Addition Of CaO Research Articles

Investigation of hydrogen-rich syngas production from biomass gasification with CaO and steam based on real-time gas release behaviors

Real-time gas release behaviors in biomass gasification using steam and CaO under various operating conditions were investigated by on-line gas analysis to mechanistically understand the enhanced production of hydrogen-rich syngas. Without steam and CaO, the syngas yields increased from 146.6 mL/g at 600 °C to 831.5 mL/g at 850 °C with improved cold gas efficiency (CGE) but corresponding to a low H2/CO ratio of 0.14. By introducing steam with CaO, the syngas yield further increased to > 1000 mL/g with 4 times growth in H2/CO ratio, and the CGE increased to 71.6%. The release of H2 was prolonged and intensified with the synergistic use of steam and CaO, while CH4 and CO almost unchanged. The increase in steam/biomass ratio mainly contributed to the elevated releasing rate of H2 after 6 min, and the growth in CaO dosage led to improved H2 evolutions all through the reaction period where the peak was from 33.1 mL/min∙g without catalyst to ∼100 mL/min∙g under catalyst/biomass = 2. Ternary diagram analysis indicated that CaO and steam with higher addition amount (e.g., CaO/biomass = 1, steam/biomass = 7.5) were more suitable for producing hydrogen-rich syngas with less CO2 emission and the elevated CGE. These synergistic effects were possibly due to that CaO addition in the presence of steam can catalyze the volatiles cracking and absorb CO2 to drive the chemical equilibrium of steam reforming and water gas shift reactions shifting forward, which consequently facilitated H2 formation. The current work will provide fundamentals for efficient conversion of biomass waste to high quality syngas.

Combustion performance of pulverized coal and corresponding kinetics study after adding the additives of Fe2O3 and CaO

Combustion performance of pulverized coal and corresponding kinetics study after adding the additives of Fe2O3 and CaO

Study on the multiple roles of CaO on nitrogen evolution mechanism of protein inside sewage sludge pyrolysis

The aim of this study was to clarify the multiple influence mechanisms through which Ca influences the emission of NOx precursors (NH3 and HCN) during sewage sludge pyrolysis and to establish a scientific correlation between the mechanisms and temperatures. In this study, the effects of CaO on pyrolysis kinetics and NOx precursor emission temperature of deashed sludge were estimated using Thermogravimetry-mass spectrometry. Based on this, the NH3 and HCN evolution pathways were investigated at these nitrogen emission temperatures by employing sludge protein model compounds in a self-designed all-quartz pyrolysis system. Results showed that the addition of CaO reduced the activation energy of sludge pyrolysis by approximately 0–40 kJ/mol. CaO promoted the retention of nitrogen in char and the conversion of nitrogen into gas phase while hampering its migration to tar. The Ca-fixed nitrogen in char reacted with NH3/HCN to form CaCxNy, such as CaCN2 and CaN2. Notably, results revealed the overwhelming effects of temperature on nitrogen evolution. Specifically, CaO was found to affect only the dominant reaction at the target temperature. At lower temperatures (255–350 °C), CaO promoted the conversion of protein-N to NH3 and inhibited nitrile-N decomposition to HCN in char. In contrast, at comparatively higher temperatures (490–750 °C), CaO inhibited the production of NH3 by promoting the hydrogenation of heterocyclic-N in char and the dimerization of amino acid molecules in tar, while CaO increased HCN release by promoting the dehydrogenation of amine-N in tar and ring opening of heterocyclic-N to form nitrile-N and subsequently HCN. These results would guide NOx control for obtaining energy from nitrogen-rich solid waste for industrial applications and the targeted regulation of NH3 (carbon-free hydrogen-rich fuels) utilization.

