Patent Description:
Hydrogen production by; sorption enhanced steam methane reforming (SE-SMR), see reaction a), or sorption enhanced water gas shift (SE-WGS), see reaction b) are known processes, see <CIT>.

Energy efficient CaO absorbent regeneration, (CaCO<NUM> = CaO + CO<NUM> (T at about <NUM>)) is very important in this connection.

Heat or waste heat from SOFC has been suggested for regeneration of the absorbent in the Ca-looping process by many previous experts in the field (for example: <CIT> and <CIT>), where the heat transfer from the SOFC system to a Ca-looping regenerator, would be sufficient for the regeneration process, if SOFC with stack temperatures above <NUM> are used, which can be achieved by use of ceramic interconnects (Lasosipojana, et al.

One critical parameter for design of a SOFC stack is lifetime and cost of materials; ceramics, rear earth materials and/or metals. Today the suppliers mostly focus on SOFC stacks at lower temperatures, in the range of <NUM> - <NUM> or in the range of <NUM> - <NUM>.

The lower SOFC stack temperatures mentioned above, limit in practical terms the SOFC running temperature to about <NUM> (Megel et al. <NUM>), and the heat of the SOFC exhaust air (consisting of nitrogen and oxygen, when H<NUM> gas is used as fuel) to the same temperature level. The exhaust SOFC air temperature is thus not high enough for the CaO absorbent regeneration mentioned above, unless the CaO regeneration system is run at lower pressure than <NUM> Atm. A cost and energy efficient method to increase the temperature of the SOFC exhaust air is therefore needed to reach the temperature level necessary (<NUM>, or above) for the CaO absorbent regeneration process if the SOFC systems is run at a temperature level of <NUM>-<NUM>.

Furthermore, depending of the fuel type used, to feed the reformer it is also important to be able to vary the amount of high temperature heat supplied to the regenerator. The fuel types used may be: natural gas/methane, syngas (made from any carbon containing solids of fossil or biogenic origin), bio gas from organic waste (with about, <NUM>% CH<NUM> and <NUM>% CO<NUM>) or landfill gas (with about, <NUM>% CH<NUM> and <NUM>% CO<NUM>).

If raw biogas or landfill gas, after removal of Sulphur components are used directly, with considerable amounts of CO<NUM> (more than <NUM>%, no prior capture of CO<NUM> before introduction to the Reformer), a Ca-looping system with higher (and flexible) capacity compared to fuels with no or little initial CO<NUM> (fossil or biogenic) would be a demand. This in turn, would result in the need for an exhaust heating device (see figures) capable of supplying variable amounts of high temperature heat.

In addition, the amount of available biogas and/or landfill gas may vary, simply because of varying production rates. Thus, in order to be able to supply the SOFC system with constant flow of fuel, it would be desirable to be able to switch between two Reformer/Regenerator systems;.

This option would also demand a need for an exhaust heating device (see figures) capable of supplying variable amounts of high temperature heat.

To be able to keep a constant fuel (mainly H<NUM>) flow rate to the SOFC system a storage tank for the reformed fuel (mainly H<NUM>) may also be needed.

An increase of the exhaust air temperature (<NUM>) to a level high enough for CaO absorbent regeneration by adding/supplying fuel to an exhaust heating device capable of supplying variable amounts (based on variable amounts of CO<NUM> in the initial raw biogas) of high temperature heat, have previously not been addressed.

<CIT> describes a process for oxidizing fuel and transferring the heat produced to a particular use in a combustion system such as fuels conversion. A bed of a mixture of materials forming an unmixed combustion catalyst, which in an oxidized state is readily reducible and in a reduced state is readily oxidizable, is placed in efficient thermal contact with a heat receiver for use in the combustion system. Fuel and air are alternately contacted with the bed, whereby the fuel is oxidized, the air is depleted of oxygen, and heat is liberated. The heat is efficiently transferred to the heat receiver by careful selection of the materials of the bed such that the temperatures produced when the fuel is oxidized and when the air is depleted of oxygen are advantageous to the particular use in the combustion system.

<CIT> describes a biomass gasification method and apparatus for production of syngas with a rich hydrogen content. In the gasification process the gasification energy is supplied by the sensible heat carried by a high temperature agent combined with the heat released by the chemical reaction between calcined lime and carbon dioxide.

