Doğal gaz dağıtım şebekesinin dizaynı

Abstract

Petrol ve doğal gazın önümüzdeki 2000 yılına kadar ana enerji kaynağı olma özelliğini sürdürmesi beklenmektedir. Doğal gazın kullanımı da gün geçtikçe artmaktadır. Doğal gazdaki üretim dolayısıyla tüketimin gelişmesi isbatlanmış rezervlerin artmasıyla paralellik göstermektedir. Sosyalist blokta doğal gaz rezervi dünya toplamının % 45.2 sini tutmaktadır. Birinci enerji kaynakları içerisinde doğal gazın payının 1995 ' te % 20.3 ' e çıkması beklenmektedir. Türkiye ' nin doğal gaz rezervleri, Mardin ve Trakya bölgesinde toplanmış olup, toplam üretilebilir rezervimiz 479 m3 tür. Doğal gazın ortaya çıkışı birçok ülkede gaz şebekelerinin yeni yerleşim bölgelerine doğru hızla genişlemesine yol açmıştır, bu gelişmeyi eskiyen şebekelerin geliştirilmesi ve kısmen yenilenmesi çalışmaları izlemiştir. Her iki faaliyet için kullanılan malzemeler de aynıdır, ancak mühendise yeni buluşlar ve başarılı bir yönetim açısından daha geniş bir ufuk sağlayan olay muhtemelen eskiyen boru sisteminin tekrar yenilenmesidir. Bu ödevin birinci bölümünde doğal gaz hakkında genel bilgiler verilmektedir. İkinci ve üçüncü bölümlerde gaz dağıtım şebekelerine giriş yapılmakta, şebeke tiplerinden, malzemeden bahsedilmektedir. Dördüncü bölümde,, gaz şebekelerinin dizaynı ile ilgili bilgiler verilmekte, dizayn için gerekli yöntemlerden, formüllerden bahsedil - inektedir. Beşinci bölümde, kısaca doğal gaz şebekelerinin inşaat metodları anlatılmaktadır. Altıncı bölüm doğal gaza geçiş faaliyetlerinin idarî ve teknik yönlerini detaylı bir şekilde anlatmaktadır. Yedinci ve son bölümde şebeke dizaynına örnek olması açısından ger çek bir uygulamaya yer verilmiştir. Bu bölümde İstanbul Doğal Gaz Projesi ' nden, bu projede kullanılan malzemelerden, yöntemlerden bahse dilmektedir. Ayrıca İstanbul Doğal Gaz Projesi nde, dağıtım şebekesinin bazı semtleri için gerçek sonuçlar sunulmaktadır.

Natural gas, which was once an almost embarrassing and unwan ted by-product or more correctly a coproduct-of crude oil production now provides about one-fifth of all the world's primary energy requ irements. This remarkable development has taken place in only a few years with the increased availability of the gas resources of the countries, and the construction of long-distance, large-diameter steel pipelines which, have brought these ample suppies of gaseous fuel to domestic, commercial, and industrial users many miles away from the fields themselves. Since its discovery in the United States at Fredonia, New York in 1821, natural gas has been used as feul in areas immediately sur rounding the gas fields. In the 1920s, a few long-distance pipeli nes from 22 to 24 in. in diameter, operating at 400 to 600 psi, were instaled to transport gas to industrial areas remote from the fields. In the early years of the natural gas industry, when gas accompanied crude oil, it had to find a market or be flared; in the absence of effctive conservation practices, oilwell gas often flared in huge quantities. Consequently, gas production at that time was often short lived, and gas could be purchased for as little as 1 or 2 cents per 1000 cu ft in the field. The natural gas industry of today did not emerge until after World War 11. The consumption of natural gas in all end-use classi fications has increased rapidly since then. This growth has resul ted from several factors, including development of new markets, rep lacement of coal as a fuel for providing space and industrial pro - cess heat, use of natural gas in making petrochemicals and fertili zers, and strong demand for low-sulfur fuels which emerged in the middle 1960s. The resultant expansion of natural gas service has been remarkable. The rapidly growing energy demands of Western Europe, Japan and the United States could not be satisfied without importing gas from far afield. Natural gas, liquefied by a refrigeration cycle can now be transported efficiently and rapidly across the oceans of the weald by insulated tankers. The use of refrigeration to liqu efy dry natural gas, and hence reduce its volume to the point where it becomes economically attractive to transport across oceans by tanker, was first attempted on a small scale in Hungary in 1934 and later used in the United States for moving gas in liquid form from fehe §g§ fiildi İn Louisiana up th§ Mississippi River to Chigago in 1951. VII k The first use of a similar process on a large scale outside the United States was the liquefaction by a refrigerative cycle of some of gas from the Hassi R'Mel gas field in Algeria and the export from 