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As the world’s largest energy consumer (i.e., 24% of the world) and one of the largest biomass resource reserve countries (i.e., total reserves of 73.42 × 108 t a–1), for China, using biomass to pr...

A good understanding of the catalytic mechanism of alkali and alkaline earth metal species during pyrolysis is required for the development of biomass utilization, to take advantage of its special thermochemical properties. The mechanism of the volatile–biochar interaction, especially between H radical/CO2/H2O and K/Ca in biochar, was systematically investigated by combining experimental analyses and density functional theory calculation. The results indicate that, at 500–900 °C, the yield of biochar from rice husk pyrolysis is basically constant, which mainly shows the mutual conversion between gas and liquid products. With the increase of loading alkali and alkaline earth metal species (AAEMs), the tar yield gradually decreased, and with it reaching a certain content, a significant catalytic effect of AAEMs can be observed. K is more beneficial to maintain the stability of the biochar structure than Ca. The intensities of CO and C–O–C functional groups would appear with a certain increase with the increasing concentration of bond-linking AAEMs. At 700–900 °C, the precipitation ratio of K is almost twice that of Ca and even more. The presence of AAEMs can largely inhibit the formation of three-ring tar components, and more converted to one-ring tar components. The H radicals in the volatile can be bonded to C in the C–O–K structure, thereby causing the K element to decouple with the functional group, and tend to be adsorbed on the carbon matrix. For the Ca-loaded structure, it is manifested in strong adsorption of H radicals by Ca, resulting in the weakening of C–O bonds and the looseness of the biochar structure. The interaction between K/Ca in biochar and H2O/CO2 is reflected in the mutual attraction of AAEMs and the O atom in the H2O/CO2 molecule.

The heterogeneous NO reduction characteristics with biomass char and coal char blends in a microfluidized bed reaction analyzer (MFBRA) and its kinetic analysis were investigated. Sawdust char had ...

Methane steam reforming (MSR) is studied experimentally and numerically. The intrinsic kinetics of the reaction are determined using a micro fluidized bed with a catalyst containing more than 50 wt % NiO/α-Al2O3. Intrinsic kinetic models are developed for parallel and serial reaction mechanisms, but the parallel mechanism is found to better match the experimental data. The activation energies for CO and CO2 formation are 81.69 kJ/mol and 59.38 kJ/mol, respectively, and the pre-exponential factors are 316.6 mol/(g h kPa0.85) and 0.00263 mol/(g h kPa3.1), respectively. As the reaction temperature increases, the rate of CO formation increases and that of CO2 decreases. At 800 °C, almost all the CH4 is converted to CO and H2, and the methane conversion rate (XCH4), the hydrogen production rate (YH2), and the CO selectivity (SCO) are 92.28%, 3.34, and 0.99, respectively. The effects of the steam-to-carbon ratio (S/C), inlet velocity, and preheating temperature at different reaction temperatures are simulated using the FLUENT software package. As S/C increases, XCH4 and YH2 increase, but SCO decreases. The higher the reaction temperature, the less S/C promotes XCH4 and YH2. When the reaction temperature is 700 °C and the inlet velocity is 0.2 m/s (residence time is 0.5 s), XCH4 is above 95%, and changes in the inlet velocity strongly influence the formation of CO. With increasing preheating temperature, XCH4, YH2, and SCO all increase gradually.

Fuel conversion and clean energy reaction systems involve a variety of catalytic and non-catalytic gas-solid thermochemical reactions. A good understanding of the correct reaction mechanism and kinetics, as well as the profiles of reaction products, is of great significance to the development, design, and operation of such reaction systems. The micro fluidized bed reaction analysis provides an efficient and reliable method to acquire this essential information with low capital and operating costs, low energy consumption and enhanced safety. This paper provides an overview of the system and its characteristics for the micro fluidized bed reaction analyzer that has been well proven to be a reliable new approach as well as an instrument for characterizing various gas-solid thermochemical reactions.

To investigate pyrolysis characteristics of Shenhua bituminous coal under pressurized conditions, the effects of pressure (0-1.2 MPa) on the physicochemical structure and combustion reactivity of pyrolysis char samples prepared at 1073 and 1273 K were studied in a pressurized drop tube furnace (PDTF). The low temperature nitrogen adsorption test was used to characterize the physical structure of char samples. The results showed that, the increase of pyrolysis pressure is conducive to formation of mesopores, and the specific surface area is larger at 1273K. Raman and XPS analysis were used to characterize the chemical structure of char samples. The results showed that, the increase of pressure can promote the transformation of smaller aromatic structure into larger aromatic structure, and the graphitization degree are more obvious at 1273K. With the increase of pressure, the proportion of C=C/C-C bond in char structure increases and the proportion of C-H bond decreases. It indicates that the unst...

