Current research deals with numerical simulation of two-phase turbulent flows (gas and solid particles), which appear in Circulating Fluidized Bed (CFB) boilers, combusting Estonian local fuel - oil-shale. Many thermal processes in industry take advantage of the significant fluid-solid contacting in fluidized beds to carry out fluid-solid reactions, eterogeneous catalysis and particle drying. Gas-solid fluidization process in circulating fluidized beds is widely applied in many industries. The scientific novelty of the thesis is a gas-solid particle turbulent flow numerical simulation, taking in the advance the real initial data of CFB power plants using Estonian oil-shale ash. The results of the simulation describe the behaviour of oil-shale ash particles in CFB, which could be helpful in improving the efficiency of the combustion process.