Ash Fusion Temperatures Research Articles

Investigation into the fusibility of biomass ashes and their mineral phase transformations at elevated temperatures by using the HT-XRD technique

In this paper, the fusibility of biomass ashes with varying chemical and mineral compositions were investigated and their mineral phase transformations were characterised in-situ by using the HT-XRD technique. Results showed that ash fusion temperatures (AFTs) of the analysed biomass increased in the order of walnut shell (WS) < wheat straw (WHS) < peanut shell (PES) < pine sawdust (PS). This is attributed partially to their chemical compositions, since WS and WHS ashes had high K2O contents (30.77%), but the PES and PS ashes were abundant in SiO2, Al2O3 and/or CaO. HT-XRD analysis showed that K-bearing minerals were firstly identified but then diminished in WS ash as temperature, confirming their role for slag formation. For WHS ash, the release of KCl and the formation of K silicates or aluminosilicate at different temperatures were confirmed, leading consequently to a decreased AFTs. In the PES ash, SiO2, MgO, CaAl2Si2O8, CaAl2SiO6 were identified, which also did not melt at the temperatures examined. Likewise, minerals in PS ash including CaO, Ca3SiO5 and Ca2SiO4 remain identified at elevated temperatures. Macro- and micro-morphological analysis shows that the WS and WHS ashes were prone to be sintered at temperatures as low as 650 °C, yet PES and PS ashes were less sintered even at 850 °C. These were confirmed by thermodynamic calculations when the phase and mineral transitions were considered. These mineral phases were also compared with those from conventional XRD, confirming the advantages of HT-XRD in determining mineral phase transformation and comprehending fusibility of the biomass ashes.

Formation and transformation of mineral phases in biomass ashes and evaluation of the feedstocks for application in high-temperature processes

Biomasses are known for their variety of ash systems, often accompanied by limiting effects such as fouling, sintering, slagging, agglomeration and corrosion, which affect thermochemical conversion processes (combustion, gasification, pyrolysis etc.). To explore those limiting effects, five different feedstocks from agricultural, woody, and processed biomasses are investigated after ashing in a temperature range between 200 and 815 °C. The ash composition and their specific distribution inside the particles are studied using X-ray fluorescence (XRF) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). Distinct differences are detected in the ashes from various biomasses, indicating that the ash systems can be homogeneous (mainly authigenic origin) or heterogeneous (with significant contributions of detrital/technogenic origin). Using X-ray diffraction (XRD), the formation and transformation of mineral phases are monitored in the ashes produced at various temperatures. The data are then compared to the results of thermochemical calculations. The experimental findings agree almost completely with those calculated using the FactSage™ software package. In connection with the identified mineral phases, the release behavior of the main alkali species, potassium, is monitored as a function of the ashing temperature. Based on these results indicating the ashes' mineral phase composition and their observed heterogeneity, the high-temperature behavior of the ash fusion temperatures (AFT) and ash fusion interval (AFI) between deformation and flow temperature can be ascertained. Finally, based on their ashing behavior, the biomasses’ potential use in thermochemical conversion processes at high temperatures is evaluated.

Effect of Carbon-Containing Solid Waste from Calcium Carbide Production on Combustion and Slagging Characteristics of Zhundong Coal Blend

ABSTRACT Co-combustion in pulverized coal boilers is one of the best methods to achieve harmlessness, reduction and resource disposal for carbon-containing solid wastes. This work aims to study the effect of dried dust (DD) generated from CaC2 production on the combustion and slagging characteristics of Zhundong (ZD) coal blend. The combustion of ZD coal blend with different ratios (0%, 2.5%, 5.0%, 7.5%) of DD was conducted in a thermal gravimetric analyzer under air atmosphere. The ash fusion temperature tests and slagging experiments were carried out to understand the effect of the addition of DD on the slagging behavior of ZD coal blend. The results showed that the ignition and burnout temperatures of ZD coal showed different varying tendency with the blending ratio of DD increasing. Increasing the adding ratio of DD could raise the ash fusion temperatures of ZD coal blend. The addition of 5% DD promotes the formation of gypsum in deposited slags, and it also alters the chemical components of fine particles adhered onto the surface of molten particles. Meanwhile, in comparison with raw ZD coal blend, more Ca would combine into silicates in sampled slags. After the overall evaluation, a low blending proportion of DD (<5%) is suggested for pulverized boilers.

