H2 Content In Syngas Research Articles

Quantitative investigation of explosion behavior and spectral radiant characteristics of free radicals for syngas/air mixtures

The combustion characteristics and explosive hazard of syngas (H2/CO)/air mixtures are affected by its exact composition and equivalence ratios. In this paper, the explosion pressure and spectral radiant intensity of free radicals were quantitatively examined for syngas with different H2 proportions ([H2 in syngas] = 0, 30, 50, 70, 100 vol%) and equivalence ratios (φ = 0.8, 1.0, 1.2, 1.4, 1.6, 2.0, 2.5). The results show that the explosion process of syngas/air mixtures can be separated into the initial slow combustion stage, the violent deflagration stage and the deflagration ending stage. The peaks of explosion pressure, pressure rise rate, OH*spectral intensity and rise rate of spectral intensity first increase and then decrease with increasing the equivalence ratio, and they reduce gradually with the decrease of H2 proportion in syngas. The H2 content in syngas greatly affects the heat release and the concentration of excited state OH*, especially for the syngas/air mixtures with smaller proportion of H2. Additionally, the presence of H2 greatly increases the deflagration index and spectral radiant index of OH* for syngas/air mixtures. The average rise rates of explosion pressure and spectral intensity of free radicals are introduced and the coupling model between them is established based on the first law of thermodynamics and the principle of chain reaction. The established model is furthermore verified by the experimental results. It is indicated that there is a linear relationship between average rise rates of explosion pressure and spectral intensity (OH*). The results can be used to improve the combustion efficiency of syngas and to guide theoretically the prevention, mitigation and control of syngas explosions.

Syngas production from municipal sewage sludge by gasification Process: Effects of fixed bed reactor types and gasification agents on syngas quality

In this experimental study, the results obtained from sewage sludge gasification carried out in two different fixed bed gasifiers, up draft and down draft, are presented. In addition, the effects of using three different heating temperatures (700, 800, 900 °C), two different gasification agents (dry air and pure oxygen), and their different flow rates (0.05, 0.1, 0.2, 0.4 L/min for dry air, 0.01 L/min for pure oxygen) on gasification efficiency are investigated. 75 g of sludge sample was used in each experimental study. The syngas composition produced from sludge gasification studies was measured by using online syngas analyzers. The maximum H2 content in syngas from updraft and downdraft gasifiers was achieved as 42 vol% and 46 vol% by using dry air as gasifying agent. H2 content for updraft and downdraft gasifiers was also obtained as 40 vol% and 45 vol%, respectively in the case of pure oxygen used as a gasifying agent. This paper presents a critical discussion identifying key points and contributing to a deeper understanding of its remarkable potential for sludge gasification by using different fixed bed gasifier configurations.

INVESTIGATION OF MICROALGAE GASIFICATION UNDER STEAM ATMOSPHERE IN DOWNDRAFT GASIFIER BY USING ASPEN PLUS®

Energy production is facing the environmental and economic issues due to growing population and uncertainties about the fossil fuels. These concerns prompt the researchers to find widely available and renewable alternative such as biomass instead of the fossil fuels. Microalgae is one of the promising biofuels owing to its rapid growth speed and higher calorific value. Steam gasification is an alternative way converting biomass to syngas with higher H2 and lower CO2 content compared with the other thermochemical conversion processes. In the present work, the downdraft gasifier model was developed by using Aspen Plus® program that has the capability to investigate the performance of microalgae gasification. Before the performance evaluation of the gasification, validation of the model successfully completed and exit gas compositions of H2, CO2, CO and CH4 were found very close for experimental study and the developed model. Effects of the main parameters of the process such as steam/biomass ratio and gasification temperature were assessed on the syngas composition and higher heating value (HHV) of syngas. The obtained results were stated that the increment in the temperature showed great effect on the H2 and CO compositions of syngas, they increased from 50.72% to 56.47% and 28.11% to 28.84% respectively. The simulation results also illustrated that the rising of the S/B ratio was favored the steam related reactions and increased the H2 content in syngas. However decreasing trend of the CH4 caused reducing of the HHV of syngas as a function of temperature and steam as well.

Microwave pyrolysis coupled with conventional pre-pyrolysis of the stalk for syngas and biochar

The study presented a novel approach microwave pyrolysis coupled conventional pre-pyrolysis (MCCP) to dispose of the stalk for syngas and biochar. Impacts of preheating temperature (250 ∼ 450 °C) on pyrolysis property and products characteristics were investigated. Compared with microwave-assisted pyrolysis (MAP), the initial time for rapid temperature ramp in MCCP was distinctly advanced from 124 s to within 20 s; the biochar yields significantly increased from 24.19% to 33.24%, and the H2 content of syngas in the second stage reached up to 64.65%. The biochar from MCCP had higher carbon content (greater than 70%), carbon retention (greater than 50%), and BET surface area (141.69 m2/g) than MAP. A high degree of aromatization and complete carbon skeleton structure was observed in the biochar from MCCP. Finally, a mobile application system based on MCCP was proposed, increasing the energy efficiency from 13.5 ∼ 27% (MAP) to 58.5 ∼ 76.5%.

