Simulation of Limestone Calcination for Calcium Looping: Potential for

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Kinetics, Catalysis, and Reaction Engineering

Simulation of Limestone Calcination for Calcium Looping: Potential for Autothermal and Hydrogen-Producing Sorbent Regeneration Arian Ebneyamini, John R. Grace, Choon Jim Lim, Naoko Ellis, and Said Salah Eldin Elnashaie Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b00668 • Publication Date (Web): 24 Apr 2019 Downloaded from http://pubs.acs.org on April 25, 2019

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Industrial & Engineering Chemistry Research

Simulation of Limestone Calcination for Calcium Looping: Potential for Autothermal and Hydrogen-Producing Sorbent Regeneration A. Ebneyamini*, J.R. Grace. C.J. Lim, N. Ellis and S.S.E.H. Elnashaie Department of Chemical and Biological Engineering, University of British Columbia. Vancouver, Canada V6T 1Z3 *

Email Address: [email protected] (A. Ebneyamini)

Abstract Combined limestone calcination, catalytic methane reforming and combustion in a membrane reactor are simulated as a possible means to achieve autothermal and hydrogen-producing sorbent regeneration for calcium-looping technology. Aspen simulation is employed in order to analyze the equilibrium performance of the process, while a simple one-dimensional, steady-state isothermal plug flow model is applied to provide a first estimate of the performance under fluidization conditions. The simulation results demonstrate that the performance of the process depends strongly on the operating temperature, CaCO3/gas molar feed ratio and methane feed composition. Two separate correlations are proposed for estimating the optimal methane feed composition, resulting in autothermal and complete sorbent regeneration at 800 and 850C, respectively. The simulation results confirm the applicability of the proposed correlations, and demonstrate the high potential of this novel technology for producing a highly concentrated hydrogen stream, if robust high-temperature hydrogen-selective membranes can be installed inside the sorbent regenerator.

Introduction Increasing world consumption of fossil fuels has resulted in the release of more and more greenhouse gases (GHG), generating major concern with respect to climate change.1 Among many possible alternatives, hydrogen is considered a clean and promising energy carrier. In addition, it is required in various applications such as proton exchange fuel cells, hydrocracking and production of methanol and ammonia.1–3 Steam Methane Reforming (SMR) is the leading industrial process to produce a relatively highly concentrated hydrogen stream.4,5 One of the most substantial constraints of the SMR set of reactions (Table 1) is that the feedstock conversion is restricted by the thermodynamics of the reversible reactions.2,4,6 According to Le Chatelier's principle, the thermodynamic equilibrium can be

1 ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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favourably shifted by removing either H2 or CO2 from the reactor.2,4,6–10 H2 perm-selective membranes and CO2-acceptor sorbents have been studied extensively in order to remove hydrogen and carbon dioxide, respectively, from the gaseous mixtures inside reformers. Recent studies9–12 have shown that combining CO2-acceptor sorbents and hydrogen perm-selective membranes within a reformer reactor, resulting in what is called the Membrane-Assisted Sorbent-Enhanced Steam Methane Reforming (MA-SE-SMR) process, can greatly enhance both the hydrogen production rate and purity. Table 1. Main reactions involved in steam methane reforming9

Reaction

Stoichiometry

Water-Gas Shift

H 2O  CO € H 2  CO2

Steam Methane Reforming

CH 4  H 2O € 3H 2  CO

Overall Reaction

CH 4  2 H 2O € 4 H 2  CO2

Palladium-based membranes are the most commonly-used materials for the removal of hydrogen from reformer gaseous mixtures.13–16 However, palladium loses its hydrogen selectivity and mechanical stability at operating temperatures exceeding 550-620C.14,15 In addition, these membranes are highly sensitive to poisoning when contacting species such as CO and sulfur compounds.17 Alternative hydrogen-selective materials, including nickel, cermet/cement and Vb metals, have been also studied for high-temperature hydrogen separation purposes.14,18–23 However, these materials normally suffer from low hydrogen permeability, low hydrogen selectivity, unfavorable reactivity (with other syngas species) or low mechanical stability.14 Limestone-based sorbents have been studied extensively for high-temperature CO2 removal, including in steam methane reformers. Their main advantages are their low market price, abundance and high CO2 capture capability.24–28 From a practical point of view, a calciner (regenerator) reactor is normally placed in parallel with a carbonator unit in order to continuously regenerate spent sorbent particles for further CO2 capture.29,30 Temperature swing adsorption (TSA) is the conventional sorption/desorption cyclic route, with calcination at a much higher operating temperature (e.g. 850-920C) compared to the carbonator temperature.9 Although the TSA method provides rapid and complete calcination of spent sorbents, the high temperature applied in calciner reactors commonly changes the pore structure of the sorbents by shrinking the micro pores (called pore sintering). This reduces the active surface area of the sorbent, leading to a sharp decay in the sorbent utilization