Effects of sludge on the ash fusion behaviors of high ash-fusion-temperature coal and its ash viscosity predication

The co-gasification of sludge and coal is a promising way to regulate coal ash fusion characteristics and recover energy from sludge simultaneously. In this paper, the ash fusion behaviors of high ash-fusion-temperature (AFT) Datong coal, textile dyeing sludge (TDS), their mixtures, and the corresponding AFT modification mechanisms on laboratory scale were investigated by an AFT tester, X-ray diffractometer, Raman spectrometer, and FactSage software. The AFTs of Datong coal mixtures decreased slowly when TDS share was in the range of 0–6%, quickly (6–9%), and then nearly stable (>9%) because of its corresponding increasing basic oxide values (the total content of SO3, CaO, MgO, Fe2O3, Na2O, and K2O). The generations of low melting-point minerals of hercynite and anorthite with TDS additions resulted in the AFT decrease. The decreasing intensity of Si–O–Si peak and the increasing ratio bond of bridging oxygen and non-bridging oxygen led to the AFT decrease. Both the decreases in the temperature at which all minerals change into liquid-phase and the continuously increasing liquid-phase content (at the same relative high temperature) in Datong coal mixed ashes with increasing TDS mass ratio were contributed to the variations of AFT. The viscosity-temperature characteristics variation was also predicted using FactSage calculation. The 9.0–12.0% mass ratio of TDS might be suitable for Datong coal entrained-flow bed gasification.

Regulation of ash slagging behavior of palm oil decanter cake by alum sludge addition

Combustion of palm oil decanter cake (PODC) is a propitious alternative waste to energy means. However, the mono-combustion of PODC prompt severe ash slagging behavior which give rise to reduction in heat transfer and also shorten the lifespan of combustion reactors. In this study, alum sludge (AS) was introduced at different proportion of 30%, 50% and 70% to revamp the slagging characteristics of PODC during combustion. The addition of AS improved ash fusion temperature of PODC during co-combustion as ash fusion temperature increased significantly under high AS dosage. Slagging and fouling indices showed that at 50% AS addition, slagging tendency of the co-combustion ashes can be ignored. The predictive model for PODC-AS combustion showed good correlation coefficient with 0.89. Overall, co-combustion of PODC and AS is an ideal ash related problem-solving route. The proposed PODC slagging preventive method by AS was based on: (1) limited amount of aluminum content in PODC-AS system resulted in development of refractory ash (2) reduction in proportion of basic oxide which act as ash bonding glue played important role in the regulation of slagging (3) reduction of cohesive bond by formation of spongy and porous structure which prevented ash slagging.

Synergistic effects and mechanism of the ternary flux system Fe2O3-CaO-MgO on the coal ash slag fluidity

Basic oxides are usually widespread in low-rank coals and cause many ash-related problems in gasification applications. In this paper, the synergistic effects of the ternary flux system of Fe2O3-CaO-MgO in lowering the ash fusion temperature and improving the viscosity-temperature characteristics were verified by testing the properties of samples with different Fe2O3/(CaO + MgO) ratios. The flow temperatures and temperatures of the critical viscosity decreased and then increased with the decrease of Fe2O3/(CaO + MgO) ratio and reached the lowest point when the iron oxide and alkaline earth metal oxide (CaO, MgO) contents were close to each other. From the perspective of mineral transformation, the formation of low melting point ferroan spinel and the eutectic between anorthite and ferroan spinel are the main mechanisms of synergism. No severe crystallization was observed in the iron-rich slags because Fe2+ could reduce the crystallization tendency. As CaO and MgO dominated the basic oxides, a CaO/MgO ratio of 4:6 effectively limited the crystallization and lower the temperature of critical viscosity (TCV). Thus, when regulating the coal ash fluidity, the content of iron oxide and the ratio between CaO and MgO should be consciously balanced to meet the requirements of the gasifier for slag removal.

The effects of additives on deposit formation during co-firing of high-sodium coal with high-potassium and -chlorine biomass

