Natural gas is used for the production of almost 20% of total energy today. The natural gas security of the Republic of Serbia is an urgent strategic, political and security issue. Serbia is one of the most vulnerable countries in Southeast Europe, because it only has one supply route. This study is a contribution to efforts to better understand the factors affecting energy security through the implementation of a new methodology based on the fuzzy–AHP synthesis model for measuring energy security. This new methodology was used to identify the energy, economic, environmental, social and technical indicators that accompany energy security analysis. The fuzzy–AHP synthesis model uses the asymmetric fuzzy inference approach for an outcome finding with the asymmetric position of fuzzy sets. The most important characteristic of the proposed model is its ability to operate with numerical and linguistic data and universality of application. The result of the proposed model shows a quantified assessment of energy security and its trend in the future of the natural gas sector. It indicates an unacceptably low level of present energy security and a gas system very vulnerable to supply cuts if the current gas infrastructure remains as it is in the future.

The integration of wastewater heat pumps (using purified water) in district heating systems is analyzed in this paper. The simulation procedure is proposed to analyze the impacts of stochasticity of purified water temperature and flow to heat pump integration and operation. The analysis includes calculation of the daily and seasonal coefficient of performance, as well as fossil fuel savings and CO2 emission reduction due to wastewater heat pump use. The proposed procedure is implemented for the case study in the city of Šabac (Serbia) and obtained results are discussed and evaluated. The historical data for two heating seasons was used for simulation. It was shown that the wastewater heat pump could provide 27-28% savings in fuel consumption, and 3.6-4.1% GHG emissions reduction, while the seasonal COP could be 4.2 - 4.3. Simulation based approach shows approximately 40% less savings of fuel consumption, compared to the approach based on the average values of heat pump input parameters.

Biomass is a renewable energy source with the highest potential to contribute in meeting energy needs and providing a secure and sustainable energy supply. For combustion of biogas (low calorific gas), an efficient technology is needed. It should provide stable combustion with low emission of pollutants such as CO and NOx over a wide operating range. This paper presents the experimental investigation on emission and stability of a premixed dual feed biogas swirl combustor with a pilot burner. For the experimental investigation, swirlers with swirl numbers 1.13 for the main burner and 1.98 for the pilot burner were used. The tests were performed at atmospheric conditions. The effects of carbon dioxide content, nominal thermal power, and equivalence ratio were analyzed and briefly discussed.