Enhancement of methane storage on activated carbons in the presence of water

Methane storage was studied on the wet activated carbons by hydrate formation in the mesopore structures. Coconut shell was used as a raw material for preparation of the activated carbon samples. These highly mesoporous samples were prepared by the combination of both physical and chemical activation processes. After wetting the adsorbents with a constant water/carbon weight ratio (R) close to 1, the isotherms were obtained at 2°C up to the pressure of 80 bars. Wetted carbons exhibited stepwise isotherms at the critical pressure in the pressure range of 25–50 bars depending on the activated carbon samples. At this critical pressure, hydrate formation took place slowly. The amounts of methane uptake at 80 bars were obtained ranging from 14.9 to 24.8 mmol.g^–1 based on the dry adsorbent for different samples. By considering the density of activated carbon samples, the amounts of methane storage varied in the range of 185–237 V/V.     

The effects of sub-critical and super-critical carbon dioxide adsorption-induced coal matrix swelling on the permeability of naturally fractured black coal

Swelling of the coal matrix with the adsorption of CO₂ is one of the leading problems for CO₂ sequestration in deep coal seams as it causes coal seam permeability to be significantly reduced. The main objective of this study was to investigate the effect of coal mass swelling on the permeability of naturally fractured black coal. A series of permeability tests were conducted using a newly developed tri-axial apparatus on 38 mm by 76 mm naturally fractured black coal specimens. These tests were carried out for CO₂ and N₂ injections at 2-20 MPa injection pressures under 10 to 24 MPa confining pressures at 33 °C. Each coal specimen was then allowed to swell under sub-critical and super-critical CO₂ adsorption and the corresponding effects on CO₂ and N₂ permeabilities were examined. Results indicate that the permeability of naturally fractured black coal is significantly reduced due to matrix swelling, which starts as quickly as within 1 h of CO₂ injection. A further reduction is then observed, and the maximum swelling rate occurs within the first 3-4 h of CO₂ adsorption. The amount of coal matrix swelling due to CO₂ adsorption clearly depends on the phase condition of the CO₂, and super-critical CO₂ adsorption-induced swelling is about two times higher than that induced by sub-critical CO₂ adsorption. Interestingly, although a fractured coal specimen which has already fully swelled under sub-critical CO₂ adsorption can swell significantly more under super-critical CO₂ adsorption, after swelling under super-critical CO₂ adsorption, no further swelling effect occurs under any CO₂ pressure or phase condition. Moreover, the swelling process continues longer under super-critical CO₂ adsorption. It is concluded that super-critical CO₂ adsorption can induce more matrix swelling than sub-critical CO₂ adsorption under the same adsorption pressure.     

Thermodynamic equilibrium analysis of steam methane reforming based on a conjugate solution of material balance and law action mass equations with the detailed energy balance

Thermodynamic equilibrium analysis of the steam methane reforming (SMR) process to synthesis gas was studied. For this purpose, the system equations of the material balance and the equations of law mass action were solved by dichotomy method. The investigation was performed for a wide range of operational conditions such as a temperature, pressure, and inlet steam-to-methane ratio. The results obtained, with the help of developed algorithms, were compared with the results obtained via different commercial and open-source programs. All results are in excellent agreement. The operational conditions for the probable formation of carbon were determined. It was established that for the temperature range above 1100 K, the probability of carbon formation is absent for steam-to-methane ratio above units. In order to determine the amount of heat supplied per 1 mol to the reformer, the heat balance equation was obtained to achieve a targeted degree of methane conversion. With the help of the heat balance equation, it was established that the resulting transformation of substances in the steam methane reformer can be presented as a sequential heating of feed streams of methane and steam from the inlet temperature T₁ to the outlet temperature T₂, heat for SMR reaction at the temperature T₂, and heat for transformation of the part of the produced carbon monoxide (CO) via the water-gas shift (WGS) reaction at the temperature T₂. The presented algorithm of thermodynamic analysis gives an appearance of the dependence of the product composition and the amount of required heat from operating conditions such as the temperature, pressure, and steam-to-methane ratio.     