In the last decades, the demand for alternative fuels has been growing due to carbon-neutral regulations. Co-firing coal with biomass potentially reduces greenhouse gases emission by replacing the portion of fossil fuels in the power generation sector. However, combining high-sodium coal with high-potassium and -chlorine biomass during co-firing can increase ash-related issues in the boiler's heat exchanger surfaces. Despite the fact that various additives have shown promising results in mitigating these issues, the effectiveness of these additives has not been clearly investigated yet. This study aims to evaluate the effectiveness of MgO, Al2O3, CaHPO4, and SiO2 additives during co-firing in several parameters. The study involves an experimental setup using a drop tube furnace and ash particle observation methods, including ash fusion temperature, thermogravimetric-differential thermal analysis, probe observation, scanning electron microscopy-energy dispersive X-ray spectroscopy, and X‐ray diffraction analysis. The result shows that 1–6 wt% MgO, 1 wt% Al2O3, and 1–3 wt% CaHPO4 are more effective than other additives in minimizing deposit formation. In addition, the mentioned additives decrease sodium (from 6.99 to 3.22–1.98 wt%) and potassium contents (from 4.51 to 4.11–1.49 wt%), increase ash melting temperature, and offer a cleaner probe surface with normal ash deposit weight. In comparison, the SiO2 additive has a lower impact than other additives in overcoming ash-related problems in the boiler and could produce higher ash deposit weight.

Effectiveness of different additives on slagging and fouling tendencies of blended coal

Indonesian coal reserves are dominated by medium and low-rank coals. Despite being economically profitable, low-quality coals can trigger ash-related problems in a boiler, such as slagging and fouling. Suitable additives can be useful to overcome the issue of high-alkali coals. The main objective of this study is to determine the effectiveness of the three additives in reducing slagging and fouling risks using a drop tube furnace. Aluminum silicate-based, aluminum-based, and magnesium-based additives were used in coal combustion to comprehensively evaluate ash fusion temperature, thermal properties, ash deposit, emission, and ash mineral morphology. The results showed that additives in high-risk coal/blended coal could reduce ash sintering during the combustion. It can lower the ash fusion temperature yet reduce slagging ash deposits and flue gas emissions. Si–Al, Al, and Mg minerals play a role in increasing the ash melting point. Among three additives, the aluminum-based additive can increase the Rmax value, resulting in more stable conditions during the combustion.

Prediction of the ash melting behavior and mineral phase transformation during the co-gasification of waste activated carbon and coal water slurry

Recycling waste activated carbon (WAC) through coal-water slurry (CWS) gasification to produce syngas resources with hydrogen as the main component is a new way to dispose of WAC. The ash fusion temperature, an essential parameter for selecting gasification raw materials, and the mineralogical composition determine the melting and crystallization behavior. In this paper, WAC and CWS were used as the raw materials for co-gasification. The melting properties and mineral phase transformation process of the coal-waste activated carbon-slurry (CWACS) gasification residue were predicted by thermodynamic equilibrium calculations and then experimentally verified. The results showed that the gasification residue yield of CWACS2 was significantly lower than that of CWACS1 due to the different ash contents of WAC in the feedstock. When the gasification temperature was increased to 1200 °C, the gasification residue of the sample melted and adhered to the walls of the porcelain boat. CWACS1 showed ash fusion temperature characteristics related to WAC1, while the ash fusion temperature characteristics of CWACS2 were nearly similar to those of CWS. The liquid phase generation rate of CWACS1 during the ash softening and deformation stages was much faster than that of CWS, while CWACS2 showed more changes in its liquid phase generation rate. Since various types of sodium-containing silicates dominated the minerals in the gasification residue of WAC2, the gasification residue of CWACS2 contained significantly more nepheline than CWS. Clinopyroxene was the main mineral in the gasification residue of CWACS1, and nepheline precipitated in the gasification residue of CWACS2. The mineralogical composition determined by XRD verified the simulation results of thermodynamic equilibrium.

Determination of running temperature in entrained flow gasifier in regard to coal ash melting thermal kinetic effects

The operating temperature of entrained flow gasifier is one of the important parameters to determine its gasification efficiency, which is empirically estimated by ash fusion temperatures (AFTs) in the industry. However, the measurements of AFTs in labs are conducted at a very low heating rate (5–10 °C/min) compared to industrial entrained flow gasifiers (several hundred °C/s). The melting behaviors of coal ash under such huge varied conditions are different due to thermo-kinetic effects. Here, the factors concerning coal ash melting thermo-kinetics including heating rate, particle size, and retention time are explored by AFTs analyzer, thermal mechanical analysis, in-situ hot stage microscope and differential scanning calorimetry. The results of the investigation demonstrated that ash particle size and retention time showed limited influence on ash fusion behavior, while the influence of heating rates can not be ignored. Furthermore, an Arrhenian-based regression model covering major thermo-kinetics was developed to quantitatively predict the running temperature. The developed model suggested using the temperature that shrinkage corresponds to 75% to extrapolate the running temperature. The model can help to determine the operating temperature of slagging gasifiers.

