BACKGROUND
Hydrogen production is currently associated with substantial CO2 emissions. It is imperative to reduce the carbon footprint of H2 production to minimize the impact of H2 production on the environment.
The state of the art teaches two main solutions to capture CO2 in a hydrogen production unit:
- pre-combustion, i.e. capturing the CO2 before any combustion reaction takes place (e.g. in the burners of fired heater)
- post-combustion, i.e. capturing the CO2 after a combustion reaction (e.g. in the burners of fired heater) took place and before releasing the CO2 containing gas to the atmosphere
Pre-combustion CO2 capture can achieve an overall CO2 capture of ˜ 50-60% with conventional steam methane reforming (SMR) based H2 generation process. In Autothermal reforming based H2 generation process, intrinsic CO2 capture of 85-90% is achieved from produced syngas. The CO2 capture rate can be increased by firing a small split stream of product H2 in the fired heater as fuel. This method reduces the hydrocarbon fuel consumption and thereby reduces the carbon emission through the fired heater.
However, to generate this additional H2 to be used as fuel, more hydrocarbon feed needs to be reformed and the carbon footprint of the process is increased by that resulting in higher scope 3 emissions. Also, to reform more hydrocarbon feedstock, more oxygen intake is also required, which means higher power consumption and higher capital cost for the Air Separation Unit. Hence, enhancing the CO2 capture is realized by increasing the Scope 2 (electricity import) and Scope 3 (hydrocarbon feedstock) emissions which is counter-productive in terms of overall emissions. Or in other words, direct emissions are minimized by increasing indirect emissions.
In one embodiment of the current invention, the proposed novel solution allows achieving a direct CO2 capture rate of >99% by the autothermal reforming based hydrogen generation process with one CO2 removal unit with an efficient thermal integration and without any fired heater.
SUMMARY
Process and method to generate hydrogen with high CO2 capture rate. The invention entails production of hydrogen in an efficient and innovative way without any continuous carbon emissions within the hydrogen production unit by use of only one CO2 removal unit. The proposed novel solution allows achieving a direct CO2 capture rate of >99% by the autothermal reforming based hydrogen generation process with one CO2 removal unit with an efficient thermal integration and without any fired heater.
BRIEF DESCRIPTION OF THE FIGURES
For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:
FIG. 1 is a schematic representation of a basic state-of-the-art hydrogen plant utilizing autothermal reformer, in accordance with one embodiment of the present invention.
FIG. 2 is a schematic representation of one embodiment of a hydrogen plant, in accordance with the present invention.
FIG. 3 is a schematic representation of another embodiment of a hydrogen plant, in accordance with the present invention.
FIG. 4 is a schematic representation of another embodiment of a hydrogen plant, in accordance with the present invention.
FIG. 5 is a schematic representation of another embodiment of a hydrogen plant, in accordance with the present invention.
ELEMENT NUMBERS
100=hydrogen plant as known in the art
101=hydrocarbon feedstock stream
102=fired heater
103=heat exchange coils
104=preheated feedstock stream
105=steam stream
106=pre-reformer feed stream
107=pre-reformer
108=pre-reformed stream
109=preheated pre-reformed stream
110=ATR feed stream
111=ASU
112=oxygen containing stream
113=ATR
114=raw syngas stream
115=water-gas shift reactor
116=shifted syngas stream
117=hydrogen separation device
118=product hydrogen stream
119=purge gas stream
120=purge gas fuel stream
121=purge recycle stream
122=flue gas stream
123=hydrocarbon fuel stream
200=hydrogen plant according to the present invention
201=hydrocarbon feedstock stream
202=feedstock preheater
203=heat transfer line for feedstock preheater
204=heat transfer line for feedstock preheater
205=heated feedstock stream
206=steam stream
207=ATR feed stream
208=ATR feed preheater
209=heat transfer line for ATR feed preheater
210=heat transfer line for ATR feed preheater
211=heated ATR feed stream
212=combined ATR feed stream
213=ASU
214=oxygen containing stream
215=ATR
216=raw syngas stream
217=waste heat boiler
218=boiler feedwater stream
219=saturated steam stream
220=cooled raw syngas stream
221=first heat exchanger
222=heat transfer line for first heat exchanger
223=heat transfer line for first heat exchanger
224=further cooled raw syngas stream
225=water-gas shift reactor
226=shifted syngas stream
227=first shifted syngas stream
228=second shifted syngas stream
229=second heat exchanger
230=heat transfer line for second heat exchanger
231=heat transfer line for second heat exchanger
232=third heat exchanger
233=heat transfer line for third heat exchanger
234=heat transfer line for third heat exchanger
235=first cooled shifted syngas stream
236=second cooled shifted syngas stream
237=cooled shifted syngas stream
238=hydrogen separation device
239=product hydrogen stream
240=purge gas recycle stream
DESCRIPTION OF PREFERRED EMBODIMENTS
Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
In one embodiment of the present invention a method of producing low carbon hydrogen is described, wherein the direct carbon emissions are minimized without increasing any indirect emissions, thus reducing the carbon intensity of the process.
