Ash Fusion Temperatures Research Articles

Influence of the Direct Coal Liquefaction Residue on the Fusion Characteristics of Jincheng Coal with a High Ash Fusion Temperature

Nowadays, entrained flow bed gasification technology is the foundation of the modern coal chemical industry, while its liquid slag discharge process generally requires the flow temperature (FT) of ...

Effects of Pyrolysis Temperature and Retention Time on Fuel Characteristics of Food Waste Feedstuff and Compost for Co-Firing in Coal Power Plants

Food waste is an underutilized organic resource given its abundance and high potential energy. The purpose of this study was to confirm the suitability of pyrolyzed food waste as a co-firing fuel by adjusting the pyrolysis temperature (300–500 °C) and retention time (15–60 min). Both high moisture (compost) and low moisture (feedstuff) food waste were examined. Increasing the temperature and retention time yielded more volatile H and O as well as C sequestration, resulting in reduced H/C and O/C ratios. Notably, the van Krevelen diagram increased in similarity to that of coal. Upon pyrolyzing food waste compost, more than half of the chloride was volatilized, the highest carbon content of the compost and feedstuff were 61.35% and 54.12%, respectively, after pyrolysis at 400 °C for 60 min; however, the calorific value of the pyrolyzed feedstuff was reduced owing to the high salt concentration. The pyrolyzed compost and feedstuff had high Ca contents, which contributed to an increased ash fusion temperature. Therefore, food waste byproducts are advantageous as co-firing fuels in terms of energy regeneration. Nevertheless, further research is required regarding the removal of salt and alkali earth metal ion materials.

Alkali metals association in biomass and their impact on ash melting behaviour

Selected agricultural and energy crop biomass ashes represented by two mixed cereal straws, corn straw, Miscanthus × Gigantus and Salix Viminalis were chosen for ash behaviour investigation and prediction of operating problems during biomass combustion. The presence of aggressive species in the ash generate operational problems of heat exchanging surfaces in power boilers connected with slagging and fouling processes, limiting the use of biomass direct combustion for energy production. In this work, thermal behaviour characteristics, transformation properties of the inorganic components and ash fusion temperatures of biomass ashes were investigated using thermal analysis (STA), X-ray diffraction (XRD) and high-temperature microscope. The special attention was focused on the evaluation of potassium compounds presented in ashes. Potassium was detected as KCl, K2SO4, K2CO3 and K3PO4. It was noted, that presence and concentration of alkali metals, silicon and calcium compounds has the major impact on fusion temperatures of studied ashes. Leaching process of ash elements using water, ammonium acetate and hydrochloric acid solutions was performed to determine the association of alkali metals in the raw material. Based on the results, a mineral matter composition recalculation model was proposed to predict alkali compounds concentration in the fuel. The model might be also used to determine the risk of eutectics formation, which have the strongest influence on ash melting behaviour.

Viscosity Analysis of Indian Origin Coal by Using FactSage at Different Temperatures

Slagging of the ash inside the furnace boiler causes operational problems such as furnace shutdowns and low heat exchange efficiency. To avoid this problem, ash fusion temperature (AFT) parameter has been well accepted for determining the ash fusion characteristics since many years. In this paper, an extensive study has been conducted on the deposition characteristics of ash particles based on the viscosity and phase transformation properties in boiler operation. The FactSage thermodynamic software package is utilized for the phase transformations and viscosity predictions of coal ash in furnace operating temperatures. The effect of solid or crystalline fractions in slag phase on the viscosity is calculated by using the Roscoe equation. Calculations show that an increase in solid fractions increases the viscosity of the slag phase. AFT analysis of coal samples for the present study shows that their IDT and FT values are higher than 1340 °C and 1470 °C, respectively. The reason for the high IDT and FT in Indian origin coals is the formation of high-temperature-stable phases—tridymite and sillimanite. Furthermore, the numerical viscosity models developed by using the Roscoe viscosity equation are correlated with the experimental AFT results.

