Aspen Plus Simulation of a Sorption-Enhanced Steam Methane Reforming Process in a Fluidized Bed Reactor Using CaO as a Sorbent for CO₂ Capture

Abstract

In this work, Aspen Plus was used to simulate a sorption-enhanced steam methane reforming (SE-SMR) process in a fluidized bed reformer using a Ni-based catalyst and CaO as a sorbent for CO₂ removal from the reaction environment. The performances of the process in terms of the outlet gas hydrogen purity (y_H2), methane conversion (X_CH4), and hydrogen yield (η_H2) were investigated. The process was simulated by varying the following different reformer operating parameters: pressure, temperature, steam/methane (S/C) feed ratio, and CaO/CH₄ feed ratio. A clear sorption-enhanced effect occurred, where CaO was fed to the reformer, compared with traditional SMR, resulting in improvements of y_H2, X_CH4, and η_H2. This effect, in percentage terms, was more relevant, as expected, in conditions where the traditional process was unfavorable at higher pressures. The presence of CaO could only partially balance the negative effect of a pressure increase. This partial compensation of the negative pressure effect demonstrated that the intensification process has the potential to produce blue hydrogen while allowing for less severe operating conditions. Indeed, when moving traditional SMR from 1 to 10 bar, an average decrease of y_H2, X, and η by −16%, −44%, and −41%, respectively, was recorded, while when moving from 1 bar SMR to 10 bar SE-SMR, y_H2 showed an increase of +20%, while X_CH4 and η_H2 still showed a decrease of −14% and −4%.

1. Introduction

Although the development of energy transition solutions in terms of renewable energy such as solar, wind, and clean fuels (e.g., hydrogen) are widely spreading, it appears increasingly evident that the short-term reduction of fossil fuel exploitation is an even more urgent and challenging process. The implementation of short- to mid-term options towards a low-carbon world, acting at the source to prevent carbon emissions, proves to be crucial [1]. Among these decarbonization strategies, the increased support and deployment of carbon capture technologies and low-carbon hydrogen infrastructure are included [2]. Hydrogen is widely recognized as a technically viable and environmentally friendly energy carrier for applications ranging from small-scale off-grid power supply to large-scale chemical power export [1]. The deployment of hydrogen as an alternative energy carrier is severely limited by the lack of low-cost hydrogen generation, storage, transportation, and conversion technologies [3]. Global hydrogen demand, which reached 97 Mt in 2023, is concentrated in the refining (42%) and chemical sectors, mainly as feedstock to produce ammonia (35%) and methanol (15%). The entire demand is essentially covered by hydrogen produced from fossil fuels [4,5]. Based on announced projects involving electrolysis and fossil fuels with carbon capture, utilization, and storage (CCUS) to obtain, respectively, the so-called green or blue hydrogen, low-emission hydrogen production could significantly increase by 2030 [4]. Potential new applications include the use of hydrogen as a reducing agent in 100%-hydrogen direct reduced iron (DRI), long-distance transport, the production of hydrogen-based fuels, biofuel upgrading, high-temperature heating in industry, and electricity storage and generation.

Global hydrogen production emitted 920 Mt CO₂ last year, with natural gas representing the source of nearly two-thirds of the entire production [4]. Around 50% of the global hydrogen production from natural gas (gray hydrogen) relies on steam methane reforming (SMR), the most cost-effective process [6]. This process is operated at a high pressure (20–30 bar) and high temperature (800–900 °C) in a reformer where the following highly endothermic reactions occur:

CH₄ + H₂O ↔ 3H₂ + CO   ΔH_298K = 206.4 kJmol⁻¹

(1)

CH₄ + 2H₂O ↔ 4H₂ + CO₂   ΔH_298K = 165 kJmol⁻¹

(2)

While high temperatures meet the thermodynamic requirements, high pressures, which disadvantage thermodynamics, are operated since they are economically viable based on several assessments including, for example, the cost of gas compression that, if carried out downstream, would involve a higher number of moles.

The syngas from the reformer is then fed to a shift converter, where the water–gas shift (WGS) reaction takes place:

CO + H₂O ↔ H₂ + CO₂   ΔH_298K = − 41.1 kJmol⁻¹

(3)

Traditionally, Ni-based catalysts, presenting a good price-to-activity ratio, are applied in the SMR process.

