Chemical Looping Combustion Of Coal Research Articles

Understanding the Impacts of Different Impurities on Elemental Mercury Removal by CaS in Chemical Looping Combustion of Coal: A First Principle Study.

CaSO4 has the advantages of abundant yield, high oxygen-carrying capacity, low cost, and no heavy metal pollution, making it promising as an oxygen carrier for chemical looping combustion (CLC). In comparison with other oxygen carriers, CaS as the reduced product of CaSO4 exhibits superior adsorption efficiency for Hg0 in the flue gas. In this paper, density functional theory (DFT) was used to investigate the adsorption mechanism of Hg0 on the adsorbent surface of CaS(001). The adsorption energies of different oxidized mercury species such as HgS, HgCl, and HgBr over the CaS surface were summarized. Furthermore, the effects of various flue gas components including SO2, H2S, S, HCl, Cl2, CO, H2, H2O, and C on Hg0 adsorption over the CaS(001) surface were evaluated. The results show that Hg0 can be adsorbed on the CaS(001) surface in a chemisorption manner with a reaction energy of -65.1 kJ/mol. The adsorption energy of different forms of mercury on the CaS(001) surface varies greatly, and mercury in the oxidized state is more easily captured by CaS. SO2 inhibits while other flue gas components promote Hg0 adsorption over the CaS surface. Overall, CaS tends to adsorb mercury in the reduction reactor and release mercury when CaS is re-oxidized to CaSO4 in the oxidation reactor. This is detrimental to mercury removal in the CLC of coal. This study sheds light on the migration and transformation of mercury in the CLC of coal with CaSO4 as the oxygen carrier.

Evolution mechanism of functional groups during coal chemical looping combustion

Chemical looping combustion (CLC) plays a vital role in coal combustion which released pure CO2 in the exhaust gas with low energy consumption. Researchers have developed over 1000 oxygen carriers (OCs) to enhance the properties of OCs. This study focus on the microstructural changes of coal during CLC process which could provide the performance improvement direction for OCs. Results showed that the phenolic -OH group can easily be removed by CuO while the free -OH group and the self-associating -OH group are hard to be consumed by the lattice oxygen in CuO at 800 °C, showing good stability in CLC process. Aliphatic hydrocarbons could be consumed in the gas phase rapidly. The functional group of C=O maintains high reactivity with CuO which explains why the addition of CO2 promotes the reaction rate in coal CLC. But C=C group was nonpolar bond and hard to be consumed while the -CH2 and -CH3 group and C-O-C group showed good reactivity with CuO. Higher reaction temperature affords higher reactivity of coal CLC process. But the -OH group changed slowly at higher temperature which could because that higher temperature makes the organic big molecular of the coal char decomposed and produce more -OH group.

Migration and emissions of selenium during chemical looping combustion of coal

AbstractSelenium is one of the most volatile toxic elements in coal, and its emissions must be strictly controlled. Chemical looping combustion (CLC) is a clean and efficient technology for coal. Herein, the iron‐based oxygen carrier (OC) was used as an adsorbent to study the migration and emissions of selenium during the CLC of coal. Due to the oxidation and adsorption of selenium by iron‐based OC, most of the selenium was retained in OC or distributed in the CO2 stream. The proportion of gaseous selenium released into the atmosphere was less than 10%—significantly lower than that from the traditional combustion process of coal, which had a value of 91.79%. The presence of OC increased the distribution phase of selenium, promoted the conversion of gaseous selenium to solid selenium, and reduced selenium emissions in flue gas. During CLC of coal, the fuel reactor (FR) temperature and the number of OC re‐oxidation cycles played an important role in the emissions and retention of selenium. The increasing FR temperature increased the gaseous selenium in the CO2 stream, reduced the particulate selenium absorbed by OC, and reduced the selenium emissions in the atmosphere. After 10 continuous CLC cycles, the selenium concentration in OC increased from 0.889 to 8.20 mg kg−1. The continuous cycling of CLC could realize the enrichment of selenium from coal to OC. Furthermore, the migration and transformation mechanism of selenium during CLC was deduced by experiments and thermodynamic simulation. This research provides a suitable reference for reducing selenium emissions and developing CLC technology.

