Exergy optimization rotary kiln calcination

Energetski bilans rotacione peći za kalcinaciju dolomita u preduzeću za proizvodnju magnezijuma identifikovao je plašt peći (26,35% od ulazne energije) i produkte sagorevanja (18.95%), kao glavne izvore toplotnih gubitka. Da bi se smanjio gubitak toplote, u zoni kalcinacije koristi se razmenjivač toplote koji formira strujni prostor prstenastog oblika između plašta peći i unutrašnje površine razmenjivača. Predloženo rešenje je: brzo primenljivo, profitabilno (prost period otplate je manji od 6 meseci), omogućava iskorišćenje konvektivnih i zračnih gubitaka toplote sa plašta peći, sprečava pregrevanje peći, ne narušava njene tehnološke parametre rada, ne zahteva povišeni pritisak vazduha i može se primeniti na različitim vrstama rotacionih peći sa sličnim površinskim raspodelama temperatura. Razvijeni matematički model omogućava da se dobije geometrija razmenjivača toplote tako da se od peći oduzima samo ona količina toplote koju rotaciona peć bez njega predaje okolini. Primena rekuperatora smanjuje potrošnju goriva za 12,00%, i povećava energetski za 7,35% i eksergijski stepen korisnosti za 3,81%. U radu je razvijen program na osnovu koga su dimenzionisani rekuperatori kontinualne geometrije za slučajeve kada se za sagorevanje u rotacionoj peći koristi vazduh obogaćen kiseonikom. Rezultati su pokazali da se rekuperator na ispitivanoj peći ne može primeniti ukoliko se za sagorevanje u njoj koristi vazduh obogaćen sa više od 24% kiseonika. Obogaćivanje vazduha za sagorevanje kiseonikom praćeno je blagim povećanjem energetskih i eksergijskih stepena korisnosti peći sa i bez rekuperatora toplote. Od analiziranih mogućnosti za korišćenje otpadne toplote u dimnim gasovima za: zagrevanje vazduha i vode, zagrevanje vode u kombinaciji sa rekuperatorom i proizvodnju električne energije u sistemu kogeneracije organskim rankinovim ciklusom, poslednje rešenje pokazalo se kao energetski, eksergijski i ekološki najprihvatljivije.The energy balance of a rotary kiln used for calcination of dolomite in a magnesium production company identified the kiln shell (26.35% of the input energy) and exhaust gases (18.95%) as the major sources of heat losses. To decrease the heat loss, a heat exchanger that forms an annular duct over the calcination zone of the kiln is used to preheat combustion air. The exchanger uses both the convective and radiant heat loss from the mantle, prevents overheating, does not require air tightness, and could be implemented over rotary kilns with the similar surface temperature distribution. A mathematical model that defines the geometry of the heat exchanger so as the heat transfer from the kiln to the combustion air to be equal to the heat dissipated from the bare kiln is presented. The exchanger decreases fuel consumption of the kiln for 12.00%, and increases its energy and exergy efficiency for 7.35% and 3.81%, respectively. To obtain a better performance the airflow and geometry of the exchanger should be arranged to achieve the smallest possible temperature difference between the kiln surface and the preheating air, whose amount should always be kept at the optimal value for the used fuel. In the thesis, the software that determines the continual geometry of the recuperator was developed for the case when low oxygen-enriched air is used for fuel combustion inside the kiln. The recuperator can not be implemented over the kiln when the combustion air is enriched with more than 24 vol% of oxygen. The air enrichment causes a slight increase in energy and exergy efficiencies of the kiln whether it uses or not the recuperator. Several systems that utilize the sensible heat of the kiln exhaust gases for: (i) central heating, (ii) combustion air preheating, (iii) central heating for the case when the kiln operates with the recuperator, and (iv) cogeneration with the organic Rankine cycle were analyzed. Among these systems, the cogeneration system is energetically, exergetically, and ecologically the most suitable solution

EKSERGIJSKI STEPEN KORISNOSTI PRI SAGOREVANJU I GASIFIKACIJI BIOMASE

U radu je izvršena uporedna analiza eksergijskih stepena korisnosti pri sagorevanju biomase i gasovitog goriva koje nastaje u procesu istosmerne gasifikacije. Uporedna anliza je pokazala da se viši eksergijski stepen korisnosti ostvaruje sagorevanjem gasovitog goriva, odnosno da termičku transformaciju biomase treba obaviti nakon potpune gasifikacije u reaktorima istosmernog toka, i naknadnim sagorevanjem gasa u spregnutom sistemu istosmerni reaktor – ložište za sagorevanje.Publishe

POVEĆANJE STEPENA KORISNOSTI KOTLA KONTROLOM PROCESA SAGOREVANJA I KORIŠĆENJEM GORNJE TOPLOTNE MOĆI GORIVA

U radu je izvršena analiza korićšenja fizičke toplote gasovitih produkata za povećanje stepena korisnosti kotla i smanjenje emisije štetnih polutanata. Rezultati analize su pokazali da se korišćenjem gornje toplotne moći goriva stepen korisnosti kotla može povećati do 16%.Publishe

PRIMENA KONVEKTIVNOG REKUPERATORA ZA KORIŠĆENJE OTPADNE TOPLOTE STAKLARSKE PEĆI

U radu je prikazano toplotno postrojenje za korišćenje otpadne toplote koja nastaje u procesu proizvodnje staklenih vlakana. Rezultati materijalnog i toplotnog bilansa dobijenih na osnovu eksperimenta pokazuju da se korišćenjem fizilke toplome može smanjiti toplotnog gubitka sadržan u toploti produkata za 63%.Publishe

