Regulation of Ash Fusibility Characteristics for High-Ash-Fusion

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Regulation of Ash Fusibility Characteristics for High Ash Fusion Temperature Coal by Bean Straw Addition Xiuwei Ma, Fenghai Li, Mingjie Ma, Shanxiu Huang, Shaohua Ji, and Yitian Fang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01013 • Publication Date (Web): 16 May 2018 Downloaded from http://pubs.acs.org on May 16, 2018

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Regulation of Ash Fusibility Characteristics for High Ash Fusion

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Temperature Coal by Bean Straw Addition

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Xiuwei Ma,†,‡ Fenghai Li,*,†,‡,§ Mingjie Ma,† Shanxiu Huang†, Shaohua Ji§, and Yitian Fang§

4 5 6

†

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‡

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College of Chemistry and Chemical Engineering, Henan Polytechnic University, Jiaozuo, Henan 454003, People,s Republic of China College of Chemistry and Chemical Engineering, Heze University, Heze, Shandong 274015, People,s Republic of China §

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001, People,s Republic of China

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ABSTRACT: The effects of bean straw (BS) on ash fusion behaviors of coals (Jiaozuo (JZ) and

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Zaozhuang (ZZ)) with high ash fusion temperature (AFT) and the regulating mechanism were

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investigated from the perspectives of ash chemical composition and mineralogical property. The

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results showed that the AFT of JZ ash mixture reduced with increasing the BS ash mass ratio;

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while the AFT of ZZ ash mixture decreased rapidly (0–12%), then increased slowly (>12%). The

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existence form of Al2O3 and SiO2 was converted from high melting point (MP) mullite into low

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MP alumino-silicates and their eutectics with BS ash addition, leading to a decrease in AFT. With

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increasing BS ash ratio, the major mineral reducing the AFT was changed from feldspar into

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leucite. Magnesia spinel had a weaker effect on improving the AFT than that of mullite or quartz

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due to their different molecular structures. The experimental ash samples were divided into three

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categories based on the total contents of SiO2 and Al2O3 (A) (I: A ≥ 78.6%; II: 72.2% ≤ A< 78.6%;

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III: 62.7% ≤ A < 72.2%). With the decreasing A content, the existing form of Na2O and K2O was

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transformed from feldspar into leucite and nepheline; the CaO together with some FeO and MgO

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was transformed from anorthite or cordierite into the more easily fusible melilite and

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clinopyroxene.

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ACS Paragon Plus Environment

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1. INTRODUCTION

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The co-utilizations of coal with biomass such as co-pyrolysis, co-combustion,

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co-gasification, etc. have been recognized as a promising way to reduce the high dependence on

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fossil fuels and environmental stress (e.g. global warming, ozone depletion, and acid rain).1–3

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Meanwhile, it can optimize the product structure and avoid some operational problems.4,5 Among

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all the co-utilization technologies, the co-gasification has attracted increasing attention, which

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converts different kinds of biomass and coal into clean synthetic gas for generation of electricity,

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synthetic liquid fuels, hydrogen, fuel cells, etc.6

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Compared with the fixed-bed or fluidized-bed gasification technology, entrained-flow bed

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(EF) gasification is generally operated on higher temperature and pressure, and the smaller

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feedstock particles in EF gasifier are in a strong turbulent flow state.7 Therefore, during the EF

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gasification, the difference of coal and biomass gasification reactivity is small and the carbon

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conversion efficiency is high,8 which is more suitable for co-utilization of biomass with different

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rank coals. However, EF gasifier has higher requirements for the viscosity and flow characteristics

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of ash/slag, which is closely related to the feedstock ash fusion temperature (AFT).9,10 The molten

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slag flow out of gasifier smoothly is the key factor to ensure the stable and long-term running of

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EF gasifier. In a typical EF gasifier (e.g., GSP, Shell, and Texaco), the ash flow temperature (FT)

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of feedstock is generally below 1380 oC and its viscosity is approximately in the range of 2.5–25

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Pa·s at the operating temperatures between 1300 oC and 1500 oC. For high AFT coal (FT >1380

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o

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efficiency and the stable operation of gasification system.11 Improving the operating temperature

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can mitigate the operational problem, however, this increases the additional consumption of

C), it is easy to cause ash deposition and slag blocking, which directly influences the gasification


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oxygen and energy largely; and the lifetime of refractory materials is reduced if the temperature is

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too high.12 Thus, in industrial practice, some measures (e.g. blending coal, fluxing agent, and

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leaching) are generally used to regulate the ash fusion behaviors of high AFT coal to satisfy the

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demands of slag tapping for EF gasifier.13,14

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High AFT coal accounts for over 57% of Chinese coal.10 It is of great significance to

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regulate these coals AFT to realize the clean and high efficiency utilization by EF gasification.

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Biomass ash is highly rich in alkaline and alkaline earth oxides,15 therefore, the biomass is not

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only the feedstock but also the fluxing agent to decrease coal AFT in their co-gasification process.

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However, the mixed ash fusion behavior of coal and biomass is much different from the feedstock.

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Although some AFT models have been established,16,17 most of them are not suitable for blended

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ash directly, especially for the blended ash of coal with biomass because of the enormous

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discrepancies in ash chemical compositions and the complex mineral reactions. Several

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investigations have been performed on the mixed ash fusibility characteristics of coal with

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biomass. Reinmöller et al.18 explored the mixed ash fusion behavior of German brown coal and

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wheat straw: with the increasing biomass mass ratio, the deformation temperature (DT) of mixed

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ash decreased rapidly, however, the hemispherical temperature (HT) and FT decreased when the

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wheat straw mass ratio was from 0% to 50%, and then increased at the ratio of 50–100%. Fang et

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al.19 investigated the AFT of bituminous coal and corn straw: the variations in four characteristic

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temperatures (DT, softening temperature (ST), HT, and FT) showed a “V” shape trend with

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increasing corn straw mass ratio. Xu et al.20 explored the blended ash flow behavior of straw and

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Guizhou coal: the blended slag with 20% straw content was glassy type, and the operating

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temperature range was higher than that of other blended ashes, which was more suitable for EF


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gasification. Chen et al.21 found that the biomass (cotton stalk and sargassum natans) with high

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AFT could also be used to reduce the coal AFT to meet the requirements of EF gasifier slagging.

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Most of the previous studies on blended ash fusibility characteristics were concentrated on

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biomass and low-rank coals (usually have a low AFT).18,19,22,23 The explorations on the effect of

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biomass on ash fusion behaviors of high AFT coal under reducing atmosphere were relatively less.

