• Energy Research

Abstract The CO2 capture behavior of carbide slag as industrial waste dumped from a chlor-alkali plant in calcination/carbonation cycles was investigated in a fixed-bed reactor and a thermogravimetric analyzer, which was furthermore compared with that of hydration of CaO (Hy-CaO) and limestone. The main component of the carbide slag was the same as that of Hy-CaO which was Ca(OH)2. The effects of reaction temperature, particle size and cycle number on CO2 capture of the carbide slag were discussed. The carbide slag exhibited greater ultimate carbonation conversion than Hy-CaO and the limestone for the same number of cycles. For the same number of cycles, the calcined carbide slag had a smaller volume of pores 155 nm in diameter than the two other calcined sorbents. This was maybe a reason why the carbide slag exhibits a higher ultimate carbonation conversion than the Hy-CaO and the limestone. The cyclic carbonation conversion of the carbide slag was lower than that of the limestone before a certain time (called transition time); however, the converse result was observed after that time. It was attributed to the difference in the volume of pores

Abstract A novel calcium-based synthetic CO2 sorbent with hollow core-shell structure was prepared by a carbon microsphere template route where carbide slag, alumina cement and glucose were employed as the low-cost calcium precursor, support and carbon source, respectively. The effects of the alumina cement addition, the pre-calcination temperature during the preparation process, the carbon template addition and calcination conditions on CO2 capture performances of the calcium-based synthetic sorbents were studied during calcium looping cycles. The synthetic sorbent containing 5 wt.% alumina cement possesses the highest CO2 capture capacity during calcium looping cycles, which is mainly composed of CaO and Ca12Al14O33. The CO2 capture capacities of the synthetic sorbent under mild and severe calcination conditions can retain 0.37 and 0.29 g/g after 20 cycles, which are 57% and 99% higher than those of carbide slag under the same conditions, respectively. The synthetic sorbent possesses a hollow micro-sphere morphology with a nano-structured shell and meso-porous structure, which decreases the diffusion resistance of CO2. Periodic density functional theory (DFT) calculations are used to explain why Ca12Al14O33 can effectively retard both agglomeration and sintering of the synthetic sorbent. The hollow core-shell model is proposed to explain the CO2 capture mechanism of the synthetic sorbent. For the same CO2 capture efficiency, the energy consumption in the calciner using the synthetic sorbent is much lower than those using carbide slag and natural limestone. This work designs a good method to prepare the hollow sphere-structured synthetic sorbents with high CO2 capture capacity and provides a promising way to integrate efficient CO2 capture with the utilization of industrial waste.

The sorption-enhanced steam gasification of biomass (SEBSG) is considered a prospective thermo-chemical technology for high-purity H2 production with in-situ CO2 capture. Fundamental concepts and operating conditions of SEBSG technology were summarized in this review. Considerable industrial demonstration units have been conducted on pilot scales for large-scale availability of the SEBSG process. The influence of process parameters such as reaction temperature, Steam/Biomass (S/B) ratio, feedstock characteristics, cyclic CO2 capture capacity of CaO-based sorbents, and catalysis, were critically reviewed to provide theoretical recommendations for industrial operation. Bifunctional materials that have high catalytic activity and CO2 capture activity are crucial for ensuring high H2 production in the SEBSG. The application of density functional theory (DFT) and reactive force field molecular dynamic (ReaxFF MD) simulations on microcosmic reaction mechanisms in the SEBSG process, such as pyrolysis, WGS and reforming reactions, and CO2 capture of CaO-based materials are comprehensively overviewed. Several research gaps, like the exploitation of more efficient and low-cost bifunctional material, integrated process economics and revelation of well-rounded mechanisms, need to be filled for the following large-scale industrial applications.