The objective of the present invention is to provide a method that allows a cost and energy efficient operation of an SOFC based power plant using gas reforming with CaO for CO<NUM> capture, and an SOFC exhaust heating device.

It is a derived object to provide the above with no CO<NUM> climate effect and that allows the primary fuel (fuel to the Reformer) to be of any origin (bio- or fossil related; solid, liquid or gas).

It is also an object to be able to handle fuel gases to the Reformer of different compositions, hereunder different initial CO<NUM> content.

It is also a derived object to arrange the total hydrogen (and electricity) production system in a flexible manner, making it easy to switch between Reformer fuel with little or no CO<NUM> (for ex. CH<NUM>) and Reformer fuel with considerable amounts of initial CO<NUM> (for ex. biogas (<NUM>% CH<NUM> and <NUM>% CO<NUM>) made from organic household waste),.

In one aspect of the invention describes a method for production of electrical energy and H2 gas in a power plant comprising a Solid Oxide Fuel Cell (SOFC). Said power plant being charged with a feed gas selected from the group consisting of natural gas, bio-gas and syngas. Said feed gas, prior to being fed to the SOFC, is reformed in a reformer with a CaO containing CO2 absorber, thereby producing a carbon free H2 gas as feed for the SOFC while converting CaO to CaCO3. The CaCO3 is regenerated to CaO in an endothermic reaction in a CaO regenerator at a temperature of at least <NUM> utilizing heat from the SOFC to heat the regenerator.

The invention is characterized in that a dedicated heat exchange medium collecting heat in the SOFC is subjected to temperature increase in a heating device separated from the CaO regenerator, before being subjected to heat exchange in the CaO regenerator. The dedicated heat exchange medium is circulating in a closed loop between the SOFC, the heating device and the CaO regenerator. The heating device is charged with one of:.

The heating device is operated so as the dedicated heat exchange medium leaving the heating device has a temperature of at least <NUM>, preferably at least <NUM> and most preferred at least <NUM>.

In an embodiment of the invention the heating device is a burner charged with substantially pure H2 as a fuel gas in amount sufficient to increase the temperature of the exhaust gas from the SOFC by at least <NUM>.

In yet an embodiment of the invention at least a part of the fuel gas charged to the heating device is H2 gas deviated from the reformer.

In yet an embodiment of the invention at least part of the fuel gas charged to the heating device is H2 gas deviated from the H2 discharge of the SOFC.

In yet an embodiment of the invention the exhaust gas from the SOFC is hot air of about <NUM>.

According to another aspect the invention it is described a power plant for production of electrical energy and H2 gas in a power plant comprising a solid oxide fuel cell (SOFC)'. The power plant is arranged to be charged with a feed gas selected from the group consisting of natural gas, bio-gas and syngas. Said feed gas, prior to being fed to the SOFC, is arranged to be reformed in a reformer with a CaO containing CO2 absorber, thereby producing a carbon free H2 gas as feed from the SOFC while converting CaO to CaCO3, which is regenerated to CaO in a regenerator at a temperature of at least <NUM>.

The power plant is characterized in that a heating device is connected between the SOFC and the regenerator, such that the heating device is separated from the regenerator. Said heating device is arranged to allow a dedicated heat exchange medium collecting heat from the SOFC to be further heated therein and thereafter used for heat exchange in the regenerator. said heating device being arranged to receive the dedicated heat exchange medium arranged to circulate in a closed loop between the SOFC, the heating device and the CaO regenerator, wherein the heating device is charged with one of:.

Said heating device is arranged to heat the dedicated heat exchange medium leaving the heating device to a temperature of at least <NUM>, preferably at least <NUM> and most preferred at least <NUM>.

In an embodiment of the invention the oxygen required by the heating device is supplied by a separate air supply, by a discharge flow from the solid oxide fuel cell or a combination thereof.

In yet an embodiment of the invention a discharge flow from the solid oxide fuel cell is heat exchanged with a charge flow of pure oxygen to the heating device.

As will be seen by a person skilled in the art, the present method maintains the beneficial features of <CIT> (mentioned above) and <CIT>. Sustainability is still a keyword and a common denominator for the overall process. Thus, the process allows total CO<NUM> capture, or climate neutral CO<NUM> handling.

Technically the heat transfer between the SOFC system and the Regenerator, via the exhaust heating device, can be performed in two different manners,.