Effect of coal blending on ash fusion behavior for blast furnace injection of high calcium bituminous coal

AbstractIn order to expand the range of bituminous coal injected into blast furnace, the ash melting behavior and regulation mechanism of bituminous with high calcium and low ash fusion temperature (AFT) were investigated by coal blending. And the mineral transformation behavior in the blended ashes was investigated by X‐ray powder diffractometry with normalized reference intensity ratio software and FactSage software. The experimental results manifest that the softening temperature (ST) of coal D is 8°C lower than that of the hot blast temperature. By adequately mixing coal B and coal D, it is easy to meet the requirements of pulverized coal injection. And coal D has become a standard bituminous for blast furnace injection. However, the high content of CaO in the coal S ash makes the AFT much lower than the hot blast temperature, which leads to the reluctance of the steel industry to inject coal S. With the increase of coal B mass ratio, the content of high‐melting eutectic matters (3Al2O3·2SiO2 and tridymite) increases at high temperature, while the content of low‐melting anorthite, andradite, gehlenite, and grossularite decreases, which leads to the increase of AFTs. The variation in the liquid phase under certain conditions reflects the change in AFT. In summary, by blending with coal B, the ST of blended coals S/B is higher than the hot blast temperature (1250°C), so that coal S can be applied to blast furnace injection. And the injection ratio of coal S in blended coals can reach about 50%.

Effect of CaO/Fe2O3 ratio on fusibility of coal ashes with high silica and alumina levels and prediction

Ash fusibility which is usually investigated and evaluated by the ash chemical compositions is widely used to guide the coal selection in boiler and gasifier. Calcium and iron are the main basic oxides in coal ash, which tend to decrease ash fusion temperatures (AFTs). However, the change of AFTs varied with CaO/Fe2O3 mass ratio is not yet revealed. In this work, effect of CaO/Fe2O3 ratio on the fusibility of ash with high silica and alumina levels was explored under weak reducing atmosphere (CO: CO2 = 3/2, volume ratio). Thermodynamic calculations were applied to investigate the fusion behavior. A general rise of AFTs with the increasing CaO/Fe2O3 ratio was verified, especially for the coal ash with low SiO2 + Al2O3 level and SiO2/Al2O3 mass ratio. Mullite and anorthite are main refractory minerals phase of the ash samples with high SiO2 and Al2O3 levels. The fusion of the ash in anorthite primary phase is the “soft-melting” mechanism, and liquidus temperature was well used to predict flow temperature (FT). However, the liquidus temperature should not be used to predict FT of the ash in mullite primary phase due to the “melting-dissolve” mechanism. A Tmullite model was proposed to predict FT for the ashes in mullite primary phase. The deviation of predicted and measured FT was within the measuring error range (±40 °C), which was supported by 25 real coal ashes.

The mechanism of the ash fusion characteristics of gasification coke affected by SiO2/Al2O3 ratio and CaO content in blending coals

ABSTRACT To replace the high-cost lump coals for fixed bed/moving bed gasification and broaden the utilization of the coke ovens with periodic overcapacity problems, the gasification coke with a large amount of low-rank coal and coals with high ash content has been prepared at low cost. To further understand the ash fusion characteristic of gasification coke affected by minerals in blending coals, the effects of SiO2/Al2O3 ratio and CaO content which were controlled by additive on the transformation of minerals and the ash fusion characteristics were investigated. The increase of SiO2/Al2O3 ratio and CaO content resulted in the decrease of ash fusion temperatures of coke, due to the inhibition of the formation of minerals with high melting point (such as mullite and hercynite) and the enhancement of the formation of low-temperature eutectic systems. The ash fusion characteristics of gasification coke affected by coal blending were dominated by the SiO2/Al2O3 ratio and CaO content in blended coal. The variation of ash fusion characteristics of gasification coke affected by coal blending could be well explained by the mechanism of the ash fusion characteristics of gasification coke affected by the SiO2/Al2O3 ratio and CaO content controlled by additional minerals.

