Drying processes of lignites with high moisture content in packed and fluidized bed

Уклањање влаге из нискоквалитетних угљева се сматра важним поступком побољшања квалитета угља. У раду је приказан преглед тренутног стања технологија оплемењивања нискоквалитетних угљева, са посебним нагласком на процесе сушења као и одстрањивања влаге (у течном стању). Да би се израчунали значајни параметри процеса уклањања влаге развијен је и представљен модел конвективног сушења угља у флуидизованом слоју, заснован на двофазном моделу мехурастог флуидизованог слоја са гасом и честицама у суспензионој фази и гасом у мехурастој фази. Основна концепција развијеног модела је да се процес сушења у суспензионој фази разматра као за непокретни слој честица, коришћењем концепта "коефицијент сушења", при чему се врши прорачун за елементарне слојеве (запремине) и уопштава за цео слој честица. Мешање честица које се јавља у флуидизованом слоју урачунава се преко дифузионог члана у диференцијалним једначинама. Топлотна проводљивост непокретног слоја коју су дефинисали Zehner, Bauer и Schlünder је коришћена за дефинисање механизама преноса топлоте који се јављају у суспензионој фази флуидизованог слоја. Дискретизација система диференцијалних једначина извршена је нумеричком методом контролних запремина. Добијени систем линеаризованих алгебарских једначина је решаван помоћу ТДМА алгоритма (Три- Дијагонални Матрични Алгоритам). Релације зависне од материјала (пренос супстанције унутар чврсте фазе, равнотежно стање влаге између гасне и чврсте фазе), које се односе на одговарајућу врсту угља (лигнит Колубара), добијене су претходним истраживањима...Removal of moisture from low-rank coals is deemed an important quality upgrading method. An overview of the current status of low-rank coal upgrading technologies is presented in the paper, particularly with respect to drying and dewatering procedures. In order to calculate the significant parameters of the moisture removal process, a model of convective coal drying in a fluid bed, based on the two-phase bubbling fluidization model with gas and particles in suspension phase and gas in bubbling phase, is developed and presented. Basic assumption of the model is that the drying process in suspension phase is considered as for packed bed of particles by applying concept "drying coefficient", where the calculation is performed for elementary layers (volumes) and generalized for the entire bed of particles. The mixing of particles is calculated by means of diffusion term in the differntial equations. Effective thermal conductivity of the packed bed as defined by Zehner/Bauer/Schlünder is used to define heat transfer mechanisms occurring in the suspension phase of the fluid bed. A control volume numerical method is used for discretization of the differntial equations. Discretization equations have been solved by means of TriDiagonal-Matrix Algorithm. Product-specific data (intraparticle substance transfer, gas-solid moisture equilibrium) related to the particular coal variety addressed here (Kolubara lignite) are obtained through preliminary investigations. Тwo series of experimens in fluidized bed and one series in packed bed were performed. A completely new set of experimental results obtained has been successfully used to validate the model additionally. Comparison of obtained numerical simulation results and experimental results and results of other authors from available literature have shown a good agreement..

Optimization of the flue gas-flow controlling devices of the electrostatic precipitator of unit A4 in TPP "Nikola Tesla"

Homogeneity of the flue gas-flow through the chamber of an electrostatic precipitator is one of the basic influencing parameter on dedusting efficiency. This paper presents results of a multiobjective optimization study of the flue gas controlling devices of electrostatic precipitator of 324 MWe lignite fired Unit A4 of TPP "Nikola Tesla" in Serbia. The aim was to achieve better flow homogeneity in the cross-section of the precipitator compared to the original design. Additional constraints were to maintain the minimum as possible overall weight of the proposed design as well as pressure drop through the precipitator. Numerical simulations based on CFD were used to investigate dependence of the velocity distribution in the ducts and precipitator’s chamber with respect to the geometrical parameters of tested concepts of turning blades. A series of 22 detailed full-scale numerical models of the precipitator with different concepts of turning vanes designs were developed. Assessment of the flow field uniformity for each tested design was performed based on the analysis of several homogeneity parameters calculated for selected vertical cross-sections of the precipitator. After the reconstruction according to optimized design, results of measurements confirmed significant improvements of the velocity distribution in the vertical cross-sections of the precipitator, increase of dedusting efficiency and reduction of PM emission