The heat transfer medium, can in this case be different gases, such as for example; hydrogen, CO<NUM>, air, helium, water vapor, different gas mixtures or fluids such as mineral oils, hydrocarbons and different types of molten salts.

The fuel for this heating process can be derived from biological, or from fossil sources.

If the CO<NUM> (<NUM>%) from the Regenerator is stored or used and some of the hydrogen from the SOFC system (see figures) is used as fuel in the heating device (see figures), the total system for hydrogen and electricity production would for all embodiments not have any climatic consequences.

It is also possible to obtain this (no climate consequence), if other types of fuels (carbon containing, hydrocarbons, fossil or biogenic) are used both in the Regenerator and in the temperature heating device, as can be seen from the different embodiments given below.

Different embodiments of the invention are illustrated below with reference to the enclosed drawings, where;.

Attention is drawn to <FIG>, showing a hydrogen production plant where an SOFC system is combined with a fuel reformer, a CaO CO<NUM>-absorbent regenerator and an exhaust heating system <NUM> for enhancement of the temperature.

A fuel flow <NUM> is charged to a Reformer unit <NUM> being part of a Ca-looping system <NUM>, arranged to reform the fuel and to take care of initial CO<NUM> (if needed) and CO<NUM> released in the reforming process. The fuel is typically natural gas, other methane-rich gas, such as gas produced in fermentation units or syngas. A substantially pure hydrogen gas <NUM> leaves the reformer unit <NUM>. In the reformer unit <NUM>, the process of reforming involves a reaction between the fuel, water (steam) and CaO in which the latter is converted to CaCO<NUM> in an exothermic reaction. The CaCO<NUM> made both from the initial CO<NUM> (if present) and from the reforming process is subsequently regenerated to CaO in an endothermic process to be described. Water <NUM> in vaporized form is also charged to the reformer unit <NUM>.

The substantially pure hydrogen gas <NUM> leaving the reformer unit <NUM> is heated in a first heat exchanger <NUM> before being charged to a solid oxide fuel cell (SOFC) <NUM>, as a heated hydrogen flow <NUM>. The SOFC produces electricity and releasing varying amounts of hydrogen <NUM>. Air <NUM> is also charged to the SOFC, typically after having been heated in a second heat exchanger <NUM>.

The exhaust gas <NUM> from the SOFC <NUM> is substantially pure air due to the fact that the fuel <NUM> charged to the fuel cell is substantially pure hydrogen. The temperature of the exhaust gas from the SOFC <NUM> is typically about <NUM> and may be somewhat less.

As indicated above, the CaCO<NUM> generated in the reformer unit <NUM> needs to be regenerated to CaO for reuse as capturing agent in the reformer. This takes place in a regenerator <NUM> forming a second part of the Ca-looping system <NUM>. However, the regeneration of CaCO<NUM> needs a temperature of at least <NUM>, more preferably at least <NUM> to operate efficiently and it is an endothermic process consuming energy. The regenerator <NUM> also needs some water <NUM> for its operation, said water typically being preheated in a third heat exchanger <NUM> in order not to act as a coolant.

The exhaust gas <NUM> from the SOFC is a promising candidate for maintaining the temperature of the regenerator <NUM>, but its temperature is typically not high enough to perform the task on its own. In practice, the temperature of the exhaust gas <NUM> is too low to effectively maintain a sufficient temperature in the regenerator <NUM> at which the CaCO<NUM> is converted to CaO for further use. The core of the present invention is the use of a dedicated system, integrated with a fuel reformer, a CaO CO<NUM>-absorbent regenerator, and an exhaust temperature increasing system <NUM> arranged to elevate the temperature of the exhaust gas <NUM> to allow it to be used for the purpose of maintaining an effective temperature in the regenerator <NUM> by using a heating device <NUM> for enhancement of the temperature.

<FIG> gives a schematic view of a hydrogen production plant, in which an SOFC system <NUM>, is combined with a fuel reformer <NUM>, a CaO CO<NUM>-absorbent regenerator <NUM> and an exhaust heating device <NUM>, which is fueled for enhancement of the temperature. In this embodiment the fuel charged to the exhaust heating device <NUM> is burned in air <NUM>.

If all the fuel to both the Reformer <NUM>, and the exhaust heating device <NUM> is of biogenic origin the total system would be climate neutral. Furthermore, if the fuel, for the heating system through <NUM>, is derived from biological sources, these can typically be:.

