Abstract:
Processes and systems for producing hydrogen gas utilizing a sorbent enhanced reformer in combination with a calciner operating at atmospheric pressure. Feed material is introduced into the sorbent enhanced reformer to produce carbon dioxide and hydrogen gas. Sorbent material within the reformer acts to absorb carbon dioxide and form a used sorbent. The used sorbent is introduced into the atmospheric calciner to heat the used sorbent to desorb carbon dioxide from the used sorbent to produce regenerated sorbent which can be recycled to the reformer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application 62/167,871, filed 28 May 2015, the disclosure of which is incorporated by reference herein and made a part hereof, including but not limited to those portions which specifically appear hereinafter. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    This invention relates generally to hydrogen production and, more particularly, to hydrogen production via sorbent enhanced reforming with atmospheric calcination. 
         [0004]    Discussion of Related Art 
         [0005]    Sorbent Enhanced Reforming (SER) is an emerging processing technology for hydrogen production with integrated CO 2  capture. 
         [0006]    Such processing typically employs Le Chatelier&#39;s principle to assist in producing high purity hydrogen. Essentially, such processing utilizes a sorbent material to adsorb carbon dioxide produced during the reforming reaction, causing the reaction to produce more carbon dioxide which is subsequently removed. The removal of the carbon dioxide preferentially shifts the thermodynamic equilibrium to a high purity hydrogen equilibrium. 
         [0007]    A secondary benefit of SER processing is that nearly all of the carbon dioxide is retained by or in the sorbent material. To desirably enable re-use of the sorbent material, the captured carbon dioxide must subsequently be liberated from the sorbent material. The regeneration of the sorbent material is typically performed in a component known as a calciner. 
         [0008]    There are two typical types of calcination processing: direct and indirect firing. Direct firing calcination utilizes hot gas, such as from combustion or an electrical heating processes, and mixes such hot gas directly with the sorbent material. Such direct firing calcination processing typically simplifies the solids handling approach, and reduces the calcination temperature that is required by decreasing the partial pressure of the carbon dioxide. Indirect firing calcination utilizes heat such as provided from an outside source which physically separated from the sorbent material. Such indirect firing calcination processing typically complicates the heat transfer process and increases the required calcination temperature, but provides a nearly pure carbon dioxide stream such as may be found useful for carbon capture and sequestration or co-production needs. 
         [0009]    In the past, the calcination processing has commonly been performed at a pressure within 5% of the reactor system pressure which typically ranges from 30-363 psia. 
       SUMMARY OF THE INVENTION 
       [0010]    A general object of the subject development is to provide or result in improved hydrogen production. 
         [0011]    In accordance with one embodiment, the general object of the subject development can be attained, at least in part, through a process for producing hydrogen gas that involves introducing feed material into a sorbent enhanced reformer to produce carbon dioxide and hydrogen gas. The sorbent enhanced reformer desirably contains a quantity of a sorbent material to absorb carbon dioxide and form a used sorbent. The process further involves introducing the used sorbent into a calciner operating at atmospheric pressure to heat the used sorbent to desorb carbon dioxide from the used sorbent to produce regenerated sorbent. At least a portion of the regenerated sorbent can be desirably recycled to the sorbent enhanced reformer such as to be employed in further processing. 
         [0012]    In accordance with another embodiment, the subject development provides a process for producing hydrogen gas that involves introducing feed material including natural gas and H 2 O into a sorbent enhanced reformer operating at a pressure of at least 35 psia to produce carbon dioxide and hydrogen gas. The sorbent enhanced reformer desirably contains a quantity of a CO 2 sorbent material to absorb carbon dioxide and form a used sorbent. Sorbent enhanced reformer products gases including hydrogen gas are separated from the used sorbent. The used sorbent is introduced into a direct firing calciner operating at atmospheric pressure to heat the used sorbent to desorb carbon dioxide from the used sorbent to produce regenerated sorbent. If desired, at least a portion of separated sorbent enhanced reformer product hydrogen gas can be subsequently purified such as via pressure swing adsorption. Further, at least a portion of the regenerated sorbent is recycled to the sorbent enhanced reformer. 