Simulation and Optimization of a Multistage Interconnected Fluidized Bed Reactor for Coal Chemical Looping Combustion.

This work established a three-dimensional model of a chemical looping system with multistage reactors coupled with hydrodynamics and chemical reactions. The thermal characteristics in the chemical looping combustion (CLC) system were simulated using coal as fuel and hematite as an oxygen carrier (OC). Some significant aspects, including gas composition, particle residence time, backmixing rate, wall erosion, carbon capture rate, etc., were investigated in the simulation. Owing to the optimization by adding baffles in the fuel reactor (FR), the gas conversion capacity of the multistage FR was high, where the outlet CO2 concentration was as high as 93.8% and the oxygen demand was as low as 3.8%. Through tracing and analyzing the path of char particles, we found that the residence time of most char particles was too short to be fully gasified. The residual char will be entrained into the air reactor (AR), reducing the CO2 capture rate, which is only 80.3%. In the simulation, the wall erosion on the cyclone could be relieved by increasing the height of the horizontal pipe. In addition, improving the structure of the AR loop seal could control the residual char entrained by OC particles to the AR, and the CO2 capture rate was increased up to 90% in the multistage CLC reactor.

Behavior of coal-chlorine in chemical looping combustion

This work focuses on two aspects: (i) the behavior of coal-derived chlorine in chemical looping combustion (CLC); (ii) the potential adverse impacts of primary gaseous chlorine (i.e., HCl) on Cu-based oxygen carrier (OC). The inactivation mechanism of the sol-gel-derived CuO/Al2O3 OC is investigated. Systematic experiments are conducted in a batch fluidized reactor. First, in CLC of coal, chlorine distribution including HCl, Cl2, Cl adsorbed in the outlet tube and Cl in solid phase is studied under various bed inventories, temperatures and gas atmospheres. The main gaseous Cl from coal is HCl, which shows a high reactivity towards CuO and is partially physically adsorbed by Al2O3. Unconverted HCl is 15.63 ± 0.20%, which could result in corrosion of the CO2 transportation line and compression equipment. What's more, the coal ash exhibits a dechlorination function by forming KCl and CaCl2. The CO2 atmosphere and high temperature in fuel reactor show a promotion on the conversion of coal-Cl to HCl. Then, the corrosion of various OC components is evaluated by a mixture gas with 400 ppm HCl, i.e., Cu-Al (whole OC), CuO (active phase) and Al2O3 (inert support phase). It is found that a part of HCl is converted to Cl2 via the Deacon reaction (4HCl + O2 = 2H2O + 2Cl2) and oxidized by CuO (2CuO + 4HCl = 2CuCl + Cl2 + 2H2O). At the high concentration of HCl (400 ppm) atmosphere, CuO is partially lost from the OC, producing the gaseous copper chlorides, i.e., CuCl and (CuCl)3, which are found to be condensed in the outlet tube. Besides, the solid-phase copper chlorides also degrade the oxygen donation capacity of the OC. Finally, the migration path of coal-chlorine during CLC is summarized. This work will contribute to the development of Cl-resistance OCs and control approaches for Cl emission.

