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ÖZET Günümüzde, doğal gazın Batılı sanayileşmiş ülkelerde kullanımının artışına paralel olarak Denizyolu ile doğal gaz taşımacılığı da büyük gelişme göstermiştir. Bununla birlikte Türkiye'de de doğal gaz tüketimi ve talebi hızla artmaktadır. Doğal gaz tüketiminin 2005 yılında % 153 artışla 32,000milyon m3'e, 2010 yılında % 289.5 artışla 55,102 milyon m3'e, 2020 yılında ise %479.6 artışla 82,000 milyon m3 'e ulaşması öngörülmektedir. Hızla artan talebin en büyük bileşenini, elektrik enerjisi üretimi için doğal gaz tüketimi oluşturmaktadır. Aynı zaman diliminde, sanayiinin doğal gaz tüketimi içindeki payının ise %100 artması öngörülmüştür. LNG taşımacılığı, üretim kuyuları, LNG tankerleri, boru hatları, sıvılaştırma üniteleri, alıcı ve satıcı ülkelerdeki depolama şartlarını içine alan büyük bir kompleksten oluşmaktadır. Çalışmamda, LNG gemilerinin yapıları, tank sistemleri, doğal gazın sıvılaştırılması LNG taşımacılığı, LNG gemilerinde yükleme-boşaltma işlemleri ve LNG gemilerinde emniyet konulan ele alınmış olup doğal gaz sektöründe mevcut ve öngörülen yatırımlar da ele alınmaktadır. Doğal gaz temin, iletim ve satışının piyasa kurallarına göre düzenlenmesini öngören Doğal Gaz Piyasası Yasası irdelenmekte ve sektörde yapılması gereken düzenlemelerle ilgili görüş ve öneriler yer almaktadır. Ülkemizde kullanımı giderek artan doğal gazın ana kaynağı Rusya ' dan ülkemize ulaşan boru hattıdır. Ancak tek bir kaynağa bağlı kalmamak, alternatif doğal gaz kaynakları da yaratmak üzere ülkemize Cezayir ve Nijerya'dan denizyolu ile de doğal gaz temini sağlanmaktadır. Bununla birlikte 2005 yılından itibaren Türkmenistan ve Azerbeycan' dan boru hatları ile doğal gaz temini başlayacaktır. Denizyolu ile doğal gaz taşınmasının en önemli öğelerinden biride LNG gemileridir. Şu anda ülkemizin LNG gemisi bulunmamaktadır. Çalışmamda ileride edinilmesi planlanan LNG gemisinin, çeşitli gemi tipleri karşılaştırılarak en uygun kapasite ve sayısı tespit edilmeye çalışılmıştır. Bu çalışma yapılırken arz-talep, gemi kapasiteleri ve mevcut teknoloji faktörleri birbirleri ile karşılaştırılmış ve denge noktalarında sonuca ulaşılmaya çalışılmıştır. vıAyrıca LNG' nin hangi bölgelerden ithal edilmesinin ekonomik olacağı, Akdeniz'de Cezayir, Basra körfezinde ise Katar ele alınarak karşılaştırma sonucu bulunmaya çalışılmıştır. VII SUMMARY There is a trend in the world for using fuels that are economic, safe and harmless to the environment. Because of these reasons usage of natural gas has been becoming prevalent. Demand for natural gases generally obtained by pipelines established between import and export countries. Natural gas can also be transported by sea as LNG (Liqued Natural Gas). Transportation of Natural gas by sea is sometimes an alternative way, sometimes a supporting way to the pipelines. Although transportation by pipeline is the cheapest way of transportation, dependence to one source of energy is the main disadvantage of pipelines. Also the geographical reasons causes the improvement of LNG transportation, by sea. Steps from the production of the LNG to the presentation to the consunmers are like following: 1. Natural gas is transported from production areas to the liquefaction facilities by producer country, and liquefied at -150°C-168°C at atmospheric pressure. 2. LNG is transported by the LNG tankers which are maintaining the liquefaction temperature. 3. In storage terminals, LNG is stored in Crygenic tanks. In re- vaporization facilities, LNG is turned to be gas from liquid. The most important difficulty in LNG transportation is, low liquefaction temperature of natural gas. For instance methane can be liquefied at atmosphere pressure at temperature -1 62°C. Thermal stresses caused by low temperatures are also important problems. The leakage of the LNG at -162°C from cargo tank may crack shell plates ot the vessel for this reason cargo tanks and shell plates of the vessel are resistant to the thermal stresses are used in the construction of cargo tanks. The cost price of the cargo tanks and their VIIIinsulation is the 42% of total price of the LNG vessels. Parallel to the searches on the cryogenic metals, the cost prices are decreased and the cargo tanks become larger so transportation costs are decreased, LNG transportation became economical. The main LNG importer