Use of Pyrite Cinder as an Iron-Based Oxygen Carrier in Coal-Fueled

Article pubs.acs.org/EF

Use of Pyrite Cinder as an Iron-Based Oxygen Carrier in Coal-Fueled Chemical Looping Combustion Shuai Zhang,† Sharmen Rajendran,‡ Samuel Henderson,§ Dewang Zeng,† Rui Xiao,*,† and Sankar Bhattacharya‡ †

Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, Southeast University, Nanjing 210096, China Department of Chemical Engineering, Monash University, Clayton, Victoria 3800, Australia § Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom ‡

ABSTRACT: Selection of low cost oxygen carriers with abundant reserves while being environmentally benign is preferred in the chemical looping combustion (CLC) process. Pyrite cinder is characterized as a waste material and poses potential environmental risk while having issues associated with disposal. In this study, pyrite cinder was utilized as a potential iron-based oxygen carrier. The reactivity, recyclability, and attrition behavior of pyrite cinder were evaluated in a laboratory scale fluidized bed reactor. The oxygen carrier to fuel ratio, steam concentration in the fluidization gas, fuel particle size, and temperature on the reactivity of pyrite cinder were investigated. The attrition behavior of pyrite cinder under both inert and reacting conditions was evaluated. The chemical and physical analyses of pyrite cinder confirmed it as a ready source of oxygen carrier. It displayed sufficient reactivity to convert char gasification products to CO2 and H2O. The performance of the system was found to be improved with respect to the carbon conversion rate and gasification rate under the following conditions: higher oxygen carrier to fuel ratio, higher steam concentration in the fluidization gas, smaller fuel particle size, and higher temperature. Cyclic redox tests of pyrite cinder over 20 cycles revealed that it behaved steadily with a stable CO2 yield being achieved. Additionally, pyrite cinder exhibited good resistance to sintering and agglomeration. The attrition behavior of pyrite cinder under inert conditions showed that the collisions of pyrite cinder particles with each other and with reactor wall at high superficial fluidization velocity was the predominant factor influencing its attrition behavior. The cyclic attrition tests showed that the attrition rate was higher in the initial cycle, but this reduced as the redox cycles progressed. It can be inferred from this study that pyrite cinder is a suitable ironbased oxygen carrier for CLC of coal while alleviating the environmental problems associated with its disposal.

1. INTRODUCTION It is widely accepted that the large amount of carbon dioxide (CO2) emitted into the atmosphere from coal-fired power plants is a significant contributor to the heightened greenhouse gas effect.1 With the increasing drive for CO2 capture to migrate global warming, developing cost-effective and energyefficient CO2 capture technology is becoming more important, particularly due to the low efficiency and high cost associated with current CO2 separation technologies. Chemical-looping combustion (CLC) is such a promising technology and has received extensive attention in the past decade. The CLC process involves the combustion of fuel by the oxygen provided from the oxygen carrier in the fuel reactor and the oxidation of the oxygen-depleted oxygen carrier to its original oxidation state. Therefore, the use of oxygen carriers instead of air in the CLC process eliminates the dilution of the generated CO2 gas stream by N2 in the flue gas, allowing for easier compression and sequestration of CO2. Since the exhaust gas from the fuel reactor consists predominantly of CO2 and steam, a dried CO2 gas stream can be obtained by condensation of steam without consuming extra energy. To date, research on CLC with gaseous fuels has been studied extensively and demonstrated successfully both in bench scale reactors2−4 and continuous large scale units5,6 with the fuel conversion being higher than 99%. As the major source of energy, coal plays a dominant role in China’s energy sector due to its abundance and lower cost relative to natural gas and © 2015 American Chemical Society

petroleum. Coal resources account for 94% of all fossil-based fuels in China with more than 50% of the total power generated in coal-fired power plants.7 Therefore, the application of coal as a fuel in CLC is important and necessary in China. Two sets of gas−solid reactions occur in a coal-fueled CLC process which are coal gasification (R1−R2) and subsequent oxidation of intermediate gasification products by the oxygen carrier (R3−R5). Although solid−solid reactions between coal and the oxygen carrier have been observed by some researchers using a thermogravimetric analyzer (TGA),8 this has little or no significance for the process conducted under fluidized conditions,2,9 as coal gasification products are the major reactants with the oxygen carrier particles. With regard to the strategy to accomplish the coal-fueled CLC process, direct introduction of the coal into the fuel reactor is recognized as the preferred choice among the proposed strategies.10,11 In such a configuration, coal is first pyrolyzed and then gasified by steam or CO2 to produce volatiles (mainly CO, CO2, H2, and CH4) and char gasification intermediates which simultaneously get oxidized by the oxygen carrier into CO2 and steam. With this arrangement, no air separation unit is needed, and the coal gasification products can be oxidized rapidly by the oxygen carrier. Received: January 26, 2015 Revised: March 31, 2015 Published: April 1, 2015 2645

DOI: 10.1021/acs.energyfuels.5b00194 Energy Fuels 2015, 29, 2645−2655

Article

Energy & Fuels Table 1. Chemical Composition of the Calcined Pyrite Cinder Fe2O3

CaSO4

SiO2

Al2O3

MgO

MnO

K2O

CuO

ZnO

TiO2

Other

65.50

14.28

11.05

4.21

3.40

0.72

0.32

0.16

0.13

0.08

0.17

Table 2. Proximate and Ultimate Analyses of Lignite Char proximate analysis (ad, wt %)

a

ultimate analysis (ad, wt %)

sample

moisture

volatile

fixed carbon

Ash

Cad

Had

Oada

Nad

Sad

lignite char

3.96

5.34

79.49

11.21

80.71

2.94

0.00

0.76

0.42

Calculated by difference. ad: Air-dried basis.