Comprehensive Combustion Performances of Water Hyacinth and Pistia stratiotes Pellet Fuels

AbstractFor efficient combustion of aquatic biomass, the effects of heating rate on the combustion and dynamic characteristics of two typical aquatic species (water hyacinth, Pistia stratiotes), and the effects of temperature and additives on ash K and Cl concentrations are studied. The two types of pellets have ignition temperatures of 252.7 and 250.3 °C, respectively. At a heating rate of 10 °C min−1, where combustion is most stable, the comprehensive combustion efficiencies reach their maximum at 4.7 × 10−6 and 2.2 × 10−6 mg2min−1°C−2, respectively. The K and Cl concentrations in the ash decrease steadily with increasing temperature, falling to 10.3% and 0.41% for water hyacinth and 11.1% and 1.85% for P. stratiotes, respectively. X‐ray diffraction (XRD)shows that abundant Ca minerals form in the ash after the addition of CaO, which inhibit KCl formation, and K and Al silicates form in the ash after the addition of kaoline, which reserve K in the ash. These findings provide a starting point for the development of efficient aquatic biomass combustion.

Sorption enhanced aqueous phase reforming of biodiesel byproduct glycerol for hydrogen production over Cu-Ni bimetallic catalysts supported on gelatinous MgO

Hydrogen production from sorption enhanced aqueous phase reforming (APR) of biodiesel byproduct glycerol was studied by Ni-based monometallic and bimetallic catalysts supported on gelatinous MgO supports. Compared with Ni-based monometallic catalyst, the H2 selectivity and glycerol conversion of the Cu–Ni bimetallic catalyst were found to be increased more than 3% and 30%, respectively. Meanwhile, higher reaction temperature was found to have higher H2 yield with lower H2 selectivity. The H2 yield using the catalyst with gelatinous MgO support was 1.25 times higher than that of calcined support. Through in-situ CO2 capture, the addition of CaO to the Cu–Ni bimetallic catalyst increased more than 58.3% and 14.4% of the H2 yield and selectivity, respectively. An analysis about liquid product component indicate that the presence of CaO promote the further cleavage of the C–C bond, which further increased the conversion of glycerol. Furthermore, it was found that the presence of CaO could also improve the stability of the catalyst through the control experiments.

Copper Stabilization in Glass-Ceramics: Effect of CaO and SiO2 on CuAlxFe2-xO4 Formation

Industrial activities discharge heavy metal-laden wastes; and copper is one of these metals that can be stabilized after ceramic sintering by Al- or Fe-containing precursors. Besides traditional precursors, Al- and Fe-containing solid wastes (e.g., sewage sludge incineration ash, coal fly ash) were found equally capable of copper stabilization when they were adopted in the reaction matrices. However, the effect of CaO and SiO2, the predominant components in most of the inorganic solid wastes, on metal transformation and stabilization has not been addressed. Therefore, a CaO-SiO2-CuO-Al2O3-Fe2O3 reaction matrix was proposed in this study, focusing on the effect of CaO and SiO2 on copper transformation and immobilization. Results showed that a single-phase CuAlxFe2-xO4 spinel solution was developed in the system without CaO and SiO2, whereas the addition of CaO led to the generation of two separate spinel phases: CuAl2O4 and CuFe2O4. Compared with CaO, the existence of SiO2 showed less impact on the phase transformation. The effect of sintering temperature and additive dosage was also illustrated in this study and the results provided useful guidance for the optimization of reaction systems to achieve beneficial utilization of solid wastes for heavy metal stabilization.

Kinetic study in selective reduction of limonitic and saprolitic nickel ore

ABSTRACT Saprolite and limonite have different behaviour in the carbothermic reduction process due to the differences in their atomic structures. This work investigates the kinetic study of these two different kinds of lateritic nickel ores. Nickel ore, coal, sodium sulfate, and calcium oxide were mixed, then pelletised into 10–15 mm diameters. The pellets were reduced with a non-isothermal condition using a muffle furnace at 950–1150 °C for 5–120 min. The reduced pellets were crushed into less than 74 µm prior to the wet magnetic separation process to obtain concentrates (ferronickel) and tailings (impurities). The result showed that the reduction rate for both lateritic nickel ores increased with the increase of reduction temperature and holding time. The Ginstling-Brouhnstein model was appropriate to describe the diffusion mechanism of the reduction process of limonite and saprolite. The activation energy in the reduction of limonite was lower than in saprolite. It indicated that the iron and nickel in magnesium silicate in saprolite have lower reducibility than the oxide structure in limonite. Modifying basicity in nickel laterite with CaO addition could also reduce the activation energy.