Characterization of Empty Fruit Bunch of Palm Oil as Co-firing Biomass Feedstock

Empty fruit bunches of Palm Oil (EFB) are a potential source of biomass energy because they contain lignocellulose (cellulose, hemicellulose and lignin) so that they can be converted into biopellets for co-firing. The purpose of this research is to determine the raw material properties of EFB in the form of proximate, ultimate, lignin, and biopellets. Using a pelletizer, biopellets are created by adding starch as an adhesive. The raw material characteristics of EFB from proximate analysis revealed moisture content of 11.98%, ash content of 6.53%, volatile matter content of 65.15%, and fixed carbon content of 16.44%. According to the final study results, the biopellets from empty fruit bunches included 48.53% C, 6.05% H, 0.32% N, 36.8% O, and 0.08% Sulphure. The atomic ratio obtained from the final analysis results could be used to determine the calorific value that can be used for fuel; the biopellet calorific value of EFB is 4,583 kcal/kg, with Hardgrove Grindability Index (HGI) values of 78.6 and Ash Fusion Temperature (AFT) 1100oC. The lower the value of the atomic ratio contained, the higher the calorific value contained in a specific fuel.

Gasification of a typical low-rank coal in 65MWth KEDA® circulating fluidized-bed gasifier

The KEDA® circulating fluidized-bed (KEDA®CFB) gasifier is a high-temperature air-blown circulating fluidized bed developed by KEDA (ANHUI) Clean Energy Co., Ltd to produce clean industrial gas. This project describes the design and the initial operating results of using low-rank coal to produce industrial fuel gas in a 65MWth KEDA®CFB industrial-scale plant with a feeding rate of 13 ton/hr. The gasification process was carried out at an ambient pressure and temperatures at 980 ± 10 °C. A long-term stable operation was achieved for more than 20 days. Cold gas efficiency could reach 73% with a gas high heating value of 5.89MJ/Nm3 at a steam-to-coal ratio of 0.38 and an equivalence ratio of 0.3. During the stable operation, it was also observed that the operational bed temperature has to be kept under the residual ash fusion temperatures (AFTs) to avoid aggregation and defluidization.

Comprehensive analysis on the in-situ ash fusibility and mineral reactions of ash mixtures in the co-gasification process

Biomass can effectively modify coal ash fusibility and alleviate several operational issues like agglomeration, sintering, and erosion for slagging gasifiers. The key issue is to clarify the ash fusion properties and mineral transformation during the heating process. The fusion temperatures, mineral evolutions, in-situ morphology observation and thermodynamic analysis of the coal, biomass and biomass-coal blended ash samples were systematically evaluated in this paper. The ash fusion temperatures (AFTs) presented V-type curves with the increasing rape straw ratio. Then the bottom point occurred at the ratio of 50 wt% due to the reduction of refractory minerals (mullite, quartz, < 50 wt%; kalsilite, oldhamite, >50 wt%) and the increase of low-melting-point minerals and their eutectics (leucite and anorthite). Besides, the thermodynamic calculation can provide the basis for the prediction of ash fusion behavior. The in-situ morphology evolutions of blended ashes further revealed the relationship between ash fusion behaviors and morphological changes. Namely, the terminative sintering and melting temperature were highly related to the ash deformation temperature and flow temperature, R2 was 0.9901 and 0.9846, respectively. The significant work could guide the mixing conditions during the co-gasification of high‑silicon‑aluminum coal and biomass and improve the ash fusion properties.

Effect of iron on crystallization and flow properties of coal ash slag: A combined computational-experimental study

The crystallization and viscosity behavior of coal ash slag play a decisive role in the stable slagging of industrial gasifiers. However, the influence of iron on the crystallization and flow properties of slag is still poorly understood for its heterovalent component. Therefore, the influence of iron on the melting and crystallinity of slag was studied by preparing synthetic ashes with different iron contents, in this work. The results demonstrated that the ash fusion temperature (AFTs) could be significantly lowered with the increase of Fe content. This was because of the low-temperature eutectic reaction in slag caused by the increased iron content, which led to the transformation of the sub-liquid phase in slag from high-melting mullite to low-melting anorthite and spinel. At high temperature, iron was mainly presented in slag as Fe2+. At the same time, Fe2+ as an alkaline component could terminate the interconnection between [SiO4]4- and [AlO4]5- tetrahedral by replacing Si4+ and Al3+ in slag. This consequence destroyed the slag network structure and lowered the polymerization degree. Slag with lower polymerization degree exhibited lower viscosity and stronger ionic transport capacity, which was favorable for crystal growth. Meanwhile, thermodynamic and quantum chemical calculations revealed that anorthite was a crystalline mineral during slag cooling.