This technology, although well established, presents important limitations, such as the high temperatures and pressures needed, with consequent energy-intensive operations, numerous steps involved, and low hydrogen yields (<80%), which must be improved to enable the large-scale implementation of hydrogen as an energy carrier. Moreover, the process is associated with large emissions of CO₂ in the atmosphere after the purification steps of the raw gas product [1,7]. The application of CCS technology to SMR entails a cost penalty of about USD 76/t_CO2captured and a reduction of the overall process efficiency (65–70%).

Among the opportunities for the development of sustainable blue hydrogen production, sorption-enhanced steam methane reforming (SE-SMR) is an advanced technology in which the reforming and CO₂ separation steps are integrated in a single reactor. The concept of sorption-enhanced reaction for hydrogen production was proposed by Gluud et al. [8] to shift the equilibrium of the reaction towards a higher hydrogen production by simultaneously removing the produced CO₂ using a proper solid sorbent, according to Le Chatelier’s principle. The steam reforming and CO₂ removal reactions occur in the reformer/adsorber in the presence of a catalyst and a sorbent. The sorbent is then regenerated in another reactor [2]. This technology leads to a more compact (two-in-one) process unit with the reduction of operational complexity and, thus, of capital cost (CAPEX), improving hydrogen yield at a lower cost of gas post-processing compared with traditional hydrogen production technologies such as SMR. Furthermore, quite moderate operating conditions, even up to 450–490 °C, 180–890 kPa, with the production of a gas stream with 90–98% hydrogen, can be applied, potentially decreasing operational expenses (OPEX) [1]. Overall, when considering blue hydrogen, SE-SMR presents, when compared with SMR combined with commercial CCS technologies, higher yields of H₂ and conversions of methane as well as lower reforming temperatures, with no multiple shift reactors and subsequent purification steps. The main challenge of SE-SMR technology lies in the energy-intensive sorbent regeneration processes, such as oxyfuel combustion or indirect heating, required to sustain calcination without emitting CO₂ into the atmosphere. Several integrated solutions are studied for decarbonized and high-purity hydrogen production with reduced energy penalties and CO₂ emissions from the regeneration of the CO₂ sorbent [9]. The configurations studied for SE-SMR, both experimentally and by means of modeling, include trickle beds [10], fixed beds, which are focused mainly on the development of highly performing sorbent materials [11,12], and fluidized bed reactors, known to be favorable for large-scale continuous operation [13,14,15,16,17]. In these investigations, the reforming and water–gas shift reactions occurred together with the in situ CO₂ sorption reaction at temperatures ranging between 550 °C and 650 °C and generally under atmospheric conditions. On the other hand, CFD (1-D, 2-D and 3-D) is the most adopted tool for modeling SE-SMR in fluidized bed reactors [2]. Fluidized bed experimental studies involved lab-scale reactors operated in the bubbling regime, with mostly traditional catalysts and natural dolomites as sorbents, showing the expected reduction in sorption capacity with an increasing number of carbonation–calcination cycles. The distinct operating conditions of the reforming and regeneration stages make it favorable for the two stages to operate in different reactors to ensure the continuous production of hydrogen by periodically regenerating the sorbent, with an important impact on the final design of the SE-SMR system in a potential scale-up to commercial size.

When considering fixed bed configurations, whose advantages include compact design and easier operability at high pressures, batteries of several fixed beds are required, alternating their operation between reforming and regeneration, to overcome their discontinuous operation. On the other hand, for fluidized beds presenting good gas–solid contact and better heat management, the solution of interconnected fluidized beds is widely studied, enabling the continuous solids looping between the reactors.

In the literature it is reported that, under specific operating conditions, a hydrogen concentration ranging from 96 to 99 vol% on a dry basis can be obtained [2,14,15]. SE-SMR is still transitioning to TRL 6; three pilot scale projects exist with configurations involving single or two interconnected bubbling fluidized bed (BFB) reactors [2,18,19,20]. Two pilot plants are already operated at low pressure (1–3 bar), with ongoing tests showing hydrogen concentrations higher than 80% up to around 95% and about 90% carbon capture rate [18,19]. Finally, a 1.5 MW_th pilot plant is currently being developed to produce blue hydrogen under high pressure conditions (up to 30 bar); the HyPER project is focused on unlocking technical challenges and scaling up hydrogen-enabled aviation to meet net zero emissions targets [20].