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The present study investigated the influence of biomass on ash fusion behaviors of high AFT coal

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and explored its variation mechanism through experiment (X-ray fluorescence (XRF) and X-ray

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diffraction (XRD)) and theoretical calculation (FactSage software). It is expected to supply some

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basic data and theoretical support for the developments of co-gasification technologies for

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biomass and high AFT coal.

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2. EXPERIMENTAL SECTION

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2.1. Raw Materials Quality Analysis

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Two high AFT coals (Jiaozuo coal (JZ) and Zaozhuang coal (ZZ)) and bean straw (BS) were

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used as experimental materials. The raw materials were pulverized and sieved to < 0.200 mm

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before analyses. Proximate analyses (biomass: GB/T28731-2012; coal: GB/T212-2008) and

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ultimate analyses (GB/T476-2001) of three samples were listed in Table 1. The contents of fixed

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carbon and ash in two coals were higher than that of BS, however, the volatile matter content in

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BS (65.27%) was higher evidently than that of coals (JZ: 7.24% and ZZ: 9.85%). Besides, BS had

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a lower sulfur and nitrogen levels. Table 1 should be place here.

90 91 92

2.2. Preparation of Ash Samples Ash fusion behavior is influenced by the ashing temperature especially for biomass, the


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ashing temperature of 500–600 oC can better reflect the chemical properties of biomass ash as the

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volatility of Na and K is relatively less.19,24,25 Therefore, the ash samples of three raw materials

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were prepared based on the standards ASTM E1755-01.21 Three raw samples in muffle furnace

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were ashed under air atmosphere with the following procedure: initially the raw materials were

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heated from room temperature to 250 oC with a heating rate of 10 oC /min and held for 30 min,

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then the residues were heated up to 575 oC within 30 min and maintained for 3 h (for coals, the

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time lasted for 6 h to guarantee the organic matters were burned entirely).26 Finally, the ash

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samples were ground to a particle size less than 0.075 mm.

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To compare the fluxing effects of BS on the two coal ashes and explore the mixed ash

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fusion mechanism, the blended ash samples were prepared by adding BS ash into coal ash. The BS

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ash mass ratios in ash mixtures were 6%, 12%, 18%, 24%, and 30%, respectively (BS mass ratio

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(air-dry basis): 10.94%, 20.78%, 29.69%, 37.79%, and 45.19% for JZ; 9.19%, 17.77%, 25.81%,

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33.35%, and 40.47% for ZZ). The prepared samples were put into a cabinet dryer for AFT

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determination and further analyses.

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Ash samples used for XRD analyses were prepared through the following steps: the ash

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sample was added into ceramic crucible and heated in an ALHR-2 AFT auto-analyzer (Aolian Co.

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Ltd., China) with a maximum temperature of 1500 oC. Mixed gas (H2/CO2, 1:1 volume ratio) was

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introduced into the AFT analyzer to simulate the gasification atmosphere.6,13,27 As the target

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temperature reached, the ceramic crucible was taken out and immediately immersed into ice water

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to prevent the mineral phase transformation and crystal segregation of ash samples.28 The

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quenched ash samples were taken out and crushed to < 0.075 mm.

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2.3. AFT Measurements


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The AFTs were measured according to Chinese GB/T219-2008 standard. Triangular ash

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cones with a bottom of 7 mm equilateral triangle and a height of 20 mm were heated in the AFT

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auto-analyzer under reducing atmosphere. Ash cone was heated from room temperature to 900 oC

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at the rate of 15 oC min–1, then changed into 5 oC min–1. The four characteristic temperatures (DT,

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ST, HT, and FT) were recorded through the specific deformation of ash cone. The AFTs of three

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raw materials were presented in Table 2, the FT increased in the order ZZ < BS < JZ. Their FTs

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were higher than 1380 oC, indicating that they were not suitable for EF gasification directly from

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the perspective of AFT.

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Table 2 should be place here. 2.4. Characterization of Ash Samples

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The ash chemical compositions of raw materials were tested using XRF-1800 spectrometer

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(Shimadzu, Japan) with a Rh target X-ray tube under the conditions of 50 kV and 40 mA. The

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minerals phases of ash samples were examined by D/max-rB X-ray powder diffractometer

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(Rigaku, Japan) with Cu Kα radiation under the conditions of Kα1 = 0.15408 nm, 40 kV, and 100

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mA; the scanning was conducted at 5o 2θ/min scanning speed in the 2θ range from 10o to 70o with

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0.01o step size.26 Jade 5.0 software package was selected for peak identification.

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Thermodynamic calculations were performed by FactSage software (version 7.1). The

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equilibrium module together with the data base of FToxid and FactPS was used for predicting the

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theoretical mineral compositions at different temperatures.29,30 The major ash chemical

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compositions (SiO2, Al2O3, K2O, CaO, Na2O, MgO, and Fe2O3) were input into the calculation.

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The calculation temperature was from 900 to 1500 oC with an interval of 20 °C. From the previous

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investigations,31,32 Cl in biomass ash was mostly volatilized in form of sylvite (KCl) at high


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temperature. Thus, based on the Cl content, the K2O content was optimized according to the

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formula: K2O = (K2O)1– (K2O)2. Where (K2O)1 represented the original K2O content in ash

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samples, (K2O)2 was the content of K2O required for the KCl formation. Besides, the Gibbs free

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energy (∆G) of the important reactions at different temperatures was calculated by the reaction

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module.

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3. RESULTS AND DISCUSSION

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3.1. Variations in Coal AFT with Increasing BS Ash Blending Ratio

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Figure 1 presented the AFT variations of coals (JZ and ZZ) with increasing the BS ash

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mass ratio. Although the FTs of three raw materials were high, the FTs of coal and BS mixtures

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were lower than that of each single one. The BS fluxing effect for ZZ was more efficient than that

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of JZ. For JZ, while the DT and ST of the mixed ash increased slightly at 24%, the HT and FT

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decreased gradually with increasing BS ash ratio (Figure 1a). When the BS ash mass ratio reached

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18%, the FT of JZ mixed ash decreased to 1333 oC, which could satisfy the demand of EF gasifier

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slag tapping. For ZZ, the AFT of mixed ash reduced obviously in the mass ratio of 0–12% (Figure

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1b), the FT was lower than 1380 oC at 6%, and the FT decreased by 176 oC at ratio of 12%. With

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the blending ratio increased continuously (>12%), the AFT increased slightly; while the FT (1292

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o

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among ZZ blended ashes was only 23 oC. In addition, the ash fusion temperature range (FT–DT)

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of JZ or ZZ mixture reduced with increasing BS blending ratio. The narrow fusion range was not

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beneficial for slag tapping, because the solidification might emerge rapidly with temperature

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fluctuation.33 Thus, small BS blending ratio was more suitable for EF gasifier stable operation

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under the precondition of normal slag tapping.

