Understanding Ash Fusion and Viscosity Variation from Coal Blending

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Understanding Ash Fusion and Viscosity Variation from Coal Blending Based on Mineral Interaction Fenghai Li, Meng Li, Hongli Fan, and Yitian Fang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02686 • Publication Date (Web): 06 Dec 2017 Downloaded from http://pubs.acs.org on December 7, 2017

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Energy & Fuels

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Understanding Ash Fusion and Viscosity Variation from Coal Blending

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Based on Mineral Interaction

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Fenghai Lia,b,c,* Meng Lib, Hongli Fana, Yitian Fangc

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a

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b

School of Chemistry and Chemical Engineering, Henan Polytechnic University, Jiaozuo 454003, China

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c

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan,

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030001, China

Department of Chemistry and Chemical Engineering, Heze University, Heze, 274000, China

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ABSTRACT: The ash-fusion and viscosity–temperature characteristics (AFV) of three typical coals

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(high-silica–alumina Changzi coal [CZ], high-calcium Hebi coal [HB], and high-iron Zhaolou coal

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[ZL]) and their mixtures were analyzed, and the AFV variation mechanism by blending was

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investigated. Each of the three coals is unsuitable for entrained-flow gasification. With an increasing

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HB mass ratio, the CZ mixture ash-fusion temperature (AFT) decreased (0–30%) and then increased

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slowly (>30%) and the critical-viscosity temperature (Tcv) decreased (0–40%) and then increased (>

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40%). With an increase in ZL mass ratio, the AFT and Tcv decreased gradually. For CZ mixture

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entrained-flow gasification, the appropriate blending ratios of HB and ZL were 20%–60% and

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60%–100%, respectively. The AFV characteristics were determined from the mineral and

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amorphous-matter content through the interaction and evolution of different minerals. The formation of

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low-melting-point minerals (e.g., anorthite, gehlenite, and hercynite) and their eutectics resulted in

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decreases in AFT and Tcv. Crystal precipitation (gehlenite (Ca2Al2SiO7) and spinel ((Fe,Mg)Al2O4))

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from molten ashes at a certain temperature increased the ash/slag viscosity. The FactSage calculation

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can simulate the AFV variation, and provide a promising tool to predict the AFV of mixed ashes.

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Keywords: Ash-fusion characteristics; Ash-viscosity-temperature characteristics; Variation behavior; Coal blending; Mineral interaction

*

Corresponding author at: Department of Chemistry and Chemical Engineering, Heze University, Heze 274015, China.

E-mail address: [email protected] (F. Li). 1

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1. INTRODUCTION

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Gasification technology has been developing rapidly worldwide because of environmental

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pressures and versatile synthetic products,1 such as liquid fuels (methanol, ethyl ether, gasoline, and

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diesel 2), chemical products or intermediates (ammonia, hydrogen olefin, alkylene oxide, and lipid

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compounds 3), and synthetic natural gas. By implanting the “low-carbon globalization” philosophy into

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economic development, the application of integrated gasification combined with cyclical power plants

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has a promising future.4 Entrained-flow reactor (EFR) gasification has gained great interest in most

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parts of the world because of the following advantages: feedstock diversification, a high carbon

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conversion, and near-zero pollutant emissions. 5 In the EFR gasifier, organic compositions are gasified

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and changed into syngas, whereas inorganic minerals are converted into two parts: some fine mineral

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particles rise up with the syngas, and exit the cyclone separator in the form of fly ashes; others change

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into molten slag, flow along the inner wall of the EFR, and discharge from the slag-drip port (bottom

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ashes). 6, 7 However, during gasification, the EFR is susceptible to ash-related problems (e.g., slag port

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blockage and refractory wall damage). These problems are closely related to ash-fusion and

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viscosity–temperature characteristics (AFV) under operating conditions. At low ash-fusion-temperature

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(AFT, softening temperature, ST < 1150 °C) coal gasification in the EFR, the membrane or refractory

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wall may be damaged because of the absence of slag-layer protection; for high AFT coal (flow

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temperature, FT > 1400 °C), EFR gasification may require shut down because of clogging from slag

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solidification. Unfortunately, the AFV for most coals does not meet the EFR gasification requirement

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(e.g., in China, high-AFT coal accounts for more than 50% of coal reserves; 8 whereas low-AFT coal

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comprises approximately one third). Thus, the regulation of AFV is of great significance for coal EFR

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gasification. 2


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As temperature increases, the pore network in the ashes swells and micro- or large pores and

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low-melting-point eutectics (LME) form gradually. A few LME flow into nearby pores, which causes

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adhesion and the merger of adjacent ash particles. High-density sinter forms, 9 which may cause further

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ash-particle agglomeration into large aggregates.10 The agglomeration slag in fluid-bed gasifiers

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contains extensive calcium aluminosilicate LME.11 Slag formation during Jincheng anthracite

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fluidized-bed gasification is caused mainly by the LME of hercynite and anorthite.2 The co-presence of

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ferrous and calcium minerals could promote slag generation through the LME formation of

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SiO2–A12O3–CaO/FeO.

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oxides may convert into amorphous matter. 14 The X-ray diffraction (XRD) patterns of the slag samples

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(quenched liquid slag from Huainan coal gasification in the Shell gasifier,15 and from Shenfu coal

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gasification in the Texaco gasifier 16) have an obvious amorphous/vitreous character.

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12,13

Under a given condition, LME that is composed of calcium and iron

In the EFR gasifiers, crystal precipitation and its content increases inside liquid slag and leads to an 6, 17

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increase in slag viscosity,

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AVF are closely related to the total silica and alumina content; to the silica/alumina ratio;

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the calcium,

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atmosphere, and residual carbon content.23,24 The distribution of crystallized spinel with an irregular

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shape in the ash (slag) and the network formation results in a sharp increase in ash (slag) viscosity, and

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a linear relationship between crystallization temperature and base/acid ratio has also been explored.18, 25

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Crystal precipitation from high-temperature silicate melts (coal ashes at a high temperature could be

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considered a silicate melt because of its high silica content and similar composition to glass and

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magma26) under certain conditions may be related to the LME decomposition or to the decrease in

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network-former (e.g., silicon and aluminum) content in the melts.18

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iron,4,

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which affects the operating conditions obviously. The characteristics of 18,19

and to

and magnesium contents;22 and they are affected by the cooling rate,

3


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In general, the adjustment of coal AFV is achieved by coal blending, additives, biomass, and other

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industrial wastes (red mud, paper-making black liquid, and sludge).27 In industrial practice, additives

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(e.g., minerals that contain iron or calcium 4, 28–29) are usually used to regulate the AFV of high-AFT

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coals; however, this consumes more energy and oxygen.30 Coal blending provides an efficient and

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economic way to regulate the AFV because of complementary raw materials and product-structure

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optimization.