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during the first few carbonation/calcination cycles.26,27,31,32 Various attempts, including sorbent modification (e.g. by steam reactivation, doping and adding inert materials) and producing synthetic sorbents (e.g. Li2ZrO3) have been made to prevent the decay of sorbent utilization, while enhancing their CO2 capture capability.27,32–35 However, these modified/synthetic sorbents are generally expensive compared to natural limestone and economically viable only if they show stable and high performance over many cycles (e.g. >10,000 for Li2ZrO3).25,30 The highly endothermic limestone calcination reaction conventionally occurs at high operating temperatures (> 850C) and is normally much faster than the carbonation reaction, especially if the calcination driving force exceeds 30 kPa.25,36–38 The overall calcination rate is mainly controlled by the intra-particle resistance to gas diffusion, governed by internal pore diffusion. As a result, reducing the partial pressure of CO2 on the particle surface (by using either sweep gas or vacuum) can decrease the diffusion resistance, and thereby enhance the calcination reaction rate.39 Fast atmospheric calcination in the presence of non-CO2 gaseous media can occur at any temperature above 850C when the calcination driving force is roughly 45 kPa, calculated by the Baker model.40,41

PEq ,CO 2  1.826 107 exp(

19680 T

)

(1)

However, calcination in the presence of non-CO2 gaseous media can result in a dilute CO2 off-gas, consequently requiring further CO2 separation to purify the off-gas prior to sequestration. More recently, steam calcination has been proposed to produce a highly concentrated CO2 stream after condensing the steam from the calciner off-gas.33,39 Nevertheless, steam generation is highly energy-consuming, drastically reducing the overall process thermal efficiency. The energy required for the endothermic calcination reaction is conventionally supplied through the reactor wall, resulting in radial temperature gradients and hence low calciner thermal efficiency. As an alternative, in situ oxy-combustion of methane (or fuel in general), can provide the required calcination energy within the sorbent regeneration reactor. However, a highly-concentrated oxygen stream (e.g. enriched-air) would be required to achieve a CO2-enriched dry off-gas, crucial for further carbon storage and sequestration (CSS). In addition, initial rapid and complete methane combustion produces a gaseous medium containing nearly 33% CO2 molar fraction (assuming stoichiometric methane and oxygen feeding), which then reduces the calcination reaction rate and extent along the



length of the reactor. Therefore, the operating temperature of oxy-fuel calciners (900C

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42,43)

is

normally higher than the temperature required for steam and air calcination, resulting in more sorbent pore sintering upon cycling. The CO2 partial pressure of the calciner gaseous medium could be diminished by feeding methane-enriched feed gas (with oxygen as the combustion limiting reactant), resulting in excess methane after initial rapid combustion at the inlet of the calcination reactor. The excess methane can potentially participate in endothermic and hydrogen-producing steam and dry methane reforming reactions, boosting the reactor heat duty. Therefore, the methane feed composition plays a vital role in minimizing the absolute regenerator heat duty, together with increasing the calcination rate and extent by lowering the CO2 partial pressure within the reactor. Several studies have been reported on the combination of methane combustion and reforming with limestone calcination for non-catalytic syngas production at elevated operating temperatures (1123-1400K).44–46 Nevertheless, the applicability of such a process for thermo-neutral regeneration of limestone in the presence of catalyst particles (which circulate between the sorbent-enhanced reformer and calciner units) has not attracted much research attention. A conceptual comparison of different potential calcination media is presented in Figure 1, including the reactions involved, potential products, and their pros and cons.

