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Gas turbine design and operation training course

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Gas turbine design and operation training course

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Gas turbine design and operation training course

  1. 1. ‫ء‬ ‫وا‬ ‫ء‬ ‫ا‬ ‫وزارة‬ ‫ـ‬ ‫ر‬ ‫ــ‬ ‫وا‬ ‫داري‬ ‫ا‬ ‫ــ‬ ‫ا‬ ‫إدارة‬ Gas Turbines Design & Operation Training Course Over 100 Question & answer Over 200 Pictures ********FULLFULLFULLFULLY ILLUSTURATEDY ILLUSTURATEDY ILLUSTURATEDY ILLUSTURATED******** OPERATION ENGINEER: ABDULLAH ZAMAN ALMERZA 20-24/10/2007
  2. 2. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 2 Table of Content Page Gas turbines general notes ……………………………………………….. 10 Gas Turbine air intake system……………………………………………… 34 Gas turbine compressor………………………..……………………..……… 40 Gas turbine combustion chambers………………………….……………. 69 Gas turbine – turbine section……………………………………………… 94 Gas turbine blade cooling technique…………………………………… 108 General notes in shaft design……………….……………………………. 121 Gas turbine - start up unit………………………………………………….. 133 Gas turbine operation, control & protections…………………….. 138 Gas turbine efficiency & optimization…………………………………... 158 Appendix - a ………………………………………………………………………… 182 References ………………………………………………………………………… 187
  3. 3. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 3 List of questions ‫ـــــــــ‬ ‫ا‬ ‫ول‬ ‫ـــــــ‬- ‫؟‬ ‫وآ‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ه‬ What is the operating principal of gas turbine? 1 ‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ه‬ Gas turbine history & stages of development? 2 ‫؟‬ ‫ا‬ ‫ـــ‬ ‫ا‬ ‫اق‬ ‫ــــ‬ ‫ــــ‬ ‫ا‬ ‫ت‬ ‫اع‬ ‫ـــ‬ ‫أ‬ ‫ه‬ ‫ــ‬ What are the main types of internal combustion engine? 3 ّ ‫آــــــ‬‫ز‬ ‫ـــــــ‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ــــ‬ ‫ا‬ً‫؟‬ How can gas turbine classified? 4 ‫؟‬ ‫ان‬ ‫ـــــ‬ ‫ــــ‬ ‫ا‬ ‫ـــــ‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ـــــ‬ ‫ر‬ ‫ا‬ ‫آ‬ How aircraft gas turbines is classified? 5 ‫؟‬ ‫وا‬ ‫ا‬ ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫آ‬ How can land base gas turbines classified? 6 ‫؟‬ ‫ر‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫و‬ ‫ا‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ What is the difference between Internal & external combustion engine? 7 ‫؟‬ ‫ر‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫وا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ What is the difference between gas turbines & steam turbines? 8 ‫ا‬ ‫ا‬ ‫ه‬‫؟‬ ‫ر‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫ت‬ What are most common examples of external combustion engines? 9 ‫ا‬ ‫و‬ ‫ه‬‫؟‬ ‫دد‬ ‫ا‬ ‫وا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ر‬ What is the difference between gas turbines & reciprocating engines? 10 ‫؟‬ ‫ا‬ ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫م‬ ‫أ‬ Where are land base gas turbines used? 11 ‫ت‬ ‫ر‬ ‫ا‬ ‫م‬ ‫ذا‬‫رات؟‬ ‫ا‬ ‫ز‬ ‫ا‬ Why gas turbine doesn't used as car engine? 12 ‫؟‬ ‫ره‬ ‫أ‬ ‫ع‬ ‫ر‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫زا‬ ‫ذا‬ Why gas turbines are more expensive than reciprocating engines? 13 ‫ر‬ ‫ا‬ ‫ا‬ ‫دن‬ ‫ا‬ ‫دد‬ ‫ا‬ ‫ا‬ ‫ذا‬‫ض‬ ‫أ‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫ارة‬ ‫ا‬)‫س‬ ّ ‫ا‬ ‫دا‬ ‫اق‬ ‫ا‬ ‫ارة‬(‫؟‬ Why reciprocating engines are not made from same materials that gas turbine is made although they are suffer from very high temperature just like gas turbines? 14 ‫ا‬ ‫آ‬‫ع‬ ‫ر‬ ‫وا‬‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ How could weather conditions affect gas turbines? 15
