Search

Hierarchical HZSM-5 zeolites were prepared by desilication of commercial HZSM-5 in aqueous NaOH solutions with the assistance of tetrapropylammonium hydroxides (TPAOH), and applied for the catalytic upgrading of bio-oil derived from the fast pyrolysis of sunflower stalk. The hierarchical HZSM-5 by using 0.2 M NaOH with 0.25 M TPAOH for the desilication exhibited the best catalytic performance and the relative total peak area related to the aromatic hydrocarbons reached 65.8% with a yield of the detected aromatic hydrocarbons up to 45.2 mg/g-bio-oil. With the assistance of 0.25 M TPAOH for the desilication, the formation of mesopores became highly controllable, resulting in the increase in the surface area and maintainment of enough acid amounts, however, the coking on the surface of catalyst was not hindered. To solve the coking problem and increase the aromatic hydrocarbons production, the hierarchical HZSM-5 with the best performance was modified by various metals. It is found that 0.25 wt% Cu loaded hierarchical HZSM-5 increased the yield of the detected aromatic hydrocarbons up to 54.5 mg/g-bio-oil with a decrease in the coke formation.

Co-pyrolysis of two different types of biomass among apple tree branch (ATB), knotweed stem (KWS), seaweed (SW) and rice straw (RSt) was conducted to obtain co-pyrolysis char (co-char), and then the steam gasification of those co-chars was compared with the steam co-gasification of the physically mixed individual biochars to investigate the synergetic effect resulted from alkali and alkali earth metal (AAEM) in each biomass involved. It is found that the silica species in the RSt had negative effect on the activity of co-char due to the formation of alkali silicate compounds. However, combination of RSt with some non-woody biomass such as SW also showed promoting effect. In particular, the gasification of the co-char from the combination of various biomass with low or no silica content showed improved gasification efficiencies due to the synergetic effect AAEM species in the co-char from the different biomass. Therefore, the biomass selection should play a significant role in the co-pyrolysis of different biomass in the two-stage gasification system.

A transport bed flash calcination (TBFC) process applied to magnesite is systematically investigated through process simulation to optimize the energy-saving strategy. The high-temperature calciner flue gas is used to preheat the fed magnesite, while the sensible heat with the caustic calcined magnesia (CCM) product is cooled by air sent to the calciner. Pre-decomposition of magnesite during preheating is considered on basis of the kinetics measured using a micro fluidized bed reaction analyzer that allows the minimized effect of external diffusion on reaction. With staged fuel gas supply the TBFC process allows the equivalence ratios around 1.2 for combustion. The preferred arrangement of stages for magnesite preheating and CCM cooling are respectively 4 and 2, leading to the energy consumption of 4100 kJ/kg-CCM and the energy efficiency of 66.8%, which is almost doubly higher than the 33.9% of the conventional reverberatory furnaces (RF). The pre-decomposition occurs mainly in the 1st-stage preheater, and the maximal conversion is about 13%. Varying the stages of preheating appears more influential on the energy saving than varying the cooling stages, while residence time above 1 s in the preheaters has limited effect.

In this study, the gas production behavior from the steam gasification of the biochar derived from the pruned apple brunch was investigated using a fixed-bed reactor. The optimal biochar obtained at the pyrolysis temperature of 550 °C was gasified under different operating conditions for the hydrogen rich gas production. The experimental results indicated that high reaction temperature and high water flow rate were both beneficial to the hydrogen gas yield, but excess steam had a negative impact contrarily. Besides, the small size particles (0.5–1.0 mm) showed better performance in the hydrogen gas production at the low water flow rates (0.05–0.20 g/min); while the large size particles (1.0–2.8 mm) showed better performance at the high water flow rates (0.25–0.30 g/min). The suitable operating conditions for the gasification of the biochar were determined as the reaction temperature of 850 °C, water flow rate of 0.25 g/min, and particle size of 1.0–2.8 mm.

