| Drying is a critical process in the treatment and disposal of dehydration of dredged sediments, and also an important factor for reutilization and innocent. It is important to find a new drying method to instead of the conventional ones, beeause the later are of the low processing efficiency, high energy consumption and serious environmental pollution and so on. The former aims to achieve its continuous and harmless disposal, which reduces the moisture content to a reasonable range.In this paper, continuous microwave drying experiments of dredged sediment were carried on a tunnel microwave drying equipment. Effects of different factors on drying were preliminarily discussed, including microwave power, feed rate, transmission speed, ventilation, moisture content and drying promoters. And the relationships between the required dying time and microwave power or feed rate were analyzed respectively. Kinetic parameter of first order reaction activation energy (Ea) and pre-exponential factor (A) were obtained by kinetic analysis. Based on electricity price, unit energy consumption was respectively calculated for microwave drying of sediments with different feed rates under different microwave powers. The main research results are as follows:Continuous microwave drying process of dredged sediment could be divided into three evident periods:the accelerated drying, constant-speed drying and decelerated drying period. The required drying time was shorten with the increasing microwave power, the decreasing feed rate and transfer speed, as well as the falling rate of moisture ratio. The influence of ventilation on continuous microwave drying was not obvious. The sediment of low moisture (40%) was clearly affected by microwave power in the same feed rate, and its maximum drying rate had a tendency to rise with the increasing water content. Adding the appropriate amount of fly ash into dredging sediment to remove water for the continuous microwave drying was helpful, and quick lime could improve the maximum drying rate, and effects of bentonite, rice husk and corn straw on continuous microwave drying characteristics of sediments were not obvious.Nonlinear fitting results showed that the relationship between the required drying time and microwave power was suitably described by one step exponent attenuation model(y=Aexp(-x/b)+y0), R2≥0.98. Linear fitting showed that the required drying time was positively proportional with feed rate (R2>0.96). In order to achieve the same drying effect with less energy,3 kW was the most appropriate choice for drying with feed rate from 1.28 to 5.12 kg·min-1.For the different microwave power and feed rate, kinetic analysis showed that Ea of continuous microwave drying process was 82.95 kJ·mol-1 under different microwave powers and Ea with different feed rate was 12.94 kJ·mol-1, it also indicated that in the microwave drying the reaction of dredged sediment, activation energy needed to completely remove its internal moisture is low, and the drying process could be conducted under low temperature.For microwave drying of sediments, unit energy consumption indicated that the appropriate feed rate and the microwave power, that achieving the purpose of drying and also improving the economic benefit, was conducive to reducing energy consumption. Comprehensive analysis showed that with the feed rate of 5.12 kg·min-1, microwave power of 3 kW, the required processing costs in 21～37 yuan per under water in this test. Continuous microwave drying efficiency was about 68%. |
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