C) was substantially lower than 1380 oC at 30%, meanwhile, the maximum difference of FTs


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Figure 1 should be place here. 3.2. Influence of Base to Acid (B/A) Ratio on Ash Fusion Behaviors

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Ash sample can be regarded as a network of tetrahedral silicates during its fusion process.

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Therefore, the AFT is closely correlated to the proportion of network formers and its transformers.

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The B/A ratio (B: the total content of Na2O, K2O, CaO, MgO, and Fe2O3; A: the total content of

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SiO2, Al2O3, and TiO2) is a more accurate parameter to reveal the ash fusion behavior.27 The acidic

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oxides (A) are prone to form larger polymeric networks of silicates or alumino-silicates through

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the bridging oxygen bound (Si–O–Si) for their high ionic potentials, increasing the AFT. While the

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basic components (B), as the network transformers, can convert the Si–O–Si into non-bridging

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oxygen bound (O–Si) through Lewis acid–base reaction with anionic [SiO4]4– network,34 reducing

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the AFT. Generally, the AFT is the lowest as the B/A is around 1 from the network theory; the

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more the B/A deviates from 1, the higher the AFT is.29 Table 3 listed the ash chemical

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compositions and B/A values of different ash samples, the B/A values of ash samples were < 1

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except for BS (2.66). Compared to ZZ, the B/A value of JZ was lower, which meant the stability

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of the silicate network in JZ was stronger than that of ZZ, resulting in a higher AFT of JZ. With

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the rising of BS ash ratio, the B/A value of blended ash increased; BS ash rich in basic oxides

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provided more O2– to depolymerize silicate network gradually through the following reaction:

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[SinO3n+1]2(n+1)– + O2– → [Sin–1O3n–2]2n– + O2– ·········· + O2– → [SiO4]4–

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The amount of Si–O–Si bound in silicate melt decreased with the basic oxide (O2–) addition, and

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the amount of O–Si bound increased, thus, the large silicate network was depolymerized to low

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polymers. In the presence of the basic oxides, the reaction would continue to occur, finally, the

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silicate network was changed into neso-silicates. Therefore, the AFT reduced in the absence of the


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large stable network. This might explain the coal AFT decrease with increasing the BS ash ratio.

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The B/A value of JZ mixture was lower than that of ZZ mixture at the same BS blending ratio,

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causing that the AFT of JZ mixture was higher than that of ZZ mixture except for the mixture with

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30% BS ash. The slow AFT increase for ZZ (>12%) might be attributed to the modes of element

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occurrence in minerals. The Cl in blended ash evaporated in form of KCl during ash fusion

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process, causing that some K2O could not play the fluxing role.32 The B/A value of BS ash was >1,

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the basic component destroyed the network adequately; the excessive basic components, such as

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MgO and CaO with high melting point (MP) of 2852 oC and 2572 oC respectively, existed in the

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form of oxides.35 Although K2O content was high in BS ash, it was prone to form kaliophilite

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(KAlSiO4) with high MP (~1800 oC) as the contents of SiO2 and Al2O3 were low.26 This might be

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the main reason for higher AFT of BS.

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Table 3 should be place here.

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3.3. Analysis of Mineralogical Properties During Ash Fusion

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3.3.1. Mineral Evolution in Two Coal Ash Samples

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Figure 2 presented the XRD patterns of two coal ashes under reducing atmosphere at

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different temperatures. For the same mineral, its content variation can be approximately reflected

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by the change of diffraction intensity.36 As illustrated in the Figure 2a, for the JZ ash, the Si and Al

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were mainly existed in form of muscovite (KAl3Si3O11) and quartz (SiO2) at 1000 oC, the Ca and

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Fe were existed in anhydrite (CaSO4) and hematite (Fe2O3), respectively. The hematite resulted

200

from the pyrite (FeS2) during ashing process. As the temperature increased to 1100 oC, the

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diffraction intensity of quartz diminished and the diffraction peaks of muscovite, anhydrite, and

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hematite disappeared along with the generations of mullite (Al6Si2O13), hercynite (FeAl2O4),


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gehlenite (Ca2Al2Si2O7), and anorthite (CaAl2Si2O8). The muscovite transformed into mullite.

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Meanwhile, anhydrite and hematite converted to CaO and FeO, which reacted with Al2O3 and

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SiO2 to form the two Ca-bearing minerals and hercynite. With the further increase in temperature,

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the gehlenite and hercynite melted into amorphous phase; the diffraction intensity of quartz

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decreased appreciably, which might react with Al2O3 to form mullite. The Si in mullite existed in

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form of [SiO4]4–-tetrahedron,

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[AlO6]9–-octahedron, and the [AlO4]5–-tetrahedron was the major existing form;37 the

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[SiO4]4–-tetrahedron and [AlO4]5–-tetrahedron formed a stable double chain structure, resulting in

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a high MP (~1860 oC). The high MP mullite and quartz (MP: ~1723 oC) became the major

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minerals at 1300 oC, especially for the mullite,27 resulting in a high AFT of JZ.

the Al existed

in form of [AlO4]5–-tetrahedron and

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Compared with JZ ash at 1000 oC, obvious diffraction peak of clay mineral containing Si

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and Al was not detected in the ZZ ash (Figure 2b), because the clay mineral content was small and

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mostly decomposed into other minerals, besides, the diffraction peak was also influenced by

216

crystal quality and other minerals.38 When the temperature reached 1100 oC, the hercynite

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diffraction intensity was stronger than that of JZ for its high Fe2O3 content (10.87%); and the

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diffraction peaks of sanidine (KAlSi3O8) and albite (NaAlSi3O8) were detected, while the mullite

219

was not observed. The important reactions during ash fusion process were presented in Table 4,

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the ∆G of mullite formation (–18.06 kJ/mol) was higher markedly than that of feldspar formation

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(anorthite: –133.60 kJ/mol; albite: –397.51kJ/mol; sanidine: –497.88 kJ/mol) at 1100 oC,

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indicating the mullite formation needed more energy. With temperature continuing to increase

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(>1100 oC), the feldspar (sanidine and albite) and hercynite transformed into amorphous matters,

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and mullite produced. The diffraction intensity of the mullite in JZ ashes was stronger than that in


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ZZ at 1200 oC and 1300 oC, causing that JZ had higher AFT than that of ZZ. Figure 2 should be place here.

