Atık depolanmasının ve endüstriyel atıklardan termik santral küllerinin maden ocaklarında depolanmasının incelenmesi

Abstract

Günümüzde ister zararlı, ister zararsız olsun; atıklar önemli bir problem oluşturmaktadır. Atıkların miktarı, nüfus artışı ve endüstrideki gelişmelere paralel olarak artmakta, bununla birlikte içerikleri de karmaşık ve tehlikeli hale gelmektedir. Gerek son yıllarda gelişen çevre bilinci doğrultusunda çıkartılan yasaların getirdiği sınırlamalar, gerekse atıkların depolanması ve uzaklaştırılması amacı ile kullanılacak karasal alanların azalması nedeniyle; bilimsel çalışmalarda ağırlık atık depolanması ve uzaklaştırılmasından ziyade; atık miktarının azaltılması ve geri dönüşüm teknolojilerine verilmektedir. Bu çalışmada, endüstriyel atıkların özellikle depolama ve uzaklaştırma yöntemleri üzerinde durulmuştur. Atıkların, gerek yeraltı maden ocaklarında ve gerekse açık ocak işletmelerinde üretim sonucu oluşan hazır boşluklara, çevreye zarar vermeksizin depolanması konu edilmiştir. Örnek olarak, bir endüstriyel atık olan "termik santral külleri" alınmış, bu atıkların Türkiye'deki genel durumu ve depolanma yöntemleri üzerinde durulmuştur. Çalışmalar örnek olarak seçilen Seyitömer ve Çayırhan Termik Santrallerinde sürdürülmüştür. İlk etapta, atıklar genel olarak sınıflandırılmış; termik santral küllerinin bu sınıflamadaki yeri belirlenmiştir. Atıkların depolanması ve uzaklaştırılması ile ilgili hukuki sınırlarının belirlenmesi amacıyla; ilgili yurtiçi ve yurtdışı (ABD) yönetmelikler karşılaştırmak olarak incelenmiştir. Yönetmeliklerde ağırlıklı olarak depoların inşaatı ile ilgili teknik bilgiler üzerinde durulmuştur. Daha sonra uygulananan tüm yeraltı ve yeryüzü atık depolama ve uzaklaştırma teknikerinin (landfill, surface impoundments) genel özellikleri anlatılmıştır. Kül depolanmasında kullanılan bu yöntemlere, uygulamalardan örnekler verilmiştir. Depolamada asıl amaç çevreye zarar vermeksizin uygulamaların yürütülebilmesidir; bu bağlamda deponun sızdırmazlığı yeraltı ve yerüstü su kaynaklarının kirlenmemesi için önemlidir. Bu nedenle landfill, surface impoundment gibi atık depolama alanlarında yalıtım görevini üstlenen astar sistemleri (taban ve örtü astar sistemleri) anlatılmıştır. Bu sistemlerin bileşenleri olan geçirimsiz kil astarlar, jeosentetik malzemeler ayrıca liç toplama ve uzaklaştırma sistemleri teknik özellikleri verilerek ayrı ayrı incelenmiştir. Son bölümde örnek olarak alınan Çayırhan ve Seyitömer Termik Santrallerinde kullanılan kömür ve çıkan kül miktarları verilmiş; santrallerin çalışma prensiplerinden kısaca bahsedilmiştir. Ayrıca kül depolama sahalarının konumu ve özellikleri üzerinde durulmuştur. Külün, santralden itibaren kül sahasına taşınması, kül sahasında uygulanan depolama sistemleri; drenaj ve baraj özellikleri de dahil olmak üzere, ayrıntılı birşekilde anlatılmıştır.