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ash chemical composition, and pressure.33 Blended coal-ash viscosities are similar at a high

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temperature; however, an obvious divergence exists in the blended-coal viscosity–temperature curve

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patterns below 1450 °C.34 Correlations between the AFV of coal blending and their mineral factor, and

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their corresponding mechanism have been investigated.35 The mineral reaction and melting behaviors,

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and the AFV modification mechanism have been explored through experimental analyses and

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simulation (e.g., FactSage and Gaussian).32, 33

31, 32

The variation in AFV of blending coal is influenced mostly by the blending ratio,

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To date, most studies have focused on the AFV regulation of high-AFT coal by low-AFT coal

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addition. 32-35 Although high-calcium and high-iron coals are abundant in China, 36 minimal regulation

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of the AFV of high-AFT coal through blending with high-calcium or high-iron coals occurs, especially

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for high-calcium coal with a high AFT. Thus, three typical coals (high-calcium coal, high-iron coal,

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and high-silicon–aluminum coal) were selected to conduct coal-blending experiments and to investigate

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their regulating mechanism using X-ray florescence spectrometry, XRD, and FactSage software

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calculations. It is expected that some references will be provided to modify the coal AFV

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characteristics by coal blending.

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2. EXPERIMENTAL SECTION

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2.1. Characteristics of Raw Materials 4


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Three air-dried bituminous coals, Changzhi coal (CZ, from southern Shanxi, China), Zhaolou

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coal (ZL, from western Shandong, China), and Hebi coal (HB, from northern Henan, China) were

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selected. The samples were crushed to < 0.15 mm, dried at 105 °C in nitrogen for 24 h, and stored in a

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cabinet dryer. The proximate and ultimate analyses and their AFTs in a reducing atmosphere (CO2/H2,

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1:1, volume ratio) are shown in Table 1. Based on their AFTs, CZ and HB are considered to be

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high-AFT coals, whereas ZL is a low-AFT coal. Their ash chemical compositions are given in Table 2.

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Based on their ash composition, the CZ is classified as a typical high-silica–aluminum coal (Al2O3 +

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SiO2 > 80.00%, Al2O3: 39.10%; SiO2: 45.63%), HB is a typical high-calcium coal (CaO > 15.00%,

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CaO: 40.17%), and ZL is a typical high-iron coal (Fe2O3 > 15.00%, Fe2O3: 18.47%). In general, the

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base/acid ratio (B/A, B/A = ((Fe2O3 + CaO + MgO + Na2O + K2O)/(SiO2 + Al2O3 + TiO2))) is used to

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highlight differences in ash composition and behavior.37 The B/A value of the three ashes increases as

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CZ (0.13) > ZL (0.42) > HB (1.19), as presented in Table 2.

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Tables 1−2 should be placed here

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2.2 Preparations of Ash Samples

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2.2.1 Preparation of Laboratory Ashes

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To investigate the influence of high-calcium and high-iron coal on the AFV of

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high-silica–aluminum coal, HB and ZL (air-dried basis) were mixed with high-AFT CZ (air-dried basis)

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in mass ratios from 0%−100% in 10% intervals, until the mixtures were uniform. The resulting samples

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were termed H0−10C10−0 and Z0−10C10−0. The mixed coal samples were transferred into a muffle furnace

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and ashed according to a Chinese standard (GB/T1574-2001).

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2.2.2 Preparation of Mixed Ashes at Different Temperatures

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The ash samples were prepared in a modified ALHR-2 AFT analyzer (Aolian Co. Ltd., China).

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First, the ceramic crucible with the ashes (1.00 g) was inserted into the AFT analyzer, and mixed gases

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(H2/CO2, 1:1, volume ratio) were introduced to discharge air and retain a reducing atmosphere. 1,8 The

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AFT analyzer was heated to preset values at 10 °C/min, and maintained at this temperature for 5 min.

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The ash samples in the muffle furnace were transferred rapidly to ice water to prevent phase variation

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and crystal segregation.32 Finally, the quenched samples were placed in a vacuum drying oven at 105

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°C for 24 h, crushed to less than 0.198 mm, and stored in a cabinet dryer before measurements.

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2.3 Analytical Methods

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2.3.1 Analyses of Coal and Ash Characteristics

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Proximate analyses of coal samples were performed on a SDLA 718 proximate analyzer (SUNDY

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Co. Ltd., China), and ultimate analyses were obtained on a PE 2400 analyzer (PerkinElmer, USA). The

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AFT measurements in a reducing atmosphere (H2/CO2, 1:1 volume ratio) were conducted on an

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ALHR-2 AFT analyzer (with a high-temperature limit of 1500 °C) according to a standard test method

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(ASTM D1857). The ash chemical compositions were determined by X-ray fluoresence (XRF-1800,

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Shimadzu, Japan).

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2.3.2 Measurement of Ash-Viscosity–Temperature Characteristics

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The ash sample viscosity was determined using a high-temperature rotating viscometer

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(Rheothonic II, Theta Co., US) that consisted of a programmable rheometer, a high-temperature furnace,

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and a computer. Ash samples (~30 g) were placed into a 66-ml cylindrical corundum crucible (purity, >

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99.9%), and the crucible were fixed at the center of furnace with a pedestal that contained three fluted

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rods made from high-purity corundum.38 After the sample crucible had been set up and the system

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evacuated, a reducing atmosphere (1:1, H2/CO2, volume ratio) was introduced at 100 ml/min to flow 6


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over the ash samples. The ash samples were heated according to a programmed procedure (20 °C/min

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below 900 °C and 5 °C/min to 1650 °C) and kept at this temperature for 15 min to melt the crystalline

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solids.39 Thereafter, the spindle was immersed into the molten ash slowly, and the temperature was

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cooled at 1°C/min at a constant shear rate of 15 rpm until the sample viscosity exceeded the viscosity

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measurement. The viscosity data were recorded in intervals of 0.1 °C by a computer throughout the

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measurement. The sample temperature was tested using a type-B platinum thermocouple in an alumina

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pedestal at the bottom of the crucible, which was calibrated in a previously determined temperature

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calibration experiment with a thermocouple inside the magnesium-oxide-filled crucible. The

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viscometer was calibrated using standard silicone oil at a high temperature, to ensure that its

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measurement deviation was less than 1.0%. 34

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2.3.3 XRD Analyses of Ash Samples

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The XRD patterns of the ash samples were recorded on a D/max-rB X-ray powder diffractometer

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(40 kV, 100 mA, Ka1 = 0.15408 nm, Rigaku Co., Japan) at 5o 2-Theta/min with a step size of 0.01o from

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10−70o. The mineral content was calculated using a normalized reference intensity ratio method (based

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on the pure phase intensity of standard Al2O3), the precision of which was ± 10% for strongly

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diffracting phases and ± 25% for weakly diffracting phases. 14 The proportion of amorphous phase was

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evaluated by XRD using the Rietveld-based SIROQUANT software.