Reaction characteristics of Shenmu coal pyrolysis volatiles with an iron-based oxygen carrier in a two-stage fixed-bed reactor

The reaction of volatiles with oxygen carriers (OCs) is a common issue in the chemical looping combustion of coal or chemical looping reforming of hot pyrolysis gas. A two-stage fixed-bed reactor was used to determine the characteristics of the reaction of pyrolysis volatiles of Shenmu coal with an Fe-based OC. The effects of the oxygen/carbon ratio (O/C, φ, 0–1.31) and temperature (750–900 °C) on the three-phase products (carbon deposition, tar, and gas) were systematically studied. The results showed that an increase in φ caused a decrease in the carbon content in tar, whereas carbon deposition and the gaseous carbon content increased. Moreover, the amount of reducing gases slowly decreased while CO2 significantly increased, indicating that the increase in CO2 mainly originates from the carbon in tar. Additionally, phenols decreased fast, but naphthalene decreased rapidly at φ > 0.63. Rise in temperature decreased carbon deposition, and tar substances, whereas increased the CO content, notably, naphthalene significantly decreased only when the temperature exceeded 800 °C. The reaction of volatiles with OCs consisted of volatiles complete oxidation, tar catalytic cracking, and carbon deposition oxidation, for which the effects of the O/C ratio and temperature were evaluated.

Oxygen-Induced Elemental Mercury Oxidation in Chemical Looping Combustion of Coal.

Mercury emission is an important issue during chemical looping combustion (CLC) of coal. The aim of this work is to explore the effects of different flue gas components (e.g., HCl, NO, SO2, and CO2) on mercury transformation in the flue gas cooling process. A two-stage simulation method is used to reveal the reaction mechanism of these gases affecting elemental mercury (Hg0) oxidation. Furthermore, using this method, Hg0 oxidation by eight oxygen carriers (Co3O4, CaSO4, CeO2, Fe2O3, Al2O3, Mn2O3, SiO2, and CuO) commonly used in CLC are investigated and their Hg0 oxidation efficiencies were compared with the existing experimental results. The results show that HCl, NO, and CO2 promote Hg0 oxidation during flue gas cooling, while SO2 inhibits Hg0 oxidation. The stronger the oxygen release capacity of oxygen carriers, the higher the oxidation efficiency of Hg0 becomes. The order of Hg0 removal efficiency from high to low is Co3O4, CuO, Mn2O3, CaSO4, Fe2O3, CeO2, Al2O3, and SiO2, and this sequence is in good agreement with the existing experimental results. Different flue gas components directly or indirectly affect the O2 content, thus affecting the content of gaseous oxidized mercury (Hg2+). Different oxygen carriers have different oxygen release capacities and different Hg0 oxidation efficiencies. Therefore, O2 is the core species affecting the mercury transformation in CLC.

Transformation and Migrant Mechanism of Sulfur and Nitrogen during Chemical Looping Combustion with CuFe2O4

Chemical looping combustion (CLC) is a key technology for capturing CO2. Different types of oxygen carrier (OC) particles are used in coal CLC. The migration and transformation behaviors of sulfur and nitrogen are basically the same when CaFe2O4 and Fe2O3/Al2O3 are used as OC. CLC can be divided into two reaction stages: coal pyrolysis and char gasification; SO2 and NO show bimodal release characteristics, both of which show a basic trend of rising first and then falling down. The contents of H2S and NO2 increased rapidly at the beginning of the reaction and then decreased slowly at the stage of char gasification. H2S is released rapidly during coal pyrolysis and discharged from the reactor with flue gas, and then part of H2S is converted to SO2 during the char gasification stage by OC particles. NO can be oxidized by OC particles and form NO2. The increase in the reaction temperature and oxygen-to-carbon ratio (O/C) contributes to the release of sulfur and nitrogen and higher reaction temperature and O/C can inhibit the formation of metal sulfide. O2 released by CuFe2O4 significantly increases the contents of SO2, H2S, NO and NO2 in flue gas. This work is helpful for improving control strategies for pollutants.

