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1.
Steam gasification of a typical Chinese bituminous coal for hydrogen production in a lab-scale pressurized bubbling fluidized bed with CaO as CO2 sorbent was performed over a pressure range of ambient pressure to 4 bar. The compositions of the product gases were analyzed and correlated to the gasification operating variables that affecting H2 production, such as pressure (P), mole ratio of steam to carbon ([H2O]/[C]), mole ratio of CaO to carbon ([CaO]/[C]) and temperature (T). The experimental results indicated that the H2 concentration was enhanced by raising the temperature, pressure and [H2O]/[C] under the circumstances we observed. With the presence of CaO sorbent, CO2 in the production gas was absorbed and converted to solid CaCO3, thus shifting the steam reforming of hydrocarbons and water gas shift reaction beyond the equilibrium restrictions and enhancing the H2 concentration. H2 concentration was up to 78 vol% (dry basis) under a condition of 750 °C, 4 bar, [Ca]/[C] = 1 and [H2O]/[C] = 2, while CO2 (2.7 vol%) was almost in-situ captured by the CaO sorbent. This study demonstrated that CaO could be used as a substantially excellent CO2 sorbent for the pressurized steam gasification of bituminous coal. For the gasification process with the presence of CaO, H2-rich syngas was yielded at far lower temperatures and pressures in comparison to the commercialized coal gasification technologies. SEM/EDX and gas sorption analyses of solid residues sampled after the gasification showed that the pore structure of the sorbent was recovered after the steam gasification process, which was attributed to the formation of Ca(OH)2. Additionally, a coal-CaO–H2O system was simulated with using Aspen Plus software. Calculation results showed that higher temperatures and pressures favor the H2 production within a certain range.  相似文献   

2.
Solid sorbents can be used to capture CO2 from pre-combustion sources at various temperatures. MgO and CaO are typical medium- and high-temperature CO2 sorbents. However, pure MgO is not active toward CO2. The addition of Na2CO3 increases the operating temperature and significantly increases the reactivity of sorbents to capture CO2. Na2CO3-promoted MgO is a promising medium-temperature CO2 sorbent. In this study, the thermodynamic performance of integrated gasification combined cycle (IGCC) systems with Na2CO3–MgO-based warm gas decarbonation (WGDC) and CaO-based hot gas decarbonation (HGDC) is evaluated and compared with that of an IGCC system with methyldiethanolamine (MDEA)-based cold gas decarbonation (CGDC). Assuming that the average CO2 capture capacities of solid sorbents are one-third of their theoretical maxima, we reveal that the IGCC system undergoes approximately 2.8% and 3.6% improvement on net efficiency when switching from CGDC to WGDC and to HGDC, respectively. The net efficiency of the system is increased by improving the CO2 capture capacity of the sorbent. The IGCC with Na2CO3–MgO experiences more significant increase in efficiency than that with CaO along with the improvement of sorbent average CO2 capture capacity. The efficiency of the IGCC systems reaches the same value when the average CO2 capture capacities of both sorbents are 53% of their theoretical levels. The effects of gas turbine combustor fuel gas inlet temperature on IGCC system performance are analyzed. Results show that the efficiency of the IGCC systems with HGDC and WGDC increases by 0.74% and 0.53% respectively as the fuel gas inlet temperature increases from 250 °C to 650 °C.  相似文献   

3.
This paper examines the average carbonation conversion, CO2 capture efficiency and energy requirement for post-combustion CO2 capture system during the modified calcium-based sorbent looping cycle. The limestone modified with acetic acid solution, i.e. calcium acetate is taken as an example of the modified calcium-based sorbents. The modified limestone exhibits much higher average carbonation conversion than the natural sorbent under the same condition. The CO2 capture efficiency increases with the sorbent flow ratios. Compared with the natural limestone, much less makeup mass flow of the recycled and the fresh sorbent is needed for the system when using the modified limestone at the same CO2 capture efficiency. Achieving 0.95 of CO2 capture efficiency without sulfation, 272 kJ/mol CO2 is required in the calciner for the natural limestone, whereas only 223 kJ/mol CO2 for the modified sorbent. The modified limestone possesses greater advantages in CO2 capture efficiency and energy consumption than the natural sorbent. When the sulfation and carbonation of the sorbents take place simultaneously, more energy is required. It is significantly necessary to remove SO2 from the flue gas before it enters the carbonator in order to reduce energy consumption in the calciner.  相似文献   