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2. 4 Thermodynamic Equilibrium Calculation

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The mineral compositions and proportions of liquid and solid phases in the reducing atmosphere

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(H2/CO2, 1:1, volume ratio) were predicted using FactSage software (version 7.0) with the data from

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FToxid, FTsalt, and FactPS.

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M2O3 (Corundum), AOlivine, and Cordierite have been used.

33, 40, 41

The solution species ASlag-liq, ASpinel, AMonoxide, Amullite, 42

The main compositions, SiO2, Al2O3,

7


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K2O, CaO, Na2O, MgO, and Fe2O3, were selected for the calculations in the equilibrium module, which

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were carried out from 1000 °C to 1500 °C at 50 °C intervals.

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The liquid temperatures of the mixed ashes in the SiO2–Al2O3–CaO and SiO2–Al2O3–FeO

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systems and their component variations of solid and liquid phase with increasing temperature were

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calculated using the FactSage software. 25 The calculations were carried out based on an ash chemical

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composition from 1000 °C to 2200 °C at 0.1 M Pa in a reducing atmosphere (1:1, H2/CO2, volume

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ratio).

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3. RESULTS AND DISCUSSION

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3.1 AFV Characteristics of Three Coals

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Table 1 shows that the AFT of the three coals decreases from CZ to HB to ZL. CZ has a high

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AFT (its four characteristic temperatures, i.e., deformation temperature [DT], ST, hemispheric

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temperature [HT], and FT, exceed 1500 °C) because of its high silicon and aluminum contents, the

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interactions of which lead to the formation of mullite with a high melting point (MP: 1850 °C). For ZL

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ashes, its high iron content (Fe2O3: 18.74%) in a reducing atmosphere transfers into low-MP

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mineral-containing iron elements (e.g., ferrocordierite and orthopyroxene), and reduces its AFT; HB

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ashes with an obvious high calcium content (CaO: 41.07%) lead to the existence of high-MP simple

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lime (2572 °C), which results in a relatively high AFT.

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The viscosity–temperature characteristics of the samples that were performed on the Rheothonic II

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high-temperature rotating viscometer are presented in Figure 1. The critical viscosity temperatures (Tcv,

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where the ash (slag) fluid that coexists with the crystal melt is transformed from Newtonian flow to

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non-Newtonian flow

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relatively low (~1360°C). When CZ and HB are gasified in the EFR gasifier, to ensure that the slag

39,43

) for CZ and HB are relatively high (~1600 °C), whereas the Tcv of ZL is

8


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taps smoothly, their operating temperatures must be sufficiently high because of their high FT and Tcv

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(in general, higher than its FT of 50−100 oC,

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damaged at a high temperature because of the chemical interaction between the slag and the refractory,

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which leads to a dissolution of the refractory and spalling by the formation of new mineral phases. The

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FT and Tcv of ZL are comparatively low; when gasified at the regularly operating temperature

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(1400−1600 °C) in the EFR gasifier, a protective slag layer may not form, which results in damage to

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the gasifier. In general, to guarantee flow stability during coal EFR gasification, the FT must below

184

1380 °C, the ash/slag viscosity should range from 5 to 10 Pa·s, and its maximum should be < 25 Pa·s

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at the operating temperature.38 Thus, each of the three typical coals is unsuitable for EFR gasification.

186

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and higher than its Tcv 7). The gasifier may become

Figure 1 should be placed here

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3.2 AFV Variation in Mixture by Coal Blending

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3.2.1 AFT Variation

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The variations in mixture AFT with increasing HB or ZL mass ratio are presented in Figure 2.

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With an increase in HB mass ratio, the mixed AFT firstly decreases visibly (0%−30%) and then

191

increases slowly (> 30%), and reaches a minimum at 30% (FT, ~1300 °C). The HB mass-ratio range for

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its FT below 1380°C ranges from 20% to 70%. For the ZL mass-ratio increase, the mixed AFT (e. g.,

193

FT) decreases slowly, and when the mass ratio is ~ 60%, its FT drops below 1380 °C.

194 195

Figure 2 should be placed here 3.2.2 Variation in Mixed-Ash-Viscosity Characteristics

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The variation in CZ mixed-ash-viscosity characteristics with an increasing coal-blending mass

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ratio is presented in Figure 3. When the HB mass ratio increased from 0% to 40%, the viscosity of the

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mixed ashes decreased rapidly. Thereafter, the viscosity increased (40%−100%). The viscosity of the 9


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mixed ashes (20%−80%) in the operating-temperature range of the EFR (1400–1600 °C) ranged from

200

5–25 Pa·s. With an increase in ZL mass ratio, the mixed ash Tcv decreased gradually. When the ZL

201

mass ratio reached 20%, the variation in mixed-ash viscosity–temperature characteristics was small.

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The ZL mass ratio increased from 40% to 100%, and its viscosity ranged from 5 to 25 Pa·s.

203 204

Figure 3 should be placed here 3.2.3 Selection of Coal-Blending Mass Ratio

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In general, in industrial practice, to avoid the occurrence of ash-related problems, the ash FT

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should be less than 1380°C, its viscosity should range from 5 to 25 Pa·s at the operating temperature,

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and its ash content should be ~20.0%.34 Because the ash content of the three coals is close to 20.0%

208

(CZ: 18.15%; ZL: 20.45%; HB: 22.92%), the effects of blending proportion on their ash content is

209

relatively low. Thus, from the perspective of the FT and viscosity–temperature characteristics, an

210

appropriate HB and ZL mass ratio is 20%–60% and 60%–100%, respectively.