The CO<NUM> related to/released from these processes would be climate neutral and can after the heat transfer <NUM> to the Regenerator <NUM> be released to air as flow <NUM> without undesired climate consequences. Hydrogen, the most preferred fuel for the exhaust heating device, can be delivered from the downstream side of the reformer <NUM> through <NUM>, or more preferred as flow <NUM> which constitutes part of the hydrogen discharge flow <NUM> from the SOFC, after having had its temperature reduced in a heat exchanger, such as first heat exchanger <NUM>, used to heat the inlet flow <NUM> of hydrogen to the SOFC <NUM>.

It is, however, also possible to obtain a situation with no climate consequences if the fuel <NUM> charged to the Reformer <NUM> is of fossil origin and the fuel to the exhaust heating device <NUM> is of biogenic origin (see above). This is because the CO<NUM> from the reforming process in the Reformer <NUM> is efficiently absorbed by the CaO absorbent, cf. reaction a) (SE-SMR) and reaction b) (SE-WGS), and can thus easily be collected <NUM>% pure from the Regenerator <NUM> for storage or use as flows <NUM>, <NUM>.

Attention is now directed to <FIG>, showing a hydrogen production plant where an SOFC system is integrated with a fuel reformer, a CaO CO<NUM>-absorbent regenerator and to an exhaust heating device for enhancement of the temperature. In this embodiment the heat integration is provided with a closed heat loop <NUM>'.

Most of the components of <FIG> are the same as the ones in <FIG>. The difference between <FIG> is mainly that the heat transfer between the SOFC <NUM> and the Regenerator <NUM>, via the exhaust heating device <NUM>', is provided by a closed heat loop <NUM>, <NUM>, <NUM>, <NUM>.

If all the fuel to both the Reformer and the exhaust heating device, in the embodiment illustrated in <FIG> is of biogenic origin the total system would also be climate neutral. Similar to the embodiment given in <FIG> it is in this case also possible to obtain a situation with no climate consequences if the fuel to the Reformer is of fossil origin and the fuel to the exhaust heating device is of biogenic origin (see above).

If the fuel to the temperature heating device <NUM>' is derived from fossil sources, these can typically be:.

This would for the carbon containing fuel require a separate CO<NUM> collection system at <NUM>', to obtain a climate neutral situation.

The heat transfers medium of the heat loop <NUM>-<NUM> in <FIG>, can be different gases, such as for example; Hydrogen, CO<NUM>, air, helium, water vapor, different gas mixtures or fluids such as; mineral oils, hydrocarbons and different types of molten salts. The heat of the heat medium <NUM> leaving the SOFC system <NUM>, is about <NUM>. The heat of this heat loop is enhanced in the temperature heating device <NUM>' to at least <NUM>, more preferable at least <NUM> and most preferred at least <NUM>, in order to meet the temperature regeneration requirement of the CaO absorbent in regenerator <NUM>.

The heated exhaust flow <NUM>' from the SOFC system <NUM> provides the oxygen for the heating process in <NUM>'. The oxygen to the heating device may if needed also be provided by air inlet <NUM>. The exhaust from <NUM>' is heat exchanged in second heat exchanger <NUM> to heat the air at flow <NUM> through <NUM> into the SOFC <NUM>, before leaving the system as flow <NUM>' for release to atmosphere. If the fuel for the heating device is mainly or solely hydrogen, there will be little or no CO<NUM> in the exhaust gas at <NUM>'. If the heating device <NUM>' is fed wholly or partially by a different fuel, though a fuel of organic, non-fossil, origin, the exhaust gas at <NUM>' will be climate-neutral.

The regeneration of the absorbent also releases substantial amounts of pure CO<NUM> shown as flow <NUM>, which needs to be taken care of (used or stored) preferably after having been used for heat exchange in a third heat exchanger <NUM>.

As shown in <FIG>, water (vapor) <NUM> is added to the reformer unit <NUM> in order to furnish the reaction zone with required amounts of oxygen and hydrogen.

The principle illustrated by <FIG> is generally that heat produced by the SOFC <NUM> is used to regenerate the absorber used to absorb CO<NUM> in the process of reforming the feed gas, but since the temperature of the exhaust gas from the SOFC is typically a little too low to be used alone, its energy and temperature is increased in a subtle and efficient manner. Most elegant is perhaps the present process when hydrogen already being part of the system, is used for boosting the energy, then without the formation of any additional CO<NUM>.

