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Much attention has been given to the valuable products from sewage sludge pyrolysis. In this study, the pyrolysis of sewage sludge, biomass (wheat straw) and their mixtures in different proportions were carried out in a thermogravimetric analyzer (TGA) and fixed-bed reactor. The effects of pyrolysis temperature and percentage of wheat straw in wheat straw-sewage sludge mixtures on product distributions in terms of gas, liquid and char and the gas composition were investigated. Results indicate that there is a significantly synergetic effect during the co-pyrolysis processes of sewage sludge and wheat straw, accelerating the pyrolysis reactions. The synergetic effect resulted in an increase in gas and liquid yields but a decrease in char yield. The gas composition and the synergetic effect degree are strongly affected by the wheat straw proportions, and the strongest synergetic effect of sewage sludge and wheat straw co-pyrolysis appears at the biomass proportion of 60 %. With an increase of temperature, the gas yield from sewage sludge pyrolysis increased but the liquid and char 2 / 22 yields decreased. Moreover, the required heat of co-pyrolysis is significantly reduced compared with the pyrolysis of sewage sludge and wheat straw pyrolysis alone, because of the exothermic reactions between the ash components in two fuel samples.

a b s t r a c tCement industry is one of the largest carbon emitting industrial sectors. It is responsible for about 5% of anthropogenic CO 2 in the world. Therefore, it is a relevant industrial sector for CO 2 emission regulation strategies. Bearing in mind the importance of cement industry in Croatia, and because of the fact that Croatia will soon become an EU member state, the present paper analyses the potential to reduce CO 2 emission in the Croatian cement industry. There are several measures that can reduce CO 2 emissions from the cement manufacturing process: the use of waste heat as an alternative source of energy; CO 2 capture and storage technologies; reduction of clinker to cement ratio; the use of alternative and biomass fuels; the use of alternative raw materials; an energy efficient combustion process. The most energy efficient technology for cement manufacturing today is the use of a rotary kiln together with a multi-stage preheater and a calciner. Since the use of cement calciners is a relatively new technology, further improvement of their operating conditions is still needed. This paper also highlights the results of research in the field of computational fluid dynamic (CFD) simulations that are used for the investigation of process and combustion emissions. The above mentioned measures together with numerical investigations can reduce the effect of cement manufacturing in Croatia on the environment and can make it more competitive with cement manufacturers from the EU.

a b s t r a c tCalcination is a thermo-chemical process, widely used in the cement industry, where limestone is converted by thermal decomposition into lime CaO and carbon dioxide CO 2 . The focus of this paper is on the implementation and validation of the endothermic calcination reaction mechanism of limestone in a commercial finite volume based CFD code. This code is used to simulate the turbulent flow field, the temperature field, concentrations of the reactants and products, as well as the interaction of particles with the gas phase, by solving the mathematical equations, which govern these processes. For calcination, the effects of temperature, decomposition pressure, diffusion and pore efficiency were taken into account. A simple three-dimensional geometry of a pipe reactor was used for numerical simulations. To verify the accuracy of the modelling approach, the numerical predictions were compared with experimental data, yielding satisfying results and proper trends of physical parameters influencing the process.

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The use of waste wood biomass as fuel is increasingly gaining significance in the cement industry. The combustion of biomass and particularly co-firing of biomass and coal in existing pulverized-fuel burners still faces significant challenges. One possibility for the ex ante control and investigation of the co-firing process are computational fluid dynamics (CFD) simulations. The purpose of this paper is to present a numerical analysis of co-firing pulverized coal and biomass in a cement calciner. Numerical models of pulverized coal and biomass combustion were developed and implemented into a commercial CFD code FIRE, which was then used for the analysis. Three-dimensional geometry of a real industrial cement calciner was used for the analysis. Three different co-firing cases were analysed. The results obtained from this study can be used for assessing different co-firing cases, and for improving the understanding of the co-firing process inside the calculated calciner.