Progress of the technique of coal microwave desulfurization

Abstract

With the advantages of its fast speed, effective and moderate controllable conditions, desulfurization of coal by microwave has become research focus in the field of clean coal technology. Coal is a homogeneous mixture which consists of various components with different dielectric properties, so their abilities to absorb microwaves are different, and the sulfur-containing components are better absorbers of microwave, which makes them can be selectively heated and reacted under microwave irradiation. There still remain controversies on the principle of microwave desulfurization at present, thermal effects or non-thermal effects. The point of thermal effects of microwave is mainly base on its characters of rapidly and selectly heating. While, in view of non-thermal effect, direct interactions between the microwave electromagnetic field and sulfur containing components are proposed. It is a fundamental problem to determine the dielectric properties of coal and the sulfur-containing components to reveal the interaction of microwave and sulfur-containing compounds. However, the test of dielectric property of coal is affected by many factors, which makes it difficult to measure dielectric properties accurately. In order to achieve better desulfurization effect, the researchers employ methods of adding chemical additives such as acid, alkali, oxidant, reductant, or changing the reaction atmosphere, or combining with other methods such as magnetic separation, ultrasonic and microorganism. Researchers in this field have also put forward several processes, and have obtained a number of patents. Obscurity of microwave desulfurization mechanism, uncertainties in qualitative and quantitative analysis of sulfur-containing functional groups in coal, and the lack of special microwave equipment have limited further development of microwave desulfurization technology.

Adsorption properties of CFBC ash–cement pastes as compared with PCC fly ash–cement pastes

“…Circulating fluidized bed combustion (CFBC) ash is produced from the combustion of coal with injection of limestone for desulphurization (Gunka and Pyshyev 2014;Ni et al 2014;Tao et al 2014). CFBC ash is classified into two categories, the fly ash and the bottom ash collected from the flue and the hearth, respectively.…”

Desulfurization of Vulcanized Rubber Particles Using Biological and Chemical Methods

“…Up to 97% of inorganic sulfur can be removed by acid washing in combination with microwaves. In the presence of microwaves, the binding energy of C-S is weakened, facilitating its breakdown in the presence of acids; this result has been veri ed by FTIR analysis [43]. It is noteworthy to mention that a low acid concentration (1%) is used in the proposed chemical method, versus other described methods for treating rubber, which use high acid concentrations such as H 2 SO 4 (95%).…”

“…The polar molecules of a medium with dielectric characteristics move in the electric's direction eld where thermal movement interferes with other molecules and the obstruction of intermolecular interactions generates internal friction. This converts the energy absorbed from the electrical eld into thermal energy, increasing the temperature of the system [43]. The thermal effects of microwaves can be associated with the ability to convert electromagnetic energy into thermal energy at a particular temperature and frequency; this capacity can be measured with the tangent of loss of the material (tan δ) ( [44], where ε" is the dielectric of material loss (which indicates the e ciency of the conversion of electrical energy into thermal energy) and ε' is the dielectric constant that indicates the polarization capacity [45].…”

Biodegradation of dibenzothiophene and its application in the production of clean coal

“…Microwave treatment also causes secondary pollution, which needs to be addressed before setting up a successful microwave desulphurization process. Apart from that, the microwave irradiation technique offers fewer economic benefits due to certain constraints like the operating frequency of equipment and the problem in crafting such equipment for industrial application [128].…”