Jiejie Huang

Interaction and its induced inhibiting or synergistic effects during co-gasification of coal char and biomass char

Co-gasification of coal char and biomass char was conducted to investigate the interactions between them. And random pore model (RPM) and modified random pore model (MRPM) were applied to describe the gasification behaviors of the samples. The results show that inhibiting effect was observed during co-gasification of corn stalk char with Hulunbeier lignite coal char, while synergistic effects were observed during co-gasification of corn stalk char with Shenmu bituminous coal char and Jincheng anthracite coal char. The inhibiting effect was attributed to the intimate contact and comparable gasification rate between biomass char and coal char, and the loss of the active form of potassium caused by the formation of KAlSiO4, which was proved to be inactive during gasification. While the synergistic effect was caused by the high potassium content of biomass char and the significant difference of reaction rate between coal char and biomass char during gasification.

Effect of CO2 on pyrolysis behaviors of lignite

Abstract The pyrolysis of Huolinhe lignite under CO2 atmosphere was carried out in a thermobalance and a fast heating-up fixed bed reactor. The distribution of gases, char yield and its property such as element, surface structure, FT-IR spectra were analyzed. By this, the effect of CO2 on the pyrolysis behaviors was studied. The results show that CO2 gasification of the nascent char, which destroys the hydrogen-containing char structure, not only promotes cracking of benzene ring and fracture of hydroxyl, methyl and methylene groups etc., but also weakens the interaction between H and char matrix and increases the H fluidity, leading to the increase in the generation of H radicals. These H radicals can combine with other free radical fragments generated from fracture of the coal macromolecules to produce more volatiles. This will produce the char with a high specific surface and high pore volume and porosity. The introduction of CO2 promotes the coal pyrolysis and generation of volatile, resulting in decrease in char yield and increase in the evolution amount of H2, CO, CH4 and other small molecules hydrocarbons.

Experiment and mathematical modeling of a bench-scale circulating fluidized bed gasifier

Abstract The gasification of two different coals and chars with CO 2 and CO 2 /O 2 mixture in a 48-mm-i.d. circulating fluidized bed (CFB) gasifier is investigated. The effects of operation condition on gas composition, carbon conversion and gasification efficiency were studied. A simple CFB coal gasification district mathematical model has been set up. The effects of coal type and CFB operating conditions on CFB coal gasification are discussed based on the CFB gasification test and model simulation. The main operation parameters in CFB gasification system are coal type, gas superficial velocity, circulating rate of solids and reaction temperature. It is found that CO concentration and carbon conversion increase with increasing solids circulating rate and decreasing gas velocity due to the increase in gas residence time and solids holdup in the CFB. The carbon conversion increases with increasing temperature and O 2 concentration in the inlet gas. The experimental results prove that the CFB gasifier works well for high volatile, high reactivity coal.

Regeneration characteristics of sulfided zinc titanate sorbent for hot gas cleaning

Abstract The regenerated zinc titanate sorbent is one of the leading candidates for hot coal-derived gas desulfurization. The effects of the regeneration temperature, O 2 concentration, and sorbent granular size on the regeneration performance of the Zn 2 TiO 4 sorbent were investigated using the thermogravimetric analyzer. Zinc sulfate formed through side reactions was inferred from TGA curves and confirmed by XRD analysis when the sorbent was regenerated at higher concentration of O 2 and lower temperature ( 2 with regenerated ZnO in the presence of O 2 may be the main reason for the formation of ZnSO 4 . The reasonable regeneration conditions must avoid the sulfate formation. Regeneration kinetic studies were also performed at regeneration temperatures ranging from 725 to 800°C. Higher regeneration temperature and O 2 concentration, and smaller granular size can increase the regeneration rate. The reaction order with respect to O 2 can reasonably be assumed to be 1. Kinetic model tests show that the regeneration process can be well fitted by the shrinking core model. The kinetic controlling steps change with the sorbent regenerating. The chemical reaction rate is the controlling step at the early regenerating stage (x 75%). The reaction rate constants and the effective diffusivities were calculated according to the model. The apparent activation energy of chemical reaction and the corresponding frequency factor are 19.11 kJ/mol and 8.01×10 −2 m/s, respectively, and the diffusion activation energy and the corresponding frequency factor are 48.84 kJ/mol and 3.12×10 −4 m 2 /s, respectively.

Coal gasification in a stirred bed reactor

Two Canadian non-caking coal chars of millimetre particle size were gasified in a stirred bed reactor at atmospheric pressure using steam-nitrogen mixtures. Experimental results showed that the reaction atmosphere changed with carbon conversion and the unit operated as a typical integral reactor. Some properties of the partially reacted chars were measured. The effects of gas superficial velocity, char particle size, steam partial pressure and temperature on conversion were examined. The role of transport resistance was assessed and empirical kinetic models were tested.