A Eulerian-Eulerian model incorporating the kinetic theory of granular flow was adopted to simulate the gas-solids flow behaviors in a dense downer below a conventional downer, which could be used for the further pyrolysis of coal and/or decomposition of tar on the generated char before the char and tar are completely separated in a triple-bed combined circulating fluidized bed (TBCFB) system. The high solids holdup in the dense downer can enhance the heat transfer to completely pyrolyze coal as well as decompose the heavy tar, avoiding the negative impact of pyrolysis products on char gasification. In order to obtain the optimal structural parameters and operating conditions and evaluate the performance of this dense downer, the influences of downer diameter, cone angle and solids mass flux on the hydrodynamic behaviors were investigated in details. The results demonstrate that the solids holdup in the dense downer can be increased, however, the maximum solids holdup is limited to approximately 0.4 owing to the ultimate carrying capacity. Moreover, it is found that there is a peak solids holdup in the annular region near the wall whereas many particles concentrate at the center in the high-density operation states. Meanwhile, the unique solids radial distribution could be caused by the radial movement of particles. Moreover, the intense collisions and turbulence caused by high velocity could inhibit agglomerates, which should be benefit for the heat transfer. It is expected that these results could offer a guidance for the design of such a dense downer for effective improvement of the efficiency of the pyrolyzer.

A small-scale separated-type biomass gasification system composed of a screw pyrolyzer, a steam tar reformer, an air-steam char fluidized bed gasifier, and a spent char combustor with heat carrier particles circulating is designed to convert woody biomass into combustible gas which can be applied for gas-engine power generation. In this study, the simulation results of this system based on two biomass pyrolysis routes, i.e., fast and slow pyrolysis, are analyzed and compared. During the simulations, the empirical equations as well as the main experimental data from the published literature are applied to analyze the elemental, mass, and energy balances of each process by using sets of assumptions at a certain condition to predict final energy efficiency and the potential electricity generated from the system. As a result, 12.5 kg/h of wood biomass feeding to this system has power generation ability of 16.8 kWe and 16.3 kWe with cold gas efficiencies of 73.8% and 71.7% for the fast and slow pyrolysis routes respectively. Comparison of product yields and compositions obtained in the present system with the reported data shows that the prediction gives a reasonable accuracy which could indicate what occur within the system. The calculation methods presented in this study could be utilized for preliminary engineering design of comprehensive biomass thermal conversion processes.

Dealkaline lignin (DAL) was used as a carbon and sulfur source to prepare MoS2/Mo2C-based catalysts (Mo-DAL) with a facile impregnation-pyrolysis two-step process for the hydrogen production from the formic acid decomposition. Comparison of the catalytic performance of the Mo-DAL catalyst with the carbon black-based one (Mo2C-CB) revealed that the Mo-DAL catalyst exhibited superior activity to the Mo2C-CB catalyst. When 20 wt % of Mo was loaded on DAL, the catalyst produced hydrogen quite selectively (99.2%) with almost complete conversion of formic acid (97.4%) at 220 °C. In addition, the catalyst showed stable activity for at least 50 h in these conditions. This catalytic activity and hydrogen selectivity are superior to the other reported nonprecious metal catalysts. Since DAL contains not only carbon but also sodium and sulfur species, multiple kinds of active sites such as Na-intercalated MoS2, MoS2, and β-Mo2C were formed on the Mo-DAL catalysts. Investigation of additional effects of sulfur and sod...

In this study, steam gasifications of a kind of marine biomass, i.e., Zostera marina (eelgrass), and the biochars derived from pyrolysis of it were carried out for the biohydrogen production in a fixed-bed reactor. The effects of reaction temperature and water injection rate on the hydrogen production were investigated. In order to understand the effect of sea salts attached on the surface of eelgrass for the hydrogen production, the eelgrass washed by water (washed-eelgrass) was also used as the feedstock. It was observed that hydrogen productions from the gasification of washed-eelgrass as well as its biochar were higher than those of raw eelgrass and its biochar, indicating that the impurities of raw eelgrass had a negative effect on the hydrogen production. The biochar derived from the pyrolysis of washed eelgrass at 550 °C had the largest amount of hydrogen yield at the gasification temperature of 850 °C with a water injection rate of 0.15 g/min. It was found that both the hydrogen production and reaction rates were enhanced by mixing washed-eelgrass biochar obtained at 350 °C with the calcined seashells at a weight ratio of 1 to 2, especially at the gasification temperature of 650 °C. Meanwhile, in the presence of the calcined seashell, CO2 content decreased sharply whereas the hydrogen yield had no obvious increase.