  4. 4. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 4 ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫وا‬ ‫ان‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫أه‬ ‫ه‬ ‫؟‬ ‫ا‬ What is the main deference between land base gas turbines & gas turbine used in aircrafts? 16 ‫؟‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫م‬ ‫ح‬ Explain air intake filter house in details? 17 ‫؟‬ ‫و‬ ‫ه‬ ‫و‬ ‫ا‬ ‫ه‬ What is the main purpose of a compressor? 18 ‫ا‬ ‫ف‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫ا‬ ‫ج‬ ‫ذا‬‫؟‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫و‬ ‫اق‬ Why do we need to compress air before it is enter to the combustion chamber? 19 ‫؟‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫ا‬ ‫اع‬ ‫أ‬ ‫ه‬ What are the main types of compressors which are used in gas turbine engines? 20 ‫ذا‬‫؟‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫دد‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫م‬ Why reciprocating compressors are not used in gas turbine engines? 21 ‫؟‬Centrifugal Compressor ‫ي‬ ‫آ‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ذو‬ ‫ا‬ ‫ه‬- What are the operating principals of Centrifugal Compressor? 22 ‫؟‬Axial compressor ‫ه‬‫ري‬ ‫ا‬ ‫ا‬- What are the operating principals of axial compressor? 23 ‫؟‬ ‫ا‬ ‫ه‬ What is compressor washing process? 24 ‫؟‬ ‫ا‬ ‫ا‬ ‫ى‬ ‫ا‬ ‫ق‬ ‫ا‬ ‫ه‬ What are the alternative methods used for compressor cleaning? 25 ‫ري؟‬ ‫ا‬ ‫وا‬ ‫ي‬ ‫آ‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ذو‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ What is the difference between axial & centrifugal compressors? 26 ‫؟‬Axial Compressor Design ‫ري‬ ‫ا‬ ‫ا‬ ‫ح‬- Explain Axial Compressor in details? 27 ‫ه‬ ‫و‬ ‫ا‬ ‫ط‬ ‫أه‬ ‫ه‬‫؟‬ ‫ا‬ What are the advantages of using blow off lines in axial compressor? 28 ‫؟‬Axial Compressor‫ري‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ه‬ What are the main design considerations in axial compressor? 29 ‫؟‬ Axial Compressor ‫ا‬ ‫ه‬‫ري‬ ‫ا‬ ‫ا‬ ‫ط‬ ‫ا‬ ‫ء‬ ‫أ‬ ‫اء‬ ‫ا‬ ‫ت‬ What are the types of air effects during compression process in axial compressor? 30
  5. 5. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 5 List of questions - ‫ـــــــــ‬ ‫ا‬ ‫ول‬ ‫ـــــــ‬ ‫؟‬Axial Compressor ‫ري‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ ‫ة‬ ‫ه‬ ‫ه‬ What is the definition of compressor surge? 31 Axial Compressor ‫ري‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ ‫ب‬ ‫أ‬ ‫ه‬ What are the main reasons of compressor surge? 32 ‫؟‬ Axial Compressor ‫ري‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ ‫ا‬ ‫ق‬ ‫آ‬ How can compressor surge be avoided by improving compressor design? 33 ‫؟‬Compressor Surge Protection ‫ري‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ ‫و‬ ‫ه‬ What is compressor surge protection? 34 ‫اق؟‬ ‫ـــــــ‬ ‫ا‬ ‫دئ‬ ‫ـــــ‬ ‫ه‬ What are the main principals for combustion? 35 ‫؟‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫ت‬ ‫ــــ‬ ‫ه‬ What is the requirement for a good combustion? 36 ‫اق؟‬ ‫ا‬ ‫ء‬ ‫ا‬ ‫ا‬ ‫ه‬ What are the important factors for combustion to start? 37 ‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫ف‬ ‫ـــ‬ ‫اع‬ ‫أ‬ ‫ه‬ What are the main types of combustion chamber which are used in gas turbines? 38 ‫اق؟‬ ‫ـ‬ ‫ا‬ ‫ـــ‬ ‫اء‬ ‫أ‬ ‫ه‬ What are the main parts of combustion chamber? 39 ‫؟‬ ‫اق‬ ‫ا‬ ‫ء‬ ‫أ‬ ‫د‬ ‫وا‬ ‫اء‬ ‫ا‬ ‫ط‬ ‫ا‬ ‫أه‬ ‫ه‬ What is the importance of good mixing between fuel & air during combustion process? 40 ‫؟‬ ‫اق‬ ‫ا‬ ‫ا‬ ‫ط‬ ‫ا‬ ‫ه‬ What are the important points to be considered in a combustion process? 41 ‫؟‬ ‫اق‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫أه‬ ‫ه‬ What are the factors that affect combustion process? 42 ‫اق؟‬ ‫ا‬ ‫ء‬ ‫أ‬ ‫ا‬ ‫ل‬ ‫ا‬ ‫ه‬ What are the different configurations of the flame during combustion process? 43 ‫؟‬diffusion Flame - ‫د‬ ‫ا‬ ‫د‬ ‫ا‬ ‫و‬ Premix Flame ‫ط‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ق‬ ‫ا‬ ‫ه‬ What is the difference between Premix flame & diffusion flame? 44 ‫؟‬Hybrid Burner ‫ا‬ ‫اق‬ ّ‫ـ‬ ‫م‬ ‫ا‬ ‫ا‬ ‫ه‬- What is the general configuration of the hybrid burner? 45 ‫؟‬ ‫س‬ ‫ذا‬ ‫و‬ Flame Humming ‫ــ‬ ‫ا‬ ‫ي‬ ‫ا‬ ‫ا‬ ‫ه‬- What is flame humming & why it is important to measure it? 46 ‫اق؟‬ ‫ــــ‬ ‫ا‬ ‫ء‬ ‫أ‬ ‫اء‬ ‫ا‬ ‫ا‬ ‫ـــ‬ ‫ه‬ What are the stages of the air during combustion? 47
