Research On Municipal Solid Waste Shredder And Effect Of Particle Size On Pyrolysis & Gasification Performance

The breakage pretreatment of municipal solid waste (MSW) is necessary to increase the uniformity and ratio of surface area and of MSW to improve the efficiency of the subsequent processing step, while the breakage of MSW mainly concentrates on the hard and brittle materials of MSW in china. The ductile solid waste which makes the hammer crusher difficult to meet the requirements of the breakage of MSW, however, accounts for a large proportion of MSW. It is powerless for the hammer crusher to crush the moisture and ductile material.Based on the composition and volume-mass properties of MSW (i.e., unit weight, void ratio, and water content), a novel shear shredder for organic MSW was presented. The reliability of the shredder was investigated and the influencing factors were studied.(1) Some certain composition MSW (kitchen garbage 57.6 wt.%, paper 6.9 wt.%, textile 7.2 wt.%, wood 19.7 wt.%, plastic 8.6 wt.%.) was chosen as testing materials, and the product size distribution and specific energy were taken as measurement index. The breakage tests were carried out in the lab-scale shear shredder to evaluate the effects of working parameters:hydraulic pressure, rotor speed, distances between rotating blades, working load and feeding mode. The results show that the shredder is suitable for the pulverization of MSW with specific energy and fine particles proportion being 13.2 J/g and 85.7%, respectively, under optimal operating conductions. With increasing hydraulic pressure the specific energy is reduced, and size distribution of product is finer. When hydraulic pressure is constant, the specific energy decreases with increasing rotor velocity, while the products size distribution is coarser; the fines proportion (particles below 10mm) shows increasing trend with decreased distances between rotating blades, however, the specific shows opposite trend. For the breakage of plastic, the distance should be smaller than the desired particle size. The specific energy is the lowest when the shredder is operated at the designed working load. Compared with single-course shredder, the two-inlet operation mode improves shredding efficiency and reduces energy consumption to a great extent. With the double-inlet operation, about 73%as much energy is used per gram as with the single-course shredder; (2) The effects of raw materials characteristics such as feed composition, feed moisture and raw materials size are investigate in the paper. The shredder is much more effective for the pulverization of soft, ductile and fibrous materials (kitchen garbage and leaves in the test), but it is not good at the brittle material (branch). There is a tendency for the fine production in products to decrease with the increasing amounts of water content in the feed; with the increasing feed moisture, specific energy shows an increasing trend; under lower hydraulic pressure, the specific energy and product size distribution are more sensitive to the feed moisture than under higher hydraulic pressure. The effect of raw materials size on product size distribution is not evident, while smaller size would result in lower specific energy.(3) Pyrolysis and steam gasification of MSW were carried out in a small-scale fixed bed reactor in order to evaluate the effects of particle size at different bed temperatures on product yield and composition. Particle size and temperature had integrated effects on product yield and composition:higher temperature resulted in higher gas yield with less tar and char, and, at the same temperature, dry gas yield increased with a decrease in particle size, and char and tar yield decreased. The differences due to particle sizes in pyrolysis and gasification performance practically disappeared at the highest temperatures tested. Smaller particle sizes resulted in higher H2 and CO contents for both pyrolysis and gasification of MSW. Smaller particle size leaded to lower C and H contents, as well as higher ash content in the char.(4) The MSW compaction tests were carried out in the self-designed compaction facility in order to evaluate the effect of feeding pressure and material size on volume compression ratio. And MSW catalytic pyrolysis was conducted in the pilot-scale reactor to investigate the influences of particle size on fuel gas quality. The results show decreasing feed size and increasing feeding pressure could increase MSW volume compression ratio, resulting in the decreasing of O2 and N2 contents in the fuel gas. With the increase of feeding pressure, the effect of particle size becomes less pronounced.