating a fuel cell at a reduced heat ratio may be a method of performing excessive reforming of fuel so as to balance heat generation and consumption in the fuel cell and/or consume more heat than the generated heat. Reforming reformable fuel to form H ₂ And/or the CO may be an endothermic process, while the anodic electrochemical oxidation reaction and the one or more cathodic combustion reactions may be exothermic. During conventional fuel cell operation, the amount of heat consumed to supply the reforming amount of the feed components for fuel cell operation may generally be less than the amount of heat generated by the anodic oxidation reaction. For example, conventional operation at a fuel utilization of about 70% or about 75% may result in a heat rate substantially greater than 1, such as a heat rate of at least about 1.4 or greater, or 1.5 or greater. Thus, the output stream of the fuel cell may be hotter than the input stream. Unlike this type of conventional operation, the amount of fuel reformed in the reforming stage associated with the anode may be increased. For example, additional fuel may be reformed such that the heat generated by the exothermic fuel cell reaction may be (approximately) balanced by the heat consumed in reforming and/or consume more heat than is generated. This can result in a significant excess of hydrogen relative to the amount of hydrogen oxidized in the anode for generating electricity, and can result in a thermal ratio of about 1.0 or less, such as about 0.95 or less, or about 0.90 or less, or about 0.85 or less, or about 0.80 or less, or about 0.75 or less.

Hydrogen or synthesis gas may be extracted from the anode exhaust as chemical energy output. Hydrogen can be used as a clean fuel that does not produce greenhouse gases when burned or combusted. In contrast, for hydrogen gas produced by reforming of hydrocarbon (or hydrocarbon-containing compound), CO ₂ May have been "trapped" in the anode loop. In addition, hydrogen may be a valuable input to various refining processes and/or other synthesis processes. Syngas can also be a valuable input to various processes. In addition to being fuel-valued, the synthesis gas may also be used as a feedstock for producing other higher value products, such as by using the synthesis gas as a Fischer-Tropsch synthesis and/or methanol synthesisAnd (5) forming process input.

In some aspects, the reformable hydrogen content of the reformable fuel delivered to the anode and/or the input stream to the reforming stage associated with the anode can be at least about 50% greater than the net content of hydrogen reacted at the anode, such as at least about 75% greater or at least about 100% greater. Additionally or alternatively, the reformable hydrogen content of the fuel in the input stream delivered to the anode and/or to the reforming stage associated with the anode can be at least about 50% greater than the net content of hydrogen reacted at the anode, such as at least about 75% greater or at least about 100% greater. In various aspects, the ratio of the reformable hydrogen content of the reformable fuel in the fuel stream relative to the amount of hydrogen reacted in the anode can be at least about 1.5:1, or at least about 2.0:1, or at least about 2.5:1, or at least about 3.0:1. Additionally or alternatively, the ratio of the reformable hydrogen content of the reformable fuel in the fuel stream relative to the amount of hydrogen reacted in the anode can be about 20:1 or less, such as about 15:1 or less, or about 10:1 or less. In one aspect, it is contemplated that less than 100% of the reformable hydrogen content in the anode inlet stream can be converted to hydrogen. For example, at least about 80% of the reformable hydrogen content in the anode inlet stream can be converted to hydrogen at the anode and/or in one or more associated reforming stages, such as at least about 85% or at least about 90%. Additionally or alternatively, the amount of reformable fuel delivered to the anode can be characterized based on the Lower Heating Value (LHV) of the reformable fuel relative to the LHV of hydrogen oxidized in the anode. This may be referred to as a reformable fuel excess ratio. In various aspects, the reformable fuel excess ratio may be at least about 2.0, such as at least about 2.5, or at least about 3.0, or at least about 4.0. Additionally or alternatively, the reformable fuel excess ratio may be about 25.0 or less, such as about 20.0 or less, or about 15.0 or less, or about 10.0 or less.

Example 1

Steady state fuel cell models created using commercially available process modeling platforms were used to simulate the cathode flow patterns of both fuel cell configurations. In the first configuration, the pair size is 250cm ² Is a single piece of (2)Modeling the fuel cell. In a second configuration, the combined dimension of the pair connected in series in parallel cross-flow is 166cm ² Two fuel cell modeling (approximately 2/3 of the area of a single fuel cell). For each configuration, the anode input gas into the first stage was modeled as 72% H ₂ 18% CO ₂ And 10% H ₂ O (mole gauge). The cathode input gas was modeled as 4% CO ₂ 10% O ₂ 10% H ₂ O and 76% N ₂ (molar meter). In each configuration, the first (or unique) level is modeled as 120mA/cm ² Is a fuel efficiency of 85% and a CO of 72% ₂ Utilization operation. For the second configuration, the first stage has a power of 120mA/cm ² And 85% fuel utilization, while the second stage has a current density of 120mA/cm ² And a fuel utilization of 70%. Clean CO on two stages of the second configuration ₂ The capture or utilization is 72% so that the same net CO content is used in both configurations ₂ . However, due to the CO in the first configuration ₂ A significant amount of additional alternative ion transport occurs, as well as depletion. This results in a reduced transfer rate. This explains the origin of the larger fuel cell area in the first configuration having the same current density as the smaller fuel cell area in the second configuration.

