Ash Fusion Research Articles

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 Jincheng coal fine char from fluidized-bed gasifier on ash fusion and CO2 gasification behaviors of biomass

Effects of Jincheng coal fine char from fluidized-bed gasifier on ash fusion and CO2 gasification behaviors of biomass

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.

Biomass Entrained Flow Gasification Technology and CFD Numerical Simulation

Aiming at the dry pulverized biochar fuel refined by thermochemical conversion technology, its properties were obtained through experiment. By blending 5% additives to improve the ash fusion characteristics of biomass particles and considering the viscosity-temperature characteristics and the matching principle of CO2 reaction activity, the entrained flow gasification technology scheme of biomass particles was formulated. Based on the gasification reaction kinetics of dry pulverized biochar, a numerical simulation model was established to predict the flow characteristics, syngas composition, and particle conversion process in the gasifier. The results show that under the swirling entrainment and centrifugal force, the oxidizing reaction of particles is completed in the upper part of the gasifier quickly after mixing with oxygen. And the gasification reduction reaction occurs in the recirculating area and the pipe flow area. These effectively complete the conversion of char. The simulation results are in good agreement with the equilibrium calculation values, which proves the feasibility and rationality of the biomass particle entrained flow gasification technology scheme based on the HT-L.

Investigation on influencing mechanisms of phosphogypsum (PG) on the ash fusion behaviors of coal

Investigation on influencing mechanisms of phosphogypsum (PG) on the ash fusion behaviors of coal

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.

Study on Slagging Characteristics of Co-Combustion of Meager Coal and Spent Cathode Carbon Block

The harmless disposal of spent cathode carbon blocks (SCCBs) has become an urgent issue in the primary aluminum industry, and the disposal of SCCBs by co-combustion in pulverized coal boilers is expected to be the most effective treatment method. A muffle furnace at 815 °C was used in this study to perform a co-combustion experiment of meager coal and SCCBs. The ash fusion characteristics (AFTs), microscopic morphology, and minerals composition of co-combustion ash were characterized. The interaction mechanism of different mineral components and the change in AFTs and viscosity-temperature characteristics were investigated using FactSage software. Results show that the change in the ash deformation temperature (DT) is correlated linearly with the SCCB addition ratio, whereas other characteristic temperatures exhibit a nonlinear relationship. The contents of SiO2, Al2O3, and Na2O collectively determine the DT in the ash, and the influence degree from high to low is in the order of SiO2, Na2O, and Al2O3. The phase diagram of Na2O–Al2O3–SiO2 is used to accurately predict the changing trend of the melting point of co-combustion ash. The ratio changes between refractory and fusible minerals in the ash, as well as the degree of low-temperature eutectic reaction between sodium- and calcium-containing minerals, are the main factors affecting the melting point of ash. When the blending amount of SCCBs is 5%, mostly complete combustion is achieved, and slagging does not occur easily. The optimal blending ratio of SCCBs is obtained using the co-combustion method from the aspect of AFTs and viscosity-temperature characteristics. This work lays a theoretical foundation for industrial application.

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.

The synergy of CaO/MgO flux on ash fusion behaviors for high-silicon–aluminum coal

The synergy of CaO/MgO flux on ash fusion behaviors for high-silicon–aluminum coal

Co-Firing Zhundong Coal with Its Gangue: Combustion Performance, Sodium Retention and Ash Fusion Behaviors

Fouling and slagging are intractable ash-related problems for boilers burning high-sodium coals (HSC) to produce electricity or heat. Reduction and resource utilization of solid waste, coal gangues, is urgent because of stringent environmental regulations and economic benefits. Based on the sodium-rich character of Zhundong coal (ZDC) and the mineralogical features of the coal gangues (ZDG), this work investigated their co-firing performance, the sodium retention behaviors as well as the slagging and fouling tendency of the ashes. Results show that combustion performance of ZDC is not reduced despite ofthe lower reactivity of ZDG. The co-firing reaction follows the 3D diffusion model (cylinder symmetry) which probably reflects the gas diffusion of oxygen to combustible matter. During co-firing, the enriched silica and alumina components in ZDG efficiently react with the alkali and alkaline earth metals (sodium, magnesium and calcium) in ZDC to form complex minerals, thus effectively capturing and retaining sodium. The slagging and fouling propensity of ashes are notably reduced. Overall, co-firing provides an alternative means to solve the ash slagging and fouling issues, and also for the reduction and resource utilization of coal gangues.

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.

Enhancement of ash properties on alkali and alkaline earth metal retention by coal additives in the gasification condition

Biomass gasification is a promising technology to realize low carbon emission and clean energy generation processes, while the ash-related problem is the main limitation of its large-scale application. The coal additives can effectively alleviate ash sintering and melting issues. The in-situ ash fusion behavior, mineral transformation, and potassium retention process were explored in the co-gasification condition of soybean straw and coal. The formation of alkali and alkaline earth metal (AAEMs) based minerals led to the low ash slagging propensity with the coal additives due to the reaction between SiO2, Al2O3 and AAEMs. Then the in-situ observation indicated that the formation of refractory minerals promoted the reduction of shrinkage and the increase of AFTs. In this sense, the mineral evolution at different quenching temperatures further revealed that the alkaline earth metals were prone to react with SiO2 or Al2O3. Moreover, the decreasing amount of gaseous potassium meant that the K could be effectively retained by coal additives. Based on this in-situ analysis, the combinative thermodynamic calculation suggested that the priority areas were in the anorthite, melilite and leucite primary phase zones to ensure the smooth operation of the co-gasification process.

Quality assessment of induction furnace control for biomass ash fusibility determination

The quality of the control of an induction furnace for the determination of ash meltability at high temperature by the tube method was evaluated. For this purpose, the dynamic characteristics of the control object were measured and recorded on the test stand. The characteristics was the basis for developing a simulation model of the object. This model was tuned and its correspondence to the object was confirmed by computer simulation. Based on this model simulation models of the control system were created in the configuration with controllers, parallel PID and PID+DD. During subsequent computer simulations, control parameters were determined and the effect of the noise signal on the modelled system was evaluated. To evaluate the quality of the control, integral quality indices were used.

Experimental study on combustion, ash fusibility and slagging propensity during co-combustion of organic solid waste and lignite

Rapidly growth of organic solid waste (OSW) has caused serious social and environmental problems. Incineration as one of the most good public acceptance and environmentally friendly method attains increasing attention. In this study, the co-combustion characteristics of OSW and lignite, including the ignition and burnout temperature, ash melting and slagging propensity were studied. The experimental results show that the ignition temperature almost remains stable while the burnout temperature of the blends decreases as the increase of the OSW blending ratio, since the heat release during volatile combustion is beneficial for the burnout of coal char, but the polymer may melt and block the pores of the coal char at high temperature when the OSW blending ratio is higher than 30%. Besides, the slagging propensity of blending fuel is severe when the OSW blending ratio is 30%, and special attention should be paid to avoid slagging during the combustion process.