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3.3.2. Thermodynamic Calculations of Coal Ash Samples

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FactSage software can predict mineral transformation behavior based on the ash chemical

229

compositions. Figure 3 showed the variations in theoretical mineral compositions and their

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relative contents of coal ashes with increasing temperature. The major minerals of mullite,

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anorthite, cordierite, and quartz formed during JZ ash fusion process (Figure 3a).

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Magnesium-cordierite (Mg2Al4Si5O18) and ferro-cordierite (Fe2Al4Si5O18) were not identified by

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XRD at 1100 oC (Figure 2a), which might result from the short reaction time. It was more

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difficult to generate the cordierite compared with the other alumino-silicates containing basic

235

elements for its relative high ∆G at 1100 oC (magnesium-cordierite: –117.44 kJ/mol;

236

ferro-cordierite: –46.07 kJ/mol). Thus, longer time was needed for cordierite formation, while

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kinetics was not taken into account in the calculation.33,39 As the temperature raised from 1000 oC

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to 1300 oC, the mullite content increased and reached maximum at around 1300 oC; only a small

239

amount of mullite melted as the temperature was >1300 oC. The major theoretical minerals

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occurred in ZZ ash fusion process were similar to JZ (Figure 3b), while the contents of cordierite,

241

feldspar, and hercynite were higher than that of JZ at the same temperature. The mullite was not

242

formed until the temperature above 1160 oC. As the temperature was >1100 oC, the fusible

243

cordierite and feldspar melted into liquid slag gradually. The mullite melting rate in ZZ ash was

244

faster than that in JZ, because the liquid slag in ZZ ash with more basic components had a lower

245

viscosity.21 The major theoretical minerals influencing the AFT was basically in accord with the

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XRD results (Figure 2).


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Figure 3 should be place here.

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Table 4 should be place here.

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3.3.3. Variations in Mineral Composition with Increasing BS Ash Blending Ratio

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AFT modification can be reflected by the variation in mineral species and their relative

251

contents at 1100 oC.26,27 Figure 4 illustrated the XRD patterns of coal mixed ashes with different

252

BS ash mass ratios at 1100 oC under reducing atmosphere. As shown in Figure 4a, when the

253

blending ratio was 6%, the diffraction intensities of quartz and mullite reduced evidently,

254

accompanied by the generation of albite with low MP (~1100 oC) and the increase in anorthite

255

content. The contents of basic components (CaO and Na2O) in JZ ash increased with BS ash

256

addition. Based on the acid-base theory, CaO and Na2O were basic constituents, Al2O3 was

257

regarded as neutral component, and SiO2 belonged to acidic component. Thus, in the presence of

258

CaO and Na2O, the abundance of Al2O3 and SiO2 in JZ ash preferentially reacted with them,

259

producing the Na-bearing mineral or Ca-bearing mineral instead of mullite. In addition, Ca2+ and

260

Na+ with lower ionic potential (20.20 nm–1 and 10.53 nm–1, respectively) could cause the rupture

261

of covalent bonds Al(1)–O(13) and Al(8)–O(13) in mullite and change its crystal lattice,

262

generating anorthite and albite.37 As the blending ratio reached 12%, the diffraction intensities of

263

anorthite and albite increased continuously; meanwhile, the gehlenite re-emerged, which reacted

264

with anorthite to form low MP eutectic. Compared with JZ ash, the contents of high MP minerals

265

diminished, causing the AFT to reduce. With the blending ratio continued to increase (≥18%),

266

K2O reacted with SiO2 and Al2O3 to produce low MP leucite (KAlSi2O6) (~1100 oC). The leucite

267

content increased evidently with a rise in blending ratio, which was attributed to its lower ∆G

268

(–489.12 kJ/mol) at 1100 oC;39 while the diffraction intensities of anorthite and albite reduced,


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Energy & Fuels

269

only a weak diffraction peak was detected at 30%. It was possible that the CaO and Na2O were

270

mostly transformed into amorphous phase at 1100 oC. Besides, minor amount of low MP

271

nepheline ((K,Na)AlSiO4) generated as the blending ratio was ≥ 24%. The total contents of low

272

MP minerals (especially for leucite) and amorphous matter increased and became the major

273

factor decreasing the AFT further (>12%).

274

As the BS ash mass ratio reached 12%, ZZ blended ash was mainly composed of anorthite,

275

quartz, albite, and hercynite (Figure 4b). Anorthite and albite reacted with quartz to form low MP

276

eutectics,21 resulting in AFT decrease. With the blending ratio increased continuously (≥18%), the

277

leucite generated and minor amounts of magnesia spinel (MgAl2O4) and forsterite (Mg2SiO4)

278

produced from the reaction (8) and (9) (Table 4). The formations of magnesia spinel and forsterite

279

required more energy for their high ∆G at 1100 oC (magnesia spinel:–32.22 kJ/mol; forsterite:

280

–59.61 kJ/mol).39 The two Mg-bearing minerals were high MP ionic crystal compound (magnesia

281

spinel, ~2135 oC; forsterite, ~1900 oC) due to their high lattice energies. In addition, magnesia

282

spinel was not easy to form low MP eutectics with other minerals, causing the AFT increase.40 The

283

two Mg-bearing minerals were not the high polymeric compounds and forsterite was a typical

284

neso-silicate, thus, the effect of improving AFT was weaker than that of mullite or quartz. A new

285

phase kaliophilite produced due to the abundance of K2O when BS ash ratio was 30%, which

286

could raise the AFT to some extent.26 However, the amounts of leucite and amorphous matter

287

increased markedly, leading to AFT not increasing greatly. From the mineralogical analysis

288

(Figure 4), the feldspar played a significant role in reducing the AFT when the blending ratio was

289

small (≤12%), while the leucite became the major fluxing mineral decreasing the AFT further at

290

higher blending ratio (>12%).


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

291 292

Figure 4 should be place here. 3.3.4. Mineral Evolution in Mixed Ash Samples

293

Two coal mixed ashes (JZ+18%BS and ZZ+12%BS) were selected to investigate the

294

fluxing mechanism of BS ash, because the AFTs reduced markedly at the two blending ratios.

