Filip Kokalj

Utilization of bottom ash from the incineration of separated wastes as a cement substitute

Waste incineration is still an essential technology in the concept of integrated waste management. Most of the combustion residues are incinerator bottom ash. It has been discovered that incinerator bottom ash from the incineration of separated waste in the primary chamber of the modular two-stage incinerator mainly consists of metal oxides, especially SiO2 and CaO, in proportions that are quite similar to those in cement and so the feasibility of its application as a substitute for cement in concrete was investigated. It was found that after 28 days, the flexural and compressive strengths of the binder using bottom ash were practically comparable with those of a pure cement mixture. The results show that it is reasonable to use a binder containing incinerator bottom ash for applications in which an early-stage lower strength of concrete element is acceptable.

Advanced CFD modelling of air and recycled flue gas staging in a waste wood-fired grate boiler for higher combustion efficiency and greater environmental benefits

Grate-fired boilers are commonly used to burn biomass/wastes for heat and power production. In spite of the recent breakthrough in integration of advanced secondary air systems in grate boilers, grate-firing technology needs to be advanced for higher efficiency and lower emissions. In this paper, innovative staging of combustion air and recycled flue gas in a 13 MWth waste wood-fired grate boiler is comprehensively studied based on a numerical model that has been previously validated. In particular, the effects of the jet momentum, position and orientation of the combustion air and recycled flue gas streams on in-furnace mixing, combustion and pollutant emissions from the boiler are examined. It is found that the optimized air and recycled flue gas jets remarkably enhance mixing and heat transfer, result in a more uniform temperature and velocity distribution, extend the residence time of the combustibles in the hot zone and improve burnout in the boiler. Optimizing the air and recycled flue gas jet configuration can reduce carbon monoxide emission from the boiler by up to 86%, from the current 41.0 ppm to 5.7 ppm. The findings of this study can serve as useful guidelines for novel design and optimization of the combustion air supply and flue gas recycling for grate boilers of this type.

Combustion of Municipal Solid Waste for Power Production

The average MSW in developed countries has a calorific value between 8 and 12 MJ/kg. Based on this property the MSW can be compared with the fresh wood or lignite, which is low grade coal. The amount of waste generated is still slightly rising over the years with some fluctua‐ tions, due to general economy reasons (at the time of writing – recession) and technical measures in waste management in recent years. The amount of deposited MSW at landfills is getting lower in recent year despite the rise of total generated MSW due to better separate collection and treatment technologies utilized.

Thermal treatment of sewage sludge: One of possible disposal methods

Waste water treatment is a standard process in developed countries. It is intended to minimize the influence of waste water on the environment. The treatment process produces various remains that are generally called sewage sludge. In general, the remaining material is treated physically to dewater the sludge to reduce the volume and mass before disposal. This treated sewage sludge has around 25% of dry solids. The chemical and physical properties of the sewage sludge have to be monitored to determine the correct method of disposal. If the sewage sludge contains higher concentrations of heavy metals the only method for the disposal is thermal treatment. This article will present possible technologies for sewage sludge thermal treatment and the experience of Slovene waste thermal treatment plant that incinerates sewage sludge.

Numerical Optimization of a Waste-to-Energy Plant Under Different Operating Conditions

The combustion process for using municipal solid waste (MSW) as a fuel within a waste-to-energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as MSW proximate and ultimate analysis, the season of the year, primary and secondary air-inlet velocity and, secondly, on output parameters such as the temperatures or mass-flow rates (MFR) of the combustible products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Moreover, another problem is how these parameters can be tuned to achieving optimal combustion with minimal pollutant emissions during the initial plant-design phase. In order to meet these goals, a waste-to-energy plant with bed-combustion was investigated by using a computational fluid dynamics (CFD) approach with ANSYS CFX 12.0 code within a WORKBENCH 2 environment. In this paper, the adequate variable input boundary conditions based on the real measurement and practical calculations of known MSW composition compared with other authors are used and the whole computational work is updated using real plant geometry and the appropriate turbulence, combustion and heat transfer models. Furthermore, the operating parameters were optimized on output parameters through a trade-off study. The different operating conditions were varied and the fluid flow direction, residence time, temperature field, velocity-field, nitric oxide formation and combustion products through the plant’s combustion chamber and preheat intersection in 3D were predicted and visualized. Optimization in real-time has showed the amounts for each input parameter when meeting the optimal operating conditions. Finally, the response charts between the input and output parameters are presented in order to monitor the dependence among these parameters. Further simulations have to be done to include the geometry dimensions as input parameters when applying the CDF simulation and numerical optimization within the project phase.Copyright