FIG. 5 shows CO in the cathode in steady state based on a flow pattern modeled according to the first configuration ₂ Concentration. The anode flow and cathode flow directions are also indicated. As shown in FIG. 5, although the concentration in the cathode output stream was about 1.0mol% (based on 72% CO) ₂ Utilization) but CO within the cathode ₂ Distributed in a highly non-uniform manner. In particular, at the corners corresponding to the anode inlet and the cathode outlet, CO ₂ The concentration drops to almost zero, whereas at the corners corresponding to the cathode inlet and anode outlet, the CO ₂ The concentration was almost 4.0mol%. Due to CO over the whole cathode ₂ Significant changes in concentration, CO in cathode ₂ The amount of alternative ion transport may increase in localized areas of low concentration.

FIG. 6 shows the firstCathode CO in steady state for two stages of both configurations ₂ Concentration. As shown in fig. 6, CO in two cathode stages ₂ The variation in concentration is reduced or minimized. In addition, in FIG. 5, the lowest concentration corresponds to CO of 0.08mol% or less ₂ Concentration. In contrast, the lowest concentration presented in fig. 6 is 0.3mol%.

Example 2

In this example, two configurations using two molten carbonate fuel cells are used. In a first configuration, two fuel cells are arranged in parallel such that the two fuel cells receive half of the anode input stream and half of the cathode input stream. In the parallel configuration, the two fuel cells operate under the same operating conditions. The operating conditions are selected so that the current density of each of the parallel fuel cells reaches 90mA/cm ² . In a second configuration, two fuel cells are arranged in series with respect to the cathode flow. Thus, in the second configuration, each cell receives half of the anode input stream, while the first fuel cell receives all of the cathode input stream. The cathode exhaust from the first fuel cell is then used as the cathode input stream to the second fuel cell. For the second configuration, the first fuel cell was operated at 120mA/cm ² And the second fuel cell operated at 60mA/cm ² And (3) operating. The fuel utilization rates of both configurations are the same.

As explained above, the net current density for operating the parallel and series configurations is the same, since the average value of the two cells in both configurations is 90mA/cm ² . However, by using a series configuration, the transfer rate increases from 0.683 for the parallel configuration to 0.693 for the series configuration. This increase in transfer rate indicates a decrease in the amount of alternative ion transport in the tandem configuration. Thus, even for the same current density generation, a staged fuel cell can provide unexpected benefits by reducing or minimizing the amount of alternative ion transport when operated with a large amount of alternative ion transport. However, it is worth noting that even if the net substitution ion transport is reduced, the first cell in the series configuration operates at a lower voltage than the parallel configurationAn operating voltage. This suggests that even if the net substitution ion transport is reduced, this reduction is based on an increase in the first stage followed by a larger decrease in the second stage of the series configuration.

Further embodiments

Embodiment 1. A method for generating electricity, the method comprising: will include H ₂ An anode input stream of reformable fuel, or a combination thereof, is introduced into a first anode stage of the plurality of molten carbonate fuel cell stages; will include O ₂ And CO ₂ Is introduced into a first cathode stage of the plurality of molten carbonate fuel cell stages; passing a second anode input stream into a second anode stage of the plurality of molten carbonate fuel cell stages; causing an intermediate cathode output into a second cathode stage of the plurality of molten carbonate fuel cell stages; and operating the plurality of molten carbonate fuel cell stages to produce: i) Average current density of 60mA/cm ² Or greater electrical power, ii) anode exhaust from the plurality of molten carbonate fuel cell stages, the anode exhaust comprising H ₂ CO and CO ₂ And iii) cathode exhaust from the plurality of molten carbonate fuel cell stages, the cathode exhaust comprising CO in an amount of 2.0vol% or less ₂ H in an amount of 1.0vol% or more ₂ O and O in an amount of 1.0vol% or more ₂ At least one of the first cathode stage and the second cathode stage operates at a transfer rate of 0.97 or less.