4.
Sorption-enhanced-steam-reforming (SESR) is a thermochemical conversion technology that produces a high-purity hydrogen stream by utilizing in-situ removal of CO2 with a sorbent. In this paper, the advantages and disadvantages of CaO based sorbents, alkali-metal based sorbents (Na2ZrO3, Li2ZrO3 and Li4SiO4), hydrotalcite based sorbents, bifunctional materials and sorbents prepared from wastes are briefly discussed, and the techniques to improve the sorption properties of these CO2 sorbents are summarized. In the process of hydrogen production by sorption-enhanced-steam-reforming, the selection of suitable high-temperature CO2 sorbent is the key to produce high purity hydrogen. Furthermore, the hydrogen-production performance of the above-mentioned sorbents in the SESR process is investigated and summarized. Finally, a future perspective and some suggestions regarding these five types of sorbents are put forward.  相似文献   

5.
Cu and Zn modified 13X zeolites prepared by ion exchange or impregnation and activated carbons (ACs) treated with KOH, NaOH or Na2CO3 solutions were studied as H2S sorbents for biogas purification for fuelling molten carbonate fuel cells. H2S sorption was studied in a new experimental set-up equipped with a high sensitivity potentiometric system for the analysis of H2S. Breakthrough curves were obtained at 40 °C with a fixed bed of 20 mg of the samples under a stream (6 L h−1) of 8 ppm H2S/He mixture. The adsorption properties of 13X zeolite improved with addition of Cu or Zn:Cu exchanged zeolite showed the best performances with a breakthrough time of 580 min at 0.5 ppm H2S, that is 12 times longer than the parent zeolite. In general, unmodified and modified ACs were more effective H2S sorbents than zeolites. Treating ACs with NaOH, KOH, or Na2CO3 solutions improved the H2S adsorption properties: AC treated with Na2CO3 was the most effective sorbent, showing a breakthrough time of 1222 min at 0.5 ppm, that is twice the time of the parent AC.  相似文献   

6.
In this study, highly pure hydrogen is produced in sorption enhanced chemical looping steam methane reforming (SE-CLSMR) using cobalt-based oxygen carrier (OC) and cerium promoted CaO-based sorbent. In addition, the CO2 removal from a gas stream at high temperatures is investigated via calcium looping process prior to SE-CLSMR process. The prepared samples are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and energy dispersive X-ray spectroscopy (EDX) techniques. The effect of Ca/Ce molar ratio (100/0.00–0.91/0.09), sorption temperature (550–650 °C) and sorbent lifetime are studied to find the optimal sorbent. The characterization results show the uniform and orderly CeO2 dispersed sorbent nanoparticles that notably improved the sorbent morphology compared with blank CaO. The sorption results revealed the negative effect of temperature on CO2 uptake of all the samples. In addition, the CO2 sorption evaluations indicate that the molar ratio of cerium to calcium plays a significant role in the stability of sorbent and improved the CO2 sorption capacity significantly. The high CO2 removal efficiency in the cerium modified sorbents could be due to decrease in diffusion resistance of CO2 through the sorbent structure during the carbonation reaction. Furthermore, results show that the addition of cerium to the sorbent structure, effectively improves the thermal resistance of synthesis sorbents. The SE-CLSMR results showed that the H2 purity could be increased up to about 95% considering Co3O4/SiO2 oxygen carrier and cerium promoted calcium-based sorbent at relatively low temperature of 550 °C, which is comparable with 84% in CLR process.  相似文献   