  6. 6. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 6 List of questions - ‫ـــــــــ‬ ‫ا‬ ‫ول‬ ‫ـــــــ‬ ‫؟‬NOx emission ‫ا‬ ‫اق‬ ‫ا‬ ‫ف‬ ‫ا‬ ‫و‬ ‫ا‬ ‫أآ‬ ‫ث‬ ‫إ‬ ‫ق‬ ‫ه‬‫ر‬ What are the various methods used to educe NOx emission form gas turbines? 48 ‫؟‬SOx emission ‫ر‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫ف‬ ‫ا‬ ‫ا‬ ‫أآ‬ ‫ث‬ ‫إ‬ ‫ق‬ ‫ه‬- What are the various methods used to reduce SOx emission from gas turbines? 49 ً ‫ت‬ ‫ر‬ ‫ا‬ ‫آ‬ How can turbines in general are classified? 50 ‫؟‬Radial ‫آ‬ ‫أوا‬ Axial ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫أآ‬ ‫ام‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ع‬ ‫أي‬ Which types of turbines is most common radial or axial turbine? 51 ‫؟‬ Reaction turbine ‫ر‬ ‫و‬‫ا‬ ‫رد‬ Impulse turbine ‫ــ‬ ‫ا‬ ‫ر‬ ‫ت‬ ‫أ‬ ‫ه‬ What are the main principals of impulse &reaction turbines? 52 ‫؟‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ه‬ What are the main considerations that used in turbine design? 53 ‫؟‬Reaction Turbine ‫ا‬ ‫رد‬ ‫ر‬ ‫و‬ Impulse turbine ‫ا‬ ‫ر‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ What is the main difference between impulse & reaction turbines? 54 ‫؟‬ ‫ــ‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ل‬ ‫ا‬ ‫ه‬ What are the different configurations of impulse turbine? 55 ‫أي‬‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫م‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ع‬ Which type of turbines is used in gas turbines? 56 ‫؟‬ ‫ــ‬ ‫ز‬ ‫ا‬ ‫ــ‬ ‫ر‬ ‫ا‬ ‫ح‬ ‫ــ‬ Explain gas turbine design? 57 ‫؟‬ ‫ـ‬ ‫ر‬ ‫ـ‬ ‫وا‬ ‫آ‬ ‫ا‬ ‫ا‬ ‫ق‬ ‫ه‬ What are the methods used to cool turbine fixed & moving blades? 58 ‫ء؟‬ ‫وا‬ ‫اء‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ What is the main deference between air cooled blades & water cooled blades? 59 ‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫م‬ ‫ا‬ ‫ا‬ ‫م‬ ‫ءة‬ ‫آ‬ ‫س‬ ‫آ‬ How blade cooling effectiveness is measured? 60 ‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫آ‬ ‫وا‬ ‫ا‬ ‫آــ‬ ‫وا‬ ‫ا‬ ‫ه‬ What is the definition of Corrosion & Erosion for gas turbine blades? 61 ‫؟‬ ‫ر‬ ‫ا‬ ‫د‬ ‫إ‬ ‫ض‬ ‫ي‬ ‫ا‬ ‫ا‬ ‫ه‬ Which part in gas turbine is suffered from the highest thermal stress? 62 ‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫آ‬ ‫وا‬ ‫ا‬ ‫آــ‬ ‫وا‬ ‫ا‬ ‫ب‬ ‫أ‬ ‫ه‬ What are the main causes of Erosion & Corrosion on turbine blades? 63 ‫؟‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫و‬ ‫آ‬ ‫ا‬ ‫ل‬ ‫ا‬ ‫ه‬ What are the methods used to reduce Corrosion & protect turbine blades? 64
  7. 7. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 7 ‫؟‬ ‫ر‬ ‫ا‬ ‫آ‬ ‫ا‬ ‫ا‬ ‫ض‬ ‫ا‬ ‫ا‬ ‫دات‬ ‫ا‬ ‫اع‬ ‫أ‬ ‫ه‬ What are the types of loads that exerted on rotating turbine blades? 65 ‫؟‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫اآ‬ ‫آ‬‫ر‬ ‫ا‬ ‫ءة‬ ‫آ‬ How does deposits formation on turbine blade affect turbine efficiency? 66 ‫؟‬ ‫ر‬ ‫ا‬ ‫ءة‬ ‫آ‬ ‫ا‬ ‫ث‬ ‫ي‬ ‫ا‬ ّ ‫ا‬ ‫آ‬ How does the damage to turbine-blades tell upon the efficiency of the unit? 67 ‫ا‬ ‫ن‬ ‫وآ‬‫؟‬ ‫ذاة‬ Shaft Alignment ‫وار‬ ‫ا‬ ‫ا‬ ‫ذاة‬ ‫ذا‬- Why shaft alignment process is important & how can we perform this process correctly? 68 ‫ت‬ ‫ر‬ ‫ا‬ ‫ه‬ ‫دون‬ Journal Bearings ‫ة‬ ‫ا‬ ‫ذات‬ ‫ا‬ ‫ا‬ ‫آ‬ ‫م‬ ‫ذا‬ ‫ز‬ ‫ا‬‫؟‬ ‫ر‬ ‫وا‬ Why Journal bearings are used in large turbines? 69 ‫؟‬ ‫ا‬ ‫ا‬ ‫وار‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ز‬ ‫م‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫م‬ ‫ذا‬ Why lifting oil is used in some turbines to lift their shafts? 70 ‫آ‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫م‬ ‫ذا‬‫ا‬ ‫آ‬ ‫م‬ ‫وا‬ ‫ري‬ ‫دة؟‬ ُ Why we use only one axial bearing in turbine shaft instead of multiple bearings? 71 ‫؟‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫وا‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫وار‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫ه‬ What are the main deference between gas turbine shaft & steam turbine shaft? 72 ‫ج؟‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫أآ‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ن‬ ‫ذا‬ Why gas turbine is larger than steam turbine for the same power output? 73 ‫ذا‬ ‫و‬ ‫ر‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫ه‬‫؟‬ What is critical speed for turbine rotor & why do we have to avoid it? 74 ‫؟‬ ‫ر‬ ‫ا‬ ‫د‬ Sagging ‫ء‬ ‫ر‬ ‫وا‬- hogging ‫س‬ ‫ا‬ ‫وث‬ ‫ا‬ ‫ب‬ ‫ا‬ ‫ه‬- What are the main reasons for shaft Hogging & Sagging? 75 ‫ا‬ ‫ب‬ ‫ا‬ ‫ه‬‫؟‬ ‫ر‬ ‫ا‬ ‫د‬ ‫ازات‬ ‫ه‬ ‫ا‬ ‫وث‬ What are the main reasons of shaft vibration in turbine 76 ‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫و‬ ‫ارة‬ ‫ا‬ ‫و‬ ‫وران‬ ‫ا‬ ‫م‬ ‫ن‬ ‫آ‬ How is the torque, pressure & temperature distribution on gas turbine 77 ‫؟‬ ‫ر‬ ‫ا‬ ‫آ‬ ‫ا‬ ‫ا‬ ‫ة‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ازات‬ ‫ه‬ ‫ا‬ ‫م‬ ‫ا‬ ‫ا‬ ‫ه‬ What are the methods used to reduce vibrations at last stage of turbine? 78