Figure 1. Schematic of the laboratory scale fluidized-bed reactor system.

coal → volatiles + char

(R1)

C + H 2O/CO2 → CO + H 2

(R2)

CH4 + MexOy → CO2 + H 2O + MexOy − 1

(R3)

H 2 + MexOy → H 2O + MexOy − 1

(R4)

CO + MexOy → CO2 + MexOy − 1

(R5)

magnetite (Fe3O4). Generally, around 0.7−1.0 ton of pyrite cinder is generated to obtain 1.0 ton of sulfuric acid, depending on the scale of the sulfuric acid manufacturing plant.17 Therefore, large quantities of pyrite are discharged as a byproduct of the sulfuric acid industry. In China, over 10 million tons of pyrite cinders is generated yearly and this amount is roughly 30% by weight of the total chemical wastes produced.18 However, because of the limited areas for potential use of pyrite cinder, such as in the brick production industry as a dye, the paint industry as a pigment, and the cement industry as an additive,19 only 30 wt % of pyrite cinder is recycled, while the rest is disposed in landfills or dumped into the sea. As environmental awareness increases and regulations become more stringent, finding alternative means of disposing pyrite cinders at a low cost becomes important. The utilization of pyrite cinder as a substitute for synthetic iron-based oxygen carriers and natural iron ores appears to be a propitious choice for the management of these solid wastes. The reason is that it has a high Fe2O3 content and relatively lower cost (around 16− 65 U.S. dollars per ton) compared to iron ore (around 130− 160 U.S. dollars per ton) in China. Until now, the use of pyrite cinder as an oxygen carrier in a CLC process has not been reported. The aim of this work is to evaluate the performance of pyrite cinder as low-cost iron-based oxygen carrier in a coal-fueled CLC process. The reactivity, recyclability, and attrition behavior

In a coal-fueled CLC process, the effect of coal ash on the oxygen carrier should be taken into account, as the separation of coal ash from the system would result in the loss of some oxygen carrier particles.12 Thus, utilizing inexpensive oxygen carriers is desired. Abundantly available natural iron ores and industrial iron-based wastes having low environmental impacts are examples of such materials that could meet the requirements as an oxygen carrier. Such oxygen carriers have been shown to exhibit high reactivity and recyclability and possess high mechanical strength to reduce attrition at both atmospheric and pressurized conditions.3,12−16 In this context, pyrite cinder, a solid waste derived from sulfuric acid manufacturing plants, was investigated as an oxygen carrier in this work. Pyrite cinder is the compound derived from the roasting of pyrite (FeS2) at high temperatures and subsequent desulfurization in boiler furnace. The major component of pyrite cinder is iron oxides in the form of hematite (Fe2O3) and 2646


Article

Energy & Fuels

The gaseous products leaving the reactor passed through a cooler and a dryer to generate a dry, clean, and cool flue gas before being introduced into an MRU multicomponent gas analyzer. After each experiment, the reactor was cooled under a N2 atmosphere, and the reacted pyrite cinder was collected for further characterization analysis. Each pyrite cinder sample was tested over three consecutive cycles. 2.3. Data Evaluation. 2.3.1. Molar Flow Rate of Outlet Gas. The total molar flow rate of the outlet dry flue gas, ṅout, was calculated based on the volume fraction of outlet N2 (xN2,out) from the measured data using the gas analyzer and the known values of both the inlet molar flow rate (ṅin) and the volume fraction (xN2,in) of N2: x N2,in nout ̇ = n in ̇ x N2,out (1)

of pyrite cinder were evaluated under different experimental conditions in a laboratory scale fluidized-bed reactor. The attrition performance of pyrite cinder was evaluated under inert condition and redox cycles. Orthogonal experimental design (OED) was adopted to determine the factor that most influenced the attrition of the oxygen carrier under inert conditions.

2. EXPERIMENTAL METHODS 2.1. Materials. In this study, pyrite cinder particles were purchased from Fude Chemical Co., Ltd. in Tongling of Anhui Province in China at a price of 26 U.S. dollars per ton and used as the nominated oxygen carrier. As the particle size of the received pyrite cinder was smaller than 0.1 mm, an initial pelleting step using the double roller squeezing granulator20 was employed to generate bigger particles. The pelleting process was done without the addition of any binder or water in the pyrite cinder particles so as to not alter the chemical composition of the pyrite cinder during the pelleting process. The pelletized particles were then calcined at 950 °C for 2 h in a muffle furnace to fully oxidize the particles and increase its mechanical strength. After the calcination process, the particles were crushed and sieved to the size range of 0.10−0.35 mm for the experiments. The chemical composition of the calcined pyrite cinder is shown in Table 1. It can be seen that the calcined pyrite cinder was mainly composed of active components (Fe2O3, CaSO4) and silicon dioxide (SiO2). Both Fe2O3 and CaSO4 were considered as promising candidates in CLC process.13,21,22 Also, combination of Fe2O3 and CaSO4 could create a synergistic effect to enhance the fuel conversion and suppress the release of sulfur dioxide (SO2) in a calcium-based CLC process23 as well as to raise the calcium sulfide (CaS) yield in sulfur recovery (elemental sulfur) industry.24 A lignite char from Inner Mongolia of China was used as the fuel. The proximate and ultimate analyses of this coal sample are shown in Table 2. The char particle size used in this study ranged from 0.20 mm to 0.45 mm, and this is bigger than the particle size of pyrite cinder to achieve a good contact between the coal and oxygen carrier particles. 2.2. Reactivity Test. A laboratory scale stainless steel fluidized-bed reactor with a porous distributor located 450 mm from the bottom of the reactor was used for the experiments. The inner diameter of the reactor was 30 mm with an effective height of 900 mm. The schematic of the reactor system is shown in Figure 1. A detailed description of the reactor system could be found in the following ref 14. As for the inlet gas feeding unit, the inlet pipelines were wrapped by heat pipe and heated to 250 °C during all tests, so the steam generated from the steam generator was immediately carried by the heated carrier gas (N2) to the reactor. The distance between the three-way valve and the inlet of the reactor was long enough to ensure that the steam and N2 mixed well. Prior to each experiment, 60 g of the pyrite cinder particles was placed atop the reactor distributor and then heated in air to the desired temperature. When the experimental conditions became stable, the air stream was switched over to a mixture of steam balanced by N2. The reduction test was then initiated by feeding the char particles into the reactor. During the reduction period, the gas flow rate was 5 times higher than the minimum fluidization velocity (umf) of the pyrite cinder, and the effects of oxygen carrier to fuel ratio, steam concentration in the fluidization gas, fuel particle size, and temperature on the reactivity were evaluated. When the product gas concentrations dropped below the detection limit of the gas analyzer, the reduction period was assumed to be finished. Then pure N2 was introduced for 10 min to avoid back mixing between the reduction and oxidation stages. After the N2 purge stage, the N2 stream was replaced with 5% O2 in N2 to oxidize the reduced oxygen carrier. The relatively low oxygen concentration used during the oxidizing period was to avoid an excessive temperature rise in the oxygen carrier. The oxidization period lasted for 30 min at which the outlet O2 concentration measured by the gas analyzer was already equal to the inlet O2 concentration, indicating that the reduced pyrite cinder particles were fully oxidized to its original oxidation state. After the oxidation period, pure N2 was introduced to the reactor to initiate the next redox cycle.

