Carbonation Kinetics of Ca(OH)2 Under Conditions of Entrained Reactors to Capture CO2

Enhancement of H2 and light oil production and CO2 emission mitigation during co-pyrolysis of oily sludge and incineration fly ash

The proper treatment and utilization of oily sludge (OS) and incineration fly ash (IFA) remains a significant challenge due to their hazardous nature. To attain effective recovery of petroleum hydrocarbons and synergistic disposal, this study investigated the co-pyrolysis of OS and IFA, resulting in successful energy recovery, CO2 mitigation, and heavy metal immobilization. Results revealed that the peak ratio of light oil to heavy oil fractions reached 179.42% with 20 wt% IFA addition, accompanied by the highest aromatic hydrocarbons selectivity of 30.72% and the lowest coke yield of 106.13 mg/g OS under the optimal temperature of 600 °C. In-depth analysis indicated that IFA inhibited the poly-condensation of macromolecular PAHs and promoted their cracking into light aromatic hydrocarbons. The addition of 50 wt% IFA significantly increased H2 yield (21.02 L/kg OS to 60.95 L/kg OS) and facilitated CO2 sequestration due to its higher content of Ca-bearing minerals. Moreover, high IFA ratios promoted the reduction of Fe species in OS to a low-valence state. Heavy metals in co-pyrolysis char were well immobilized into stable fractions with lower environmental risks. This work highlights the potential of co-pyrolysis as a viable approach for simultaneous disposal of multiple hazardous wastes and offers new insights for their utilization.

Mechanochemical synthesis of calcium-biochar for decontamination of arsenic-containing acid mine drainage

Ca-biochar is an efficient material for As(III)-containing acid mine drainage (AMD) decontamination, while it is challenging to fabricate Ca-biochar with oyster shell waste as the Ca source due to its complex structure. Herein, a mechanochemical method was proposed to activate oyster shell waste and wood waste for Ca-biochar design and production, and its efficacy and relevant mechanisms for AMD detoxification were evaluated. The smaller size Ca-biochar produced by the medium-speed ball milling showed a higher As(III) removal (74.0 %) compared to high-speed ball milling (60.9 %), attributed to the formation of finer Ca(OH)2 while avoiding particle aggregation, which could release more Ca (89.0 mg/g) and alkalinity for the co-precipitation of As. Meanwhile, wood-based biochar substrate served as a platform for co-precipitation, and its surface functionality supported the oxidative immobilization of As. This study presents a promising route for upcycling food and wood waste to produce Ca-biochar for AMD decontamination.

Analysis of Operation Conditions of Ca(OH)2 Entrained Carbonator Reactors for CO2 Capture in Backup Power Plants

The share of renewables in the energy sector is increasing, and energy storage and backup power combustion systems to cover the periods of time with low renewable energy production are becoming increasingly needed. Flexible calcium looping configurations based on the storage of solids are a promising alternative to capture the CO₂ produced in such backup combustion systems. The use of Ca(OH)₂ instead of CaO is better suited to these applications due to the faster reaction kinetics and higher carbonation conversions as Ca(OH)₂ in powder form can achieve conversions of up to 0.7 in just a few seconds at temperatures of 550-650 °C. To take advantage of these fast reaction kinetics, compact carbonator reactors with short gas-solid contact times (i.e., a few seconds) can be designed. However, the low enthalpy of the carbonation reaction of Ca(OH)₂ makes it challenging to find the optimum conditions which maximize the CO₂ capture efficiency. In this work, a basic entrained reactor with recent experimental reaction kinetics has been used to determine suitable operational windows for this kind of carbonator. CO₂ capture efficiencies above 90% can be achieved for flue gases with low CO₂ concentrations (4%_v CO₂) when they are fed into the carbonator at temperatures of around 500-600 °C while maintaining low F _Ca/F _CO2 ratios (<2) and feeding the sorbent at ambient temperature. When capturing from a flue gas with a higher CO₂ concentration (14%_v CO₂), the sorbent needs to be fed at higher temperatures to effectively capture CO₂ in short contact times (i.e., 6 s).