The characteristics of gas–liquid–solid products during corn straw–H2O gasification were studied by the one-stage fluidized-bed/fixed-bed quartz reactor. The results indicate that the transformation between gas and solid products is mainly presented with the increase of feeding time (0–40 min). The aromaticity of biochar decreases slightly in the feeding period of 10–20 min but gradually increases in 20–40 min. The oxygen-containing functional groups in biochar increase gradually with the increase of the feeding time. The K content in biochar increases by 27% in 10–30 min, while that of Ca increases by 36% in 10–20 min. When the carbon conversion rate is less than 8%, the reactivity of biochar produced by 30 min of feeding is highest. The contents of phenol and 2,3-dihydrobenzofuran of tar increase by 25 and 34%, respectively in 20–40 min. The char–tar–H2O interaction in biomass gasification is a two-stage reaction. The first stage is dominated by the volatile–char interactions, while the second stage is ...

The reaction characteristics of different mixing ratios of coal/char to NO reduction were investigated under the conditions of relatively low O2 concentration at 1073–1203 K. The inlet NO concentra...

Pressurized O2/H2O combustion is a promising oxy-fuel technology for reducing CO2 emissions while improving the overall efficiency of power plants. However, this process is complex, and the associated char-N conversion are not well understood. In the present work, a pressurized horizontal furnace reactor was used to investigate the effects of different factors on the migration and transformation of char-N. Flue gas analysis and X-ray photoelectron spectroscopy were employed to assess the effects of pressure (over the range of 0.1–1.3 MPa), steam concentration (0%–60%) and residence time (60–240 s) on NO emissions and the transformation of char-N. Pressure was found to affect NO emissions and the lowest relative migration of char-N to NO was at 0.4 MPa. With increases in pressure, the proportions of N-5 and N-X groups increased and decreased, respectively·H2O promoted the migration of char-N to NO and the formation of N-X functional groups. As the reaction time prolonged, the proportion of N-5 groups decreased in the early stage of the reaction, that of N-X groups increased in the late stage and N-6 and N-Q groups remained stable.

The pressurized O2/H2O combustion technology can achieve nearly zero CO2 emissions during coal-fired power generation. In order to explore the influence of pressurized O2/H2O conditions on the thermal conversion characteristics of pulverized coal, Zhundong demineralized coal was used as raw material to prepare pyrolyzed char at 0.5 MPa and then the O2/H2O combustion experiments with different H2O concentration (0–40%), temperature (850-1000℃) and residence time (100–250 s) were carried out under the same pressure by a pressurized horizontal furnace. The carbon transformation, pore structure, carbon skeleton structure, and surface functional group structure of char under different experimental conditions were obtained by weighing method, Nitrogen adsorption test, Raman, and X-ray photoelectron spectroscopy methods, respectively. In addition, the reactivity of char was tested by thermogravimetric analyzer and micro fluidized bed reaction analyzer (MFBRA) to explore the relationship between the char structure and reactivity.

This study aims to examine the char-steam reactions in-situ, following the pyrolysis process of a demineralized coal in a micro fluidized bed reactor, with particular focuses on gas release and its kinetics characteristics. The main experimental variables were temperatures (925 °C−1075 °C) and steam concentrations (15%–35% H2O), and the combination of pyrolysis and subsequent gasification in one experiment was achieved switching the atmosphere from pure argon to steam and argon mixture. The results indicate that when temperature was higher than 975 °C, the absolute carbon conversion rate during the char gasification could easily reach 100%. When temperature was 1025 °C and 1075 °C, the carbon conversion rate changed little with steam concentration increasing from 25% to 35%. The activation energy calculated from shrinking core model and random pore model was all between 186 and 194 kJ/mol, and the fitting accuracy of shrinking core model was higher than that of the random pore model in this study. The char reactivity from demineralized coal pyrolysis gradually worsened with decreasing temperature and steam partial pressure. The range of reaction order of steam gasification was 0.49–0.61. Compared to raw coal, the progress of water gas shift reaction (CO + H2O ↔ CO2 + H2) was hindered during the steam gasification of char obtained from the demineralized coal pyrolysis. Meanwhile, the gas content from the char gasification after the demineralized coal pyrolysis showed a low sensitivity to the change in temperature.

