PROCJENA UTJECAJA SADRŽAJA VLAGE U UGLJENOJ PRAŠINI NA PREDVIĐANJE INDEKSA NJEZINE EKSPLOZIVNOSTI

Exploring the mechanism of coal dust explosions is essential for the development of safety techniques to prevent coal dust explosions. An explosion index can be used to estimate explosion severity. In this study, the moisture content parameter, one of the intrinsic characteristics of coal dust, was used to estimate the explosion index. For this purpose, 32 samples of coal with different moisture content were collected from different mines in Iran and were prepared as coal rounds. The coal dust explosion process was carried out in a 2-litre closed chamber. After determining the most important and influential parameters, prediction models of the explosion index were presented using linear regression. For this purpose, 75 percent of data was randomly assigned for training and 25 percent of data was used for testing and validation. The performance of these models was assessed through the root mean square error (RMSE), the proportion of variance accounted for (VAF), the mean absolute percentage error (MAPE) and the mean absolute error (MAE). Then the results of the laboratory method were compared with the results of the regression model. The results show that there is a good correlation between the laboratory results and the predictive model obtained through linear regression analysis.Istraživanje eksplozivnosti ugljene prašine iznimno je važno kod razvoja sigurnosnih tehnika za sprječavanje eksplozije ugljene prašine. Indeks eksplozivnosti koristi se za procjenu težine (snage) eksplozije. Pri tomu je sadržaj vlage jedna od intrinističkih varijabli same prašine izravno rabljena za izračun indeksa. U istraživanju su analizirana 32 uzorka različitoga sadržaja vlage prikupljena u različitim iranskim rudnicima. Eksplozivnost prašine ispitana je u dvolitarskim zatvorenim komorama. Određeni su najvažniji, tj. najrizičniji, parametri kojima se predviđa indeks eksplozivnosti uporabom linearne regresije. Skup od 75 % podataka, slučajno odabranih, uporabljen je za uvježbavanje, a 25 % za provjeru. Kvaliteta modela ispitana je korijenom srednje kvadratne pogrješke, udjelom varijance, srednjom apsolutnom postotnom i srednjom apsolutnom pogrješkom. Uspoređeni su rezultati laboratorijskoga testiranja i oni linearne regresijske analize

SIMULTANI UČINAK VLAGE I PIRITA NA SPONTANO IZGARANJE UGLJENA ANALIZIRAN METODAMA TPT I R70

Among fossil fuels, coal is the most widely used all over the world for generating power and electricity and it is a stable source of energy. Despite all these benefits, coal mining has serious hazards, such as coal spontaneous combustion. There are many factors that influence the tendency for coal to spontaneously combust in coal mines. Pyrite can promote the risk of this phenomenon. This promotion is accelerated by the combination of pyrite and moisture content at the same time. This combination is very rarely discussed in literature. So, in this research, the accelerating effect of reactive pyrite and moisture content on coal spontaneous combustion was measured experimentally using crossing point temperature (CPT) and R70 test methods. For this purpose, a new experimental apparatus was assembled and made in Iran. Reaction rate data obtained from the experimental results showed that pyrite has a twofold action. It first catalyzes the oxidation reaction. Then, in a moist environment, pyrite is itself oxidized, which provides a secondary heat source, and so accelerates the process of coal spontaneous combustion. Since the pyrite oxidation reaction consumes moisture, there is a mutual effect of accelerated heating as less heat is used up in moisture evaporation. The results show that pyrite content can linearly accelerate the coal spontaneous combustion process, while moisture content under 20% increases it, and if the moisture exceeds 20%, the rate of this process is reduced. The results of this research are helpful in the assessment and management of coal spontaneous combustion issues in coal mines.Ugljen je stabilan izvor energije i ujedno najčešće korišteno fosilno gorivo za proizvodnju električne energije u svijetu. Unatoč brojnim koristima, eksploatacija ugljena sa sobom nosi i ozbiljne rizike kao što je spontano izgaranje (samozapaljenje) u rudnicima. Brojni čimbenici utječu na sklonost ugljena samozapaljenju. Pirit može povećati rizik samozapaljenja, a u kombinaciji s vlagom rizik dodatno raste. Takva kombinacija rijetko je opisana u literaturi. Stoga je ovim istraživanjem prikazano ubrzanje učinka reaktivnosti pirita i vlage na samozapaljenje. Oni su izmjereni primjenom točke prijelazne temperature (TPT) i testa R70. U tu svrhu u Iranu je osmišljen i izrađen novi uređaj. Prikazani su eksperimentalni podatci brzine reakcije pri čemu pirit ima dvostruko djelovanje. Najprije katalizira oksidacijsku reakciju, a zatim u vlažnome okruženju i sam oksidira postajući tako sekundarni izvor topline te na taj način ubrzava samozapaljenje ugljena. Budući da oksidacija pirita troši vlagu, postoji zajednički učinak ubrzavanja zagrijavanja, a manje topline troši se na isparavanje vlage. Rezultati su pokazali da sadržaj pirita može linearno ubrzati proces spontanoga izgaranja ugljena, dok ga sadržaj vlage manji od 20 % ubrzava, a veći od 20 % usporava. Rezultati ovoga istraživanja korisni su pri procjeni i upravljanju spontanim izgaranjem ugljena u rudnicima

