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Abstract: Performances of calcium propionate (CP) on nitric oxide (NO) reduction are experimentally investigated on a drop tube furnace system from basic reburning (BR), Thermal De-NO x and advanced reburning (AR) and it is demonstrated to be feasible of using CP as reburning fuel. BR could supply about 80% efficiency with reburning fuel fraction (Rff) and residence time (τ) kept 20–25% and 0.7 s, respectively. Also, oxygen concentration is required to be less than 4%. However, initial NO concentration is not important to reduction. Characteristics of Thermal De-NO x are also studied. The maximum efficiency of 85.34% could be achieved at 1273 K with mole ratio of ammonia to nitric oxide (β) equaling to 1.75. The corresponding “temperature window” is 1215–1341 K. From 2% to 6% of oxygen concentration, the efficiency of Thermal De-NO x is constantly depressed by 16.17%. The performances of advanced reburning are greatly optimized and higher efficiency could be achieved using less calcium propionate and ammonia. At 1273 K, efficiency of 93.37% is supplied by AR with Rff = 19.83% and β = 0.8. Also, the corresponding “temperature window” is broadened to 1195–1355 K which is 1.27 times of the one in Thermal De-NO x at β = 1.75. Meanwhile, the impact of oxygen concentration on NO reduction is weakened in AR. [Copyright &y& Elsevier]

Graphical abstract Highlights • A bifunctional system integrating with CO 2 capture and heat storage is proposed. • Original carbide slag can be used in CaO/Ca(OH) 2 thermochemical heat storage process. • High Cl content results in low cyclic CO 2 capture capacity of carbide slag. • Hydration performance of carbide slag with Cl is improved after CO 2 capture cycles. • CaO after CO 2 capture cycles is promising to be used for heat storage. Abstract Carbide slag is an industrial waste generated from ethylene gas production in chlor-alkali plants. Here, a novel system coupling calcium looping and CaO/Ca(OH) 2 thermochemical heat storage using carbide slag were proposed to simultaneously capture CO 2 and store heat. For CaO/Ca(OH) 2 thermochemical heat storage, the hydration/dehydration performance of original carbide slag and carbide slag that experienced calcium looping cycles for CO 2 capture was investigated. The performances of the two types of carbide slag with and without chlorine were compared. The dehydration conversions of carbide slag improved with the increase of dehydration temperature. The chlorine content has no apparent effect on the hydration/dehydration performance of original carbide slag. However, for CO 2 capture, carbide slag with high chlorine content shows lower carbonation conversion than that of carbide slag without chlorine. The hydration/dehydration conversions of carbide slag that experienced CO 2 capture cycles are lower than those of original carbide slag. For carbide slag with chlorine, the hydration conversion can be improved by more than one CO 2 capture cycle. Therefore, carbide slag that experienced various CO 2 capture cycles is still suitable to be used in CaO/Ca(OH) 2 thermochemical heat storage although calcium looping has an adverse effect on the hydration/dehydration performance of carbide slag. [ABSTRACT FROM AUTHOR]

• In-situ conversion mechanism of captured CO 2 by CaO in H 2 was studied by DFT theory. • Detailed reaction paths of direct reduction of CaCO 3 to form CO and CaO by H 2. • The presence of H 2 reduces a 0.35 eV in the energy barrier for CaO generation. • H 2 addition leads to reduced C O orbital overlap and electron cloud disturbances. In-situ conversion of the captured CO 2 by CaO to CO is realized by using renewable H 2 in the calcination stage of calcium looping process, which effectively reduces the decomposition temperature of CaCO 3 and alleviates the sintering of CaO. However, the mechanism for this reaction is unclear which is difficult to determine just by experimental methods. In this work, the reaction mechanism for in-situ conversion of captured CO 2 by CaO to CO in presence of H 2 during calcium looping process was investigated by density function theory (DFT) analysis. The CaCO 3 direct decomposition was compared to clarify the effect of H 2 on CaO regeneration. The electron differential densities (EDD) and partial density of states (PDOS) for HCO 3 * and CO 3 * models were also compared. The results show the detailed reaction pathway for in-situ conversion of the capture CO 2 by CaO in presence of H 2 in the calcination stage of CaCO 3. H 2 is adsorbed on the CaCO 3 surface to form OH*, CO 2 *and HCO 3 *. CO 2 * further is decomposed into CO and O*. HCO 3 * is decomposed into CO 2 and OH*. Then, two OH* are attracted to each other to form H 2 O and O*. The CO 3 * hydrogenation is the rate control step in this reaction with energy barrier of 3.12 eV. The presence of H 2 causes a 0.35 eV reduction in the energy barrier for CaO generation on CaCO 3 surface. The overlap of C O orbitals and the disturbance of electron clouds around O atom all confirm that the addition of H 2 makes C and O atoms in HCO 3 * have small interaction energy. The DFT calculations reinforce the possible mechanism of in-situ conversion of the captured CO 2 by CaO in presence of H 2 during calcium looping process. [ABSTRACT FROM AUTHOR]