  8. 8. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 8 ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫أآ‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫د‬،‫؟‬ ‫ذا‬ Why the number of steam turbine stages is larger than gas turbines stages? 79 ‫؟‬ ‫ر‬ ‫ا‬ ‫د‬ ‫ا‬ ‫دارة‬ ‫ا‬ ‫أه‬ ‫ه‬ What is the importance of turning gear operation for turbine rotor? 80 ‫دارة‬ ‫ا‬ ‫ء‬ ‫ز‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ج‬ ‫ذا‬‫؟‬ Why are gas turbines needs start up unit? 81 ‫رات‬ ‫ا‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫دارة‬ ‫ا‬ ‫ء‬ ‫ـ‬ ‫ة‬ ‫أ‬ ‫اع‬ ‫أ‬ ‫أ‬ ‫ه‬‫؟‬ What are the most common starters which are used in aircraft gas turbine engines 82 ‫ا‬ ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫دارة‬ ‫ا‬ ‫ء‬ ‫ة‬ ‫أ‬ ‫اع‬ ‫أ‬ ‫ه‬‫؟‬ What are the most common starters which are used land base gas turbines? 83 ‫ه‬‫ــ‬‫ا‬‫ــــــ‬‫ا‬‫ــــ‬‫ــــ‬‫ا‬ ‫ة‬‫ـــ‬‫؟‬ What is the main purpose of control system? 84 ‫ا‬ ‫اآ‬ ‫ا‬ ‫اع‬ ‫ا‬ ‫ه‬/‫ر‬ ‫ا‬ ‫ا‬ ‫ا‬‫؟‬ ‫ر‬ ‫ا‬ ‫ت‬ What are the main types of speed/load controller that used in steam turbines? 85 ‫ه‬‫ا‬ ‫آ‬ ‫ا‬ ‫اع‬ ‫ا‬/‫ا‬‫؟‬ What are the main types of speed/load controllers? 86 ‫ت‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫ن‬ ‫أن‬ ّ ‫ذا‬‫إ‬ ‫ة‬ ‫وا‬ ‫ا‬ ‫؟‬ Why it is preferred to make speed droop setting same for all turbines which are connected to the same network? 87 ‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫اآ‬ ‫ا‬ ‫اع‬ ‫أ‬ ‫ه‬ What are the types of governors which are used in gas turbine? 88 ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫دة‬ ‫ز‬ ‫ن‬ ‫آ‬‫؟‬ Describe the process of increasing gas turbine load? 89 ‫ح‬ ‫ر‬ ‫ا‬ ‫آ‬ ‫ا‬ ‫ا‬ ّ‫ن‬‫أ‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ة‬ ‫ا‬ ‫دة‬ ‫ز‬ ‫ه‬ 100%‫؟‬ Could we increase the gas turbine load even if compressor inlet guide vanes are fully open? 90 ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ــ‬ ‫ا‬ ‫ط‬ ‫ا‬ ‫ه‬‫؟‬ What are some of the factors that may determine the service life of gas turbine components? 91
  9. 9. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 9 ‫ا‬ ‫ا‬ ‫ه‬‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ب‬‫؟‬ What is the method used to calculate gas turbine service life? 92 -‫ا‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫ارة‬ ‫در‬ ‫ه‬‫؟‬ What is the effect of compressor inlet temperature on gas turbine output power? 93 ‫ه‬‫؟‬ ‫ــ‬ ‫ز‬ ‫ا‬ ‫ــ‬ ‫ر‬ ‫ا‬ ‫ات‬ What is the start up sequence of land base gas turbine? 94 ‫ا‬ ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫أه‬ ‫ه‬‫؟‬ What are the most important protections used in land base gas turbines? 95 ‫ا‬ ‫ه‬‫د‬‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ What are the losses in gas turbine? 96 ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ءة‬ ‫ا‬ ‫ر‬ ‫ق‬ ‫ه‬‫؟‬ What are the methods used to improve land base gas turbine efficiency? 97 ‫؟‬Axial Compressor ّ ‫ء‬ ‫ا‬ ‫ا‬ ‫ن‬ ‫ذا‬‫ي‬ ‫ر‬ ‫ا‬ Why compressor intercooling is not wildly used in axial compressors? 98 ‫؟‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ق‬ ‫ا‬ ‫ب‬ ‫و‬ ‫ات‬ ‫ه‬ What are the main advantages & disadvantages of cooling systems which are used for compressor inlet cooling? 99 ‫آ‬ّ‫ـ‬‫ــ‬‫وا‬ ‫ا‬‫ــــ‬‫آ‬ ‫ا‬‫ـــ‬‫؟‬ How combined cycles are classified? 100 ‫؟‬ ‫آ‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫ا‬ ‫اررة‬ ‫ا‬ ‫ع‬ ‫إ‬ ‫ا‬ ‫اع‬ ‫ا‬ ‫ه‬ What are the main Configurations of heat recovery steam generator? 101
  10. 10. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 10 GAS TURBINE GENERAL NOTESGAS TURBINE GENERAL NOTESGAS TURBINE GENERAL NOTESGAS TURBINE GENERAL NOTES ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ــ‬ MS6001B-G.E.
