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1.
In this work, a Fe/Mg-bearing metallurgical waste (upgraded slag oxide, UGSO) was, for the first time, investigated as a stabilizer for increasing the cyclic stability of CaO-based sorbents. The sorbents were prepared through the wet mixing of the ball-milled UGSO particles with the limestone-derived calcium citrate under sonication. The sorption capacity of samples containing different waste loadings (5, 10, 15, and 25 wt%) was studied for 18 carbonation/regeneration cycles under conditions similar to the sorption-enhanced glycerol steam reforming process. A significant improvement of the cyclic stability was observed for all doped sorbents; however, the sample with 10 wt% UGSO showed the highest sorption capacity among all tested samples. This optimum sorbent was further used to synthesize a UGSO stabilized CaO–NiO hybrid sorbent-catalyst material (20 wt% NiO loading), whose performance was tested in sorption-enhanced steam reforming of glycerol. A H2 purity of around 95% was obtained in the pre-breakthrough period that lasted for about 30 min. In summary, the results showed a better stability of UGSO stabilized sorbents compared to pure CaO and a good performance of the CaO-UGSO10/NiO sorbent-catalyst hybrid material in the sorption-enhanced reforming process.  相似文献   

2.
This work proposes the production of high-purity hydrogen by an intensified non-isothermal sorption-enhanced bio-oil steam reforming (SEBOSR) process, by combining the bio-oil steam reforming over a Ni/La2O3-αAl2O3 catalyst and in-situ CO2 adsorption over Li2CuO2. The kinetics of CO2 adsorption on Li2CuO2 was studied experimentally and applied to assess the performance of SEBOSR in a fixed bed reactor via a non-isothermal mathematical model. Model simulations show that the prebreakthrough stage of the SEBOSR process, which corresponds to high purity H2 production, can be extended by increasing the adsorbent loading and the S/C ratio, as well as by decreasing the inlet gas velocity. Increasing inlet temperature generates longer prebreakthrough step times but leads to a reduction in hydrogen purity. This intensified process allows to diminish the catalyst deactivation, which ultimately only occurs in the inlet region of the packed bed to some extent. In addition, SEBOSR indirectly uses sustainable CO2-neutral biomass as a source of hydrogen; highly pure and renewable H2 can be produced in one step (without the need of additional gas purification), via a process with enhanced thermal efficiency.  相似文献   

3.
The concentration of CO in the high-purity hydrogen from sorption-enhanced steam reforming (SESR) processes is usually too high to be directly used in fuel cells. Herein, we report a production of fuel-cell grade H2 with <30 ppm CO through SESR of glycerol (SESRG), a by-product of biodiesel manufacture. High purity H2 can be produced by employing a catalyst-sorbent hybrid material composed of Ni as catalyst, CaO as CO2 sorbent and Ca12Al14O33 as spacer. By introducing copper as promoter, the performance of the bi-functional catalyst could be modified to produce a 97.15 vol% purity of H2 with 28 ppm CO. With an optimized Ni/Cu ratio, the 7.5Ni–7.5Cu catalyst shows the excellent stability for producing about 97% H2 with <30 ppm CO for ten cycles. The characterizations and model reaction tests indicate that copper can affect CO, CO2 hydrogenation and water gas shift reaction to adjust the performance of SESRG reaction. The results presented here show the promise of tuning the catalyst composition for achieving high quality H2 through SESR processes.  相似文献   