Analysis of the performance of the shell and tube heat exchanger: Influence of the baffles and the position of fluid inlet and outlet

The constant need for heat exchangers that are easy to manufacture and maintain, and that have a standardized and already known manufacturing technology, has led to the fact that shell and tube heat exchangers are one of the most common devices used in the process industry. In this paper, the analytical and numerical models of the basic shell and heat exchanger have presented with dimensions of 3750 x 1000 mm and a nominal heat capacity of 410 kW. Using the flow simulation, the influence of different numbers and arrangement of baffles and the changing the position of the inlet and outlet of warmer fluid are considered. The temperatures of the fluids on the inlet and outlet are taken into account as the main parameters for heat exchanger performance. From obtained results, it can be concluded that with the increase in the number of baffles, the performance of the heat exchanger is increased. The position of the inlet and outlet of the warmer fluid greatly influence the heat exchanger performance.Publishe

THE MODEL FOR DETERMINATION OF THE TEMPERATURE AND THE GAS COMPOSITION OF BIOMASS GASIFICATION PRODUCTS BY THE USE OF MATERIAL AND ENERGY BALANCES

The paper presents the model for the analytical determination of the temperature and the gas composition of biomass gasification products in downdraft gasification reactors at atmospheric pressure. The temperature and the gas composition were determined by the use of material and energy balances.http://www.hm.kg.ac.rs/Publishe

Energetic and Exergetic Evaluation of 4 Systems for a Rotary Kiln Improvement

The energy balance of a rotary kiln used for calcination of 4400 kg/h of dolomite in a magnesium production company identified the kiln shell (26.35% of the input energy) and exhaust gases (18.95%) as the major sources of heat losses. To increase the efficiency of the kiln, the following systems are analyzed by the use of energy and exergy analysis: (i) system for preheating of the combustion air by heat exchange with the exhaust gas; (ii) system for space and DHW heating in the company by water heating with the exhaust gas sensible heat; (iii) system that consists of a recuperator that use sheat loss from the kiln shell to preheat the combustion air (designatedas iii-a) and the system given in (ii); and (iv) system that consists of (iii-a) and an cogeneration system that uses organic Rankine cycles upplied with heat by heat exchange with the exhaust gas. The system (ii) is the optimal solution by economic criteria because the company uses relatively expensive heavy fuel oil for space heating, where as exergetically, the most efficientis the the system (iv), which enables the kiln to have the exergetic efficiency of 36.02%.https://www.hm.kg.ac.rs/documents/Proceedings2014.pdfPublishe

Design improvement of a side water intake on a small hydropower plant

This paper deals with the problem of flow distribution at the water intake of a small hydropower plant (SHPP). The plant, with the capacity of 1.25 MW, has been in operation since the end of 2013. At the side intake of the SHPP an uneven distribution of water flow in three parallel chambers of a settling basin has been observed. This anomaly has been noticed during the rinse of different chambers of the settling basin. Each chamber precipitated different amounts of sand. In this paper, water intake is simulated using computational fluid dynamics (CFD) and a technical solution for equalizing flow in three chambers of the settling basin is recommended. The solution should be characterized by: minimal price, simplicity and the lowest possible pressure drop.Publishe

The proposal of the recuperator design for the rotary kilns with a driving mechanism in the calcination zone

The rotary kilns have been used in the industry in various applications, mostly in the cement industry and for calcination of dolomite ores. The rotary kilns characterize the high-temperature processes and therefore the heat losses are very high. In the order to increase the efficiency of the kiln and reduce fuel consumption, several different designs of recuperators are developed. One of the problems in the design of the recuperator is the position of the driving mechanism or tyre of the rotary kiln. This paper has presented a solution of the two separated recuperators in order to resolve the previous mentioned problems and increase the overall efficiency of the rotary kiln. The analytical model has been used for the determination of the geometry and heat losses of the recuperator while the CAD model has been used for the calculation of the heat losses and analysis of the airflow in the recuperator. The results obtained from both models have shown a good correlation and show that with the presented two-part recuperator design is possible to increase the efficiency of the rotary kiln when the driving mechanism or tyre is placed on the kiln shell in the calcination zone.Publishe

Optimization of the Flow Schemes in Radiant Recuperators

In glass production and metallurgical processes, radiant recuperators are used to preheat combustion air by heat exchange with high temperature flue gases. For these recuperators, the most popular is concurrent flow arrangement, which compared to other solutions has the lowest interface temperature and the longest lifetime. Compared with concurrent, radiant countercurrent recuperators have only one drawback: the interface temperature is higher at the flue gas entrance. Their comparative advantages are: lower average interface temperature, higher efficiency and smaller pressure drop. Compared with pure concurrent and countercurrent radiant recuperators, designs with double air annulus are slightly more efficient and have a bit smaller interface temperatures, whereas cost and pressure drop are their disadvantages. In the paper, all these four flow configurations are combined by the division of airflow and by the use of different airflow schemes. The improved design is a combination of a countercurrent and a concurrent radiant recupreators. Depending on the geometry, there is an optimal airflow division in the combined recuperator. For the analysis, a cell modeling method validated on a 15 m high, concurrent radiant recuperator used in a glass fiber production process is used. Different solutions are analyzed comparing their effectiveness, energy and exergy efficiencies, and interface temperatures.Publishe