Patent Application
20090050522
The invention resides in the field of hydrogen generation through the reformation of hydrocarbon fuels.
Fuel cells are being considered for many applications beyond vehicle transportation, including stationary and transportable electrical power plants. These applications, unlike industrial or automotive vehicles, function predominately as steady state operations over significant time periods, although there are transient loads applied to these electrical power generation systems. Given relatively stable operating loads and conditions, the principle technical approach to providing a hydrogen feed stream to the fuel cell stack has been an effort to implement an endothermic process generically referred to as steam reforming. This process has been used by industry, in one embodiment or another, for nearly 100 years to generate hydrogen from hydrocarbons, primarily from methane (CH4) found in natural gas.
For transportable power generation systems, liquid hydrocarbon fuels are the preferred fuels due to the higher hydrogen densities offered by these liquids over any compressed gas, such as methane. A problem with using an endothermic reforming process is that this type of system does not have the ability to follow large increases in load demand. Primarily because of this problem, steam reformation has been largely abandoned for transportation applications dominated by highly fluctuating transient loads. Steam reforming, in different system configurations, is still being pursued as a possible method to generate hydrogen for those applications in which transient load changes are significantly less frequent, such as stationary/transportable electrical power generation. However, even for these applications, meeting transient load demands is still problematic due to the inherent endothermic investment that needs to be made at the very beginning of the reforming process.
One solution that has been proposed to compensate for the inherently slow response characteristics of steam reforming is to capture, divert and store under pressure a portion of the final hydrogen feed stream product during moments of excess production for latter use during sudden electrical load increases. While it is certainly possible to store a portion of the gaseous hydrogen feed stream in this manner, this intermittent hydrogen source is only useful in meeting dynamic load demands placed upon a Fuel Cell Power System (FCPS). This approach does not provide any assistance in overcoming the fundamental problem of steam reforming, which is the up-front endothermic investment required to create a subsequent increase in overall hydrogen production.
Traditional as well as newer steam reforming processes also suffer in their ability to respond to rapid increases in hydrogen demand due to the significant cleanup difficulties of the reactant gases. All of these reforming processes rely upon air as the oxygen source. While this source is readily available, the component makeup of air causes significant problems in these systems. While oxygen makes up approximately 21% of air by volume, nitrogen comprises approximately 78% of air by volume. This low oxygen ratio causes several problems including the formation of undesirable chemical compound formations. One particularly significant problem is that steam reforming requires that the air be compressed to differing pressures depending upon the particular steam reforming process being utilized. Small-scale gas compression, required for FCPS output, ranging from 5 kW to 500 kW is typically inefficient, resulting in large parasitic electrical loads to the FCPS. The large presence of nitrogen in the air also increases parasitic energy losses from the compressor, because the nitrogen must be compressed as well.
The presence of nitrogen leads to other undesirable consequences in a typical steam reforming processes. One of these undesirable consequences is the chemical formation of nitrogen-oxides (NOx), primarily NO and NO2. NOx formations start during the initial hydrocarbon oxidation phase. The formation of these compounds in turn causes two other problems with respect to overall system efficiency. First, NOx is a heavily regulated pollutant and must be catalytically cleaned in an elevated thermal environment. This process further consumes hydrogen as the oxygen bonds are stripped from the NOx as it progresses to a final mixture of N2+CO2+H2O, Second, NOx formation causes the loss of available oxygen to fully oxidize carbon, which releases the sought after hydrogen. Consequently, the steam reforming processes which use air, experience further increases in parasitic compressor losses when additional air is compressed and introduced into the overall process to compensate for the loss of oxygen due to NOx formation.