Enhanced performance of red mud for chemical-looping combustion of coal by the modification of transition metal oxides

Red mud has been considered a promising candidate of low-cost oxygen carriers (OCs) for chemical looping combustion (CLC) technology due to its relatively high Fe2O3 content, but it shows poor stability during long-term redox cycling. In the present work, NiO, MnO2 and CuO are used as additives to tune the components of red mud used for the CLC of coal. The results show that the addition of NiO (e.g. 15 wt%) can significantly improve the reactivity of red mud for coal combustion, but it suffers a sharp decline after a chemical looping. In the case of MnO2, it significantly improves the selectivity for coal oxidation to CO2, which yields relatively high-purity CO2 in the combustion step. The presence of CuO in the red mud oxygen carriers obviously enhances the reactivity, selectivity and redox stability. The sample with 20 wt% CuO (20Cu-RM) shows a stable carbon capture rate with a CO2 purity higher than 90% during the long-term chemical looping process. The XRD and H2-TPR characterization results for the cycled 20Cu-RM sample shows that part of Cu element was separated from CuFe2O4 spinel structure and may act as active phase for improving redox performance.

Effects of pressure on the chemical looping combustion of coal with CuFe2O4 combined oxygen carrier

Chemical looping combustion (CLC) has fast developed as an attractive technology for clean utilization of coal as well as inherent CO2 separation at the low energy penalty. Increase of the system pressure has been acknowledged as one of the effective measures in CLC for sufficient conversion of coal along with affiliated benefits for CO2 sequestration, but the complex consequences as incurred should be well considered. In this research, reaction of a typical Chinese bituminous coal of high sulfur content (designated as LZ) with CuFe2O4 combined oxygen carrier (OC) within 0.1–3.0 MPa in the CO2 atmosphere was systematically investigated, with focus on the effect of the system pressure to the conversion of LZ coal, transfer of the oxygen involved in CuFe2O4, sulfur evolution and redistribution. Sequential reactions of CuFe2O4 with the volatiles emitted from pyrolysis of LZ coal and further reaction with the released gasification products and residual char were accomplished, which was beneficial to overcome the mass transfer limitation of the reducing gases evolved from LZ coal to OC under the pressurized conditions and alleviate the inhibition effect resulting from accumulation of the transferred reactive gases around the surroundings of OC. And thus, under the pressurized conditions, improved conversion of LZ coal was reached by oxidization of more intractable C-C/C-H groups to oxygen bound carbon groups. Meanwhile, deep reduction of the added CuFe2O4 occurred with deficient Fe3O4 at the lower valence being formed, which would interact with the silicon minerals present in LZ coal to form various iron silicates. Furthermore, sulfur evolution from coal was found to directionally interact with the reduced CuFe2O4 to mainly form solid Cu2S due to their high combination potential. And deeper reduction of Cu2S was instigated especially at 3.0 MPa with Cu1.8S formed, and the total solid sulfur fraction was increased with the elevated system pressure. Overall, comprehensive information on the interaction of coal of high sulfur content with CuFe2O4 under the extended pressurized conditions around 0.1–3.0 MPa was provided, which would be meaningful for the realistic pressurized CLC in the future.

Chemical Looping Combustion of Coal Chars Using Iron Ore of Different Grades as Oxygen Carriers

Chemical Looping Combustion of Coal Chars Using Iron Ore of Different Grades as Oxygen Carriers

Pinch combined with exergy analysis for heat exchange network and techno-economic evaluation of coal chemical looping combustion power plant with CO2 capture

A coal chemical looping combustion (CLC) power plant (600 MW) with CO2 capture was established and validated. The key operation parameters and conditions for the coal chemical looping combustion process were tested and optimized. Heat exchange network (HEN) was established and optimized using the combined pinch and exergy analysis method for matching and integrating different levels or grade energy, from flue gas and exhaust steam waste heat, in coal chemical looping combustion power plant to maximize the energy efficiency output. Followed by conducting a techno-economic evaluation and exergy distribution analysis which showed that the net energy efficiency of the CLC power plant (34.8 %, improved by 1.9 %) is 2.4 % higher than the monoethanolamine (MEA)-based ultra-supercritical coal power plant (32.4 %) with the same CO2 capture ratio (90 %). The CLC power plant also provides a lower cost of electricity (0.088–0.127 $/kWh) and less coal consumption (381 g/kWh), compared to the MEA-based power plant (0.143 $/kWh, 408 g/kWh). The cost and energy penalty of CO2 enrichment and separation are less when compared to traditional MEA-based ultra-supercritical coal power plants due to the intrinsic nature of in-suit CO2 capture, the lower exergy destruction in the chemical looping combustion process, and sufficient energy integration and recovery from HEN.