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3.3 AFV Variation Mechanism in Mixed CZ Coal with Increasing Coal-Blending Mass Ratio

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3.3.1 Mineral Variation

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For a given mineral, the diffraction intensity variation in the XRD patterns indicates a content

214

change.27 The mineral components of the CZ ashes at different temperatures are shown in Figure 4. The

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CZ ashes at 815 °C were composed mainly of quartz (SiO2), metakaolin (Al2Si2O7), anhydrite (CaSO4),

216

calcite (CaCO3), and hematite (Fe2O3). With an increase in temperature, the contents of calcite and

217

anhydrite decreased because of their decomposition. At 1000 °C, mullite (Al6Si2O13) was generated,

218

and quartz was transformed to tridymite. The interactions of calcium oxide and mullite formed

219

anorthite (CaAl2Si2O8), and the generation of cordierite (Al4(Fe,Mg)2Si5O18) resulted from the

220

interaction of minerals that contain ferrous ions or magnesium and metakaolin. These interactions are 10


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listed as follows.

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calcite (CaCO3) → calcium oxide (CaO) + carbon dioxide (CO2)

(1)

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andydrite (CaSO4) → calcium oxide (CaO) + sulfur dioxide (SO2)

(2)

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kaolinite (Al2Si2O7 ·2H 2O) → metakaolin (Al2Si2O7)

(3)

225

metakaolin (Al2Si2O7) → mullite (Al6Si2O13)

(4)

226

mullite (Al6Si2O13) +calcium oxide (CaO)→Anorthite (CaAl2Si2O8)

(5)

227

metakaolin (Al2Si2O7) + Ferrous oxide (FeO) + magnesium oxide (MgO) →

228

cordierite (Al4(Fe,Mg)2Si5O18)

(6)

229

With an increase in temperature, the contents of quartz, anorthite, and gehlenite decrease,

230

because some basic composition with a low ionic potential (e.g., Ca2+ and Fe2+) is transferred into

231

the amorphous matter.14 At 1200 °C, the minerals were mostly in the form of mullite, which resulted

232

in a high AFT.

233


234

In ash fusion, the mineral components and contents vary with the interaction and evolution of

235

minerals.45 Thus, it is reasonable to assess the AFV characteristics by mineral components and their

236

contents under certain conditions. To explore the AFT different variations of mixed CZ ashes for

237

different blending coals, and the XRD patterns of mixed CZ ashes at 1200 °C (the crystal minerals

238

contents are moderate, which could better reflect the AFT variation 8) were investigated and shown

239

presented in Figure 5. When the HB mass ratio reaches 20%, a decrease in mullite content and the

240

formation of low-MP gehlenite and anorthite lead to a decrease in the AFTs of the CZ mixture. At a HB

241

mass ratio of 40%, low-MP spinel (Fe(Mg)2Al2O4, MP: 1238°C) and akermanite (Ca2MgSi2O7, MP:

242

1450°C) are detected. The LME formation of anorthite and gehlenite (MP: 1170 °C or 1265 °C) results 11


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in a decrease in the mixture AFT. However, when the HB mass ratio reaches 60%, high-MP simple lime

244

(2572°C) appears. The lime content increases with an increasing HB mass ratio (80%), which leads to a

245

corresponding increase in AFT. For ZL, the generation of low-MP ferrous minerals (such as

246

ferrocordierite [Al4Fe2Si5O8], magnesium cordierite [Al4Mg2Si5O18], and orthopyroxene [(Fe,

247

Mg)2Si2O6]), and the increase in amorphous-matter content results in a decrease in their mixed AFT

248

with an increase in ZL mass ratio.

249 250


3.3.2 Ash Composition of Mixed Ashes

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Coal ash at a high temperature can be considered to be a molten silicate network because of the

252

abundant silica content in the ash.46 Thus, coal ash at a certain temperature is supposed to be a

253

homogeneous system that is composed of various networks that contain different amounts of silica. The

254

AFV characteristics of coal ashes are closely related to the tightness of the main network.

255

compositions, the trace elements (e.g., K2O and Na2O) may exert a certain influence on the ash fusion

256

behavior and slag viscosity. However, considering gasification environment, the ternary systems of

257

FeO-SiO2-Al2O3 and CaO-SiO2-Al2O3,

258

accounting for more than 85%, these four components are selected to predict the ash characteristics.

259

The normalized composition of the four main compositions of the CZ mixed ashes based on Table 2 are

260

presented in Table 3 (elemental iron exists as FeO in the coal gasifier). For mixed ashes of CZ and HB,

261

because the normalized content of FeO is less than 10%, their main network consists mostly of silica,

262

calcium oxide, and alumina. Table 4 shows the mole mass ratio of the three elements of mixed ashes.

263

The elemental calcium mole ratio increases and the mole ratios of silicon and aluminum decrease with

264

an increase in HB mass ratio. The mole ratios of calcium, silicon, and aluminum in mullite, anorthite,

12

37

In ash

and the total contents of SiO2, Al2O3, CaO, and Fe2O3

12


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Energy & Fuels

265

and gehlenite are also presented in Table 4. The mass ratio of the three elements in the CZ ashes is

266

1:6.33:6.42, which results in its mineral content being mostly mullite and quartz. When the HB mass

267

ratio reaches 20%, the mole ratio of the three elements results in a large amount of anorthite formation,

268

which causes a further rapid increase in ash viscosity.

269

based on their elemental mole ratio, which makes the AFT and Tcv increase rapidly (HB mass ratio of

270

40%).21 When HB increases from 20% to 60%, which is conducive to the LME formation of anorthite

271

and gehlenite,

272

AFV characteristic variation of CZ mixed ashes with an increase in HB mass ratio. For ZL, the

273

elemental iron increases with an increase in ZL mass ratio. In a reducing atmosphere, the low-MP

274

ferrous mineral formation (especially for hercynite) results in a decrease in AFT and a sharp increase in

275

Tcv. 4, 25

276 277

47

6

Gehlenite and lime are predisposed to form

their ash viscosity increases slowly from 1400 °C to 1600 °C. This may explain the

Tables 3–4 should be placed here 3.4 Thermodynamic Calculations of Coal-Blending Mixed Ashes

278

Although some deviations exist between the experimental results and the thermodynamic

279

equilibrium module, the ash composition position on the ternary phase reflects the approximate AFV

280

characteristics.48 The iron content and its variation is low in the mixed ashes of CZ and HB, and that for

281

the mixed ash of CZ and ZL is calcium (Table 3). Thus, the ternary phase diagram SiO2–Al2O3–CaO or

282

SiO2–Al2O3–FeO was selected for the two mixed ashes respectively, and their position variation is

283

presented in Figure 6. The same colored lines in the diagram show the compositions at a certain

284

liquidus temperature. Lines 1–5 in the ternary phase diagrams (Figure 6) show the range of blended ash

285

compositions of CZ. The CZ ash composition lies in the mullite region (MP > 1600°C) of the

286

SiO2–Al2O3–CaO and SiO2–Al2O3–FeO ternary phase diagram, which indicates that CZ has a high AFT. 13


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 14 of 34

287

With an increase in HB mass ratio, the mixed-ash-composition position changes along lines 1–5 from

288

the mullite to the anorthite region (MP: 1550 °C) to gehlenite (MP: 1593 °C) in the SiO2–Al2O3–CaO

289

system, and the liquidus temperature decreases initially and then increases (Figure 6 a). This behavior

290

may explain the AFV variation of the mixed ash of CZ and HB. Although mixed ashes also existed in

291

the mullite region with an increasing ZL mass ratio, their liquidus temperature decreased obviously

292

(Figure 6 b). This result is consistent with the AFV variation trend of the mixed ash of CZ and ZL.

