Yeraltı kömür madenciliğinde alçıtaşlarının yangın barajı malzemesi olarak kullanılabilirliğinin araştırılması

Abstract

Bu çalışmada alçı malzemenin yangın barajı malzemesi olarak kullanılabilmesi için gerekli mekanik özelliklere sahip olup olmadığı baraj yapımı açısından uygulanabilirliği, grizu ve kömür tozu patlamalarına karşı boyutlandırma ilkeleri ve ekonomisi yeraltındaki koşullar gözönüne alınarak araştırılmıştır. Çalışma toplam 7 bölümden oluşmaktadır. 1. Bölümde çalışmanın konusu ve amacı tanıtılmaktadır. 2. Bölüm alçıtaşının oluşumu, üretimi, özellikleri ve madencilikte kullanımı ile ilgili genel bilgilerden oluşmaktadır. 3. Bölümde ocak yangınları, yangınla mücadelede uygulanan yöntemler ve yangın barajlarının özellikleri anlatılmaktadır. Çalışmada sürdürülen deneysel çalışmalar 4. bölümde toplanmıştır. Alçı malzeme ile yangın barajı yapımında, sızdırmaz ve patlamaya dayanıklı bir barajın boyutlandırılabilmesi için kullanılan alçı malzemenin fiziksel özellikleri ve dayanımlarının bilinmesi gerekmektedir. Bu nedenle alçı malzemenin dayanımları üzerinde etkili olan parametreler (su/alçı oranı, kür süresi, sıcaklık, hızlandırıcı katkı kullanımı, deney numunesinin boyutları) dikkate alınarak basınç, çekme, ve eğilme dayanımı deneyleri gerçekleştirilmiş ve elde edilen sonuçların değerlendirmesi yapılmıştır. Ayrıca deneylerde ulaşılan sonuçların önceki çalışmalarla karşılaştırması yapılmıştır. Yangın barajının boyutlandırma ilkeleri ve patlamaya dayanıklı baraj kalınlığının boyutlandırılması 5. Bölümde açıklanmıştır. Baraj kalınlığının hesaplanmasında alçı malzemenin baraj yerindeki dayanımları ve oluşabilecek patlama basıncı dikkate alınmıştır. Nümerik bir örnek olarak TTK ocaklarında yaygın olarak kullanılan B10 tipindeki bir galeride yapılacak bir alçı barajın kabul edilen koşullar için boyutlandırması yapılmıştır. Patlama basıncına bağlı olarak belirlenen baraj kalınlığının, sızdırmazlık açısından da yeterli olması için barajın stabilitesi arazi yükü ve zeminin taşıma kapasitesine göre irdelenmiştir. Ayrıca değişik kesitteki galeriler için, madencilikte kullanılan baraj kalınlığı bağıntıları ile baraj kalınlıkları hesaplanmış ve birbirleriyle karşılaştırmalar yapılmıştır. 6. Bölümde alçı malzeme ile baraj yapım yöntemleri anlatılmış ve alçı baraj ile farklı malzeme ile yapılan barajların karşılaştırması yapılmıştır. TTK 'da uygulanan barajlarda maliyet etüdleri yapılmış ve alçı için teorik olarak hesaplanan maliyetlerle karşılaştırılmıştır. 7. ve son bölümde ise, çalışmada ulaşılan sonuçlar belirli bir sıra içinde kısaca özetlenmiş ve çalışmanın değerlendirmesi yapılmıştır.