Carbon Monoxide (CO) concentrations above a few parts per million are unacceptable to the long-term reliability and durability of the PEM Membrane Electrode Assembly (MEA). As such, a CO contaminated hydrogen gas stream must be exposed to a water-gas shift reaction to convert CO to carbon dioxide (CO2), which is acceptable to the MEA. When air is used as the oxygen source, the presence of nitrogen not only creates the previously described NOx pollutants, but also further encourages the formation of CO due to the reduced availability of oxygen to fully react with the carbon. As the percentage of CO formation increases for any given gas flow rate, the water-gas shift reaction bed must also grow in size. Elevated temperatures are needed for this catalytic bed to function correctly. Thus, as the bed mass increases, it will take longer to elevate the bed, or a new section of the bed, to the necessary temperature. Until this event occurs, the product gas stream can not be supplied to a PEM fuel cell due to the contamination caused by the excessive CO levels. This high CO gas stream must be diverted away from the fuel cell, once again inhibiting the reformer's ability to meet sudden increases in hydrogen demand as well as further deteriorating the reformer's overall conversion efficiency.
In order to accomplish an increase in the hydrogen reforming rate, steam reformers require that more steam be made available, which is the crux of the slow response characteristics of this reforming process. Typically, this endothermic investment needs to be made by heating liquid water to steam at the very beginning of the reforming process. A downstream hydrogen reformate holding tank is only able to provide a limited amount of time for the primary reforming system to boil additional water. The actual amount of time available to boil this water is dependent upon the size and storage pressure of the holding tank.
Another considerable obstacle that must be addressed in configuring a hydrogen or reformate holding tank is that while it is possible to supplement the hydrogen source for the typical duty cycle, it becomes much more difficult to do so when non-typical duty cycles are considered. If electrical power generation cannot fail, such as hospital emergency or telecommunications power backup, then the secondary hydrogen storage system must be forced to grow in size and pressure in order to meet all high demand scenarios. While this is possible, the size increase adds to the cost, complexity and maintenance of the entire fuel delivery system.
Another difficulty that steam reforming faces is the limited degree of adjustability in the output rate of the hydrogen reformate. The ratio of maximum output to minimum output is typically referred to as the turndown ratio. Current steam and/or autothermal type reforming systems have a turndown capability between 2 or 3 to 1 compared to typical power generation which has a turndown between 5 and 10 to 1. While it may be possible to improve the reformer's turndown, there are fundamental obstacles that resist this change. Steam based reforming of hydrogen from hydrocarbons that uses air as the oxidation source, must provide a means for maximized hydrogen conversion as well as the NOx, CO and sulfur-based compound cleanup described above. This clean up is currently performed by specialized, sequential catalytic beds that need to be at specific minimum/maximum temperature range to function correctly. One means of providing increased turndown capability is to subdivide the fixed catalytic processing volume(s) into several smaller mass, parallel processing paths or processing sections. Even with a significantly small catalytic mass, which a subdivided Flow Section would allow, starting a new reformer or catalytic bed would take several minutes to reach the minimum operational temperatures required to produce hydrogen compatible with a PEM fuel cell. For applications requiring a fast startup and electricity delivery capability, this delay in electrical power generation is unacceptable.
Thus, a reformation process that could quickly and efficiently follow increases in transient load demand is desired. Preferably, such a system would not rely on air as a source of oxygen and would be highly adjustable between the minimum and maximum system output.
The present invention provides methods of using hydrogen peroxide to aid and improve the ability of a hydrocarbon reforming process to meet fast startup and dynamic changes in hydrogen production.
In one embodiment, the present invention provides a method of contacting a hydrogen peroxide solution with water to produce heat, steam and oxygen. These products are supplied to a hydrocarbon reforming system. The system for contacting the hydrogen peroxide solution and water may be either external to the hydrocarbon reforming system or integrated internally into the hydrocarbon reforming system.
In a preferred embodiment, the chemical reaction process pathways of the reforming system are subdivided into at least two parallel process paths. Each parallel process pathway may be isolated from the other process pathways. The parallel process paths preferably have a uniform geometry and an interior accessible by at least one end. The interior of the process pathways optionally contains at least two catalytic beds. In a specific embodiment, an element interconnects the catalytic beds. The element may be composed of at least two materials, such as an assembly of at least one rod and at least one plate in contact with the at least one rod.
