Study On Efficiency Of Drying Sewage Sludge By Microwave Radiation

As the ratio of sewage water treatment in our country increases year after year, sludge volume brought by the sewage treatment process grows larger, thus sewage pollution results in the formation of sludge pollution, and therefore it is urgent to dispose of dewatered sludge properly.The paper mainly targets at investigating sludge drying technology which was efficient, economical and easy to administrate. The microwave heating and drying system is simple in operation and rapid in drying, so it was applied in drying sewage sludge. Influencing factors of microwave-drying sludge and its mechanism were discussed. Orthogonal Experiments were carried out to inspect comprehensive influences of microwave radiation power, radiating time and sludge volume to microwave drying efficiency. Quantitative relation in comprehensive influence of each factor to moisture content and energy utilizing ratio of microwave drying system was concluded. Then the kinetic model of microwave drying sludge was established. The following is the main conclusion of the research:①The result of a single factor experiment of radiating time, radiation power and sludge volume to microwave drying showed that: when microwave drying was applied under the situation that the microwave radiation power was 580W and the moisture of sludge was 77.4%, the moisture dropped to 60%, 38% and 3.42% correcting to the microwave heating time was 10 min, 14 min and 17 min respectively. So the demand of sludge semi-drying and drying could be met.When microwave power is increased frome 140W to 580W, maximal drying rate of sludge increase from 3.1g/min to 10.8g/min,microwave power has a significant influence on drying efficiency. The moisture of the sludge decreased gradually as the time of the microwave drying increased; the greater microwave radiation power, the higher sludge drying rate, and the shorter the drying time. Less sludge volume meant that the temperature increased rapidly and drying time was reduced.②During the course of drying sludge by microwave, there are three stages that included preheating-up, constant temperature and rapid heating-up. The microwave drying velocity according to them accelerated the drying, constant-speed drying and falling rate of drying. It showed significant difference among each step.③The result of the orthogonal experiment in comprehensive influence of microwave power, radiation time and sludge volume shows: microwave power and radiation time have obvious effect on sludge microwave drying efficiency. However sludge volume has no obvious effect. Orthogonal regression equation of comprehensive influence on microwave power and radiation time to moisture ratio is showed below: p=76.27-0.01N-1.16T+0.01NT. There was an obvious effect on microwave power, radiation time and their cross correlation to moisture ratio. The orthogonal regression equation of comprehensive influence on microwave power, radiation time and sludge volume to energy utilization of microwave drying system was showed below:η=93. 777?0.021N ?0.95T+0.029W, Microwave radiation time is the most effect on energy utility, followed by microwave power and sludge volume.④The Energy balance equation and mass-balance equation were established, and then the sludge microwave drying mathematical model was made available:Results above provided scientific basis for engineering practice of sludge microwave drying and has some guided significance.