The main experimental efforts, at all levels of technological development, involved the mitigation of catalyst deactivation and sorbent sintering, demonstrating that research on catalyst substrates and sorbents can significantly improve the materials’ endurance. Among the possible CO₂ sorbents for SE-SMR, the most attractive are the CaO-based ones due to their abundance, low cost, high theoretical sorption capacity, and fast carbonation kinetics [7].

When these materials are applied in the reformer/carbonator the following reaction occurs:

CaO(s) + CO₂(g) ↔ CaCO₃(s)   ΔH_298K = − 178 kJmol⁻¹

(4)

The combined reforming/carbonation reaction may be thermally neutral, with the exothermic carbonation reaction providing enough heat for the endothermic reforming reaction and producing CaCO₃ that is then regenerated in a calciner operated at around 900 °C with directly or indirectly provided heat [2].

Different works in the literature deal with the improvement of the initial sorbent capacity and its durability over multiple cycles, involving thermal pre-treatments, acid treatments, and water/steam reactivation. Furthermore, studies involved the incorporation of different inert refractory materials or the preparation of entirely synthetic CaO with different precursors and using different methods [7,21,22]. In addition to calcium oxide, other sorbent materials of interest for this type of high-temperature (>600 °C) application are sodium and lithium silicates/zirconates [8]. More recently, bi-functional materials combining catalytic and CO₂ sorption properties on the same structure are receiving interest since they could compact and integrate the process and lead to significant cost reductions. However, further advances are still needed so that such materials can effectively maintain high performance over several cycles [7,23,24]. With regard to process models and optimization studies, most of them merely simulate and apply equilibrium reactors. In this work, Aspen Plus was used, including fluidization regimes and kinetic limitations by means of its “Fluidbed” block, to simulate the process in a fluidized bed reactor, with the aim of providing a preliminary characterization before completing the study in a chemical looping configuration based on dual interconnected fluidized bed reactors. A mapping of the possible favorable operating conditions to carry out the process, based on the various and diverse hydrogen uses, was provided.

2. Modeling

The SE-SMR process was modeled in Aspen Plus using the Fluidbed block, which describes a simplified one-dimensional and isothermal fluidized bed fluid mechanics to simulate the carbonator/reformer. This block takes into account particle size and density, terminal velocity, vessel geometry, chemical reactions, and the interaction with the fluid dynamics. Several correlations are automatically implemented to calculate minimum fluidization velocity, transport disengagement height (TDH), and solids drag and elutriation. The FluidBed is schematized by two zones: a lower dense bed and an upper freeboard zone. When considering chemical reactions, the gas phase is modeled as a plug flow and the solids as perfectly mixed, with the balances performed in single cells approximated to a CSTR. In the Aspen ‘Properties’ section, the components are listed and defined with a ‘Type’ describing their nature and the applied thermodynamic models, in our case the gaseous species (CH₄, H₂O, CO, CO₂, and H₂) as ‘CONVENTIONAL’ and the solids as ‘SOLID’ type. Still, an appropriate ‘Property method’ must be chosen, namely the set of estimation methods used by the software to calculate thermodynamic and transport properties of the components: the ‘Ideal’ model was used for simulations involving low pressures, while for high pressures, the SRKKD model (Soave–Redlich Kwong–Kabadi–Danner) was used, which is more suitable for modeling real gases. Moving on to the simulation section, the main flowsheet and chemical reactions are defined. The flowsheet is shown in Figure 1. In this preliminary study it was chosen not to model the whole circulation loop including the regeneration process in a second interconnected reactor. This work therefore strictly focused on the sorption-enhanced effect in the reformer due to the utilization of a fresh CaO sorbent.