Effects of additives blended in corn straw to control agglomeration and slagging in combustion

Four additives including two specimens of kaolin clay, limestone, and a byproduct of a sugar mill (BSM) (mainly CaCO3) were utilized to increase ash fusion temperature (AFT) of corn straw. The results showed that the ash softening temperature (ST) was increased by 250 to 380 °C and agglomeration or slagging could be avoided during combustion with each additive. Meanwhile, the slagging/fouling tendency of all ash samples fell within the “low” range according to alkali index. Lime was shown to have the best effect, which indicated that calcium oxide was the best compound to increase the AFT of corn straw densification (CSDF). Both kaolin specimens made the fusion range very narrow. BSM had the least effect on ST among the four. All the additives diluted the concentration of chlorine by more than 50%. No agglomeration or slagging phenomenon appeared in real boilers burning CSDF with lime blended as additive.

Understanding fusibility characteristics and flow properties of the biomass and biomass-coal ash samples

The fusibility characteristics and flow properties of the biomass and biomass-coal ash samples were investigated in this paper. Ash fusibility of the biomass-coal blended samples was evaluated systematically. The mineral matters variation and liquidus temperature of the biomass-coal blended samples were demonstrated by FactSage. The results show that the ash fusion temperature of biomass-coal blended samples decreases and then increases with the increasing content of biomass (straw). The ash fusion temperature reaches the minimum when straw content is 50%. Moreover, the liquidus temperature reflected in the phase diagram can predict the variation of ash fusion temperature well. Furthermore, the flow properties of high temperature ash (HTA) and low temperature ash (LTA) straw samples at different atmosphere were observed using the heating stage microscope. In the heating process, the HTA and LTA straw samples show the similar variation: shrinkage, fusion and spreading. However, the volume changes of the HTA and LTA straw samples are different considerably attributing to the mineral matters variation. It was revealed that the volume change of HTA and LTA straw samples is not obvious at the lower temperature. For the LTA straw sample in air atmosphere, the maximal volume change is obtained.

Ash fusion characteristics and gasification activity during biomasses co-gasification process

The ash fusion characteristics and co-gasification activities of different biomasses (corn straw (CS), rice straw (RS) and rice husk (RH)) are investigated in an ash fusion temperature (AFTs) analyzer and a thermo-gravimetric analyzer (TGA). Moreover, the transformation behaviors of mineral matters during CS/RH and RS/RH co-gasification processes are calculated by FactSage software. Results show that the ash fusion characteristic temperatures (AFTs) of CS/RH and RS/RH mixtures both increase with increasing RH ratio, and the maximum ratio of 75% CS and 55% RS in CS/RH and RS/RH mixtures can avoid the melting and slagging problems during co-gasification processes. Under the desirable RH ratio, the gasification activities of CS/RH and RS/RH mixtures increase with increasing CS or RS ratio. Besides, the increased AFTs of CS/RH and RS/RH mixtures are mainly ascribed to the increased contents of high-melting point quartz [SiO2] and tridymite [SiO2] and the decreased content of low-melting point silicate with the increase of RH ratio.

Experimental comparative study on ash fusion characteristics of Ningdong coal under oxidizing and reducing atmosphere by means of SiO2-Al2O3-(CaO + MgO + Na2O + K2O) pseudo-ternary diagrams

Concern about the serious slagging during combustion and the troublesome liquid slag tapping during gasification has motivated the study on ash fusion characteristics of Ningdong coal under oxidizing and reducing atmosphere by SiO2-Al2O3-(CaO + MgO + Na2O + K2O) pseudo-ternary diagrams of ash fusion temperatures (AFTs). The AFTs contours in the pseudo-ternary diagrams presented inverted V-shape distributions. Al2O3 showed positive effect on the AFTs; with unchanged Al2O3 content (less than 0.5), the AFTs went down first and then up with increasing SiO2 content; whereas with consistent AAEM (CaO + MgO + Na2O + K2O), the AFTs decreased with increasing SiO2 content. By doping SiO2 and Al2O3 or the mixtures into the coal, the AFTs increased significantly due to the formation of high-melting quartz, corundum, silicates, and aluminosilicates, which impeded melt-induced slagging under both oxidizing and reducing atmosphere. On the contrary, when doping AAEM, the AFTs plunged because of the formation of low-melting akermanite, which favored liquid slag tapping during gasification. The pseudo-ternary diagrams indicated that the AFTs under reducing atmosphere were higher than that under oxidizing atmosphere, with an exception of around the limited region of SiO2:Al2O3:AAEM = 0.25:0.45:0.3. Ningdong coal located in the singularity region, where the existing forms of Fe as low-melting FeS and FeO under reducing atmosphere and high-melting Fe2O3 under oxidizing atmosphere resulted in slightly higher AFTs under oxidizing atmosphere. Besides, the atmosphere difference had more influence on IDT, ST, and HT, and less influence on FT. This research provides valuable practical guidance for the selection and dosage of additives during the combustion and gasification of Ningdong coal.