Biomass is one of the most promising renewable energy sources for power generation. Recently, there is increase interest in utilization of chemical looping process for converting biomass into energy based on combined heat and power (CHP) concept. In this study, the possibility of combining biomass direct chemical looping combustion (BDCLC) process with the organic Rankine cycle for the waste heat recovery (ORC-WHR) in a small-scale power generation system is investigated. The effects of various working fluids in the ORC-WHR unit and operating pressure of BDCLC unit on the performance of system are analyzed. It is found that 191.2 kWe can be generated from 1000 kWth biomass input, in which the expansion-compression process in the BDCLC unit contributes 170.2 kWe and the ORC-WHR unit contributes the other 21.0 kWe for the system with an efficiency of 19.1 % for the overall system and an ORC-WHR efficiency of 19.9 % when benzene is used as the working fluid. It is expected to provide a more promising small-scale biomass-based power generation system.

Small-scale biomass power generation will play an important role in ensuring the regional power supply by using the local biomass resource and protecting the environment in the future. In this study, a small-scale high-efficient combined heat and power generation system with a separated-type biomass gasification process combining the energy/exergy recuperation is proposed for the first time. The spatial subdivision of the processes for the biomass pyrolysis, char combustion, tar reforming and catalyst regeneration is adopted by using a separated-type biomass gasifier design to realize the optimization of each conversion step and improve the whole system performance. To obtain the maximum power generation efficiency, the energy flow and exergy flow in the system are analyzed in details and the operating condition of the gasification system is optimized. The results demonstrate that the relatively low temperature as well as low steam/carbon ratio in the tar reformer should be conducive to the improvement of energy and exergy efficiencies. In the optimum operation condition, the biomass input of 548.86 kW (higher heating value) could generate 263.65 kW of electrical power with the total energy and exergy efficiencies of 37.9% and 43.2%, respectively, in which 153.44 kW of energy could be recuperated back to the gasification process by air and steam with 136.56 kW of energy obtained from gas turbine exhaust to enhance the whole power generation efficiency. It is expected to provide a new design concept for the development of high-efficient small-scale biomass gasification system for the combined heat and power generation.

Biomass to hydrogen is becoming a promising way to produce clean energy with zero or even negative carbon emission. In this study, a novel system containing a biomass pyrolysis process, a catalytic steam reforming of bio-oil process, a chemical looping unit using biochar as the reducing agent and other auxiliary processes including H2 separation and thermal energy circulation processes for hydrogen production is proposed and simulated based on the previous studies. While, a waste heat recovery system is recommended for energy recuperation to make the entire system become auto-thermal. The effects of steam to carbon ratio in the catalytic steam reforming reaction and temperatures at reducing and steam reactors in the chemical looping unit on the system performance are analyzed in details. Under the optimum condition in the proposed system, about 6.9 kg/h of hydrogen could be produced from 100 kg/h of wood biomass with 58.3 kW of net power. Compared with the biomass direct chemical looping process for H2 production, separating the bio-oil and biochar after the pyrolysis process and combining the steam bio-oil reforming process with the chemical looping unit using biochar for H2 production can increase H2 production efficiency from biomass by more than 50%. It is expected that this proposed system could be implemented in a practical application.

Biomass gasification to provide gas fuels for power generation is considered as one of the best ways for substituting fossil fuels. Large scale unit of biomass gasification with capacity over 2 MW is preferably chosen due to its efficiency to investment ratio even though collecting large amount of biomass takes high cost. To effectively utilize the biomass resources in local and regional areas, it is expected to apply more small-scale biomass gasifiers with a capacity less than 200 kW for a small community or even a family. This will make bioenergy more popular in our daily life. In this review, developed gasification techniques and the effects of biomass composition, gasifying agents, biomass particle size, operating condition of gasification (temperature and pressure) on the gasification efficiency, and type of gasifier are introduced at first and then, the research and development (R&D) and application progresses of the small-scale biomass gasification systems with capacities of 10–200 kW over the world are summarized, and the challenges and prospects in the future renewable energy markets are analyzed and discussed. European, North American and Asia areas are developing and begin to apply various small-scale biomass gasification systems, and African, Latin America, and Oceania countries should be the growing and promising potential regions for the application of this technique in the future, especially in the developing countries. In addition, lowering investment cost and making supporting policies are significantly required to utilize such small-scale renewable energy system.