Figure 1. Schematic comparison of MA-MRC-CAL, steam and air calcination (green boxes: exothermic reactions; red boxes: endothermic reactions; blue boxes and lines: in situ hydrogen separation)


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In this work, the combination of catalytic methane combustion and reforming (sometimes referred as a methane tri-reforming process47) with sorbent calcination in a single reactor (simply called “MRC-CAL”) is evaluated as a means of achieving rapid and autothermal sorbent regeneration with the capability of producing hydrogen-enriched off-gas. The over-arching objective of this research is to perform an initial isothermal analysis on the effect of different operating conditions (temperature, CaCO3/total gas and CH4/enriched-air molar feed ratios) on the reactor heat duty and sorbent conversion via the MRC-CAL sorbent regenerator unit. In addition, the effectiveness of partial hydrogen recovery via a membrane-assisted MRC-CAL process (called “MA-MRC-CAL”) is studied by considering in situ hydrogen separation via high-temperature hydrogen-selective nickel capillary membrane tubes. Note that the main goal of the process introduced in this research is to rapidly calcine limestone particles (for Ca-looping technology - schematically demonstrated in Figure 2) without the need for external reactor heating supply. Nevertheless, the hydrogen production of the MA-MRC-CAL reactor is also studied as an additional bonus for this novel sorbent regeneration technology.

Figure 2. Schematic diagram of sorbent circulation in a dual fluidized bed reactor (MA-SE-SMR integrated with MA-MRC-CAL sorbent calciner)

Simulations in Aspen Plus are applied to evaluate the equilibrium performance of the MRC-CAL process at different operating temperatures and feed ratios. A one-dimensional, steady-state isothermal plug flow model is then employed to investigate the kinetics and hydrogen-productivity of



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the MA-MRC-CAL process under fluidization conditions. The authors recognize that a single plug flow reactor model is an over-simplification of the complex contacting and mixing patterns in gas-fluidized beds, but, given the complexity of the other issues examined in the process under consideration, a simple reactor model is appropriate at this stage. To the best of authors’ knowledge, this work is a pioneering study on rapid, autothermal and hydrogen-producing sorbent regeneration, combined with calcium looping technology. Further comprehensive analysis is required to evaluate the non-isothermal performance of the proposed process, including the best strategy for introducing enriched-air along the bed length.

Equilibrium Analysis of the MRC-CAL Process Aspen Simulation Setup Aspen PlusTM software (V8.0) was employed to evaluate the effect of gaseous feed composition (CH4 balanced with enriched-air), CaCO3/total gas molar feed ratio (simply referred to henceforth as CaCO3/gas feed ratio) and operating temperature on sorbent conversion, reactor heat duty and the MRC-CAL off-gas higher heating value (HHV). A minimum CH4/enriched-air molar feed ratio of 0.5 was specified for all simulations in order to maintain oxygen as the limiting reactant for methane combustion. Figure 3 demonstrates the process flow sheet of the Aspen simulation, including gas mixer and splitter, solid and gas preheaters, calcination reactor and solid separator (cyclone). An off-gas cooler and a gas burner are also included at the end of the Aspen Plus flow sheet in order to estimate the HHV of the MRC-CAL off-gas (identical to gas burner heat duty) at atmospheric pressure and 0C. A gaseous feed flow rate of 0.2 mol.s-1 (close to the values applied in the kinetic simulations of this study, fixed via splitter) was selected for the Aspen simulation, while the performance was analyzed by varying the operating temperature and dimensionless CaCO3/gas and CH4/enriched-air molar feed ratios. Theoretically, a highly concentrated oxygen stream is required to avoid diluting the MRC-CAL off-gas, crucial for carbon storage and sequestration upon burning the ultimate reactor off-gas. However, cryogenic production of a highly-enriched O2 stream would be extremely costly, directly reducing the economic viability of the process. Therefore, an enriched-air stream of 95% O2 (balance nitrogen) was applied for the process simulation owing to its much cheaper production cost and sufficiently low inert content.48 Tables 2 and 3 indicate the properties of the feed streams and blocks in the Aspen simulation, respectively.


