Search

The greenhouse gas emissions from the boiler of pulp and paper industries can be minimized by adapting chemical looping combustion (CLC) technology. This work aims to analyze the energy, exergy, economic, and exergoeconomic performance of an industrial scale CLC plant for district heat and electricity generation using waste bark from the paper and pulp industry. The CLC plant with one natural ore and one industrial waste oxygen carrier (OC) is modeled using Aspen Plus. The performance of the CLC plant has been compared to Örtofta combined heat and power plant without CO2 capture and with post‐combustion CO2 capture as the reference cases. Results showed that the CLC‐based power plant is energetically, exegetically, and economically efficient compared to the reference cases. The circulating fluidized bed boiler unit contributes the highest exergy destruction (about 50–80%). Among the CO2 capture plants, the CLC plant with ilmenite has the lowest levelized cost of district heat (4.58 € GJ−1), and a payback period (9.69 years) followed by the CLC plant with LD slag (5.91 € GJ−1 and 11.84 years), and the plant with PCC (6.94 € GJ−1 and 13.58 years). The exergoeconomic analysis reveals that the CLC reactors have the highest cost reduction potential, followed by the steam turbine. [ABSTRACT FROM AUTHOR]

A steel slag from the Linz-Donawitz process, called LD-slag, having significant calcium and iron-fractions, was investigated as an oxygen carrier in a recently developed 10 kW th chemical-looping combustor with three high-volatile biomass fuels. In order to improve operability, the LD-slag was found to require heat-treatment at high temperatures before being used in the unit. In total, operation with the biomasses was conducted for more than 26 h at temperatures of 870–980 °C. The fuel thermal power was in the range of 3.4–10 kW th. The operation involved chemical looping combustion (CLC), chemical looping gasification (CLG) and oxygen carrier aided combustion (OCAC). Around 12 h was in CLC operation, 13.3 h was conducted in CLG-conditions, while the remaining 0.7 h was OCAC. Here, the results obtained during the CLC part of the campaign is reported. Increased temperature in the fuel reactor and higher airflows to the air reactor both lead to better combustion performance. Steam concentration in the fuel reactor has little effect on the performance. The LD-slag showed higher oxygen demand (31.0%) than that with ilmenite (21.5%) and a manganese ore (19.5%) with the same fuel and normal solids circulation. However, with the LD-slag, there is possibility to achieve a lower oxygen demand (15.2%) with high solids circulation. [ABSTRACT FROM AUTHOR]

• Analytical reactor model is presented in detail for CLC with biomass solid fuels. • Kinetic rate constants for CH 4 , CO and H 2 with Mn ore were obtained by fluidized bed. • The analytical model was validated against 10 kW th CLC operation. • Fuel and oxygen carrier contact efficiency was estimated from the model. • Reactivity of EB manganese ore is compared with ilmenite in the analytical model. Manganese ores are promising oxygen carriers for chemical looping combustion (CLC), due to their high reactivity with combustible gases. In this work, a manganese ore called EB (Elwaleed B, originating from Egypt) is studied for its reaction rate with CH 4 , CO and H 2 and the data are used in an analytically solved reactor model. The reactivity of fresh and three used EB samples from previous operation in a 10 kW th pilot was examined in a batch fluidized bed reactor with CH 4 and syngas (50%CO + 50%H 2). In comparison with other manganese ores, the EB ore has a lower rate of reaction with CH 4 , while showing a significantly higher reactivity with syngas. Nevertheless, this manganese ore always presents a better conversion of CH 4 and syngas than the benchmark ilmenite. Mass-based reaction rate constants were obtained using a pseudo first-order reaction mechanism: 1.1·10-4 m3/(kg·s) for CH 4 , 6.6·10-3 m3/(kg·s) for CO and 7.5·10-3 m3/(kg·s) for H 2. These rate constants were used in an analytical reactor model to further investigate results from previous operation in the 10 kW th unit. According to the analytical model, in the 10 kW th operation, 98% of the char in the biomass fuels was gasified before leaving the fuel reactor, while the char gasification products (CO and H 2) have a 90% contact efficiency with the bed material. On the contrary, the volatiles have a much lower contact efficiency with the oxygen carrier bed, i.e. 20%, leading to low conversion of volatiles released. Thus, the results emphasize the importance of improving the contact between volatiles and bed material in order to promote combustion performance in the CLC process. [ABSTRACT FROM AUTHOR]