A laminar coflow CH4/air diffusion flame was experimentally and numerically studied to elucidate the mechanism of flame attachment and the importance of preheating, thermal boundary condition at the fuel tube, and burner geometry to the flame attachment location. OH*-chemiluminescence images were captured using an intensified CCD camera. The temperature of the outer surface of fuel tube at 2 mm below the burner exit was measured using a K-type thermocouple. Detailed simulations based on five different burner wall models were conducted to investigate the influence of preheating effect and burner geometry on flame attachment. The conjugate heat transfer between the heat-conducting burner wall and the surrounding gas flows was considered in the overall flame model to account for the preheating effect without or with less ad hoc assumptions for the burner inlet conditions. The effect of different thermal boundary conditions imposed at the fuel tube on the predicted flame attachment location was investigated. Results show that it is paramount to specify the inlet location at a certain distance upstream the burner exit to model the flame attachment phenomenon. This finding can be explained in terms of the direct heating of the fuel and air streams by the flame base or the mixing process between the fuel and air streams associated with the hydrodynamics and diffusion in the vicinity of the burner rim. The thermal boundary condition at the fuel tube only slightly affects the predicted flame attachment location. The fuel decomposition occurs inside the fuel tube mainly due to preheating by the fuel tube wall and the key chemical pyrolysis process was revealed through a detailed kinetics analysis. The efflux of CH4 to the air side over the burner rim was found responsible for the flame attachment under current conditions. The flame base kernel is established around the stoichiometric mixture and its location is controlled by the thermal condition and geometry of the burner wall. The burner geometry influences the position of flame attachment on the outer surface of the fuel tube through the fuel tube heat capacity and the shape.

To study the role of gasifying agents (H 2 O/CO 2 ) on the improvement and maintenance of biochar catalytic activity for in situ biomass tar reforming, experiments were carried out in a two-stage fluidized-bed/fixed-bed reactor. The physicochemical properties of biochar, which are responsible for its catalytic activity during tar reforming, were analyzed by ICP–AES, SEM–EDX, BET and XPS methods. The conversion of biomass tar was investigated by GC–MS. Adding H 2 O or CO 2 was found to improve the homogeneous and heterogeneous reforming of biomass tar, the latter of which involved first forming an intermediary coke product that was subsequently gasified by H 2 O/CO 2 . Activation of biochar by H 2 O/CO 2 impacted the biochar surface's morphology and distribution of metal species. During tar reforming, the presence of H 2 O/CO 2 also affected the creation and regeneration of pore structures, influencing the biochar's structure and dynamically distributing AAEM species, which ensured enough surface active sites to maintain the biochar's catalytic activity. CO 2 produced more micropores in the biochar, whereas H 2 O favored the formation of mesopores, which are more important for tar reforming. The addition of H 2 O/CO 2 was found to notably enhance in situ reforming of both large and small aromatic ring systems in biomass tar over biochar.

The laminar flame speeds of H2/air with steam dilution (up to 33 vol%) were measured over a wide range of equivalence ratio (0.9–3.0) at atmospheric and elevated pressures (up to 5 atm) by an improved Bunsen burner method. Burke, Sun, HP (High Pressure H2/O2 mechanism), and Davis mechanisms were employed to calculate the laminar flame speeds and analyze different effects of steam addition. Four studied mechanisms all underestimated the laminar flame speeds of H2/air/H2O mixtures at medium equivalence ratios while the Burke mechanism provided the best estimates. When the steam concentration was lower than 12%, increasing pressure first increased and then decreased the laminar flame speed, the inflection point appeared at 2.5 atm. When the steam concentration was greater than 12%, increasing the pressure monotonously decrease the laminar flame speed. The chemical effect was amplified by elevated pressure and it played an important role for the inhibiting effect of the pressure on laminar flame speed. The fluctuations of the chemical effect at 1 atm were mainly caused by three-body reactions, while the turn at 5 atm was mainly caused by the direct reaction effect. Elevated pressure and steam addition amplified the influences of uncertainties in the rate constants for elementary reactions, which might leaded to the disagreement between experimental and simulation results.