The reforming system supplemented with the products of the dissociation of hydrogen peroxide may use only hydrogen peroxide as an oxygen source or may use only air as an oxygen source.
The method may also be implemented in a reformer system that includes at least one heat exchange device placed in a discharge gas stream of the reforming system and interconnected by at least one rod to at least one of the process paths.
The hydrogen peroxide solution used in the methods of the present invention is preferably a diluted hydrogen peroxide solution having a concentration of between about 60% by weight and about 50% by weight. The hydrogen peroxide used may also be concentrated from a more dilute solution. In this manner, a hydrogen peroxide having a concentration below about 50% by weight is concentrated to form a diluted hydrogen peroxide solution having a concentration of between about 50% by weight and about 70% by weight prior to contacting the hydrogen peroxide and water solution with a disassociating catalyst to form oxygen, hydrogen and heat. The processes may also be carried out using a diluted hydrogen peroxide solution having a concentration between about 35% by weight and about 55% by weight.
In a specific embodiment, these processes include contacting the steam and oxygen generated by the reaction of the water and hydrogen peroxide with a hydrocarbon fuel to form a hydrogen reformate stream which is then supplied to the a second hydrocarbon reforming device. The hydrocarbons used in this system are preferably at least one of methane, methanol, ethanol, gasoline, diesel, DME, JP5, and JP8. Most preferably, the hydrocarbon is liquid ethanol. Similarly, the chemical reaction process pathways of this reforming system may be subdivided into at least two parallel process paths which may be isolated from the other process pathways. The parallel process pathways preferably have a uniform geometry and an accessible interior containing at least two catalytic beds. Preferably, at least one element composed of at least two materials interconnects the catalytic beds. The elements are typically an assembly of at least one rod and at least one plate in contact with the rod. This reforming system may also use either hydrogen peroxide as the sole oxygen source or air as the sole oxygen source.
The ability of an air based reforming system to respond to any increase in hydrogen production demand is highly dependant upon that system's ability to provide appropriate thermal increases to the water feed stock, catalytic beds and other thermal masses of the containment components. The rate at which the thermal management system must respond is identical to the rate at which demand for hydrogen production changes. One system level approach to supplying more hydrogen for transient load increases, while the reformer's thermal management system struggles with maintaining the necessary process conditions, is to produce and store excess pressurized hydrogen in holding tanks.
An alternative approach to obtaining supplemental hydrogen from a holding tank would be to introduce a supplemental, exothermic oxygen source at the beginning of the primary reforming process. To be effective, the oxygen source would ideally need to be free or substantially free of contaminates such as nitrogen and other compounds that either create a cleanup requirement or potentially damage the various catalytic beds or the fuel cell MEA. Furthermore, for any such supplemental oxygen generation/delivery subsystem to be effective, it must not only generate oxygen but also generate sufficient heat to ideally flash an excess quantity of liquid water into steam. These compounds can then be subsequently used to accelerate the reforming of the hydrocarbon fuel, which is itself a highly exothermic reaction. Such an approach meets both the immediate load following demand for increased hydrogen, and accelerates the addition of new thermal energy to move the primary reforming system to a higher rate of hydrogen production. When the primary reforming system has been brought up to temperature and can sustain the higher flow rate demand on its own, the supplemental oxygen, heat and steam system may be turned off.
Solid and liquid oxidizers are a traditional source for oxygen. When activated, most solid or liquid oxidizers release considerable quantities of thermal energy as they disassociate and release the chemically stored oxygen. The supplemental oxygen generation/delivery system needs to capture this energy for use in vaporizing water into steam and to deliver either the thermal energy or the desired steam directly to the steam reforming section.