A new perspective on Belite-ye'elimite-ferrite cement manufactured from electrolytic manganese residue: Production, properties, and environmental analysis

In this research, the electrolytic manganese residue (EMR) based belite-ye'elimite-ferrite (E-BYF) clinker composed of 51.6 % belite, 25.6 % iron phase, 15.8 % ye'elimite and 6.5 % over-burned anhydrite phase was manufactured successfully at 1200 °C _ 30 min by utilizing EMR (45.5 %) and additional CaO and Al2O3. The existence of iron-rich and heavy metal phases was a potential driving force for achieving near complete calcination at 1200 °C _30 min. The iron ions (8.4 %) and the over-burned anhydrite phase partially replaced the Al3+ ions by entering the ye'elimite lattice and provided enough SO3 (5.9 %) to help stabilize ye'elimite and β-C2S formation, respectively. Layered double hydroxides such as AFm phase and strätlingite formed dense microstructure and improved pastes strength as a new rigid skeleton. The formation of rigid solid skeleton-flexible gel embedded co-support system provided a reliable solution for eliminating inherent strength plateau (3-day of 45.9 MPa and 60-day of 107.0 MPa). In this system, the solid-phase hydrates as the main skeleton offered sufficient rigid-supporting, while the gels hydrates as the auxiliary fluid that filled into the pores of the formed skeleton gave the adequately flexible-supporting. In addition, thepastes showed an excellent stabilization ability of heavy metals. The E-BYF system has great potential in reducing CO2 emissions (0.58 kg/kg and 1.36 kg·/MPa·m3) and cost. This work provides a new perspective for a high-quality solution to the strength plateau while achieving a high value-added utilization of EMR.

Effects of sodium aluminate and reverse osmosis brine on hydration and mechanical properties of slag

In this study, reverse osmosis brine (ROB) and sodium aluminate (NA) were used as mix water and an activator for ground granulated blast furnace slag (GGBFS), respectively, to investigate the hydration reaction and mechanical properties of the GGBFS. Samples with NA alone and a combination of NA and 5% and 10% CaO were fabricated using tap water (TW) and ROB as mix water. The addition of CaO enhanced the effect of the NA activator in increasing the strength of the samples. With the NA–CaO combination, TW samples promoted the formation of C2ASH8 and C3AH6 phases more than the ROB samples. In the ROB samples, Friedel’s salt was formed. The strength of the TW samples was lower than that of the ROB samples, attributed to the abundantly formed C3AH6 phase in the TW samples. The NA–CaO–ROB samples improved the chloride ion adsorption capacity by increasing the Ca/Si ratio of the hydration reactant. However, in the ROB samples, Friedel's salt was decomposed due to carbonation by air exposure, increasing the concentration of chloride ions in the pore solution and promoting calcite formation. The NA–CaO–ROB samples confirmed the effectiveness of NA as a new GGBFS activator and the potential of ROB as a building material.

Effect of temperature, oxygen concentration, and CaO addition on SO2 and NOx emissions during oxygen-fuel combustion of municipal sludge

Oxygen-fuel combustion is an effective and promising method of steadily minimizing municipal sludge volume at the same time exploiting available heat and falling emissions. The effects of temperature, oxygen concentration, and CaO addition on SO2 and NOx emissions from municipal sludge combustion in CO2/O2 atmosphere were systematically explored via a lab-scale electrically heated tubular furnace in this work. The results show that the minimum average emissions of both SO2 and NOx were observed at 800 °C. Compared with air, all oxygen-fuel atmospheres reduced SO2 emission, and a salient effect was observed with 30% of oxygen concentration. In contrast, the inhibition of NOx emission was inconspicuous and exacerbated in some cases. With a lower oxygen concentration (21%), CaO evidently reduced SO2 emission and 8 wt% addition performed the best. The removal efficiency of NO by CaO addition was poor and only exhibited slight inhibition with 5 wt% addition.

