Kömür yakıtlı bir termik santralin sistem modellemesi
System modelling of a coal fired power plant
Yazar: TANILAY ÖZDEMİR
Danışman: PROF. DR. ÜNER ÇOLAK
İstanbul Teknik Üniversitesi / Enerji Enstitüsü / Enerji Bilim ve Teknoloji Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Bilim ve Teknoloji = Science and Technology

Özet:
Enerji, insan hayatının her aşamasında kullanılması zorunlu bir unsur haline gelmiştir. Nüfus artışı başta olmak üzere gelişen sanayileşme ve teknoloji çağının bir etkisi olarak enerjiye duyulan ihtiyaç artmaktadır. Bu ihtiyacı karşılama amaçlı kurulmuş enerji dönüşüm santralleri, enerji kaynaklarından elde edilen ısı, mekanik ya da potansiyel enerjiyi elektrik enerjisine çevirirler. Ülkemizde bulunan yeraltı kaynaklarının yetersizliği dolayısıyla enerji üretiminin büyük çoğunluğu dış ülkelerden temin edilen kaynaklar ile karşılanır. Ülkemizin ekonomik yönden dışa bağımlılığının azaltılması ve halihazırda yerli enerji üretim kaynağı olarak bulunan kömür rezervlerinden faydalanılması için kömür ile çalışan termik santrallerin kurulması önemlidir.
Dünya enerji üretiminde en çok kullanılan enerji kaynağı kömürdür. Kömür, yapısı gereği dünyanın çoğu bölgesinde rastlanabilen bir yeraltı madenidir. Özellikle düşük ısıl değerine sahip linyit kömürü, santrallerde elektrik üretimi amaçlı kullanılmaktadır. Ülkemiz elektrik üretiminin %14'ü yerli kömür, %12,3'ü ise ithal kömür ile sağlanmaktadır. Bu bağlamda kömür yakıtlı santrallerin iyi analiz edilmesi ve verim artırma uygulamalarıyla birlikte ülkemizin sahip olduğu kömür rezervinin ihtiyatlı biçimde kullanımı elzemdir.
Yapılan bu tez çalışmasında kömürün dünyada ve ülkemizdeki elektrik üretimine katkısından kısaca bahsedilmiş, kömür yakıtlı termik santrallerin çalışma prensibi ayrıntılı olarak ele alınmıştır. Bir termik santralin verim değerinin iyileştirilmesi için yapılan çalışmalar anlatılmıştır. Kömür yakıtlı bir termik santrali oluşturan elemanlar ve görevleri hakkında gerekli bilgiler verilmiştir. Çalışmada kullanılan Flownex SE modelleme programı ve programın işleyiş biçiminden bahsedilmiştir. 
Örnek bir termik santrali oluşturan elemanlar, belirtilen değerler doğrultusunda ayrı ayrı modellenmiştir. Oluşturulan modeller birleştirilerek santral çevrimi tamamlanmış ve santral verileri üzerinde yapılan uyarlamalar yardımı ile sistemin kütle ve enerji dengesi sağlanmıştır. Çevrimin zamandan bağımsız kararlı hal durumu için enerji analizi yapılmış, her bir komponente ait güç veya ısı değerlerinin gerçek duruma uygun olduğu gözlemlenmiştir.
Program tarafından hesaplanan veriler doğrultusunda elektrik enerjisine çevrilen toplam türbin gücü 603 MW, kazanda suya aktarılan enerji 1272,6 MW, kondenserde dışarı atılan ısı miktarı 657,7 MW, toplam pompa gücü -3,5 MW, besleme suyu pompası türbini gücü 16,6 MW ve bu türbin ile tahrik edilen pompanın gücü -16,4 MW olarak bulunmuştur.
Santralde kazana gitmekte olan akışkana ön ısıtma yapılmıştır. Alçak basınç ısıtıcılarında 169,4 MW ısı akışkana aktarılmıştır. Yüksek basınç ısıtıcılarında ise 192,5 MW ısı akışkana aktarılmıştır. Böylece kazana gitmekte olan suya türbinlerden çekilen ara buharlar aracılığıyla toplam 361,9 MW ön ısıtma yapılarak kazan giriş sıcaklığı 276,3 oC'ye çıkartılmış ve santral verimi artırılmıştır.
