ISIJ International, Vol. 59 (2019),ISIJ International, No. 8 Vol. 59 (2019), No. 8, pp. 1404–1412 Effects of Hydrocarbon Addition on Increase in Dilatation of Coal Hideyuki HAYASHIZAKI,1,2)* Koji KANEHASHI,1) Kazuya UEBO,1) Seiji NOMURA,1) Yasuhiro SAITO,3) Yohsuke MATSUSHITA2) and Hideyuki AOKI2) 1) Research & Development, Nippon Steel & Sumitomo Metal Corp., 20-1 Shintomi Futtsu, Chiba, 293-8511 Japan. 2) Department of Chemical Engineering, Graduate School of Engineering, Tohoku University, 6-6-07, Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8579 Japan. 3) Department of Applied Chemistry, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu, Fukuoka, 804- 3301 Japan. (Received on January 16, 2019; accepted on June 17, 2019) The addition of coal tar pitch mainly composed of polycyclic aromatic hydrocarbons (PAHs), increases the dilatation of coal. We investigated the effect of PAHs on the maximum dilatation (MD) of hard coking coals and semi-soft coking coals. Twenty-six kinds of PAHs and aliphatic hydrocarbon were used as addi- tive agents. The use of a PAH with a molecular weight in the range 152.19–178.23 as an additive agent almost unchanged the MD. When a PAH with a molecular weight in the range 178.23–378.47 was added to the coal, the MD of the coal increased. The increase in MD achieved with the addition of 9,10-dihydrophen- anthrene was larger than that obtained with the addition of phenanthrene. This is likely because the hydrogen atoms in the ninth and tenth positions in 9,10-dihydrophenanthrene inhibit the polymerization of the coal structure. The MD was hardly affected by the addition of a linear aliphatic hydrocarbon (C28H58) but MD decreased due to the addition of anthraquinone with carbonyl carbon. When a PAH with non- planar structure was added to the coal, the increase in MD was smaller than when a PAH with planar structure was added. KEY WORDS: coal; metallurgical coke; dilatation; coal tar pitch; polycyclic aromatic hydrocarbon. coke than by the physical properties of the coke matrix. In 1. Introduction another previous study, the elastic moduli of the coke matrix High-strength coke is required to perform blast furnace before and after solution loss reaction were measured, and operations with high productivity and low reducing agent the stress analysis of a coke model generated by image- ratios because coke sustains the permeability of gas and based modeling of the optical microscopic images of coke liquid. Although hard coking coal can produce high-strength was performed.4,5) The researchers suggested that changes in coke, its price increases and its reserves decrease. Thus, we pores have a stronger effect on the stress distribution than need to develop a technique to produce high-strength coke do variations in the elastic modulus of the coke matrix due from a large quantity of semi-soft coking coal (i.e., low- to the solution loss reaction.4,5) quality coal). Cracks and pores are defects in coke and affect the coke Coke is a porous material, and its strength is affected strength.1) In particular, micro-cracks of the order of mil- by two factors, namely, the physical properties of the coke limeters were thought to influence coke strength and be matrix and its defects.1) With regard to the physical proper- caused by the difference between contraction coefficients ties of the coke matrix, previous researchers have measured of inertinite and vitrinite in the coke matrix.6) Kubota et al. the elastic modulus of the coke matrix using the nano- indicated that coke strength decreased with an increase of indentation method by eliminating the effects of defects.2,3) the size of inertinite blended.6) When a packed bed of coal They indicated that coke produced from hard coking coal particles was heated in a coke oven, pores were formed was not very different than that produced from semi-soft between the coal particles during the softening and dilata- coking coal in terms of the elastic modulus of the active tion of coal. After the coal particles were charged into the component of the coke matrix.2,3) In general, the strength of oven, the coke layer was immediately formed around the coke obtained from hard coking coal is higher than that pro- packed bed and inhibited the dilatation of the entire packed duced from semi-soft coking coal. Thus, the coke strength bed. Arima and Sakurai revealed that heated coal particles would be more affected by the defects generated in the dilated, filled voids between particles, and adhered to each other.7) When the dilatation of coal was sufficiently high, the * Corresponding author: E-mail: [email protected]. coal particles completely filled the voids between particles com and adhered to each other on all the surfaces. On the other DOI: https://doi.org/10.2355/isijinternational.ISIJINT-2019-033 hand, when the dilatation was low, the voids were not filled, © 2019 ISIJ 1404 ISIJ International, Vol. 59 (2019), No. 8 resulting in adhesion failure (i.e., non-adhesion grain bound- Table 1. The properties of the coals used as samples. 