1964 onward of the resultant liquefied naturall gas (LNG) by speci ally designed insulated tankers to v Britain and France. Natural gas is in this way reduced to about one six-hundredth of its original vo lume and nonme thane components are largely eliminated. At the receiving terminals, the LNG is reconverted into a gase ous state by passage through a regasifying plant, whence it can be fed as required into the normal gas distribution grid of the impor - ting country. Alternatively, it can be stored for future use in in sulated tanks or subsurface storages. Apart from its obvious appli cations as a storable and transportable form of natural gas, LNG has many applications in its own right-particularly as a nonpolluting fu el for aircraft and ground vehicles. Current production from conventional sources is not sufficient to satisfy all demands for natural gas; however, there has been lack of agreement as to the extent of the gas shortage. With the excep - tion of past production, all recource base parameters are subject to some uncertainly. Standardized definitions for natural gas supply indicators are not always used, estimation procedures differ, and pro fessional judgment must be exercised in making resource estimates. Estimates of the undiscovered natural gas reserves that may eventu - ally be found also differ greatly. The following definitions will help distinguish between the etrms proved reserves and potential resources : Proved reserves are those quantities of gas that have been found by the drill. They can be proved by known reservoir characteristics such as production data, pressure relationships, and other data, so that volumes of gas can be determined with resasonable accuracy. Potential resources constitute those quantities of natural gas that are believed to exit in various rocks of the earth's crust but have not yet been found by the drill. They are future supplies be - yond the proved rezerves. Different methocologies have been used In arriving at estimates of the future potential of natural gas. Some estimates were based on growth curveş;, extrapojl.std.ons of past production, exploratory, foo tage drilled, aha' discovery rates. Empirical models of gas discori- es and production have also been developed and converted to mathema tical model. Future gas supplies as a ratio of the amount of oil to be discovered is a hethod that has been used also. Another approach is a volumetric appraisal of the potential of undrilled areas. Dif ferent limiting assumptions have been made, such as drilling depths, water depths in offshore areas, economies, «nd technological factors. Suppements to natural gas produced from conventional sources may provide portions of the world's future energy. Such supplements may include gas production resulting from simulation of tight gas reservoirs in the western United States, methane gas occluded. in co al, and natural gas contained' in geopressured reservoirs. Artificial or substitute natural gas may include gas generated by gasifying coal, oil shale, or hydrocarbon liquids. İn addition, gas genera - ted from organic wastes and plant material and hydrogen gas produ - ced from either water or other hydrogen compounds are potential subs titute gaseous fuelds. A recent study by the American Gas Association (AGA) indicates that worldwide capability exists for sustantially increasing con - ventional natural gas production in the coming decade and for susta ining production well above today's level until at least the year 2020. This study estimates the level of production that could be achieved, rather than a projected "actual" production volume, since it not possible to predict the economic and political factors that will influence future production decisions within a region. The major findings of this study may summarized as follows 1. While annual world conventional natural gas. production is now only about 50 trillion cu ft (Tcf), proved reserves are estimated at about 2200 Tcf, and remaining undiscovered resources are estima ted at about 7500 Tcf. 2. Cumulative worldwide conventional production of natural gas to 1975 is estimated at about 854 Tcf or about 40% of presently estima ted proved reserves and only 11% of remaining undiscovered gas re sources. 3. Even at an annual world natural gas production rate of double the present rate, that is, 100% Tcf /year, the estimated world remai ning conventional natural gas resource base would be large enough to sustain production at or near this level for at least another 50 years. 