Buhar kazanında harcanan yakıt enerjisi, santralde kullanılan kömürün üst ısıl değeri ve saniyede yakılan kömür miktarına bağlı olarak 1433 MW bulunmuştur. Yukarıda hesaplanan değerler doğrultusunda, kararlı hal durum analizi sonucunda toplam santral verimi %41,84 olarak hesaplanmıştır. 
Flownex ile kararlı hal için oluşturulmuş santral çevriminin dinamik analizi yapılmak üzere; yoğuşturucu soğutma suyu sıcaklığı, buhar kazanı çıkış sıcaklığı, yoğuşturucu pompası devir sayısı ve besleme suyu pompası devir sayısı değişken olarak belirlenmiş ve zamana bağlı davranışlarının çevrim üzerindeki etkisi incelenmiştir.
Yapılan dinamik analiz sonucunda yoğuşturucu soğutma suyu sıcaklığının 5 oC artırılması ile santral veriminin %41,28'e düştüğü, aynı miktarda azaltılması durumunda ise %42,4'e çıktığı gözlemlenmiştir. Buhar kazanı çıkış sıcaklığının ultra kritik üstü kazan sıcaklık değeri olan 600 oC'ye çıkartılması durumunda santral veriminin %42,36'ya yükseldiği, ileri düzey ultra kritik üstü kazan sıcaklık değeri olan 700 oC'ye çıkartıldığında ise santral veriminin %44,12'ye ulaştığı görülmüştür.
Yoğuşturucu pompası devir sayısının 100 dev/dak artırıldığı durumda  santral verimi %41,66'ya düşmüş, aynı miktarda azaltılması durumunda ise santral verimi %42 olarak hesaplanmıştır. Besleme suyu pompası devir sayısının 100 dev/dak artırılması ile santral verimi %41,29'a düşmüş, aynı miktarda azaltıldığında ise santral veriminin %42,46 değerine ulaştığı gözlemlenmiştir.

Abstract:
Energy has become a mandatory property at every stage of human life. It is a feature that improves our standard of lives. We need energy for everything, to use devoloping techology, power our homes, even to feed us. Increasing population, industrialization and the development of technology led to rapid growth in demand for energy. Energy conversion plants are established to meet the energy requirement. They converts heat energy that is obtained from fossil fuels into electrical energy. The large part of the electricity generation in our country are met by the resources that come from outside. Coal based power plants are important to reduce our economically dependence on foreign countries and benefit from the domestic coal reserves in the energy production 
Recent researches have been doing for renewable energy power plants since fossil fuels are finite and can not be used in several decades. Renewable energy will play an important role in electricity generation in the future. However, it is currently not common in use due to the high initial investment cost, low power generation and thermal efficiency amount. Even if they are effective and cheap, there should be power plants to achieve sustainability in energy production.
Development level and economical status of countries are determined by the amount of energy consumption and production. Turkey is 65th in the world and last in europe with the 1,551 kg of oil equivalent consumption per capita according to the datas obtained from central bank in 2012. Insufficiency of the energy production in our country can be inferred from these datas. It is necessary to take advantage of thermal power plants since each one may increase installed power of our country between 1 and 2 percentage. 
Coal is the most widely energy source for the generation of electricity in the world. It  is an underground mine that can be found in most parts of the world due to its physiological structure. Coal can be classified in many ways. Lignite, one of the coal types, has the lowest rate of carbon. Therefore, it is most useful for the generation of electricity at coal fired power plants. In our country 14 percent of electricity production is provided by domestic coals, while 12,3 percent provided by imported coals. In this context, coal fired power plants must be analyzed well and plant efficiency should be increased with the diverse applications.
In this thesis, status of coal in electricity generation has been briefly discussed. Coal fired thermal power plants operating principles were mentioned in detail. The main cyle of a thermal power plants which is ideal Rankine cycle was examined thermodynamically and the studies were done to improve cycle efficiency. Essential informations about the elements that constitute a coal based power plant were given. The task of these elements in the system was described.
Flownex SE modelling program was used to model a coal fired power plant. The elements that compose this program were described in detail.  The design criteria of these elements had been explained. A sample coal based power plant was modeled step by step with the help of modelling program Flownex SE. These steps were told particularly to understand how it works. Nominal operating conditions of the sample plant were used as data. As a result, the models that created for each element were combined and plant cycle was completed as required.
The datas of a sample plant were adapted to created plant cycle so that energy and mass balance were provided. Energy analysis was performed for steady state case. The designed power plant datas were obtained same in accordance with the analysis that is made by Fownex SE. All the components completing a plant; power consumer, power generator, heat rejector and heat extractor systems power and heat values were observed via the modelling program.
