Marta Trninić

Energy audit as a tool for improving overal energy efficiency in Serbian industrial sector

The paper presents characteristics of energy consumption in industrial sector of Serbia, the methodology and results of energy audits (EA) performed in industrial sites and potentials for energy efficiency (EE) improvements. The present state of industrial energy in Serbia could be characterized by significant technological out-of-date, low EE and low level of environmental protection. Presented analysis of the results of conducted EAs in selected industrial companies in previous period has shown the significant potentials for EE improvements in Serbian industrial sector (upgrading or replacement of equipment in the industrial energy sources and processes, introduction of energy management, improvement of steam supply and condensate return systems, the waste heat utilization, introduction of EE technology, improvement of EE in electrical equipment, usage of waste materials etc).

A steady state model of agricultural waste pyrolysis: A mini review

Agricultural waste is one of the main renewable energy resources available, especially in an agricultural country such as Serbia. Pyrolysis has already been considered as an attractive alternative for disposal of agricultural waste, since the technique can convert this special biomass resource into granular charcoal, non-condensable gases and pyrolysis oils, which could furnish profitable energy and chemical products owing to their high calorific value. In this regard, the development of thermochemical processes requires a good understanding of pyrolysis mechanisms. Experimental and some literature data on the pyrolysis characteristics of corn cob and several other agricultural residues under inert atmosphere were structured and analysed in order to obtain conversion behaviour patterns of agricultural residues during pyrolysis within the temperature range from 300 °C to 1000 °C. Based on experimental and literature data analysis, empirical relationships were derived, including relations between the temperature of the process and yields of charcoal, tar and gas (CO2, CO, H2 and CH4). An analytical semi-empirical model was then used as a tool to analyse the general trends of biomass pyrolysis. Although this semi-empirical model needs further refinement before application to all types of biomass, its prediction capability was in good agreement with results obtained by the literature review. The compact representation could be used in other applications, to conveniently extrapolate and interpolate these results to other temperatures and biomass types.

Biomass gasification technology: The state of the art overview

The reduction of imported forms of energy, and the conservation of the limited supply of fossil fuels, depends up on the utilization of all other available fuel energy sources. Biomass is a renewable energy source and represents a valid alternative to fossil fuels. The abundance of biomass ranks it as the third energy resource after oil and coal. Moreover, when compared to fossil fuels, biomass fuels possess negligible sulphur concentrations, produce less ash, and generate far less emissions in to the air. In other words, biomass can deliver significant greenhouse gas reductions in electricity, heat and transport fuel supply. The energy in biomass may be realized by different thermochemical technologies of which gasification is most promising alternative routes to convert biomass to power/heat generation and production of transportation fuels and chemical feedstock. This paper deals with the state of the art biomass gasification technologies, evaluating advantages and disadvantages, the potential use of the syngas and the application of the biomass gasification. Also, this paper provides short overview of the current status of the biomass gasification in Serbia.

Mathematical Modelling and Performance Analysis of a Small-Scale Combined Heat and Power System Based on Biomass Waste Downdraft Gasification

The paper presents a simple mathematical model for designing, optimizing and simulating small–medium CHP scale plant with use of biomass waste downdraft gasification. A downdraft gasifier has been used as the starting point in the study, due to its low tar content and effective way of using heat in the engine’s exhaust gases to dry and pyrolyze the different solid biomass waste. Hot water from the cooling circuit of the engine and from producer gas cooling is directly used for the district heating network, air or steam preheating. The mathematical model includes modelled components as a downdraft gasifier, an internal combustion engine using the characteristic equation approach method. The mathematical model enables the outputs of the plant to be evaluated and calculated for different types of biomass and operating conditions. The results demonstrate that it is a useful tool for assessing the performance of CHP plants using several types of biomass waste and enables comparisons to be made between operating conditions for real applications.

Experimental study on the efficiency of pulverized coal-fired steam boiler

The results of experimental investigation of pulverized coal combustion process with the aim to improve energy efficiency of an industrial steam boiler are presented in the paper. The investigation included measurement of combustion process parameters in four typical operating conditions, from minimum to maximum steam boiler load, and visualization of combustion process by using the camera with thermal imaging sensor. Several organizational and technical measures to improve energy efficiency of the industrial steam boiler are proposed and discussed in the paper. The measures are evaluated in terms of a possible reduction in the coal consumption and CO2 emissions.

Effect of small deviation of incident angle on thermal performance of parabolic-trough solar collector

The paper analyzes the effect of small deviation of incident angle relative to the focal plane on thermal performance of parabolic-trough solar collector. Decrease of solar collector thermal output is presented in form of coefficient of performance i.e. function of the incident angle deviation. In solar collector operation mode, working fluid (e.g. water) can become overheated. In that case, decreasing the thermal output would influence temperature drop of working fluid. Rotation of a parabola for a small angle relative to the focal plane will decrease the output thermal power of the solar collector. This analysis contributes to calculate deviation of incident angle relative to the focal plane in order to achieve the given thermal output for defined input parameters - collector type, local and real conditions (i.e. Sun position, orientation, time and date). In this paper, two-dimensional analytic geometry was used as a basic methodology for calculations and simulations.

Airflow measurements and mass and heat balance in a cardboard mill hall to approach energy efficiency

The results of field measurements conducted in Umka Cardboard Mill hall are presented in the paper. The points of interest were air temperature and humidity distribution inside the hall as well as the temperatures of the cardboard machine surfaces and inner walls of the hall. Temperature, humidity and velocity of air at supply-air openings were also measured. Based on the results material and heat balance of the hall was calculated and discussed. The aims of the study were to evaluate the thermodynamic properties and waste heat potentials of the air extracted from the hall by mechanical ventilation system.