2.3.2. Gas Yield. The gas yield ( f i) of each component (CO, CO2, CH4, and H2) in the outlet dry flue gas was calculated as shown below: t

fi =

̇ xi dt ∫0 nout t

̇ (xCO + xCO2 + xCH4 + x H2) dt ∫0 nout

(2)

where xi denotes the volume fractions of the outlet gas species. 2.3.3. Carbon Conversion. The carbon conversion, XC, was calculated from the accumulated amount of carbon in the carboncontaining gases (CO, CO2, and CH4) in the reduction period divided by the total amount of carbon in the introduced char nC, coal: t

XC =

̇ (xCO + xCO2 + xCH4) dt ∫0 nout nC,coal

(3)

2.3.4. Average Carbon Conversion Rate. The average carbon conversion rate was defined as follows:

XCavg =

0.95 t0.95,C

(4)

where t0.95,C represents the time when 95% of total carbon has been converted during the reduction period. 2.3.5. Instantaneous Gasification Rate. The instantaneous gasification rate, rC, was defined based on the homogeneous model and calculated from the instant amount of carbon in the carbon-containing gases divided by the amount of residual carbon in the char sample at a given point in time: rC =

dX C 1 1 − X C dt

(5)

2.3.6. Attrition Rate. During the cyclic tests, the attrition rate (Lf) of pyrite cinder particles was estimated and calculated by the weight of fine particles (Δmfines) collected after the experiment, divided by the time interval (Δt) and the primary weight (m) of oxygen carrier samples: Lf =

Δmfines 1 Δt m

(6)

3. RESULTS AND DISCUSSION 3.1. Reactivity Performance of Pyrite Cinder. In this section, the effects of oxygen carrier to fuel ratio, steam content in the fluidization gas, fuel particle size, and temperature on the reactivity performance of pyrite cinder were evaluated. Effort was taken to focus on the parameters such as gas yield, carbon conversion rate, and instantaneous gasification rate which could be used to help identify the effect of the investigated variables on the reactivity of pyrite cinder. 3.1.1. Effect of Oxygen Carrier to Fuel Ratio. The oxygen carrier to fuel ratio, Ω, was defined to evaluate the extent of fuel combusted by the lattice oxygen available in the oxygen carrier. 2647


Article

Energy & Fuels

Figure 2. (a−d) Effect of oxygen carrier to fuel ratio on the outlet gas concentrations, gas yield, and average carbon conversion rate.

Ω = 1 represented the complete conversion of fuel to CO2 and H2O by the Fe2O3 component presented in pyrite cinder at the stoichiometric ratio. In CLC of coal, only the reduction of Fe2O3 to Fe3O4 was considered, as further reduction of Fe3O4 to FeO or Fe would possibly result in the uncompleted conversion of intermediate gasification products to CO2 and H2O. The Ω was calculated as shown below:

Ω=

R OCmOC ϕfuelmfuel

Figure 2a−c depicts the representative outlet gas concentration profiles during the reduction period to illustrate the general features of the raw data. The effect of oxygen carrier to fuel ratio on the performance of pyrite cinder is presented by the difference in the outlet gas components and concentrations. As shown in Figure 2a,b for the reduction reaction with 0.25 and 0.5 g of fuel fed into the reactor, i.e., at the Ω of 2.1 and 1.1 respectively, the pyrite cinder behaved similarly in both cases and exhibited good performance with the fuel. The outlet gaseous products mainly consisted of CO2 with minor amounts of CO and CH4. H2 was not detected at the outlet, which indicated that most of the char gasification products were converted to CO2 and H2O by reacting with the pyrite cinder particles. The increased reactivity of H2 relative to CO and CH4 for iron-based oxygen carriers has been reported by many researchers.25,26 The initial reduction stage was characterized by a maximum in the concentration of CO2, followed by a sharp decrease following the char gasification stage. The CO2 peak could be ascribed to the reactions between the pyrite cinder and the residual volatile matter in char as well as with the char gasification products, whereas the presence of CH4 could be associated with the unreacted residual volatile matter in the char. As the reaction progressed, the concentration of CO2 dropped while becoming the only gaseous product at the outlet of the reactor. In the case of the reduction test at the Ω of 0.73 as shown in Figure 2c, however, pyrite cinder behaved differently with respect to the outlet gas species and concentrations compared to the cases with less fuel. Initially, pyrite cinder behaved normally with only a small amount of CO being detected at the outlet of the reactor during the first 2 min. However, H2 was

(7)

where ROC is the oxygen transport capacity of pyrite cinder, which is defined based on the lattice oxygen from the Fe2O3 component in pyrite cinder, CaSO4 component was confirmed not involved in the CLC reduction as shown in section 3.2 below; mOC and mfuel are the masses of oxygen carrier and lignite char introduced into the reactor; ϕ fuel is the stoichiometric kilogram of lattice oxygen needed for complete conversion of 1 kg of fuel to CO2 and H2O. The variations in the outlet gas concentrations as a function of time, gas yield, and average carbon conversion rate at different oxygen carrier to fuel ratios are presented in Figure 2. The tests were conducted with different fuel masses (0.25 g, 0.5 g, and 0.75 g) while maintaining the mass of pyrite cinder (60 g), corresponding to the Ω value of 2.1, 1.1, and 0.73 respectively. The fuel particle size ranged between 0.20 mm and 0.45 mm. The flow rates of water and carrier gas (N2) were 1.0 mL/min and 150 mL/min respectively, corresponding to a steam volume fraction of 0.9 with the balance being N2. The reaction temperature was 950 °C. 2648


Article

Energy & Fuels

Figure 3. Effect of steam content on the gas yield (a), average carbon conversion and instantaneous gasification rate (b).