Numerical simulation of thermo-fluid properties and optimization of hot water storage tank in biomass heating systems

Za potrebe zagrevanja 1 ha plastenika na poljoprivrednom dobru u Padinskoj Skeli, koje se nalazi u okviru PKB korporacije, izgrađen je grejni sistem sa kotlom na biomasu, u kome se toplota dobija sagorevanjem balirane sojine slame. Zbog nestacionarnih efekata zagrevanja pojavila se potreba za uključivanjem akumulatora toplote u sistem grejanja. Ovaj rad ima za cilj numeričku i eksperimentalnu studiju izvršenu sa ciljem optimizacije akumulatora toplote u predmetnom grejnom sistemu, kao i optimizaciju celokupnog grejnog sistema. U akumulatoru toplote kapaciteta 100 m3, u kome se skladišti zagrejana voda, izvršena su merenja u 256 tačaka, kako u stacionarnom tako i u nestacionarnom režimu rada kotla. Analiza optimizacije je izvršena numeričkom simulacijom koja je obuhvatala i stacionarne i nestacionarne režime. Dobijeni rezultati pokazuju dobro poklapanje rezultata dobijenih eksperimentom i numeričkom simulacijom.A 1.5 MW combustion facility burning large bales of soy straw has been built for the purpose of heating 1 ha of vegetable greenhouses located within the complex of Agricultural Plant PKB in Padinska Skela, Serbia. The paper addresses numerical and experimental study of temperature distribution in a cylindrical, 100 m3 (8 m high, 4 m in diameter) hot water storage tank. The water tank optimization, as well as optimization of the heating facility as a whole, were identified as the main goals of the study performed. Water temperature was measured by a temperature probe inserted in the tank. Measurements were conducted in 256 measurement points, both under steady and unsteady water flow conditions. Water tank optimization analysis was carried out utilizing both steady and unsteady state numerical simulation. The results obtained indicated good agreement between the experimental and computational data acquired

Prinos i komponente prinosa zrna stočnog graška u zavisnosti od tipa lista

A three-year small-plot trial (2000-2002) was established at the Rimski Šančevi Experiment Field of the Institute of Field and Vegetable Crops in Novi Sad to study pea genotypes with common and afila-type leaves. Used in the trial were three common cultivars (Javor, Tyrkys and Accord) and three afila-type ones (Jezero, Consort and Harmony). The highest average plant height (91 cm), first pod height (47 cm) and grain number per plant (37) were found in the cultivar Accord, while the largest number of pods per plant (10) were found in the cultivar Harmony. The greatest plant mass (14.1 g) was found in Jezero and the largest grain yield per plant in Tyrkys (7.3 g). Consort had the highest harvest index (0.57) and Harmony the largest grain yield per unit area (3.412 t ha-1).Trogodišnji (2000-2002) mikroogled sa genotipovima graška običnog i afila tipa lista bio je postavljen na oglednom polju Naučnog instituta za ratarstvo i povrtarstvo na Rimskim Šančevima. Obuhvatao je tri sorte običnog (Javor, Tirkis i Akord) i tri sorte afila tipa lista (Jezero, Konzort i Harmoni). Najvećom prosečnom visinom biljke (91 cm), visinom prve mahune (47 cm) i najvećim brojem zrna po biljci (37) odlikovala se sorta Akord, dok je najviše mahuna po biljci (10) imala sorta Harmoni. Najveća masa biljke (14,1 g) bila je kod sorte Jezero, a najveći prinos zrna po biljci kod sorte Tirkis (7,3 g). Sorta Konzort ostvarila je najveći žetveni indeks (0,57), a sorta Harmoni najveći prinos zrna po jedinici površine (3,412 t ha-1)