295

The XRD patterns of mixed ash at different temperatures under reducing atmosphere were shown

296

in Figure 5. As shown in Figure 5a, mineral phases of the JZ blended ash at 1000 oC were similar

297

to that of JZ ash. However, the modes of element occurrence were greatly different from JZ ash

298

at 1100 oC; the formation of mullite was inhibited, the large amounts of SiO2 and Al2O3 were

299

involved in the formation of fusible alumino-silicates (leucite, anorthite, albite, and gehlenite).

300

The diffraction intensities of anorthite and leucite increased when the temperature increased to

301

1200 oC; the ∆G of reactions (1) decreased from –131.64 kJ/mol to –137.71 kJ/mol with an

302

increasing temperature (1000–1300oC), and it decreased from –486.19 kJ/mol to –494.04 kJ/mol

303

for reactions (7), which indicated increasing temperature was beneficial to the formation of

304

anorthite and leucite. Meanwhile, the magnesia spinel generated at a relative high temperature,

305

corresponding to its high ∆G (1200 oC: –32.98 kJ/mol; 1300 oC: –33.77 kJ/mol). With the

306

temperature increased further, most of the crystal minerals melted into amorphous matter; the

307

major high MP mullite was replaced by magnesia spinel at 1300 oC compared with JZ ash. The

308

large amount of molten liquid phase resulted in the AFT decrease.13

309

In addition to the quartz, hematite, and anhydrite, the sanidine was identified in the ZZ

310

blended ash at 1000 oC (Figure 5b). With the temperature increased, the quartz diffraction

311

intensity diminished gradually. The sanidine transformed into amorphous state at 1100 oC and

312

hercynite generated. As the temperature was >1100 oC, the major minerals were similar to JZ


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Energy & Fuels

313

blended ash except for leucite. Comparing to the Figures 2 and 5, the diffraction intensities of

314

anorthite and albite increased firstly, then reduced with increasing temperature; while the

315

maximum diffraction intensity occurred at 1200 oC (for JZ and JZ blended ash) and 1100 oC (for

316

ZZ and ZZ blended ash), respectively. This because ZZ ash and ZZ blended ash had a higher

317

hercynite content, the hercynite reacted with feldspar to generate low MP eutectic in temperature

318

range of 1100 oC–1200 oC.6 Minor amount of magnesia spinel existed as the temperature

319

was >1200 oC. The large amount of low MP minerals and amorphous phase caused the ZZ AFT

320

decrease.

321 322

Figure 5 should be place here. 3.3.5. Thermodynamic Calculations of Mixed Ash Samples

323

Figures 6 and 7 showed the variations in theoretical mineral compositions and their relative

324

contents of mixed ash with increasing temperature. When the BS ash blending ratio was 6%

325

(Figure 6a) or 12% (Figure 6b), the minerals species emerged in JZ mixed ash fusion process were

326

similar to JZ ash (Figure 3a), while the contents of mullite and cordierite reduced at the same

327

temperature and the feldspar increased due to the increasing of basic oxide. As the blending ratio

328

increased continuously (Figure 6c–e), the mineral species changed markedly. The abundance of

329

SiO2 and Al2O3 were transformed into more easily fusible alumino-silicates instead of mullite and

330

cordierite. The feldspar and leucite were the major minerals dominating the ash fusion behavior at

331

ratio of 18%, which corresponded to the XRD results (Figure 4a). Along with the declining of the

332

feldspar, more clinopyroxene (Ca(Mg,Fe)Si2O6), nepheline ((Na,K)AlSiO4), and melilite

333

(Ca2(Mg,Fe)Si2O7, Ca2Al2SiO7) formed; they were the complex alumino-silicates containing basic

334

ions with the same valence, which was prone to form the low MP eutectic. All the minerals


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

335

transformed into liquid slag at 1360 oC as the blending ratio was ≥18%, while their melting rates

336

were accelerated as the temperature was >1100 oC, causing the AFT decrease further.

337

Figure 6 should be place here.

338

When the BS ash blending ratio was 6% for ZZ, the mineral species was consistent with the

339

JZ mixture with 12% BS ash. A small amount of corundum (Al2O3) was precipitated, because

340

more SiO2 was involved in the feldspar formation with BS ash addition (Figure 6b and Figure 7a),

341

and there was no excessive FeO or MgO reacting with Al2O3 to produce spinel.32 With the BS ash

342

blending ratio increased, more easily fusible alumino-silicates (olivine, nepheline, clinopyroxene,

343

and melilite) formed and melted quickly at the temperature interval of 1050 oC–1100 oC, resulting

344

in an increase in liquid slag (Figure 7c–e). While the high MP magnesia spinel melted slowly with

345

increasing temperature. As can be seen from Figures 6 and 7 that the major fusion temperature

346

range of minerals except for spinel reduced with an increasing BS ash ratio. This might explain

347

the ∆T of coal mixture diminished with increasing BS ash ratio (Figure 1), because the AFT was

348

determined by the proportion of solid and liquid phase in ash cone.7

349 350

Figure 7 should be place here. 3.4. Variations in Element Existence Form with BS Ash Addition

351

The modes of element occurrence influenced the ash fusion behavior greatly, which was

352

closely correlated to the total contents of SiO2 and Al2O3 (A) according to the XRD analyses and

353

theoretical calculations. Most of the high AFT coal had a high A content; JZ and ZZ were the

354

representative high AFT coals with different A contents. Thus, on the basis of the A content

355

variation, the experimental ash samples were divided into three categories approximately. Three

356

mean values of A contents (JZ and ZZ, JZ+12%BS and ZZ+12%BS, JZ+30%BS and


Page 16 of 35

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Energy & Fuels

357

ZZ+30%BS) were selected as the breaking points respectively, and the corresponding element

358

existence forms were listed in Table 5, which was more efficient to guide the biomass selection

359

and blending ratio determination for co-gasification of high AFT coal with biomass.

360

The major oxides in coal ash were recombined with BS ash addition. As the A content

361

was high (A ≥ 78.6%; the first category), the Al2O3 and SiO2 existed mostly in form of mullite

362

and regulate the ash fusion behavior. Most of the other minerals were alumino-silicates; the small

363

amounts of CaO, K2O, and Na2O existed in feldspar and the main existence form of MgO and

364

FeO was cordierite, while their fluxing effect was weaker due to stable alumino-silicate network.