SIMULACIJA DOSTUPNOSTI I ANALIZA RADA OKLOPNOGA TRANSPORTERA U ŠIROKOČELNOME RUDARENJU

Since coal mining production systems are very complex, repairing equipment is expensive. If a system failure occurs, it will cause disturbances such as inoperable equipment, reduced operating time, increased production costs, and reduced equipment performance. Therefore, it is necessary to consider the availability of the coal mining industry more than ever. For this purpose, the Armored Face Conveyor (AFC) machine failure data was gathered over a period of 29 months from the Tabas Coal Mine. Descriptive statistics, trends, and serial correlation tests of the data were calculated. Then, the system’s mean and point availability were simulated. Based on the results, the mean availability (all events) and point availability (all events) at 360000 h are 96% and 95%, respectively. The mean time to first failure (MTTFF) of the AFC machine was about 23.61 h. The ReliaSoft Failure Criticality Index, ReliaSoft Downing Event Criticality Index, and ReliaSoft Downtime Criticality Index electrical equipping have the largest effect, whereas the main drive subsystem is the least important. Analysis showed that availability has a direct correlation to activity management and improvements in the quality, efficiency, and the product extraction.Sustavi proizvodnje ugljena u rudnicima vrlo su složeni, stoga je i popravak opreme skup. Kvar sustava uzrokovat će smetnje kao što je nedostupna oprema, smanjeno vrijeme rada, povećani troškovi proizvodnje i smanjene performanse opreme. Stoga je nužno da se dostupnost industrije ugljena razmatra više nego ikad. U tu svrhu 29 mjeseci prikupljani su podatci o kvaru stroja tipa oklopljenoga širokočelnoga transportera iz rudnika ugljena Tabas. Izračunane su opisna statistika, trendovi i test serijske korelacije podataka. Zatim su simulirane srednje vrijednosti i dostupnost bodova u sustavu. Na temelju rezultata prosječna dostupnost (svi događaji) i dostupnost točke (svi događaji) na 360 000 h iznose 96 % odnosno 95 %. Prosječno je vrijeme do prvoga kvara (MTTFF) transportnog stroja oko 23,61 h. U trima metričkim vrijednostima, ReliaSoft indeksu kritičnosti kvara, ReliaSoft indeksu kritičnosti pada sustava i ReliaSoft indeksu kritičnosti zastoja, električno opremanje ima najveći učinak, dok je glavni pogonski podsustav najmanje važan. Utvrđeno je da analiza dostupnosti kontrolira upravljanje operacijama i poboljšanja u kvaliteti, učinkovitosti i izvedbi linije

AN INVESTIGATION OF THE EFFECT OF TOUGHNESS AND BRITTLENESS INDEXES ON AMPERE CONSUMPTION AND WEAR RATE OF A CIRCULAR DIAMOND SAW