293


294

To explore the AFV variation mechanism of the mixed ashes further, FactSage was used to predict

295

the liquidus temperature of the mineral phases, the solid proportion, and the multi-phase equilibrium at

296

different temperatures in a reducing atmosphere (H2/CO2, 1:1 volume ratio) at 0.1 MPa. Although coal

297

industrial gasification usually occurs at a high pressure (sometimes 20–40 bar), Factsage calculations at

298

0.1 MPa are usually used to explain the mineral-transformation behaviors.

299

mineral compositions of CZ ashes at different temperatures. The liquid phase appears at 1150°C, and

300

the minerals exist mostly as mullite, anorthite, cordierite, and tridymite below 1150 °C. The cordierite

301

and tridymite disappear at ~1300 °C, anorhite disappears at 1400 °C, and even at 1500 °C, the mullite

302

mass ratio accounts for ~30%, which causes its high AFT and high viscosity at a high temperature.

303

49,50

Figure 7 shows the


304

Figure 8 shows the mineral compositions of CZ mixed ashes at different temperatures. The

305

mineral compositions in the same CZ mixed ashes at 1200 °C from FactSage calculations are similar to

306

the XRD results (Figure 5). Small minor differences may result from the calculation that is based on an

307

ideal chemical equilibrium. An increasing HB mass ratio causes a rapid decrease in mullite and then

308

mullite cannot be detected (40% HB). The mineral with free calcium oxide converts to a mineral with a 14


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low calcium-oxide content (e.g., orthopyroxene [(Fe,Mg)2Si2O6] → clinopyroxene [Ca(Mg,Fe) Si2O6];

310

mullite → anorthite → gehlenite), and the akermanite content increases, which results from its high

311

calcium content in the HB ashes (CaO: 41.07%). With an increase in HB mass ratio, the temperature

312

point of the full liquid phase decreases initially and then increases (> 1500°C [20% HB], 1440°C [40%

313

HB], 1400°C [60% HB], 1475°C [80% HB]) (Figure 8 a). These results explain the trend in AFV

314

variation of the mixed ashes with an increase in HB mass ratio.

315

The mineral compositions of CZ-mixed ashes change visibly with an increase in ZL ash mass ratio

316

(Figure 8 b). Ferrocordierite and magnesium cordierite form for a ZL mass ratio of 20%, and when ZL

317

reaches 60%, orthopyroxene emerges because of the high iron content in the ZL ash (Fe2O3: 18.47%).

318

The content of the high-MP mullite decreases gradually with an increasing ZL mass ratio. Moreover,

319

the liquid-slag content of the mixed CZ ashes at 1450 °C increases with an increasing mass ratio of ZL

320

(80% [20% ZL], 85% [40% ZL], 92% [60% ZL], 100% [80% ZL]). These results indicate why the AFT

321

or Tcv decreases with an increase in ZL mass ratio.

322


323

This discussion indicates consistency between the AFV variation trend and the FactSage

324

calculation results. However, the correlation between ash viscosity and mineral composition that is

325

precipitated from high-temperature ash melt during cooling, and the effects of the equilibrium state on

326

the ash viscosity require further investigation.

327

4. CONCLUSION

328

These research findings are summarized as follows. (1) Each of the three typical coals

329

(high-silica–alumina CZ, high-calcium HB, and high-iron ZL) is unsuitable for EFR gasification. (2)

330

To satisfy the EFR gasification of CZ, an appropriate blending ratio for HB and ZL is 20%−60% and 15


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

331

60%−100%, respectively, from the perspective of the AFV characteristics. (3) The formation of a

332

low-MP mineral and their eutectics results in a decrease in AFT and Tcv. Crystal precipitation

333

(gehlenite [Ca2Al2SiO7] and spinel [(Fe,Mg)Al2O4]) from liquid slag at a certain temperature leads to

334

an increase in the ash/slag viscosity. (4) In comparison, although some deviations exist between

335

Factsage calculations and real mineral transformations, the results are consistent with the AFV

336

variation, and the model provides an effective tool to predict the AFV of the mixed ashes.

337

ACKNOWLEDGMENTS

338

This work was financially supported by the Natural Science Foundation of Shandong Province,

339

China (ZR2014BM014) and Youth Natural Science Foundation of Shanxi Province, China

340

(Y5SJ1A1121), and we are thankful to all workers in the Institute of Energy Chemical Engineering,

341

Heze University.

342

REFERENCES

343

(1)Ma, X.; Li, F.; Ma, M.; Fang Y. Investigation on blended ash fusibility characteristics of biomass and coal with high

344

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

345

(2) Li, F.; Li, Z.; Huang, J.; Fang, Y. Understanding mineral behaviors during anthracite fluidized-bed gasification based

346

on slag characteristics. Appl. Energ. 2014, 131,279–287.

347

(3)Guo, Q.; Zhou, Z.; Wang, F.; Yu, G. Slag properties of blending coal in an industrial OMB coal water slurry

348

entrained-flow gasifier. Energ. Convers. Man. 2014, 86, 683–688.

349

(4)Li, H.; Xiong, J.; Tang, Y.; Cao, X. Mineralogy study of the effect of iron-bearing minerals on coal ash slagging

350

during a high-temperature reducing atmosphere. Energy Fuels 2015, 29, 6948−6955.

351

(5)Schulze, S.; Richter, A.; Vascellari, M.; Gupta, A.; Meyer, B.; Nikrityuk, P. A. Novel intrinsic-based submodel for

352

char particle gasification in entrained-flow gasifiers: Model development, validation and illustration. Appl. Energ. 2016,

353

164, 805−814.