Proizvodnja semena lucerke u Vojvodini

The main production region of alfalfa seed in Serbia is the Vojvodina Province. Alfalfa seed production is estimated on 3000 ha, with average yield of 250 kgha-1 (Figure 1). Annual seed production in the Vojvodina Province is around 750 tons with estimated value of 1.7-2 million euros. The main characteristic of this production is significant seed yield variation (from 50 to 800 kgha-1), depending on climatic conditions, first of all rainfall amount and distribution (Figure 2). Because alfalfa plants are lush, they easily lodge after the stages of budding or flowering and produce a low seed yield. To ensure high and stable seed yields, it is necessary to prevent the luxuriant growth of alfalfa plants and their subsequent lodging. Cutting is the most effective practice to limit the luxuriant growth. Furthermore cutting may be used to time the beginning and duration of the stage of flowering, i.e., to synchronize the flowering with the maximum activity of pollinating insects, which is of key importance for seed yield performance in alfalfa. Variations in alfalfa seed yield level may be controlled to some extent by the cut system (Table 1). Late cuts ensures a reduced stand density and maximum number of productive shoots. Also, plant height is reduced and dry matter content in the stem significantly increased in relation to the systems of early and medium cuts (Table 2). Consequently, plant sensitivity to lodging is considerably reduced while conditions for alfalfa flowering and activity of pollinating insects are improved, which results in increased seed yield. Application of modern cultural practice in alfalfa seed production with average climatic conditions, resulting in seed yild of 350-400 kgha-1. In favourable climatic conditon it is posibele to achive 600-800 kgha-1 of alfafa seed.Proizvodnja semena lucerke u Srbiji najvećim delom locirana je u Vojvodini na oko 3.000 ha, sa prosečnim prinosom od 250 kgha-1. Prosečna godišnja produkcija semena u Vojvodini iznosi oko 750 tona, a vrednost ove proizvodnje procenjuje se na 1,7-2 miliona Eura. Osnovno obeležje proizvodnje semena lucerke u Vojvodini je veliko variranje prinosa od 50 do 800 kgha-1 u zavisnosti od vremenskih uslova godine (od količine i rasporeda padavina). Sistemom kosidbe semenskog useva moguće je smanjiti varijacije prinosa semena lucerke, odnosno moguće je u određenom stepenu ublažiti nepovoljno dejstvo uslova godine. Za proizvodnju semena najčešće se koristi drugi otkos na ranije zasnovanim (starim) lucerištima. Prvi otkos koristi se za proizvodnju krme, a kosi se u fazi punog cvetanja, odnosno u trećoj dekadi maja. Primenom svih neophodnih agrotehničkih mera, pri prosečnim ekološkim uslovima, postiže se prinos semena 350-400 kgha-1, a pri povoljnim uslovima može se dobiti 600-800 kgha-1