While there are several solid oxidizers available, many of which have been used to provide emergency oxygen in airplanes, submarines or emergency rescue gear, a preferred approach utilizes a liquid oxidizer. Most preferably, the liquid oxidizer is diluted hydrogen peroxide (H2O2). Diluted hydrogen peroxide is a mixture of hydrogen peroxide and water. The mixture may also include stabilizers. The relative concentration by weight of peroxide varies from standard plant production of approximately 70% down to about 3% found in many over the counter preparations for household use. A H2O2 concentration of between about 65% by weight to about 45% by weight is the preferred concentration to best meet the requirements of the chemical reactions, as well as the general safety and handling requirements of any large market implementation. The dissociation of this compound (H2O2→Heat+H2O+O−) is highly exothermic and directly generates the three desired components of water, oxygen and thermal energy.
The use of hydrogen peroxide as the oxidizer is advantageous over the use of other oxidizers as there is no need to capture thermal energy and transfer it to liquid water. Instead, water content is directly vaporized without the need for heat exchangers and pumps, thereby avoiding further system cost and complexity. An additional benefit is that there are no contaminates that must be cleaned up in the primary reforming system. In particular, there is no nitrogen released. The lack of additional nitrogen in the supplemental oxygen stream prevents increasing the NOx formation rate within the primary reforming system, though total process mass does increase. Instead, the NOx cleanup catalysts of the primary reforming system can be brought up to the necessary operating temperatures as the NOx free reactants generate and distribute exothermic energy throughout the entire reformer system, prior to shutting down a supplemental oxygen system.
In selecting a solid or liquid oxidizer for this use, the impact of any associated chemical contaminates that would be released and how those contaminates would affect the catalytic beds or the fuel cell membrane must be considered.
One specific embodiment is shown as a process block diagram in
When an oxidizer is used that does not contain nitrogen or other contaminates, it is not necessary for the catalytic beds, which are required to cleanup these formations, to be immediately and fully functional. These beds can initially be well below their minimum operational temperature without causing an adverse effect upon the quality of the hydrogen reformate feed stream provided to the fuel cell. As long as the contamination-free oxygen source is used, these beds can be brought up to the particular minimum temperature ranges over time, in preparation to perform their particular cleanup function. The catalytic beds need to be at their operational functional level whenever the transition is made from the oxidizer back to air as the oxygen source.
As such, the current Flow Section through the reformer system can either be further heated to provide for increased reforming rates, or an entirely new Flow Section can be the recipient of all or part of the contamination-free reformate stream. In this latter process, the new “cold” Flow Section could be quickly brought thermally online in preparation for eventually performing all of the oxidation, water gas shift reactions and cleanup required when air is used as the oxidation source. During this time period, the supplemental hydrogen stream is immediately usable by the fuel cell stack, allowing for the entire Fuel Cell Power System (FCPS) to perform load following power production.