Embodiment 2. The method of embodiment 1 wherein the first cathode stage is operated at a transfer rate of 0.97 or less and the second cathode stage is operated at a transfer rate of 0.97 or less.

Embodiment 3. The method of any of the preceding embodiments, wherein the at least one of the first cathode stage and the second cathode stage operates at a transfer rate of 0.95 or less, or 0.90 or less.

Embodiment 4. The method of any of the preceding embodiments, wherein the second anode input stream comprises at least a portion of an intermediate anode output stream, the intermediate anode output optionally comprising an output from the first anode stage.

Embodiment 5. The method of embodiment 4, further comprising: passing a second anode intermediate output into a third anode stage, the anode exhaust comprising an output from the third anode stage; and passing a second cathode intermediate output into a third cathode stage, the cathode exhaust comprising an output from the third cathode stage, wherein the first anode stage, the second anode stage, and the third anode stage are arranged in parallel flow or in countercurrent flow relative to the first cathode stage, the second cathode stage, and the third cathode stage.

Embodiment 6. The method of any of the preceding embodiments, wherein the transfer rate of the first cathode stage is different from the transfer rate of the second cathode stage.

Embodiment 7. The method of any of the preceding embodiments, wherein at least the first anode stage, the second anode stage, the first cathode stage, and the second cathode stage are operated in a co-current cross-flow manner; or wherein at least the first anode stage, the second anode stage, the first cathode stage and the second cathode stage are operated in countercurrent cross-flow.

Embodiment 8. The method of any of the preceding embodiments, wherein the anode exhaust comprises an anode output from the second anode stage, or wherein the cathode exhaust comprises a cathode output from the second cathode stage, or a combination thereof.

Embodiment 9. The method of any of the preceding embodiments, wherein the intermediate cathode output comprises an output from the first cathode stage.

Embodiment 10. The method of any of the preceding embodiments, wherein during operation of the plurality of molten carbonate fuel cells, the combined measured CO in the first cathode stage and the second cathode stage ₂ The utilization is 75% or more, or 80% or more.

Embodiment 11. The method of any of the preceding embodiments, wherein the electrical power is generated at an average current density of 100mA/cm2 or more, or 120mA/cm2 or more, or 150mA/cm2 or more.

Embodiment 12. The method of any of the preceding embodiments, wherein the voltage drop across the cathode is 0.4V or less, or wherein the power is generated at a voltage of 0.55V or more, or a combination thereof.

Embodiment 13. The method of any of the preceding embodiments, wherein the fuel utilization in the anode is 60% or greater, or wherein the fuel utilization in the anode is 55% or less, or wherein the H in the anode exhaust gas ₂ A concentration of 5.0vol% or more, or wherein H in the anode exhaust gas ₂ And CO is 6.0vol% or more, or a combination thereof.

Embodiment 14. The method of any of the preceding embodiments, wherein the fuel cell is operated at a thermal ratio of 0.25:1.0; or wherein the amount of reformable fuel introduced into the first anode stage, an internal reforming element associated with the first anode stage, or a combination thereof, is at least about 75% greater than the amount of hydrogen reacted in the first anode stage to produce electricity; or a combination thereof.

Embodiment 15. The method of any of the preceding embodiments, wherein the cathode input stream comprises 5.0vol% or less CO ₂ Or wherein the cathode exhaust gas comprises 1.0vol% or less of CO ₂ Or a combination thereof.

Alternative embodiment

Alternative embodiment 1. A method for generating electricity, the method comprising: will include H ₂ An anode input stream of reformable fuel, or a combination thereof, is introduced into a first anode stage of the plurality of molten carbonate fuel cell stages; will include O ₂ And CO ₂ Is introduced into a first cathode stage of the plurality of molten carbonate fuel cell stages; passing a second anode input stream into a second anode stage of the plurality of molten carbonate fuel cell stages; causing an intermediate cathode output into a second cathode stage of the plurality of molten carbonate fuel cell stages; operating the molten carbonate Fuel cell stage to produce: i) Average current density of 80mA/cm ² Or greater electrical power, ii) anode exhaust from the plurality of molten carbonate fuel cell stages, the anode exhaust comprising H ₂ CO and CO ₂ And iii) cathode exhaust from the plurality of molten carbonate fuel cell stages, the cathode exhaust comprising CO ₂ 1.0vol% or more of O ₂ And 1.0vol% or more of H ₂ O, wherein CO measured across a combination of the plurality of molten carbonate fuel cell stages ₂ A utilization of 70% or more (or 75% or more, or 80% or more), and wherein calculated CO in the plurality of molten carbonate fuel cell stages calculated based on the current density ₂ Utilization ratio of CO measured from the combination ₂ The utilization is 5% or more (or 10% or more, or 20% or more).