8) aries ) in the coal packed bed. At this time, the dilatation Proximate analysis Petrographic Dilatometry behavior of the coal particles was not constrained by heating (wt% d. b.) analysis wall, and the coal particles freely dilated. Subsequently, the Coal Total Maximum Maximum Volatile Reflactance thin film around the particles burst and led to the formation Ash inerts Contraction Dilatation Matter (%) of connected pores.8) Thus, adhesion failure and connected (%) (%) (%) pores can function as defects and decrease the strength of Coal A 9.1 24.0 32.0 1.22 25 107 coke. Based on the above research, the dilatation of coal is Coal B 9.9 20.1 32.1 1.59 24 −4 thought to be an important factor affecting the strength of coke, and therefore, it is needed to develop a technique to Coal C 9.6 36.5 17.6 0.73 27 −2 increase the dilatation of coal. It is known that the caking properties of coal, such as dilatation and fluidity, are increased by the addition of lar weights in the range 152.19–394.77 g/mol were used, coal tar pitch,9,10) asphalt pitch (ASP),10–12) solvent refined the these included carbazole, acridine, 7,8-benzoquinoline, coal (SRC)13,14) produced by thermally reacting coal with anthraquinone and octacosane. Carbazole, acridine and hydrogen solvent, hyper-coal,15) and extracts from coal.16–18) 7,8-benzoquinoline were used as aromatic hydrocarbons Among these additives, coal tar pitch is used as an industrial containing nitrogen, anthraquinone as an aromatic hydro- binder for briquetting19) and is known to consist of vari- carbons containing oxygen, and octacosane as an aliphatic ous components such as polycyclic aromatic hydrocarbons hydrocarbon. For comparison, coal tar pitch (includes 5% (PAHs).20) In the previous study, changes in the fluidity of of quinolone insoluble and 9% of toluene insoluble) was coal were investigated when several hydrocarbon reagents also used. were used. For example, polycyclic aromatic hydrocar- bons,21) aromatic hydrocarbons containing nitrogen,21–24) 2.2. Dilatometer Test and aromatic hydrocarbons containing oxygen.21,25) These According to the dilatometer test of JIS M8801, the investigations revealed that the fluidity of coal increased softening temperature, maximum contraction tempera- when a PAH with a high boiling point or an aromatic ture, resolidification temperature, contraction, dilatation, hydrocarbon containing nitrogen was used, but decreased and maximum dilatation of coal with additive (MDadditive) when an aromatic hydrocarbon containing oxygen was used. were measured. The coal samples were crushed to lower It is also known, on the other hand, that the fluidity of coal than 150 μm in diameter, and the powdered hydrocarbon increased substantially with the addition of a material with reagents with diameters less than 74 μm were added by a low softening point, such as straight asphalt (softening 1 wt% of coal. Because the viscosity of coal tar pitch is high point 46.0°C) and propane deasphalting asphalt (softening at room temperature, coal tar pitch was heated up to 130°C point 77.3°C), but dilatation did not increase considerably.9) to reduce the viscosity before it was added to and mixed Therefore, although the addition of coal tar pitch increased with the coal. When coronene was used as the reagent, the dilatation of coal, little is known about the components the maximum dilatation (MD) obtained with the addition of coal tar pitch contributing to the increases in the dilata- of 3 wt% of coronene was also measured. In addition, the tion of coal. maximum dilatation of coal only (MDcoal) was also mea- If it is possible to identify the effective component among sured. The difference in the maximum dilatation (ΔMD) was additives for increasing the dilatation of coal and to clarify calculated by subtracting MDcoal from MDadditive. the mechanism of interaction between the hydrocarbon MD MDadditivec MD oal reagent and coal, high-performance additives can be pro- duced. Furthermore, by using high-performance additives, high-strength coke can be produced even under a condition 2.3. Thermogravimetric Analysis that a large amount of semi-soft coking coal is blended. In To investigate the release of volatile matter during car- the present study, the dilatation of coal with hydrocarbon bonization, the weight losses of the samples were measured reagents was measured to identify the hydrocarbon con- using a thermogravimeter (Rigaku Corporation, Thermo tributing to the increase in the dilatation. Furthermore, to plus EVO2 TG-DTA). The samples were maintained at investigate the interaction between the hydrocarbon reagent 25°C for 30 min in a nitrogen atmosphere, and then heated and coal, the decrease in the weights and the changes in the to 105°C at a heating rate of 5°C/min, and maintained at infrared (IR) spectra of coal with hydrocarbon reagents were that temperature for 1 h.