  11. 11. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 11 1-‫؟‬ ‫وآ‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ه‬ 1-What is the operating principal of gas turbine? Gas turbine is an internal combustion engine, it is designed to accelerate a stream of gas, which is used to produce a reactive thrust to propel an object or to produce mechanical power to turn a load, the principal of operation of the gas turbine can be explained by the following examples: *-Example (1): Figure (1)1500AD-Old Style Gas Turbine for BARB-Q not for Power generation! (The sketch is drawn by Leonardo de Vinci) Cold air is enter from the hole at bottom of the oven, as its mix with the hot gases that released from the combustion its temperature will increase & hence its density will drop, then it will move up word & another cold air will replace hot air with continues action, due to the movement of hot air to the top, it will create a natural draft that pass through a series of blades that turned the roasting spit so provide power to the attached mechanism. *-Example (2): Figure (2.A) shows a cylinder cross section with a fan on each end, now if the left hand fan is started via an limited speed electric motor, it will draw air inside the cylinder which will cause the right hand fan to
  12. 12. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 12 rotate at the same speed of the other fan (if we neglect air pressure losses yet velocity losses inside the cylinder). If we drill a hole in the cylinder surface between both fans & we ignite a continues flame Figure (2.B), the temperature of the air that passes through the flame will increase & also its specific volume, this will cause the right hand fan to rotate even faster than the left hand fan (because the air occupied a larger area than before after being heated since its specific volume increased & hence its volumetric flow rate will increase). Now, if we disconnect the electric motor that rotates the left hand fan & we connect the left hand fan with right hand fan by a shaft & we insure a continuous flam Figure (2.C), the right hand fan will produce a mechanical power that is sufficient to rotate the left hand fan & another applied load. Figure (2) Simplified gas turbine Now the idea of gas turbine is clear: 1- The left hand fan represents the COMPRESSOR 2- The right hand fan represents the TURBINE 3- The flame represents the COMBUSTION CHAMBER 4- The electric motor represents the START UP UNIT of the gas turbine.
  13. 13. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 13 5- Another applied load could be an electric generator, pump, or thrust propulsion as in aircraft ….etc. 6- There is additional part of the gas turbine which is the AIR FILTER to insure clean air entrance. Now if we look to Figure (3) we can realize real gas turbine configuration. Figure(3) open cycle gas turbine 2-‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ه‬ 2- Gas turbine history & stages of development? a- First successful design for a gas turbine is done by a lot of pioneers at the same time, one of them is Sir Frank Whittle (England); he make painting for first gas turbine on 1930 but similar patent record in Germany & Italy on the same year. Whittle developed a working gas turbine engine in April 1937 which was used to drive the first successful turbojet airplane in Britain; His early work on the theory of gas propulsion was based on the contributions of most of the earlier pioneers of this field. b-After the Second World War, the jet engine became the most popular method of powering aero planes and consequently the gas turbine rapidly developed to generate electric power. c-The reason why the gas turbine appeared so much later than other types of internal combustion engines was because of the difficulty of finding materials for the working parts, especially the turbine blades, as they would have to with stand extremely high temperatures of the burning gas without melting or weakening. Figure(4) Sir Frank Whittle
  14. 14. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 14 *-The following table summarizes the history of the gas turbines: Table(1) History of gas turbine development
  15. 15. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 15 3-‫؟‬ ‫ا‬ ‫ـــ‬ ‫ا‬ ‫اق‬ ‫ــــ‬ ‫ــــ‬ ‫ا‬ ‫ت‬ ‫اع‬ ‫ـــ‬ ‫أ‬ ‫ه‬ ‫ــ‬ 3-What are the main types of internal combustion engine? Most popular internal combustion engines: 1-Reiprocating engines There are two ways in which reciprocating engines classified which are: a-spark ignition engines (that burn kerosene) b-compression ignition engines (that burn diesel) other way of reciprocating engines classification is: a-Two stroke engines Figure(5) 4-stroke Reciprocating Engine
  16. 16. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 16 Figure(6) 2-Stroke Reciprocating Engine b- Four stroke engines Figure(7) 4-stroke Reciprocating Engine 2-Rotary Pistons Engine(Wankel Engine) In wankel engine, the piston has triangular shape & it produce rotating motion rather than reciprocal motion as in reciprocating engines. Main advantages of Wankel engine are its extremely lower weight compare to its power output & its low noise & vibration level. Its main disadvantages is higher fuel consumption & higher pollution level compare to reciprocating engines.