Selection of optimal coal blends in terms of ash fusion temperatures using Support Vector Machine (SVM) classifier - a case study for Polish coals

Selection of optimal coal blends in terms of ash fusion temperatures using Support Vector Machine (SVM) classifier - a case study for Polish coals

Investigation on regulation mechanism of red mud on the ash fusion characteristics of high ash-fusion-temperature coal

Red mud (RM) used as a flux to decrease coal ash fusion temperature (AFT) has great economic and environmental attractions. The effects of Bayer RM (BRM) and Sintering RM (SRM) on the AFTs of high silicon-aluminum coal (Jiaozuo coal (ZJ)) or high aluminum coal (Pingsuo coal (PS)) were investigated by X-ray fluorescence analysis, X-ray diffraction, and FactSage calculation. With increasing BRM/SRM mass ratio, the AFTs of JZ or PS mixture firstly decreased quickly and then slowly. When ash flow temperatures were decreased to <1400 °C, for ZJ mixtures, the mass ratio of BRM or SRM should not be <1.38% or 0.65%; while for PS, BRM or SRM should not be <2.76% or 1.81%, respectively. SRM lower AFT’s of two coals compared to the addition of BRM resulted from that SRM higher CaO content (20.12 wt%) than that of BRM (8.87 wt%), and its lower A/B value (1.15) than BRM (1.53). The increasing contents of Na2O, Fe2O3, and CaO inhibited high melting-point (MP) mullite formation and prompted the formations of low MP albite, hercynite, and anorthite with increasing RM mass ratio. This caused the respective decrease in the AFTs. The mineral evolution based on FactSage calculation could explain the AFT changing trend with increasing BRM or SRM mass ratio.

Exploration of potassium migration behavior in straw ashes under reducing atmosphere and its modification by additives

To investigate potassium behaviors during biomass gasification, the potassium migration of wheat straw (WS) or corn stalk (CS) ashes and their modification mechanisms by additives (kaolinite and dolomite) under reducing atmosphere were explored by an X-ray fluorescence spectrometers, X-ray powder diffractometer (XRD), and FactSage software. With increasing temperature, most of potassium in WS or CS ashes transferred into gaseous phase potassium chloride. The kaolinite addition retarded the release of potassium due to dystectic compound kalsilite formation. Kaolinite was suitable for straw circulating fluidized-bed gasification because the amount of potassium captured by kaolinite increased firstly and then decreased with increasing temperature. At high temperature, K+ in silicates gradually replaced by Ca2+ or Mg2+ with dolomite addition, this accelerated potassium release (promote alkali-induced slagging) and increased the ash fusion temperatures of mixtures (decrease silicate melt-induced slagging). Dolomite was effective for low chlorine straw gasification. The combination method of XRD and FactSage software could explain the modification mechanisms of potassium migration behaviors through two additives under reducing atmosphere.

