Article Cite This: Energy Fuels XXXX, XXX, XXX−XXX
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Relevance between Various Phenomena during Coking Coal Carbonization. Part 1: A New Testing Method Developed on a Sapozhnikov Plastometer Qi Wang,* Huan Cheng, Xue-fei Zhao, Song Zhang, and Wen-jia Hu
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Key Laboratory for Chemical Metallurgy Engineering of Liaoning Province, University of Science and Technology Liaoning, Anshan, Liaoning 114051, People’s Republic of China ABSTRACT: A method for studying the relevance between the various phenomena during coking coal carbonization has been wistfully developed because the occurrence of the gas−liquid−solid phase makes the measurement very complicated. A thermogravimetry−plastometer−swelling pressure (TG−P−SP) apparatus was developed on a standard Sapozhnikov plastometer for simultaneously measuring not only the thickness of plastic layer but also the swelling pressure of plastic layer and its expansion effect on coal charge as well as volatile matter escaping. TG−P−SP employs an electronic balance and a Sapozhnikov plastometer, which is located on an electronic balance, with a pneumatic-loaded cylinder, linear displacement transducer, and pressure sensor. The characteristics and advantages of this method are able to give some information on the initial states of various phenomena of carbonization and pictures of complexity- and uncertainty-related behaviors in the carbonization process for coals with various rank and plasticity. These may have an important role in revealing the carbonization mechanisms and evaluating the properties and quality of coals for coke making.
1. INTRODUCTION During the transformation of coal into coke, there is a striking phenomenon that coals of a very definite range of rank soften upon heating, swell upon decomposition, and resolidify during continued degasification.1 The development of techniques for studying the various phenomena connected with carbonization, especially the relations between them, has been playing an important role in establishing the phenomenological theory of carbonization, making quick classification and distinction of coals for the coke quality and coking operation. The different techniques for studying the various phenomena of carbonization were proposed. The best known measuring techniques in carbonization research are with small mass coals under homogeneous heating, briefly including the thermogravimetric analyzer for studying the decomposition,2−6 the standard Gieseler plastometer,7−9 the standard Audibert−Arnu dilatation test10−12 for deriving the plasticity, under unidirectional heating as in a coke oven, including the standard Sapozhnikov plastometer13−16 for determining the thickness of the plastic layer and expansion, and after shrinkage of coal, the patented Koppers− INCAR test17−21 for determining the expansion and contraction of coal. It is generally accepted that the capacity of good coking coal is sufficiently plastic and good swelling properties on the whole process, but too much swelling pressure in the plastic layer can generate an excessive coking pressure, which damages the chamber walls. To study the swelling pressure, some techniques have been developed in recent years, involving a sole heated oven for permeability experiments, by which a probe of small diameter designed for gas injection is introduced at half of the height of the coal charge,22 the plastic coal layer permeability apparatus23,24 for measuring the changes in the pressure drop in the permeability test with the temperature in a constant volume cell, a small coking reactor for simultaneously measuring the © XXXX American Chemical Society
volumes of gaseous volatiles, which were released from the coal and coke exits of the reactor, and either the internal gas pressure or the pressure (permeability) by maintaining a constant flow of nitrogen into the center of the charge.25 In fact, a technique for studying the relations between various phenomena of carbonization, wistfully developed, has not been achieved thus far. Because the occurrence of a gaseous phase beside the solid and liquid phases renders the system on which the measurement has to be made very complicated, the results do not give a general picture of the way in which the coking properties of coals and blends are directly affected by the decomposition.1 For these reasons, the criteria for using coal or blends are obtained from the comparison of data from various plastometers and semi-scale commercial or commercial oven tests,19,20,26−31 and therefore, care should be taken in the use of the results. The present work will develop a new method on a standard Sapozhnikov plastometer to simultaneously measure the thickness of the plastic layer and expansion−contraction of coal, swelling pressure, and volatile matter (VM) escaping with the development of a plastic layer for studying the relations between various phenomena of carbonization.
2. MATERIALS AND METHODS 2.1. Coal Samples. Table 1 gives out proximate analysis and Sapozhnikov’s index (maximum plastic layer thickness, ymax) for six coal samples (C1−C6) from China. These coals have a wide range of rank and plasticity, with the VM from 41.5% of coal C1 decreasing to 16.1% of coal C6 and ymax from 10.18 mm of coal C1 increasing to 26.88 mm maximum of coal C3 and then decreasing to 7.90 mm of coal C6 with an Received: April 7, 2018 Revised: June 11, 2018
A
DOI: 10.1021/acs.energyfuels.8b01217 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
temperature to 250 °C at 8 °C/min and from 250 to 800 °C at 3 °C/min. The plastic layer is manually punctured by the upper edge resistances of about 1−3 N and lower edge resistances of about 15−20 N, as given in the literature.32 2.4. Data Treatment and Parameter Calculation. 2.4.1. Contraction−Expansion Extent. The contraction−expansion extent of the coal charge, x (%), derived from the height data of the coal charge, and is defined as
Table 1. Proximate Analysis and Sapozhnikov’s Index for Coals coal sample
C1
C2
C3
C4
C5
C6
Proximate Analysis ash (wt % db)a 4.8 7.2 8.4 8.8 10.4 8.9 VM (wt % db)a 41.5 35.1 30.2 28.8 20.4 16.1 Sapozhnikov Measurementb maximum plastic layer 10.18 11.14 26.88 21.06 16.04 7.90 thickness, ymax (mm)
x=
a
Dry basis. bChinese National Standard GB/T 479-2000.
ht − h 0 × 100 h0
(1)
where h0 is the initial height (mm), ht is the height at time t (mm), x < 0 is contraction, and x > 0 is expansion. 2.4.2. Thickness of the Plastic Layer. The thickness of the plastic layer, y (mm), is the distance between the upper and lower edges punctured. The y curve is fitted from the data of the plastic layer thickness. The maximum thickness of the plastic layer, ymax (mm), is obtained from peak value of the y curve. 2.4.3. VM Escaping. The extent of VM escaping, f (%), is derived from the mass loss data of the coal charge and is defined as
increasing of rank. These coals can be classified into low-rank and lowplasticity coals C1 and C2, medium-rank and high-plasticity coals C3 and C4, higher rank and medium-plasticity coal C5, and high-rank and low-plasticity coal C6. About 1 kg of coal sample is crushed and sieved to