Effect of Ni precursor salts on Ni-mayenite catalysts for steam methane reforming and on Ni-CaO-mayenite materials for sorption enhanced steam methane reforming

In view of climate change containment, sorption enhanced steam methane reforming (SESMR) appears as an interesting production route for H₂ with the additional advantage of CO₂ capture application performed by high-temperature solid sorbents. CaO is largely employed as CO₂ sorbent because of its low-cost mineralized forms (limestone and dolomite), of its high sorption capacity in the high temperature range compatible with steam methane reforming (SMR). Many recent studies have proposed purposely synthesized Ni-based reforming catalysts, used with high-temperature CO₂ solid sorbents, or combined sorbent-catalyst materials (CSCM). For this last purpose, we studied the effect of Ni salt precursor (Ni nitrate hexahydrate or Ni acetate tetrahydrate) on properties and reactivity of Ni-mayenite catalysts or Ni-CaO-mayenite CSCM, synthesized by an already validated sequence of wet mixing (for sorbents synthesis) and wet impregnation (for catalysts and CSCM synthesis) methods. Although Ni acetate tetrahydrate was often reported as the best choice to improve textural properties, our study identified Ni nitrate hexahydrate as a definitely more suitable precursor than Ni acetate tetrahydrate in the purpose of developing efficient materials for SESMR. The dissimilar behaviors observed in reforming reactivity are related and explained by the differences in textural properties, Ni species dispersion, and reducibility.     

煤层气发动机CO排放量数值模拟及试验

根据化学反应动力学原理,建立了火花点火武变组分煤层气发动机CO的生成模型,该模型由碳氢燃料高温氧化生成CO以及CO在火焰中及火焰后氧化两部分组成。以MATLAB程序设计语言为应用平台,对CO的瞬时排放量进行了模拟计算,得到了发动机缸内CO的变化规律。同时,计算和分析了煤层气组分变化对CO排放的影响,并与实验结果进行了比较。研究结果证实．所建立的CO排放模型是合理的。理论和试验结果表明,提高煤层气中的甲烷浓度和发动机的负荷有利于降低发动机的CO排放量。     

Improvement of hollow cylinders on the conversion of coal mine methane to hydrogen in packed bed burner

Coal mine methane (CMM) combustion in the porous media burner (PMB) of boiler system contributes to the simultaneous production of hydrogen and heat, and the hydrogen can be used as the main raw materials for solid oxide fuel cell (SOFC). In this study, the double-layer burners were built by filling the downstream with the hollow cylinders of different sizes and pore numbers due to the high porosity of hollow-structure units compared with the common packed bed of pellets. The distributions of temperature, species concentration and reforming efficiency were obtained on the consideration of operating condition and preheating temperature. Results shows that the reforming efficiency of the 10-6-10 mm cylinder burner was optimal in all one-pore cylinder burners with the highest concentration of 12.3% (H₂) and 8.8% (CO). As for the packed bed of 8 mm cylinders, the four-pore cylinder burner showed the highest peak temperature and maximum yields of hydrogen. With the increasing of preheating temperature, the stabilization time of the flame propagating decreased. Moreover, the peak temperature and reforming efficiency increased with the increasing of the inlet velocity and the largest efficiency of 54.2% appeared at the velocity of 18 cm/s in the 10 mm cylinder burner.     

Effect of pressure equalization on methane enrichment from stranded natural gas using PSA with amorphous Kenaf and microporous palm kernel shell adsorbents

Improvement of quality fuels has gained traction as a result of growing demand for higher quality fuels because of health concern, environmental issues and tighter emission control by regulatory bodies. Low quality, unprocessed fuels produce household air pollution on burning that can be fatal. In this work, Kenaf and palm kernel adsorbents were used in pressure swing adsorption to enrich methane from stranded natural gas containing extraordinarily high carbon dioxide content of 70 vol%. Microporous palm kernel activated carbon from this work was found effective in methane enrichment process to produce better quality fuel that met the gas pipeline quality standard. Methane with 85.0% purity and 94.2% recovery was achieved at 1 minute of adsorption time due to the methane flow-through and effective carbon dioxide retention. Increased adsorption time of higher than 1 minute resulted in the reduction of both purity and recovery of the gases due to the delayed cross-over of methane. Methane compression at three bars consumed 10.0 kJ/min out of 33.0 kJ/min. Methane expansion released 8.0 and 2.0 kJ/min from methane and carbon dioxide rich stream, respectively during blowdown. The total entropy change from the compression and expansion of the gas was nil, suggesting that the process induced no disorder to the surrounding. Pressure swing adsorption with equalization mode reduced the methane purity to 76% and carbon dioxide recovery to 70% but increased the methane recovery to almost 100% and carbon dioxide purity to 97% in a criss-cross procession.     