Iron status among blood donors deferred due to low haemoglobin level

Uvod/Cilj. Određivanje nivoa hemoglobin (Hb) je rutinski deo selekcije dobrovoljnih davalaca krvi. Prethodno publikovane studije pokazale su da se nedostatak gvožđa javlja kod redovnih davalaca krvi. Cilj ove prospektivne studije je bio da se utvrdi status gvožđa kod davalaca kod kojih je pre davanja utvrđen nizak nivo Hb i da se proceni stepen korelacije kapilarnih metoda, sa referentnom metodom određivanja Hb iz venske krvi, kao i sa i nivoom feritina. Metode. U periodu od februara 2017. do decembra 2018. godine, bilo je uključeno 200 dobrovoljnih davalaca sa niskim nivoima Hb, starosne dobi 19-64 godine (medijana 39 godina). Hb je određivan primenom metode bakar sulfat, kapilarnom metodom "HemoCue", i iz venske krvi u sklopu određivanja kompletne krvne slike (KKS). Nivo feritina određivan je primenom turbodimetrijske metode. Rezultati. Nizak nivo feritina utvrđen je kod 42,7% muškaraca i 57,3% žena (p = 0,008). U odnosu na nivo feritina lt 12 mg/L, odnosno gt 50 mg/L, zabeležena je značajna razlika između polova (p = 0,023, odnosno p = 0,022). Poređenje vrednosti Hb dobijenih kapilarnim metodama u odnosu na referentne vrednosti Hb, određene iz KKS, pokazalo je da metoda s bakar sulfatom daje lažno niske vrednosti Hb kod 10,5% slučajeva (p lt 0,001). Vrednosti Hb dobijene metodom "HemoCue-a" značajno su korelirale sa vrednostima Hb iz KKS, dok korelacija između nivoa feritina i Hb, određenog pomoću obe kapilarne metode, nije uočena. Zaključak. Kod 51,5% naših davalaca krvi koji su vraćeni zbog niskih vrednosti Hb utvrđen je snižen nivo feritina. Na osnovu ovih rezultata neophodno je odrediti algoritam za detekciju nedostatka gvožđa, dok je kapilarna metoda (HemoCue) pogodnija metoda za testiranje Hb pre davanja krvi.Background/Aim. Haemoglobin (Hb) determination is a routine part of the blood donor selection process. Previously reported studies have revealed that iron deficiency is common in frequent donors. This prospective investigation was aimed at examining iron status among blood donors with low circulating Hb and evaluating correlation between Hb values determined by capillary methods and those obtained by reference method from venous blood count (BC), as well as ferritin level. Methods. Between February 2017 and December 2018, 200 consecutively recruited regular blood donors with low Hb, aged 19 to 64 years (median 39), were included. Hb level was determined using the copper sulphate method, the HemoCue capillary method, and also from venous blood within the complete blood count (CBC) test. Plasma ferritin was determined turbidimetrically. Results. In 42.7% of men and 57.3% of women, ferritin concentration was low (p = 0.008). The relative numbers of males and females, with levels lt 12 mg/L (p = 0.023) or gt 50 mg/L (p = 0.022), differed. Comparison of the values obtained with the capillary methods with reference Hb levels obtained from the CBC test showed that the copper sulphate procedure gave false fails in 10.5% of cases (p lt 0.001). Hb values from HemoCue were significantly correlated with Hb values from the CBC test, but no correlation was observed between ferritin levels and Hb levels determined by both capillary method. Conclusion. Low ferritin was observed in 51.5% of Serbian blood donors deferred due to low Hb. Based on our results, the determination of the algorithm in the iron deficiency detection is necessary, while the capillary method (HemoCue) represents a more convenient method for Hb testing prior to blood donation

Numerical Analysis of the Flue Gas-Coal Particles Mixture Flow in Burners Distribution Channels with Regulation Shutters At the Tpp Nikola Tesla-A1 Utility Boiler

Pulverized coal particles concentration distribution across the burners distribution channels, especially where plasma torches are installed, is one of the key issues for efficient implementation of plasma system for liquid fuel free combustion support at the pulverized coal fired boilers. The possibility of pulverized coal particles concentration increase at the lower burner channels of TPP Nikola Tesla - A1 boiler using regulation shutters is analyzed experimentally and numerically. Subject of present work is two-phase flue gas-particles mixture flow in burners distribution channels with regulation shutters installed at the TPP Nikola Tesla A1 boiler. Aim of this work is to optimize position of implemented system of shutters to achieve desired concentration and velocity distribution in channels with plasma torches, using numerical modelling. Experimental investigation was performed for the verification of proposed mathematical model for the prediction of the analyzed two-phase flow. Based on verified model, numerical parametric analysis was done. Obtained results of gas phase velocity field. coal particles concentration field, velocity and concentration profiles clearly show the dependence between shutters position and the coal particles mass flow rate and concentration distribution at the outlet cross-section of the burners distribution channels. According to the numerical optimization results suitable modification of the shutter system is proposed