Turning to FIG. 1, a basic state-of-the-art hydrogen plant 100 utilizing autothermal reformer 113 is illustrated. ASU 111 produces oxygen containing stream 112. Hydrocarbon feedstock stream 101 is introduced into fired heater 102 wherein it is preheated in heat exchange coils 103, thus producing preheated feedstock stream 104. Preheated feedstock stream 104 is combined with steam stream 105, thus forming pre-reformer feed stream 106. Pre-reformer feed stream 106 is then introduced into pre-reformer 107, thereby producing pre-reformed stream 108. Pre-reformed stream 108 is introduced into fired heater 102 wherein it is preheated in heat exchange coils 103, thus producing preheated pre-reformed stream 109.
Preheated pre-reformed stream 109 is combined with purge recycle stream 121, thereby forming ATR feed stream 110. ATR feed stream 110 is then introduced into ATR 113 along with oxygen containing stream 112, thereby forming raw syngas stream 114. Raw syngas stream 114 is then introduced into water-gas shift reactor 115, thereby producing shifted syngas stream 116. Shifted syngas stream 116 is then introduced into hydrogen separation device 117. Hydrogen separation device 117 may be utilized for carbon capture, or simply to produce product hydrogen stream 118. Hydrogen separation device 117 produces purge gas stream 119. Purge gas fuel stream 120 is combined with hydrocarbon fuel stream 123 and introduced as fuel into fired heater 102. Second portion 121 is combined with preheated pre-reformed stream 109 to produce ATR feed stream 110.
State-of-the-art autothermal reforming technologies are associated with at least one fired heater 102 including one or more heat exchange coils 103 providing sufficient process heat. The temperature required for the different process steps of the production unit is provided by these heat exchanges. The heat duty required for this heat exchange is provided by firing of hydrocarbon fuel 123 that leads to CO2 emissions in the flue gas stream 122 exiting the fired heater.
Preheating of hydrocarbon feedstock and/or preheating of feed+steam mix and/or boiling of water and/or superheating of medium or high-pressure steam is typically done by the heat exchange coils in the fired heater (not shown). The more heat exchange that happens in fired heater 102, the heat duty requirement by fuel increases, and so increases the CO2 emissions.
To compensate for these CO2 emissions and to ensure a higher target CO2 capture rate, more hydrogen is produced than required as product by additional feedstock processing (reforming, shift, CO2 removal) and firing that additional H2 product in the fired heater and that is how direct CO2 emissions are minimized.
However, this additional processing of feedstock has a direct adverse impact on both operating and capital cost and above all, on carbon intensity. Additional feedstock consumption, therefore higher oxygen, power and other utility consumption increases the operating cost. On the other hand, due to higher effective material flow, all equipment becomes oversized and thus the capital investment goes higher.
Therefore, there is a need to invent an efficient solution to reduce direct emissions from an autothermal reforming based low-carbon H2 generation process to achieve ≥99% carbon capture rate without impacting indirect emissions i.e. Scope 2 and Scope 3 emissions.
Turning to FIGS. 2-5, various embodiments of a hydrogen plant 200 in accordance with the present invention are illustrated. FIG. 2 illustrates the generic arrangement of the present invention, and FIGS. 3-5 illustrate specific embodiments.
Turning first to FIG. 2, ASU 213 produces oxygen containing stream 214. Hydrocarbon feedstock stream 201 is heated in feedstock preheater 202, thus producing heated feedstock stream 205. The heat for this preheating, as indicated by heat transfer lines 203 and 204, may come from various internal heat sources, as discussed in detail below.