The aim of this study is to investigate the gypsum as a construction material of stopping for sealing-off fires in underground coal mining This study contains the following 7 chapter; 1. Introduction of the subject and purpose of the study. 2. General information about gypsum, its origin, occurrence, productions, properties and its use in mining. 3. General information about mine fires, fire-fighting methods and principles of sealing-off and desirable features of stoppings. 4. Experimental studies and discussion of the results 5. Calculation of explosion-proof stopping thickness 6. Design and construction of gypsum stopping and its properties 7. Results and recommendations In the first chapter, the subject and the purpose of the study have been introduced. In the second chapter, gypsum and its physical and mechanical properties have been presented. Naturally occurring calcium sulfate can be called, in general, natural gypsum. It occurs in several forms, most common among which are the dihydrate {CaSOA-2H20) and anhydrite (CaSO^). The chemical composition of pure dihydrate, expressed by weight as oxides, is CaO 32.5%; S03 46.6%; H20 20.9%. Its bulk weight is about 2.3 t/m3, its hardness is 1.5-2.0 on the Mohs scale, and its color is white and colorless. Only commercial dihydrate minerals rarely reach this purity. They usually contain varying amounts of clay, slate, anhydrite, chalk, dolomite, silica and iron compounds, as well as water. Depending on the specific impurities presents their color may be gray, brown, red or pink. As applied to the gypsum industry, calcining is the step of reducing the dihydrate of calcium sulfate to the hemihydrate (CaS04 1/2. H20) or anhydrous (CaS04) forms. It is the consensus that hemihydrate is the only lower hydrate of calcium sulfate whose identity has been established with any degree of certainty. Two forms of hemihydrate, a and (3, have been identified, both the same crystalline form; however, the (3 form has a definitely higher energy content and a higher solubility rate, and the two forms can only be distinguished one from the other by highly XX) 1 sophisticated analytical methods. The a form of hemihydrate is more stable, or less reactive, than the P form, and has a slower rate of strength development. As is well known, gypsum is an air-hardening cementitious material. It is capable of crystallizing and hardening in water as well, but does not subsist in water due to its solubility. When not exposed permanently to water, it is more durable as is evidenced by extensive experience. Shortly after mixing hemihydrate with water, setting begins, dihydrate is formed, and the material hardens. The setting mechanism of gypsum based materials is explained by Le Chatellier's law. The strength of hardened gypsum derives from crystallization of the gypsum. Growth and interlocking of the contracting crystals impart strength to the gypsum paste. Strength of hardened gypsum is determined by the following factors; 1. the quality of the cementitious material (gypsum and additives); 2. the water/gypsum ratio (by weight); 3. the age of product; and 4. the conditions of storage of the product, both during strengthening, and after the strengthening period. Gypsum products contract on drying to a limited extend. The linear change does not exceed 0.01% (ordinary concrete contracts 0.03-0.08%). It can thus be concluded that hardened gypsum does not undergo any appreciable volume change as a result of moisture changes. Gypsum is a non-flammable material and the fire resistance of gypsum products derives primarily from its content of water of crystallization, amounting to 17% of its weight. In the third chapter mine fires, fire fighting methods and sealing off fires have been discussed and fire fighting methods and sealing of fires applied in some Turkish Collieries have been presented. Mine fires are one of the major hazards of underground coal mining, both from the safety aspect and on economic grounds. They occur whenever and wherever combustible materials are present in mine workings. Every incident, however small, if it is not dealt with effectively in the early stages can develop into open fire, or explosion of gas or coal dust. On the economic side, even dealing with small incidents is costly in labor and materials, and where the sealing off of a district becomes necessary, in modern mechanized coal mining, the loss of machinery and sterilization of reserves is potentially great. Thus expense and effort in prevention and detection of heatings, together with a high state of preparedness for dealing with an incident, are fully justified, and may be considered as a sound investment. Most mine fires start very small and can be extinguished, if detected in time, with a bucket of water or a bag of stone dust. It is only when a fire is discovered late or improper fire-fighting procedures are adopted that it gets out of control. For a mine fire to break out, the following three conditions must be fulfilled: 1. Combustible materials must be available in sufficient quantity, xxtu 2. Sufficient supply of oxygen must be available and 3. A source of ignition of adequate energy must be present. If any of these three conditions is not fulfilled, a mine fire will not break out. The various causes of mine fires may be grouped under the following main headings: Open flames Spontaneous Combustion Electricity Friction Blasting Explosions Miscellaneous The relative importance of these causes varies from district to district in the same mine and depends to great extend on the equipment and supplies used, on the training and discipline among the workmen, and on the liability of the coal to spontaneous combustion The common methods of fighting mine fires are: 1) Fighting by direct attack; 2) Fighting by indirect attack;. Isolation of the fire;. Sealing off the fire area or the entire mine; 3) Flooding the fire area or the entire mine; 4) Flushing the fire area with sand or other suitable solid materials conveyed with water; 5) Introducing an inert gas into the fire area; and 6) Special methods of fire-fighting. There can be no fixed rules for the