Investigation on variation mechanisms of ash fusion and viscosity of high calcium-iron coal by coal blending

In this work, the ash fusion temperature (AFT) and viscosity modification behaviors of high calcium-iron coal ash (MO) were investigated by blending coal with high silicon-aluminum coal ash (P4). X-ray powder diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), Raman, and FactSage thermodynamic software were selected to investigate the AFT and viscosity change mechanisms. With the increase of P4 mass ratio, the AFT of MO mixtures increased from slowly (0–20 %) to rapidly (20 %–30 %), and then to slowly (30 %–50 %), and the ash viscosity also increased correspondingly. When the amount of P4 was in the range of 30–40 %, the flow temperature (FT) and viscosity of ash samples were 1368–1395 °C and 4.28–5.02 Pa·s, respectively, which met the requirements of entrained-flow bed gasification slag tapping. The XRD results showed that the disappearance of hauyne and the formation of anorthite were the main reasons for the mixed MO AFT increase. With the increasing P4 mass ratio, Si-O and Si-O-Al in ash samples moved to the high-frequency region in FT-IR, indicating the formations of more stable silicate network structures; the R-value (R = (Q3 + Q2)/(Q1 + Q0)) gradually increased indicating the increases in polymerization degree. The both led to the increases in viscosity. The decreasing ratio of non-bridged oxygen bond to bridged oxygen bond with increasing P4 percentage also explained the AFT and viscosity variation.

Effects of phosphorous-based additive on flow properties of high silicon-aluminum coal ash

• Effects of Ca 3 (PO 4 ) 2 addition on the fluidity of Huainan coal ash were revealed. • Phosphorus decreased ash fusion temperatures and temperature of critical viscosity. • Phosphorus contributed to the formation of slag during the ash fusion process. • Polymerization of slag structure was enhanced by phosphorus at high temperatures. • Crystallization in the slag during cooling was restricted by phosphorus. Co-gasification with coal is a promising way to dispose the sewage sludge with high phosphorus content, but the lack of data on the flow properties of phosphorus-containing ashes and slags under reducing atmosphere limits the gasification of this fuel. In this study, Ca 3 (PO 4 ) 2 was chosen as the phosphorus model compound of sewage sludge and was added into one high-silicon-aluminum coal (Huainan, HN). Ash fusion temperatures (AFTs) and viscosity-temperature properties of blends were measured and the mechanism of effects of phosphorus were explored based on the results of X-ray diffraction (XRD), thermodynamic software FactSage, Fourier transformation infrared spectroscopy (FTIR) and scanning electron microscope with energy dispersive spectrometer (SEM-EDS). To eliminate the interference of calcium, a phosphorus-free control group was set up with CaCO 3 and the same tests were conducted. The experimental and modelling results showed that phosphorus had a significant fluxing effect on the fusion of coal ash by providing the initial liquid phase and changing the main minerals. The effects of phosphorus on slag viscosity were rather complex. At the temperature above 1530 °C, phosphorus-bearing slags had slightly higher viscosity values than phosphorus-free slags due to the increased polymerization degree of the network structure. However, at the cooling process, phosphorus restricted the crystallization in the slag and decreased the viscosity values and the temperatures of critical viscosity (T CV ). In this paper, a suitable addition ratio of Ca 3 (PO 4 ) 2 for the slagging gasification of HN coal was concluded.

Melting solidification of oily sludge with coal fly ash: Fusion characteristics, phases transformation and metals leaching behavior

Melting solidification is a promising method to achieve the harmless treatment of oily sludge (OS). In this study, the coal fly ash (CFA) was used as an additive to co-treat with OS. The effects of CFA addition on the fusion characteristics and phases transformation of OS were studied, and the leaching behavior of heavy metals after melting solidification was also evaluated. The results indicated that the addition of CFA had a synergistic effect on the thermal characteristics of OS. SiO2 and Al2O3 in CFA reacted with CaO in OS to form gehlenite (Ca2Al2SiO7), which reduced the ash fusion temperatures (AFTs) of OS. But the AFTs of mixed samples increased with the addition of CFA from 10 wt% to 50 wt%, and this might be due to more anorthite (CaAl2Si2O8) formation based on the gehlenite. As the increase of CFA into OS, the microstructures of co-treated mixtures were gradually loose. In addition, the leaching concentrations of heavy metals in the co-melting samples were reduced by 13.22–76.70 mg/L, which were lower than the standard limit, and the products presented low ecological risk indices. The obtained results indicated that the CFA effectively regulated the melting behaviors of OS and promoted the solidification of heavy metals, which provided a safe and stable disposal approach for OS treatment.