• Novel SiC/Mn co-doped CaO pellets are prepared for calcium looping heat storage. • Co-doped pellets show good heat storage capacity in multiple heat storage cycles. • Optical and thermal capacities of pellets rise by 16.6 and 2.2 times, respectively. • Co-doped pellets exhibit high crushing strength and attrition resistance in cycles. To achieve high heat storage capacity, excellent mechanical, optical and thermal properties in calcium looping thermochemical heat storage, the novel SiC/Mn co-doped CaO pellets were fabricated by the extrusion-spheronization method. The heat storage performances of the novel CaO pellets were studied under harsh calcination (pure CO 2 , 950 °C) and pressurized carbonation (pure CO 2 , 13 bar, 800 °C) conditions in a dual fixed-bed reactor system. The additions of SiC and Mn enhance the cyclic stability of CaO pellets during the multiple heat storage cycles. When the mass ratio of CaO:SiC:MnO 2 is 100:5:5, the co-doped CaO pellets exhibit an excellent heat storage performance. The effective conversion and heat storage density of the co-doped CaO pellets are 41.5% higher than those of original CaO pellets, respectively. Meanwhile, the co-doped CaO pellets possess a good optical absorption capacity and a high thermal conductivity, which are 17.6 and 3.2 times as high as those of original CaO pellets, respectively. In addition, the co-doped CaO pellets show much higher crushing strength and lower weight loss during the attrition test. The stronger interaction between SiC and CaO cluster mitigates the movement of CaO, which is determined by density functional theory simulation. The adsorption of CO 2 onto the CaO surface is enhanced by the addition of Mn. Therefore, SiC/Mn co-doped CaO pellets used in the calcium looping thermochemical heat storage process appear promising. [ABSTRACT FROM AUTHOR]

A Ca 3 Al 2 O 6 -stabilized carbide slag from calcium looping cycles for CO 2 capture was proposed as a H 2 S sorbent in zero emission carbon process. The H 2 S removal performance of Ca 3 Al 2 O 6 -stabilized carbide slag experienced different calcium looping cycles was investigated in a muti-fixed-bed reactor. The fabricated sorbent containing the mass ratio of CaO to Ca 3 Al 2 O 6 = 73:27 shows higher CO 2 capture capacity. The sulfidation temperature and H 2 S concentration exhibit the important effects on H 2 S removal by the fabricated sorbent from CO 2 capture cycles. The number of CO 2 capture cycles has a little effect on H 2 S removal by the fabricated sorbent. The sulfidation conversions of the fabricated sorbent after 100 CO 2 capture cycles at 60 and 120 min can reach 1.3 and 1.6 times as high as those of carbide slag, respectively. Ca 3 Al 2 O 6 restrains the rapid growth of CaO grains in the fabricated sorbent in CO 2 capture cycles. Compared with carbide slag, the fabricated sorbent possesses larger surface area and more stable structure during CO 2 capture cycles because of the support of Ca 3 Al 2 O 6 , so it exhibits higher sulfidation conversion. H 2 S removal using Ca 3 Al 2 O 6 -stabilized carbide slag from calcium looping cycles seems promising in zero emission carbon process. • C3A-modified carbide slag has high CO 2 uptake and stability in multiple CaL cycles. • The modified carbide slag after CO 2 capture cycles shows excellent H 2 S uptake. • C3A improves CO 2 and H 2 S removal capacities of carbide slag from CaL cycles. • CO 2 capture and H 2 S removal by modified carbide slag can be realized in ZEC process. [ABSTRACT FROM AUTHOR]