354

(6)Chen, L.; Yong, S. Z.; Ghoniem A. F. Modeling the slag behavior in three dimensional CFD simulation of a

355

vertically-oriented oxy-coal combustor. Fuel Process. Technol. 2013,112, 106−117. 16


Page 16 of 34

Page 17 of 34 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

356

(7) Xuan, W.; Zhang, J.; Xia, D. Crystallization characteristics of a coal slag and influence of crystals on the sharp

357

increase of viscosity. Fuel 2016, 176,102−109.

358

(8)Li, F. ; Fang, Y. Ash fusion characteristics of a high aluminum coal and its modification. Energy Fuels, 2016, 30,

359

2925−2931.

360

(9) Nowok, J. W.; Hurley, J.P.; Benson, S.A. The role of physical factors in mass transport during sintering of coal ashes

361

and deposit deformation near the temperature of glass transformation. Fuel Process. Technol. 1998, 56,89−101.

362

(10)Yan, T.; Kong, L.; Bai, J.; Bai, Z.; Li , W. Thermomechanical analysis of coal ash fusion behavior. Chem. Eng.

363

Sci. 2016, 147,74−82.

364

(11) Al-Otoom, A. Y.; Elliott, L. K.; Moghtaderi, B.; Wall, T. F. The sintering temperature of ash, agglomeration and

365

defluidization in a bench scale PFBC. Fuel 2005, 84,109−114.

366

(12) Wu, X.; Zhang, Z.; Piao, G.; He, X.; Chen, Y.; Kobayashi, N.; Itaya, Y. Behavior of mineral matters in Chinese coal

367

ash melting during char-CO2/H2O gasification reaction. Energy Fuels 2009, 23, 2420−2428.

368

(13)Cheng, X.;Wang, Y.; Lin, X.; Bi, J.; Zhang, R. ; Bai, L. Effects of SiO2 -Al2O3-CaO/FeO low-temperature eutectics

369

on slagging characteristics of coal ash. Energy Fuels 2017,31, 6748−6757.

370

(14) Li, F.; Fan, H.; Fang, Y. Exploration of slagging behaviors during multistage conversion fluidized-bed (MFB)

371

gasification of low-rank coals. Energy Fuels 2015, 29,7816−7824.

372

(15) Song, W.; Tang, L.; Zhu, X.; Wu, Y.; Rong, Y.; Zhu, Z.; Koyama, S. Fusibility and flow properties of coal ash and

373

slag. Fuel 2009, 88, 297–304.

374

(16) Song, W.; Tang, L.; Zhu, X.; Wu, Y.; Zhu, Z.; Koyama, S. Flow properties and rheology of slag from coal

375

gasification. Fuel 2010, 89, 1709–1715.

376

(17) Seebold, S.; Wu, G.; Müller, M. The influence of crystallization on the flow of coal ash-slags. Fuel 2017, 187,

377

376–387.

378

(18)Xuan, W.; Whitty, K. J.; Guan, Q.; Ba, D.; Zhan, Z.; Zhang, J. Influence of SiO2/Al2O3 on crystallization

379

characteristics of synthetic coal slags. Fuel 2015, 144,103–110.

380

(19)Xuan, W.;

381

characteristics of synthetic coal slags. Fuel 2017, 189, 39–45.

382

(20)Kong, L.; Bai, J.; Li, W.; Li, Z., Bai, Z.; Guo, Z.; Li, H. The internal and external factor on coal ash slag viscosity at

383

high temperatures, Part 3: effects of CaO on the pattern of viscosity-temperatures curves of slag. Fuel 2016, 179, 10–16.

Wang, Q.; Zhang, J.; Xia, D. Influence of silica and alumina (SiO2 + Al2O3) on crystallization

17


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

384

(21)Hu, X.; Guo, Q.; Liu, X.; Gong Y.; Yu, G. Ash fusion and viscosity behavior of coal ash with high content of Fe and

385

Ca. J. Fuel Chem. Technol. 2016, 44(7), 769−776.

386

(22)Bai, J.; Kong, L.; Li, H.; Guo, Z. Bai Z.; Yuchi W.; Li, W. Adjustment in high temperature flow property of ash from

387

Shanxi typical anthracite.J. Fuel Chem. Technol. 2013, 44(7), 805−813.

388

(23) Kong, L.; Bai, J.; Li, W.; Li, X.; Bai, Z.; Guo, Z.; Li, H. The internal and external factor on coal ash slag viscosity at

389

high temperatures, Part 1: Effect of cooling rate on slag viscosity, measured continuously. Fuel 2015, 158, 968−975.

390

(24) Kong, L.; Bai, J.; Li, W.; Li, X.; Bai, Z.; Guo, Z.; Li, H. The internal and external factor on coal ash slag viscosity at

391

high temperatures, Part 2: Effect of residual carbon on slag viscosity. Fuel 2015, 158, 976−982.

392

(25)Wei, Y.; Li, H.; Yamada, N.; Sato, A.; Ninomiya, Y.; Honma, K.; Tanosaki, T. A microscopic study of the

393

precipitation of metallic iron in slag from iron-rich coal during high temperature gasification. Fuel 2013, 103:101–110.

394

(26)Hsieh, P.; Kwong, K-S.; Bennett, J. Correlation between the critical viscosity and ash fusion temperatures of coal

395

gasifier ashes. Fuel Process. Technol. 2016,1 42,13−26.

396

(27) Xiao, H.; Li, F.; Liu, Q.; Ji, S.; Fan, H.; Xu, M.; Guo, Q.; Ma, M.; Ma, X. Modification of ash fusion behavior of

397

coal with high ash fusion temperature by red mud addition. Fuel 2017,192,121−127.

398

(28)Kong, L.; Bai, J.; Bai, Z.; Guo, Z.; Li, W. Effects of CaCO3 on slag flow properties at high temperatures. Fuel

399

2013,109,76−85.

400

(29) He C, Bai J, Kong L, Guhl S, Schwitalla DH, Xu J, Bai Z, Li W. The precipitation of metallic iron from coal ash

401

slag in the entrained flow coal gasifier: By thermodynamic calculation. Fuel Process. Technol. 2017, 162, 98−104.

402

(30) Wang, Z.; Bai, J.; Kong, L.; Wen, X.; Li, X.; Bai, Z.; Li, W.; Shi, Y. Viscosity of coal ash slag containing vanadium

403

and nickel. Fuel Process. Technol. 2015, 136, 25−33.

404

(31)Bryant, G. W.; Browning, G. J.; Emanuel, H.; Gupta, S. K.; Gupta, R. P.; Lucas, J. A.; Wall, T. F. The fusibility of

405

blend coal ash. Energy Fuels 2000, 14, 316−325.

406

(32) Li, F.; Fan, H.; Fang, Y. Investigation on the regulation mechanism of ash fusion characteristics in coal blending.