7.
In this study, the continuous sorption-enhanced steam reforming of glycerol to high-purity hydrogen production by a simultaneous flow concept of catalyst and sorbent for reaction and regeneration using two moving-bed reactors has been evaluated experimentally. A Ni-based catalyst (NiO/NiAl2O4) and a lime sorbent (CaO) were used for glycerol steam reforming with and without in-situ CO2 removal at 500 °C and 600 °C. The simultaneous regeneration of catalyst and sorbent was carried out with the mixture gas of N2 and steam at 900 °C. The product gases were measured by a GC gas analyzer. It is obvious that the amounts of CO2, CO and CH4 were reduced in the sorption-enhanced steam reforming of glycerol, and the H2 concentration is greatly increased in the pre-CO2 breakthrough periods within 10 min both 500 °C and 600 °C. The extended time of operation for high-purity hydrogen production and CO2 capture was obtained by the continuous sorption-enhanced steam reforming of glycerol. High-purity H2 products of 93.9% and 96.1% were produced at 500 °C and 600 °C and very small amounts of CO2, CH4 and CO were formed. The decay in activity during the continuous reaction-regeneration of catalyst and sorbent was not observed.  相似文献   

8.
A sorption-enhanced water–gas-shift reaction process (SEWGS) combines the WGS reaction and CO2 removal into a single process step in an integrated gasification combined cycle (IGCC) power plant. In the SEWGS, a solid sorbent is employed to capture the CO2 generated by the WGS reaction. A key technical issue for the SEWGS is to identify and develop sorbents that can capture CO2 under high pressure and high temperature syngas conditions and minimize or even eliminate the need for WGS catalysts. We present the results from a thermodynamic analysis and process simulation study that aimed to identify sorbents and optimal temperature windows to maximize the thermal efficiency of an IGCC + SEWGS plant. The results from the thermodynamic analysis identified two metal oxides, one silicate, three zirconates, and one titanate sorbents that are suitable for the SEWGS application. The results from the process simulation study revealed that the overall thermal efficiency of a 1187 MWth (thermal input) IGCC + SEWGS plant gasifying an Illinois coal, and using the seven sorbents selected from the thermodynamic analysis, was between 0.5 and 2.4 percentage points greater than that of a reference IGCC + Selexol plant.  相似文献   

9.
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   

10.
In this study, sorption-enhanced ethanol steam reforming (SEESR) is investigated using a Ce-Ni/MCM-41 as a catalyst in the presence of Na or/and Zr promoted CaO-based adsorbents. Ce-Ni/MCM-41 and promoted sorbents were synthesized by wet impregnation method. The catalyst was characterized by XRD, FTIR, TGA, EFSEM, TEM, H2-TPR and N2 adsorption/desorption and promoted sorbents were studied by XRD, EFSEM, BET, TEM and TGA analysis. Sorption experiments were performed to verify sorbent activity for CO2 removing. The results indicated that with doping different promoter on CaO sorbent and also with increasing Na loading, there was an increase in BET surface area, the reduction in particle size and thereupon an enhancement in CO2 sorption capacity. Higher BET surface area, smaller particle size, and superior CO2 sorption capacity were obtained on Na-Zr-CaO sorbent. Sorption-enhanced steam reforming process of ethanol on synthesized catalyst and sorbents were performed at 600 °C and water to ethanol molar ratio of 6. The effect of sorbent to catalyst ratio and the arrangement of sorbent and catalyst (like two separated layers and the mixture of sorbent and catalyst in a single layer) were also studied. The best results were demonstrated on Na-Zr-CaO sorbent and with the separated array. Hydrogen production via a SEESR process with Na-Zr-CaO as sorbent was ∼94% that is 24% more than that of conventional ethanol steam reforming (ESR) reaction.  相似文献   

11.
This work investigates the synthesis and performance of double salts for H2/CO2 separation. A series of NaMg double salts were prepared based on xMg(NO3)2: yNa2CO3: zH2O and characterised. The best sorbents reached CO2 uptake of 17.9 wt% at 0.62 MPa and 375 °C. The NaMg double salts preferentially sorbed CO2 as determined by breakthrough tests. The NaMg double salts were packed in a sorbent bed and tested for H2/CO2 separation at the back end of a water gas shift reactor. The space velocity had the largest impact on the performance of the sorbent bed, as increasing the space velocity from 2.16 × 10?3 to 9.51 × 10?3 s?1 sped up the breakthrough time by 84%. Increasing the feed gas pressure from 0.3 to 0.6 MPa reduced the breakthrough time by ~45%. The NaMg double salt sorbents were exposed for over 1000 h of continuous temperature including 28 cycles of sorption and desorption, and proved to be stable during changes of operating conditions such as flow rates and pressures.  相似文献   

