柱塞式平模生物质成型机设计与试验

针对传统生物质平模成型机能耗高、磨损严重的问题,该文提出了一种柱塞式平模生物质致密成型方法,并设计了成型机样机。该样机通过斜盘与弹簧配合,驱动柱塞往复运动,柱塞在运动过程中仅对模具内的原料进行挤压。成型模具部分采用组合式设计,主要由平模与成型套筒组成,可在成型套筒外部加热,同时可更换长径比不同的成型套筒以适应不同生物质原料。该文以不同颗粒度玉米秸秆和刺槐为原料,在原料含水率为15%,斜盘转速为50 r/min,原料温度为室温的条件下进行了试验,结果表明柱塞式平模生物质成型方法可行,颗粒成型率均高于98%,成型密度大于1.1 g/cm3,机械耐久性高于97%。该文提出的成型方法为生物质致密成型技术提供参考。

Design and experiment of flat die pellet mill with plunger

Abstract: A flat ring die mill is frequently used for producing pellets. In the densification process, a great amount of energy is required to avoid spring back and to overcome the friction between the material and the channel surface of the die. However, extra energy is unnecessarily consumed because of friction between densified material and the pressure between the roller and the die, where there are no opening channels. The aim of this work was to attempt to eliminate a portion of the frictional and compaction energy based on an improving method of densification using a flat die. A new flat die pellet mill with plunger was developed. The self-developed flat die pellet mill mainly consisted of three parts: a flat die, plungers, and a swash plate. When the swash plate rotated, it drove the rolling bearing which was set up on one side of the plungers 16 mm in diameter to reciprocate along with the sliding bearing. The moment the plunger reached to the end position without the urge of swash plate, the return spring began to push the plunger back to the other end position. With the reciprocating motion of the plungers, the raw material under the plungers was compacted precisely only on the spot of the opening channel of the flat die to avoid compaction and friction that exists in the conventional flat die. Then the pellets were squeezed out through open end pelleting cylinders connected to the flat die. The pelleting cylinder was 16 mm in diameter and 80 mm in length, so the ratio of the length to the diameter of the pelleting cylinder was 5. The pelleting cylinders can be changed, then they can suit for different raw material. Moreover, each pelleting cylinder was wrapped by a heating tape with a thermocouple to preheat the cylinder die to a certain temperature when necessary controlled by a temperature controller and monitor. A series of experiments on its feasibility were carried out at ambient temperature. Corn straw and acacia were used as the experimental material. Corn straw was milled into fibrous pieces at three levels of particle size (0-2, >2-4, and >4-6 mm) with moisture content of 15%, while acacia was milled into fibrous pieces at three levels of particle size (0-3, >3-5, and >5-7 mm) with moisture content of 15%. The results demonstrated the pellet mill exhibited a good feasibility and capacity, which met preliminary requirements of pelletization. When working at the speed of 50 rpm, the molding rate in all the trials were above 98%. The productivity of using acacia was greater than that of using corn straw because of its higher bulk density. Furthermore, the density values of all the pellets were over 1.1 g/cm3, and the mechanical durability values of pellets were above 97%. After 4 weeks' trials working, there were no obvious signs of wear on the plungers and the cylinder dies. The results above revealed the feasibility of the improving densification method, and the flat die pellet mill had the ability to produce the qualified pellets and to avoid the unnecessary wear and deformation on the flat die, which would be a new way for biomass densification technology.