Pljevlja lignite carbon emission charateristics

The anthropogenic emission of GHG especially CO has to be limited and reduced due to their impact on global warming and climate change. Combustion of fossil fuels in the energy sector has a dominant share in total GHG emissions. In order to reduce GHG emission, European Union established a scheme for GHG allowance trading within the community, and the implementation of the European Union emission trading scheme, which is a key to GHG reduction in a cost-effective way. An important part of emission trading scheme is prescribed methodology for monitoring, reporting, and verification of the emission of GHG including characterization of the local fuels combusted by the energy sector. This paper presents lignite characteristics from open-pit mine Borovica-Pljevlja, which has highest coal production in Montenegro (>1.2 Mt per year), including evaluation of its carbon emission factor based on the laboratory analysis of 72 coal samples. Testing of the samples included proximate and ultimate analysis, as well as, net calorific value determination. In accordance with the obtained results, linear correlations between net calorific value and combustible matter content, carbon content and combustible matter content, hydrogen content and combustible matter content, carbon content and net calorific value, were established. Finally, the non-linear analytical correlation between carbon emission factor and net calorific value for Pljevlja lignite was proposed, as a base for the precise calculation of CO emission evaluation

Determination of mutual ratios for specific activity in coal, slag and fly-ash samples from “Kolubara” power plant

Ugalj,iporedsve intenzivnijeg razvoja i korišćenja obnovljivih izvora energije, ima i dalje značajnu ulogu u proizvodnji električne energije širom sveta. U Republici Srbiji prema godišnjem izveštaju “Elektroprivrede Srbije” za 2013. godinu u termoelektranama, čije jepogonsko gorivo lignit, proizvedeno je 26 537GWhod ukupno37 433 GWh električne energije[1]. Proizvodnja uglja, koji se koristi u termoelektranama “Elektroprivrede Srbije”, odvija se na površinskim kopovima rudarskih basena Kolubara (75 %) iKostolac(25 %) [2].Coal as the fossil fuel contains naturally occurring radionuclides and belongs toNORM (Naturally Occurring Radioactive Materials). On the other hand, slag and fly-ash belong to TENORM (Technically Enhanced Naturally Occurring Radioactive Material), and if they are released into the environment an increase and/or redistribution of natural radionuclide content can occur. For the purposes of this study, six sets of samples (18 in total) of “Kolubara” coal, slag and fly-ash were collected during the periodical emission tests in May 2012th at steam boilers K3 and K4 of TPP “Kolubara”, Serbia. Coal, slag and fly-ash samples were prepared for analysis (milled, dried, sieved and weighed) by appropriate standard methods. Prepared samples were placedin 125 mL PVC cylindrical boxes, weighted and sealed with natural wax. Sealed samples were measured with a semiconductor HPGe spectrometer (37 % relative efficiency) after the radioactive equilibrium was reached. The obtained values of specific activity for coal (Ac), slag (As) and fly-ash (Af) do not differ significantly compared to the values available in the literature. Analysis of determined mutual ratiosAs/Ac andAf/Ac are consistent, taking into account uncertainties ofactivity concentrations, with values of approximately 2 and 4, forK3, and1.5 and 4, forK4. Discrepancies were notedonly for40K (bothsteam boilers) ofAs/Ac.Results indicate that further investigation with more samples should be undertaken, and also correlation between radiological and proximate analysis should be determined.Zbornik radova 10. simpozija Hrvatskog društva za zaštitu od zračenj

Investigation of Pressure Pulsations in the Furnace and Flue Gas Tract of the Pulverized Coal Combustion Utility Boiler

The paper presents new experimental method developed and new measuring system developed and installed into flame-gas tract of utility boiler. Investigations have been performed at the steam boiler of unit 2 at TPP Ptolemais. Ptolemais, Greece. which suffered from very unstable combustion and great pressure oscillations Experimental method. based on high-speed acquisition system. was developed and used for detection of pressure oscillations and determination of the origin of boiler unstable operation. Signals were obtained from piezoelectric pressure sensors located along the flame-gas tract of the steam boiler and time and frequency domain analysis were used for post processing of collected data. Investigations of the pressure oscillations in boiler gas tract have contributed to reveal origin of the boiler unstable operation. and have been of the great help in establishing proper boiler operatio