This study aims to investigate the mechanisms of tar destruction during volatile-char interactions at low temperature (400–700 °C). A bio-char was subjected to interactions with biomass volatiles at different temperatures (400–700 °C). The results indicate that tar is converted into gaseous and solid products (coke) during volatile-char interactions and the proportion of coke formed on the bio-char from the total converted tar steadily increases with increasing temperature. The non-aromatic structures (e.g. aliphatic and/or O-containing structures) in tar are mainly converted into gases by catalytic cracking and/or reforming reactions on char, while the aromatic structures in tar primarily go through condensation/polymerisation reactions to form coke on char surface. The UV-fluorescence spectroscopic results imply that the non-aromatic structures in tar are easier converted on char than aromatic structures at low temperature (e.g. 400–500 °C) and the conversion of aromatic structures through coke formation on char will be enhanced at higher temperature (e.g. 600–700 °C). The Raman spectroscopic results show that some O-containing species in tar molecules are transferred to the char and form additional O-containing structures into the entire char matrix during the volatile-char interactions.

In actual combustion facilities, coal chars are often generated using a variety of pyrolysis processes, such as secondary pyrolysis, which is characterized by a long residence time in high temperature zone. The effects of such processes on the conversion of char N to NO during combustion have seldom been explored. In this study, the releases of NO during the combustion of coal chars obtained from different pyrolysis processes in a drop tube and in a fixed bed reactor were investigated. In addition, the extent of char N/NO conversion was studied in relation to the char reactivity, pore surface structure and carbon conversion in a horizontal tube furnace. The results show that, compared with chars generated by a single pyrolysis, chars treated by a subsequent secondary pyrolysis process exhibit larger pore surface areas but less reactivity because of the thermal annealing resulting from a longer thermal history. Chars with higher intrinsic reactivity were also found to release a lower amount of NO. However, a weak correlation was identified between the apparent reactivity and char N/NO conversion, indicating that intrinsic reactivity is more important and directly determines the NO reduction process under combustion conditions. Moreover, char N/NO conversion was significantly affected by the coal rank, and a greater extent of conversion of char N to NO was observed in the case of high-rank coal chars. At a high combustion temperature (1373 K), variations in the bulk O2 concentration had little effect on the char N/NO conversion, and an apparent correlation was found between the extents of char N/NO conversion and the accessible pore surface area. These results indicate that at high temperatures, the char N/NO conversion is directly determined by the accessible pore surface area due to transportation limitations. The NO/(CO + CO2) ratio increased with increasing burn-off in the latter stages of char conversion, which can be attributed to decreases in both the BET surface area and accessible pore surface area available for NO reduction during combustion.

To understand the detailed catalytic mechanism of ion-exchanging AAEM species on biochar structure and its specific reactivity during CO2/H2O gasification, the experiments were carried out in a laboratory fixed-bed reactor at 800 °C, with two kinds of AAEM-loading methods. The migration and precipitation characteristics of AAEM species was evaluated by ICP-AES, while the transformation of biochar structures were analyzed by FTIR and Raman. The specific reactivity of H2O/CO2 gasification biochar was determined by TGA analysis in Air at 370 °C. The results show that the stronger catalytic properties of K and Ca species in H2O atmosphere are obtained than that in CO2. The effect of K is mainly on the formation of O-containing functional groups (e.g. alcohol/phenolic-OH, aldehyde/ester C O and carboxylic COO groups) and the transformation from small ring systems to larger ones, while the catalytic effect of Ca is only to increase the proportion of large aromatic ring structures (≥6 fused benzene rings). The biochar-CO2 reaction took place mainly at the gas-solid interface of biochar, while biochar-H2O one existed throughout the biochar particle. A better distribution of active sites (i.e. surface K/Ca species and O-containing groups) on biochar surface would result in the high specific reactivity of biochar during gasification.

The char reactivity generally determines the overall efficiency of the whole gasification process of coal, so it is of great significance to deeply understand the factors influencing the char reactivity and the coupling mechanism between them. This study aims to investigate the combined impacts of intrinsic alkali and alkaline earth metals (AAEMs) and chemical structure of organic matter on char reactivity, and provide new evidence for confirming the controversial role of water-soluble AAEMs during char gasification. Four series of char samples prepared from Zhundong coal containing different forms of intrinsic AAEMs were isothermally gasified by air in TGA, obtaining the specific reaction-rate curves, and a reasonable evaluation index of char reactivity was established. The carbon skeleton structure of char surfaces was analyzed by Raman spectroscopy. The comprehensive discussion of chemical structure, AAEMs state and char reactivity indicates that the water-soluble AAEMs reduce the char reactivity in the early part of gasification process, which is due to the catalytic cracking of aromatic C H caused by these substances on char surfaces during pyrolysis, while improving the char reactivity in the later part because of the original catalysis of these substances on gasification; the ion-exchangeable AAEMs significantly catalyze the opening of aromatic rings in char during gasification, especially the small rings, which weakens the reaction priority of aliphatic structures; the increasing pyrolysis temperature results in the ordering of chemical structure and the enrichment of ion-exchangeable AAEMs, and the former reduces the char reactivity, while the latter has the opposite effect; at the pyrolysis temperature of 400–600°C, the enrichment of ion-exchangeable AAEMs is the main factor controlling the char reactivity, while at 700–1000°C, the ordering of chemical structure plays a dominant role.