Alternative embodiment 2. The method of alternative embodiment 1 wherein the cathode input stream comprises 5.0vol% or less CO ₂ (or 4.0vol% or less), or wherein the cathode exhaust gas comprises 1.0vol% or less of CO ₂ Or a combination thereof.

Alternative embodiment 3. A method for generating electricity, the method comprising: will include H ₂ An anode input stream of reformable fuel, or a combination thereof, is introduced into a first anode stage of the plurality of molten carbonate fuel cell stages; will include O ₂ And 5.0vol% or less of CO ₂ (or 4.0vol% or less) cathode input stream is introduced into a first cathode stage of the plurality of molten carbonate fuel cell stages; passing a second anode input stream into a second anode stage of the plurality of molten carbonate fuel cell stages; causing an intermediate cathode output into a second cathode stage of the plurality of molten carbonate fuel cell stages; and operating the molten carbonate fuel cell stage to produce: i) Average current density of 80mA/cm ² Or greater electrical power, ii) anode exhaust from the plurality of molten carbonate fuel cell stages, the anode exhaust comprising H ₂ CO and CO ₂ And iii) cathode exhaust from the plurality of molten carbonate fuel cell stages, the cathodeThe polar exhaust gas includes CO in an amount of 1.0vol% or less ₂ Wherein CO is measured across a combination of the plurality of molten carbonate fuel cell stages ₂ A utilization of 70% or more (or 75% or more, or 80% or more), and wherein calculated CO in the plurality of molten carbonate fuel cell stages calculated based on the current density ₂ Utilization ratio of CO measured from the combination ₂ High utilization, the calculated CO ₂ Utilization ratio of CO optionally measured over the combination ₂ The utilization is 5.0% or more (or 10% or more, or 20% or more).

The method of any of the preceding alternative embodiments, wherein the second anode input stream comprises at least a portion of an intermediate anode output stream, the intermediate anode output optionally comprising an output from the first anode stage.

Alternative embodiment 5 the method of alternative embodiment 4, further comprising: passing a second anode intermediate output into a third anode stage, the anode exhaust comprising an output from the third anode stage; and passing a second cathode intermediate output into a third cathode stage, the cathode exhaust comprising an output from the third cathode stage, wherein the first anode stage, the second anode stage, and the third anode stage are arranged in parallel flow or in countercurrent flow relative to the first cathode stage, the second cathode stage, and the third cathode stage.

Alternative embodiment 6 the method of any one of the preceding alternative embodiments, wherein the measured CO in the first cathode stage ₂ Utilization rate of CO measured from the combination is different from that of CO measured from the combination ₂ Utilization rate.

The method of any one of the preceding alternative embodiments, wherein at least the first anode stage, the second anode stage, the first cathode stage, and the second cathode stage are operated in co-current cross-flow; or wherein at least the first anode stage, the second anode stage, the first cathode stage and the second cathode stage are operated in countercurrent cross-flow.

The method of any of the preceding alternative embodiments, wherein the anode exhaust comprises an anode output from the second anode stage, or wherein the cathode exhaust comprises a cathode output from the second cathode stage, or a combination thereof.

The method of any of the preceding alternative embodiments, wherein the intermediate cathode output comprises an output from the first cathode stage.

Alternative embodiment 10. The method of any of the preceding alternative embodiments, wherein the electrical power is generated at a current density of 120mA/cm2 or greater (or 150mA/cm2 or greater).

Alternative embodiment 11 the method of any one of the preceding alternative embodiments, wherein the voltage drop across the cathode is 0.4V or less, or wherein the electrical power is generated at a voltage of 0.55V or greater, or a combination thereof.

The method of any one of the preceding alternative embodiments, wherein the fuel utilization in the anode is 60% or greater, or wherein the fuel utilization in the anode is 55% or less.

Alternative embodiment 13 the method of any one of the preceding alternative embodiments, wherein H in the anode exhaust gas ₂ A concentration of 5.0vol% or more, or wherein H in the anode exhaust gas ₂ And CO is 6.0vol% or more, or a combination thereof.

The method of any one of the preceding alternative embodiments, wherein the fuel cell is operated at a thermal ratio of about 0.25:about 1.0; or wherein the amount of reformable fuel introduced into the first anode stage, an internal reforming element associated with the first anode stage, or a combination thereof, is at least about 75% greater than the amount of hydrogen reacted in the first anode stage to produce electricity; or a combination thereof.