Experimental and kinetic modeling study on NH3/syngas/air and NH3/bio-syngas/air premixed laminar flames at elevated temperature

Ammonia (NH3) can help achieve large-scale storage and long-distance transportation of renewable energy. The co-firing of NH3 with syngas and bio-syngas and increasing the initial temperature of reactants are economical and effective methods to enhance the reactivity of NH3 flames in boilers and gas turbines. An accurate kinetic model is essential for developing corresponding burners. The current kinetic models are not accurate enough in temperature dependence. Laminar burning velocities (SL) of NH3/syngas/air and NH3/bio-syngas/air mixtures were measured at various H2 contents in syngas and NH3 contents in the mixtures, equivalence ratios of 0.7~1.4, atmospheric pressure, and elevated temperature up to 423 K in a high-pressure constant-volume combustion vessel. A detailed kinetic model was developed for NH3/syngas combustion and validated based on the literature data. The experimental results show that slightly rich flame, high mole fractions of syngas/bio-syngas, and elevated initial temperature contribute to increasing the SL. Kinetic modeling analysis was performed for interpreting the effect of fuel composition, equivalence ratio and initial temperature on the laminar flame propagation characteristics. The elevated H2 content in syngas provides a stronger chemical effect and the enhanced laminar flame propagation of NH3/syngas/air and NH3/bio-syngas/air mixtures is dominated by chemical effect. Due to the presence of diluent (CO2 and N2), thermal effect has a negative influence on the enhancement of NH3/bio-syngas/air flame propagation. Although diluent hardly changes the NH3 consumption pathways, it will significantly reduce the NH3 consumption. Different NH3 consumption pathways are preferred by lean and rich flame. Sensitivity analysis shows that NH2 chemistry is favored by rich flames. Since NH2 + NH = N2H2 + H promotes the production of H radical in rich flames, it has the greatest influence on the SL of rich flames. H2 is more capable of improving the temperature dependence of NH3/syngas/air flame than CO. The increased importance of NH3 chemistry accounts for the strong temperature dependence of NH3/bio-syngas/air flame.

Influence of different fluidization and gasification parameters on syngas composition and heavy metal retention in a two-stage fluidized bed gasification process.

Herein, we investigated the influence of gasification and fluidization parameters on the H2 content of syngas and the retention of heavy metals (Cu and Pb) in a bed material during a two-stage fluidized bed gasification process. The results indicated that a temperature of 900°C in both stages resulted in the highest H2 content (32.4mol%) in syngas. When different equivalence ratios (ERs) were investigated, it was found that the highest H2 content in syngas (25.4mol%) was achieved at an ER of 0.3. A particle size of 0.46mm in the fluidized bed led to an increase in the H2 content of syngas. Moreover, increasing the operating gas velocity led to an increase in the H2 content of syngas. The heavy metal concentration in the bed material was the highest at 500°C. When the influences of different particle sizes and operating gas velocities were compared, it was observed that a particle size of 0.46mm and gas velocity of 1.5U/Umf resulted in increased heavy metal concentrations in the bed material, which indicates that the reduction in the particle size and the increase in the operating gas velocity enhanced gasification and improved the retention of heavy metals.

Simulation Analysis of the System Integrating Oxy-Fuel Combustion and Char Gasification

Abstract To explore the feasibility of converting hot flue gas into valuable syngas through char gasification process, Aspen Plus is applied to evaluate the performance of the integrated system including oxy-combustion, pyrolysis, gasification, and flue gas recirculation. The impact of feedstock type (reed straw and municipal solid waste (MSW)), feeding rate (0.1–1 t/h), and flue gas recycle ratio (FGR) (10%–30%) is investigated. The economic analysis of the integrated system is also performed. The results indicate that higher oxygen consumption is required for biomass gasification to reach the same temperature as MSW gasification. The gasification temperature is 750 °C–950 °C under 10%–30% FGR. The CO + H2 content in syngas from biomass gasification is slightly higher than that from MSW gasification. For the integrated system, more natural gas (NG) can be saved and more fossil CO2 can be reduced under biomass gasification. When the feedstock input is 1 t/h, the fossil CO2 emission can be reduced by 70% when taking biomass, the CO2 reduction is double of that when taking MSW. The total OPEX cost can be 26% saved by biomass and 62% saved by MSW due to the government subsidy. If CO2 tax is considered, the advantage of biomass for saving OPEX cost will be more obvious.