  17. 17. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 17 Figure(8) Wankel Engine • Typically, it is more difficult (but not impossible) to make a rotary engine meet U.S. emissions regulations. • The manufacturing costs can be higher, mostly because the number of these engines produced is not as high as the number of piston engines. • They typically consume more fuel than a piston engine because the thermodynamic efficiency of the engine is reduced by the long combustion-chamber shape and low compression ratio. 3-Gas turbines
  18. 18. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 18 4-‫ز‬ ‫ـــــــ‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ــــ‬ ‫ا‬ ‫آــــــ‬‫؟‬ 4-How can gas turbine is classified? Gas turbines can be classified as: a- Gas turbine that produce mechanical power to drive a load (land base). b- Gas turbine that produces thrust (propulsion) which is used to move an air planes. c- Open cycle or closed cycle or combined cycle. 5-‫؟‬ ‫ان‬ ‫ـــــ‬ ‫ــــ‬ ‫ا‬ ‫ـــــ‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ـــــ‬ ‫ر‬ ‫ا‬ ‫آ‬ 5-How can aircraft gas turbine is classified? Figure (9) Turbojet Engine Most common gas turbines that used in turbojet aero plane are: 1-Turbojet Engine: The original concept, the turbojet, is the simplest form of gas turbine and relies on the high velocity hot gas exhaust to provide the thrust. Its disadvantages today are its relatively high noise levels and fuel consumption. Figure (10) Turbojet Engine
  19. 19. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 19 2- Turbofan Engine: A turbo fan engine is based on the principal that for the same power, a larger volume of slower moving air will produce more thrust than a small volume of fast moving air. Turbofan engine is the most widely used in aircraft propulsion. There are two main types of Turbofan engines: First type: Low bypass turbofan Engines. Figure(11) Low bypass turbofan Engine Figure(12) High-bypass turbofan engine a-In the turbofan or ‘bypass’ engine the partly compressed airflow is divided, some into a central part - the gas generator or core - and some into a surrounding casing - the bypass duct. b-The gas generator acts like a turbojet whilst the larger mass of bypass air is accelerated relatively slowly down the duct to provide ‘cold stream’ thrust. The cold and hot streams mix to give better propulsive efficiency, lower noise levels, and improved fuel consumption. Second type: High-bypass turbofan engines. a-In the high bypass ratio turbofan, as much as seven or eight times as much air bypasses the core as passes through it. It achieves around 75% of its thrust from the bypass air and is ideal for subsonic transport aircraft. b-A low bypass ratio turbofan, where the air is divided approximately equally between the gas generator and the bypass duct, is well suited to high-speed military usage. 3- Turboprop Engine: As its name implies, a turboprop uses a propeller to transmit the power it produces. The propeller is driven through a reduction gear by a shaft from a power turbine, using the gas energy which would provide the thrust in a turbojet. Turboprop engines are generally used on small or slow subsonic aircraft.
  20. 20. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 20 Figure(13) Turboprop Engine Figure(14) Turboprop & Turbofan Engines comparison 4- Ramjet Engine: Figure(15) Ramjet Engine
  21. 21. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 21 A ramjet, is a type of jet engine. It contains no (major) moving parts and can be particularly useful in applications requiring a small and simple engine for high speed use; such as missiles. In a ramjet, due to the high flight speed, the ram compression of air is sufficient to provide the compressed air need for thrust. 4- Scramjet Engine: A scramjet (supersonic combustion ramjet) is a variation of a ramjet where the flow of the air and combustion of the fuel air mixture through the engine happen at supersonic speeds. This allows the scramjet to achieve greater speeds than a conventional ramjet which slows the incoming air to subsonic speeds before entering the combustion chamber. Figure(16) Scramjet Engine 5-Pulse jet engine: A pulse jet engine is an engine where its combustion occurs in pulses and the propulsive effort is a jet. A typical pulsejet comprises an air intake fitted with a one-way valve, a combustion chamber, and an exhaust pipe. Figure(17) Pulse jet schematic. First part of the cycle: air intake (1), mixed with fuel (2). Second part: the valve (3) is closed and the ignited fuel-air mix (4) propels the craft.
  22. 22. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 22 Fig (18) Mach number for various aircraft engines 6-‫؟‬ ‫وا‬ ‫ا‬ ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫آ‬ 6-How can land base gas turbines classified? a-Open cycle gas turbines: 1-Single shaft gas turbine It's the simplest form of land base gas turbines where compressor & turbine are connected via the same shaft yet they have the same speed of rotation. Figure(19) Land Base – G.E. Gas turbine
  23. 23. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 23 2-Twin spool gas turbine More complex configuration of gas turbine, in this engine there are two concentric shafts the first shaft is low pressure shaft & the other is high pressure shaft & both shafts are rotating with different speeds, the main advantages of this configuration is that the star up torque required to turn the machine is minimized compare to single shaft with the same load since only high pressure shaft needed to be turned, also compressor surge is minimized in this configuration, also its is shorter smaller & lighter than single shaft engine & has less number of blow off lines ,the main disadvantage of this configuration is additional complexity to the design & added cost. Figure(20) Twin spool - Gas turbine
  24. 24. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 24 b-Gas generator & power turbine: In this configuration, the gas turbine is used as GAS GENERATOR, the gas turbine provide stream of hot gases which turns the power turbine on the left & the power turbine turns the load. Figure(21) Gas generator with power turbine configuration c-Combined cycle gas turbines: 1- Single shaft combined cycle (Steam & gas turbines are on the same shaft via synchro self shifting clutch. Figure(22) Single shaft combined cycle
  25. 25. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 25 2-Two shaft combined cycle Figure(23) Two shaft combined cycle d-Closed cycle gas turbines: Closed cycle gas turbines are not so common like open cycles, on these engines the working fluid that is exit from turbine is goes through heat rejection process & recycled a gain as input for compressor, examples of working fluid used in this cycles are hydrogen, helium. Fig (24) Closed gas turbine cycle 7-‫؟‬ ‫ر‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫و‬ ‫ا‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ 7-What is the difference between Internal & external combustion engine?
