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Alkali metals are important factors affecting the process of biomass pyrolysis. In this paper, rice straw (RS) with different occurrence forms of alkali metals was used as the research object. The heat decomposition characteristics, the release law of small molecule gases and the change law of in-situ pyrolysis tar composition were investigated by the thermal mass spectrometer (TG-MS) and thermal pyrolysis-GC/MS (Py-GC/MS) to reveal the action mechanism of different occurrence forms of alkali metals in the pyrolysis process. The results showed that with the increase of the removal degree of alkali metals from rice straw, the release temperature of small molecules during the pyrolysis shifted to the high temperature region, due to the catalytic effect of alkali metals on the escape of small molecules. The different occurrence forms of alkali metals had different influences on the tar components. Water-soluble alkali metals inhibited the production of alcohols and promoted the production of ketones and aldehydes. Ion-exchanged alkali metals had different effects on oil composition at different temperatures. At the pyrolysis of 300°C, the presence of ion-exchanged alkali metals inhibited the production of aldehydes and ethers, and promoted the production of esters and ketones, but opposite effect was obtained at the temperature higher than 400°C. Kinetic analysis showed that both water-soluble alkali metal ions and exchanged alkali metals could reduce the activation energy of biomass pyrolysis.

The carbon content in fine slag during entrained-flow gasification is very high, at present, most of the fine slag was disposed by landfill. It is expected to provide a favorable technology by adding the fine slag to the circulating fluidized bed boilers to participate in combustion reaction. In this study, the gasification fine slags generated from GE, OMB and GSP gasifier, which are typical gasification processes in Ningdong energy and chemical base, was selected for investigation. The structural features and combustion reactivity of the residual carbon in the gasification fine slag were systematically studied by physical adsorption apparatus, laser Raman spectrum and thermogravimetric analyzer. The results showed that the materials in the original gasification fine slag could be divided into cohesive spherical particles, porous irregular particles and isolated large spherical particles, while the acid-washed gasification fine slag was mostly composed of loose fine particles and porous irregular massive particles. Additionally, the particle size of the residual carbon was clustered to 4–8 nm, and the specific surface area and active sites of that decreased orderly as follows: GE>OMB>GSP. The order degree of the residual carbon structure in GE slag was the lowest, and the amorphous carbon structure in it was the highest, while the case in GSP was the opposite. The combustion rate of the residual carbon in GE slag was the fastest, mainly due to its large specific surface area, more amorphous carbon structure and active site, and the comprehensive combustion index of residual carbon in GE slag was 5.26×10−7 %2/(min2·°C3).

A thermogravimetric analyzer and in-situ heating microscope were used to study gasification reaction of coal char particles on the interface of ash layer and slag at 1100, 1200 and 1300°C, using typical Ningdong coal-Yangchangwan coal as gasification raw material. The results show that the shape change of ash layer interface and slag interface under different gasification temperature is the main factor that affects the gasification reactivity of coal char particles. When the gasification temperature is 1100°C, the ash layer shrinks and wraps on the surface of coal char particles at high temperature, preventing the contact between gasifying agent and coal char particles and reducing the gasification reaction of char particle. However, the interface of slag does not change significantly, and the gasification reaction rate of coal char on the slag interface remains unchanged. When the gasification temperature is 1300°C, the interface of both ash layer and slag turns into a liquid phase. Under the surface tension, the char particles are broken, the effective reaction area became larger, and the heat transfer rate increases, thereby increasing gasification reaction rate of the coal char.

Meihuajing coal and Yangchangwan coal from Ningdong, China are chosen as raw materials to study char gasification reactivity using thermogravimetric analyzer and in-situ heating stage microscope, and typical gasification coal-Shenfu bituminous coal char is used as reference char sample. The char physicochemical properties are systematically characterized. The results show that the order for gasification reactivity of 3 chars at the same gasification temperature is Yangchangwan char > Meihuajing char > Shenfu char. In-situ study of heating stage microscope shows that with the progress of char-CO2 gasification, most of char particles react with CO2 as shrinking particle mode, and the particle reaction form changes from shrinking particle mode to shrinking core mode at high carbon conversion level. Additionally, it can be found from the results of shrinkage ratio variation of the particle projected area during gasification that Yangchangwan char shows the largest shrinkage area when undergoes the same reaction time, followed by Meihuajing char and Shenfu char. The difference in gasification reactivity is mainly attributed to the difference of physicochemical properties of chars. i.e.,Yangchangwan char shows the largest specific surface area and the total contents of K, Na and Ca and the lowest order degree of carbon structure, followed by Meihuajing char and Shenfu char.

Based on the bench-scale opposed multi-burner (OMB) coal-water slurry gasification experimental platform, the transformation and release characteristics of sodium during the reaction of coal in the gasifier were studied. Particles sampled at different axial distances from burner plane to top and bottom along the gasifier chamber were analyzed. After the microwave digestion and chemical fractionation analysis, the content of sodium was tested by flame atomic absorption spectrometer (FASS). The morpholo gy and elements of particles were analyzed by scanning electron microscopy and energy spectrum application system (SEM-EDS). The FASS results showed that the release rate of sodium increased first then decreased with increasing distance to the burner plane. The area near the burner plane was the major release area of sodium. With the reaction in progress in the gasifier the occurrence form of sodium was transformed from water-soluble sodium and ion-exchangeable sodium into the acid-soluble sodium and residual sodium. Combining the SEM-EDS and FASS results, the spherical particles which were formed through melt minerals reacted with sodium in the gas phase to form silicate and sialic acid salt in gasifier. The increasing number of spherical particles led to an increase in the sodium content in the particles.