         [0013]    In accordance with another aspect of the invention, a system for producing hydrogen gas is provided. Such a system may contain or include a sorbent enhanced reformer such as containing a quantity of a sorbent material, wherein a feed material produces carbon dioxide and hydrogen gas and the sorbent material absorbs carbon dioxide and forms a used sorbent. The system may further include a separator for separating the used sorbent from sorbent enhanced reformer products gases. A calciner operating at atmospheric pressure is provided or included to heat the used sorbent to desorb carbon dioxide from the used sorbent to produce regenerated sorbent. The system further includes a recycle line to introduce at least a portion of the regenerated sorbent from the calciner to the sorbent enhanced reformer. 
         [0014]    The removal of the carbon dioxide via the sorbent serves to advantageously preferentially shift the equilibrium to a high purity hydrogen equilibrium. 
         [0015]    Further, nearly all of the carbon dioxide is retained in the sorbent material. The development&#39;s use of an atmospheric calciner which operates at local ambient pressures advantageously serves to disengage the calciner from the operating pressure of the reactor. 
         [0016]    Those skilled in the art and guided by the teachings herein provided will appreciate that the calciner can desirably be operated with a partial pressure of CO 2  at atmospheric pressure (e.g., up to 25%, 20%, or 10% above or below atmospheric pressure) or a partial pressure of CO 2  below atmospheric pressure with the introduction of steam or other diluent. Inputs to the calciner may include fuel, air, and a higher pressure sorbent from the SER hydrogen generator. The calcination process causes the sorbent to be raised to a higher pressure. Off-gas from the calcination process may be captured and/or further processed. 
         [0017]    As used herein, references to an “atmospheric” calciner, a calciner operating at “atmospheric pressure” or the like are to be understood to refer to calciners and operation at atmospheric pressure ±25%, at atmospheric pressure ±20%, or at atmospheric pressure ±10%. 
         [0018]    Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a simplified schematic drawing showing a processing system for the production of hydrogen gas in accordance with one aspect of the subject development. 
           [0020]      FIG. 2  is a simplified schematic drawing showing an alternative processing system for the production of hydrogen gas in accordance with another embodiment of the subject development. 
           [0021]      FIG. 3  is a graphical presentation of the mathematical relationship between CO 2  partial pressure and temperature for the equilibrium relationship between CaCO 3  and CaO. 
           [0022]      FIG. 4  is a graphical presentation regarding the sintering of Fredonia Derived and Ultrapure CaO at different selected temperatures. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIG. 1  shows a processing system, generally designated by the reference numeral  110 , for the production or generation of hydrogen gas in accordance with one embodiment of the subject development and which processing system  110  employs or utilizes a sorbent enhanced reformer  112  to produce used sorbent, hydrogen gas, and residual gases. As detailed further below, the processing system  110  also employs or utilizes indirect firing calcination and thus includes an indirect firing calciner  114 , such as to appropriately process and regenerate used sorbent. 
         [0024]    Suitable inputs to the SER hydrogen generator may include a suitable hydrocarbon fuel (e.g., natural gas), steam, a pressurized sorbent such as desirably at least in part from the calciner and may include an off-gas such as from a system associated pressure swing absorber. 
         [0025]    The processing system  110  includes a feed material processing section generally designated as  120  for appropriately processing the feed prior to entry into the sorbent enhanced reformer  112  for hydrogen generation or production. 
         [0026]    The feed material processing section  120  may, as shown, contain or include a feed water treatment and pump section  122  and a natural gas supply and compression section  124 , with feed water being introduced via a line  126  into a vaporizer and preheater unit  130  and at least a portion of the natural gas being introduced into the vaporizer and preheater unit  130  via a line  132 . Feed material from the vaporizer and preheater unit  130  is conveyed via a line  134  to a final feed preheater  136 , with the resulting heated feed introduced via a line  140  to the hydrogen gas (H 2 ) sorbent enhanced reformer hydrogen generator  112 . 
         [0027]    Suitable sorbent material is introduced to the hydrogen gas (H 2 ) sorbent enhanced reformer hydrogen generator  112  via a line  144 . 