Coke deposition is a critical issue for catalysts in tar reforming. Steam is conducive to tar removal and hydrogen production in biomass pyrolysis, while its effect on coke formation is not well known. Thus, a two-stage fluidized bed/fixed bed reactor was used to study the effect of steam addition on coke deposition. The primary conclusions are as follows: combining steam and biochar, the tar removal efficiency is more than 90% within 20 min of time on stream (TOS). After the TOS reaches 30 min, the biochar surface is saturated with coke deposition and the specific surface area of the biochar stops decreasing. The addition of steam leads to a reduction in the combustion reactivity of the biochar. Besides, the aromatization of the biochar increase and the number of O-containing structures decreases. For the tar, the addition of steam reduces the aliphatics content and increases the O-containing aromatics content. For the gas composition, the addition of steam results in the decrease of CH4 yield while the H2 yield increases to 0.12 L/g. The H/C atomic ratio of the gas composition decreases while the O/C atomic ratio increases. The active coke is consumed and decomposed after the introduction of steam. The remaining coke is dominated by inert coke. This contributes to the relatively developed pore structure but a weakened combustion reactivity of biochar.

Coal-derived carbon black is the main composition of PM2.5, used in the rubber industry and energy storage fields. The formation and structure control of carbon black have attracted significant attention. Alkali metals have influence on the dynamic formation of coal-derived carbon black. To analyze the mechanism of Na in the formation of carbon black, a high-temperature drop tube furnace was used to analysis of carbon black from the pyrolysis of acid-washed coal and Na-containing coal at 1250 °C. DFT was applied to simulate the stepwise inhibitory effect of Na on the polymerization of PAHs into carbon black. The results show that Na promotes the oxidative cracking of large PAHs into small PAHs during the formation of coal-derived carbon black (reaction energy barrier is reduced by 17.7%), and inhibits the condensation of small PAHs molecules to form carbon black molecules (reaction energy barrier is increased by 74.7%), which causes the length of carbon black is shortened by 14.3%, and its curvature is increased by 1.7%. Na could change the spatial structure of formed carbon black-graphite crystallites, which increases the spacing of carbon black by approximately 6.2% to 16.3%. Na enhances the electrochemical performance of carbon black by 2 to 3 times.

This work investigates the heterogeneous reactions of biochar involved activation/gasification and tar reforming in H 2 O and CO 2 atmospheres. The effects of simultaneous and stepwise H 2 O/CO 2 -activation and the addition of nascent tar on the biochar's structure and reactivity during gasification are studied using a two-stage fluidized/fixed bed reactor. FTIR, XPS and Raman analyses are used to investigate changes in the biochar's structure while thermogravimetric analysis is used to characterize its reactivity. Simultaneously activating the biochar in an H 2 O atmosphere and adding nascent tar inhibits biochar's gasification efficiency, while carrying out the same tests in a CO 2 atmosphere promotes it. The nascent tar is mainly reformed in a sequence of coking and coke-gasification reactions, rather than via direct tar reforming over biochar. More O-functional groups are formed on the biochar's surface for the simultaneous process with CO 2 , while there is little difference between the synergies and progressive processes in an H 2 O atmosphere. For both types of treatment, the biochar surface's C O content was greater in CO 2 atmospheres than in H 2 O atmospheres. The synergies and progressive effects of H 2 O and nascent tar on biochar aromatic structure are similar in many ways to that in CO 2 . When nascent tar is present, CO 2 has a stronger positive impact than H 2 O on biochar reactivity (maintaining it or even increasing it throughout the reaction).