When a PEM type fuel cell is used, CO will be one of the incompatible compounds generated by these processes. The formation of CO can be controlled in the new Flow Section through both the manipulation of the oxidizer/water to fuel ratio as well as reliance upon the final CO clean up stage of the primary reforming system. The final CO to CO2 conversion process, typically referred to as the low temperature water-gas shift and the Selective Oxidation or Preferential Oxidation (PROX) process (
In a preferred embodiment, depicted in
Cost is always a design issue for consumer-oriented products. Two broad approaches of addressing cost through design are to minimize the total number of components and to identify simpler manufacturing and assembly approaches to those remaining components. The need to meet specific performance requirements is typically a countering design factor that has the tendency to increase cost. With that perspective, the oxygen assist approach of the present invention, which is generally characterized by the process block diagram in
The following description illustrates how the above process of using hydrogen peroxide as a thermal/process assist functions in a hydrocarbon reforming system, starting from a “cold” non-operating state. Referring to
The dissociated peroxide, (steam and oxygen mix) with the injected hydrocarbon fuel enter the reduction and/or oxidation catalyst bed (90) to begin stripping hydrogen atoms from the hydrocarbon. Since this reaction is highly exothermic, efforts are typically made to transfer this energy to the task of pre-heating the input fluids, primarily the water and the hydrocarbon fuel. To this end, thermal conduction rods (50) begin the transfer of thermal energy to the steam generating beds (40) in preparation for the transition back to air as the oxygen source. While the Primary Reforming System (10) may continue to use other external, thermal transfer means to heat process water, the depicted approach (30, 40) assists the reforming system (10) to quickly adjust to smaller increases in hydrogen production demands without the need to inject any hydrogen peroxide/water solution. The thermal conduction rods (50) may also be extended from the highly exothermic oxidation/reduction beds (90) to down stream catalytic beds (100, 110) used for gas clean up such as NOx to N2 and CO to CO2 conversion. The geometry, material construction, location and member of these rods (50, 50a, 50b, 50c of
As the catalytic beds in those Flow Sections are actively brought up to operating thermal conditions, using hydrogen peroxide as the sole oxygen source, the flow control valve begins to open in a manner similar to that depicted by valve 20c, to allow ambient air or air/steam to begin to mix in with the reforming process. In turn, the rate at which the hydrogen peroxide/water solution is injected (60) would be proportionally reduced. Eventually, the active Flow Section would be operating entirely on air as the oxygen source.
At this point, the Primary Reforming System (10) may continue to operate on the active Flow Sections or bring a non-active Flow Section online using the process described above. The new Flow Section (for example 10b) is isolated from the external air or air/steam gas flow by fully closing the flow control valve (20b). As thermal conditions in Flow Section (10b) reach those required to allow for air operation, the flow control valve (20b) begins to open, initiating the transition to 100% air operation in that Flow Section.
At any point in time during the Primary Reforming System's (10) operation on 100% air, one or more of the Flow Sections may have additional, intermittent amounts of hydrogen/peroxide solution injected (60) into the Flow Sections to meet sudden increased demands for hydrogen production (transient load demands). Likewise, additional quantities of water may be injected (30) into the vaporization beds (40) to ensure sufficient process steam was also present for these transient load conditions.
There are those applications in which the cost of fully duplicated hydrogen generating systems, as depicted in the process diagram of
The primary differences would be that the Reaction Vessel (5b) needs to be included and since all of the input compounds are liquids and the output product is a gas stream, the vessel (5b) is not a flow through design as shown in the Flow Sections (10a, 10b, 10c) of
The effective thermal transfer of the heats of dissociation and combustion from the point of generation to the regions in need of thermal energy is an important determinant to the success of the assisted reforming approaches of the present invention. One approach to this energy transfer described above utilizes internal, thermal conductive structures (50, and 50a, 50b, 50c of
Steam reforming of hydrocarbons utilizes several different catalytic beds to accomplish different tasks including steam generation, hydrocarbon fuel oxidation, NOx cleanup, and water gas shift for CO to CO2 conversion. All of these beds need to be at elevated temperatures in order for them to function as designed. Of the beds listed, only the catalyst beds and/or regions in which carbon oxidation/reduction is occurring will have an exothermic release of energy. This exothermic release has been traditionally used to heat the follow on catalytic beds to their required temperature range. A traditional mechanism to accomplish this thermal transfer has been the hot gas molecules themselves as they travel through the various subsystems of the steam reformer.
Because steam based reforming is being applied to generate hydrogen for fuel cells, and for PEM type fuel cells in particular, the product gas stream from the reformer can not be delivered to the fuel cell until the gas has been cleaned of CO, and NOx, assuming that there is no sulfur present. The clean up of these pollutants cannot occur to the degree necessary until the various catalytic beds are up to their operational temperatures. Steam reforming has another consideration that internal, thermal conduction structures would be of value. In particular, the heating and eventual formation of steam is a process that is upstream of the exothermic oxidation of the hydrocarbon fuel. Consequently, the use of the gas flow to transfer thermal energy is not possible. However, thermal conduction structures would be able to efficiently and cheaply transport the thermal energy against the flow stream. Effective thermal transfer to the upstream steam generation bed allows for reduced parasitic loads used to pump and heat water external to the reforming process. This will also allow for an increase in the reforming system's ability to generate steam, thereby improving the overall load response capability.