Consequently, steady state analysis results of each components were found as below. Total turbine power output converted into electrical energy was calculated as 603 MW. The amount of energy transferred to the water in steam boiler was found as 1272,6 MW. Heat rejection at the condenser was found as 657 MW. Total energy consumed by the pump are -3,5 MW. Feedwater pump drive turbine power output was calculated as 16,6 MW. Feedwater pump power output was found as 16,4 MW.
The fluid which goes to the boiler was exposed to preheating process at different pressures. 169,4 MW energy transferred to the working fluid through the low pressure feedwater heaters. Also, 192,5 MW energy supplied to the working fluid through the high pressure feedwater heaters. Thus, the working fluid was exposed to 361,9 MW total preheating process via the steams that extracted from different stages of turbines. Therefore inlet temperature of steam boiler was inreased to 276,3 oC also plant efficiency was increased by using feedwater heaters.
Fuel energy burned in the boiler was calculated 1433 MW with the help of the coal higher heating value and the amount of coal burned in seconds. As a result of steady state analysis, total plant efficiency was calculated as 41,84% in accordance with the values found above.
Steady state analysis were done for the sample power plant so that Flownex can be used for dynamic analysis by removing boundary conditions. After that process, specified input conditions of some components have to choose as variables. In this study, these were determined as condenser cooling water temperature, steam boiler outlet temperature, condensate pump speed and feed water pump speed. Dynamic analysis were done to investigate the time-dependent behavior of these variables and observe their influences on power plant cycle.
In this thesis, four different scenarios analysed in detail based on the results of a dynamic analysis made by Flownex SE. In the first scenario, the influence of the boiler outlet temperature on power plant efficiency was investigated. Steam boiler outlet temperature was increased up to super critical boiler temperature which is 600 oC. Therefore, power plant efficiency was increased to 42,36%. There is a direct proportion between steam boiler outlet temperature and power plant efficiency so that high temperature resistant materials are being developed to increase the plant efficiency. As an imaginary study, boiler outlet temperature was accepted 700 oC which is the advanced ultra super critical boiler temperature and examined that the plant efficiency had reached 44,12%. However, today it would be quite costly to obtain the materials that resist 700 oC in power plant. Although this is a method that increasing the efficiency of plant cycle, it will cause very high amount of initial investment cost in todays condition. With this study, it was understood that power plant efficiency could be achieved about 45% just by increasing the boiler temperature. By using the other enhancement applications, there would be 50% efficient coal fired power plants in the future.
In the second scenario, the effect of the condenser cooling water temperature to the power plant efficiency was examined. 5 oC increment in condenser cooling water temperature caused power plant efficiency to decrease 41,28%. On the other hand, same amount of temperature decrease raised the plant efficiency to 42,4%. As shown from Scenario- 2, 10oC reduction in the cooling water temperature caused an increase on power plant efficiency of 1,12%. However, applications to increase the cycle efficiency by reducing the cooling water temperature is limited since the water temperature can not be reduced below 0 oC.
In the third scenario, the relationship between the condensate pump speed and plant efficiency was examined. As a result, 100 rpm increase in the pump speed caused 1376,54 tones of mass flow at condensate pump per hour so the efficiency of plant had decreased to 41,66%. Same amount of pump speed decrease caused 1235,42 tones of mass flow at condensate pump per hour so that the efficiency of plant had increased to 42%.
In the fourth scenario, feedwater pump speed was changed and its impact on power plant efficiency was observed. In conclusion, 100 rpm increase in the pump speed caused 1766,24 tones of mass flow at feedwater pump per hour, thereby the efficiency of power plant had decreased to 41,29%. Same amount of decrement in pump speed caused 1596,92 tones of mass flow at feedwater pump per hour so the efficiency of power plant had become 42,46%. Entire pump calculations were done by using scaling method to the pump curves that are generated from Flownex SE. It can be inferred from case 3 and 4 that the using optimum pump speed is effective on the plant efficiency and must be well analyzed.
In this thesis, energy analysis of a sample coal fired power plant  was made by using steady state analysis method. Also 4 different scenarios were created by the help of dynamic analysis and methods to increase the power plants efficiency were discussed. In the light of these analyses, it is understood that there are lots of ways to increase the efficiency of coal fired power plants by rearranging some input parameters but the price of these adjustments must be decreased as the technology develops.