The Test Study On Sewage Sludge Drying Under Superheated Steam

The sludge is a by-product of wastewater treatment plant with the outstandingcharacteristics of huge volume, high moisture content as well as contains variouspollutants. There are four sludge disposal methods currently, which is land application,landfill, building materials application and incineration. Due to the strict requirementsof the moisture content in the process of sludge disposal, sludge drying has become animportant part of the sludge disposal.Decreasing the moisture content of sludge is the key of sludge in harmlessness andvolume reduction treatment, which is also the premise of resource utilization.Superheated steam drying is a new technology developed recently, compared withconventional hot air drying, it has some advantages, such as high drying efficiency, lowenergy consumption, better products’ quality and so on. In superheated steam drying,there is no oxygen in drying medium, resulting in the enhancement of product qualityand the reduction of a hazard to explosion.A set of the superheated steam drying device of sludge was studied and designed.The saturated steam is produced by the steam generator, the superheated steamtemperature for the test is heating through the steam heating box, the superheated steamin the loop is realized by using the fan. The system merits is using online weighing,having the characteristics of continuity, real-time, etc.The paper has conducted the study on drying the humidity material sludge withsuperheated steam, carried on the superheated steam drying of sludge in the superheatedsteam drying experiments built by ourselves. The experiment is using the swage sludgeas raw material, conducting various thickness of sludge drying erperiments underdifferent temperature of superheated steam. According to the experiment data, thedrying curve was drawed and analyzing the drying characteristics.The result is summarized as followed:(1) At the initial stage, there will happen condensation phenomenon when usingsuperheated steam to dry sludge. The amount of cooling water will change with thevariation of the superheated steam’s temperature and sludge’s thickness. With enhancedthe superheated steam’s temperature and the sludge’s thickness, the amount of coolingwater will reduced. Otherwise, the opposite result is obtained. (2) With the improvement of superheated steam’s temperature, the drying time ofsludge is reduced, the drying rate was accelerated. With the increase of thickness ofsludge, the drying time of sludge is increased, the drying rate was reduced.(3) During the same temperature of superheated steam, the thicker the sludge, thehigher the critical moisture content. In the same thickness of sludge, the highertemperature of superheat steam, the higher the critical moisture content.(4) In the same thickness of sludge, the higher temperature of superheat steam, thesmaller proportion of the period of constant drying rate in the drying time. During thesame temperature of superheated steam, the thickness has no effect on the proportion ofthe period of constant drying rate of drying time.