  26. 26. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 26 ‫ر‬ ‫ا‬ ‫اق‬ ‫ا‬ External Combustion Engine ‫ا‬ ‫ا‬ ‫اق‬ ‫ا‬ Internal Combustion Engine 1 Heat addition take place outside the engine Heat addition take place inside the engine 2 Ability to burn any fuel Liquid or gaseous fuel are required 3 Complete combustion is insured Cannot utilize all of fuel energy 4 Less pollution since complete combustion More pollution since incomplete combustion 5 Mostly closed cycle (better to fix & control the properties of the working fluid) Mostly open cycle 6 Lower heat rate ( more efficient) Higher heat rate (less efficient) 8-‫ر‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫وا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬‫؟‬ 8-What is the difference between gas turbines & steam turbines? Figure(25) Installation cost of Figure(26) Requirements for water in gas turbine, steam turbine various power station & combined cycle stations
  27. 27. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 27 ‫ر‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ Steam Turbines ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ Gas Turbines 1 External combustion engine Internal combustion engine 2 More complex & required more auxiliaries Simple & has much less auxiliaries 3 Start up time is long Startup time is much less 4 Higher efficiency (less heat rate) Lower efficiency (larger heat rate) 5 Installation cost is very expensive Installation cost is cheap in comparison 6 Required large area (more civil work) Can be build any where & less civil work 7 Cannot be portable Portable gas turbine is available 8 Strongly depend on water (cannot build far away from large water source) Some configurations does not use water at all 9 Weather condition has small effect on unit performance (condenser vacuum in winter) Strongly affected by weather condition 10 Required long time for installation Shorter installation time 11 Lower noise level Higher noise level 12 Steam turbines are not as flexible as gas turbines (additional cycles cannot be added). More flexible & has different configurations 13 Long life if good maintenance is applied Shorter life 14 Much larger capacity per unit up to 1800 MW single unit Smaller in capacity up to 340 MW open cycle 15 Lower operating cost since lower heat rate Higher operating cost since higher heat rate 16 Lower operating temperature Higher operating temperature 17 Can utilize any fuel Mostly depend on natural gas or diesel 18 Load changing is slow in comparison Load changing is very fast Figure(27)Compare the efficiency of various cycles 9-‫ر‬ ‫ا‬ ‫اق‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫ا‬ ‫ه‬‫؟‬ 9-What are the examples of external combustion engines?
  28. 28. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 28 Most famous example of external combustion engine is: 1-steam turbine 2-Stirling engine ‫؟‬ ّ‫د‬‫د‬ ‫ا‬ ‫وا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ -10 10-What is the difference between gas turbines & reciprocating engines? ‫ا‬‫دد‬ ‫ا‬ Reciprocating engines ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ Gas Turbines 1 Larger size & weight Much smaller in size & weight 2 Higher efficiency for medium range Only (1-10 MW) Lower efficiency in medium range but higher efficiency for range of power >10 MW 3 The engine put in operation very fast Startup time is longer 4 Not affected by weather condition Extremely affected by weather condition 5 Cheap in comparison Very expensive 6 Required reinforced foundation to counter unbalance force produced from reciprocating motion Lower vibration energy because of its direct rotary motion 7 Produce higher vibration level & noise More smooth (lower vibration level & noise) 8 Practical for low speed - high torque applications (cannot used in high speed) preferred for high speed - low torque applications 9 Lower fuel consumption Higher fuel consumption 10 Useful in application which need higher power to heat ratio Useful in application which need lower power to heat ratio 11 Supplied fuel pressure is lower Supplied fuel pressure is higher 12 Ability to burn even heavy fuels Gas turbines firing heavy fuels is uncommon 13 Fuel consumption is proportional to the power output Consume more fuel when they are idling (compressor work) 14 Can be operated with variable load but with good fuel consumption Better fuel consumption in a constant load rather than a fluctuating load 15 Required higher maintenance cost (more moving parts) Required lower maintenance cost 16 Limited power output (up to 15 MW) Much higher power output (up to 258 MW as land base)
  29. 29. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 29 ‫ا‬‫دد‬ ‫ا‬ Reciprocating engines ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ Gas Turbines 17 Engine exhaust temperature is relatively low & hence additional firing is required to produce higher quality steam Higher turbine exhaust temperature can be utilizes to produce higher quality steam 18 In reciprocating engine, all 4-processes (intake-compression-power-exhaust) are occur in one section (the piston) Each process has a separate section 19 Igniters are needed at all time of operation Igniter used only one time during speed up Fig(28-a) Compare between internal combustion engines 11-‫؟‬ ‫ا‬ ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫م‬ ‫أ‬ 11-Where are land base gas turbines used? Gas turbine is used as prime mover in powers stations, marine propulsion, Helicopters & Tanks. *-Gas turbines are used for electric power generation in several different ways: 1-used during peak load time 2- Provide stand-by power 3-to provide a power source for black starts 4-to act as base load generating units (Recently only due to the improvement on their design which result in higher efficiency & also when they are used in combined cycles).