Mercury removal by Co3O4@TiO2@Fe2O3 magnetic core-shell oxygen carrier in chemical-looping combustion

Mercury pollution has received much attention due to its severe harm to human and ecological system. The major source of mercury emission is from coal combustion. In the flue gas, elemental mercury (Hg0) is the most abundant and difficult form to be removed. In the chemical-looping combustion of coal (CLCC), oxygen carrier (OC) plays the role of oxygen storage and release, and it also has catalytic ability for Hg0 removal. In this study, a magnetic material Co3O4@TiO2@Fe2O3 (CTF) with a core–shell structure was prepared by combining sol–gel and impregnation methods. The Co: Ti: Fe ratio was obtained as 1:2:4, which was optimized to achieve strong magnetism and catalytic ability. The Hg0 removal efficiency increased with the increase in temperature in the temperature range of 800–900 °C. The mercury removal efficiency of Hg0 + CTF + HCl was higher than that of Hg0 + HCl, indicating that CTF promoted the conversion of Hg0 to Hg2+/HgP. Both homogeneous and heterogeneous reaction pathways are important for Hg0 removal. CTF promotes the oxidation of Hg0 in HCl atmosphere by reacting with HCl to produce more Cl2, which is more reactive towards Hg0. Furthermore, Hg0 is adsorbed on CTF to form adsorbed Hg0 and HgO. Mercury on CTF is mainly desorbed in the form of HgO, which is beneficial for mercury removal. Ten redox cycles were applied on CTF, which still maintained a high Hg0 removal efficiency and strong magnetism. CTF can be used as a recycled OC in CLCC.

Binary-ore oxygen carriers prepared by extrusion–spheronization method for chemical looping combustion of coal

In this study, composite oxygen carriers (OCs) were prepared by the extrusion–spheronization method, using disused fine (<100 μm) iron and copper ores as raw materials. A range of inert aluminosilicates (namely diatomite, montmorillonite, rectorite, pseudo-boehmite, pumice, and attapulgite) were tested as binders to achieve uniform physical mixing of iron ore and copper ore powders in a single OC particle, one-step particle shaping, and synergistic effect between active components. Firstly, the extrusion-spheronization process was optimized to achieve a sufficient crushing strength. It was found that FeCu-10 M (72 wt% iron ore, 18 wt% copper ore, and 10 wt% montmorillonite added as a binder) and FeCu-5P (76 wt% iron ore, 19 wt% copper ore, and 5 wt% pumice) OCs showed a relatively high crushing strength (greater than 2 N). Subsequently, the coal chemical looping combustion performance tests were conducted in a batch-fluidized bed. FeCu-10 M performed better at a bed temperature of 950 °C and for an oxygen-to-fuel ratio of 2.5 to 3.1. The OC also demonstrated excellent reactivity and stability during multiple redox cycles. The X-ray diffraction (XRD) pattern revealed that no obvious interphase side reaction occurred among different components within the particles. Scanning electron microscopy (SEM) characterization indicated no obvious sintering within the particle or agglomeration between the particles. The experimental results demonstrated that the extrusion–spheronization method is suitable for large-scale preparation of OC particles. The binary-ore OCs prepared by extrusion–spheronization exhibited good performance in terms of reactivity, stability, and economy.