The reported Aspen flowsheet consists of two reactors: a fluidized bed reactor (FB) and an RGibbs reactor, which calculates the equilibrium concentrations through the minimization of the Gibbs free energy of the species involved in the process. The latter was used to compare the performance of the more realistic FluidBed reactor with kinetic limitations with that of an ideal thermodynamic equilibrium reactor. The ‘SOLIDS’ stream contains the selected catalyst (Ni/Al₂O₃) and the sorbent (CaO). This stream was duplicated resulting in two equal flows, S-IN and S1, fed to the FluidBed and the RGibbs reactors, respectively. The GAS stream was also duplicated for the same reason, and contained the steam and methane reactants mixture. The design specifications for the FluidBed block were set to 0.129 m and 5 m for the diameter and the height, respectively, with a bed inventory of 5 kg and considering Geldart B solid particles in a size range of 400–600 µm.

Among the possible reactions that can take place in a SMR process, three main reactions are generally considered: steam reforming to CO (1), steam reforming to CO₂ (2), and water gas shift (3). In the ‘Reactions’ section of the simulation environment, the name and type of kinetics and the chemical reactions need to be specified. Calculator blocks are used in the simulations to manipulate the expressions to have the Aspen required structures and units.

The selected kinetics follow two main models: Power Law for the carbonation, and the Langmuir–Hinshelwood–Hougen–Watson (LHHW) model for the other simulated reactions. After the implementation of the reaction stoichiometry, the parameters to define a kinetic factor, a driving force expression, and, for the LHHW reactions, an adsorption expression are required in the ‘Reactions’ section.

The kinetics of the reactions implemented in this work were taken from the well-known Xu and Froment study [25]. Regarding the carbonation reaction (4), kinetics derived from the work of Bhatia and Perlmutter [26] were used, as follows:

$${\displaystyle \frac{dX}{dt}}={k_S{S}_N \left(1-X\right)}^{{\displaystyle \frac{2}{3}}} (C_{C{O}_2}-C_{{CO}_2}^{eq})$$

(5)

The molar concentration of CO₂ at equilibrium was taken from Baker [27], whereas the other parameters can be obtained from several studies in the literature, such as those by Grasa et al., Alvarez et al., and Abanades et al. [28,29,30].

The sensitivity analysis involved temperature, pressure, steam to methane (S/C) feed ratio, and CaO/CH₄ ratio to assess their influence on the process performance. The temperature range explored in this study varied between 500 and 725 °C, in line with the possible best operating temperatures of an SE-SMR process, as observed in the literature [7]. Regarding pressure, a range of 1–20 bars was explored to be closer to possible industrial requirements. The S/C ratio is an important parameter that allows the reforming equilibria to be pushed towards the products and limits the formation of solid carbon in the reactor responsible for catalyst deactivation. It is good practice to work with excess steam, considering that the use of large amounts of steam has a negative impact on the operating costs; in this study the ratio varied between 1 and 5, a commonly studied range [7]. Finally, the molar sorbent/methane feed ratio was investigated in a range of 0.3–1. Beyond this value, the effects of further sorbent addition can be assumed to be negligible, as also reported in the literature [31].

The performance indicators examined are the H₂ purity and yield, and the CH₄ conversion, defined as follows:

$$y_{H_2}^{dry}={\displaystyle \frac{n_{H_2}^{out} }{n_{tot}^{out}-n_{H_{2}O}^{out} }}$$

(6)

$${\eta }_{H_2}={\displaystyle \frac{n_{H_2}^{out}}{4 n_{C{H}_4}^{IN}}}$$

(7)

$$X_{C{H}_4}={\displaystyle \frac{n_{C{H}_4}^{IN}-n_{C{H}_4}^{out}}{n_{C{H}_4}^{IN}}}$$

(8)

To quantify the “SE effect”, the percentage variation of the performance variables between the SMR and the SE-SMR was calculated under the simulated conditions:

$$\%SE effect={\displaystyle \frac{y_{SE-SMR}-y_{SMR}}{y_{SMR}}}·100$$

(9)

Given the large number of variables involved, the results were represented by contour maps.