Grand Canonical Monte Carlo simulations of hydrogen adsorption on aluminophosphate molecular sieves

The hydrogen adsorption simulations were carried for several model AlPOs (VPI-5, AlPO-5, AlPO-11 and AlPO-25) employing the Grand Canonical Monte Carlo (GCMC) simulations at 77 K to investigate the effect of pore size and the pore volume on the hydrogen uptake. The adsorption capacity showed no relationship with the pore size, surface area and micropore volume of AlPOs. However, the adsorption capacity per unit micropore volume increased as the pore size decreases. The heat of adsorption also increased as the pore size decreases. For all model AlPOs, the hydrogen exists homogeneously near the oxygen atoms in the framework.     

Enhancement of heat recirculation on the hysteresis effect of catalytic partial oxidation of methane

The hysteresis characteristics of catalytic partial oxidation of methane (CPOM) in a Swiss-roll reactor are predicted numerically by varying Damköhler number. Particular attention is paid to the influences of heat recirculation, gas hourly space velocity (GHSV), and atomic O/C ratio on the hysteresis loop and performance of CPOM. The reactions of methane combustion, steam reforming, and CO₂ or dry reforming are simultaneously considered. The results reveal that preheating reactants through excess enthalpy recovery is conducive to the ignition of CPOM and extending its extinction limit, so the ignition and extinction Damköhler numbers are lowered. The analysis also suggests that steam reforming is more sensitive to the heat recovery than methane combustion and dry reforming. An increase in GHSV reduces the residence time of reactants in the catalyst bed, thereby enlarging the ignition and extinction Damköhler numbers of CPOM. A higher O/C ratio facilitates the ignition of CPOM, stemming from more oxygen supplied, but the ratio should be controlled below 1.2. From the hysteresis phenomena, hydrogen can be produced from methane at a lower Damköhler number to save more energy for performing CPOM.     

Effects of H2 or CO2 addition, equivalence ratio, and turbulent straining on turbulent burning velocities for lean premixed methane combustion

Using hydrogen or carbon dioxide as an additive, we investigate the bending effect of turbulent burning velocities (ST/SL) over a wide range of turbulent intensities (u^′/SL) up to 40 for lean premixed methane combustion at various equivalence ratios (?), where SL is the laminar burning velocity. Experiments are carried out in a cruciform burner, in which a sizable downward-propagating premixed CH₄/diluent/air flame interacts with intense isotropic turbulence in the central region without influences of ignition and unwanted turbulence from walls. Simultaneous measurements using the pressure transducer and pairs of ion-probe sensors at various positions of the burner show that effects of gas velocities and pressure rise due to turbulent combustion on ST of lean CH₄/H₂/air flames can be neglected, confirming the accuracy of the ST data. Results with increasing hydrogen additions (δ=10, 20, and 30% in volume) show that the bending of ST/SL vs u^′/SL plots is diminished when compared to data with δ=0, revealing that high reactivity and diffusivity of hydrogen additives help the reaction zone remaining thin even at high u^′/SL. In contrast, the bending effect is strongly promoted when CO₂ is added due to radiation heat losses. This leads to lower values of ST/SL at fixed u^′/SL and ?, where the slope n can change signs from positive to negative at sufficiently large u^′/SL, suggesting that the reaction zone is no longer thin. All ST data with various δ can be well approximated by a general correlation (ST−SL)/u^′=0.17Da^0.43, covering both corrugated flamelet and distributed regimes with very small data scatter, where Da is the turbulent Damköhler number. These results are useful in better understanding how turbulence and diluents can influence the canonical structures of turbulent premixed flames and thus turbulent burning rates.     

Strategic planning on carbon capture from coal fired plants in Malaysia and Indonesia: A review

Malaysia and Indonesia benefit in various ways by participating in CDM and from investments in the GHG emission reduction projects, inter alia, technology transfer such as carbon capture (CC) technology for the existing and future coal fired power plants. Among the fossil fuel resources for energy generation, coal is offering an attractive solution to the increasing fuel cost. The consumption of coal in Malaysia and Indonesia is growing at the fastest rate of 9.7% and 4.7%, respectively, per year since 2002. The total coal consumption for electricity generation in Malaysia is projected to increase from 12.4 million tons in 2005 to 36 million tons in 2020. In Indonesia, the coal consumption for the same cause is projected to increase from 29.4 million tons in 2005 to 75 million tons in 2020. CO₂ emission from coal fired power plants are forecasted to grow at 4.1% per year, reaching 98 million tons and 171 million tons in Malaysia and Indonesia, respectively.