         [0028]    Desirable continuous SER processing can make the use of fluidized bed reactor technology desirable for continuous operation. The utilization of fluidized bed reactors can result or produce numerous associated benefits including, for example, increased or improved temperature homogeneity and/or heat transfer. 
         [0029]    The SER hydrogen generator  112  utilizes the sorbent material to adsorb carbon dioxide produced during the reforming reaction, causing the reforming reaction to produce additional hydrogen gas and carbon dioxide, with carbon dioxide preferably being removed via the sorbent material. Thus, the removal of the carbon dioxide preferentially shifts the equilibrium to a high purity hydrogen equilibrium. 
         [0030]    Taking CaO as the adsorbent material, the primary reactions involved in the sorbent enhanced reforming operation are reactions 1-3 below: 
         [0000]                                        CH 4 (g) + H 2 O(g) → 3H 2 (g) + CO(g)   Reforming   (1)       CO(g) + H 2 O(g) → H 2 (g) + CO 2 (g)   Water-Gas Shift   (2)       CaO + CO 2 (g) → CaCO 3  + Heat   Sorbent   (3)           Carbonization       CH 4 (g) + 2H 2 O(g) + CaO → 4H 2 (g) + CaCO 3     Overall SER   (4)       CaCO 3  + Heat → CaO + CO 2     Sorbent Calcination   (5)                    
The overall SER operation is defined in reaction (4) above, with the calcination operation shown in reaction (5).
 
         [0031]    A product stream  152  exiting from the hydrogen gas (H 2 ) sorbent enhanced reformer hydrogen generator  112  is introduced into an appropriate separator or processing device  154  to separate the solid used sorbent from gaseous product materials. Suitable separator or processing devices in particular embodiments can include filters, cyclones or the like or combinations thereof. 
         [0032]    An off-gas stream  160  from the separator  154  is passed to an off-gas cooler  162  for appropriate temperature reduction. Appropriately cooled off-gas, primarily composed of hydrogen gas, is passed via a line  164  for subsequent processing such as further purification such as via a pressure swing absorber, for example. 
         [0033]    Solid used sorbent from the separator  154  can be collected in a hopper  166  such as with a valve (not shown) on the solid inlet and a valve  170  on the solid outlet. Once the hopper is appropriately filled, the inlet to the hopper can be closed and the pressure can be vented from the hopper such as via a suitable vent port (not shown). Once the pressure is sufficiently reduced, the sorbent outlet valve  170  is opened to permit discharge of the used sorbent into the atmospheric indirect firing calciner  114 . 
         [0034]    The calciner  114  serves to desorb the carbon dioxide from the sorbent, which is now regenerated. The carbon dioxide and any other gases pass via a line  174  to a cooler  176  and via a subsequent line  178  such as to a vent stack or other suitable disposal or discharge. 
         [0035]    Regenerated sorbent from the calciner  114  is collected via a line  180  in a separate hopper  182  and can be appropriately re-pressurized to a pressure slightly above the reactor pressure. Once the desired pressure is achieved, the regenerated sorbent is metered such as via the line  144  to the SER reactor  112 . 
         [0036]    The processing system  110  includes a calciner burner feed section generally designated  184  and such as including a combustion air compressor unit  186  which feeds combustion air via a line  188  to a combustion air preheater unit  190  which feeds preheated air via a line  192  to a main calciner burner unit  194 . The main calciner burner unit  194  also receives natural gas via a line  196 , such as from the natural gas supply and compression section  124 , with the combustion products introduced into indirect burner duct  115  which transfers heat into the calciner  114  but is physically separated from the internals of the calciner  114 . The residual combustion gases are collected and passed via a line  175  and sent to a heat recovery system  177  where residual heat is extracted from the combustion gases and vented to the atmosphere  179 . 
         [0037]    As will be appreciated by those skilled in the art and guided by the teachings herein provided, such indirect firing calcination processing provides a nearly pure carbon dioxide stream such as may be found useful for carbon capture and sequestration or co-production needs. As a result, in certain preferred embodiments, the utilization of indirect firing calcination will be preferred. 