Waste may be generated in the form of solids, liquids, gases and any combination thereof. With increasing industrialisation the quantity of waste has increased immensely. Depending on the source of generation some of these wastes may degrade into harmless products whereas others may be non- degradable and hazardous. In United States regulations; "solid waste" İs defined as, any garbage, refuse, sludge, and other discharged material, including solid, liquid, semisolid, or contained gaseous material resulting from industrial, commercial, mining, and agricultural operations. This does not include solid or dissolved materials in domestic sewage, in irrigation return flows or industrial discharges that are point sources. Hazardous waste refers to any solid, semisolid, liquid, or gaseous waste that cannot be handled by routine waste management methods because of chemical, biological or physical properties that present a significant threat to human health, the health of other organisms or the environment. The United States' regulations define hazardous waste as being either: (1) a listed hazardous waste or (2) specific characteristics of hazardous waste like, ignitability, corrosivity, reactivity, toxicity, infectivity, etc. In United States The Federal regulations governing waste are given in the "Resource Conservation and Recovery Act" (RCRA) and "Code 40 of the federal Regulations" (40 CFR). The objective of the act is to promote the protection of health and environment to conserve valuable materials and energy resources. The act is administered by "Environmental Protection Agency" (EPA). The federal EPA regulations are explained in Title 40 of the Code of Federal Regulations. The technical requirements for EPA regulations are explained in Title 40 of the CFR, part 260-270. Subtitle C of RCRA establish a detailed "cradle to grave" provision for hazardous waste management. An effective hazardous waste management system is an efficient record-keeping system to track the transfers of hazardous waste from a registered generator to a licensed hauler and from the hauler to an approved and licensed treatment, storage, or disposal facility. Such a record keeping system is called "cradle-to-grave management" The purpose of this manifest system is to prevent illegal dumping by unscrupulous generators and haulers who wish to avoid paying the cost of proper disposal. Subtitle D of RCRA is governing non-hazardous wastes. The 40 CFR 257 and 258 are about municipal waste disposal. Municipal landfills are heterogeneous mixtures of wastes that are primarily of residential and commercial origin. The XIV composition of the fill materials will depend on the type of the commerce and industry. The RCRA regulations established practices for safe disposal of hazardous waste currently being generated, but they did not address the problem of many existing sites where hazardous waste was dumped at some time in the past. To address the problem of old dump sites, the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) or "Superfund" was passed. The purpose of this legislation was to provide funds to identify and remediate dump sites judged to present serious hazards to humans and environment. An important aspect of CERCLA was assign the financial responsibility for cleanup of contaminated disposal sites to the generator. In Turkey, "Control of Solid Waste Regulation" and "Hazardous Waste Control Regulation" are the regulations that govern solid waste disposal. While "Solid Waste ControP'which is passed 1991 is about municipal waste; "Hazardous Waste Control" which is passed in 1995 concerns hazardous wastes and disposal techniques. In this study especially industrial waste disposal techniques are considered. Disposal of wastes in underground or open pit mines is explained. Thermal power plant ash in Turkey and its disposal is taken as an example of industrial waste. Mine wastes are group of waste materials resulting from the extraction of metals and non-metals. The wastes include solid as well as liquid waste and can be inert or can contain hazardous constituents. In general mine waste consists of high volume, low toxicity wastes. Solid mine wastes usually consist of (1) waste rock from mine development or overburden (2) stockpiles of low-grade ore or ore with unfavourable milling mineralogy (3) leach dumps or heaps and (4) milling waste. With the increasing demand on natural resources, ores of poorer quality are being mined and proceed, generating ever larger amounts. In thermal power plants, burning of coal ends up as fly ash and bottom ash. In coal burning industry, depending on its technology four types of fly ash is produced; conventional fly ash, spend-bed ash, fluidized bed combustion ash and scrubber sludge. Conventional fly ash is formed in furnaces where pulverised coal is burned. The fly ash is composed of very fine spherical shaped particles; typically 65% of particles are less than 0.01 mm. Fly ash produced burning sub- bituminous coal or lignite is called class C. This type of fly ash contains lime and other compounds that impart to it self-cementing properties. The fly ash formed by burning bituminous coal or anthracite is known as class F. Though this type of fly ash is pozzolonic, it shows little self-cementing properties. In US every year 90 million tons of coal combustion products are produced by the electric utility. Currently, only 1/3 of generated by-products can be utilised, the remaining is disposed of in surface facilities or landfills near the power plants. XV In US RCRA specifically exclude "ash" from regulation as a hazardous waste treatment. Most states treat the ash as non-hazardous. However on May 2, 1994 US Supreme Court ruled that exclusion provided to the facilities does not extend to the ash. Ash must be tested to determine whether or not it is qualified as hazardous. According to Turkish Regulations "ash" is considered as a "hazardous waste". The rules related with ash are determined by "Environmental Agency". But the study being done by agency has not finished. So there is a big confusion and uncertainty about fly ash disposal in Turkey now. Turkey is generating 50% of its energy demand from thermal power plants. As a result 12 million tones of fly ash was produced in 1996. In this study case studies are carried out in Seyitömer and Çayyrhan Thermal Power Plants. The properties and the amount of coal burned in the furnace and the fly ash's are given. The working principles of the plants are explained briefly. The place of ash disposal areas and properties are given. The tansportation of ash from plant