Figure 4. Effect of fuel particle size on the gas yield (a), average carbon conversion and instantaneous gasification rate (b).

observed. Higher value of Ω resulted in a higher average carbon conversion rate, indicating that less time was needed to completely convert the carbon in the lignite char, consistent with the findings shown in Figure 2a−c where the reaction times needed for the complete fuel conversion were 10.2, 11.3, and 18.1 min for the tests at the Ω value of 2.2, 1.1, and 0.73 respectively. On the basis of the above findings, the Ω value at 1.1 will be applied in the subsequent reactivity and recyclability tests considering the fuel consumption and CO2 yield. 3.1.2. Effect of Steam Content. The tests were conducted at a temperature of 950 °C and the Ω value of 1.1 with a constant total inlet flow rate. The steam fraction was changed by varying the flow rates of the inlet water and carrier gas (N2). The steam contents investigated here were 54%, 72%, and 90% respectively, corresponding to inlet water flow rates of 0.6, 0.8, and 1.0 mL/min mixed with 682, 416, and 150 mL/min of N2 respectively. Figure 3 shows the variations of gas yield, average carbon conversion rate, and instantaneous gasification rate as a function of the steam content. It can be seen that the average carbon conversion rate increased with the increase in the steam content, particularly when going from 72% to 90%. This also applied to the char gasification rate as shown in Figure 3b, where the improvement in the instantaneous gasification rate was achieved with more steam added in the fluidization gas, irrespective of the carbon conversion extent. Also, the carbon conversion was found to increase from 90.30% to 93.55% with the increase in the steam content. Therefore, a higher steam

observed in large amounts as the char gasification reaction progressed and became the major component in the outlet combustible gases. The H2 was continually generated along with CO2 until the end of the reduction period. The poor performance of pyrite cinder in this case could be associated with the ease of scavenging the oxygen available in the pyrite cinder particles, as the value of Ω was lower than 1. During the initial reduction stage, the surface lattice oxygen of the pyrite cinder particles was progressively exhausted under chemically controlled conditions, and then the reduction reaction entered into the diffusion controlled stage. Char gasification products would have had to diffuse into the inner part of the pyrite cinder particles to obtain more oxygen for their conversion to CO2 and H2O. With the progressing reduction reaction, the diffusional resistance became higher and less oxygen was available, resulting in more char gasification products being unconverted. The larger amount of H2 compared to the detected CO amount at the outlet of the reactor could be due to the water gas shift reaction. Figure 2d shows the effect of oxygen carrier to fuel ratio on the gas yield and average carbon conversion rate. In the case of the reduction tests with Ω higher than 1.1, a CO2 yield higher than 99.4% was achieved in both cases. With the decrease of Ω to 0.73, however, a significant decrease in the CO2 yield along with the increase of H2 yield was observed. Therefore, Ω lower than 1.1 did not facilitate the production of CO2 and H2O in the investigated Ω range. As for the average carbon conversion rate, a similar trend as the variation of CO2 concentration was 2649


Article

Energy & Fuels

Figure 5. Effect of temperature on the gas yield (a), average carbon conversion rate and instantaneous gasification rate (b).

the temperature range between 850 and 950 °C was adopted in this study to evaluate the reactivity of pyrite cinder as a function of temperature. The other experimental conditions such as the steam concentration of 90%, fuel particle size ranging from 0.2 mm to 0.45 mm, and the Ω value of 1.1 were kept as constant when varying the temperature. The variations in the gas yield, average carbon conversion rate, and instantaneous gasification rate as a function of temperature are shown in Figure 5. With respect to the gas yield, there was almost no change when the temperature was increased from 850 to 900 °C; the CO2 yields were 99.86% and 99.82% at the temperatures of 850 and 900 °C respectively, and no CH4 and H2 were detected at the outlet for both temperatures. At 950 °C, however, the CO2 yield decreased to 99.42% with a higher CO yield, and a small amount of CH4 was also detected. This indicated that there was poorer contact between the pyrite cinder particles and fuel gas. In an industrial scale CLC system operated in an interconnected fluidized bed unit, the pyrite cinder may perform better with more combustible gases converted to CO2 and H2O at a higher temperature by changing the location of the coal feeding point from the top of the reactor as used in this study to a point located in the emulsion phase of the pyrite cinder particles28 or at the bottom of fuel reactor as typical of a spout fluid bed.29 As for the effect of temperature on the average carbon conversion rate and instantaneous gasification rate, a significant increase in both parameters were observed in the temperature range between 850 and 900 °C, corresponding to a decrease in the reaction time from 20 to 11 min. The carbon conversion also showed an increase from 86.67% to 93.55% as evidenced in Figure 5b. With a further increase in the temperature, the average carbon conversion rate, instantaneous gasification rate, and carbon conversion were found to improve, but the extent was less pronounced compared to the case in the lower temperature range. Overall, the temperature was found to play a positive role in the coal-fueled CLC process using pyrite cinder as the oxygen carrier, and the effect of temperature was more apparent compared to the other factors as discussed above. It is known that the gasification of solid fuel is the ratelimiting step in the CLC process.30 To evaluate the effect of pyrite cinder particles on the char gasification process, experiments were conducted in the absence of pyrite cinder in the reactor at 950 °C for comparison purposes. The results are shown in Table 3. It can be seen that the performance of the char gasification process was significantly enhanced by the

content accelerated the gasification of the char to gaseous products and allowed the char conversion to complete within a shorter time. As for the variation of the gas yield with steam content in Figure 3a, a linear increase in the CO2 yield accompanied by a decrease in the CO yield was observed with the increase in the steam content. H2 was detected at the outlet at a steam content of 54%, but this disappeared with a further increase in the steam content. Although the enhanced char gasification rate at a higher steam concentration resulted in more gasification products being released per unit time, this did not lead to more combustible gases detected at the outlet of the reactor, which was observed by Zhao et al.27 using a natural copper ore as the oxygen carrier, this indicated a good performance of pyrite cinder with the gasification intermediates. It can be concluded from this section that a higher steam content could enhance the char gasification process and complete the reduction reaction within a shorter time. 3.1.3. Effect of Fuel Particle Size. The tests focusing on the effect of the fuel particle size were conducted by varying the particle size range from 0.20 to 0.45 mm to 0.60−0.80 mm while keeping the other experimental conditions constant, such as a temperature of 950 °C, the steam concentration of 90%, Ω value of 1.1. The effect of fuel particle size on the gas yield, average carbon conversion rate, and instantaneous gasification rate is shown in Figure 4. As observed in Figure 4a, the fuel particle size showed little impact on the gas yield, with the change in the CO2 yield being hardly distinguishable. But the fuel with a larger particle size needed a longer time to be completely converted, as confirmed by the average carbon conversion rate in Figure 4a and the instantaneous gasification rate in Figure 4b. It can be seen that the larger the fuel particle, the lower the average carbon conversion and instantaneous gasification rates. This could be due to the greater diffusional resistance of steam into the inner part of the larger fuel particles. Therefore, larger fuel particle sizes are not preferred in a CLC system when taking into account the balance between the thermal efficiency of the system and the reaction time to fully consume the fuel while ensuring that the CO2 yield is maintained at a high value. 3.1.4. Effect of Temperature. The operating temperature is of particular importance when evaluating the physicochemical properties of the oxygen carriers. Because of the limitation of the softening point of oxygen carrier whereby it starts to initiate agglomeration, CLC tests are generally conducted at temperatures lower than 1000 °C to avoid a significant change in the structure of the oxygen carrier particles. It is for this reason that 2650