application of one or the other method for dealing with mine fires as each fire presents a problem of its own which requires careful thinking. The position, intensity and extent of a fire, depth and layout of workings, degree of gassiness of mine, and immediate availability of fire fighting facilities govern the selection of a method. In any method of extinguishing a fire, safety should be given the utmost consideration. Statistics show that the odds are one in two that unless a fire is extinguished within a few minutes, more than eight hours will require to control it (see Table 1). The odds are one in twenty that such a fire will not be controlled at all by underground attack, necessitating that the mine or at least a portion of it, will have to be sealed xxiv Table 1. Probability of Success of Active Fire-Fighting (%) Sealing of a fire area causes the fire extinguish itself after consuming the entire oxygen in the sealed area. Stoppings are erected in mine workings mainly for the following reasons: 1) to prevent the access of air to a fire or heating, so that the oxygen in the vicinity of the fire is consumed; 2) to provide an explosion-proof barrier in the event that mixtures of gas, or coal dust with air are ignited by the active fire; 3) to minimize changes in the composition of the atmosphere within sealed area, which result from changes in barometric pressure and the contraction due to a cooling of the fire area; 4) to control the de-gassing of sections of mine workings during recovery of a sealed-off district; 5) to seal abandoned workings; and 6) to effect a temporary diversion of the ventilation. The employment of workers for long periods in underground may of itself, be dangerous. If air is to be excluded from the fire, then the sooner a seal is erected, the more quickly will the fire extinguish itself. The building of a stopping by traditional methods may take 24 hours or more before the seal is complete and the air finally cut off. During this time the fire may have developed considerably, thus increasing the hazard. The manner of sealing off a fire depends on whether any explosion hazard exists untill the time of completion of the stoppings and also on the area to be sealed would be reopened at a later date. When it is known from the knowledge of firedamp emission that there is no explosion hazard during the sealing off operations, one restricts the air supply so that little oxygen reaches the fire. Temporary stoppings are then erected on the intake and return sides of the fire followed by permanent or main stoppings at selected places for final sealing-off. The temporary stoppings are erected with any available materials that will require minimum time for construction with reasonable air tightness such as brattice line, sand bags, stone dust bags, glasswool, boards, clay, concrete or fly ash blocks, etc. The main stoppings may be built of bricks, cement concrete or fly ash blocks, monolithic concrete, gypsum or packwalls of various kinds. XXV When there is danger of a fire gas or firedamp explosion during, or after sealing-off operations, utmost care must be taken to see that an explosion does not take place during sealing. If it occurs after sealing, it is contained by explosion-proof stoppings. As temporary stoppings sand bag or stone-dust bag stoppings and gypsum stoppings have been found to be effective. The main stoppings, with explosion hazard, are wooden or concrete block wedge stoppings and gypsum stoppings. Stoppings constructed of a quick setting gypsum compound offer a quick, easy and safe means of sealing off fire areas. In the forth chapter, the experimental studies and discussion of the experimental results has been presented and compared with the other researchers results. The hemihydrate gypsum, manufactured by ABS (Alçı Blok Sanayi A.Ş. Bozüyük- Bilecik), used in the experimental studies. Some properties and particle size distribution obtained from the manufacturer. Chemical composition, bulk weight and setting time have been determined by experiments. During the experiments,, compressive strength, tensile strength and bending strength of the gypsum for different water/gypsum ratio and setting time have been determined. According to the results of the experiments the strength of gypsum depends largely on its water/gypsum ratio and setting time. Strength of gypsum increases with time. Experiments show that, under normal conditions, approximateley75% of the total strength of the setting time of 28 day. During the experiments, accelerators have been used to reduce the setting time of gypsum. Potassium and Ferro sulfate used as accelerators. Addition of accelerator to gypsum accelerates the hydration reaction but it causes to reduce the strength. The effect of specimen size and shape on compressive strength of gypsum has been investigated. Experiments show that the greater the specimen size, the lower the compressive strength. The effect of loading rate on compressive and tensile strength of gypsum has also been investigated. Different conditions during the strengthening period of gypsum will yield products having different strength. The effect of temperature on compressive strength, tensile strength and bending strength of gypsum, is investigated for different temperature and setting time. In the fifth chapter, optimum thickness of an explosion-proof gypsum stopping has been investigated according to strength of gypsum and the expected forces created by explosion. Calculation method of stopping thickness and assumptions have been explained and a numerical example has been given for a gallery with cross-sectional area of 10 m2 which is commonly used widely in TTK (Turkish Coal Enterprises in Zonguldak). In the sixth chapter, construction of gypsum stoppings and its advantages and disadvantages has been explained. An economical analysis has been made and the cost of the gypsum stopping compared with the cost of the present applications in TTK. Gypsum stopping is found to be one third cheaper than present application. Finally, in the seventh chapter, results obtained from this study and some recommendations has been given.