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Figure 3. Aspen process flow sheet for simulating the MRC-CAL process



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Table 2. Stream properties for Aspen Plus simulations

Stream

Temperature (C)

Flow Rate (mol.s-1)

Pressure (bars)

Composition

Methane

25

0.075-0.3

1

100% CH4

EnAirA

25

0.15

1

95% O2 + 5% N2

Feed

25

0.2

1

CH4/Enriched-Air: 0.5-2

Sorbent

25

1

100% CaCO3

EnAirB

0

0.1 - 0.3* 50% Excess

1

95% O2 + 5% N2

*Corresponding to CaCO3/gas molar ratio of 0.05-1.5.

Table 3. Block properties in Aspen Plus simulations

Unit

Configuration & Notes

Temperature (C)

Pressure (bars)

Mixer

Mixing Air and CH4

25

1

Splitter

Provide 0.2 mol.s-1 reactor feed flow

25

1

HX1

Electrical Heater

To Calciner Temperature

1

HX2

Electrical Heater

To Calciner Temperature

1

Calciner

Gibbs reactor

750-850

1

Cyclone

Separator (for solid)

Calciner Temperature

1

Cooler

Cooling prior to burning

To 0

1

Burner

Gibbs reactor

0

1

Equilibrium Simulation Results and Discussion Figures 4(a)-(e) compare the MRC-CAL heat duty, sorbent conversion and off-gas equilibrium HHV (equal to gas burner heat duty at 1 bar and 0C) for various feed compositions and operating temperatures with a fixed CaCO3/gas molar feed ratio of 0.5. The data in these figures indicate that increasing the methane content of the feed mixture results in moving from exothermic calcination toward an autothermal and endothermic reactor. This is due to increasing the proportion of methane converted by highly endothermic methane reforming (dry and wet), compared to the exothermic combustion at gaseous feed compositions richer than the methane combustion stoichiometric molar value (CH4/O2 = 0.5). Simultaneously, the excess methane (remaining after rapid initial combustion, consuming all of the oxygen fed) can react with the generated CO2 (released from sorbent calcination and combustion) and steam (generated by combustion), resulting in the formation of syngas containing hydrogen and carbon monoxide. Therefore, a higher off-gas HHV can be expected when


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the MRC-CAL methane feed concentration is increased. Note that the observed kinks in Figures 4(a)-(c) are simply due to transition from incomplete to complete sorbent regeneration, causing abrupt slope changes in the reactor heat duty. The results in Figures 4(a)-(e) also show that complete sorbent regeneration can occur at all of the methane feed compositions studied if the operating temperature exceeds 825C. On the other hand, a richer methane feed composition is required to achieve complete sorbent calcination at lower operating temperatures, while the minimum required CH4/enriched-air feed ratio for complete sorbent regeneration increases with a reduction of operating temperature. In addition, no CH4 /enriched-air feed ratio was observed that resulted in autothermal and complete sorbent regeneration at operating temperature of 750C. These results are in agreement with numerous studies on limestone calcination where it has been reported that decreasing the bulk CO2 partial pressure (e.g. by lowering the CO2 generation via methane combustion at high CH4/enriched-air molar feed ratio) and increasing the operating temperature result in higher calcination rate and extent.33,39 In addition, increasing the methane feed concentration could result in reducing the CO2 partial pressure in the MRC-CAL gaseous mixture due to in situ CO2 consumption via dry methane reforming (CO2+CH4↔2CO+2H2) and reverse water-gas shift reactions (Table 1), with the penalty of increasing the reactor heat duty, as shown in Figures 4(a)-(e). Figure 4(f) compares the hydrogen and carbon monoxide concentrations of the MRC-CAL gaseous product (syngas) at different operating temperatures, with CaCO3/gas and CH4/enriched-air molar feed ratios of 0.5 and 1.21, respectively. The results in this figure reveal that the MRC-CAL gaseous product contains roughly 30-33% hydrogen and 28-31% carbon monoxide (molar basis), while the variation of off-gas composition with operating temperature is nearly negligible. Such a hydrogen content can result in a hydrogen permeation driving force of nearly 30 kPa (assuming a reactor at atmospheric pressure, with vacuum on the permeate side). Therefore, implementation of high-temperature hydrogen-selective membranes inside the regeneration reactor (such as the MA-MRC-CAL process) can recover a portion of the generated hydrogen, resulting in a highly concentrated hydrogen stream on the permeate side of the membrane reactor. In addition, the high H2 and CO contents of the sorbent regenerator off-gas potentially result in a high heating value by-product, which can be further used as the process fuel or as a reduction medium for chemical looping combustion technology. More in-detail analysis of the MA-MRC-CAL hydrogen



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productivity is presented in the next sections of this paper, considering both reaction kinetics and permeation rates along a membrane reactor.