         [0038]    The use of an atmospheric calciner, such as herein described, can desirably reduce system capital cost such as by eliminating the need for either or both air and PSA off-gas compressors. Additionally, the power required for the operation of such compressors is eliminated which leads to reduced operation cost and increased system efficiency. Further, as in the subject calcination, the calcination temperature is a direct result of carbon dioxide partial pressure, by reducing the pressure, the temperature is desirably also reduced, thus practice in accordance with the subject development can desirably increase the length of life of the sorbent and extend the time period before the sorbent must be replaced. 
         [0039]    While processing in accordance with the subject development has been described above making specific reference to a processing system that utilized an indirect firing calciner, the broader practice of the invention is not necessarily so limited as, for example, if desired, the development can be suitably practice utilizing a direct firing calciner. To that end, reference is no made to  FIG. 2  which depicts a processing system, generally designated by the reference numeral  210 , for the production or generation of hydrogen gas in accordance with another embodiment of the subject development. The processing system  210  is generally similar to the processing system  110  described above except rather than indirect firing calcination and an indirect calciner, the processing system  210  employs or utilizes direct firing calcination and thus includes a direct firing calciner  214  to appropriately process and regenerate used sorbent. 
         [0040]    Similar to the processing system  110 , the processing system  210  includes a feed material processing section generally designated as  220  for appropriately processing the feed prior to entry into the sorbent enhanced reformer  212  for hydrogen generation or production. The feed material processing section  220  may, as shown, contain or include a feed water treatment and pump section  222  and a natural gas supply and compression section  224 , with feed water being introduced via a line  226  into a vaporizer and preheater unit  230  and at least a portion of the natural gas being introduced into the vaporizer and preheater unit  230  via a line  232 . Feed material from the vaporizer and preheater unit  230  is conveyed via a line  234  to a final feed preheater  236 , with the resulting heated feed introduced via a line  240  to the hydrogen gas (H 2 ) sorbent enhanced reformer hydrogen generator  212 . 
         [0041]    Suitable sorbent material is introduced to the hydrogen gas (H 2 ) sorbent enhanced reformer hydrogen generator  212  via a line  244 . 
         [0042]    As with the SER hydrogen generator  112  in the system  110 , the SER hydrogen generator  212  utilizes the sorbent material to adsorb carbon dioxide produced during the reforming reaction, causing the reforming reaction to produce additional hydrogen gas and carbon dioxide, with carbon dioxide preferably being removed via the sorbent material. Thus, the removal of the carbon dioxide preferentially shifts the equilibrium to a high purity hydrogen equilibrium. 
         [0043]    A product stream  252  exiting from the hydrogen gas (H 2 ) sorbent enhanced reformer hydrogen generator  212  is introduced into an appropriate separator or processing device  254  to separate the solid used sorbent from gaseous product materials. Suitable separator or processing devices in particular embodiments can include filters, cyclones or the like or combinations thereof. 
         [0044]    An off-gas stream  260  from the separator  254  is passed to an off-gas cooler  262  for appropriate temperature reduction. Appropriately cooled off-gas, primarily composed of hydrogen gas, is passed via a line  264  for subsequent processing such as further purification such as via a pressure swing absorber, for example. 
         [0045]    Solid used sorbent from the separator  254  can be collected in a hopper  266  such as with a valve (not shown) on the solid inlet and a valve  270  on the solid outlet. Once the hopper is appropriately filled, the inlet to the hopper can be closed and the pressure can be vented from the hopper such as via a suitable vent port (not shown). Once the pressure is sufficiently reduced, the sorbent outlet valve  270  is opened to permit discharge of the used sorbent into the atmospheric direct firing calciner  214 . 
         [0046]    The calciner  214  serves to desorb the carbon dioxide from the sorbent, which is now regenerated. The materials from the direct calciner  214  are passed via a line  271  into an appropriate separator or processing device  272  to separate the regenerated sorbent solid from gases materials, including desorbed carbon dioxide. Suitable separator or processing devices in particular embodiments can include filters, cyclones or the like or combinations thereof. 
         [0047]    Carbon dioxide and any other gases pass via a line  274  to a cooler  276  and via a subsequent line  278  such as to a vent stack or other suitable disposal or discharge. 
