谈膨化颗粒饲料的干燥

Discussion on drying method of extruded feed pellets

膨化颗粒现最常用的是湿法膨化加工工艺,膨化颗粒从湿法膨化机内出机时,颗粒的水分一般都在22%~28%。膨化颗粒需经过干燥脱水这一工序,使膨化颗粒的水分降到安全水分以内。国内外水产膨化颗粒的干燥工段采用“卧式链板连续高温干燥机”。干燥气流的温度在110~130℃左右,干燥时间约为15 min,干燥后颗粒的水分在10%左右,颗粒水分的不均匀度在2%~3%。经高温干燥的膨化颗粒最大缺陷:使鱼对饵料的消化吸收率将下降15%以上。当饵料干燥温度在70~90℃时或低温真空状态下干燥,其消化吸收率明显优于高温条件下干燥。因膨化颗粒的结构较松,内部多孔的特性,采用真空低温干燥是较理想的干燥工艺。干燥室的真空度只需控制在0.02~0.03 MPa,干燥加热的介质为95~100℃的热水,干燥室内物料的干燥温度可在60~80℃,干燥室内真空度宜用缓苏的脉冲真空度,来提高物料的干燥速度和干燥效率。真空低温干燥的膨化颗粒水分不均匀度可小于1%。实际就能将膨化颗粒料的成品水分提高到12%,这不仅节约了颗粒饵料的加工成本,又提高膨化颗粒料的养殖效果。

The wet extrusion process is the most commonly used method for extruded feed pellets.When the extruded pellets are discharged from the extruder,the moisture content of the pellets is gen?erally 22%~28%.The expanded pellets need to be dried and dehydrated to safe water content."Hori?zontal chain plate continuous high temperature dryer"is generally used in the drying section for extrud?ed aquatic feed pellets at home and abroad.The drying air temperature is about 110~130℃,the dry?ing time is about 15 minutes,the water content of the dried pellets is about 10%,and the moisture un?evenness of the pellets is about 2%~3%.The defect of this method is:after drying at high tempera?ture,the digestion and absorption rate of the extruded pellets as fish bait will be reduced by more than 15%.On the contrary,with loose and porous in?terior structure,the digestion and absorption rate will significantly increase if the pellets are dried with low temperature at 70~90℃ or under vacu?um condition.So vacuum drying with low temperature is an ideal drying method for extruded aquatic feed pellets.The vacuum degree of drying cham?ber only needs to be controlled at 0.02~0.03 MPa,the medium of drying can be hot water at 95~100℃,the optimal temperature in drying chamber is at 60~80℃.With its tempering effect,pulse vac?uum is preferred in drying chamber to improve the drying speed and efficiency.After low-temperature vacuum drying,the moisture unevenness of the pellets can be less than 1%and the water content of the product can be increased to 12%.This drying method can not only save the processing cost,but al?so improves the breeding effect of the feed pellets.