Ash fusion temperature regulation mechanism of Xiangyang coal by coal blending

The modifications in the low ash fusion temperature (AFT) of Xiangyang coal (XY) were investigated by blending it with three high AFT coals [Jincheng coal (JC), Sunjiahao coal (SJH), and Shajuzi coal (SJZ)], respectively. These three coals all improved XY AFT effectively. With the JC mass ratio varying from 0 to 50%, the AFT of XY/JC gradually increased. The AFT of XY/SJH increased significantly (0–30%), slowly (30–40%), and rapidly (40–50%) with increasing SJH content. For SJZ, the AFT of XY/SJZ increased quickly (0–30%) and very slowly (30–50%). For XY entrained-flow gasification, the appropriate blending ratios of JC, SJH, and SJZ were 40–50%, 30–40%, and 20–40%, respectively. X-ray diffraction, scanning electron microscopy, and FactSage thermodynamic calculation were applied to investigate the effects of mineral transformation on AFT. Quartz (SiO2), anorthite (CaAl2Si2O8), diopside (CaMgSi2O6), and hedenbergite (CaFeSi2O6) were detected in XY ash at 1100 °C. As the mass ratios of high AFT coals increased, the obvious increase in anorthite content led to the rise in the AFT of XY/JC; mullite (Al6Si2O13); and corundum (Al2O3) with a high melt point formed in ashes causing the increase in the AFTs of XY/SJH and XY/SJZ, respectively.

Evaluation of the fusion and agglomeration properties of ashes from combustion of biomass, coal and their mixtures and the effects of K2CO3 additives

This study investigated the ash fusion and agglomeration characteristics of a Chinese bituminous, “Neimongol” (NM) coal, soybean straw (SS) material and their blends, as well as the effects of high biomass blending ratio (20–80 wt%) and the addition of K2CO3 (0–20 wt%) on the ash agglomeration propensity of the mixtures in a muffle furnace at 815 °C. The ash fusion and agglomeration characteristics of the fuel blends and their modified behaviours based on the blending ratio and flux were examined using ash fusion temperature (AFT) analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The results indicated that, compared to Neimongol coal ash (NMA), the contents of SiO2 and Al2O3 in soybean straw ash (SSA) were lower, and the contents of basic oxides were higher, which was the main reason for the lower AFT of SSA. The AFT curves for the NM/SS blends showed a “bathtub” shaped trend with increasing SS mass ratios. For a given coal/biomass blend, XRD analysis indicated that for blends without added K2CO3, mineral phases were dominated by arcanite and quartz; with increasing SS mass ratios, the diffraction intensity of quartz decreased obviously. With increasing the K2CO3 additions, the content of potassium feldspars and sylvine in ash increased, and the quartz content decreased. The EDX analysis confirmed that the K2CO3 addition made it possible for kyanite and mullite to react with K-bearing minerals and form low melting point eutectics. The SEM images revealed that the fused particles in SSA were coated with KCl, whereas the NMA particles mostly contained aluminosilicate minerals. As the K2CO3 addition increased, the morphologies of the ashes from blends changed from slightly agglomerated to seriously slagged, and the molten and solidified zone on the slag surface featured high contents of sylvine, quartz, and potassium aluminosilicates.

Detrimental effects of low-rank coal utilization to the operational condition of large capacity updraft moving-bed gasifier

ABSTRACT The feedstock of updraft Fixed-Bed Gasifier must meet very strict criteria such as low fragmentation, non-caking property and high ash fusion temperature (AFT), which represent the general characteristic of medium rank coal. In this paper, the properties of low-rank coal were carefully selected according to literature recommendations such as high AFT (above 1500°C), low grindability (HGI 55), swelling index (FSI 1) and lump size ranging from 30 to 80 mm. Thermal fragmentation was also evaluated by using sieve analysis and show Fd value of 0.81. After 90 h of service time, the temperatures of the vessel body declined gradually and 580 kg/h gasifier reactor was forced to shut down after 300 h. The rotating grate was found severely damaged with a large deposit of char. The OES, SEM, EDS and XRD analysis results confirmed each other that rotating grate has experienced excessively high temperature during gasification. It is likely that high breakage during devolatilization is the root cause of all operational problems. It causes melting of the cone, block the air exit ports, localize pressure drop, aggravate bed channeling, and so on. It is possible that FSI value is not necessarily to be low to maintain uniform pressure drop of the gasifier.