Article

Energy & Fuels

ilmenite or raw pyrite having a naturally occurring physical structure, the pyrite cinder is a byproduct of pyrite and undergoes multiple conversion processes. Therefore, the received pyrite cinder could have a higher surface area with more accessible inner pores, whereas this may not be the case in the natural occurring iron ore. To confirm this, the surface morphologies of the calcined and reduced pyrite cinder samples at typical cycles were characterized by scanning electron micrography (SEM) and the result is shown in Figure 7. It can be observed that the calcined pyrite cinder particles showed a porous structure with individual grains being formed on the surface, better than the naturally occurring iron ore with a more compact physical structure. On the other hand, the irregular-shaped particles shown in the low-magnification image in the left column were commonly observed in both the natural iron ores and industrial wastes. Compared to the SEM image of the calcined pyrite cinder sample, no appreciable change in the morphology of the reduced pyrite cinder samples was observed after repeated redox cycles. This indicated that these particles could still maintain their porous structure with the evidence of individual grains clearly visible on the surface. Such an observation confirmed the good structural property of pyrite cinder and the findings are shown in Figure 6. As mentioned in section 2.1, both Fe2O3 and CaSO4 were active components in pyrite cinder. Our previous study on the evaluation of Fe2O3/CaSO4 composite oxygen carriers showed that the reactivity of Fe2O3 with fuel gas was better that that of CaSO4.23 To confirm whether both components participated in the reduction period, X-ray diffractometry (XRD) was used to characterize the crystalline structures of the reduced pyrite cinder samples at typical cycles, and the result is shown in Figure 8. It can be seen that Fe3O4 was the only reduced product in the samples of the 10th and 20th reduction reaction; neither CaS nor CaO diffraction peak was detected, and this indicated that the CaSO4 component did not participate in the reduction. The CaSO4 component not involved in the chemical reaction was preferred in the CLC process, as the reaction of CaSO4 with fuel gas generally produces sulfur-containing gases (SO2 and H2S),31 which would pollute the produced CO2 stream. 3.3. Attrition Behavior of Pyrite Cinder. The attrition behavior of an oxygen carrier is one of two important factors (chemical deactivation and attrition) in determining its longevity,32 particularly in the widely adopted interconnected fluidized-bed reactor design. The oxygen carrier with a low attrition rate is generally preferred, as the makeup oxygen carrier requirements and the solids disposal costs could be reduced. The study on the attrition of solid calcium-based sorbents used in the calcium-looping process has been extensively investigated,33−36 and the results showed that particle attrition was influenced by many factors, such as the particle size, operating temperature, exposure time, superficial fluidization velocity, the inventory of bed material,34 and so on. In a CLC process, however, few studies have focused on the attrition behavior of the oxygen carrier32,37,38 and the evaluation of the different influencing factors have not been reported. Therefore, the attrition behavior of pyrite cinder under different experimental conditions was evaluated in the batch fluidized-bed reactor. 3.3.1. Attrition Test under Inert Condition. The attrition test under inert conditions used air as the fluidizing agent to investigate the effect of operating temperature, exposure time, and superficial fluidization velocity on the attrition performance

Table 3. Comparison of Char Gasification Process with and without the Presence of Pyrite Cinder Particles at 950 °C specific gasification rate (1/min)

char gasification in situ CLC reduction char gasification alone

XCavg (%/min)

Xc = 0.2

Xc = 0.4

Xc = 0.6

Xc = 0.8

17.27

0.48

0.57

0.61

0.40

11.31

0.31

0.29

0.29

0.14

presence of pyrite cinder particle; the average carbon conversion rate increased by 5.96%/min, corresponding to a decrease in the reaction time by 3 min. This represented a large improvement in the reaction time since the total reaction time was around 11 min for the char gasification in situ CLC reduction process at 950 °C. The instantaneous gasification rate at the specific carbon conversion was also greatly enhanced by the pyrite cinder presented in the char gasification process. 3.2. Recyclability Performance of Pyrite Cinder. Previous research on low-cost iron-based oxygen carriers such as natural iron ores,15 industrial wastes,2 and ilmenite25,26 in a CLC process with gaseous or solid fuels showed good recyclability during the cyclic tests. It was reported that ilmenite underwent an activation process as the number of cycles increased, while most of natural iron ores and industrial wastes showed stable reactivity with increasing redox reactions. To determine the cyclic performance of pyrite cinder, cyclic tests were conducted with 20 successive redox cycles consisting of 20 min reduction reactions followed by 30 min oxidation reactions. The experimental conditions were based on the identified optimal conditions from the above reactivity tests: temperature of 950 °C, steam concentration of 90%, Ω value of 1.1, and fuel particle size range between 0.2 mm and 0.45 mm. The variation of the gas yield as a function of the cycle number is shown in Figure 6. It can be seen that pyrite cinder

Figure 6. Effect of cycle number on the gas yield in the cyclic test of pyrite cinder.

behaved similar to the iron ore and industrial wastes as no activation process was observed when using the pyrite cinder. The CO2 yield was found to stabilize at around 99.56% from the beginning to the end of the cyclic test, indicating that pyrite cinder exhibited good resistance to reactivity decay during the cyclic tests. The good cyclic performance of pyrite cinder could be ascribed to its inherent physical properties. Unlike iron ore, 2651


Article

Energy & Fuels

Figure 7. SEM images of the calcined and used pyrite cinder samples at typical cycles.