4.
The transient chemical reaction phenomena of the sorption-enhanced steam methane reforming (SE-SMR) by using Ni/Al2O3 catalyst and CaO sorbent in a tubular fixed-bed reactor were numerically investigated by an experimentally verified unsteady 2D model. Four chemical reactions are involved in SE-SMR including steam reforming (SR), water gas shift (WGS), global steam reforming (GSR), and CO2 sorption. The reaction process in time is divided into period 1, transient period, and period 2. The high-purity H2 is produced in period 1 which is defined as the outlet molar fractions of H2 ≥ 90% and CO ≤ 1% (dry basis) in this work. In the first half of period 1, the endothermic reaction rates of SR and GSR are dominant in the entrance region of catalyst/sorbent bed. The WGS and CO2 sorption reactions are triggered by SR and GSR reactions. The heat transfer from the wall plays an important role. Higher CaO conversion, temperature, and reaction rates appear first near the wall region, then they gradually expand to the central region.In the second half of period 1, a sharp wave-shaped curve of strong CO2 sorption reaction occurred in downstream becomes dominant and it moves to downstream almost at a constant speed, as time progresses. The peak value of the CO2 sorption reaction is more than twice larger than that of SR or WGS. The SR and WGS reaction rates are significantly enhanced by CO2 sorption reaction. The great sorption, WGS, and SR reactions result in a high-purity H2 production with the outlet molar fractions of 95.8% H2, 0.998% CO, and 0.73% CO2 at the end of period 1, based on the parameters used in this work such as reactor temperature of 600 °C. The maximum CaO conversion is about 76% in end of period 1 and the average CaO conversion in the reactor is 51%. The 2D distributions of CaO conversion, temperature, and reaction rates are also presented and discussed.  相似文献   

5.
This work presents the effect of calcium and carbonate precursors on properties of CaCO3. The synthetic CaCO3 samples were transformed into CaO and tested their application to high-temperature CO2 capture. Four different sorbent precursors were investigated in this work, including calcium chloride (CaCl2) and calcium acetate (CaAc2) as calcium precursor, and sodium carbonate (Na2CO3) and urea (CO(NH2)2) as carbonate precursor. The results show that both calcium and carbonate precursors affect morphologies of CaCO3; CaCO3,Cl-Urea, and CaCO3,Cl-Na have calcite phase, whereas mixed-phases of calcite (30%) and vaterite (70%) are observed with CaCO3,Ac-Na, and aragonite is found with CaCO3,Ac-Urea. CaCO3,Cl-Na exhibits small cubic (rhombohedral) particle, CaCO3,Cl-Urea possesses spherical particle with rough surface, CaCO3,Ac-Na has spherical-like morphology with smooth surface, and CaCO3,Ac-Urea possesses aggregated form of CaCO3 particles. For application to CO2 capture, CaO derived from CaCO3,Ac-Urea provides the highest CaO conversion of 80% at 700 °C. The synthetic CaO-based sorbents were further incorporated with nickel oxide to form one-body bi-functional catalysts for H2 production from sorption-enhanced steam ethanol reforming. The results show that 87%H2 purity could be obtained with pre-breakthrough period of 60 min. Sorbent reactivity can be maintained the production of H2 for at least 10 consecutive cycle tests.  相似文献   

6.
Coupling CO2 desorption and methanation in the presence of hybrid materials offers a promising alternative to convert the CO2 in-situ removed during sorption-enhanced steam glycerol reforming (SESGR) avoiding the high energy-intensive CO2 sorbent regeneration. The all-inclusive integrated process exemplifies an option for glycerol valorization via consecutive SESGR and CO2 conversion by catalytic hydrogenation. The dual-function catalyst performing successively, in the same reactor, SESGR and CO2 desorption/conversion encompasses reforming/methanation catalyst (10%Ni5%Co) and dispersed nano-sized CaO on γ-Al2O3. Simultaneous CO2 desorption/conversion integrated process is explored in a fixed-bed reactor via an unsteady-state, two-scale, non-isothermal model, highlighting the impact of key parameters on the process performance. At large adsorbent/catalyst mass ratio (2.0) and high CaO conversion (0.5) in preceding SESGR, CO2 is released and hydrogenated for an extended period with extra hydrogen consumption, without a balance between CO2 desorption and CO2 hydrogenation rates. Increasing pressure (3.0 MPa) and gas velocity offers a match between these competitive reaction rates, resulting low CO2 concentration in the exit stream. Desorption/methanation thermal behavior controls the magnitude of CO2 low concentration period and the methanation efficiency.  相似文献   