A systematic numerical study of the laminar burning velocity of iso-octane/syngas/air mixtures

The laminar burning velocities of iso-octane/syngas/air mixtures were numerically investigated using a detailed reaction mechanism over a wide range of equivalence ratio (0.4–1.4) at atmospheric and elevated pressure at an initial temperature of 423 K. The mole fraction of syngas in the fuel mixture was varied from the entire range of 0 (pure iso-octane) to 1 (pure syngas). To take into account the large variations of syngas compositions, the following three syngas compositions are considered: 75%H2-25%CO, 50%H2-50%CO, and 25%H2-75%CO by volume. The results show that the laminar burning velocity of iso-octane/syngas/air mixtures increases with the content of syngas, especially for higher H2 content in syngas and rich mixtures. The enhanced burning velocity is attributed to the chemical effects of H2 in syngas. The burning velocity correlates linearly with the level of syngas dilution of the fuel mixture, regardless of how the syngas dilution ratio is defined when the dilution level is low. The linear correlation remains over a wide range of syngas dilution when the dilution ration is defined as that introduced by Yu et al. (1986). H2 addition and CO addition affect the radical pool differently and H is found to be a kinetics indicator for the burning velocity of iso-octane/syngas/air mixtures under the current conditions. Detailed sensitivity and pathway analysis was also conducted to identify reactions that significantly affect the burning velocity of iso-octane/syngas/air mixtures and to illustrate the kinetics interactions between H2, CO, and iso-octane in iso-octane/syngas/air mixtures.

Effect of Hydrothermal Temperature on the Steam Gasification Performance of Sewage Sludge: Syngas Quality and Tar Formation

Hydrothermal pretreatment enhances both dewaterability and energy density of the municipal sewage sludge before steam gasification. Nevertheless, the effect of treatment condition on syngas quality and tar production was not clear. In this study, the hydrochars derived at different hydrothermal temperatures of sewage sludge were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and BET analysis. Then, the gasification experiment of raw sludge and hydrochars was conducted in a fixed bed reactor to evaluate key parameters of syngas and tar including yield, chemical composition, and higher heating value. The results showed that the treatment substantially improved the diffusion condition on the sludge surface, while raising the temperature led to a certain extent of pore collapse. The surface area and pore volume of the raw sludge was increased by 7.66 and 1.73 times after treatment at 200 °C, leading to 4.2% increase in H2 content in syngas from gasification of derived ...

An experimental and computational study of OH formation in laminar coflow syngas diffusion flames

This paper presents an experimental and numerical study to elucidate the suppressing influence of H2 content in syngas on OH formation in laminar syngas diffusion flames burning in coflow oxidizer of 25%O2/75%H2O. Such an influence was found different from the effect of H2 content in syngas on OH formation when the oxidizer stream consists of O2/N2. OH∗-chemiluminescence images were captured using an intensified CCD (ICCD) camera, the centerline temperatures were measured by a Pt-6%Rh/Pt-30%Rh thermocouple, while a two-dimensional flame code was adopted to simulate these laminar coflow diffusion flames using a detailed reaction mechanism. The different effects of H2O including chemical, thermal, transport, and radiative were examined and detailed kinetics analyses were conducted to gain insights into how H2O in the oxidizer stream alters the influence of H2 content in syngas on OH formation.

Steam/oxygen gasification of dried sewage sludge in a two-stage gasifier: Effects of the steam to fuel ratio and ash of the activated carbon on the production of hydrogen and tar removal

Steam/oxygen gasification of dried sewage sludge was performed in a two-stage gasifier to produce an H2-rich and tar-free syngas. The experiment mainly investigated the effects of activated carbon, ash of activated carbon, steam to fuel ratio and the combination of additives on syngas quality. In the results, all the syngases obtained with activated carbon did not contain any tar. Activated carbon increased the H2 production and decreased the NH3 content in syngas. Acid-treated activated carbon, which has less ash content than the original activated carbon, was less active in tar cracking and H2 production. The steam to fuel ratio had a strong influence on syngas quality, causing a significant rise in the H2 and NH3 contents in syngas at a high steam to fuel ratio. The extra addition of CaO and activated carbon to the base additive (activated carbon) led to increased H2 production and active tar cracking. The maximum H2 content in syngas (52.2 vol%) was obtained with 2.5 kg of activated carbon at a steam to fuel ratio of 0.52. The minimum NH3 content in syngas was 20 ppm.

Optimization of the Three-stage Biomass Gasification Characteristics in High-temperature Entrained-flow Bed

The raw material requirements for the indirect liquefaction of biomass are strict. In particular, the ratio of H2/CO must be greater than or equal to 1. However, traditional biomass gasification has problems that include a low H2/CO ratio and low carbon conversion rates. This study proposes a three-stage gasification optimization model in which pyrolysis products are separated before being put through a second gasification step. The optimized model simulation used MATLAB software and the experiments were carried out in a biomass, high-temperature entrained-flow bed. The results demonstrate that, compared to traditional mixing gasification, three-stage gasification can effectively increase the H2 content in syngas. The H2 content can reach 42.3%, which is 4.6% higher than in traditional gasification. Additionally, this process can increase the H2/CO ratio to 1.23, which is 43% higher than the ratio 0.86 in traditional gasification. This also could provide raw materials for the indirect liquefaction of syngas. Thus, three-stage gasification can eliminate the need for intermediate steps such as steam reforming and adding external H2. Experiments indicated that the best gasification conditions were a first gasification time of 0.6s and a gasification temperature of 1100 °C, under which the H2/CO ratio reached a maximum of 1.2.