Transformation of sodium during gasification of a lignite with addition of NaCl and NaAc

Abstract The transformation and releasing characteristics of sodium during steam gasification of the chars from rapid pyrolysis of lignite with addition of different concentrations of NaCl and NaAc have been studied in a fixed bed at 900 and 950°C under atmospheric pressure. The results show that part of water-soluble sodium and acid-insoluble sodium are transformed into water insoluble but acid soluble during gasification when the concentration of sodium in char is lower. And almost all the sodium is released to gas phase when the addition of sodium is higher. The transformation characteristics of additive NaAc is different from NaCl. Nearly, all the sodium is released to gas phase during gasification. The gasification temperature and the sodium concentration show little influence on the volatility behavior.

Mineral behavior of low-temperature lignite ashes under gasification atmosphere

To investigate the mineral behavior of lignite ashes under gasification conditions, 450 °C Xiaolongtan lignite ash samples (XLT-LTA) treated at different temperatures or pressures under reducing atmosphere (H2/CO2=1: 1, volume ratio) have been examined by means of an SC-444 apparatus, a scanning electron microscope with an energy dispersive X-ray detector (SEM-EDX), and by X-ray diffraction (XRD). The results showed the sulfur content in the XLT-LTA to be much higher than that in ashes prepared at 815 °C, as a result of the release of sulfur dioxide during the oxidization of pyrite. With increasing temperature, the XLT-LTA particles gradually agglomerate and form partially molten surface entities with obvious apertures, and the content of iron and calcium in the congeries or molten parts increases due to the fusion of fine ash particles with the enrichment of iron and the formation of low-temperature eutectics of calcium and iron. An increase of pressure restrains the decomposition of calcite and muscovite, and promotes the formation of iron minerals (e.g., hercynite, cordierite, and sekaninaite) and orthoclase. The content of amorphous material also increases with increasing pressure.

Slagging characteristics of fly ash from anthracite gasification in fluidized bed

Abstract An experimental procedure was tested for studying the sintering and fusion characteristics of fly ash from anthracite fluidized bed gasification at the temperature approaching the ash deformation temperature (DT), and the slagging characteristic was investigated. The quantitative analysis on the composition of crystalline mineral matter and the amorphous phases in the thermal treated ash was carried out using X-ray diffraction analysis (XRD). Experimental results show that the slagging tendency of fly ash is related to the transformation of minerals. AFTs of fly ash are lower than those of original coal due to higher contents of Fe, Ca, and Mg. The formation of melting matrix causes a liquid-phase sintering at 100–200°C below the DT, which leads to a shrinkage deformation and clinkering due to the formation and transformation of feldspar that plays a ‘glue’ role in sintering. A great amount of Ca and all of Fe are found in the glass phase, which improves the amorphous phase in concentration. These fluxing components in the glass phase that do not crystallize during thermal treatment can promote the densification process of sintering and the slagging or agglomeration tendencies.

Reaction characteristics research of coal char chemical looping gasification for hydrogen production with an Fe-Zr oxygen carrier modified by K2CO3

Abstract An Fe-Zr oxide (Fe2O3 and ZrO2) modified by K2CO3 was prepared as the oxygen carrier (denoted as K3-Fe70Zr30) to examine the effects of temperature and char mass/oxygen carrier (OC) ratio on gas yield and composition during coal char chemical looping gasification for hydrogen production. The results of temperature-programmed experiments show that the reaction of oxygen carrier and coal char starts at 500°C, and the reaction rate increases sharply above 750°C. The reduced oxygen carrier begins to react with steam at 400°C, and the concentration of hydrogen significantly increases above 500°C. The results of isothermal experiments indicate that the reaction rate is accelerated with increasing reaction temperature. However, the H2 production yield decreases as the temperature rises when the ratio of CO/CO2 volume ratio increases. In addition, with the increase of char/OC ratio, the ratio of CO/CO2 in the outlet gas increases. As a result, the hydrogen production firstly increases and reaches a maximum value of 1.734 L/g, and then decreases. The activity of oxygen carrier can keep stable during the first 2 redox cycles, but decreases in the 3rd one. The activity can be renewed by the supplement of K2CO3, suggesting that the decreased activity of oxygen carrier can ascribe to the loss of K2CO3.

Characteristics of fine chars from fluidized bed gasification of Shenmu coal

Abstract The ash fusion characteristics, particle-size distribution and gasification reactivity of Shenmu coal (SM) fine chars from ash agglomerate fluidized bed gasification were explored by ash fusion point analyzer, scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDX), and thermo-gravimetric analyzer. The results show that the decrease in basic ingredients (e.g. iron and calcium) and the increase in acidic ingredients make the ash fusion temperature (AFT) of SM fine chars lower than that of SM. There is a wide particle-size distribution in SM fine chars, which shows a significant multi-peak distribution, and a large difference of the elemental distribution in fine char particles with different sizes. The moisture content is lower and ash content is higher in fine power than that in SM, respectively. SM fine char has higher surface area than that of SM char, and relatively rich in meso-pores and macro-pores, which results in its higher gasification reactivity than SM char.