7.
Calcium precursor and surfactant addition on properties of synthetic alumina-containing CaO-based for CO2 capture and for sorption-enhanced steam methane reforming process (SE-SMR) were investigated. Results showed that the sorbent derived from calcium d-gluconic acid (CG-AN) offered CO2 sorption capacity of 0.38 g CO2/g sorbent, which is greater than 0.17 g CO2/g sorbent of the sorbent derived from calcium nitrate (CN-AN). Addition of CTAB surfactant during synthesis was found to enhance CO2 sorption capacity for CG-AN but not for CN-AN sorbents. Stability tests of the modified sorbents for 10 cycles showed that CG-AN-CTAB provided higher CO2 sorption capacity than CN-AN-CTAB for each corresponding cycle. Incorporation of CG-AN with Ni catalyst (Ni-CG-AN) using wet-mixing technique offered the longest pre-breakthrough period of 60 min for average maximum H2 purity of 88% at 600 °C and a steam/methane molar ratio of 3.  相似文献   

8.
The attapulgite supported transition metals (Ni, Cu, Co or Fe) catalysts were prepared by precipitation method at constant loading (10 wt%) and investigated in the glycerol steam reforming reaction for H2 production under 400–750 °C, water/glycerol (W/G) = 3, N2 flow ratio = 0.16 L/min and WHSV = 6.46 h?1. The as-prepared catalysts were characterized by N2 adsorption-desorption, XRD, H2-TPR and TEM-EDS. The results shown different active metals presented various crystalline sizes and reduction properties. The experimental results revealed Ni/ATP and Co/ATP catalysts had more active for glycerol steam reforming than Cu/ATP and Fe/ATP catalysts, due to the fact that active metal Ni and Co have superior capacity to promote the necessary CC rupture and facilitate the water gas shift reaction. In addition, the results revealed that CH4 production was favored at low temperatures while CO production was presented at high temperatures, which were induced by the different reaction networks over catalysts. In addition, the stability test shown all catalysts had different various degrees of inactivation, resulting from the sintering of active metals and carbon deposition. The characterizations of XRD, TEM and TG-DTG for spent catalysts revealed the smallest amount of carbon deposited for Cu/ATP, which was attributed to the lowest Cu particle size. Additionally, two different types of carbon was found, namely filamentous carbon for Ni and Co/ATP and encapsulating carbon for Cu and Fe/ATP.  相似文献   

9.
Sorption-enhanced steam reforming of ethanol (SE-SRE) with in-situ CO2 removal is an environmentally friendly and sustainable approach for hydrogen production. Researches on continuous production of high-purity H2 by SE-SRE over the modified Li4SiO4 sorbent were conducted using two parallel reactor in this work. The low cost Li4SiO4 derived from rice husk ash (RHA) is a promising high-temperature CO2 sorbent. However, the poor adsorption kinetics of RHA-Li4SiO4 sorbent at low CO2 concentration is the major challenge. The metallic elements (K, Ca, Al, Mg) were employed to modify the RHA-Li4SiO4 for efficient CO2 capture. The developed sorbents were characterized and tested to study the role of dopants on the crystal, textural, microstructure and CO2 adsorption kinetics and cyclic stability. Results indicated that K doping effectively inhibited the growth of crystal aggregation and resulted in a fluffy morphology with abundant pores and higher specific surface area, while the addition of Ca, Al and Mg formed a nubby structure with larger particle size. K-doped RHA-Li4SiO4 exhibited the best CO2 uptake properties and the optimal K doping molar content was 0.02 with the maximum capture capacity of 34.16 wt%, which is higher than 27.1 wt% of pure RHA-Li4SiO4. Then, the effect of operating conditions on the enhancement behaviors was considered in the SE-SRE system. High-purity H2 (above 96%) was achieved by coupling K(0.02)/RHA-Li4SiO4 sorbent with Ni-based catalyst under the optimum condition (T: 525 °C, liquid hourly space velocity: 0.9 mL/(g·h), sorbent/catalyst: 4 and steam/carbon: 8.0). The adsorption activity of K(0.02)/RHA-Li4SiO4 maintained at a high level in ten SE-SRE/regeneration cycles. Finally, a scheme including two parallel fixed-bed reactors was designed and operated periodically for continuous production of high-purity H2. The reaction switching time was shown to depend strongly on the pre-breakthrough time and operating conditions. As the reaction switching time was 40 min, the products were always only H2 and CH4 (no CO and CO2 appear) and the H2 purity remained above 90% during 400 min, confirming high purity hydrogen stream can be obtained continuously.  相似文献   