3. Results

3.1. Comparison Between FluidBed and RGibbs Aspen Reactors

A preliminary analysis involved the comparison between the FluidBed reactor and the equilibrium conditions, using the results of the RGibbs reactor. The analysis was carried out in the temperature range of 500–725 °C, and, by way of example, at atmospheric pressure and for a steam-to-carbon ratio of 3. In the sorption-enhanced case the CaO/CH₄ ratio was set to 1. For the sake of brevity, the results are not depicted, but the highlights of the analysis will be summarized below. As expected, the performances of the equilibrium reactor always represent the upper limit behavior and the FluidBed indicators never overcome such limits. Thermodynamic trends are respected and an increase with temperature of the examined indicators for the SMR is evident for both the FluidBed and the RGibbs cases. When considering SE-SMR operation, the trend with temperature is non-monotonic for the H₂ yield and purity, since at higher temperatures (>650 °C) carbonation begins to be disfavored. In fact, according to the literature, temperatures around 650 °C are applied in most cases. Under these operating conditions, the FluidBed modeled with the chosen design specifications achieves equilibrium and the performances of the ideal reactor match those of the FluidBed. The performance differences between the two reactors obviously increase as the reaction temperature decreases because of kinetic limitations.

3.2. SMR vs. SE-SMR: Sensitivity Analysis

Moving to the results of the sensitivity studies, these are reported in terms of contour maps, each of which shows varying temperature and S/C. Nine maps were produced for each performance variable, for the three pressures investigated (1, 10 and 20 bar), and for three different CaO/CH₄ molar ratios (0, 0.5, 1). Figure 2, Figure 3 and Figure 4 show all the maps for the indicators H₂ dry concentration (y_H2), CH₄ conversion (X_CH4), and H₂ yield (η_H2), respectively. The maps on the left refer to a CaO/CH₄ molar ratio equal to 0, which corresponds to the traditional SMR case.

When considering SMR, for all the monitored performance variables (Figure 2, Figure 3 and Figure 4), an increasing trend is observed as temperature or S/C ratio increase. The temperature dependence is expected due to the high endothermicity of the reforming reactions. The S/C ratio also plays a significant influence on the equilibrium conditions, as already mentioned; a high excess of steam shifts the chemical equilibrium towards product formation, in accordance with Le Chatelier’s principle, leading to higher H₂ yields. Under the best operating conditions in the ranges considered, 725 °C and S/C = 5, namely the highest temperature and S/C ratio simulated, a dry hydrogen concentration of 78%, a methane conversion of over 99%, and a hydrogen yield of around 89% are achieved at 1 bar. As for the effect of increased pressure, i.e., moving downwards on the maps at CaO/CH₄ = 0 for each performance variable, the effect on the indicators is detrimental, as reforming reactions occur with an increase in the number of moles. For example, given, again, T = 725 °C and S/C = 5, the maximum values achieved by the performance variables are, at 10 and 20 bar, respectively:

$$y_{H_2}^{dry}\cong 74\%,\hspace{1em}{\mathrm{X}}_{\mathrm{CH}4}\cong 0.78,\hspace{1em}{\mathrm{\eta }}_{\mathrm{H}4}\cong 0.71\hspace{1em}(@10\mathrm{bar});$$

$$y_{H_2}^{dry}\cong 70\%,\hspace{1em}{\mathrm{X}}_{\mathrm{CH}4}\cong 0.63,\hspace{1em}{\mathrm{\eta }}_{\mathrm{H}4}\cong 0.58\hspace{1em}(@20\mathrm{bar}).$$

These results agree with those presented in the literature [14,32]. Overall, to give an idea of the strong negative effect of pressure, calculating the average decrease of the performance indicators when moving from traditional SMR at 1 bar to SMR at 10 bar, a reduction for y_H2, X and η by 16%, 44%, and 41%, respectively, was recorded.