407

Energy Fuels 2017, 31,379−386.

408

(33)Li, F.; Ma, X.; Xu, M.; Fang, Y. Regulation of ash-fusion behaviors for high ash-fusion-temperature coal by coal

409

blending. Fuel Process. Technol. 2017,166,131–139.

410

(34)Wang, D.; Liang, Q.; Gong, X.; Liu, H.; Liu, X. Influence of coal blending on ash fusion property and viscosity.

411

Fuel, 2017,189,15–22.

18


Page 18 of 34

Page 19 of 34 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

412

(35)Cao, X., Zhang, B.; Zhao, Q.; Study on mineral factor of ternary-component blended coal on coal ash fusibility and

413

its fusion mechanism. J. China Coal Soc. 2013, 38, 341–319.

414

(36)Zhou, Z.; Li D.; Liu, X.; Yu G. Characteristic of cohesiveness-temperature of coal molten ash and its adaptability to

415

entrained flow gasifier. CIESC J, 2012, 63, 3243–3254.

416

(37)Vargas, S.; Frandsen F. J.; Dam-johansen, K. Rheological properties of high-temperature melts of coal ashes and

417

other silicates. Prog.

418

(38)Liu, X.; Yu, G.; Xu, J.; Liang, Q.; Liu, H. Viscosity fluctuation behaviors of coal ash slags with high content of

419

calcium and low content of silicon. Fuel Process. Technol. 2017,158, 115–122.

420

(39)Schwitalla, H. D.; Bronsch M. A.; Klinger M.; Guhl, S.; Meyer B. Analysis of solid phase formation and its impact

421

on slag rheology. Fuel, 2017, 203, 932−941.

422

(40)Reinmöller, M.; Klinger, M.; Schreiner, M.; Gutte, H. Relationship between ash fusion temperatures of ashes from

423

hard coal, brown coal, and biomass and mineral phases under different atmospheres: A combined FactSage™

424

computational and network theoretical approach. Fuel 2015, 151,118–123.

425

(41) Carlsson, P.; Ma, C.; Molinder, R.; Weiland, F.; Wiinikka, H.; Öhman, M.; Öhrman, O. Slag formation during

426

oxygen-blown entrained-flow gasification of stem wood. Energy Fuels 2014, 28, 6941–6952.

427

(42)Bale, C.W.; Bélisle, E.; Chartrand, P.; Decterov, S. A.; Eriksson, G.; Gheribi, A. E.; Hack, K.; Jung, I.-H.; Kang,

428

Y.-B.; Melançn, J.; Pelton, A. D.; Petersen, S.; Robelin, C.; Sangster, J.; Spencer, P.; VanEnde M-A. FactSage

429

thermochemical software and databases, 2010–2016. Calphad, 2016, 54, 35−53.

430

(43)Yuan, H.; Liang, Q.; Gong, X. Crystallization of coal ash slags at higher temperatures and effects on the viscosity.

431

Energy Fuels 2012; 26, 3717−3722.

432

(44) Liu, H.; Xu, M.; Zhang, Q.; Zhao, H.; Li, W. Effective utilization of water hyacinth resource by co-gasification with

433

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

434

16436−16443.

435

(45) Qi, X.; Song, G.; Song, W.; Yang, S.; Lu, Q. Effects of wall temperature on slagging and ash deposition of

436

Zhundong coal during circulating fluidized bed gasification. Appl. Therm. Eng. 2016, 106, 1127−1235.

437

(46) Ren, X.; Zhang, W.; Ouyang, S. Effect of multiple foreign ions doping on metastable structure of alite. J. Chin.

438

Ceram. Soc. 2012, 40, 664–670.

439

(47) Ptácek, P.; Opravil, T.; Soukal, F. S.; Havlica, J.; Sinský, R. H. Kinetics and mechanism of formation of gehlenite,

440

Al-Si spinel and anorthite from the mixture of kaolinite and calcite. Solid State Sci. 2013, 26, 53–58.

Energ.Combust. 2001, 27, 237−429.

19


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

441

(48) Yan, T.; Bai, J.; Kong, L.; Bai, Z.; Li, W.; Xu, J. Effect of SiO2/Al2O3 on fusion behavior of coal ash at high

442

temperature. Fuel 2017, 193, 275–283.

443

(49) Chakravarty, S.; Mohanty A.; Banerjee, A.; Tripathy, R.; Mandal, G. K.; Basriya R. M.; Sharma, M. Composition,

444

mineral matter characteristics and ash fusion behavior of some Indian coals. Fuel 2015, 150, 96–101.

445

(50) Xu, J.; Yu, G.; Liu, X.; Zhao, F.; Chen, X.; Wang, F. Investigation on the high-temperature flow behavior of biomass

446

and coal blended ash. Bioresource Technol. 2016, 166, 494–499.

20


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Energy & Fuels

Table caption Table 1: Coal Characteristics and Its Ash Fusion Analysis. Table 2: Ash Compositions of Coal Samples and their B/A Values. Table 3: Normalized Composition of Four Main Composition of CZ Mixed Ashes(wt./%). Table 4: Mole Ratio of Three Elements in the Mixed Ashes and 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

Page 22 of 34

Table 1 Coal Characteristics and Ash Analyses coal

CZ

HB

ZL

moisture

7.49

9.54

6.29

volatile matter

13.16

20.38

21.61

ash

18.15

22.92

20.45

fixed carbon

61.20

47.16

51.65

carbon

88.92

73.93

85.75

hydrogen

2.75

4.59

5.34

nitrogen

1.24

3.22

1.62

sulfur

1.08

2.75

0.40

oxygen

5.91

15.51

6.89

DTa

>1500

1411

1160

ST

>1500

1426

1220

HT

>1500

1437

1235

FT

>1500

1442

1256

proximate analyses on air dried basis (wt.%)

Ultimate analyses on dried basis (wt.%)

ash fusion temperature/oC

a:

DT: deformation temperature; ST: soften temperature; HT: hemisphere temperature; FT: flow

temperature.