countries are Japan and Western European countries..The main LNG exporter countries are Algeria, Indonesia, Abu Dhabi, Qatar, Libya, Malaysia and Alaska. LNG transportation is generally a part of huge natural gas projects, so LNG tankers are generally built up for servicing contracts for 15-20 years. Liquefied gas tanker fleet has a small percentage in the world cargo vessel fleet(0.6-0.7%). Obligatory rules of IMO (International Maritime Organization) standards, value of cargo which is carried, special insulation of cargo tanks, necessity of careful maintenance and repair and because of all those reasons, increasing costs are effecting the development of LNG tanker fleet, in a negative way. In LNG vessels different types of tank systems are used. Of course the most important part of LNG vessels are their tanks. France, Norway and Japan have a great role in search and development of tank systems. The tank systems that are used today can be classified as below: 1. Conch Prismatic Independent Tank 2. technigaz membrane 3. GT membrane system 4. spherical mdependent tank All these tank systems have advantages and disadvantages to each other. Although great amount of aluminum alloy is used and the construction costs are high conch prismatic independent tank system has advantages as it has high reliability and easy process. Technigaz membrane is generally used in underground LNG storage tanks. It has low construction costs and high reliability. IXGT membrane system is the most economic system among others. Because of the structure and shape of tanks, spherical indepent tank system allows over-loading and easy inspection of tank insulation. On the other hand it has difficulty in installation of tanks on the deck. The liquefaction of natural gas is the one of the main step of LNG transportation. As it was mentioned before natural gas is liquefied at atmosphere pressure at -162°C. For this process special facilities are required. The main advantage of liquefaction is the reduction of the storage volume of natural gas in a ratio of 1/600. This property is very important is transportation of natural gas. For liquefaction of natural gas there are different cycles. These are: 1. Cascade liquefaction cycle 2. Arc cycle 3. Expander cycle 4. Tealarc cycle Although the usage of natural gas is a new subject for Türkiye, the demand for it, is increasing every year. As the production of natural gas of Türkiye is not enough for the demand, natural gas is imported from other counteries. The main source of natural gas for Türkiye is the pipeline arriving from Russia. But not for depending to only one source and for finding new sources, Türkiye is planning to import natural gas also by sea. For this reason BOT AS Marmara Ereğli LNG terminal was constructed. The main functions of the BOTAŞ LNG import terminal are: 1. LNG ship unloading and storage 2. LNG vaporization and natural gas send out. LNG ships will visit the terminal on a regular basis subject to available storage capacity which in turn is depend upon gas vaporization and send out rates.Three storage tanks each with a capacity of 85,000m3 are installed and provision is made for installation of a fourth tank. Various aspects of terminal operations include ship unloading, storage, vapour recovery and recondensing, regasificaiton and natural gas export. On completion of fuxture expansion the terminal will export natural gas at an average annual rate of 6.0 billion Nm3 with a peak flowrate of 685.000 Nm3/hour. Terminal has a quay where LNG vessels having capacity between 40.000m3 and 125.000m3 with max. Length of 300 m can alongside. LNG transportation by sea is a new method of sea transportation for our country. Türkiye is planning to carry LNG by its own ships, so Türkiye is planning to have LNG tankers in close future. Economic size, speed and number of LNG tankers must be decided on advance. It is planned that in 2020 natural gas demand will reach the amount of 82,000 milyon m3. It is expected that LNG carried by sea will be the 27% of the total natural gas demand in Türkiye. Two LNG export terminal Arzew in Algeria and Umm-Said in Qatar were compared to each other according to their distance to BOTAS terminal and maximum LNG that could be carried. As a conclusion Algeria or any other Mediterranean LNG export countr was found to be more suitable for importing LNG. XI 92 |
