Effect of particle density on combustion characteristics of refuse derived fuel

Waste to energy (WTE) plants have been built more and more worldwide nowadays. It is one of the most successful types to resolve the impact of city rubbish on environment. Refuse derived fuel (RDF) is the fuel of WTE plant, which is made of combustible refuse such us cardboard, paper, various plastics, textile and wood. According to literature, the incineration process has the advantage of reducing waste weight by 80% and volume by 70%, and around 25%-30% energy within RDF can be obtained through conversion of power facilities. Combustible refuse can be processed into pellets with physical density of more than 0.3 g/cm3 through extrusion forming after separating, crushing, and drying procedure. In this paper, pelleted RDF with different densities of 0.51, 0.42, and 0.31 g/cm3 was adopted in this experiment, and their combustion characteristics from 30 to 900℃ were investigated by means of thermogravimetric (TG), calorific value, and ash content analysis. Meanwhile, pelleted RDF was compared with non-pelleted RDF and straw which represented biomass fuel. By comparing TG of pelleted RDF and non-pelleted RDF, the results indicated that non-pelleted RDF was faster in burning, showing pelleted RDF can release energy slower, which is good for boiler equipment to absorb energy more efficiently. By comparing DTG of pelleted RDF and non-pelleted RDF, the ignition point of the non-pelleted RDF (0.10 g/cm3) was 234.0℃, and 3 maximum mass loss rates were 6.30, 2.21 and 0.53 percentage points per minute, respectively; While for the highest density of pelleted RDF (0.51 g/cm3), the ignition point was 238.2℃, and 3 maximum mass loss rates were 5.70, 3.11, and 0.61 percentage points per minute, respectively, showing that the higher density, the higher ignition point, and the higher burning rate got more balance. DTG data also show that pelleted RDF is more suitable for the boiler to absorb heat efficiently. After finishing burning, the content of combustion ash coming from the highest density pelleted RDF sample in this experiment was 6.7% less than that of the non-pelleted one, showing that procession of extrusion forming will help to reduce weight and volume of RDF ash, thus relieving the pressure of landfill, which is the most serious problem to our environment. For the burning calorific value, and the data from pelleted RDF and non-pelleted RDF checked by calorimeter, each sample was checked 3 times. By calculating all sample values with the method of variance analysis, F value was 0.25, while df values between groups and within group were 3 and 8, respectively, the final F0.05(3, 8) value was 4.07, and F0.01(3, 8) value was 7.59, thus F<F0.05<F0.01. The results of variance analysis show that calorific value difference between pelleted RDF and non-pelleted RDF is not obvious. Though pelleted RDF has some advantage for equipment to absorb energy, its procession is limited by many factors, such us space, equipment structure, transportation, moreover, investment cost and energy cost are also included in the consideration. On other hand, we also can make use of RDF ash as product material, so there are still many researching works to be done. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.