Moving to the SE-SMR conditions, firstly, it can be stated that increasing the S/C feed ratio always has a positive effect on the three performance indicators, and this effect is emphasized by sorption-enhanced conditions. On the contrary, since the effect of the other parameters is not so straightforward, a more in-depth discussion is presented below, considering temperature variation at different pressures and CaO/CH₄ ratios. By starting from the pressure effect, thus fixing the CaO/CH₄ ratio, for example to 0.5 (the maps in the middle of each figure), and moving downwards, in Figure 2 a worsening of the H₂ purity, with the pressure increase from 1 to 10 to 20 bar, can be observed. The reason is clear, as high pressures disadvantage reforming reactions, leading to higher concentrations of unconverted methane. Moving from 1 to 10 to 20 bar maps, both a gradual shift upwards and a shrinking of the maximum zone (red zone) occurs, i.e., higher temperatures are needed to reach equally high values, all the other parameters being the same. Although carbonation is favored by the increase of pressure, the deterioration on the reforming process determines the overall effect. In Figure 3, where the CH₄ conversion maps are reported, the above-mentioned results are also confirmed. The qualitative pattern of the 1 bar CH₄ conversion maps (Figure 3, upper maps) is different from that of the dry hydrogen concentration maps (Figure 2). In the case of Figure 3, the 1 bar map shows a ‘sigmoid’ pattern for high temperatures and low S/C ratios (S/C = 1–2). In these zones, X_CH4 reaches very high values, being conversion favored by high temperatures and atmospheric pressure. However, given the stoichiometric deficiency of H₂O, the CO produced by the reforming reactions cannot be further consumed by the WGS reaction to produce CO₂ (and consequently a stream with a higher H₂ purity); this is confirmed by the high levels of CO leaving the reactor under these operating conditions, reaching a dry concentration of 30% for S/C = 1 and 725 °C. The increase in H₂ purity under SE-SMR conditions is indeed essentially due to the CO₂ removal from the outgoing gas; the CO₂ molar fraction (on dry basis) reached values as low as 0.25%, compared with the typical values under SMR conditions around 12–13%.

Finally, as for the yield trend (Figure 4), the behavior at 10 and 20 bar reproduces that of X_CH4. The profile slightly differs at 1 bar, due to the occurrence at low S/C ratios and high temperatures of the reverse-WGS reaction, leading to a reduction in η_CH4.

When considering the effect of the CaO/CH₄ ratio, namely moving from left to right at fixed pressure, improvements are observed with a significant expansion of the area of the map characterized by high values (orange and red colors) of the performance indicators, all the other variables being the same. Thus, as expected, a higher CaO/CH₄ ratio allows greater capture of the produced CO₂, resulting in a performance improvement due to the chemical reaction shift.

For example, by setting a reasonable feed ratio of S/C = 3, a temperature of 650 °C and a pressure of 1 bar, the H₂ dry concentration goes from 86.6% for CaO/CH₄ = 0.5 to 94% for CaO/CH₄ = 1, the CH₄ conversion from 89.1% to 92.7%, while the H₂ yield from 83.6% to 90.4%. At a pressure of 20 bar, on the other hand, $y_{H_2}^{dry}$ improves from 80.5% to 87.7%, X_CH4 from 52.2% to 64.5%, and η_H2 from 52% to 64.4%. These results suggest that the use of CaO for the sorption-enhanced process may partly counterbalance the negative effect of a pressure increase and improve operation in industrially relevant conditions, which often involve pressures higher than the atmospheric one. This counterbalancing effect is only partial, since, moving from SMR at 1 bar to SE-SMR at 10 bar, for example, only y_H2 showed an increase of +20%, while X_CH4 and η_H2 still showed a −14% and −4% decrease.

Lastly, to quantify the SE effect, the percentage increase of performance under the sorption-enhanced process conditions with respect to the traditional SMR, fixing all the other variables, was evaluated and reported in

Table 1. Percentage variation of $y_{H2}$ (dry), $X_{C{H}_4}$, and $\eta$ at varying pressures and CaO/CH₄ ratios (in green performance improvement, in red performance deterioration). How to read: the percentage changes refer to the transition from the conditions indicated in the first column to the conditions indicated in the first row.

