Preliminary investigation of the microwave pyrolysis mechanism of sludge based on high frequency structure simulator simulation of the electromagnetic field distribution

Abstract

Under microwave irradiation, raw sludge was pyrolyzed mainly by evaporation of water, with a weight loss ratio of 84.8% and a maximum temperature not exceeding 200°C. High-temperature pyrolysis of SiC sludge could be realized, with a weight loss ratio of 93.4% and a final pyrolysis temperature of 1131.7°C. Variations between the electric field intensity distribution are the main reason for the differences of pyrolysis efficiencies. HFSS simulation showed that the electric field intensity of the raw sludge gradually decreased from 2.94×10V/m to 0.88×10V/m when pyrolysis ends, while that of SiC sludge decreased from 3.73×10V/m at the beginning to 1.28×10V/m, then increased to 4.03×10V/m. The electromagnetic effect is the main factor (r≥0.91) influencing the temperature increase and weight loss of raw sludge. Both the electromagnetic effect and heat conduction effect influenced temperature rise and weight loss of SiC sludge, but the former's influence was comparatively larger.

A Novel Approach to Sludge Treatment using Microwave Technology

“…As the sludge was dried (i.e. as the water content of the sludge was reduced) up to a sludge moisture content of 6% (94% DS), a the dielectric loss factor ( ε″) of 0.3 was reported (Ma et al, 2017). Similar values were also reported by .…”

“…This condition is gradually expanded until the surface of the material is completely dry. So, the drying process continued, but the evaporating surface moves into inside the material (Doran, 2013; becoming harder than before to transfer the moisture from the capillaries and interstices of the material to the surface (Ma et al, 2017). As such, the drying rate decreased since the water removal process was now being governed by internal diffusion mechanisms (much slower than the evaporation of the free water).…”

“…In addition, Ma et al (2017) and reported that the rate of the water evaporation (from the sludge surface when applying MW radiation) was influenced by the rate at which the electromagnetic energy is absorbed by the material and converted into heat (power absorption density (Pd)). This has been reported to largely depend on several factors including both the electric field strength (which depends on the MW power output and sample volume), as well as the dielectric properties of the sludge such as the dielectric loss factor (ε″) as described in Equation 26; particularly, the sludge moisture content directly impact on the dielectric loss factor (ε″) (Ma et al, 2017;. For instance, Ma et al (2017) reported dielectric loss factor (ε″) of 14.1 for municipal dewatered sludge at a moisture content of approximately 81% (19% DS).…”

“…This has been reported to largely depend on several factors including both the electric field strength (which depends on the MW power output and sample volume), as well as the dielectric properties of the sludge such as the dielectric loss factor (ε″) as described in Equation 26; particularly, the sludge moisture content directly impact on the dielectric loss factor (ε″) (Ma et al, 2017;. For instance, Ma et al (2017) reported dielectric loss factor (ε″) of 14.1 for municipal dewatered sludge at a moisture content of approximately 81% (19% DS). As the sludge was dried (i.e.…”