Abstract Increasing efficiency is a necessary target for an industrial roaster nowadays. This thesis presents some studies on efficiency improvement in the zinc roasting process - process characterisation, control design, implementation and testing. The thesis focuses on the roaster, i.e. on research regarding the phenomena in the roaster furnace. By learning more about the roasting mechanism, particle size growth and dynamics of the furnace, new control implementations have been developed. More measurements, analyses and calculated variables have been added to give more information on the state of the furnace. New control variables have been introduced to give the operators more opportunities to set the conditions so that they are more suitable for the actual concentrate feed mixture. Equipment modifications have also been done. In this research, both laboratory and plant experiments have been performed together with thermodynamic evaluations and calculations. It has been necessary to make plant trials in order to obtain information about the impacts of different variables on the process. Only full-scale experiments give reliable results of the behaviour of an industrial furnace. The experiments with the roaster furnace have emphasised the study of both the metallurgy and the dynamics of the roasting process. The on-line calculated oxygen coefficient and its active control have proved important. The particle size distribution analysis of the furnace calcine has been shown to be a significant source of information for evaluating the state of the roasting furnace. The main target is to improve the economic performance. The key is to be able to be flexible in using different kinds of raw materials, because the main income is the treatment charge. The trend is that concentrates are becoming finer, which increases the challenges for roaster furnace control. The capability to use low-grade concentrates is also a major challenge and improves the economic result. Research and development on the boiler and mercury removal has also been part of this work for many reasons. Improved boiler performance and mercury removal gives more freedom in choosing concentrates and operating the roaster furnace. The approach has been the same as in the roaster furnace research and development work. Control improvements based on existing knowledge, such as fuzzy control systems for controlling the furnace temperature and mercury removal, did stabilize the process, but they did not solve all the problems regarding process stability. The research and development concept of this thesis has provided the extra knowledge needed for further improvement of process control. The results of the process characterisation have led to the implementation of a new and effective control strategy. The research and development carried out has improved performance in a number of ways: increased running time of the furnace and boiler, in-depth knowledge of roasting phenomena which led to new control methods and instructions for the operators, improved quality of sulphuric acid and a method to control its quality, measurements and analyses that give valuable information of the state of the process – all of which are now in use. In the future, the emphasis will be placed on the research and development of roaster furnace performance, which will be a great challenge. Control of the roaster furnace is the key to the economic success of the roasting process and more information about these phenomena is needed for improving and optimising control.

<p>Na na&scaron;im prostorima napitak crne kafe veoma je cijenjen i ima dugu tradiciju pripreme i konzumiranja. Izborom optimalnih parametara procesa prženja u industrijskim uslovima proizvodnje i definisanjem recepture, nastoji se postići odgovarajući kvaliteta, odnosno najprihvatljivija senzorska svojstava napitka kafe. Da bi kafa na određenom trži&scaron;tu zadovoljila želje i očekivanja poro&scaron;ača, potrebno je definisati parametre kvaliteta kafe za potrebe svakog ciljnog trži&scaron;ta. Primjenom deskriptivne senzorske analize moguće je dati precizan opis arome, ukusa i boje napitka kafe, kao najvažnijih senzorskih svojstava, sa značajnim uticajem na kvalitet i prihvatljivost kvaliteta.<br />Cilj ove doktorske disertacije je postizanje optimalnog senzorskog kvaliteta napitka crne kafe definisanjem parametara procesa prženja kafe u industrijskim uslovim proizvodnje i definisanjem optimalnog odnosa kafe vrste Arabika i kafe vrste Robuste, kao i definisanje senzorskog profila i sistema senzorskog ocjenjivanja napitka crne kafe koji se priprema na tradicionalan način.<br />Da bi se definisali parametri procesa prženja, neophodno je odrediti optimalnu temperaturu prženja, koja će omogućiti razvoj i formiranje prijatnih senzorskih svojstava u zrnu kafe. Za pripremanje napitka crne kafe na tradicionalan način obično se koriste dvije vrste kafe, Arabika i Robusta u različitom odnosu.