Factors affecting the microwave coking of coals and the implications on microwave cavity design

Abstract

The work carried out in this paper assessed how processing conditions and feedstock affect the quality of the coke produced during microwave coke making. The aim was to gather information that would support the development of an optimised microwave coke making oven. Experiments were carried out in a non-optimised 2450 MHz cylindrical cavity. The effect of treatment time (15 -120 min), power input (750 W -4.5 kW) and overall power input (1,700 -27,200 kWh/t) on a range of coals (semi-bituminous -anthracite) was investigated. Intrinsic reactivity, random reflectance, strength index and dielectric properties of the produced cokes were compared with those of two commercial cokes to assess the degree of coking produced in the microwave system.Overall energy input and coal rank were found to be the major factors determining the degree of coking following microwave treatment. The dependency on coal rank was attributed to the larger amount of volatiles that had to be removed from the lower ranked coals, and the increasing dielectric loss of the organic component of the coal with rank due to increased structural ordering. Longer treatment times at lower powers or shorter treatment times at higher powers are expected to produce the same degree of coking.It was concluded that microwave coke making represents a potential step-change in the coking industry by reducing treatment times by an order of magnitude, introducing flexibility and potentially decreasing the sensitivity to quality requirement in the feedstock. The main challenges to development are the energy requirements (which will need to be significantly reduced in an optimised process) and penetration depth (which will require an innovative reactor design to

Production of Hydrogen‐Rich Syngas from Lignite using Different Pyrolysis Methods

“…Microwave heating is a process in which a high‐frequency alternating electromagnetic field (300 MHz∼3000 GHz) causes the high‐frequency reciprocating motion of dipolar molecules inside a medium (i.e., heat is generated by high‐frequency friction) and, thus, increases the temperature . As lignite is a nonmagnetic material, its absorption of energy in a microwave field can be represented by the absorbed power density ( P d ), as shown in Equation …”

“…[27] As lignitei san onmagnetic material, its absorption of energy in am icrowave field can be represented by the absorbed powerd ensity (P d ), as shown in Equation (1). [28] P d ¼ 2 pf e 0 e 00 jEj 2 ð1Þ P d is the power density absorbed per unit volume of lignite (W m À3 ), f is the frequency of the microwave field (Hz), e 0 is the vacuump ermittivity (8.85 10 À12 Fm À1 ), e'' is the dielectric loss factor of lignite,a nd E is the electric field intensity of the microwave field. Therefore,t he temperature increase of the lignite sample during microwave pyrolysis depends on e'' and E.H owever, the microwave electromagnetic field was distributed in the form of astanding wave in the furnace for microwave pyrolysis in our experiment, [29][30][31] and the electric field intensity was not even.…”

Formation of Metallurgical Coke within Minutes through Coal Densification and Microwave Energy

“…8,20 Several studies have used susceptors to increase the microwave absorbance of coal. [21][22][23][24] However, Lester et al 8 and Binner et al 20 showed that it is possible to produce coke with a similar vitrinite reflectance to that of conventional cokes without the use of susceptors, although the cokes formed were only in powdered form. The physical structure of coke is a key feature of blast furnace operation, 25 as it provides the bed support and permeability for the liquid phase drainage and upward flow of blast furnace gases.…”

Effect of Temperature and Microwave Power Levels on Microwave Drying Kinetics of Zhaotong Lignite

“…For example, in the pretreatment of lignite, microwaves can be used to dry lignite and improve its grinding characteristics, which are effected by the particle size and initial moisture of materials [21,22]. Microwave heating technology also has great potential for the pyrolysis and the production of coke from low-rank coal, which is inappropriate for traditional cooking plants [23,24].Studies on drying kinetics and mathematical modeling of lignite during the drying process are essential for further understanding the drying mechanism. Researchers have conducted a great deal of work on temperature, particle size, thickness, and power levels of lignite.…”