Size-dependent dissolution behavior of CaO in the CaO-SiO2-FeO slag system: A molecular dynamics study

In this study, the dissolution behavior of CaO particles of different sizes in CaO-SiO2-FeO slag system was investigated by molecular dynamics simulations. To quantitatively illustrate the dissolution process of the CaO particles in the slag, kullback–leibler divergence was introduced and proven to be a satisfying indicator for the dispersion extent measurement of the added CaO particles in the slag system. The change of oxygen networks and the system potential energies were also analyzed. The results show that the dissolution process of CaO particles with large sizes is longer. When the number of Ca atoms in each CaO particle is smaller than 16, the dissolution process can be neglected. With the addition of CaO in the CaO-SiO2-FeO slag system, bridge oxygen will break and turn into non-bridge oxygen and free oxygen. The homogeneity structure of CaO-SiO2-FeO slag system is barely affected by the added CaO particle sizes. However, the potential energy of the homogeneity system after CaO dissolution is relatively lower when the particle size of the added CaO is small, thus offering a more stable condition for the slag.

Hydrogen-Rich and Clean Fuel Gas Production from Co-pyrolysis of Biomass and Plastic Blends with CaO Additive.

The treatment and disposal of waste biomass and plastics are of great importance to achieve both waste management and resource recycling. In this work, pyrolysis of biomass and plastic blends were investigated to identify the influence of temperature and in situ CaO addition on the production of hydrogen-rich, HCl-free, and low tar content fuel gases. The results show that the increase in temperature and the use of CaO significantly improved both the quantity and quality of the fuel gas and mitigated the formation of tar compounds and HCl. Moreover, H2 yield was significantly improved from 0.30 to 3.68 mmol/g with the increase in temperature from 550 to 850 °C. Also, the use of in situ CaO significantly increased the H2 yield by 28–88%. The H2/CO ratio was also enhanced from 0.35 to 1.50 with the temperature increase and CaO addition. Tar removal efficiency reached approximately 70.09% with the use of CaO at 850 °C. The produced HCl gas could be effectively absorbed by CaO through dechlorination reactions to form CaClOH at a highest mitigation efficiency of 92.37%. The results could be used to develop clean and efficient treatment technologies of waste biomass and plastics.

Study on counter-flow steam gasification characteristics of biochar with Fe2O3/CaO in-situ catalysis in fixed bed

It is important to explore a relatively cheap and efficient biomass steam gasification process for the high-value utilization of biomass. Biochar was used as raw material for steam gasification, and the steam gasification of counter-flow biochar fixed bed was enhanced by the in-situ catalysis of Fe2O3 and CaO. By changing the steam flow rate and heating temperature, the operating characteristics of counter-flow gasification were explored and compared with updraft and downdraft gasification.The experimental results show that the addition of CaO in counter-flow gasification can improve the gasification intensity of biochar at lower temperature and steam flow rate. At 750 ℃, the biochar loaded with CaO at steam flow rate of 3.75 ml/min has a maximum heating temperature LHV of 11.49 MJ/Nm3. As the heating temperature increases, the hydrogen production yield gradually decreases. At temperature of 850 ℃ and steam flow rate of 3.75 ml/min, the gasification intensity of CaO loaded biochar was 66.44 % higher than that of unloaded biochar, and the gasification intensity was increased by 15.04 % by loading Fe2O3. However, the addition of Fe2O3 can improve the hydrogen production yield of biochar. At 850 ℃ gasification temperature, the hydrogen production yield is 23.25 % higher than that of biochar without catalysis.

Study on CO2 absorption-mineralization characteristics of mixed amine solution coupled with CaO and key influencing factors in mineralization process

Amine CO2 capture is an effective post-combustion carbon capture (PCC) technology, while CO2 mineral carbonation is a safe and stable method for CO2 storage. In this paper, these two methods were combined, and the CO2 absorption-mineralization performance of mixed amine solution coupled with CaO under different ratios of mixed amine solution, temperature, reaction time and CaO addition ratio were studied by using MEA/MDEA mixed amine solution as the CO2 absorbent and using CaO as the CO2 mineralizing raw material. The results show that CaO could effectively mineralize the CO2 absorbed in MEA/MDEA solution, realizing the regeneration of MEA/MDEA solution simultaneously under normal temperature and pressure. Meanwhile, the MEA/MDEA solution can still maintain a high CO2 conversion rate (77.4%) and CO2 cycle loading (1.03 mol/L) after five cycles of absorption-mineralization experiments. The FT-IR and XRD analyses reveal that the addition of CaO makes a large amount of Ca2+ and OH− into the MEA/MDEA solution, which could react with and protonated amine in the solution to form calcium carbonate precipitate and free amine respectively, thus realizing the mineralization of CO2 and the regeneration of MEA/MDEA solution. The main component of solid products obtained is calcium carbonate, and calcite is its main crystal form.