of pyrite cinder. To be consistent with the above tests, 60 g of calcined pyrite cinder in the particle size range of 0.10−0.35 mm was used as the bed material. An orthogonal experimental design was adopted to investigate the attrition behavior of the pyrite cinder particles. Temperature, exposure time, and superficial fluidization velocity were selected as the factors. The reactor was operated under bubbling fluidization regime with the superficial fluidization velocity varying between 3.5 umf and 6.5 umf. The operating temperature and exposure time were varied from 850 to 950 °C and 30 to 180 min, respectively. The experimental matrix for the pyrite cinder attrition with the three factors and three levels arranged for each factor is shown in Table 4. For the attrition test, a filter bag was attached to the outlet of the reactor system, and this allowed for the collection of the elutriated fine particles while permitting the gas to pass through. Before the attrition test, the pyrite cinder particles were first loaded into the feed hopper. Then the reactor was heated to the desired temperature at the preset air flow rate. When all the experimental conditions became stable, pyrite cinder particles dropped into the reactor and the attrition test began. After the exposure time for the tests as shown in Table 4

Figure 8. XRD analysis of the reduced pyrite cinder samples at typical cycles. H: hematite, Fe2O3; M: magnetite, Fe3O4; C: calcium sulfate, CaSO4; Q: quartz, SiO2.

of the pyrite cinder. The purpose here was to identity the significance of these three factors on the attrition performance 2652


Article

Energy & Fuels

time showed the least impact on the attrition performance of pyrite cinder. In conclusion, the sequence of the three factors affecting the attrition performance of pyrite cinder was superficial fluidization velocity > temperature > exposure time. In comparison to the attrition performance of solid calcium-based CO2 sorbents reported by Chen et al.,34 where temperature was found to have the biggest impact on the sorbent attrition among the three factors; this difference in the order of importance of the attrition of oxygen carrier and sorbents could be possibly attributed to the different physical properties of both types of particles. 3.3.2. Pyrite Cinder Attrition in Reduction/Oxidation Cycles. During the cyclic test to investigate the reaction performance of pyrite cinder in section 3.2, the attrition behavior of pyrite cinder was also evaluated by measuring the mass loss at typical cycles. The fine particles were sieved from the residue collected from the reactor, the cyclone, and the gas cleaning bottle. As the fine particles in the gas cleaning bottle were wet, they were put to dry in an oven for 6 h to completely dry the fine particles. The amount of particles in the gas cleaning bottle was always found to be small on every occasion. The attrition results looking at the mass loss and attrition rate in the cyclic test are shown in Figure 10. The fine particles were collected after the reduction stages of the 1st, 5th, 10th, 15th, and 20th cycles, respectively.

Table 4. Test Matrix for the Pyrite Cinder Attrition no.

temperature/°C

exposure time/min

superficial fluidization velocity (u/umf)

mass loss/g

1 2 3 4 5 6 7 8 9

850 850 850 900 900 900 950 950 950

30 90 180 30 90 180 30 90 180

3.5 5.0 6.5 5.0 6.5 3.5 6.5 3.5 5.0

0.32 0.45 0.62 0.47 0.56 0.37 0.67 0.54 0.63

came to an end, the furnace was turned off to cool down the reactor while a gas velocity lower than the minimum fluidization velocity was used. Then the pyrite cinder particles in the reactor and filter bag were collected and sieved to get the particles in the size range less than 0.1 mm. The weight of these fine particles were used to characterize the attrition behavior of pyrite cinder and the corresponding result is shown in Table 4. Figure 9 shows the results of the attrition test based on the variability analysis. k1, k2, and k3 shown for each factor

Figure 9. Effect of temperature, exposure time, and superficial fluidization velocity on the attrition behavior of pyrite cinder.

Figure 10. Attrition performance of pyrite cinder in reduction/ oxidation cycles.

represented the mean value of mass loss at a specific level. R represented the difference between the maximum and the minimum values of k1, k2, and k3 at a specific factor. The results showed that the mass loss increased with the increase of these three factors. The abrasion caused by the temperature increasing could be ascribed to the thermal stress. At a low temperature range from 850 to 900 °C, the abrasion experienced was relatively weak with a small increase in the amount of fine particles. When the temperature was increased to 950 °C, however, a greater mass loss was observed, indicating that the rapid increase of thermal stress resulted in the increased attrition of pyrite cinder. With regard to the effect of the superficial fluidization velocity, a higher degree of abrasion was obtained at a higher gas velocity, and the mass loss showed a linear increase. The heightened abrasion at higher gas velocities was mainly attributed to the collisions of the fluidized pyrite cinder particles with each other and with the reactor wall, and the amount of fine particles increased with the increase of exposure time as shown in Figure 9. Compared to the effect of temperature and superficial fluidization velocity, the exposure

As observed in Figure 10, the mass loss was found to first increase to a maximum at the fifth cycle and then gradually decrease with the increase of the number of cycles. Compared to the degree of abrasion in the subsequent cycles, the initial mass loss in the first cycle was relatively larger. The conclusion was based on the much shorter time-scale of the first cycle than that of the subsequent cycles, and this was also confirmed by the highest attrition rate shown in the first cycle. The large initial mass loss was possibly ascribed to the rounding off of the angular coarse particles of pyrite cinder by mechanically removing the surface asperities, as the calcined pyrite cinder particles were irregularly shaped. This phenomenon was also observed for the solid calcium-based CO2 sorbents in the calcium-looping process.36,39 As the redox cycles proceeded, the attrition rate showed a decreasing trend until a steady value was attained. It could be inferred that the pyrite cinder particles would have a long lifetime without the need to add a large amount of fresh particles with the redox cycles progressing as 2653


Article

Energy & Fuels

production cost while alleviating the environmental problems associated with its disposal.

long as the pyrite cinder showed a stable chemical reaction performance. The attrition behavior of pyrite cinder was also compared with the hematite/Ca2Al2SiO7 oxygen carriers used by Song et al.20 in a coal-fueled CLC process. After 20 redox cycles, the mass of pyrite cinder in the bed decreased by 4.42 wt % to 57.35 g, corresponding to an average rate of attrition of 0.23 wt %/h, which is higher than the attrition rate of hematite/ Ca2Al2SiO7 samples. In addition to the different experimental conditions (gas velocity, exposure time, etc.) adopted in both studies, the difference in the mechanical strength between pyrite cinder and hematite/Ca2Al2SiO7 is one of the most important factors that should be considered when delving into difference in the attrition rate and extent. The relatively lower mechanical strength of pyrite cinder could be possibly due to the poorer adhesion between the fine particles during the preparation process. Therefore, further studies to improve the mechanical strength of the prepared pyrite cinder are necessary to ensure a better bond. This could be achieved by increasing the temperature or duration of the calcination process or by changing the preparation method, and so on.