4. Under a gas-pricing scenario that would alio a natural gas pri ce of $20/bbl crude oil equivalent (1974 dollars) in the period af ter 1985, it is estimated that world gas production could rise to about 70 Tcf by 1985 and, fco about.1,32, Tcf by,thetyear 2000. 5. At these production rate increases (4.4%/year through 2000), it is estimated that production would peak shortly after the year 2000 and decline to about 115 Tcf by 2020. By the time, about 50% of the presently estimated remaining gas-resource base would have been pro duced. 6 Key areas of the world where substantial potential exists for IX greatly in increasing production over the next decade include the Opec groups and the USSR. These estimates do not assume any production from the numerous sources of conventional and supplemental sources of gas from geop- ressured resources, tight gas formations, coal beds, shales, and biomass. These represent an additional and substantial gas-resource base, estimated in the range of several thousand trillion cubic feet which could add significantly to world gas production in the years after 2000. In planning a pipeline system, bear in mind that the scale of operation of a pipeline has considerable effct on the unit costs. By doubling the diameter of the pipe, other factors remaining cons tant, the capacity increases more than sixfold. On the other hand the cost approximately doubles, so that cost per unit delivered dec reases to one-third of the original unit cost. ît is this scale ef fect that justifies multiproduct lines. Whether it is, in fact, e- conomical to install a large-diameter pipe line at the outset de - pends on scale and the following factors : 1. Rate of growth in demand (it may be uneconomical to operate at low-capasity factors during initial years). (Capasity factor is the ratio of actual average discharge to design capasity.) 2. Operating factor (the ratio of average throughput at any time to maximum throughput during the same time period), which will de - pend on the rate of draw-off and can be improved by installing sto rage at the consumer's end. 3. Reduced power costs due to low-friction losses while the pipeli ne is not operating at full capasity. 4. Centainly of future demands. 5. Varying costs with time (both capital and operating), 6. Rates of interest and capital availability. 7. Physical difficulties in the construction of a second pipeline if required. The transmission of gas to the consumer may be divided into fo ur distinct units s the gathering system, the Compression station the main trunk line, and the distribution lines. Pipelines, which comprise the gathering system,main truk system X greatly in increasing production over.the next decade include the Opec groups and the USSR. These estimates do not assume any production from the numerous sources of conventional and supplemental sources of gas from geop- ressured resources, tight gas formations, coal beds, shales, and biomass. These represent an additional and sustantial gas-resource base, estimated in the range of several thousand trillion cubic feet which could add significantly to world gas production in the years after 2000. In planning a pipeline system, bear in mind that the scale of operation of a pipeline has considerable effct on the unit costs. By doubling the diameter of the pipe, other factors remaining cons tant, the capacity increases more than sixfold. On the other hand the cost approximately doubles, so that cost per unit delivered dec reases to one-third of the original unit cost, it is this scale ef fect that justifies multiproduct lines. Whether it is, in fact, e- conomical to install a large-diameter pipe line at the outset de - pends on scale and the following factors : 1. Rate of growth in demand (it may be uneconomical to operate at low-capasity factors during initial years). (Capasity factor is the ratio of actual average discharge to design capasity.) 2. Operating factor (the ratio of average throughput at any time to maximum throughput during the same time period), which will de - pend on the rate of draw-off and can be improved by installing sto rage at the consumer's end. 3. Reduced power costs due to low-friction losses while the pipeli ne is not operating at full capasity. 4. Centainly of future demands. 5. Varying costs with time (both capital and operating), 6. Rates of interest and capital availability. 7. Physical difficulties in the construction of a second pipeline if required. The transmission of gas to the consumer may be divided into fo ur distinct units : the gathering system, the compression station the main trunk line, and the distribution lines.