Cirkularna dijamantna pila (skr. CDP) jedan je od glavni reznih strojeva ukrasnoga kamena. Predviđanje svojstava rada toga stroja važno je u procjeni troškova i planiranju rada. Svojstva takvih pila ovise o nekoliko važnih čimbenika koji se odnose na obilježja alata, svojstva stijena i stupnja trošenja prilikom rada. Prikazan je odnos između potrošnje struje, indeksa lomljivosti i čvrstoće, tj. otpornosti na trošenje kod takvih pila. Eksperiment je načinjen uporabom potpuno praćenoga rezanja 14 različitih uzoraka tvrdih stijena, uz stalnu brzinu te dubinu ureza. Trošenje, tvrdoća i lomljivost procijenjeni su jednostavnom i višestrukom regresijom, a zatim su izračunana predviđanja. Postoji znatna korelacija između trošenja, utroška struje i čvrstoće. Trošenje samih CDP-a može se pouzdano procijeniti uporabom višestruke regresije, koja se temelji na potrošnji struje i čvrstoći.The circular diamond saw (CDS) is one of the major sawing machines in dimension stone processing plants. Predicting the performance of a circular diamond saw is very important to estimate the cost and the planning of the stone processing plants. The performance of a CDS depends on some important factors such as machine and tool characteristics, physical and mechanical characteristics of rock and tool wear rate. In this research, it is aimed to investigate the relationship between ampere consumption, brittleness indexes and toughness with the wear rate of a CDS. This aim was pursued by using a fully instrumented cutting rig to cut 14 types of hard rock at constant feed rates, cut depths and peripheral speeds. Wear rate, toughness and brittleness indexes were evaluated using simple and multiple curvilinear regression analysis and predicted models were developed. The results indicated that there is a significant correlation between wear rate, ampere consumption and toughness. It is concluded that, the wear rate of a CDS can be reliably estimated using a multiple curvilinear model which includes ampere consumption and toughness

ISPITIVANJE ULOGE SADRŽAJA VLAGE NA SPONTANO IZGARANJE UGLJENA

The percentage of moisture content is one of coal’s inherent characteristics, which has a crucial aspect in the occurrence of the spontaneous combustion of coal (SCC) and has long been an attractive issue for analysis among scientists. A complete understanding of this phenomenon helps experts in the prediction and prevention of its occurrence. For this reason, the present work predicts this phenomenon based on moisture content. Thus, a final conclusion about the effect of this parameter was determined. Fifty-one coal samples with different percentages of moisture content were collected from underground coal fields in Iran for the practice training and testing of crossing point temperature (CPT) and R70 test methods. Then, the method of regression analysis was used for modelling and predicting the SCC tendency. The results showed that coal samples were oxidized most rapidly when the moisture content supply was under 20%, and it can reduce the prevalence of the SCC in situations when the moisture was in excess of 20% because the heat released by oxidation is used to evaporate the moisture. For validation and testing, 13 coal samples of another coalfield were collected and CPT and R70 test methods were carried out. The results of the test methods were compared through regression equations. The results obtained from the models indicate a good appropriate prediction in terms of the determination of the SCC tendency by regression analysis.Sadržaj vlage jedna je od bitnih značajki ugljena koja ima presudan utjecaj pri spontanome izgaranju ugljena i dugo je atraktivna problematika brojnim znanstvenicima. Potpuno razumijevanje te pojave pomaže stručnjacima pri njezinu predviđanju i sprječavanju. Stoga je prikazano predviđanje te pojave temeljem sadržaja vlage, koja je iznimno bitna varijabla pri pojavi ovoga procesa. Prikazan je zaključak o učinku ovoga parametra. Prikupljen je 51 uzorak ugljena s različitim sadržajem vlage iz podzemnih rudnika ugljena Irana i provedene su metode ispitivanja točke prijelazne temperature (TPT) i R70 za svaki od uzoraka. Modeliranje i predviđanje tendencije spontanoga zapaljenja ugljena provedeno je uporabom regresijske analize. Rezultati pokazuju kako ugljen najbrže oksidira pri sadržaju vlage manjem od 20 % i da se spontano zapaljenje može smanjiti pri vlažnosti većoj od 20 %. Kod vrijednosti vlage od 20 % toplina koja se oslobađa oksidacijom troši se na isparavanje vlage. Validacija i testiranje provedeni su na 13 uzoraka ugljena pri čemu su na svakome od njih provedene metode TPT i R70, a rezultati uspoređeni regresijom. Regresijska analiza pokazala je kako se potencijalno samozapaljenje ugljena može dobro predvidjeti

EXPERIMENTAL STUDY OF THE EFFECTS OF COAL DUST PARTICLE SIZE ON LAMINAR BURNING VELOCITY IN A MIXTURE OF COAL DUST AND METHAN