365

As the A content was moderate (72.2% ≤ A < 78.6%; the second category), most of Al2O3 and

366

SiO2 were combined with basic oxides to form the large amount of feldspar due to the less

367

energy demand, which became the most important mineral reducing the AFT. Some MgO and

368

FeO existed in form of spinel, the cordierite content decreased gradually with decreasing A

369

content. When the A content was low (62.7% ≤ A < 72.2%; the third category), the modes of

370

element occurrence changed greatly. The existence form of K2O and Na2O was transformed from

371

feldspar into leucite and nepheline, the leucite became the major mineral to decrease the AFT

372

continuously; their contents increased with increasing the basic component content. While the

373

CaO together with some MgO and FeO was converted into the clinopyroxene and melilite, which

374

melted at relative low temperature. The spinel content increased slowly. Table 5 should be place here.

375 376

4. CONCLUSION

377

BS can effectively reduce the AFT of JZ or ZZ for its abundance of basic components. The

378

AFT variation was greatly influenced by the ash chemical compositions and their existence form.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

379

In the presence of basic composition, the SiO2 and Al2O3 preferentially reacted with them to

380

generate low MP minerals (feldspar, gehlenite, nepheline, and leucite) instead of high MP mullite

381

based on the thermodynamic calculation, resulting in coal AFT decrease. As the MgO existed in

382

the form of magnesia spinel and forsterite, the AFT increased slightly. The classification of ash

383

samples provided a good method to understand the mineral evolution mechanism during

384

co-gasification of biomass with high AFT coal.

385

AUTHOR INFORMATION

386

Corresponding Author

387

*Telephone: +86-0530-5668162. E-mail: [email protected]

388

Notes

389

The authors declare no competing financial interest.

390

ACKNOWLEDGMENTS

391

This research was financially supported by the Natural Science Foundation of Shandong

392

Province, China(ZR2018MB037), Youth Natural Science Foundation of Shanxi Province, China

393

(Y5SJ1A1121), and the Strategic Priority Research Program of the Chinese Academy of Sciences

394

(XDA07050103).

395

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(3) Zhao, X.; Ren, J.; Cao, J.; Wei, F.; Zhu, C.; Fan, X.; Zhao, Y.; Wei, X. Catalytic reforming of volatiles from

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ash from Shanxi typical anthracite. J. Fuel Chem. Technol. 2013, 41, 805–813.

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bed biomass gasifiers on different scales. Energy Convers. Manage. 2013, 69, 95–106.

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an entrained coal gasifier, Appl. Therm. Eng. 2015, 87, 175–184.

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entrained-flow gasifier. Energy Convers. Manage. 2014, 86, 683–688.

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mineral interaction. Energy Fuels 2018, 32, 132–141.

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biomass and coal blended ash. Bioresour. Technol. 2014, 166, 494–499.

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with coal: rheological properties and ash fusion temperatures of hyacinth-coal slurry. Ind. Eng. Chem. Res. 2013, 52,

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high silica–alumina. Energy Fuels 2017, 31, 7941–7951.

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Table Captions Table 1. Proximate and Ultimate Analyses of Raw Materials. Table 2. Ash Fusion Temperatures of Raw Materials (oC). Table 3. Ash Chemical Compositions of Different Ash Samples and the B/A Values (wt%). Table 4. Major Reactions during Ash Fusion Process and Their Gibbs Free Energy at Different Temperatures. Table 5. The Modes of Element Occurrence at Different Classifications Based on Total Contents of SiO2 and Al2O3.


Page 22 of 35

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Energy & Fuels

Table 1 Proximate and Ultimate Analyses of Raw Materials. proximate analysis on an air-dry basis (wt/%) sample

moisture

ash

JZ

1.33

16.58

ZZ

2.61

BS

4.21

a Calculated b Total

volatile

ultimate analysis on a dry and ash-free basis (wt/% )

fixed carbon

C

H

Oa

Sb

N

7.24

74.85

87.94

3.08

5.48

2.36

1.14

13.66

9.85

73.88

83.86

6.95

6.99

1.57

0.63

8.62

65.27

21.90

51.16

8.22

40.15

0.10

0.37

matter

by difference.

sulfur.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 35

Table 2 Ash Fusion Temperatures of Raw Materials (oC).

a

sample

DTa

STb

HT c

FT d

JZ

1486

>1500

>1500

>1500

ZZ

1375

1400

1420

1445

BS

1401

1430

1440

1451

deformation temperature. b softening temperature. c hemispherical temperature. d flow temperature.


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Energy & Fuels

Table 3 Ash Chemical Compositions of Different Samples and the B/A Values (wt%). sample

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

K 2O

Na2O

TiO2

P2O5

Cl

B/A

JZ

49.06

33.84

5.32

4.95

0.86

2.10

1.04

1.06

1.36

0.41

-

0.16

ZZ

42.10

32.17

10.87

6.09

2.46

2.44

0.80

0.75

1.17

1.15

-

0.28

BS

16.16

9.41

4.95

19.32

10.27

3.02

28.91

5.16

0.27

1.47

1.06

2.66

JZ+6%BS

47.09

32.37

5.30

5.81

1.42

2.16

2.71

1.31

1.29

0.48

0.06

0.20

JZ+12%BS

45.11

30.91

5.28

6.67

1.99

2.21

4.38

1.55

1.23

0.54

0.13

0.26

JZ+18%BS

43.14

29.44

5.25

7.54

2.55

2.27

6.06

1.80

1.16

0.60

0.19

0.31

JZ+24%BS

41.16

27.98

5.23

8.40

3.12

2.32

7.73

2.04

1.10

0.67

0.25

0.38

JZ+30%BS

39.19

26.51

5.21

9.26

3.68

2.38

9.40

2.29

1.03

0.73

0.32

0.45

ZZ+6%BS

40.54

30.80

10.51

6.88

2.93

2.48

2.49

1.01

1.12

1.18

0.06

0.33

ZZ+12%BS

38.99

29.44

10.16

7.68

3.40

2.50

4.17

1.28

1.06

1.19

0.13

0.38

ZZ+18%BS

37.43

28.07

9.80

8.47

3.87

2.54

5.86

1.54

1.01

1.22

0.19

0.44

ZZ+24%BS

35.87

26.71

9.45

9.27

4.33

2.58

7.55

1.81

0.95

1.23

0.25

0.51

ZZ+30%BS

34.32

25.34

9.09

10.06

4.80

2.61

9.23

2.07

0.90

1.26

0.32

0.58

B/A value = (Fe2O3+ CaO + MgO + K2O + Na2O)/(SiO2 + Al2O3 + TiO2).