10.
The oxidative steam reforming of methane in a two-zone fluidized-bed reactor (TZFBR) was investigated over a Ni/Al2O3 catalyst. The effects of the main operating variables (temperature, steam/oxygen ratio, steam/methane ratio and relative velocity with respect to the minimum fluidization velocity) have been studied. A comparison has been made with results given in the literature in terms of hydrogen yield. Despite working with very low steam/methane ratios, high values of hydrogen yield at both high methane conversion and at steady state were obtained in the TZFBR.  相似文献   

11.
The operation types and operation window for high-purity H2 production for the sorption enhanced steam methane reforming (SE-SMR) with Ni/Al2O3 catalyst and CaO sorbent in a fixed-bed reactor are investigated by an experimentally verified 2D numerical method. Four chemical reactions including steam reforming, water gas shift, global steam reforming, and CO2 sorption are considered. The operation window is defined as the H2 and CO molar fractions at outlet satisfying both yH2,out ≥ 90% and yCO,out ≤ yCO,allow (= 1%, 2% or 3%) in dry base. Under the conditions of yH2,out and yCO,allow, there are six operation types, of which 2 types are within the operation window and 4 types are not within the operation window as the temperature, weight hourly space velocity (WHSV) and steam to methane (S/C) molar ratio vary. For a common case of S/C = 3, the operation windows for yCO,allow = 3% at WHSV = 8.5 h?1 and 42.5 h?1 are located at 570–670 °C and 640–690 °C respectively, based on the parameters in this work. The operation window of temperature is wider with decreasing WHSV, and it becomes wider remarkably as the S/C ratio increases. The lowest temperature inside the operation window is 550 °C. The effects of the temperature, WHSV and S/C ratio on the operating types, yH2,out and yCO,out are also presented and discussed in details.  相似文献   

12.
Highly durable catalyst for high temperature methanol steam reforming is required for a compact hydrogen processor. Deactivation of a coprecipitated Cu/ZnO/ZrO2 catalyst modified with In2O3 is very gradual even in the high temperature methanol steam reforming mainly at 500 °C, but the initial activity is considerably low. Addition of Y2O3 to Cu/ZnO/ZrO2/In2O3 increases its initial activity due to the higher Cu surface amount, while the activity comes gradually close to that for the catalyst without Y2O3 during the reaction. Coprecipitation of Cu/ZnO/ZrO2/Y2O3/In2O3 on a zirconia support triply increases the overall activity by keeping the durability while the amount of the coprecipitated portion is a half of that without the support. On the composite catalyst, sintering of Cu particles is suppressed. The surface Cu amount is similar to that without the support, but the Cu surface activity is much higher probably because of the small Cu particle size.  相似文献   

13.
Thermodynamic features of hydrogen production by glycerol steam reforming with in situ hydrogen extraction have been studied with the method of Gibbs free energy minimization. The effects of pressure (1–5 atm), temperature (600–1000 K), water to glycerol ratio (WGR, 3–12) and fraction of H2 removal (f, 0–1) on the reforming reactions and carbon formation were investigated. The results suggest separation of hydrogen in situ can substantially enhance hydrogen production from glycerol steam reforming, as 7 mol (stoichiometric value) of hydrogen can be obtained even at 600 K due to the hydrogen extraction. It is demonstrated that atmospheric pressure and a WGR of 9 are suitable for hydrogen production and the optimum temperature for glycerol steam reforming with in situ hydrogen removal is between 825 and 875 K, 100 K lower than that achieved typically without hydrogen separation. Furthermore, the detrimental influence of increasing pressure in terms of hydrogen production becomes marginal above 800 K with a high fraction of H2 removal (i.e., f = 0.99). High temperature and WGR are favorable to inhibit carbon production.  相似文献   