• Steel converter waste materials showed comparable reactivity for chemical looping. • Methane conversion was higher in the case of ilmenite at similar overall conversion. • Syngas fraction and H 2 /CO ratio were higher for ilmenite. • LD Slag is more prone to attrition as compared with ilmenite. • From economic point of view, LD Slag is a promising oxygen carrier for chemical looping. Two oxygen carriers were tested with respect to chemical looping combustion (CLC) and chemical looping gasification (CLG). Ilmenite, a natural ore composed mainly of iron–titanium oxide, and LD Slag, an iron-based industrial waste, were investigated at 850 and 900 °C in a continuous operation in a 0.3 kW chemical-looping reactor system using synthetic biomass volatiles as fuel. CLC and CLG conditions were simulated in the fuel reactor by changing the fuel flow rates. In the case of ilmenite the syngas yield and methane conversion increased with fuel flow rate. Consequently, the syngas to hydrocarbon ratio was higher for ilmenite. Methane conversion improved for both tested oxygen carriers with increasing the operating temperature. Oxygen release was observed in the case of LD Slag. The H 2 /CO ratio was between 0.7 and 0.8 for both oxygen carriers at the higher fuel flows. With respect to CLC, ilmenite showed higher gas conversion than LD slag. Analysis of the particles revealed that ilmenite possessed better mechanical properties and formed less dust compared to LD Slag during the continuous operation with fuel. [ABSTRACT FROM AUTHOR]

Chemical-Looping Combustion (CLC) of biofuels is a promising technology for cost-efficient CO 2 separation and can lead to negative CO 2 emissions when combined with carbon capture and storage. A potential challenge in developing CLC technology is the effects of alkali metal-containing compounds released during fuel conversion. This study investigates the interactions between alkali and an oxygen carrier (OC), CaMn 0.775 Ti 0.125 Mg 0.1 O 3-δ , to better understand the fate of alkali in CLC. A laboratory-scale fluidized bed reactor is operated at 800–900 °C in oxidizing, reducing and inert atmospheres to mimic CLC conditions. Alkali is fed to the reactor as aerosol KCl particles, and alkali in the exhaust is measured online with a surface ionization detector. The alkali concentration changes with gas environment, temperature, and alkali loading, and the concentration profile has excellent reproducibility over repeated redox cycles. Alkali-OC interactions are dominated by alkali uptake under most conditions, except for a release during OC reduction. Uptake is significant during stable reducing conditions, and is limited under oxidizing conditions. The total uptake during a redox cycle is favored by a high alkali loading, while the influence of temperature is weak. The implications for the understanding of alkali behavior in CLC and further development are discussed. • KCl aerosol particles are introduced to a fluidized bed of calcium manganite oxygen carrier particles. • Alkali is absorbed by the oxygen carrier under most studied conditions. • Alkali is released when the oxygen carrier is undergoing reduction. • Alkali uptake increases considerably with increasing gas phase alkali concentration. [ABSTRACT FROM AUTHOR]

Alkali metal-containing compounds are readily released during thermal conversion of solid fuels, and may have both detrimental and beneficial effects on chemical looping combustion. Here, we characterize alkali interactions with the inner walls of a laboratory-scale reactor under oxidizing, reducing and inert conditions at temperatures up to 900 °C. KCl aerosol particles are continuously introduced to the stainless steel reactor and the alkali concentration is measured on-line with a surface ionization detector. Aerosol particles evaporate at temperatures above 500 °C and KCl molecules rapidly diffuse to the reactor wall. Up to 92% of the alkali reaching the wall below 700 °C remains adsorbed, while re-evaporation is important at higher temperatures, where up to 74% remains adsorbed. Transient changes in alkali concentration are observed during repeated redox cycles, which are associated with changes in chemical composition of the wall material. Metal oxides on the reactor wall are partially depleted under reducing conditions, which allow for the formation of a new potassium-rich phase that is stable in a reducing atmosphere, but not under inert conditions. The observed wall effects are concluded to be extensive and include major transient effects depending on gas composition, and the implications for laboratory studies and improved experimental methodology are discussed. [Display omitted] • A flow of KCl aerosol particles is introduced to a laboratory-scale reactor and alkali concentrations are measured on-line. • Interactions between alkali and stainless steel reactor walls are strongly affected by gas environment and temperature. • Alkali-wall interactions need to be considered when studying thermal conversion processes in detail. [ABSTRACT FROM AUTHOR]

