The Key Technology Research Of PMMA Fluidized Pyrolysis

PMMA(the chemical name for it is polymethyl methacrylate), which commonly known as the organic glass, is a kind of high level transparent and amorphous thermoplastic materials. The waste materials of PMMA are mainly from the unqualified products in the production process(such as the existence of bubbles, the formula issues of the transparent cast board and section bar), the casting of molding process, and the offcuts in the machining process. In addition, a part of waste materials come from the circulation field. For example, the headlights of scrap car are abandoned organic glass. There are hundreds of thousands of tons of waste organic glass in China every year, however, most of these abandoned organic glass cannot be used effectively because the waste organic industry starts late in our country. Therefore, recycling organic glass and making it resourcelized is significant in practice.In this paper, we conducted a cold fluidization experiment on a fluidized bed of which the height is 3000 mm, the diameter is 100 mm. The cold fluidization experiment showed that the critical fluidization velocity of the same particle size of river sand has little relationship with the stacking height. But the critical fluidization velocity is closely related to the particle size of river sand and it will rise with the increase of particle diameter. This conclusion provides a theoretical basis for the bed material selection of subsequent thermal state experiment.This article adopts the two-dimensional numerical simulation. In the calculation, we considerate the interaction between various components and apply the Euler double fluid particle model and the Gidaspow interphacial momentum exchange model. The size of fluidized bed in the simulation is exactly the same as that of thermal state experiment equipment. We did the simulation and calculation to the temperature distribution in the fluidized bed furnace as well as the distribution of bed material. We can see from the results that the temperature of the furnace bottom is relatively low when only heating the outer wall, while the fluidization gas are preheated, at the same time the outer wall is heated, temperature in the furnace is more well-distributed. And when the gas is fluidized, the bed materials are mainly distributed in the lower chamber of the furnace.The fluidized pyrolysis experiment of the PMMA in thermal state uses the PMMA as raw material and uses the river sand as bed material to carry on the thermal cracking in the fluidized bed. The results of experiment showed that the pyrolysis products of PMMA are mainly gas and liquid. The maximum liquid yield is 91.8%. The main ingredient of the liquid products is MMA, while CO2 and CO is the main component of the gas products. When the temperature is above 400?, the content of CO2 and CO rises with the increase of pyrolysis temperature. On the contrary, the content of MMA declined with the increase of pyrolysis temperature. In the process of the fluidized pyrolysis experiment of PMMA, the temperature is equally distributed along the furnace height direction. And the temperature can be controlled in the range of 380?to 460?. The furnace temperature will distribute more uniformly when the fluidization gas gets preheated with the outer wall heating. Besides, the preheating of the fluidization gas can enhance the intensity of pyrolysis and liquid yield. More precisely, in the range of 1 ~ 10 mm, the smaller the particle size, the greater the intensity of pyrolysis and liquid yield of PMMA.