The role of residual char on ash flow behavior, Part 2: Effect of SiO2/Al2O3 on ash fusibility and carbothermal reaction

SiO2/Al2O3 weight ratio (Si/Al) in the ash content is always regarded as the key factor on ash fouling and sintering in the gasifier, and residual char is often found in gasification slag. The effect of Si/Al on the fusibility of ash containing different contents of residual char (5–15%) was investigated in this work. The residual char was added into five ash samples with different Si/Al from 1.0 to 3.0. The results show that the residual char content shows a significant effect on the AFTs and the fusion temperature range (ΔT = FT-DT) when the Si/Al of the ash is higher than 1.0, especially for the ash with more than 10% residual carbon. Carbothermal reaction products (SiC and Fe3Si) have obvious influence on hemispherical temperature and flow temperature of ash with a high Si/Al. For the ash with Si/Al of 1.0, anorthite, corundum and mullite are the major minerals at high temperatures, and formation of SiC and Fe3Si shows a slight effect on the ash fusion temperatures. However, there are less anorthite and SiO2 at high temperatures in the ashes with Si/Al of 2.0 and 3.0. Besides, Si/Al mainly affects the formation of SiC, while it does not influence formation of Fe3Si. The formation rate of SiC in ash with Si/Al = 2.0 is slower than that of the ash with Si/Al = 1.0 and Si/Al = 3.0. Furthermore, it demonstrates that a high amorphous content and less SiO2 in the ash are detrimental to carbothermal reaction (3C + SiO2 = SiC + 2CO).

Evaluation of slagging and fouling characteristics during Zhundong coal co-firing with a Si/Al dominated low rank coal

Blending is a promising method to improve ash related problems to meet combustion requirements. To evaluate the slagging and fouling characteristics of Zhundong coal (ZD) co-firing with a Si/Al dominated low rank coal (WD), the influence factors of slagging and fouling propensity based on ash composition and fusion temperatures was discussed. Release, thermal change and transformation behaviors of minerals in the mixed ashes were investigated by Thermogravimetric analysis and FactSage software. Morphology and chemical characteristics of ash deposits along heating surfaces of a practical boiler co-firing these two coals were also analyzed. The results show that when alkali/acid ratio (RB/A) is higher than 0.400 and difference value between ST and DT (ST-DT) lower than 20 °C, blending presents a severe slagging and fouling tendency. Under high temperature, ZD ash underwent a major weight loss which, is characterized by intense endothermic reactions and leads to the low ST-DT value. Feldspar, tridymite and anhydrite are the dominated minerals for blending ashes, and transformation of them contributes to the low fusion temperatures. Deposits along heating surfaces of boiler for burning ZD coal blending could be divided into two groups: condensed deposits and molten deposits. The former is due to the volatilization of mineral elements and have higher AFTs and the latter mainly due to the formation of low fusion temperature eutectics.

Ash melting behaviour of some low-grade Turkish coals and some imported steam coals

Traditional way for energy production is coal-fired power plants. Change in coal characteristics would result in change in ash properties (ash fusion temperatures, ash elemental composition) as expected and would finally and possibly result in slagging or fouling problems inside the boiler. The high temperature of combustion process and a low melting point of ash or vice versa might be considered as the main reason of these above-mentioned problems. In this study, 24 coal samples either low-grade Turkish coals or imported steam coals were collected and analysed in terms of their proximate analysis and the ash samples corresponding each parent coal were analysed in terms of elemental composition along with ash melting temperatures. Proximate analysis of each coal was performed in the order of characterisation. As regards to ash melting temperatures (AFTs), ash chemical composition contribution was deeply discussed. Still, in order to figure out what has a dominant role in terms of ash fusion temperatures (AFTs), coal and ash properties were taken into consideration at the same time. A model was proposed to predict AFTs by employing parameters of ash chemical composition and coal characteristics. The proposed model was not only user-friendly but also it is in good agreement with experimental results (R2 = 0.71, R2 = 0.77, R2 = 0.84, R2 = 0.88; DT, HT, ST and FT, respectively).