Sulfur release and migration characteristics in chemical looping combustion of high-sulfur coal

Chemical looping combustion of coal has attracted great attention due to its advantage in carbon capture. Sulfur in coal may have negative impacts on this process including deteriorating the reactivity of oxygen carrier and generating gaseous sulfur species. In this research, the release and migration characteristics of sulfur in the chemical looping combustion of Xinzhou coal with two synthetic oxygen carriers, CuO/SiO2 and NiO/Al2O3, were investigated by experiments and thermodynamic simulation. The thermodynamic analysis showed that sulfur in coal mainly migrated to metal sulfides at lower temperatures and peroxide coefficients, but the formation of SO2 was favored at higher temperatures and peroxide coefficients. Experimental results showed that the sulfur conversion efficiencies (XS,g) during the reduction stage reached 62.34 % and 61.25 % under Cu- and Ni-based oxygen carriers, respectively, and XS,g during the reoxidation stage were 6.25 % and 7.44 %, respectively. For both oxygen carriers, the share of H2S and SO2 in the sulfurous gases exceeded 96 % during the reduction stage, while SO2 was the only sulfurous gas when air was introduced. Even though the metal sulfides (Cu2S, Ni3S2 and NiS) were observed in the reduced samples, those two oxygen carriers showed satisfactory regeneration performance after one redox process.

Experimental and mechanistic study on chemical looping combustion of caking coal

Under high-temperature batch fluidized bed conditions and by employing Juye coal as the raw material, the present study determined the effects of the bed material, temperature, OC/C ratio, steam flow and oxygen carrier cycle on the chemical looping combustion of coal. In addition, the variations taking place in the surface functional groups of coal under different reaction times were investigated, and the variations achieved by the gas released under the pyrolysis and combustion of Juye coal were analyzed. As revealed from the results, the carbon conversion ratio and rate were elevated significantly, and the volume fraction of the outlet CO2 remained more than 92% under the oxygen carriers. The optimized reaction conditions to achieve the chemical looping combustion of Juye coal consisted of a temperature of 900 °C, an OC/C ratio of 2, as well as a steam flow rate of 0.5 g·min−1. When the coal was undergoing the chemical looping combustion, volatiles primarily originated from the pyrolysis of aliphatic CH3 and CH2, and CO and H2 were largely generated from the gasification of aromatic carbon. In the CLC process, H2O and CO2 began to separate out at 270 °C, CH4 and tar began to precipitate at 370 °C, and the amount of CO2 was continuously elevated with the rise of the temperature.

Fate of fuel‑nitrogen during in situ gasification chemical looping combustion of coal

In situ gasification chemical looping combustion (iG-CLC) was a promising way to inherently sequestrate CO2. Due to the nitrogen in coal, the NOx emission was a key issue in iG-CLC. In this study, we aimed to identify the nitrogen conversion and distribution characteristics in two elementary stages of coal conversion (pyrolysis and subsequent char gasification) during the iG-CLC process in a tailor-made two-stage fluidized bed reactor. HCN was the dominant precursor of NOx in iG-CLC, almost all the NOx precursors were rapidly released during the coal pyrolysis stage, and no gaseous nitrogen pollutant was detected within the subsequent CO2-char gasification process. The generated HCN could be completely converted by the Fe-based oxygen carrier (OC) to either NO or N2. The high CO2 concentration and reducing reaction atmosphere in the fuel reactor were found to exert certain inhibitory effects on the formation of NO. Meanwhile, the operating conditions, that is, the O/fuel ratio and temperature, exhibited insignificant effects on the fate of fuel-N. Finally, the fate of nitrogen in volatiles, char, and tar of coal during iG-CLC and the potential homogeneous nitrogen conversion in the iG-CLC of coal were proposed based on the results obtained from both experiments and thermodynamic simulations.