Figure 4. (a)–(e) Effect of operating temperature and feed composition on MRC-CAL and gas burner (equal to syngas HHV at 0C) equilibrium heat duties and sorbent conversion; (f) hydrogen and carbon monoxide composition of reactor off-gas at different operating temperatures with methane-to-air feed ratio of 1.21. (All results are for a CaCO3/gas molar feed ratio of 0.5.)

Figure 5 compares the equilibrium performance of a MRC-CAL unit (fixed CaCO3/gas and CH4/enriched-air ratios of 0.5 and 1.21, respectively) with air-calcination (AIR-CAL) and steam-calcination (STEAM-CAL) at 850C. These operating conditions were selected for autothermal MRC-CAL sorbent regeneration, based on the results presented in Figure 4(e). The inlet gaseous flow rates for both the air and steam calcination tests were maintained at 0.2 mol.s-1,


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consistent with the value used when simulating the MRC-CAL unit. Note that the solid feed flow rate was automatically constant for all these runs due to fixing both CaCO3/gas molar feed ratio and the inlet gas flow rate. Figure 5(a) reveals that both the AIR-CAL and STEAM-CAL processes are extremely endothermic, while, the MRC-CAL sorbent regenerator unit with its previously-mentioned input specifications can be operated autothermally. Figure 5(b) compares the CO2 molar fraction of the ultimate regenerator off-gas when the MRC-CAL, steam and air calcination units are applied. The results demonstrate that air calcination suffers from having a low off-gas CO2 concentration, requiring further purification prior to carbon sequestration. In addition, steam as the non-CO2 calcination gaseous medium can produce a highly concentrated CO2 stream after condensing the steam content of the regenerator off-gas. Nevertheless, steam generation is highly energy-consuming, directly affecting the thermal efficiency of the overall sorbent regeneration system. On the other hand, the MRC-CAL process can provide a highly concentrated CO2 stream after burning (with stoichiometric feeding of oxygen in enriched-air) and condensing the regenerator off-gas. Such a high CO2 concentration would be sufficient for carbon storage and sequestration, in addition to avoiding the need for energy-demanding steam generation.

Figure 5. (a) Simulated heat duties for MRC-CAL, STEAM-CAL and Air-CAL units at 850C. (b) Ultimate CO2 composition of off-gas from MRC-CAL reactor (after burning and condensing), STEAM-CAL (after condensing) and AIR-CAL at 850C. All results are for CaCO3/Gas molar ratio of 0.5. For MRC-CAL, CH4/enriched-air molar ratio = 1.21.



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Figures 6(a) and (b) demonstrate the effect of methane feed composition on the MRC-CAL equilibrium heat duty at different CaCO3/gas feed ratios and at operating temperatures of 800 and 850C, respectively. The simulation results (Figure S.1- Supplementary Information) indicate that incomplete limestone calcination could occur at 800C with high CaCO3/gas and low CH4/enriched-air feed ratios, simply due to the massive CO2 generation via methane combustion and sorbent calcination. Minor carbon formation was also observed at very high CH4/enriched-air and low CaCO3/gas molar feed ratios at both operating temperatures (Figure S.2- Supplementary Information). The results of Figures 6(a) and (b) reveal that the optimal methane feed composition (which corresponds to the autothermal MRC-CAL unit) strongly depends on both the operating temperature and CaCO3/gas feed ratio. Increasing the CaCO3/gas feed ratio (e.g. by increasing the sorbent feed flow rate) boosts the energy required to calcine all the sorbents and hence increases the sorbent regenerator heat duty. Therefore, the required methane feed composition for the autothermal MRC-CAL process decreases with increasing CaCO3/gas feed ratio (as shown in Figures 6(a) and (b)), while autothermal sorbent regeneration via the MRC-CAL process cannot be achieved if a critical CaCO3/gas feed ratio (depends on operating temperature) is exceeded.

Figure 6. Effect of methane feed composition on the MRC-CAL normalized heat duty at different CaCO3/gas feed ratios and at (a) 800C; (b) 850C.