Finding a suitable oxygen carrier is crucial for the development of Chemical Looping Combustion (CLC). A new manganese ore was tested with different biomass fuels in a recently commissioned 10 kW th unit. The ore maintains the capability of generating O 2 gas in N 2 after continuous operations with the fuels, however, the concentration was relatively low within 0.45–1.0 vol% at 820 to 975 °C. Influence of temperature, solids circulation and fuel power was examined for different fuels. Temperature increase enhances the carbon capture and reduces the oxygen demand, while the solids circulation and fuel power should be carefully controlled. Using biomass char the oxygen demand can be lowered to 2.6% while the carbon capture was close to 99%. The manganese ore showed a higher reactivity than the often-used ilmenite. Thus, a decrease of 8–10% in oxygen demand was achieved by using the manganese ore in comparison to ilmenite. During the 42 h of hot operation, defluidisation was not observed. Based on the analysis of the 35 fine samples collected, the initial attrition after first hours of operation was high, but gradually decreased to a relatively stable value of 0.27 and 0.12 wt%/h for hot and fuel operations, respectively, corresponding a lifetime of 370–830 h. • A new manganese ore was tested with biomass fuels in a 10 kW th continuous CLC unit. • Repeatable O 2 gas release is found for the Mn ore before and after fuel operation. • The manganese ore shows higher reactivity than the often-used ilmenite. • Lifetime of the Mn ore is 370–830 h, higher than other already studied Mn ores. • Oxygen demand decrease of 8–10% is achieved using the Mn ore compared to ilmenite. [ABSTRACT FROM AUTHOR]

• Carbon capture efficiency is >99% for high-volatiles biomass, >94% for char fuels. • Volatiles distributor helps achieve gas conversion efficiencies of up to 95%. • Ilmenite bed material absorbs >96% of biomass fuel alkali. • AR alkali emissions are constant and independent of the fuel alkali content. • FR alkali emissions exceed AR emissions only for the straw pellet mixture fuel. Chemical looping combustion of biomass-sourced fuels (bio-CLC) is a novel bio-energy with carbon capture and storage (BECCS) technology for power and heat generation with net negative CO 2 emissions. In this study, a new 10 kW th CLC pilot designed for high-volatiles biomass fuels was commissioned with ilmenite oxygen carrier and five different biomass fuels of varying volatile and alkali content fractions. The system was tested for its ability to convert high and low volatile content biomass, while achieving high carbon capture efficiency. The new pilot achieved carbon capture close to 100% for high-volatiles biomass, and >94% for low-volatiles biomass char fuels. Furthermore, due to the implementation of a volatiles distributor, the new pilot demonstrated an improvement of up to 10 percentage points of gas conversion efficiency for high-volatiles biomass vs. the previous generation reactor. Gaseous alkali emissions were measured with a surface ionization detection system. Flue gas alkali release levels were found to rise with higher fuel alkali content. Alkali emissions were found to be approximately similar in the AR and the FR for all but the straw pellet mixture fuel (highest alkali content fuel). For the straw pellet mixture, gaseous alkali release levels in the AR were up to seven times higher than those of the FR. In all cases, over 96% of the fuel's alkalis were absorbed by the ilmenite bed material. Ilmenite's strong alkali absorption characteristics were concluded to be the key determinant of gas-phase release of biomass alkali in the conducted experiments. [ABSTRACT FROM AUTHOR]