The evolution and desulfurization of sulfur in chemical looping combustion of coal

ABSTRACT Chemical-looping combustion (CLC) is a new technology that has gained great attention due to its advantages in CO2 capture during combustion. Sulfur in coal maybe harmful to the CLC process. The interactions between sulfur and oxygen carrier may reduce the purity of carbon captured, and affect the characteristics of the oxygen carrier. Therefore, the evolution of sulfur in Xinzhou coal and the desulfurization performance in this process were studied by using iron ore as an oxygen carrier. Experimental results showed that the main sulfur-containing component released was SO2, and the fractions of sulfur during the reduction and oxidation periods reached 64.28 and 3.91%, respectively. The addition of desulfurization agent (CaO) could control the release of sulfur and a higher molar ratio of Ca/S resulted in less emission of sulfur-containing gases. The desulfurization efficiency reached 36.61%, 50.72%, and 55.45% when the Ca/S molar ratio was 1.5, 2.0, and 2.5 respectively. Considering the investment and operation costs, the recommended molar ratio of Ca/S was 2.0. The formation of CaSO4 was confirmed after reaction, but the stability of CaSO4 and its effect on oxygen carrier over a longer period of time still need to be further studied.

Investigation of reactivities of bimetallic Cu-Fe oxygen carriers with coal in high temperature in-situ gasification chemical-looping combustion (iG-CLC) and chemical-looping with oxygen uncoupling (CLOU) using a fixed bed reactor

Bimetallic Fe-Cu oxygen carriers (OCs) with SiO2 as a support are attractive materials for coal chemical-looping combustion (CLC) based on their availability from naturally occurring, low cost materials. The objectives of this study are to investigate reduction reactivities and CO2 conversion efficiency of synthesized Fe-Cu-Si OCs for both in-situ gasification CLC (iG-CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU) at high temperatures (950 to 1100 °C) with varying ratios of OC to coal char (ϕ) using a fixed bed reactor-quadrupole mass spectrometer system. Two Cu-Fe-Si OCs with high iron content (40% Fe2O3 + 20%CuO by wt.) (Fe40Cu20) and high copper content (Fe20Cu40) were prepared using a pressure pelletizing method. Oxygen uncoupling efficiency and rate for the Fe40Cu20 OC were lower than the Fe20Cu40 OC due to their CuFe2O4 and CuO composition difference from XRD analysis. For Fe40Cu20 OC with ϕ = 80 in iG-CLC, the carbon conversion rate increased 37% from 950 °C to 1000 °C but only increased 5.4% from 1000 °C to 1100 °C. As the ratios ϕ dropped (80, 40 and 24), the CO2 conversion efficiencies decreased and the content of metallic Cu in the reduced OC residues increased. So, the optimum ratio ϕ is important to avoid agglomeration caused by Cu at high temperature. The Fe20Cu40 OC with ϕ = 67 in CLOU had higher the carbon conversion rate (dXc/dt = 0.0083 s−1) and CO2 conversion efficiency (Sco2 = 0.96) compared to the Fe40Cu20 OC with ϕ = 80 in iG-CLC (dXc/dt = 0.0037 s−1 and Sco2 = 0.88).

Study on the performance of the purified CaSO4 oxygen carrier derived from wet flue gas desulphurization slag in coal chemical looping combustion

Flue gas desulphurized slag was collected as the raw material and purified using the multiple steps of sour purification procedures, which was further prepared as CaSO4 oxygen carrier (OC). Reaction characteristics of the purified desulphurized slag OC with the selected lignite as well as release of the different gaseous sulfur species from the CaSO4 side reactions were investigated in a lab-scale fixed bed reactor. Several main influencing factors, including reaction temperature, OC excess number ϕ and the cycle numbers, were focused. The experimental results indicated that the purified CaSO4 OC was of high reactivity and promising to be applied in the coal-fueled chemical looping combustion process as OC. Furthermore, according to the pros and cons of the three influencing factors on the carbon conversion versus the gaseous sulfur release, the optimized reaction conditions were determined as 900°C and the OC excess number around 1.0. Finally, under this optimized reaction condition, the effect of the cycle numbers was evaluated and found that the continuous release of gaseous sulfur from the CaSO4 side reactions deteriorated the reactivity of the purified CaSO4 OC and its reaction stability was diminished with the five cycles.