Heated feedstock stream 205 is combined with steam stream 206, thus forming ATR feed stream 207. ATR feed stream 207 is heated in ATR feed preheater 208, thus producing heated ATR feed stream 211. The heat for this preheating, as indicated by heat transfer lines 209 and 210, may come from various internal heat sources, as discussed in detail below.
Heated ATR feed stream 211 is combined with purge gas recycle stream 240, thus forming combined ATR feed stream 212. Combined ATR feed stream 212 is then introduced into ATR 215 along with oxygen containing stream 214, thereby forming raw syngas stream 216. Raw syngas stream 216 is introduced into waste heat boiler 217 along with boiler feed water stream 218, thereby producing cooled raw syngas stream 220, and saturated steam stream 219. Cooled raw syngas stream 220 is then introduced into first heat exchanger 221, thereby producing further cooled raw syngas stream 224. The cooling for first heat exchanger 221, as indicated by heat transfer lines 222 and 223, may come from various internal sources, as discussed in detail below.
Further cooled raw syngas stream 224 is introduced into water-gas shift reactor 225, thereby producing shifted syngas stream 226. Shifted syngas stream 226 is divided into first stream 227 and second stream 228. First shifted gas stream 227 is then introduced into second heat exchanger 229, thereby producing first cooled shifted syngas stream 235. The cooling for second heat exchanger 229, as indicated by heat transfer lines 230 and 231, may come from various internal sources, as discussed in detail below. Second shifted gas stream 228 is then introduced into third heat exchanger 232 thereby producing second cooled shifted syngas stream 236. The cooling for third heat exchanger 232, as indicated by heat transfer lines 233 and 234, may come from various internal sources, as discussed in detail below.
First cooled shifted syngas stream 235 and second cooled shifted syngas stream 236 are combined, thus forming cooled shifted syngas stream 237. Cooled shifted syngas stream 237 is then introduced into hydrogen separation device 238. Hydrogen separation device 238 may be utilized for carbon capture, or simply to produce product hydrogen stream 239. Hydrogen separation device 238 produces purge gas stream 240.
Turning to FIGS. 3-5, ASU 213 produces oxygen containing stream 214. Hydrocarbon feedstock stream 201 is heated in feedstock preheater 202, thus producing heated feedstock stream 205. The heat for this preheating, as indicated by heat exchange lines 203 and 204, may come from various internal heat sources.
- Feedstock preheater 202 may exchange heat with third heat exchanger 232, thus obtaining heat from second shifted gas stream 228. In this arrangement, heat exchange lines 203 and 204 are thermally connected to heat exchange lines 233 and 234 (as illustrated in FIG. 3),
- Feedstock preheater 202 may exchange heat with first heat exchanger 221, thus obtaining heat from cooled raw syngas stream 220. In this arrangement, heat exchange lines 203 and 204 are thermally connected to heat exchange lines 222 and 223 (as illustrated in FIG. 4),
- Feedstock preheater 202 may exchange heat with second heat exchanger 229, thus obtaining heat from first shifted gas stream 227, In this arrangement, heat exchange lines 203 and 204 are thermally connected to heat exchange lines 230 and 231 (as illustrated in FIG. 5)
Heated feedstock stream 205 is combined with steam stream 206, thus forming ATR feed stream 207. ATR feed stream 207 is heated in ATR feed preheater 208, thus producing heated ATR feed stream 211. The heat for this preheating, as indicated by heat exchange lines 209 and 210, may come from various internal heat sources.
- ATR feed preheater 208 may exchange heat with second heat exchanger 229, thus obtaining heat from first shifted gas stream 227. In this arrangement, heat exchange lines 209 and 210 are thermally connected to heat exchange lines 230 and 231 (as illustrated in FIGS. 3 and 4)
- ATR feed preheater 208 may exchange heat with first heat exchanger 221, thus obtaining heat from cooled raw syngas stream 220. In this arrangement, heat exchange lines 209 and 210 are thermally connected to heat exchange lines 222 and 223 (as illustrated in FIG. 5).
Heated ATR feed stream 211 is combined with purge gas recycle stream 240, thus forming combined ATR feed stream 212. Combined ATR feed stream 212 is then introduced into ATR 215 along with oxygen containing stream 214, thereby forming raw syngas stream 216. Raw syngas stream 207 is introduced into waste heat boiler 217 along with boiler feed water stream 218, thereby producing cooled raw syngas stream 220, and saturated steam stream 219.