Synthetic biomass-templated cement-supported CaO-based sorbents were produced by granulation process for high-temperature post-combustion CO2 capture. Commercial flour was used as the biomass and served as a templating agent. The investigation of porosity showed that the pellets with biomass or cement resulted in enhancement of porosity. Four types of sorbents containing varying proportions of biomass and cement were subject to 20 cycles in a TGA under different calcination conditions. After first series of tests calcined at 850 °C in 100% N2, all composite sorbents clearly exhibited higher CO2 capture activity compared to untreated limestone with exception of sorbents doped by seawater. The biomass-templated cement-supported pellets exhibited the highest CO2 capture level of 46.5% relative to 20.8% for raw limestone after 20 cycles. However, the observed enhancement in performance was substantially reduced under 950 °C calcination condition. Considering the fact that both sorbents supported by cement exhibited relatively high conversion with a maximum value of 19.5%, cement promoted sorbents appear to be better at resisting of harsh calcination conditions. Although flour as biomass-templated material generated significantly enhancement in CO2 capture capacity, further exploration must be carried out to find the way of maintaining outstanding performance for CaO-based sorbents under severe reaction conditions. Keywords: Calcium looping; CO2 capture; Granulation; Limestone; Biomass; Cement

Abstract In this work, a simultaneous SO2/NO removal method using pellets made of carbide slag and coal char by extrusion-spheronization process was proposed. The effects of char type, reaction temperature, O2 concentration, initial NO/SO2 concentration and the addition of supporters on the simultaneous SO2/NO removal performance of the pellets made of carbide slag and coal char were investigated in a bubbling fluidized-bed reactor. CaO derived from carbide slag not only acts as an excellent desulfurizer but also catalyzes the reduction of NO by coal char. The results show that the pellets made of carbide slag and coal char possess better simultaneous SO2/NO removal performance than the pellets made of carbide slag and bio-char. The optimal reaction temperature range for SO2/NO removal by the pellets made of carbide slag and coal char is 850−875 °C. The addition of the supporters such as Al2O3 and high alumina cement enhances the mechanical strength of the pellets. The pellets made of carbide slag and coal char seems promising for efficient simultaneous SO2/NO removal in the circulating fluidized bed decoupling combustion.

The development of reactors with varied configurations for the pyrolysis of municipal waste is discussed in this review.

Abstract The effects of manganese salts including Mn(NO 3 ) 2 and MnCO 3 on CO 2 capture performance of calcium-based sorbent during cyclic calcination/carbonation reactions were investigated. Mn(NO 3 ) 2 and MnCO 3 were added by wet impregnation method. The cyclic CO 2 capture capacities of Mn(NO 3 ) 2 -doped CaCO 3 , MnCO 3 -doped CaCO 3 and original CaCO 3 were studied in a twin fixed-bed reactor and a thermo-gravimetric analyzer (TGA), respectively. The results show that the addition of manganese salts improves the cyclic carbonation conversions of CaCO 3 except the previous cycles. When the Mn/Ca molar ratios are 1/100 for Mn(NO 3 ) 2 -doped CaCO 3 and 1.5/100 for MnCO 3 -doped CaCO 3 , the highest carbonation conversions are achieved respectively. The carbonation temperature of 700–720 °C is beneficial to CO 2 capture of Mn-doped CaCO 3 . The residual carbonation conversions of Mn(NO 3 ) 2 -doped and MnCO 3 -doped CaCO 3 are 0.27 and 0.24 respectively after 100 cycles, compared with the conversion of 0.16 for original one after the same number of cycles. Compared with calcined original CaCO 3 , better pore structure is kept for calcined Mn-doped CaCO 3 during calcium looping cycle. The pore volume of calcined MnCO 3 -doped CaCO 3 is 2.4 times as high as that of calcined original CaCO 3 after 20 cycles. The pores of calcined MnCO 3 -doped CaCO 3 in the pore size range of 27–142 nm are more abundant relative to clacined original one. That is why modification by manganese salts can improve cyclic CO 2 capture capacity of CaCO 3 .