Investigation of reducing trace elements and PM emission from coal combustion by blending coal

The fine particles and their associated trace elements derived from coal combustion had a severe adverse effect on the environment or human health. In this paper, HLH (lignite) and HS (bituminous) were blended under the predetermined ratio, and the blended coal was burned in a drop tube furnace (DTF). The particle size distribution (PSD) of particulate matter (PM) and trace elements (As, Se, Pb and Cd) were investigated during the blending coal combustion. The experimental results demonstrated that the mass concentration of PM from HLH coal combustion was higher than that of HS coal, which was attributed to the thermal instability of the minerals in HLH (lignite). In addition, it was found that PSD of PM was not consistent with that of trace elements. The blending coal combustion not only suppresses PM formation, but also reduces As, Se, Pb and Cd emission due to lowering ash fusion temperature of blending coal and liquidus capture of fine particles. Compared with the calculated values, the mass concentration of PM0.2–0.5, PM0.5–1.0, PM1.0–2.5 and PM2.5–10 from HS1HLH1 (the mass ratio of HS/HLH was 1.0) combustion was reduced by 6.06 %, 45.02 %, 50.17 % and 55.59 %, respectively. At the same time, the reduction efficiency of As, Se, Pb, and Cd emission concentration in PM0.2–0.5 by HS1HLH3 were the highest (about 91.7 %, 71.06 %, 83.45 % and 73.50 %), and their emission concentration was 0.16, 0.95, 0.97 and 0.02 μg/m3. While HS1HLH1 was the most effective for reducing As, Se, Pb, and Cd emission in PM0.5–10. Lastly, above 50 % As, Pb and Cd in PM10 was existed as the mobile phase during raw coal combustion, which had a harmfulness for the environment or human being. HS1HLH1 could stabilize Se, Pb, and Cd, and their residual fraction in PM10 were 59.4 %, 49.1 % and 29.2 %, respectively.

Influence of water-washing pretreatment on ash fusibility of biomass

As the carbon-neutral fuel, biomass has shown great potential to partially substitute fossil fuels. However, the application of biomass combustion in boiler was restricted by the biomass compositions. To improve the ash fusibility performance of biomass, water washing pretreatment was proposed. The influences of water washing on ash composition, ash fusion temperatures (AFTs), and ash dynamic behavior during fusion process were investigated through experimental methods and thermodynamic equilibrium calculations. The results show that water washing could increase the initial deformation temperature of biomass ash by removing alkali metals. The K2O removal efficiency is within 69%–90% for six biomass fuels. Traditional fouling and slagging indexes could be employed to predict the ash fusibility of corn stalk, wheat straw, rice straw and rice hull. But these indexes are not suitable for that of candlenut wood or cotton stalk. Furthermore, a convenient and effective method to study the dynamic behavior of biomass ash during fusion process is proposed. It could reveal the interaction of solid and liquid phases in ash. The effect of water washing on AFTs could be explained by thermodynamic equilibrium calculations. Finally, 30 °C is recommended as the water washing temperature to adjust the ash fusibility of biomass.

The individual and interactive effects of acid and basic oxides on ash fusibility during oxy-biomass combustion with recycled SO2

Ash-melting problems induced by alkali metals and recycled SO2 are one of the major obstacles to oxy-biomass combustion, which depend heavily on the contents of acid or basic oxides in ash particles. In this study, the individual effects of acid or basic oxides as well as their interactions on ash melting performance of corn straw were explored. The results showed that the individual effects of SiO2 to Al2O3 (Si/Al) or acid to basic oxides (A/B) ratios on the ash fusion temperatures (AFTs) were nonlinear due to the eutectic melting of minerals. A regression model was established by response surface methodology to reveal the interactive effects of Si/Al and A/B ratios on ash slagging, in which softening temperature (ST) was the response factor. In comparison with the Si/Al ratio, the influence of the A/B ratio on ST was more significant. Furthermore, based on the regulation strategy obtained through the regression model, after modifying the ratios of Si/Al and A/B to 8 and 1.0 simultaneously, all the AFTs were dramatically increased and the ash slagging was alleviated effectively during oxy-biomass combustion with recycled SO2.