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 35

Table 4 Major Reactions during Ash Fusion Process and Their Gibbs Free Energy at Different Temperatures. ∆G/ kJ/mol

reaction

1000 oC

1100 oC

1200 oC

1300 oC

(1)

CaO + Al2O3 + 2SiO2→CaAl2Si2O8 (anorthite)

‒131.64

‒133.60

‒135.62

‒137.71

(2)

Al2O3 + Na2O + 6SiO2→ 2NaAlSi3O8 (albite)

‒395.71

‒397.51

‒396.89

‒395.08

(3)

Al2O3 + K2O + 6SiO2→ 2KAlSi3O8 (sanidine)

‒497.26

‒497.88

‒498.37

‒498.77

(4)

3Al2O3 + 2SiO2→ Al6Si2O13 (mullite)

‒15.40

‒18.06

‒20.70

‒23.33

(5)

2Al2O3 + 2FeO + 5SiO2→ Fe2Al4Si5O18 (magnesium-cordierite)

‒43.76

‒46.07

‒48.37

‒50.62

(6)

2Al2O3 + 2MgO + 5SiO2→ Mg2Al4Si5O18 (ferro-cordierite)

‒115.06

‒117.44

‒119.87

‒122.38

(7)

Al2O3 + K2O + 4SiO2→ 2KAlSi2O6 (leucite)

‒486.19

‒489.12

‒491.73

‒494.04

(8)

MgO + Al2O3→ MgAl2O4 (spinel)

‒31.49

‒32.22

‒32.98

‒33.77

(9)

2MgO + SiO2→ Mg2SiO4 (forsterite)

‒60.11

‒59.61

‒59.16

‒58.75


Page 27 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 5 The Modes of Element Occurrence at Different Classifications Based on Total Contents of SiO2 and Al2O3. classification

major minerals

content variation

Mullite (Al6Si2O13)▲b

↓c

I

Quartz (SiO2)

↓

(Aa ≥ 78.6%)

Cordierite (Fe2Al4Si5O18, Mg2Al4Si5O18)

↓

Feldspar (CaAl2Si2O8, KAlSi3O8, NaAlSi3O8)

↑d

Hercynite (FeAl2O4)

↑

Feldspar (CaAl2Si2O8, KAlSi3O8, NaAlSi3O8) ▲

↑

Mullite (Al6Si2O13)

↓

Quartz (SiO2)

↓

Cordierite (Fe2Al4Si5O18, Mg2Al4Si5O18)

↓

Hercynite (FeAl2O4)

↓

Magnesia spinel (MgAl2O4)

↑

Leucite ((KAlSi2O6) ▲

↑

Nepheline ((Na,K)AlSiO4)

↑

II ash

(72.2% ≤ A < 78.6%)

samples

III (62.7% ≤ A < 72.2%)

Clinopyroxene (Ca(Mg,Fe)Si2O6)

↑

Melilite (Ca2(Mg,Fe)Si2O7, Ca2Al2SiO7)

↑

Magnesia spinel (MgAl2O4)

↑

Feldspar (CaAl2Si2O8, KAlSi3O8, NaAlSi3O8)

↓

a

the total mass ratio of Al2O3 and SiO2.

b

The most important mineral influencing the AFT.

c

The content decreases with the declining of Al2O3 and SiO2.

d

The content increases with the declining of Al2O3 and SiO2.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure captions Figure 1. AFT variation of coal with different BS ash mass ratios. Figure 2. XRD patterns of coal ash at different temperatures. Figure 3. Phase assemblage–temperature curves for coal ash. Figure 4. XRD patterns of mixed ash with different BS ash mass ratios at 1100 oC. Figure 5. XRD patterns of mixed ash at different temperatures. Figure 6. Phase assemblage–temperature curves for JZ blended ash. Figure 7. Phase assemblage–temperature curves for ZZ blended ash.


Page 28 of 35

Page 29 of 35

DT ST HT FT

1500

o

Temperature / C

1400

1300

1200

1100

0

6

12

18

24

30

BS ash mass ratio /%

(a) DT ST HT FT

1400

o

Temperature / C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1300

1200

1100

0

6

12

18

24

30

BS ash mass ratio /%

(b) Figure 1. AFT variation of coal with different BS ash mass ratios. (a) JZ; (b) ZZ.


Energy & Fuels

4000

1

5

1

1

1

85

5

5

5

5

1

0

1

1000

1

5 1100

5

5 5

o

1 5 8 7 56 5 6 5 5 5 5 5 8 55 5 5 5 5 5

2

C

8

2

tur e/

55

1

1000

23 3

mp era

55

1

1200

Te

4

2000

2

1

Intensity/cps

3000

5 1300

10

20

30

40

2-Theta/

50

o

60

70

(a) 1

4000

2000

8

3 2 3

9 1 8+10 810 6 6

1

tur e/

1100

5 1

1200

55

0

1

1000

1

1 5 8+10 5 1810 56 5 5 1

1 3

o

3

C

1 2

5

mp era

1

Intensity/cps

6000

Te

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 35

5 1300

10

20

30

40 o

2-Theta/

50

60

70

(b) Figure 2. XRD patterns of coal ash at different temperatures. (a) JZ; (b) ZZ. 1 Quartz (SiO2); 2 Anhydrite (CaSO4); 3 Hematite (Fe2O3); 4 Muscovite (KAl3Si3O11); 5 Mullite (Al6Si2O13); 6 Hercynite (FeAl2O4); 7 Gehlenite (Ca2Al2SiO7); 8 Anorthite (CaAl2Si2O8); 9 Sanidine (KAlSi3O8); 10 Albite (NaAlSi3O8).


Page 31 of 35

100

Quartz

90 80

Relative mass /%

70

Magnesium-cordierite Slag

60

Ferro-cordierite

50

Anorthite

40

Sanidine

30

Albite

20 10

Mullite

0 900

1000

1100

1200

1300

1400

1500

o

Temperature/ C

(a) 100

Orthopyroxene Magnesium-cordierite

90 80

Slag

70

Relative mass /%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Ferro-cordierite

60 50 40

Anorthite

30

Sanidine

20

Albite Hercynite

10 0 900

1000

Mullite 1100

1200

1300

1400

1500

o

Temperature/ C

(b) Figure 3. Phase assemblage–temperature curves for coal ash. (a) JZ; (b) ZZ.