<br />Na osnovu rezultata dobijenih hemijsko-fizičkim analizama uzoraka različitih vrsta kafa i mje&scaron;avina na različitim temperaturama prženja i senzorskom analizom napitka kafe pripremljenog od ispitivanih uzoraka kafe na tradicionalan način, sa ciljem pobolj&scaron;anja kvaliteta napitka kafe izborom optimalnih uslova prženja i odnosa različitih vrsta kafe može se zaključiti da uzorci napitka kafe pripremljeni od uzoraka proizvedenih prema proizvođačkoj specifikaciji nemaju očekivani kvalitet napitka kafe, kao i da proizvodnjom uzoraka pojedinačnih vrsta kafe pržene na 167&deg;C i 175&deg;C i njihovih mje&scaron;avina nije postignut optimalni kvaliteta napitka kafe. Takođe je zaključeno da je uzorak napitka kafe pržene na 171&deg;C N1 ocjenjen kao uzorak najboljih senzorskih svojstava (82,35%). Odnos kafa Arabika II klasa, Arabika I klasa i Robusta je bio 34,28%:51,42%:14,30%. Vrijednost titracione kiselosti iznosila je 128,86, sadržaj hlorogenske kiseline 3,77%, sadržaj kofeina 2,29%, sadržaj proteina 13,79%, sadržaj slobodne masti 14,37%, odnosno sadržaj ukupno zasićenih masnih kiselina 42,65%, a sadržaj ukupno nezasićenih masnih kiselina 57,36%, vrijednost pH 5,35 i aktivnost vode 0,102. Antioksidativna aktivnost je iznosila 235,57 &mu;mola TE/g uzorka (DPPH) i 217,62 &mu;mola TE/g uzorka (ABTS).<br />Uzorak U1 napitka kafe pripremljen na tradicionalan način od mje&scaron;avine kafe pržene na 171&deg;C, sitno mljevene okarakterisan je kao veoma prijatan za konzumiranje, sa najskladnijim aromatskim profilom, usagla&scaron;ene gorčine i kiselosti, prijatne i umjerene punoće ukusa i blagog i harmoničnog utiska u ustima. Odnos kafa Arabika II klasa, Arabika I klasa i Robusta u ovom uzorku je bio 34,28%:51,42%:14,30%.</p> / <p>Consumption of black coffee prepared in a traditional way is very popular in our region. By selecting the optimum parameters of roasting in industrial conditions and defining ratio of the individual species of coffee, it aims to achieve the appropriate quality, and the most acceptable sensory properties of a coffee beverage. In order to fulfill consumers expectations, it is necessary to define the parameters of quality coffee for the needs of each target market. Using descriptive sensory analysis it is possible to give a precise description of the aroma, taste and color of coffee beverage, as the most important sensory characteristics, with significant impact on the quality and acceptability of quality.<br />The aim of this PhD thesis was to achieve optimal sensory quality black coffee beverage, by defining the parameters of the coffee roasting within the industrial conditions and defining the optimal ratio of coffee Arabica and Robusta species, as well as defining a sensory profile and the system of sensory analysis black coffee beverage which was prepared on traditional way.<br />In order to define the parameters of the roasting process, it is necessary to determine the optimum temperature of roasting, which will enable the development and formation of pleasant sensory properties of coffee beans. For the preparation of coffee beverage in the traditional way, usually used two species of coffee, Arabica and Robusta in different ratio. Based on the results of chemical and physical analysis of coffee samples (different species and blends) at different roasting temperatures and results of sensory analysis of a coffee beverage prepared from coffee samples in the traditional way, with the aim of improving the coffee beverage quality, by determining optimal conditions of roasting and ratio of different species of coffee, it could be concluded that the samples of coffee beverage prepared from samples produced according to the production specification do not had the expected quality of coffee beverage. It also could be concluded that by production of individual species of coffee samples roasted at 167 and 175&deg; C, and their blends was not reached optimal quality of coffee beverage. It was also concluded that the coffee beverage of sample roasted at 171C, N1 was rated as the sample of the best sensory properties (82.35%). The ratio of coffee Arabica Class II, Arabica Class I and Robusta was 34.28%: 51.42%: 14.30%. Value of titratable acidity was 128.86, chlorogenic acid content was 3.77%, caffeine content was 2.29%, protein content was 13.79%, the content of free fat was 14.37%, total content of saturated fatty acids was 42.65%, and total content of unsaturated fatty acids was 57.36%, pH value was 5.35 and aw value was 0.102. The antioxidant activity was amounted 235.57 &mu;mol TE/g sample (DPPH) and 217.62 &mu;mol TE/g sample (ABTS).<br />Coffee beverage prepared in the traditional way from a sample U1 roasted at 171 &deg;C, finely ground, was characterized as very pleasant, with the most harmonious aromatic profile, pleasant bitterness and acidity, pleasant and moderate body and gentle and harmonious impression in the mouth. The ratio of coffee Arabica Class II, Arabica Class I and Robusta in this sample was 34.28%: 51.42%: 14.30%.</p>