Formation of coke deposition is the main problem that restricts the development of tar reforming and even biomass thermal conversion. Biochar, prepared from gasification at 800 °C, was used for the catalytic reforming of biomass pyrolysis tar at 650 °C, monitoring the syngas formation during coke deposition. The principal consequences and conclusions are as follows: the coke yield increases from 10.9% to 18.9%, and the tar removal efficiency decreases from 89.0% to 56.7% when the feeding time of biomass is extended (10–50 min). The number of O-containing groups on the biochar surface decreases, and the proportion of minor aromatic rings increases. Biochar is more efficient in the catalytic removal of aliphatic components from tar than aromatic components. Catalytic reforming leads to the development of tar in the direction of increased aromatization. The addition of biochar has essentially no effect on CO yield and CO2 yield, while the CH4 yield decreases and the H2 yield increases. In addition to tar reforming, CH4 cracking is one of the pathways for coke generation on the biochar surface. The number of physical adsorption sites (nN2) and adsorption equilibrium constant (b) of biochar are obtained based on the N2 adsorption test.

Effects of steam dilution on flame evolution, frequency and oscillation characteristics were investigated using an optically accessible micro-mixing combustor under the lean operating condition (equivalence ratio 0.4 to 0.9). The flame profile was visualized by 5 kHz OH planar laser-induced fluorescence (PLIF), meanwhile the structural zoning analysis, frequency spectrum and dynamic mode decomposition (DMD) methods were used to investigate flame instability. The effects on frequency-shift and temporal-spatial heat-release distribution characteristics were demonstrated. Results indicated that heat-release frequency got blue-shift with the increase of hydrogen equivalence ratio while flame length gradually extended, though the second harmonic frequency only occurred in the flame arm zone. The steam content influenced the heat-release obviously, and the obvious periodic oscillation existed in the dilution ratio of 25%. Furthermore, the increasing or decreasing steam content will make the OH radical concentration and distribution change significantly, meanwhile the intensity and location of oscillation zone were also be influenced. The mode decomposition analysis revealed the growth of oscillation zone was closely related to the flame arm zone (FAZ) and experienced the transition to the flame tail zone (FTZ) with the increase of equivalence ratio.

In the present study, we report the formation rules of gas products (CO, CO2, CH4, HCN, NH3) and the evolution characteristics of the physicochemical structure during the pyrolysis of Shenhua bituminous coal under evaluated pressure using pressurized drop tube furnace (PDTF). The operating pressure, temperature, and residence time were in the range of 1073 ∼ 1273 K, 0.3 ∼ 1.2 MPa, and 0.3 ∼ 3.0 s, respectively. During the experiments, the outlet flue gas was analyzed with an online Fourier Transform Infrared Spectroscopy (FTIR) gas analyzer, and the physicochemical structure of pyrolysis char were sampled and characterized with FTIR, X-ray Photoelectron Spectrometer (XPS), and nitrogen adsorption–desorption methods. The results show that the increasing pyrolysis pressure, temperature and residence time would all promote the release of carbon and nitrogen-containing light gases. The increasing pyrolysis pressure and temperature would promote the decomposition of aliphatic hydrogen content and oxygen-containing functional group. When the pyrolysis residence time is less than 0.6 s, the decomposition of the active structure would be promoted as the residence time increases. While, when the pyrolysis residence time is in the range of 0.6–3.0 s, the active structure of the char products tends to be stabilized. As the pyrolysis residence time increases, the carbon content in the char products first shows a rapidly increase from 69.89% to 87.78%, and then slowly up to 91.25%; however, the oxygen content in the char products first decrease from 28.38% to 10.08% rapidly, and then slowly down to 6.98%; the nitrogen content has an overall downward trend. The specific surface area of the pyrolysis char reached its peak at the pyrolysis residence time of 0.6 s. When the pulverized coal particles were pyrolyzed for 0.6 s under high temperature (1273 K), high pressure (0.9 MPa) and high heating rates, most of the volatiles in the pulverized coal particles have been released.

Supercritical carbon dioxide (sCO2) semi-closed cycle is an advanced, efficient, and economical power generation system that can meet the needs of low cost and efficient utilization of coal and low carbon emissions. The Advanced System for Process Engineering software (Aspen Plus) was used to simulate different sCO2 systems. In the simplified sCO2 closed cycle, multi-stage compression and inter-cooling of CO2 compressors together can increase the system efficiency by about 5%. The system thermal efficiency increases by 0.5% with every 10 bar increase of the combustion chamber pressure between 200 bar and 500 bar, and increases by 0.35% with every 10 °C increase of the combustion temperature between 800 °C and 1500 °C. In the typical sCO2 semi-closed cycle--Allam cycle, the gas temperature in the combustion chamber decreases with the increase of CO2 backflow, and it would decrease with increase of the excess O2 ratio. The system thermal efficiency could be improved by 3% by adding reheat and graded expansion, and by 2% with ASU coupling and CO2/O2 mixing. Adding heat exchangers and proper stream distribution can improve the system efficiency by up to 10%. When the combustion chamber temperature is 1300 °C, turbine inlet pressure is 300 bar, turbine outlet pressure is 30 bar, and the split ratio of CO2 is 5:95, the sCO2 semi-closed cycle with precompression, recompression or partial cooling reaches the highest thermal efficiency (~64%). Depending on the results of the system modification and sensitivity analysis, ideas can be provided for the improvement and demonstration of the system.