As previously mentioned, equilibrium analysis by Aspen simulation reveals that sorbent regeneration might be incomplete at high CaCO3/gas and low CH4/enriched-air feed ratios, especially at low operating temperatures. Theoretically, any CO2 partial pressure less than the value in equilibrium with the sorbent material (Equation (1)) will result in calcination of carbonated sorbent, with the calcination rate strongly depending on the operating temperature and the calcination partial pressure


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driving force (PCO2,Eq-PCO2). Decreasing the methane content of the MRC-CAL gaseous feed will potentially provide more oxygen as the combustion limiting reactant, resulting in greater methane consumption toward the exothermic and CO2-productive combustion reaction. The latter will potentially lead to less calcination partial pressure driving force and consequently to a lower sorbent regeneration rate and extent under isothermal operating conditions. Therefore, a minimum methane feed concentration is needed to achieve complete sorbent conversion at different operating temperatures and CaCO3/gas molar feed ratios. Accordingly, an equation is developed to provide a rough estimate of the minimum required CH4/enriched-air molar feed ratio to achieve complete limestone calcination via the MRC-CAL process. Equation (2) was derived by assuming complete initial consumption of oxygen (as the limiting reactant) via methane combustion, resulting in steam and CO2 generation. In addition, it was assumed that each mole of un-combusted methane is completely converted to four moles of non-CO2 gases,

corresponding

to

complete

methane

conversion

by

dry

methane

reforming

(CH4+CO22H2+2CO). Although the consumption of CO2 by dry methane reforming and reverse water-gas shift reactions would reduce the CO2 partial pressure of the off-gas, this CO2 consumption was neglected in order to obtain a safe lower limit of the methane feed composition for complete sorbent regeneration. Equation (3) is a dimensionless form of Equation (2) in order to estimate the minimum required CH4/enriched-air feed ratio as a function of operating temperature, enriched-air composition (assumed 95% O2, balance N2 in all simulations) and CaCO3/gas feed ratio. The presence of steam (generated by methane combustion) could dilute the CO2 concentration of the gaseous mixture, as well as increasing the contribution of the SMR reaction in converting the un-combusted methane. For estimation purposes, the methane conversion by the SMR reaction was neglected, and the lower methane content limit for complete limestone calcination was roughly estimated by averaging the values obtained from Equation (3) in the presence and absence of steam as a gaseous dilutant. PEq ,CO2 

FCO2 ,Calcination  FCO2 ,Combustion





FCO2 ,Calcination  FCO2 ,Combustion  FCH 4  FCH 4 ,Combustion  4  FN2  FH 2O ,Combustion FCaCO3 

PEq ,CO2  FCaCO3

FO2 2

FO2      FCH 4    4  FN2  FH 2O Case 2 2  2  FO2

PTot Case 2

(2) PTot



      1  2       2  5    4    1    Case 2         1    1   2     

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  1 

yEq ,CO2

where  





FCaCO3 FGas

,

(3)

(4)

FCH 4

(5)

FEnriched  Air FO2

(6)

FEnriched  Air

Figure 7. Correlated upper and lower limits for  as a function of  at (a) 800C; (b) 850C.

Figures 7(a) and (b) plot the limiting β = CH4/enriched-air molar feed ratio as a function α = CaCO3/gas molar feed ratio at 800 and 850C, respectively, where the upper limit is for the autothermal MRC-CAL process, correlated from Aspen simulation results, and the lower limit is for


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complete sorbent calcination, roughly estimated by Equation (3). These results indicate that complete and autothermal sorbent regeneration by the MRC-CAL process can take place at both operating temperatures, while the maximum allowable CaCO3/gas feed ratio for complete calcination (read from the intersection point of the continuous and dashed dotted lines in Figure 7) is higher at 850C (0.8 at 850C compared to 0.3 at 800C). Accordingly, polynomial curve-fitting was applied via Microsoft Excel 2010 (maximizes the R2 value), and Equations (7) and (8) were developed to correlate the optimal feed composition for Autothermal and Complete Calcination (ACC) at 800 and 850C, respectively:

 ACC  2.91  2  3.3    2.21  ACC  0.87   2  2.15    2.06

0

Simulation of Limestone Calcination for Calcium Looping: Potential for

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