12.
CO2 capture and storage (CCS) has received significant attention recently and is recognized as an important option for reducing CO2 emissions from fossil fuel combustion. A particularly promising option involves the use of dry alkali metal-based sorbents to capture CO2 from flue gas. Here, alkali metal carbonates are used to capture CO2 in the presence of H2O to form either sodium or potassium bicarbonate at temperatures below 100 °C. A moderate temperature swing of 120–200 °C then causes the bicarbonate to decompose and release a mixture of CO2/H2O that can be converted into a “sequestration-ready” CO2 stream by condensing the steam. This process can be readily used for retrofitting existing facilities and easily integrated with new power generation facilities. It is ideally suited for coal-fired power plants incorporating wet flue gas desulfurization, due to the associated cooling and saturation of the flue gas. It is expected to be both cost effective and energy efficient.  相似文献   

13.
Liquid hydrogen     
It would be helpful were it economically acceptable to liquefy hydrogen. However, methanol is a liquid and could be written CH4O. The Nobel Laureate, George Olah along with two co-enthusiasts, published a book (2006) entitled “A Methanol ECONOMY”.3 If the methanol is synthesized from hydrogen and CO2 from the atmosphere, burning it as a fuel would merely replace in the atmosphere the CO2 taken from it and in the synthesis of the methanol.Let us, therefore, add “LIQUID HYDROGEN”3 to the subdivisions of uses of HYDROGEN.  相似文献   

14.
A two-stage system involving alkaline thermal gasification of cellulose with Ca(OH)2 sorbent and catalytic reforming with Ni/Fe dual-functional CaO based catalysts is proposed and applied to enhance H2 production and in-situ CO2 capture. The results show that the H2 concentration is maximized at a considerably lower temperature (500 °C) than commercialized biomass gasification processes, reducing energy consumption. Sol-gel method is deemed better than impregnation method for its lower cost and higher-concentration H2 production. Among the prepared catalysts, sol-NiCa catalyst exhibits the best performance in CO2 absorption, resistance to carbon deposition, and cyclic stability, creating maximum H2 concentration (79.22 vol%), H2 yield (27.36 mmol g−1 cellulose), and H2 conversion (57.61%). Introduction of Ni rather than Fe on the CaO based catalyst promotes steam methane reforming at moderate temperature range of 400–600 °C, generating low contents of CH4 (5.38 vol%), CO2 (4.82 vol%), and CO (10.58 vol%).  相似文献   

15.
This paper presents an experimental study for a newly modified K2CO3-promoted hydrotalcite material as a novel high capacity sorbent for in-situ CO2 capture. The sorbent is employed in the sorption enhanced steam reforming process for an efficient H2 production at low temperature (400–500 °C). A new set of adsorption data is reported for CO2 adsorption over K-hydrotalcite at 400 °C. The equilibrium sorption data obtained from a column apparatus can be adequately described by a Freundlich isotherm. The sorbent shows fast adsorption rates and attains a relatively high sorption capacity of 0.95 mol/kg on the fresh sorbent. CO2 desorption experiments are conducted to examine the effect of humidity content in the gas purge and the regeneration time on CO2 desorption rates. A large portion of CO2 is easily recovered in the first few minutes of a desorption cycle due to a fast desorption step, which is associated with a physi/chemisorption step on the monolayer surface of the fresh sorbent. The complete recovery of CO2 was then achieved in a slower desorption step associated with a reversible chemisorption in a multi-layer surface of the sorbent. The sorbent shows a loss of 8% of its fresh capacity due to an irreversible chemisorption, however, it preserves a stable working capacity of about 0.89 mol/kg, suggesting a reversible chemisorption process. The sorbent also presents a good cyclic thermal stability in the temperature range of 400–500 °C.  相似文献   