to disposal area, and disposal techniques with drenage and dam construction properties are explained. In the past, fly ash was generally disposed of by a wet method in which it is allowed to settle in ponds. Because of environmental concerns the emphasis is now shifting to dry disposal where moisture content of fly ash is controlled and it is compacted as soil. While the dry disposal of ash is used in Seyitömer, wet method is preferred in other thermal power plants. An accident was occurred in May, 1997 in Seyitömer when they were studying to change their system to wet method. Their starter dam was collapsed, and about two million metre cube of fly ash was spread to an area of 12 km long and 3 or 5 meters wide. In a study of EPRI (Electric Power Research Institute); the cost of disposing one ton of fly ash in surface landfills was reported to range from $5 to$15. Although wastes can be disposed into oceans, lakes, etc. today it has a little opportunity because of strict environmental regulations. Therefore we divided disposal systems into two groups as surface and underground. Landfills and impoundments are surface disposal applications. Landfills are specially trapezoid shaped closed volumes that are isolated from environment by liner systems. Impoundments are classified as impounding (cross-valley, side hill, incised pond, diked pond) or non-impounding (valley fills, ridge, side hill, heaped). In impounding facilities fine refuse is disposed of in slurry form behind or within the embankment, forming the impoundment. Embankments of the impounding facilities are usually made of coarse refuse, but borrowed material can also be added when there is not enough coarse refuse. Embankments of non- XVI impounding facilities can be made of either coarse refuse alone or coarse refuse mixed with drained and thickened fine refuse. Refuse disposal facilities have also been classified by their method of construction. The three types of construction are, upstream, downstream and centreline methods. In the upstream method, a small starter dam is constructed initially with coarse refuse, then fine refuse slurry is disposed of behind it. Then, over a period of time, as the fine refuse drains and settles, new, small, coarse refuse dams are built, resting partially on the previous dam and partially on the settled fine refuse, and construction progress upstream. This method requires less refuse material than the others. It is important the compressive strength of drained fine refuse must be high enough to withstand the load of the extending dams. In the downstream method, the dam is constructed by gradually expanding it on the downstream side of the starter dam. This method allows construction of high embankments and these dams are claimed to be safer. The centreline method uses coarse refuse on both sides of dam. This method has found to be useful in areas of steep terrain. In mining facilities every year, large volumes are excavated. Using these empty spaces; voids, resulted both from underground and surface mining, for waste disposal facilities will be economical. And if good precautions are taken it will also be safe for environment. Instead of using new areas for waste facilities, mining volumes are ready voids for this process. It must be taken into consideration that using abandoned mines or active mines effects the disposal techniques. So techniques of disposal in open pit or underground mines especially the construction of storage spaces and their sealing against underground water must be determined. Current regulations (40 CFR 264) require that hazardous waste land disposal facilities be constructed with liner systems that prevent any migration of waste out of unit. "Liner system" includes the liners, leak detection/ leachate collection systems and any special additional structural components such as filter layers or reinforcements. They are used for two purposes; as covers to minimise leachate generation and surface water contamination by providing a barrier from precipitation and other percolating waters, and as containment liners to contain leachate and minimise its downward migration into underlying groundwater. To meet these objectives, liners systems must have low hydraulic conductivity over long period of time. Liner systems can be constructed either in single or double system structure. The major components of both single and double liner systems are; lower permeability soil liners; flexible membrane liners, leachate collection and removal systems. A single liner system consists of one liner and one leachate collection system while a double liner system consists of two liners, primary and secondary, with a primary leachate collection system, above the primary (top) liner and secondary leak detection/leachate collection systems between the two liners. XVU Low-hydraulic-conductivity soil liners that used in liner systems, are given various names, including soil liner and clay liner. There are three types of clay liners; naturally-occurring clay liners, compacted clay liners and geosynthetic clay liners. Clay liners are low-permeability material, while drainage materials are of high permeability. Geosynthetics are defined as synthetic materials, mostly plastic, which are commonly used in place of, or to enhance the function of, natural soil materials. These include geomembranes, geotextiles, geonets, geogrids. Geomembranes are flexible, polymeric sheets that have extremely low permeability and are typically used as liquid or vapour barriers. Geotextiles are synthetic fabrics used in geotechnical engineering for various applications. The majority of geotextiles are composed of polyamide or polyethylene. Geonets and geosynthetic drainage products are extruded sheets of plastic formed into a configuration to promote drainage. They are most commonly composed of PE but may also be composed of polypropylene, polystyrene, high impact polystyrene or other materials. Leachate collection and removal systems (LCRA) are designed to minimise the leachate head above the liner by collecting and removing it to a location where it can be treated properly. Regulations require that the LCRA systems be designed and operated to ensure that the leachate depth over the liner does not exceed 30 cm. The system must also be chemically resistant to wastes and leachate, sufficiently strong to withstand landfill loading and protected from clogging trough the scheduled closure of the unit. When a landfill has reached full capacity and no longer receives waste, a final cover is put in place to minimise infiltration of moisture and erosion. XVUl