Most published works focused on the characteristics of chemiluminescence in homogeneous flames, but the research about radiation spectrum in heterogeneous flames was still limited. In this paper, improved hot oxygen burner (HOB) technology is applied to ignite coal water slurry (CWS) directly in the open space, for stable combustion. Radiation spectrum and two-dimensional OH* chemiluminescence in methane and CWS diffusion flames are measured by a fiber optic spectrometer and a high-spatial-resolution UV imaging system. The results show that OH* (309.12 nm), CH* (431.42 nm) and C2* (463.52~563.43 nm) radicals exist in both methane and CWS diffusion flame, but Na* (589.45 nm), Li* (670.88 nm), K* (766.91, 770.06 nm), H* (816.04, 819.99 nm) radiation spectrum line and continuous black-body radiation have been detected only in the CWS flame. These differences can be used to characterize the combustion or gasification of CWS and distinguish whether CWS is ignited or not. In addition, the injection of CWS into methane flame leads to a significant reduction in OH* and an increase in C2* and CH* radiation intensity. This is because a lot of heat is absorbed in the processes of CWS combustion reactions. Then the generation of CH is inhibited, and the production of OH* is reduced. The increase of C2* and CH* is due to simple substance carbon produce more after injecting CWS. Besides, axial OH* radiation intensity increases at first then decreases, and the position of peak intensity is closer to outlet of hot oxygen burner compared with methane flames. Radial OH* radiation distribution is bimodal in methane flame because reactions take place in the thin layer where methane and oxygen meet. However, in CWS flame, radial OH* radiation distribution is always unimodal since CWS diffuses fiercely and mixes with oxygen sufficiently. As the ratio of oxygen atom to carbon atom ([O/C]e) increases, the reaction region of OH* radicals becomes larger in methane and CWS flame. This indicates that increasing oxygen can promote reactions and benefit OH* radicals’ generation. Moreover, with the increase of CWS flow, reaction center is closer to burner outlet, OH* distribution range and peak intensity decrease obviously, CH*, C2*, Na*, Li*, K*, H* and black-body radiation intensities markedly rise. And these characteristics can reflect the changes of operation loads.

The entrained-flow coal gasification is an important and attractive technology in large scale coal-based synthetic natural gas (SNG) process. In this study, an integrated entrained-flow coal gasification and pyrolysis system is proposed and investigated. The gasifier is divided into two stages in this system: one is mainly for the gasification of char and the other is mainly for the coal pyrolysis. The integrated system is studied by using a process simulation model and compared with a coal gasification system with the radiant and convective coolers. The effects of the operating conditions on the gasification performance are studied and the optimized operating conditions are obtained. It is found that the optimized steam coal ratio of the integrated system is about 250–300 kg(steam)/t (dry coal) while the gasification temperature is 1400°C. The cold gas efficiency of 88.18% of the integrated system is higher than that of 84.14% of the gasification and radiant+conductive cooler system. The coal and O 2 consumptions are relative low in the integrated system. The performance of the integrated system is highly related to the yield of tar and CH 4 in the pyrolysis stage. The overall energy conversion efficiency of the integrated system (92.26%) is slightly lower than that of the gasification and radiant+conductive cooler system (93.39%). However, the exergy efficiency is enhanced by more than 2.2% in the integrated system. The integration of the gasification and pyrolysis can effectively recover and promote energy grade of the sensitive heat in the hot syngas.

The microscopic characteristics of solid particles have important influence on the formation of fluid slag, coarse slag and fine slag during entrained-flow gasification process. Based on the bench-scale opposed multi-burner (OMB) gasifier, solid particles were sampled at different axial distances along the gasifier chamber under typical operating conditions (oxygen and carbon atomic ratio at 1.0). The microscopic characteristics of solid particles were studied by using N2 adsorption-desorption and scanning electron microscopy (SEM) methods. The results show that the solid particles are comprised mainly of porous irregular particle and spherical particle, and few solid particles generated at burner plane perform as dense irregular and hollow shape. As the gasification reaction proceeds along the axis of gasifier, the surface structure of particles becomes rougher, and the pore structure increases. The isotherms of particle samples are all type II, and the particle samples consist of continuous and complete system of pores. The hysteresis loops are H3-type, and there are a large amount of fractured pores. BET surface area and pore volume increase with increasing distance from the burner plane, and average pore diameter gradually reduces, and larger changes occur in the vicinity of the burner plane. The mesopores less than 10 nm vary apparently and increase with increasing distances from the burner plane, while the pores larger than 10 nm are almost unchanged.

In order to understand the behavior of biomass pyrolysis, a series of pretreatment biomass were prepared with acid-washing and metal impregnated methods. The effects of metal ions on the yields of tar, char and gas from straw pyrolysis were analyzed in our lab scale fixed-bed reactor. Alkali metal and alkaline earth metal ions affect biomass pyrolysis process and the products heavily. The decreasing metal ions result in declining yield of semi-char and increasing yields of tar and gas. Meanwhile, the pyrolysis temperature corresponding maxium yield of tar increases. There exist marked catalytic effect of potassium, calcium and magnesium cations on the cracking of large molecular weight parts of tar and semi-char formation via recombination reaction of tar. As cause a higher production of char while a decrease of tar and gas production.

A study of pressure fluctuation signals in an impinging entrained-flow gasifier was undertaken using multifractal analysis. By applying the method of direct determination of the f(α) singularity spectrum, the values of different radial position pressure fluctuation signals’ singularity spectra were calculated. It was found that the pressure fluctuation exhibited the multifractal characteristics, the comparison of the pressure fluctuation signals from “unstable operating condition” to “stable operating condition” suggests that the combustion system is characterized by a dynamical change from heterogeneity toward homogeneity, revealed by a loss of multifractality. Origin of multifractal phenomena of the pressure signal measured in the entrained-flow gasifier was interpreted in terms of the multiplicative cascade process.