Under simulated flue gas conditions, the effect of the residence time of different chars on the evolution of physiochemical structures during the NO reduction process was evaluated. The experimental data proved that the acid-soaking treatment contributed to the development of char structures. Both biomass chars and H-form chars showed better reactivity on NO reduction, which may be related to smaller average pore diameters, larger BET surface areas and larger pore volumes. The increasing of residence time increased the graphitization degree of all chars, and main reductions of structural defects were from within and between carbon graphene layers. Besides, with the residence time increasing, N-6 and N-5 of R-form Shenmu chars were transformed into N-Q and N-X, while N-X and N-Q (and some N-5) of R-form and H-form sawdust chars were transformed into N-6, which is related to the oxidation or reduction reaction for different chars.

Pyrolysis is a fundamental part of the biomass thermal conversion and utilization. A one-stage fluidized bed reactor was used to study the characteristics of gas-liquid-solid products and the migration regulation of C/H/O elements during biomass pyrolysis. The specific conclusions are as follows: the char yield decreases from 24.3 %–14.9 % during pyrolysis from 500 °C to 800 °C. The tar yield decreases from 16.9 % to less than 5 %, while the gas yield increases from 24 % to 71.3 %. The graphitization of biochar decreases and its aromaticity increases during pyrolysis. The form of hydrogen existing in biochar is converted from aliphatic hydrogen to aromatic hydrogen during pyrolysis. The content of weaken-bound oxygen such as carboxyl and aldehyde decreases significantly while the content of strong-bound oxygen such as C O and C O C is essentially unchanged. The peak emission of CO during the instantaneous combustion of biochar increases from 0.0013 L/(g min to 0.0032 L/(g min at 500 °C to 800 °C. The tar starts its aromatization at 700 °C. The aliphatic component disappears from 33 % at 500 °C–600 °C. The double bond equivalent parameter of tar increases significantly, while its H/C ratio and O/C ratio both decrease. The yields of CO/CO2/CH4 increase significantly from 500 °C to 700 °C. H2 starts to appear at 700 °C. A noticeable CH4 steam reforming reaction starts when raising to 800 °C, leading to a decrease in CH4 yield and an increase in CO yield and H2 yield. C/H/O elements in biochar and tar are gradually lost during pyrolysis. The gas phase becomes the main existing form of C/H/O elements after raising to 700 °C.

To further advance pulverized coal (PC) combustion theory and enable the rational development of horizontal bias combustion technology, combustion experiments were conducted in a 250 kW pilot-scale bias combustion simulator; multiple research means of combustion temperatures, flame spectra, burnout rates of residual solids, and NOx formation were used. A blend of sub-bituminous coal from Indonesia and bituminous coal from Australia was tested. The effects of bias concentration ratio (BCR) on the ignition characteristics of parallel bias PC jets in a reducing atmosphere were investigated. The results indicate that with increasing BCR for parallel bias PC jets, the standoff distance gradually decreased; the peaks of subsequent combustion temperature and visible-light intensity gradually increased; the continuous flame regions became advanced and concentrated; the flame stability gradually increased; the burnout rate gradually increased; the NOx formation gradually decreased, and the ignition characteristics...

In this study, the effect of particle size on the release of NO during the char combustion under particle packed-layer conditions was investigated at combustion temperatures of 900 °C~1400 °C. The results show that after pyrolysis, the small size char favored more pores and specific surface area. No significant variations of the intrinsic reactivity of O2 and NO with char particle size were measured. By increasing char particle size, more NO conversion from nitrogen in char (char-N) was found regardless of the combustion temperature and bulk oxygen concentration. This can be explained as follows. By increasing char particle size, less O2 penetrated into the pores and more NO formed because of a less accessible pore surface area and a decreased NO reduction time. The effects of reaction temperature and bulk oxygen concentration were also discussed. A quantified description using a first-order reaction model shows that the char particle size will finally influence the accessible pore surface area and depth ...