Page 23 of 34 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 2 Ash Compositions of Coal Samples and their B/A Values. Samples

B/A

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

K2O

Na2O

TiO2

P2O5

CZ

0.13

45.63

39.10

3.26

6.88

0.86

0.80

0.26

0.19

2.55

0.47

HB

1.19

24.37

19.10

6.31

41.07

3.87

2.37

0.01

0.66

0.22

0.02

ZL

0.42

45.23

22.38

18.47

5.55

2.07

2.59

1.26

1.03

0.57

0.85


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 34

Table 3 Normalized Composition of Four Main Composition of CZ Mixed Ashes(wt./%) Samples

SiO2

Al2O3

FeO

CaO

H2C8

44.65

36.79

3.76

14.80

H4C6

40.01

33.51

4.33

22.15

H6C4

36.46

29.15

4.93

29.46

H8C2

31.98

25.29

5.44

37.29

Z2C8

47.54

36.21

9.31

6.94

Z4C6

47.95

34.19

11.17

6.69

Z6C4

48.81

31.26

13.39

6.54

Z8C2

49.57

28.15

15.92

6.36


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Energy & Fuels

Table 4 Mole Ratio of Three Elements in the Mixed Ashes and Minerals

Mole ratio Ca:Al:Si

CZ

H2C8

H4C6

H6C4

H8C2

0.12:0.76:0.77

0.26:0.72:0.75

0.40:0.66:0.67

0.53:0.57:0.61

0.67:0.50:0.53

(1:6.33:6.42)

(1: 2.77: 2.88)

(1:1.65:1.68)

(1:1.08: 1.15)

(1: 0.75: 0.79)

Mineral

Mullite

Anorthite

Gehlenite

Lime

Ca:Al:Si

0:3:1

1:2:2

2:2:1

1:0:0


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 Caption Figure 1.Ash viscosity-temperature characteristics of three raw coals Figure 2.AFT variation of mixed CZ with the increasing mass ratio of blending coal Figure 3.Viscosity-temperature curve of the CZ mixed ashes with increasing coal blending mass ratio Figure 4. XRD patterns of CZ ashes at different temperatures Figure 5. XRD patterns of CZ mixed ashes with increasing mass ratio blending coal at 1200 oC Figure 6. Position variations in CZ and its mixed ashes on ternary phase diagram Figure 7. Mineral compositions of CZ ashes at different temperatures by FactSage calculation. Figure 8. Mineral compositions of CZ mixed ashes at different temperatures by FactSage calculation.


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Page 27 of 34 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

25Pa·s

5Pa·s

Figure 1. Viscosity-temperature characteristics of three raw coal ashes


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

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1380/oC

(a)

1380/oC

(b) Figure 2. AFT variation of mixed CZ with the increasing mass ratio of blending coal : (a)HB; (b)ZL


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(a) 80 70 60

Viscosity/Pa.s

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

50 40 30

CZ Z2C8 Z4C6

Z6C4 Z8C2 ZL

20 10 0 1300

1350

1400

1450

1500

Temperature/

1550

1600

1650

o

(b) Figure 3. Viscosity-temperature curve of the CZ mixed ashes with increasing blending coal mass ratio. (a)HB; (b)ZL


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 4. XRD patterns of CZ ashes at different temperatures. 1 quartz(SiO2); 2 anhydrite(CaSO4); 3 hematite(Fe2O3); 4 calcite(CaCO3); 5 metakaolin (Al2Si2O7); 6 Mullite (Al6Si2O13); 7 anorthite (CaAl2Si2O8); 8 cordierite(Al4(Fe,Mg)2Si5O18); 9 tridymite (SiO2)


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Energy & Fuels

(a)

(b) Figure 5. XRD patterns of CZ mixed ashes with increasing mass ratio blending coal at 1200 oC: (a)HB; (b)ZL. 1 mullite(Al6Si2O13); 2 tridymite(SiO2); 3 codtierite (Al4(Fe,Mg)2Si5O18); 4 anorthite (CaAl2Si2O8); 5 gehlenite (Ca2Al2SiO7); 6 spinel((Fe,Mg)Al2O4); 7 ferrogehlenite (Ca2FeSi2O7); 8 akermanite (Ca2MgSi2O7); 9 lime (CaO); 10 ferrocordierite (Al4Fe2Si5O8); 11 magnesium cordierite (Al4Mg2Si5O18); 12 orthopyroxene ((Fe, Mg)2Si2O6)


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

(a)

(b) Figure 6. Position variations in CZ and its mixed ashes on ternary phase diagram: (a)HB; (b)CZ


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100 90 80

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

70

Tridymite Cordierite

Slag

60 50 40

Anorthite

30 20

Mullite

10 0 1000

1100

1200

1300

1400

1500

o

Temperature/ C

Figure 7. Mineral compositions of CZ ashes at different temperatures by FactSage calculation


Energy & Fuels

100

100

Orthopyroxene

90

Spinel

Slag

60

70

Relative mass/ %

Relative mass/%

70

Magnesium cordierite

80

Mullite

50

Anorthite

40

Tridymite

90

Cordierite

80

30

Ferrocordierite

60

Slag

50 40 30

Anorthite

20

20

Mullite

10

10 0 1000

1100

1200

1300

1400

0 1000

1500

1100

1200

70

Ferrogehlenite Slag

50 40

Anorthite

30

10 1200

1300

1400

Anorthite Mullite

0 1000

1500

o

Temperature/ C

1100

+40%ZL 100

Spinel

90

Slag

Akermanite

Gehlenite

50

Slag Ferrocordierite

40 30

Anorthite

10

Ferrogehlenite 1100

1200

1300

1400

0 1000

1500

1100

Spinel

Anorthite

80

Slag

50 40

Gehlenite

30

0 1000

o

1400

1500

Orthopyroxene

80 70

Tridymite


60

Slag

50 40

Ferrocordierite

30 20

20 10

90

Akermanite

60

1300

100

Relative mass/ %

70

1200

+60%ZL

B C D E F

+60%HB

100

Mullite

Temperature/ C

o

Temperature/ C

90


60

20

20

0 1000

Tridymite

70

Relative mass/ %

Relative mass/ %

Anorthite

40

10

Orthopyroxene

80

60

30

1300 o

80

50

1200

Temperature/ C

+40%HB

70

Slag

40

20

1100

Ferrocordierite

50

10

90

1500

60

20

100

1400

70

60

0 1000


80

Gehlenite

30

Tridymite

90

Relative mass/ %

Relative mass/ %

80

1500

+20%ZL 100

Clinopyroxene

Spinel Akermanite

90

1400

Temperature/ C

+20%HB 100

1300 o

o

Temperature/ C

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

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Ferrogehlenite 1100

10

1200

1300

1400

1500

Anorthite

0 1000

Mullite 1100

1200

1300

1400

1500

o

Temperature/ C

o

Temperature/ C

+80%HB

+80%ZL

(a)

(b)

Figure 8. Mineral compositions of CZ mixed ashes at different temperatures by FactSage calculation: (a)HB; (b)ZL


Understanding Ash Fusion and Viscosity Variation from Coal Blending

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