	To ⇒	SMR 10 bar	SMR 20 bar	SE-SMR 1 Bar CaO/CH4 = 0.5	SE-SMR 1 Bar CaO/CH4 = 1	SE-SMR 10 Bar CaO/CH4 = 0.5	SE-SMR 10 Bar CaO/CH4 = 1	SE-SMR 20 Bar CaO/CH4 = 0.5	SE-SMR 20 Bar CaO/CH4 = 1
From ⇓
SMR 1 bar		yH2→−16% X→−44% η→−41%	yH2→−24% X→−56% η→−54%	yH2→+14% X→+2% η→+7%	yH2→+25% X→+8% η→+15%	yH2→+9% X→−31% η→−24%	yH2→+20% X→−14% η→−4%	yH2→+7% X→−38% η→−31%	yH2→+16% X→−24% η→−15%
SMR 10 bar			yH2→−10% X→−23% η→−22%	yH2→+36% X→+85% η→+83%	yH2→+50% X→+91% η→+94%	yH2→+30% X→+24% η→+31%	yH2→+44% X→+54% η→+65%	yH2→+28% X→+11% η→+18%	yH2→+39% X→+38% η→+48%
SMR 20 bar				yH2→+51% X→+140% η→+136%	yH2→+67% X→+149% η→+150%	yH2→+44% X→+61% η→+68%	yH2→+60% X→+101% η→+112%	yH2→+42% X→+45% η→+52%	yH2→+54% X→+80% η→+90%
SE-SMR 1 bar CaO/CH4 = 0.5					yH2→+9% X→+5% η→+10%	yH2→−4% X→−32% η→−28%	yH2→+6% X→−16% η→−10%	yH2→−6% X→−39% η→−35%	yH2→+2% X→−25% η→−20%
SE-SMR 1 bar CaO/CH4 = 1						yH2→−13% X→−36% η→−34%	yH2→−3% X→−20% η→−17%	yH2→−15% X→−43% η→−41%	yH2→−7% X→−28% η→−25%
SE-SMR 10 bar CaO/CH4 = 0.5							yH2→+10% X→+24% η→+25%	yH2→−2% X→−10% η→−9%	yH2→+6% X→+10% η→+12%
SE-SMR 10 bar CaO/CH4 = 1								yH2→−11% X→−27% η→−27%	yH2→−4% X→−11% η→−11%
SE-SMR 20 bar CaO/CH4 = 0.5									yH2→+8% X→+22% η→+23%

for the three parameters investigated. By passing from SMR to SE-SMR at 1 bar and CaO/CH₄ = 1, y_H2, X and η increased by +25, +8, and +15%, respectively, while at 10 and 20 bar, y_H2, X and η increased by +44, +54, and +65% and by +54, +80, and +90%, respectively. It should be noted that, being a percentage variation, although this is clearly higher where the traditional SMR process conditions are unfavorable and thus characterized by low performance values, the best overall operating conditions of the SE-SMR process are still those corresponding to high temperatures and the lowest pressure. Just by way of example, if considering at CaO/CH₄ = 1 and pressure equal to 1 bar there are two conditions differently favorable from the point of view of the temperature and S/C, namely 550 °C and S/C = 2 and 650 °C and S/C = 3, the enhancement in the first case ranges from 41.7% to 58.8% for the three performance indicators, while in the second case only from 5.6% to 24.5%. However, given that the conditions of 650 °C and S/C = 3 are reasonable and rather less severe than a traditional process, the percentage improvement appears to be sufficient, leading to values of $y_{H_2}^{dry}$, X_CH4, and η_CH4 of 0.94, 0.93, and 0.9, respectively, representing, from an operational point of view, high-performance results of industrial interest.

4. Conclusions

This work was aimed at studying the intensification of a well-established industrial process, steam reforming of methane, to improve efficiency and carbon footprint by producing blue hydrogen through an integrated CO₂ capture step. The sorption-enhanced steam methane reforming permits work under less extreme operating conditions compared with traditional reforming, achieving very promising results. By means of Aspen Plus V10 software, a mapping of SE-SMR process performance in a fluidized bed reactor using a traditional nickel-based catalyst and a CaO-based sorbent material was carried out under different operating conditions. Based on the specifications and uses of hydrogen, this mapping provides an idea of the possible operational choices and advantages over a traditional process. Under traditional SMR, as expected, significant decreases in y_H2, X and η, by −16%, −44%, and −41%, respectively, when moving from 1 to 10 bar, occurred. Despite this worsening, the enhancement effect was clear, showing that the CO₂ sorption could partly counterbalance the negative effect of the pressure and allow more performing operations at an industrial scale, which are often carried out at high pressures. In fact, when comparing SMR at 1 bar and SE-SMR at 10 bar, despite the strong negative pressure effect, hydrogen purity showed an increase of +20%. Although the best overall operating conditions of the SE-SMR process are still those corresponding to high temperatures and the lowest pressure, if considering atmospheric pressure and CaO/CH₄ = 1, at 650 °C and S/C = 3 for example, which are reasonable and rather less severe conditions than a traditional process, the percentage improvement leads to values of y_H2dry, X_CH4, and η_CH4 of 0.94, 0.93, and 0.9, respectively, representing, from an operational point of view, high-performance results of industrial interest.