16.
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   

17.
In this work, air gasification of sewage sludge was conducted in a lab-scale bubbling fluidized bed gasifier. Further, the gasification process was modeled using artificial neural networks for the product gas composition with varying temperatures and equivalence ratios. Neural network-based prediction will help to predict the hydrogen production from product gas composition at various temperatures and equivalence ratios. The gasification efficiency and lower heating values were also established as a function of temperatures and equivalence ratios. The maximum H2 and CO was recorded as 16.26 vol% and 33.55 vol%. Intraileally at ER 0.2 gas composition H2, CO, and CH4 show high concentrations of 20.56 vol%, 45.91 vol%, and 13.32 vol%, respectively. At the same time, CO2 was lower as 20.20 vol% at ER 0.2. Therefore, optimum values are suggested for maximum H2 and CO yield and lower concentration of CO2 at ER 0.25 and temperature of 850 °C. A predictive model based on an Artificial Neural network is also developed to predict the hydrogen production from product gas composition at various temperatures and equivalence ratios. The network has been trained with different topologies to find the optimal structure for temperature and equivalence ratio. The obtained results showed that the regression coefficients for training, validation, and testing are 0.99999, 0.99998, and 0.99992, respectively, which clearly identifies the training efficiency of the trained model.  相似文献   

18.
In this work, CO2 capture and H2 production during the steam gasification of coal integrated with CO2 capture sorbent were investigated using a horizontal fixed bed reactor at atmospheric pressure. Four different temperatures (650, 675, 700, and 750 °C) and three sorbent-to-carbon ratios ([Ca]/[C] = 0, 1, 2) were studied. In the absence of sorbent, the maximum molar fraction of H2 (64.6%) and conversion of coal (71.3%) were exhibited at the highest temperature (750 °C). The experimental results verified that the presence of sorbent in the steam gasification of coal enhanced the molar fraction of H2 to more than 80%, with almost all CO2 was fixed into the sorbent structure, and carbon monoxide (CO) was converted to H2 and CO2 through the water gas shift reaction. The steam gasification of coal integrated with CO2 capture largely depended on the reaction temperature and exhibited optimal conditions at 675 °C. The maximum molar fraction of H2 (81.7%) and minimum CO2 concentration (almost 0%) were obtained at 675 °C and a sorbent-to-carbon ratio of 2.  相似文献   

19.
CaO-based regenerative sorbents for CO2 capture in power generation and H2 production are receiving growing attention. A major challenge for this technology is the decay of sorbent activity with increasing number of the sorption/regeneration cycles. Evaluation of long-term sorbent activity currently requires substantial experimental work. In this study, the dependence of the activity on the number of sorption/regeneration cycles is examined, and the apparent dependence on the number of cycles is related to the duration of sorbent regeneration. By relating the decay in activity of the sorbent to its decrease in surface area due to sintering, interesting insights can be drawn. A method for determination of the long-term activity has been proposed, which can greatly reduce the experimental work for sorbent development and process evaluation.  相似文献   

20.
A series of ordered mesoporous MgO–Al2O3 composite oxides with various Mg containing were facilely synthesized via one-pot evaporation induced self-assembly strategy. These materials with advantageous structural properties and superior thermal stabilities were used as the supports of Ni based catalysts for CO2 reforming of CH4. These mesoporous catalysts behaved both high catalytic activities and long term stabilities toward this reaction. The effects of the mesopore structure and MgO basic modifier on catalytic performances were carefully studied. Specifically, their mesoporous frameworks could accommodate the gaseous reactants with more “accessible” Ni active centers; the “confinement effect” of the mesopores would effectively suppress the thermal sintering of the Ni nanoparticles; the modified MgO basic sites would enhance the chemisorption and activation of CO2. Consequently, the catalytic activities and stabilities of these catalysts were greatly promoted. Therefore, the present materials were considered as promising catalyst supports for CO2 reforming of CH4.  相似文献   

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