14.
Steam reforming is the most favored method for the production of hydrogen. Hydrogen is mostly manufactured by using steam reforming of natural gas. Due to the negative environmental impact and energy politics, alternative hydrogen production methods are being explored. Glycerol is one of the bio-based alternative feedstock for hydrogen production. This study is aimed to simulate hydrogen production from glycerol by using Aspen Plus. First of all, the convenient reactor type was determined. RPlug reactor exhibited the highest performance for the hydrogen production. A thermodynamic model was determined according to the formation of byproduct. The reaction temperature, water/glycerol molar feed ratio as reaction parameters and reactor pressure were investigated on the conversion of glycerol and yield of hydrogen. Optimum reaction parameters are determined as 500 °C of reaction temperature, 9:1 of water to glycerol ratio and 1 atm of pressure. Reactor design was also examined. Optimum reactor diameter and reactor length values were determined as 5 m and 50 m, respectively. Hydrogen purification was studied and 99.9% purity of H2was obtained at 25 bar and 40 °C. The obtained results were shown that Aspen Plus has been successfully applied to investigate the effects of reaction parameters and reactor sizing for hydrogen production from glycerol steam reforming.  相似文献   

15.
The effect of non-uniform temperature on the sorption-enhanced steam methane reforming (SE-SMR) in a tubular fixed-bed reactor with a constant wall temperature of 600 °C is investigated numerically by an experimentally verified unsteady two-dimensional model. The reactor uses Ni/Al2O3 as the reforming catalyst and CaO as the sorbent. The reaction of SMR is enhanced by removing the CO2 through the reaction of CaO + CO2 → CaCO3 based on the Le Chatelier's principle. A non-uniform temperature distribution instead of a uniform temperature in the reactor appears due to the rapid endothermic reaction of SMR followed by an exothermic reaction of CO2 sorption. For a small weight hourly space velocity (WHSV) of 0.67 h?1 before the CO2 breakthrough, both a low and a high temperature regions exist simultaneously in the catalyst/sorbent bed, and their sizes are enlarged and the temperature distribution is more non-uniform for a larger tube diameter (D). Both the CH4 conversion and the H2 molar fraction are slightly increased with the increase of D. Based on the parameters adopted in this work, the CH4 conversion, the H2 and CO molar fractions at D = 60 mm are 84.6%, 94.4%, and 0.63%, respectively. After CO2 breakthrough, the reaction of SMR dominates, and the reactor performance is remarkably reduced due to low reactor temperature.For a higher value of WHSV (4.03 h?1) before CO2 breakthrough, both the reaction times for SMR and CO2 sorption become much shorter. The size of low temperature region becomes larger, and the high temperature region inside the catalyst/sorbent bed doesn't exist for D ≥ 30 mm. The maximum temperature difference inside the catalyst/sorbent bed is greater than 67 °C. Both the CH4 conversion and H2 molar fraction are slightly decreased with the increase of D. However, this phenomenon is qualitatively opposite to that for small WHSV of 0.67 h?1. The CH4 conversion and H2 molar fraction at D = 60 mm are 52.6% and 78.7%, respectively, which are much lower than those for WHSV = 0.67 h?1.  相似文献   

16.
17.
In order to improve the hydrogen production efficiency by glycerol steam reforming, a membrane-assisted fluidized bed reactor with carbon dioxide sorption is developed to enhance the reforming process. Low-temperature operation in a membrane reactor is necessary considering the thermal stability of membrane. In this work, the sorption-enhanced glycerol steam reforming process in a fluidized bed membrane reactor under the condition of low temperature is numerically investigated, where the hydrotalcite is employed as CO2 sorbents. The impact of operating pressure on the reforming performance is further evaluated. The results demonstrate that the integration of membrane hydrogen separation and CO2 sorption can effectively enhance the low-temperature glycerol reforming performance. The fuel conversion above 95% can be achieved under an elevated pressure.  相似文献   