■

AUTHOR INFORMATION

Corresponding Author

*Tel:+86-25-83795726. Fax: +86-25-5771 4489. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The support from National High Technology Research and Development Program of China (863 program), (Grant No. 2012AA051800), National Natural Science Foundation of China (NSFC), (Grant 51476035), the Foundation of Graduate Creative Program of Jiangsu Province (CXZZ12_0101), the Fundamental Research Funds for the Central Universities and the Scientific Research Foundation of Graduate School of Southeast University (YBJJ1217) for this study are gratefully acknowledged.

■

4. CONCLUSIONS The potential use of pyrite cinder as a low-cost iron-based oxygen carrier was investigated in terms of its reactivity, recyclability, and attrition behavior in a laboratory scale fluidized-bed reactor. The evaluation of pyrite cinder in the reactivity tests focusing on the effects of oxygen carrier to fuel ratio, steam concentration in the fluidization gas, fuel particle size, and temperature confirmed it as a suitable iron-based oxygen carrier with over 99% of the char gasification products being converted to CO2 and H2O in most cases. The Ω value lower than 1.1 was not preferred in the investigated range as a large amount of char gasification products were released without reacting with the pyrite cinder to CO2 and H2O. The increases in the oxygen carrier to fuel ratio, steam concentration, and temperature as well as the decrease of fuel particle size facilitated the char gasification process, resulting in a higher average carbon conversion rate and instantaneous gasification rate. In addition, the presence of pyrite cinder was found to accelerate the char gasification process. The optimum experimental conditions based on the reactivity tests were a Ω value at 1.1, 90% steam concentration, fuel particle size range of 0.2−0.45 mm, and a reaction temperature at 950 °C. The cyclic and attrition tests indicated that pyrite cinder was potentially suitable for long-term stable operation. The CO2 yield was found to be stable at around 99.56%. Additionally, the pyrite cinder was found to maintain a porous structure during the repeated redox cycles, exhibiting good resistance to sintering or agglomeration. The OED analysis of the attrition behavior of pyrite cinder under inert conditions showed that the superficial fluidization velocity was the factor with the greatest influence affecting the attrition when the effects of temperature, exposure time, and superficial fluidization velocity were considered. The cyclic tests showed that pyrite cinder experienced a larger attrition rate in the initial stage and then approached a low steady value as the redox cycles proceeded. It can be inferred from the above findings that pyrite cinder, which is readily available in large quantities at a low cost, could be an outstanding candidate as an iron-based oxygen carrier in a coal-fueled CLC process, and the utilization of pyrite cinder in the CLC process could significantly reduce the oxygen carrier

REFERENCES

(1) Tola, V.; Pettinau, A. Power generation plants with carbon capture and storage: A techno-economic comparison between coal combustion and gasification technologies. Appl. Energy 2014, 113, 1461−1474. (2) Mendiara, T.; Gayan, P.; Abad, A.; de Diego, L. F.; GarciaLabiano, F.; Adanez, J. Performance of a bauxite waste as oxygencarrier for chemical-looping combustion using coal as fuel. Fuel Process. Technol. 2013, 109, 57−69. (3) Olivier, J.; Janssens-Maenhout, G.; Peters, J. Trends in global CO2 emissions 2012 report, 2012. (4) Takehira, K.; Shishido, T.; Wang, P.; Kosaka, T.; Takaki, K. Autothermal reforming of CH4 over supported Ni catalysts prepared from Mg-Al hydrotalcite-like anionic clay. J. Catal. 2004, 221 (1), 43− 54. (5) Linderholm, C.; Abad, A.; Mattisson, T.; Lynyfelt, A. 160 h of chemical-looping combustion in a 10 kW reactor system with a NiObased oxygen carrier. Int. J. Greenhouse Gas Control 2008, 2 (4), 520− 530. (6) Linderholm, C.; Mattisson, T.; Lyngfelt, A. Long-term integrity testing of spray-dried particles in a 10-kW chemical-looping combustor using natural gas as fuel. Fuel 2009, 88 (11), 2083−2096. (7) Sustainable Use of Coal and Pollution Control Policy in China; CCICED Policy Research Report, 2009. (8) Siriwardane, R.; Tian, H. J.; Miller, D.; Richards, G.; Simonyi, T.; Poston, J. Evaluation of reaction mechanism of coal-metal oxide interactions in chemical-looping combustion. Combust. Flame 2010, 157 (11), 2198−2208. (9) Cuadrat, A.; Abad, A.; de Diego, L. F.; Garcia-Labiano, F.; Gayan, P.; Adanez, J. Prompt considerations on the design of ChemicalLooping Combustion of coal from experimental tests. Fuel 2012, 97, 219−232. (10) Bidwe, A. R.; Mayer, F.; Hawthorne, C.; Charitos, A.; Schuster, A.; Scheffknecht, G. Use of ilmenite as an oxygen carrier in Chemical Looping Combustion-Batch and continuous dual fluidized bed investigation. 10th International Conference on Greenhouse Gas Control Technologies; September 19−23, 2010; RAI: Amsterdam, The Netherlands, 2011; 4, pp 433−440. (11) Adanez, J.; Abad, A.; Garcia-Labiano, F.; Gayan, P.; de Diego, L. F. Progress in Chemical-Looping Combustion and Reforming technologies. Prog. Energy Combust. Sci. 2012, 38 (2), 215−282. (12) Mendiara, T.; Garcia-Labiano, F.; Gayan, P.; Abad, A.; de Diego, L. F.; Adanez, J. Evaluation of the use of different coals in Chemical Looping Combustion using a bauxite waste as oxygen carrier. Fuel 2013, 106, 814−826. 2654