- Saturated steam stream 219 may exchange heat with first heat exchanger 221, thus obtaining heat from cooled raw syngas stream 220. In this arrangement, saturated steam stream 219 is thermally connected to heat exchange line 222, which results in heat exchange line 223 containing superheated steam. (as illustrated in FIG. 3)
- Saturated steam stream 219 may exchange heat with third heat exchanger 232, thus obtaining heat from second shifted syngas stream 228. In this arrangement, saturated steam stream 219 is thermally connected to heat exchange line 233, which results in heat exchange line 234 containing superheated steam (as illustrated in FIGS. 4 and 5).
Cooled raw syngas stream 220 is then introduced into first heat exchanger 221, thereby producing further cooled raw syngas stream 224.
- First heat exchanger 221 may provide heat to saturated steam stream 219 resulting in a superheated steam stream 223. (as illustrated in FIG. 3)
- First heat exchanger 221 may exchange heat with feedstock preheater 202, thus providing heat to hydrocarbon feedstock stream 201. In this arrangement, heat exchange lines 222 and 223 are thermally connected to heat exchange lines 203 and 204. (as illustrated in FIG. 4)
- First heat exchanger 221 may exchange heat with ATR feed preheater 208, thus providing heat to ATR feed stream 207. In this arrangement, heat exchange lines 222 and 223 are thermally connected to heat exchange lines 209 and 210. (as illustrated in FIG. 5)
Further cooled raw syngas stream 224 is introduced into water-gas shift reactor 225, thereby producing shifted syngas stream 226. Shifted syngas stream 226 is divided into first stream 227 and second stream 228. First shifted gas stream 227 is then introduced into second heat exchanger 229, thereby producing first cooled shifted syngas stream 235.
- Second heat exchanger 229 may exchange heat with ATR feed preheater 208, thus providing heat to ATR feed stream 207. In this arrangement, heat exchange lines 230 and 231 are thermally connected to heat exchange lines 209 and 210. (as illustrated in FIGS. 3 and 4)
- Second heat exchanger 229 may exchange heat with feedstock preheater 202, thus providing heat to hydrocarbon feed stream 201. In this arrangement, heat exchange lines 230 and 231 are thermally connected to heat exchange lines 203 and 204. (as illustrated in FIG. 5)
Second shifted gas stream 228 is then introduced into third heat exchanger 232 thereby producing second cooled shifted syngas stream 236.
- Third heat exchanger 232 may exchange heat with feedstock preheater 202, thus providing heat to hydrocarbon feed stream 201. In this arrangement, heat exchange lines 233 and 234 are thermally connected to heat exchange lines 203 and 204 (as illustrated in FIG. 3).
- Third heat exchanger 232 may provide heat to saturated steam stream 219 resulting in a superheated steam stream 234 (as illustrated in FIGS. 4 and 5)
First cooled shifted syngas stream 235 and second cooled shifted syngas stream 236 are combined, thus forming cooled shifted syngas stream 237. Cooled shifted syngas stream 237 is then introduced into hydrogen separation device 238. Hydrogen separation device 238 may be utilized for carbon capture, or simply to produce product hydrogen stream 239. Hydrogen separation device 238 produces purge gas stream 240.
The inventive solution allows to reach a very high CO2 capture rate (up to ≥99% direct emissions) in decarbonized H2 production units based on autothermal reforming.
Two problems have been identified to be solved:
- Problem 1: Reduction/elimination of heating demand from fired heater/heat of combustion
- Problem 2: Seeking an alternative solution for treating hydrocarbons containing off gases resulting from the CO2 capture or hydrogen purification section.
The inventive solution consists of:
Addressing Problem 1)
- employing an efficient synthesis gas generation process that may consist of at least an oxygen based catalytic autothermal reforming step, at least one water-gas shift reaction step with at least one catalytic reactor and employing a CO2 capture unit.
- The efficient syngas generation process is characterized in such a way that there is no heating requirement of process and/or by-product and/or utility is required by any heat of combustion or electrical heat during normal operation. Feedstock and feed/steam mixture is preheated downstream of at least one of the shift reactors and/or upstream of the shift reactor, by the effluent gas of the boiler downstream of ATR. Further, saturated steam generated in the process of heat recovery is also superheated downstream of at least one of the shift reactors and/or upstream of the shift reactor, by the process gas effluent of the boiler downstream of ATR. The configuration preferably does not include a pre-reformer as the endothermic reaction in the pre-reformer as the pre-heating of gas/steam mixture to the temperature requirement at the inlet of the pre-reforming reactor can thus be avoided.