U radu se istražuje utjecaj promjena u veličini čestica ugljene prašine na brzinu njihova izgaranja u zatvorenoj komori volumena 2 l. Prašina je uzorkovana u trima različitim rudnicima te je testirana eksplozivnost uzoraka različite veličine (149 μm, 125 μm, 105 μm, 74 μm, 63 μm, 53 μm, 44 μm, 37 μm). K oncentracija prašine bila je konstantna (10000 g/m3), testiranje je načinjeno pri tlaku od 1,5 bara te temperaturi od 25 °C. Višestrukim testiranjem određeni su izračun iznosa gorenja te varijable svakoga uzorka (najveći eksplozivni tlak, najveći iznos povećanja tlaka, indeks eksplozivnosti). Rezultati su pokazali kako promjene veličine čestica ugljene prašine utječu obrnuto proporcionalno na promjenu brzine njihova izgaranja. Čestice od 37 i 44 μm pokazale su najveću brzinu gorenja. Rezultati su primjenjivi u analizi eksplozivnih procesa prouzročenih ugljenom (prašinom), ali i u sprječavanju takvih pojava u rudnicima.This study investigates the effect of variations of coal dust particles size on the rate of burning of coal dust particles in a 2-liter closed chamber. Coal dust was selected from three different mines with different sizes (149μm, 125μm, 105μm, 74μm, 63μm, 53μm, 44μm, 37μm) for explosion testing in a closed chamber of 2-liters. In this analysis, the concentration of coal dust was considered constant (10000 g/m3), all tests were carried out at a pressure of 1.5 bar and the initial temperature was 25 °C. To calculate the burning rate, the explosion severity parameters of each sample, such as the maximum explosion pressure, the maximum rate of increase in pressure, and the explosion index must be determined during various tests. The results of the experiments show that by variating the size of the coal dust particles, the burning rate of the particles also changes and there is an inverse relationship between them. Coal dust particles with dimensions of 44μm and 37 μm have a higher burning velocity than other dimensions. Thus, with a reduction in the size of coal dust particles, the burning velocity of coal dust increases. The outcomes acquired in this examination are not just valuable in developing information on coal dust explosion processes, but also improve the measures needed to prevent coal dust explosions in coal mines

Numerical modeling of gas flow in coal pores for methane drainage

The sudden explosion of methane during underground coal mining is a major dilemma. To mitigate its occurrence and reduce the extent of methane diffusion, gas drainage operations are carried out before mining. This paper investigates methane gas flow in a coal block in order to calculate the pressure of gas and its molecule velocity for methane gas drainage operation. A coal piece surrounded by cleats was used for geometrical modeling and numerical simulation. Movements of fluid and gas molecules in a porous medium were successfully simulated. The numerical solution is based on COMSOL Multiphysics software. The validity of the numerical simulation was assessed using an analytical model with satisfactory results

Improving coal mine safety by identifying factors that influence the sudden release of gases in outburst prone zones

In recent decades, the subject of coal and gas outburst in underground coal mines has been a focus of interest in Australia and worldwide. Much of this interest has been the result of the alarming increase in outburst related incidents and associated fatalities world wide, particularly in China, Russia, Ukraine and other major coal producing countries. Australia, on the other hand, has seen a relative decline in outburst related incidents, for the last three years no outburst related incident has been reported. Effective gas drainage programmes, better management of outburst prone zones, tougher regulations and a continuing programme of dedicated vigilance and research have collectively contributed to improvements in outburst prevention. Still, however, difficult problems remain to be addressed. Geological disturbances such as dykes, shear planes and increased mineralisation can influence coal permeability and porosity. These disturbances must be fully understood in order to develop an effective on gas drainage programme and reduce outburst risks. Accordingly, a programme of laboratory studies was undertaken to investigate the relationship between coal composition, coal volumetric change and coal permeability. Coal samples for this study were obtained from four different coalmines in Australia (Tahmoor, Metropolitan, Dartbrook and North Goonyella) and Tabas coalmine in Iran. Coal samples were tested in different types of gases and under different gas pressures and stress conditions. Coal permeability tests were conducted in the gas pressure chamber of the multi-function outburst research rig (MFORR), and the volumetric change tests were carried out in a modified pressure bomb. Microscopic studies provided a better correlation between coal composition permeability and shrinkage characteristics. A numerical model was developed to simulate single gas flow through a coal sample. The simulation further supported the experimental studies. The petrographical tests showed that most of the Australian coals tested were inertinite rich coals. The mineral matter in the Australian coal samples were mostly carbonate (calcite) and clay, but the Iranian Tabas coal had pyrite as the dominant mineral matter. Tabas coal has the highest vitrinite concentration (70%) and lowest proportion of inertinite elements (8.18%), the lowest vitrinite content was obtained from North Goonyella coal. There was a definite correlation between coal composition, coal volumetric change and coal permeability. Volumetric strain changes during the adsorption stage in all gas environments were greater than the volumetric strains in the desorption stage. The level of coal shrinkage was affected by the type of gas desorbed. Carbon dioxide appears to have the greatest influence on the matrix and nitrogen the least. The permeability of coal was also influenced by the gas type and pressure. Greater gas permeability was obtained in N2 gas, and the lowest permeability was obtained in a CO2 environment. The sorption characteristics of CO2 are a major factor. The degree of coal permeability is reduced exponentially by increasing the applied stress and also by increasing the confining gas pressure, irrespective of the gas type. The permeability tests showed that with an increased inertinite content the permeability of coal increased, except in the case of Tahmoor Colliery 900 Panel which showed a decrease. Comparison of the Tahmoor coals from 800 and 900 Panels showed that the permeability of coal was influenced by the mineral content and the carbonates, as well as the cavities. In particular; there was a reduction in coal permeability with increasing mineral content and carbonate content of the coal. With an increase in the percentage of inertinite, the permeability of coal increased. The numerical modelling provided an opportunity to quantify the flow mechanism in coal. It was possible to simulate the flow duration across the coal samples as a function of time with different gases and coal types. It was recommended that the study be extended to include more coal deposits and coals with different geological variations, so that an effective data bank can be established for Australian coals