All numbers in the detailed description and claims herein are modified by the term "about" or "approximately" to account for experimental errors and variations that may be expected by one of ordinary skill in the art.

Although the present invention has been described with specific embodiments, it is not necessarily limited thereto. Appropriate changes/modifications to the operation under specific conditions should be apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alterations/modifications as fall within the true spirit/scope of the invention.

Claims

1. A method for generating electricity, the method comprising: will include H ₂ An anode input stream of reformable fuel, or a combination thereof, is introduced into a first anode stage of the plurality of molten carbonate fuel cell stages; will include O ₂ And CO ₂ Is introduced into a first cathode stage of the plurality of molten carbonate fuel cell stages; passing a second anode input stream into a second anode stage of the plurality of molten carbonate fuel cell stages; causing an intermediate cathode output into a second cathode stage of the plurality of molten carbonate fuel cell stages; and operating the plurality of molten carbonate fuel cell stages to produce: i) Average current density of 60mA/cm ² Or greater electrical power, ii) anode exhaust from the plurality of molten carbonate fuel cell stages, the anode exhaust comprising H ₂ CO and CO ₂ And iii) cathode exhaust from the plurality of molten carbonate fuel cell stages, the cathode exhaust comprising CO in an amount of 2.0vol% or less ₂ H in an amount of 1.0vol% or more ₂ O and O in an amount of 1.0vol% or more ₂ At least one of the first cathode stage and the second cathode stage operates at a transfer rate of 0.97 or less.

2. The method of claim 1, wherein the first cathode stage operates at a transfer rate of 0.97 or less and the second cathode stage operates at a transfer rate of 0.97 or less.

3. The method of claim 1, wherein at least one of the first cathode stage and the second cathode stage operates at a transfer rate of 0.95 or less.

4. The method of any of the preceding claims, wherein the second anode input stream comprises at least a portion of an intermediate anode output stream.

5. The method as in claim 4, further comprising: passing a second anode intermediate output into a third anode stage, the anode exhaust comprising an output from the third anode stage; and passing a second cathode intermediate output into a third cathode stage, the cathode exhaust comprising an output from the third cathode stage, wherein the first anode stage, the second anode stage, and the third anode stage are arranged in parallel flow or in countercurrent flow relative to the first cathode stage, the second cathode stage, and the third cathode stage.

6. A method according to any one of claims 1 to 3, wherein the transfer rate of the first cathode stage is different from the transfer rate of the second cathode stage.

7. A method according to any one of claims 1 to 3, wherein at least the first anode stage, the second anode stage, the first cathode stage and the second cathode stage are operated in co-current cross-flow; or wherein at least the first anode stage, the second anode stage, the first cathode stage and the second cathode stage are operated in countercurrent cross-flow.

8. A method according to any one of claims 1 to 3, wherein the anode exhaust comprises an anode output from the second anode stage, or wherein the cathode exhaust comprises a cathode output from the second cathode stage, or a combination thereof.

9. A method according to any one of claims 1 to 3, wherein the intermediate cathode output comprises an output from the first cathode stage.

10. A method according to any one of claims 1 to 3, wherein during operation of the plurality of molten carbonate fuel cell stages, CO is measured in combination in the first cathode stage and the second cathode stage ₂ The utilization is 75% or more, or 80% or more.

11. A method according to any one of claims 1 to 3, wherein the electrical power is generated at an average current density of 100mA/cm2 or higher, or 120mA/cm2 or higher, or 150mA/cm2 or higher.

12. A method according to any one of claims 1 to 3, wherein the voltage drop across the first cathode stage is 0.4V or less, or wherein power is generated at a voltage of 0.55V or more, or a combination thereof.

13. The method of any one of claims 1 to 3, wherein the fuel utilization in the plurality of molten carbonate fuel cell stages is 60% or greater, or wherein the fuel utilization in the plurality of molten carbonate fuel cell stages is 55% or less, or wherein H in the anode exhaust gas ₂ A concentration of 5.0vol% or more, or wherein H in the anode exhaust gas ₂ And CO is 6.0vol% or more.

14. The method of any one of claims 1-3, wherein the plurality of molten carbonate fuel cell stages operate at a thermal ratio of 0.25:1.0; or wherein the amount of reformable fuel introduced into the first anode stage, an internal reforming element associated with the first anode stage, or a combination thereof, is at least about 75% greater than the amount of hydrogen reacted in the first anode stage to produce electricity; or a combination thereof.

15. A process according to any one of claims 1 to 3, wherein the cathode input stream comprises 5.0vol% or less CO ₂ Or thereinThe cathode exhaust gas includes 1.0vol% or less of CO ₂ Or a combination thereof.