To obtain the preliminary design data for combustion and pyrolysis of waste-tires, mixing of waste material/sand mixture in a cold model fluidized bed and thermal decomposition characteristics and combustion kinetics of waste tire in a TGA reactor have been determined. Also, the combustion characteristics and high temperature-pyrolysis of waste tires have been determined in a fluidized bed reactor. The effects of air velocity (U$_g$ = 0.08 - 0.60 m/s), particle size (d$_p$ = 0.27 - 0.53 mm) of sand, concentration (2.2 - 8 wt\%) of the waste material, the static bed height (0.11 - 0.17 m) and species of waste materials (polyethylene, waste-tire granules, PVC) on the mixing/segregation characteristics have been determined in a 169 mm-ID fluidized bed. Based on the mean deviation from the perfect mixing of binary solid mixture in the bed, a new mixing index for jetsam rich and flotsam rich systems has been proposed. Waste tire chips and polyethylene particles act as flotsam, but PVC granules act as jetsam in the fluidized bed. The mixing degree of waste tire/sand mixture in a fluidized bed decreases with increasing sand particle size but, increases with increasing the bed height at a given gas velocity. The bed of solid mixture is completely mixed at air velocity higher than 3 times of minimum fluidizing velocity (U$_{mf}$) of sand. For polyethylene/sand mixture, the mixing index has a maxima at the air velocity of 1.25U$_{mf}$ of the mixture and increases with increasing the static bed height but decreases with increasing polyethylene concentration in the bed. In the mixing of a binary mixture, the effect of jetsam particle size on the mixing index is more pronounced than that of the ratio of flotsam to jetsam particle sizes. The mixing index has been correlated with the pertinent dimensionless group as: $$M=1-\frac{\sum^N_{i=1}\mid{X_1-\overline{X}}\;h_1}{\sum^{N-k-1}_{i=1}\overline{X}hi\,+\,\sum^N_{j=N-k}(X_j-\overline{X})hj}=1/[1+0.25\exp(-z/3)]$$ $$\mbox{where}\;z=\Bigg[\frac{U_g-U_{mm}}{U_g\;\;U_{jm}}\Bigg]\exp(U_g/U_{mm})$$ $$\mbox{where}\;U_{mm}=0.8(U_{jm}\codtU_{fm})^{1/2}(2R_a)^{-0.2}$$ The data obtained from the TGA indicate that thermal decomposition of waste tires starts in the range 150 to $215\,^\circ\!C$. With heating rate of $30\,^\circ\!C$ /min, thermal decomposition is terminated at temperature below $500\,^\circ\!C$. Combustion kinetics of waste tire and bituminous coal have been determined in a thermobalance reactor. When the waste-tire chip (2 mm) is fed to the hot temperature zone ($> 750\,^\circ\!C$), devolatilization has been completed about 95\% within 30 s and then residue char is slowly burned. Combustion reactivity of tire char is similar to bituminous coal char and the combustion rate is found to be first order with respect to oxygen concentration. Activation energies for waste tire and coal are found to be 32.2, 30.8 kcal/g mol, respectively. The effects of bed temperature ($700 - 900\,^\circ\!C$), freeboard temperature ($600 - 800\,^\circ\!C$) and excess-air ratio (0 - 100\%) on CO, NO$_x$ and SO$_2$ emissions, axial temperature profiles, and combustion efficiency of shredded waste tires have been determined in a fluidized-bed combustor (76.2 mm-ID$\times$ 1.2 m-high). From waste-tire combustion, CO emissions are lower than that from coal combustion at the same operating conditions. The CO-emission levels can be maintained below 400 ppm at freeboard temperatures above $750\,^\circ\!C$ with excess-air ratios greater than 25\%. A severe temperature rise in the freeboard section is observed at bed temperatures below $750\,^\circ\!C$ and excess-air ratios less than 20\%, respectively. The overall combustion efficiency of waste tire is greater than that of bituminous coal and it increases with increasing excess-air ratio and bed temperature. It has been found that both NO$_x$ and SO$_2$ emissions increase with increasing bed temperature and excess air ratio. In addition, NO$_x$ emission is lower than 160 ppm but, SO$_x$ emission is above 800 ppm. The obtained NO$_x$ concentration in the flue gas has been correlated with the weight fraction of nitrogen in the fuel, bed temperature and excess-air ratio as: $$NO_x(vol.ppm) = 355\exp( -474 / T)\lambda^{0.83}([N]+8.82\times10^{-3}$)$$ The effects of pyrolysis temperature (700 - $850\,^\circ\!C$), feeding rate of waste-tire (37 - 88 kg/m$^2$ h), oxygen concentration in the carrier gas (0 - 5 vol.\%) and fluidizing velocity (1.5 - 3.0 U$_{mf}$) on oil, char and gas yields, total gas production rate, gas composition in the product gas, energy recovery and heating value of the produced gas have been determined. There are no significant changes in gas yield and compositions of the product gas with increasing the feed rate of waste tires in the range 30 - 88 kg/m$^2$ h. As the pyrolysis temperature increases from 700 to $800\,^\circ\!C$, char yield remains almost constant and gas yield increases from 22 to 30\%. However, at temperatures above $800\,^\circ\!C$, gas yield becomes insensitive to the bed temperature Hydrogen and methane production increase but, ethane and propene decrease with increasing the pyrolysis temperature. The heating value of the product gas linearly increases with increasing fluidizing velocity but it decreases with increasing the pyrolysis temperature and oxygen concentration in nitrogen during partial oxidation. Gas product and energy recovery exhibit maximum at fluidizing velocity of 2.0U$_{mf}$ and pyrolysis temperature $800\,^\circ\!C$. As oxygen concentration in nitrogen increase, total gas conversion increases due to the oxidation of char but, the production rates of hydrogen, methane, ethylene, ethane and propylene decrease. Energy recovery from the produced gas is not changed upto 3 vol.\% of oxygen in nitrogen but, it sharply decreases with further increase of oxygen concentration.