Article

Energy & Fuels (13) Zhang, S.; Saha, C.; Yang, Y. C.; Bhattacharya, S.; Xiao, R. Use of Fe2O3-Containing Industrial Wastes As the Oxygen Carrier for Chemical-Looping Combustion of Coal: Effects of Pressure and Cycles. Energy Fuel 2011, 25 (10), 4357−4366. (14) Xiao, R.; Song, Q. L.; Song, M.; Lu, Z. J.; Zhang, S. A.; Shen, L. H. Pressurized chemical-looping combustion of coal with an iron orebased oxygen carrier. Combust. Flame 2010, 157 (6), 1140−1153. (15) Xiao, R.; Song, Q. L.; Zhang, S. A.; Zheng, W. G.; Yang, Y. C. Pressurized Chemical-Looping Combustion of Chinese Bituminous Coal: Cyclic Performance and Characterization of Iron Ore-Based Oxygen Carrier. Energy Fuel 2010, 24, 1449−1463. (16) Ishida, M.; Jin, H. G. Greenhouse gas control by a novel combustion: No energy penalty and no CO2 separation equipment. Greenhouse Gas Control Technol. 1999, 627−632. (17) Zheng, Y. J.; Liu, Z. C. Preparation of monodispersed micaceous iron oxide pigment from pyrite cinders. Powder Technol. 2011, 207 (1−3), 335−342. (18) Zhu, D. Q.; Li, J. Preparation of high quality magnetite concentrate from pyrite cinder by composite pellet reduction-roasting and magnetic-separation. China J. Nonfer. Met. 2007, 17, 649−656 (in Chinese). (19) Abdrakhimov, A. V.; Abdrakhimova, E. S.; Abdrakhimov, V. Z. Technical properties of roof tiles made of technogenic material with pyrite cinder. Glass Ceram. 2006, 63 (3−4), 130−132. (20) Song, T.; Shen, L. H.; Guo, W. J.; Chen, D. Q.; Xiao, J. Enhanced Reaction Performance with Hematite/Ca2Al2SiO7 Oxygen Carrier in Chemical Looping Combustion of Coal. Ind. Eng. Chem. Res. 2013, 52 (28), 9573−9585. (21) Zhang, S.; Xiao, R.; Zheng, W. G. Comparative study between fluidized-bed and fixed-bed operation modes in pressurized chemical looping combustion of coal. Appl. Energy 2014, 130, 181−189. (22) Song, Q. L.; Xiao, R.; Deng, Z. Y.; Shen, L. H.; Zhang, M. Y. Reactivity of a CaSO4-oxygen carrier in chemical-looping combustion of methane in a fixed bed reactor. Korean J. Chem. Eng. 2009, 26 (2), 592−602. (23) Zhang, S.; Xiao, R.; Liu, J.; Bhattacharya, S. Performance of Fe2O3/CaSO4 composite oxygen carrier on inhibition of sulfur release in calcium-based chemical looping combustion. Int. J. Greenhouse Gas Control 2013, 17, 1−12. (24) Li, H. J.; Zhuang, Y. H. Catalytic reduction of calcium sulfate to calcium sulfide by carbon monoxide. Ind. Eng. Chem. Res. 1999, 38 (9), 3333−3337. (25) Adanez, J.; Cuadrat, A.; Abad, A.; Gayan, P.; de Diego, L. F.; Garcia-Labiano, F. Ilmenite Activation during Consecutive Redox Cycles in Chemical-Looping Combustion. Energy Fuel 2010, 24, 1402−1413. (26) Cuadrat, A.; Abad, A.; Adanez, J.; de Diego, L. F.; GarciaLabiano, F.; Gayan, P. Behavior of ilmenite as oxygen carrier in chemical-looping combustion. Fuel Process. Technol. 2012, 94 (1), 101−112. (27) Zhao, H. B.; Wang, K.; Fang, Y. F.; Ma, J. C.; Mei, D. F.; Zheng, C. G. Characterization of natural copper ore as oxygen carrier in chemical-looping with oxygen uncoupling of anthracite. Int. J. Greenhouse Gas Control 2014, 22, 154−164. (28) Xiao, R.; Chen, L. Y.; Saha, C.; Zhang, S.; Bhattacharya, S. Pressurized chemical-looping combustion of coal using an iron ore as oxygen carrier in a pilot-scale unit. Int. J. Greenhouse Gas Control 2012, 10, 363−373. (29) Shen, L. H.; Wu, J. H.; Xiao, J.; Song, Q. L.; Xiao, R. ChemicalLooping Combustion of Biomass in a 10 kW(th) Reactor with Iron Oxide As an Oxygen Carrier. Energy Fuel 2009, 23, 2498−2505. (30) Brown, T. A.; Dennis, J. S.; Scott, S. A.; Davidson, J. F.; Hayhurst, A. N. Gasification and Chemical-Looping Combustion of a Lignite Char in a Fluidized Bed of Iron Oxide. Energy Fuel 2010, 24, 3034−3048. (31) Song, Q. L.; Xiao, R.; Deng, Z. Y.; Zheng, W. G.; Shen, L. H.; Xiao, J. Multicycle Study on Chemical-Looping Combustion of Simulated Coal Gas with a CaSO(4) Oxygen Carrier in a Fluidized Bed Reactor. Energy Fuel 2008, 22 (6), 3661−3672.

(32) Brown, T. A.; Scala, F.; Scott, S. A.; Dennis, J. S.; Salatino, P. The attrition behaviour of oxygen-carriers under inert and reacting conditions. Chem. Eng. Sci. 2012, 71, 449−467. (33) Di Benedetto, A.; Salatino, P. Modelling attrition of limestone during calcination and sulfation in a fluidized bed reactor. Powder Technol. 1998, 95 (2), 119−128. (34) Chen, H. C.; Zhao, C. S.; Yang, Y. M.; Zhang, P. P. CO2 capture and attrition performance of CaO pellets with aluminate cement under pressurized carbonation. Appl. Energy 2012, 91 (1), 334−340. (35) Scala, F.; Salatino, P. Attrition of limestones by impact loading in fluidized beds: The influence of reaction conditions. Fuel Process. Technol. 2010, 91 (9), 1022−1027. (36) Scala, F.; Salatino, P. Limestone fragmentation and attrition during fluidized bed oxyfiring. Fuel 2010, 89 (4), 827−832. (37) Berquerand, N.; Lyngfelt, A. The use of petroleum coke as fuel in a 10 kW(th) chemical-looping combustor. Int. J. Greenhouse Gas Control 2008, 2 (2), 169−179. (38) Adanez, J.; Gayan, P.; Celaya, J.; de Diego, L. F.; GarciaLabiano, F.; Abad, A. Chemical looping combustion in a 10 kW(th) prototype using a CuO/Al2O3 oxygen carrier: Effect of operating conditions on methane combustion. Ind. Eng. Chem. Res. 2006, 45 (17), 6075−6080. (39) Scala, F.; Montagnaro, F.; Salatino, P. Attrition of limestone by impact loading in fluidized beds. Energy Fuel 2007, 21 (5), 2566− 2572.

2655


Use of Pyrite Cinder as an Iron-Based Oxygen Carrier in Coal-Fueled

Recommend Documents