Referring to
A preferred approach to implementing passive, thermal conductive heat transfer structures located within various catalytic and thermal mass beds is illustrated in
Another passive, low cost, thermal transfer mechanism that greatly decreases the time required to bring an adjacent, non-active Flow Section fully up to operating temperature is depicted in
As previously described, the ability of a steam reforming system, whether utilizing air or another oxidizer source, to generate a fuel cell safe hydrogen feed stream is dependent upon being able to bring the temperatures of the various catalytic beds up to operational temperatures. A subdivision of the steam reforming flow path into separate, independent Flow Sections has been presented in this disclosure as a means to reduce the mass, and therefore the time required, to heat just a portion of these critical catalytic beds to the necessary temperatures. Another addition to that concept is the utilization of the thermally energetic gaseous flow that has left the active Flow Sections to pre-warm the beds of the inactive sections. Once the reformate gas stream (250) has left a Flow Section, its thermal energy must be reduced from many hundreds of degrees Centigrade to less than approximately 80 degree C.
Once the product gases have left the catalytic beds of the Primary Flow Section, the thermal energy of that gas stream is lost to the Primary Flow Section. In order to recover additional benefit from the thermal energy of that gas stream, additional components are required. This additional recovery may be accomplished by using a gaseous compatible heat exchanger (240) device to transfer thermal energy from the exhaust (250) of the Primary Flow Section to secondary, tertiary flow sections, and so on, into adjacent Flow Sections using conduction through transfer rods (230) into heat transfer plates (220). Thermal energy applied to the heat transfer plates (220) will be conducted into the structure end plates (180), beginning the thermal heating of the adjacent Flow Section and associated catalytic beds through the previously described thermal transfer structures (50).
The reformate discharge region (250) of each Flow Section needs to be configured to facilitate the attachment of a discharge manifold (260) that interconnects all of the various Flow Sections into a common discharge flue/manifold. The gaseous heat exchanger is preferably located in the common flue area of the discharge manifold, thereby offering the opportunity to transfer thermal energy to all possible Flow Sections. This presents the ability to preferentially conduct thermal energy from the primary Flow Section to the secondary Flow Section by selecting unique cross-sectional areas of the thermal transfer rods (230). Preferential energy transfer to sequential, non-primary Flow Sections can be accomplished by designing the thermal transfer rods to each subsequent Flow Section to have different thermal conductance or capacitance. This approach is especially effective if each Flow Section has an independent external airflow control valve (20). A closed airflow control valve allows for no cooling gases (air) to flow past the catalytic beds of an adjacent Flow Section, the ability to transfer thermal energy to that Flow Section is significantly improved. As the secondary Flow Section is brought online, thermal energy will quickly stop flowing into that Section as the exothermic output exceeds the conducted thermal energy potential of (240), (230) and (220). At this point, the tertiary Flow Section receives the majority of the recovered thermal energy of the combined gaseous discharge streams of the primary and secondary Flow Sections.
A final mechanism which dramatically increases the rate of thermal transfer to the Flow Section of either process configuration represented by
The only difficulty with low concentration levels of hydrogen peroxide would be during the initial startup of a cold reforming system. At “cold” start up conditions, the diluted hydrogen peroxide solution would still dissociate but the overall temperature will be reduced due to the presence of greater water concentrations and the lack of any additional heat from the reforming process. One solution to this problem, for either type of reforming system generally described by
A preferred approach to address the thermal starting issues with highly dilute hydrogen peroxide includes the use of a concentrated quantity of the peroxide specifically for starting. To avoid the economic impracticality of two different concentrations of hydrogen peroxide available at all fueling stations, a portion of the diluted peroxide could be diverted from the system holding tank (1,
The concentrated peroxide is then exclusively used to start the entire reforming process. By design, the concentration of the hydrogen peroxide is sufficiently high to completely vaporize all water present upon its dissociation as well as contain sufficient thermal energy to begin the heating of the Flow Section components.