         [0048]    Regenerated sorbent from the separator  272  discharges into a pressurizing lock hopper system  282  which increases the pressure of the regenerated sorbent to SER reactor pressure. The pressurized regenerated sorbent is passed via the line  244  to the SER reactor  212 . 
         [0049]    The processing system  210 , similar to the processing system  110  described above, includes a calciner burner feed section generally designated  284  and such as including a combustion air compressor unit  286  which feeds combustion air via a line  288  to a combustion air preheater unit  290  which feeds preheated air via a line  292  to a main calciner burner unit  294 . The main calciner burner unit  294  also receives natural gas via a line  296 , such as from the natural gas supply and compression section  224 , with the combustion products introduced into the calciner  212  via a line  298 . 
         [0050]    As will be appreciated by those skilled in the art and guided by the teachings herein provided, whereas indirect firing calcination processing typically complicates the heat transfer process and increases the required calcination temperature, direct firing calcination processing can desirably simplify the solids handling approach, and reduce the calcination temperature that is required by decreasing the partial pressure of the carbon dioxide. As a result, in certain preferred embodiments, the utilization of direct firing calcination will be preferred. 
         [0051]    To permit a better appreciation and understanding of the subject development reference will now be made to  FIGS. 3 and 4 . 
         [0052]    More particularly,  FIG. 3  graphically depicts the equilibrium relationship between pressure and calcination temperature for the calcination of CaCO 3 , reaction (5) shown above. During the calcination of CaCO 3 , CO 2  is generated as a byproduct. The partial pressure of CO 2 , the byproduct of calcination of CaCO 3 , is represented as a function of temperature.  FIG. 3  demonstrates that as the partial pressure of CO 2  increases, the temperature required for calcination increases. The presence of the CO 2  influences the driving force of the reaction. Taking this into account, a non-limiting embodiment may desirably employ controls to adjust the temperature as the CO 2  partial pressure changes. The CO 2  partial pressure and the exit temperature may be monitored and compared to the solid particle input, fuel feed rate and calcining chamber inlet temperature to determine the efficiency of the calcination process. In the event the measured values deviate from the curve, the fuel input may be adjusted to change the temperature. 
         [0053]    The heat required for calcination may cause sintering of the solid sorbent particles which reduces surface area and pore volume. This may result in decreased reactivity and adversely affect the ability of the compound to be used in subsequent processes or be recycled for additional byproduct absorption. For example, calcium oxide (CaO) is an absorbent for carbon dioxide (CO 2 ). The absorption reaction creates calcium carbonate (CaCO 3 ). The CaCO 3  can thus be calcined back to CaO, but the resulting CaO may undesirably be sintered. The loss of pore volume and surface area reduces the ability of the newly calcined CaO to be reused in a reaction to absorb further CO 2 . 
         [0054]    The amount of sintering may be reduced through limitation of the amount of heat applied to the solid sorbent particles and the time the solid sorbent particles are exposed to the elevated temperatures. Conventional techniques for calcining typically expose the compound being calcined to high temperatures for times of one or more hours. Such durations cause a significant reduction in reactivity of the calcined product. If the calcined product is to be cycled through another reaction (for example to absorb additional CO 2 ) the sintering caused by these other calcining techniques significantly limits and reduced the capability of the calcined product to absorb additional byproduct and/or significantly reduces the number of times the calcined product can be cycled through a process for absorbing byproduct. 
         [0055]    Reference is now made to  FIG. 4  graphically depicts the sintering of Fredonia Derived and Ultrapure CaO at different selected temperatures and signifies that an increase in sintering rate will occur at higher temperatures. This will reduce the life of the sorbent (e.g., CaO). As will be appreciated by those skilled in the art and guided by the teachings herein provided, the use of an atmospheric calciner in accordance with the subject development can desirably alleviate or minimize this problem. 
         [0056]    Thus, it is to be understood and appreciated that operation in accordance with the subject development can significantly reduce sorbent sintering and enhance solids separation in the calciner. 
         [0057]    The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively. 
         [0058]    The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein. 
         [0059]    While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.