Attention is now directed to <FIG> showing a hydrogen production plant where an SOFC system is combined with a fuel reformer, a CaO CO<NUM>-absorbent regenerator and an exhaust heating device for enhancement of the temperature. In this embodiment the heat transfer is provided with a closed heat loop. The fuel (if carbon containing) to the exhaust heating device is burned in pure oxygen provided by an oxygen pump.

Most of the components of <FIG> are the same as the ones in <FIG>. <FIG> shows an embodiment where the fuel to the Reformer22, as well as to the exhaust heating device <NUM>", can be of fossil origin (CH<NUM>, natural gas syngas etc.), where it is possible to capture all CO<NUM> from the total production system, for storage or use. The fuel to the heating device, would then have to be burned in pure oxygen supplied as flow <NUM>', by an oxygen pump. The oxygen <NUM>' is typically preheated in a fourth heat exchanger <NUM>, with SOFC exhaust air <NUM>' from second heat exchanger <NUM>. (It is to be noted that the heat exchanger <NUM> shown to heat flow <NUM> in <FIG>, and <FIG> is the same heat exchanger as used to cool flow <NUM> (<FIG>), flow <NUM>' (<FIG>) and flow <NUM>' (<FIG>)).

It is worth noticing, though, that all heat exchange in the present disclosure which is not directly related to the enhancement of the temperature of the heat exchange medium to the CaO regenerator is optional and may be conducted in a number of different ways.

In general, the description of Figures relates to preferred embodiments of the invention which is defined by the appended claims.

While the present invention may have the form of a number of different embodiments, the heat exchange medium the SOFC <NUM> typically comprises at least one of exhaust gas <NUM> and a dedicated heat exchange medium <NUM>, the latter in case circulating in a closed loop between the SOFC, the heating device <NUM>, <NUM>', <NUM>" and the CaO regenerator <NUM>.

The heating device <NUM> is in one preferred embodiment a burner charged with substantially pure hydrogen gas <NUM> in an amount sufficient to increase the temperature of the exhaust gas <NUM> from the SOFC <NUM> by at least <NUM>.

At least a part of the fuel gas charged to the heating device <NUM> is typically hydrogen gas deviated from the reformer <NUM>.

Claim 1:
Method for production of electrical energy and H2 gas in a power plant comprising a Solid Oxide Fuel Cell (SOFC) (<NUM>),
said power plant being charged with a feed gas (<NUM>) selected from the group consisting of natural gas, bio-gas and syngas,
said feed gas, prior to being fed to the SOFC (<NUM>), is reformed in a reformer (<NUM>) with a CaO containing CO2 absorber, thereby producing a carbon free H2 gas (<NUM>,<NUM>) as feed for the SOFC (<NUM>) while converting CaO to CaCO3, which is regenerated to CaO in an endothermic reaction in a CaO regenerator (<NUM>) at a temperature of at least <NUM> utilizing heat from the SOFC (<NUM>) to heat the regenerator (<NUM>),
characterized in that
a dedicated heat exchange medium (<NUM>,<NUM>,<NUM>,<NUM>) collecting heat in the SOFC (<NUM>) is subjected to temperature increase in a heating device (<NUM>',<NUM>'') separated from the CaO regenerator (<NUM>), before being subjected to heat exchange in the CaO regenerator (<NUM>),
wherein the dedicated heat exchange medium (<NUM>,<NUM>,<NUM>,<NUM>) is circulating in a closed loop between the SOFC (<NUM>), the heating device (<NUM>',<NUM>'') and the CaO regenerator (<NUM>),
wherein the heating device (<NUM>',<NUM>") is charged with one of:
i. a gas having a biogenic origin, and
ii. a gas of fossil origin, wherein the gas is subjected to one of a) being burned in pure oxygen (<NUM>') to yield an exhaust gas of pure CO2 (<NUM>"), and b) being burned in air (<NUM>) yielding an exhaust gas that is subjected to a separate step of CO2 collection (<NUM>'),
wherein operating the heating device (<NUM>',<NUM>'') so as the dedicated heat exchange medium (<NUM>,<NUM>,<NUM>,<NUM>) leaving the heating device (<NUM>',<NUM>") has a temperature of at least <NUM>, preferably at least <NUM> and most preferred at least <NUM>.