Estimate of the optimum horizontal well depth for gas drainage using a numerical method in the tabas coal mine

One of the hazards in underground coal mining operations is the sudden coal gas emission leading to coal outburst. To reduce the risk of gas emissions to enable safer mining, it is necessary to pre-drain coal seams and surrounding strata. According to the experimental data, there exists a relationship between the gas flow from the coal seam and the stress changes in the upper layers above the coal seam. This is achieved by drilling horizontal drainage holes in the coal seam. Phase2 commercial software was used to investigate induced stresses caused by methane drainage operations during mining. The optimum depth of horizontal borehole from the coal face was calculated based on the actual gas production. Results of the numerical simulation showed that boreholes with a minimum distance of 30 m from the coalface provide the optimum gas drainage performance for the underground Tabas Coal mine in the South East of Iran

PROCJENA SPONTANOGA IZGARANJA UGLJENA UPORABOM METODA TESTIRANJA R70 NA TEMELJU KORELACIJE KONSTITUCIJSKIH SVOJSTAVA UGLJENA (PRIMJER RUDNIKA UGLJENA TABAS PARVADEH, IRAN)

The purpose of this research is to perform an evaluation of the spontaneous combustion of coal (SCC) in Tabas Parvadeh coal mines in Iran, by using the R70 test method based on a the correlation between intrinsic coal properties and the occurrence of its combustion. Firstly, the coal samples were collected from Parvadeh I to IV, and the intrinsic coal properties of the samples were tested. Then, the R70 test method, as the newest method for assessment of the SCC, was used. In the last step, the correlation between intrinsic coal properties and R70 test values was carried out. The results showed that the B1 seam in Parvadeh II and the C1 seam in Parvadeh III have a high propensity of the SCC. The outcomes appear, an expansion of moisture, pyrite, vitrinite, and liptinite contents enhance the SCC tendency in these mines. The results obtained have major outcomes for the management of this phenomenon in Tabas Parvadeh coal mines.Spontano izgaranje ugljena prirodni je fenomen i glavna opasnost industrije ugljena. Taj fenomen utječe na razne aspekte održivoga razvoja (gubitak života, veliki ekonomski gubitci i onečišćenje okoliša). Svrha je ovoga istraživanja procjena toga fenomena u rudniku ugljena Tabas Parvadeh u Iranu primjenom metode R70 koja se temelji na korelaciji između unutarnjih konstitucijskih značajki ugljena pri postanku. Najprije je ugljen uzorkovan iz ležišta Parvadeh I do IV i određene su konstitucijske značajke ugljena. Zatim je provedena procjena spontanoga izgaranja ugljena upotrebom R70 metode. U posljednjoj fazi određena je korelacija između konstitucijskih značajki ugljena i vrijednosti dobivenih metodom R70. Rezultati su pokazali da uzorci B1 iz Parvadeh II i C1 iz Parvadeh III imaju visoku sklonost spontanomu izgaranju. Zabilježeno je da povećanje sadržaja vlage, pirita, vitrinita i liptinita povećava tendenciju spontanoga izgaranja ugljena. Dobiveni rezultati imaju velik utjecaj na upravljanje ovim fenomenom u rudnicima Tabas Parvadeh