18.
Thermodynamics of hydrogen production from conventional steam reforming (C-SR) and sorption-enhanced steam reforming (SE-SR) of bio-oil was performed under different conditions including reforming temperature, S/C ratio (the mole ratio of steam to carbon in the bio-oil), operating pressure and CaO/C ratio (the mole ratio of CaO to carbon in the bio-oil). Increasing temperature and S/C ratio, and decreasing the operating pressure were favorable to improve the hydrogen yield. Compared to C-SR, SE-SR had the significant advantage of higher hydrogen yield at lower desirable temperature, and showed a significant suppression for carbon formation. However excess CaO (CaO/C > 1) almost had no additional contribution to hydrogen production. Aimed to achieve the maximum utilization of bio-oil with as little energy consumption as possible, the influences of temperature and S/C ratio on the reforming performance (energy requirements and bio-oil consumption per unit volume of hydrogen produced, QD/H2 (kJ/Nm3) and YBio-oil/H2 (kg/Nm3)) were comprehensively evaluated using matrix analysis while ensuring the highest hydrogen yield as possible. The optimal operating parameters were confirmed at 650 °C, S/C = 2 for C-SR; and 550 °C, S/C = 2 for SE-SR. Under their respective optimal conditions, the YBio-oil/H2 of SE-SR is significant decreased, by 18.50% compared to that of C-SR, although the QD/H2 was slightly increased, just by 7.55%.  相似文献   

19.
Steel slag, a waste from steelmaking plant, has been proven to be good candidate resources for low-cost calcium-based CO2 sorbent derivation. In this work, a cheap and sintering-resistance CaO-based sorbent (CaO (SS)) was prepared from low cost waste steel slag and was applied to enhance catalytic steam reforming of coke oven gas for production of high-purity hydrogen. This steel slag-derived CaO possessed a high and stable CO2 capture capacity of about 0.48 g CO2/g sorbent after 35 adsorption/desorption cycles, which was mainly ascribed to the mesoporous structure and the presence of MgO and Fe2O3. Product gas containing 95.8 vol% H2 and 1.4 vol% CO, with a CH4 conversion of 91.3% was achieved at 600 °C by steam reforming of COG enhanced by CaO (SS). Although high temperature was beneficial for methane conversion, CH4 conversion was remarkably increased at lower operation temperatures with the promotion effects from CaO (SS), and CO selectivity has been also greatly decreased. Reducing WHSV could increase methane conversion and reduce CO selectivity due to longer reactants residence time. Reducing C/A could increase methane conversion and hydrogen recovery factor, and also decrease CO selectivity. When being mixed with catalyst during SE-SRCOG, CaO (SS) with a uniform size distribution favored methane conversion due to the high utilization efficiency of catalyst. Promising stability of CaO (SS) in cyclic reforming/calcination tests was evidenced with a hydrogen recovery factor >2.1 and CH4 conversion of 82.5% at 600 °C after 10 cycles using CaO (SS) as sorbent.  相似文献   

20.
Interest in hydrogen, regarded as a new clean energy carrier, has been increasing with expectation of the approaching hydrogen economy. In the hydrogen economy, hydrogen will replace the conventional fuels that have caused pollution problems. As one of the methods for the mass production of hydrogen, water gas shift (WGS) reaction (CO + H2O ↔ H2 + CO2) has been highlighted for synthesis gas feed, which is produced by coal and biomass gasification. Recently, the performance of WGS reaction has been improved significantly through application of the sorption-enhanced WGS (SE-WGS) reaction concept, where WGS reaction and CO2 sorption are carried out simultaneously. High-purity hydrogen can be directly produced through the SE-WGS reaction, without need for further purification processes. In the SE-WGS reaction, uniform packing of the mixture of catalyst and sorbent is important; however, this is difficult to manage with conventional catalyst and sorbent pellets. In this study, novel one-body hybrid solid pellets consisting of the mixture of catalyst and sorbent were prepared to address this shortcoming and applied to SE-WGS reactions. From experiments, the effect of different ratio of catalyst/sorbent in one-body hybrid solid pellets was studied. A novel multi-section packing concept was also applied to SE-WGS reaction with one-body hybrid solid pellets. The experimental results showed that one-body hybrid solid pellets can be successfully used and that multi-section packing can increase the hydrogen productivity in SE-WGS reaction.  相似文献   

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