Energy & Fuels

1

2000

20

1

30

40 o

2-Theta/

60

70

0 0

12

o/%

6

18 24

50

2 2

4 8

5+6 10

1000

5 3 4 23 2 2 2 2 2 5+6 2 2 11 5 3 2 3 22 1 2 5+6 5 4 23 2 77 5+6 7 17 5 4 7 6 7 5+6 4 7 7 8 1 56

as hm as sr at i

7

2

BS

1 2 1

Intensity/cps

3000

30

(a) 5000

3000

15

1 5 5+6 3 6 5+6 1 3 1 56 7 7 7 5+6 7 1 56 11 9 7 1 5+6 7 7 11 9 7 56 12 11 9 7 10

20

30

40 o

2-Theta/

50

2000

3

1000

3 1

3

3

0

3

0 6 12

18 24

60

70

o/ %

1

10 5

as hm as sr at i

1

Intensity/cps

4000

1

BS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 35

30

(b) Figure 4. XRD patterns of mixed ash with different BS ash mass ratios at 1100 oC. (a) JZ; (b) ZZ. 1 Quartz (SiO2); 2 Mullite (Al6Si2O3); 3 Hercynite (FeAl2O4); 4 Gehlenite (Ca2Al2SiO7); 5 Anorthite (CaAl2Si2O8); 6 Albite (NaAlSi3O8); 7 Leucite (KAlSi2O6); 8 Nepheline ((K,Na)AlSiO4); 9 Magnesia spinel (MgAl2O4); 10 Sanidine (KAlSi3O8); 11 Forsterite (Mg2SiO4); 12 Kaliophilite (KAlSiO4).


Page 33 of 35

2500

1

1500

3

1000

4 1

3

1 5 6+7 5 51 8 6 51 7 6 5 6+7 5 7 8 9 1 9 1

3

1

0 1000

9

1200

9

o

1100

9

C

1

m pe ra tu re /

9

500

24 2

Te

1

Intensity/cps

2000

1300 10

20

30

40o

50

2-Theta/

60

70

(a)

2000

67 1

1

6+7 9

22

3

1 2

0 1000

11

1

6+7 9 9

1100 o

C

1 67

3

6+7

6 1 1 7

1000

10

1200

9

tur e/

1

mp era

3

1

Intemsity/cps

3000

1

Te

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1250 10

20

30

40o

2-Theta/

50

60

70

(b) Figure 5. XRD patterns of mixed ash at different temperatures. (a) JZ + 18%BS;

(b) ZZ + 12% BS.

1 Quartz (SiO2); 2 Hematite (Fe2O3); 3 Anhydrite (CaSO4); 4 Muscovite (KAl3Si3O11); 5 Leucite (KAlSi2O6); 6 Anorthite (CaAl2Si2O8); 7 Albite (NaAlSi3O8); 8 Gehlenite (Ca2Al2SiO7); 9 Spinel (MgAl2O4); 10 Sanidine (KAlSi3O8); 11 Hercynite (FeAl2O4).


Energy & Fuels

100

100

Hercynite

90

Ferro-cordierite

Relative mass /%

60

Anorthite

40 30

Sanidine

20

50

30

0 900

1000

Anorthite

40

Sanidine

10

Mullite 1100

1200

1300

1400

Slag

60

20

Albite

10

Spinel

70

Slag

50

Ferro-cordierite

80

Magnesium-cordierite

70

Magnesium-cordierite

90

Relative mass /%

80

Albite

Mullite

0

1500

900

1000

1100

o

100

80

(a)

(b) 100

Relative mass /%

Anorthite

40

Sanidine

Nepheline

50

Leucite

40 30

1000

Anorthite Sanidine

10

Spinel 1100

1300

1400

900

1500

Albite

Spinel

0 1200

1000

1100

1200

1300

1400

o

o

Temperature/ C

Temperature/ C

(c)

(d)

100

Olivine

90

Clinopyroxene 80 Melilite 70

Relative mass /%

900

Slag

60

20

Albite

0

Clinopyroxene

70

Slag

10

Slag

Nepheline

60 50

Feldapar

40 30

Leucite

20 10

Spinel

0 900

1500

Olivine

80

60

20

1400

Melilite

90

70

30

1300

Corundum

o

Temperature/ C

Leucite

50

1200

Temperature/ C

Nepheline Olivine

90

Relative mass /%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 35

1000

1100

1200

1300

1400

1500

o

Temperature/ C

(e) Figure 6. Phase assemblage–temperature curves for JZ blended ash. (a) JZ+6%BS; (b) JZ+12%BS; (c) JZ+18%BS; (d) JZ+24%BS; (e) JZ+30%BS.


1500

Page 35 of 35

100

100

Orthopyroxene

90

Slag

70

Ferro-cordierite Magnesium-cordierite

60 50

Anorthite

40

Sanidine

30 20

0 900

1000

1100

Anorthite

50 40 30

Sanidine

20

Albite

10

Corundum

Mullite

Hercynite

Slag

60

Magnesia spinel

Albite

10

Olivine

80

Relative mass /%

Relative mass /%

70

Nepheline

Leucite

90

80

Magnesia spinel

0

1200

1300

1400

900

1500

1000

Hercynite 1100

100

80

Temperature/ C

(a)

(b) 100

Relative mass /%

40

Anorthite

30

Sanidine

20

Magnesia spinel

1000

1100

Feldspar

40

Leucite

30

Magnesia spinel

10

Hercynite

0 1200

1300

1400

900

1500

1000

1100

1200

1300

Temperature/ C

(c)

(d)

(f) 100

1400

o

o

Temperature/ C

Olivine

90 80

Melilite

70

Relative mass /%

900

Slag

50

Hercynite

0

Melilite

60

20

Albite

10

Nepheline

70

Leucite

50

Slag

60

Leucite

50 40 30

Nepheline

20

Magnesia spinel

10

Hercynite

0 900

1500

Olivine

80

Slag

60

1400

Clinopyroxene

90

Olivine

70

1300

Temperature/ C

Melilite Clinopyroxene Nepheline

90

1200 o

o

Relative mass /%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1000

1100

1200

1300

1400

1500

o

Temperature/ C

(e) Figure 7. Phase assemblage–temperature curves for ZZ blended ash. (a) ZZ+6%BS; (b) ZZ+12%BS; (c) ZZ+18%BS; (d) ZZ+24%BS; (e) ZZ+30%BS.


1500

Regulation of Ash Fusibility Characteristics for High-Ash-Fusion

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