Products distribution and sulfur fixation during the pyrolysis of CaO conditioned textile dyeing sludge: Effects of pyrolysis temperature and heating rate

Textile dyeing sludge (TDS) is a typical industrial solid waste whose amount surged with the textile industry's development. Pyrolysis treatment is a promising technique for TDS to realize harmless disposal and resource reuse. However, the high content of organic compounds would cause sulfurous pollutants emission, reducing the economic feasibility during pyrolysis. This study aimed to fill the knowledge gaps about the thermal behavior, products distribution, kinetics, and sulfur transformation during TDS pyrolysis in 350–575 ℃ with the heating rate of 60, 600, and 6000 ℃/min, then investigate the sulfur fixation effect of CaO under representative conditions (350 ℃, 650 ℃ with 60 ℃/min, 6000 ℃/min). The primary decomposition stage of TDS is observed in 127–557 ℃, following the Avrami-Erofeev (n = 3) model, while the activation energy presents a convergent tendency with the increased heating rate. The pyrolysis temperature and heating rates impact the cracking of organic compounds, while a weakening effect is found for the sulfur distribution. CaO addition could efficiently realize sulfur fixation in char by absorbing sulfurous gas products, but SO2 escape appeared with the increased CaO fraction. Pyrolysis condition at 650 ℃-60 ℃/min with 10 wt% CaO addition is recommended to achieve high sulfur retention, and the sulfur transformation mechanism in char during the TDS pyrolysis with and without CaO is proposed. Our findings provide novel and fundamental insights into the efficient disposal and pollution control during TDS pyrolysis.

CaO-assisted hydrothermal treatment combined with incineration of sewage sludge: Focusing on phosphorus (P) fractions, P-bioavailability, and heavy metals behaviors

Dewatering of sewage sludge (SS) was the prerequisite for saving its drying energy and sustaining its stable combustion. Hydrothermal treatment (HT) has been a promising technology for improving SS dewaterability with high energy efficiency. However, the knowledge of phosphorus (P) transformation and heavy metals (HMs) behaviors in the combined HT and incineration process was still lack. P fractions, P-bioavailability, HMs speciation, and their environmental risk in the ash samples from this combination process were evaluated and compared with those from the co-incineration of SS and CaO. The combination process was superior to the latter one in the light of P and HMs. CaO preferred to enhance the transformation of non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP) initially with enriched P and increased P-bioavailability in the resultant ash samples. The combination process further reduced the values of risk assessment code and individual contamination factor with the increment of the stable F4 fraction in HMs. Significant reduction of potential ecological risk was observed with the lowest global risk index of 43.76 in the combination process. Optimum CaO addition of 6% was proposed in terms of P and HMs. The work here can provide theoretical references for the potential utilization of P from SS to mitigate the foreseeable shortage of P rocks.

Sorption-enhanced steam gasification of fine coal waste for fuel producing

Improving the quality of syngas from fine coal waste using the sorption-enhanced gasification process is a novel technology in the production of H2. The effect of CaO on CO2 absorption and H2 increase in the steam fine coal gasification process was determined in a fixed bed gasifier. The steam gasification process took place at 650 °C using bentonite and CaO as catalysts and absorbents. Steam increased the H2 concentration in the syngas to 58 vol%. In-situ CO2 absorption is more effective with the addition of CaO. The maximum percentage of CO2 was absorbed when the Ca/C ratio 2 was 78.33 %. The H2 content in the syngas after the CO2 was absorbed increased rapidly to 75.80 vol% at a Ca-to-carbon-mole ratio (Ca/C) of 1.5 and a steam-to-feedstock ratio (S/F) of 1.5. CaO did not produce significant results for low heating value (LHV) or cold gas efficiency (CGE), with results of 12 MJ/Nm3 and 44.53 %. The dominant water gas shift reaction due to the influence of steam and CaO increased H2/CO up to 9.11, which made the syngas from this work suitable for Fischer–Tropsch synthesis.