The concentration of peroxide needed may be determined through various approaches including measurement of specific conductance, pH, vapor pressure or density. All of these values vary in a quantitatively measurable and predictable fashion as the relative percentage of hydrogen peroxide varies. A direct or indirect measurement approach will need to be taken to determine the peroxide concentration. Concentrating the hydrogen peroxide beyond about 65% to about 70% peroxide by weight is not beneficial. In fact, beyond this concentration, there is insufficient water (steam) to oxidize a fuel such as ethanol. The need for subsequent humidification of the final hydrogen feed stream, further increases the minimum amount of water required. Additionally, peroxide in concentrations greater than 70% becomes an increasingly aggressive oxidizer and a potential health hazard if it comes into contact with skin. Measurement and control efforts (15 and 4) would need to be taken to assure that a maximum percent concentration as determined by the system requirements is not exceed.
There are several potential thermal sources (14) that can be used to evaporate excess water from the diluted hydrogen peroxide/water solution. The best approach varies depending upon the system requirements of the application in which the Fuel Cell Power System is installed. For an automotive application in which there is a significant electron storage capacity, (regenerative braking, for example) an electrical heating element would likely be the simplest and most cost efficient means of providing the thermal energy (14) necessary to evaporate the excess water. For other applications, the hot reformate gas stream can be the thermal energy (14) and allowed to pass through a heat exchanger, thereby transferring the necessary heat to vaporize the water directly. A more indirect approach is to pass the coolant from existing FCPS heat exchangers (14) through a coiled tube inside the hydrogen peroxide Concentrating Vessel (13). Two or more of the above methods can be integrated to meet multiple application requirements. For example, passive methods can be the primary mechanism used to concentrate the peroxide in order to minimize parasitic energy consumption. A back up system of indirect electrical element heating may be used as an emergency starting capability.
The Hydrogen Peroxide Concentrating Vessel (13) needs to have several features. First among these is the need for the material to be compatible with concentrated H2O2. Secondly, the vessel would need to be sealed, or sealable, from the environment as well as pressure capable since the fluids are being heated, which will increase the vapor pressure. Since vapor pressure, as a function of temperature and percent concentration of peroxide is one means to determine concentration, this is one preferable approach to concentration determination (15, 4). Upon heating the peroxide in the concentration vessel to a measured, predetermined temperature value, there will be some unique vapor pressure specific to the percent concentration of peroxide to water. At a predetermined, and/or controller-selectable vapor pressure point, selected to maximize the rate of water evaporation or oppositely minimize the quantity of hydrogen peroxide contained in the trap vapor, a vent (16) could be opened to vent the water vapor. The continued heating and subsequent venting of vapor would continue until a determination was made that the hydrogen peroxide solution was at the necessary percent concentration. The vessel also needs to include a safety vent mechanism in the case of run away pressure buildup. A second peroxide concentrating vessel may be added to ensure an adequate supply for all start/stop scenarios. While one vessel, which has previously concentrated its quantity of peroxide to the necessary level, is being used to start the reformer system, a second vessel is active in concentrating its portion of diluted peroxide.
In order to minimize the loss of peroxide during this process, temperatures well away from the boiling point of peroxide may be selected. The process controller is able to select the most appropriate temperature value and adjust that value as the concentrating process proceeds or the starting demands change. Because there is substantial run time after each start of the FCPS, the concentration of peroxide need not be an aggressive accelerated process.
The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain the best mode known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2005/024204 | 7/7/2005 | WO | 00 | 10/20/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60586192 | Jul 2004 | US |