To further understand the bias combustion behavior of new coal used for horizontal bias combustion and obtain its characteristic parameters, combustion experiments were conducted in a 250-kW pilot-scale bias combustion simulator; multiple research measurements of flame spectra, combustion temperatures, and burnout rates of residual solids were used. Bituminous coal from Australia, sub-bituminous coal from Indonesia, and a blend of these coals were tested. The effects of the raw-coal equivalent moisture (RCEM), pulverized-coal fineness (PCF), and coal type on the ignition characteristics of parallel-bias pulverized-coal jets in a reducing atmosphere were investigated. The results indicate that, with decreasing RCEM and PCF, the standoff distance gradually decreased, the flame stability gradually increased, the burnout rate gradually increased, and the ignition characteristics gradually improved. The RCEM had negative effects on ignition in the early stage but positive effects during subsequent combustion. ...

In order to investigate the detail changes of biochar physiochemical structures during the tar heterogeneous reforming with biochar under H 2 O and CO 2 atmosphere, the experiment was carried out by a two-stage fluidized bed/fixed bed reactor. The physiochemical structures of biochar samples were analyzed by the SEM-EDX, XPS, FTIR and Raman. The results show that during the heterogeneous reforming of biomass tar with biochar, H 2 O/CO 2 not only has a direct effect on the cracking of tar, but also indirectly affects tar H 2 O/CO 2 reforming by changing biochar structures. The tar heterogeneous reforming in H 2 O atmosphere takes place from the interior of biochar particles to the surface, while it only occurs on biochar surface under CO 2 atmosphere. H 2 O increases the concentration of metal catalysts (mainly K and Ca) on the surface of biochar, while CO 2 have little effect on it. Tar is thermally decomposed and reformed on biochar under H 2 O or CO 2 atmosphere, resulting in the increase of hydrocarbon C H. With the concentration of reforming agent increasing, the effect of H 2 O on the surface oxygen-containing functional groups plays a more dominant role than that of CO 2 . The increase of H 2 O/CO 2 concentration greatly promotes the transformation of small aromatic ring system to large aromatic ring structure in biochar during tar reforming.

Experimental investigations of in-situ tar H 2 O reforming over various biochar species were carried out in the two-stage fluidized bed/fixed bed reactor. The physicochemical structures of biochar were studied by SEM, mercury intrusion porosimetry and FTIR methods. The mechanism of tar H 2 O reforming over biochar was studied through the results of tar yields and quantitative analysis of typical tars by GC/MS. According to the theory of organic mass spectrometry and current mechanisms of tar transformation, the reaction path of typical tar H 2 O reforming over biochar was constructed. The results show that the tar reforming rate over sawdust biochar is the most significant among the three kinds of biochar samples (i.e., rice husk, sawdust and cornstalk). The metallic species contribute greatly to the weight loss of biochar in 15 vol% H 2 O atmosphere at 800 °C, while they are not the only determinants of tar H 2 O reforming. The selectivity of biochar on the in-situ tar H 2 O reforming is determined by the coupling effects of its physical and chemical characteristics. The biochar, with the porous surface structures, a certain amount of metallic species and the carbon structure with low polymerization, would be effective on in-situ tar H 2 O reforming.

In order to obtain the catalytic effects of K and Ca species on the biochar structure during in-situ tar H 2 O reforming over nascent biochar, the H-form/K-loaded/Ca-loaded rice husks were studied for the in-situ tar reforming in the two-stage fluidized bed/fixed bed reactor. The specific reaction pathway of K and Ca for tar reforming was investigated, associated with the changes of biochar structures, through the methods of ICP-AES, Raman, FTIR and XPS. The results indicate that the in-situ volatiles (tar and free radicals) H 2 O reforming over nascent biochar could be conducted by three possible ways: occupying reactive sites on biochar, changing biochar structures and/or changing the total/surface concentration of AAEM species. The mechanisms of in-situ tar H 2 O reforming by K and Ca species were different: tar cracking into low-quality tar or small-molecule gas may be catalyzed by K, while the combination of tar with biochar would be promoted by Ca. The volatilizations of K and Ca with the presence of volatiles were to a large extent in accordance with their valences (monovalent K + and divalent Ca 2+ ) and their boiling points. The subsequent transformation from the small aromatic ring systems to the larger ones occurred due to the volatile-biochar interaction. During the in-situ tar H 2 O reforming over biochar, K and Ca act as the active sites on biochar surface to promote the increase of active intermediates (C O bonds and C O K/Ca), which promotes the tar-biochar interactions.