H 2 -rich syngas production by sorption enhanced steam gasification of palm empty fruit bunch

Hydrogen-rich syngas from palm empty fruit bunch has been produced using CaO and bentonite as absorbent and catalyst. The gasification process is carried out at 550–750 °C at atmospheric pressure in the fixed bed gasifier with steam to biomass ratio (S/B) of 0–2.5 and Ca/C ratio of 0–2. The results showed that CaO only acts as CO 2 absorbent during the process. Increasing the ratio of Ca/C and S/B has increased the concentration of H 2 and absorption of CO 2 in the syngas. The addition of CaO did not significantly increase the production of CH 4 and CO in the syngas. The H 2 concentration reaches about 78.16 vol% at 700 °C and Ca/C 2.

Long-Term Stabilization/Solidification of Arsenic-Contaminated Sludge by a Blast Furnace Slag-Based Cementitious Material: Functions of CaO and NaCl.

Arsenic is a kind of element widely distributed in the environment that may pose a threat to the ecological environment and human health, while effective remediation and sustainable utilization of arsenic-containing sludge is a challenge. Based on stabilization/solidification blast furnace slag-based cementitious materials (BCMs), this study innovatively proposes to improve the arsenic (As) solidification efficiency and long-term stability by using the activation mode of CaO and NaCl. The effects of different factors on the properties of the BCM were measured by unconfined compressive strength (UCS) tests, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The long-term stability and safety of the BCM were verified by leaching toxicity and improved three stage continuous extraction method (BCR) tests. Experimental results show that the addition of CaO provides conditions for the formation of ettringite (AFt), thus promoting the crystal growth of AFt. The addition of NaCl can promote the formation of Cl-AFt and play a good long-term stabilizing role. When the content of the alkali activator is 10% and the modulus is 1.0, the contents of CaO and NaCl are 10 and 1%, respectively. The BCM has the best efficiency in terms of UCS and As solidification. The UCS at 28 days was 5.4 MPa, and the leaching concentration of As was 0.309 mg/L, and the As solidification efficiency was up to 99.9%. In the improved BCR test, the proportions of residual and oxidizable states of arsenic increased by 19.6 and 13.5%, respectively, and the stability of heavy metals improved. These findings show that the BCM has good long-term stability and safety. Overall, this study shows that CaO and NaCl significantly increase the output of AFt and achieve the purpose of efficient and stable solidification of As by the BCM.

Efficient and stable Pt/CaO-TiO2-Al2O3 for the catalytic dehydrogenation of cycloalkanes as an endothermic hydrocarbon fuel

The dehydrogenation of liquid hydrocarbon fuel is a potential endothermic reaction for the regenerative cooling of advanced aircraft. The high active and stable dehydrogenation catalyst plays a vital role in the catalytic heat exchange process. Herein, we show that a CaO-modified TiO2-Al2O3 supported Pt catalyst (Pt/CTA) is efficient and stable for the dehydrogenation of cycloalkanes (methylcyclohexane and decalin) under a supercritical condition. Adding an appropriate content of CaO (5 wt%) improves the catalyst durability. For the decalin dehydrogenation reaction (600 °C, 4 MPa, and WHSV = 208.8 h−1), the Pt/CTA maintains 27.9 wt% conversions at 600 min. For the methylcyclohexane dehydrogenation reaction (600 °C, 4 MPa, and WHSV = 188.4 h−1), the Pt/CTA maintains 42.6 wt% conversions at 600 min. The declines of cycloalkanes dehydrogenation conversion are < 7.0 % within 600 min, and no obvious sintering of Pt particles is observed. For a comparison, γ-Al2O3 supported Pt catalyst (Pt/A) exhibits poor catalytic activity and stability, and the conversion decreases to below 10 wt% at 180 min due to severe coke deposition and sintering of Pt particles over the catalysts. The characterization analyses demonstrate that the addition of CaO facilitates the formation of oxygen vacancy defects, thereby increasing the electron density of Pt particles (electronic effect) and promoting encapsulation of Pt particles (geometric effect). Furthermore, the addition of CaO reduces the acid amount and weakens the strength of acid sites over TiO2/Al2O3, inhibiting catalyst deactivation by mitigating coke formation. However, excessive CaO addition (10 wt%) rapidly decreases the surface area of the support, resulting in low dispersion and sintering of Pt particles, ultimately leading to poor catalytic activity and stability.