The main objective of this paper is to present a new reliability model of thermal power plant in case of power block in TE-KO Kostolac B (Serbia), with the existence of interactions of system component cancellation. It is based on the theory of probability, Weibull distribution, Monte Carlo simulation, and newly discovered mathematical models of component dismissal interaction and original software solutions. The goal of implementation of new model is increased system reliability through reducing the number of failures. Thus, increasing operational safety of thermal power, which is in accordance with the provision of energy security by applying measures of Directive 2005/89/EU. According to the directive, it is necessary to ensure reliable, safe, efficient, and quality power supply.

This aim of this study is to identify failure mechanism of ethylene pyrolysis furnace tube after five year of operation. The tubes were manufactured from centrifugally cast heat resistant steel HK 40. Failure analysis of the radiant tubes was performed by careful visual inspection of the failed tubes, scanning electron microscopy observation of crack region samples, hardness and micro-hardness measurements. Selected specimens were prepared from the four samples, measurements was carried out at inner, middle and outer sides of the samples. The experimental results showed that the mode of tube failure was a combination of high temperature carburization attack and creep damage leading to intergranular cracking. Maximum hardness is associated with internally carburized zone where the amount of carbides is maximum in this region. The hardness of the radiant tubes decreases as the distance moves from the inner surface to the middle section. The metallurgical background of the combined action of carburization and creep ductility exhaustion have been investigated and are explained. Pyrolysis tube failures can be prevented by a combination of proper furnace operation, materials choice, regular inspections and good design.

When trying to reduce energy consumption in a central heating system or in a domestic water heating system, it is necessary to consider the annual operating efficiency of the heating and the domestic hot water heating system. A boiler operates under dynamic conditions, so it essential to know the methodology and the model of annual operating efficiency calculation for thermo technical systems. The outlet temperature of the flue gases with conventional gas boilers is considerably higher than the ambient temperature and consequently the heat loss occurs; it is then vented off into the environment as a result of heat transfer. The heat loss may be reduced if a condensing heat exchanger is installed, which will, on the other hand, increase the boiler efficiency by more than 10%. This paper studies the relations between combustion and heat transfer, which will enable the appraisal of a gas boiler efficiency increase and possible ways of energy savings. The method for cost-effectiveness of the investment is used to perform a feasibility study of retrofitting a conventional boiler into a condensing boiler with necessary details. The results of the investigation show that the most cost-effective temperature range of the flue gases is 40-60 degrees C. The use of a working fluid in the heating system or the domestic cold water results in cooling the condensing heat exchanger. The temperature of the return water or the domestic cold water is lower than the water vapor dew point in the flue gases during most of the heating period in almost all parts of the Republic of Serbia where natural gas is used.

This paper provides an overview and analysis of the structure of the energy system and consumers of natural gas on the territory of the Serbia with special attention to one category of consumers - households. It gives an overview of data on the energy system of Serbia - the natural gas sector, concepts, and directions of the development with projections until 2030. In addition to the projection of consumption of natural gas, it also gives the legal framework in force in the field of energy sector in Serbia. It presents data on natural gas consumption in Serbia in the period from 2010 to 2015, with projections of future consumption until year 2030.

In the petrochemical industry, an industrial pyrolysis furnace is a complicated piece of equipment that functions as both a reactor and high-pressure steam generator. During service, hard deposits of carbon (coke) build up on the inner wall of the tube, reducing heat transfer and restricting the flow of the hydrocarbon feedstocks. In this paper, an overview of coke formation, the impact of coke formation, and the methods by which coke formation can be prevented, as well as methods that can be successful in decoking of pyrolysis furnaces, is presented.