Addressing Problem 2)
- Instead of combustion, the purge gas stream from CO2 capture of the hydrogen purification unit is not anymore sent to the fired heater. A recycle of purge gas to the process is foreseen. Depending on the selected CO2 capture unit some fraction of the purge gas might be injected in the hydrogen product still meeting the product specification.
- There are in principle 2 options for the capture capture unit.
- Option 1: CO2 capture unit where almost all (>98%) of the CO2 available in syngas. The mentioned CO2 capture unit may include at least a process of physical absorption or chemical absorption of CO2
- Option 2: Alternatively, the mentioned CO2 capture unit can be located downstream of a syngas purification step such as a Pressure Swing Adsorption process for producing higher purity (>98%) hydrogen gas enabling minimized slippage of carbon atoms along with product hydrogen.
- In this alternative method, employing a process of cryogenic removal of carbon dioxide from the off gas coming from the abovementioned purification section enabling production of very high purity dry carbon dioxide (>99.9 mole %) which can be made available at liquid and/or gaseous and/or supercritical state at the outlet of carbon dioxide removal process itself and is ready for sequestration without any further processing.
- Employing a membrane separation process at the exit of the cryogenic carbon dioxide removal process, enabling separation of at least a part of hydrogen gas molecules from the gas lean on carbon dioxide and routing the hydrogen gas molecules back to the first purification step thus improving the effective recovery of the purification step and minimizing the requirement of hydrocarbon feedstock to be processed.
- Routing at least part of the high pressure residue gas or full portion of the residue gas coming from the abovementioned membrane separation process to the syngas generation section (upstream/downstream of reforming step) in order to minimize or eliminate the loss of unconverted carbon atoms principally in the form of hydrocarbon and carbon monoxide eventually improving the process efficiency and carbon footprint. In case part of the residue gas is routed to the syngas generation section, rest of the gas is mixed with the H2 product stream downstream of the syngas purification step.
- Thus no residue gas is required to be disposed of in a fired heater and thus a fired heater can be removed from the hydrogen generation unit and the unit can experience no emission during continuous normal operation. The purge required for the process is disposed via H2 product only.
- For starting of the plant, at least one start-up fired heater or at least one start-up electric heater shall be required to ensure auto-ignition temperature is achieved inside the autothermal reforming reactor.
- It is also observed that a set-up without Fired Heater will maintain a superior energy efficiency and CO2 balance compared to a Fired Heater set-up even if the purge gas stream needs to be flared. This observation is only valid for feed gas with <3% inert content (preferably <1) and an oxygen purity of >99.5% (preferably min 99.8%). Consequently, if pure hydrogen needs to be produced, purging a small stream to an incinerator may still be a better option than installing a dedicated Fired Heater.
With these inventive steps, it is possible to furnish a configuration of a hydrogen production unit that can be built without a fired heater and thus can experience no direct CO2 emission by firing.
By directly sending the H2-rich gas downstream a physical/chemical CO2 absorption step as product or alternatively recycling the residue gas from cryogenic CO2 capture unit fully to reforming or partly to reforming and partly to the H2 product, and thereby eliminating the fired heater during continuous operation, the following can be achieved:
- Direct carbon capture rate of 99% or even more; as there is no fired heater hence no fired emission
- Recycling maximum or full portion of unconverted gas to the syngas generation/reforming section to minimize the loss of carbon atoms as well as minimizing the hydrocarbon feedstock intake to the production unit.
- Disposing some of the unconverted carbon compound molecules as well as inert molecules namely but not limited to N2, Ar to the product stream thus ensuring no accumulation and economic size of the equipment in the production unit.
This solution distinguishes itself from others for the following reasons:
- Achieving very high CO2 capture rate (≥99%) without having any need of H2 firing.
- No H2 firing need means no additional feedstock processing and thereby no additional utility consumption, hence a minimized operating cost.
- No H2 firing need also means the plant shall produce according to the product requirement and hence no oversizing leading minimized capital investment.
- No fired heater in the layout makes the H2 production unit intensely compact, smaller plot size with simpler operational control and minimum safety requirements.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.
Patent Application
20240400385