  30. 30. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 30 12-‫رات؟‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫م‬ ‫ذا‬ 12-Why gas turbine doesn't used as car engine? Gas turbine is not used in cars because: 1-They are very expensive. 2-The gas turbine consume a lot of fuel if idling because of added compressor work. 3-Gas turbine are not suitable for variable load application, if the gas turbine is running with 60% of its load, it will consume around 80% of fuel that used in full load. 4-Start up time for gas turbine is larger that start up time of reciprocating engines. 13-‫ره‬ ‫أ‬ ‫ع‬ ‫ر‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫زا‬ ‫ذا‬‫ر‬‫دد‬ ‫ا‬‫؟‬ 13-Why gas turbines are more expensive than reciprocating engines? 1- Gas turbine are manufactured by forming process which is much expensive than machining. 2-Gas turbines are subjected to very high temperature, so they are made from nickel & cobalt alloy which are much expensive than steel. 14-‫ارة‬ ‫ا‬ ‫ض‬ ‫أ‬ ‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫دن‬ ‫ا‬ ‫دد‬ ‫ا‬ ‫ا‬ ‫ذا‬ ‫ا‬)‫دا‬ ‫اق‬ ‫ا‬ ‫ارة‬ّ ‫ا‬‫س‬(‫؟‬ 14-Why reciprocating engines are not made from the same materials that gas turbine is made although they are suffer from very high temperature just like gas turbines a-Because the way that the reciprocating engine operates provide better cooling, when fuel air mixture is enter the hot pistons after the exhaust stroke, they will cool down the piston since they have much lower temperature than the piston & engine block although combustion process is complete & all air drawn into the piston is completely utilized (yet highest temperature form fuel is achieved). b-Also, the piston & engine block are subjected to heat at small intervals (pulse heating) due to engine excursive strokes (Intake ,Compression ,Power ,Exhaust).Furthermore, reciprocating engines are cooled by air , water & lubricated by oil (relatively cold) which improve overall cooling process & make the average temperature of the engine around 440ºC. While in gas turbines ,the turbine are subjected to very high temperature through entire period of operation & cooling techniques use to cool down turbine blades are
  31. 31. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 31 depend on air only since water cooled blades design are much expensive & additional cost must be considered (convection heat transfer coefficient for liquids is much larger than it for gases). 15-‫ع‬ ‫ر‬ ‫وا‬ ‫ا‬ ‫آ‬‫؟‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ 15-How could weather conditions affect gas turbines? Ideal gas equation of state: P = ρ*R*T P= Gas pressure in (KPa) ; T= Gas temperature in ( Kelvin = ºC + 273 ) ; R=Gas constant (KJ/KgK) ; ρ=Gas density(Kg/m3 ) Gas turbine is open cycle, it uses the ambient air as a working fluid, but it is strongly affected by ambient conditions which are: 1-Ambinet temperature: *-Ambient temperature is representing compressor inlet temperature for the gas turbine, if the temperature drops, the air density will increase & hence heaver air will be compressed by the compressor which will increase mass flow rate, note that compressor work requirements will increase also. *-As heavy compressed air enter turbine section, it will create extra expansion & more work from turbine will produced, now to put general statement we can say: As compressor inlet temperature drop, air density increase, turbine output power will increase but compressor work will increase, also fuel mass flow to the turbine will increase to handle the increase in air mass flow & extra turbine work. Fig(28) Effect of ambient temperature on gas turbine performance
  32. 32. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 32 2-Ambient pressure: As ambient pressure increase, air density will increase & the same result in the above point will follows. 3-Relative humidity: Most people who haven't studied physics or chemistry find it hard to believe that humid air is lighter, or less dense, than dry air, how can the air become lighter if we add water vapor to it? *-To see why humid air is less dense than dry air, we need to turn to one of the laws of nature the Italian physicist Amadeo Avogadro discovered in the early 1800s. He found that a fixed volume of gas, say one cubic meter, at the same temperature and pressure, would always have the same number of molecules no matter what gas is in the container. *-Imagine a cubic meter of perfectly dry air. It contains about 78% nitrogen molecules, which each have a molecular weight of 28 (2 atoms with atomic weight 14). Another 21% of the air is oxygen, with each molecule having a molecular weight of 32 (2 atoms with atomic weight 16). The final one percent is a mixture of other gases, which we would not worry about. *-Molecules are free to move in and out of our cubic meter of air. What Avogadro discovered leads us to conclude that if we added water vapor molecules to our cubic meter of air, some of the nitrogen and oxygen molecules would leave .Remember that the total number of molecules in our cubic meter of air stays the same. *-The water molecules, which replace nitrogen or oxygen, have a molecular weight of 18.(One oxygen atom with atomic weight of 16, and two hydrogen atoms each with atomic weight of 1). This is lighter than both nitrogen and oxygen. In other words, replacing nitrogen and oxygen with water vapor decreases the weight of the air in the cubic meter; that is, it's density decreases. * You might say, "I know water's heavier than air." True, liquid water is heavier, or denser, than air. But, the water that makes the air humid isn't liquid. It's water vapor, which is a gas that is lighter than nitrogen or oxygen. 4-air density: *-As air density increases, compressor mass flow will increases & same concept in the first point will follows. *-The air's density depends on its temperature, its pressure and how much water vapor is in the air.
  33. 33. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 33 Effect of air density on racing car: *-More dense, or "heavier" air will slow down objects moving through it more because the object has to, in effect, move aside more or heavier molecules Such air resistance is called "drag," which increases with air density. *- Cool, dense air slows a race car because drag force increases, but some race cars gain from dense air. Cars designed from the wheels up for racing are really like upside down airplane wings that the air pushes down on the track, increasing their grip going around curves. Denser air pushes them down harder. Effect of air density on Aircraft engines: *- Lower air density effect aircraft engine in three ways: The lifting force on an airplane's wings or helicopter's rotor decreases(1), the power produced by the engine decreases(2), and the thrust of a propeller, rotor or jet engine decreases(3).These performance losses more than offset of reduced drag on the aircraft in less dense air. *- Pilots use charts or calculators to find out how temperature and air pressure at a particular time and place will affect the air's density and therefore aircraft performance. In general, these calculations don't take humidity into account since its affects are so much less than the others. *-When the air's density is low, airplanes need longer runways to take off and land and they don't climb as quickly as when the air's density is high. 5-Elevation: Each 100 meter increase in altitude, 1% of gas turbine power will drop since as elevation increase, air density drops. 16-‫ر‬ ‫وا‬ ‫ان‬ ‫ا‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫ت‬ ‫ا‬ ‫أه‬ ‫ه‬‫ا‬ ‫ا‬ ‫ج‬ ‫ا‬ ‫ز‬ ‫ا‬‫؟‬ 16-What is the main deference between land base gas turbines & gas turbine used in aircrafts? Refer to the table in the next pages.
  34. 34. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 34 ‫ان‬ ‫ز‬ ‫ر‬ GT for Aircraft ‫ا‬ ‫ا‬ ‫ج‬ ‫ز‬ ‫ر‬ GT for power generation 1 Must have aerodynamic shape to reduce drag Can have any shape 2 No air filtration (to avoid blockage) Air filtration is required 3 Use only can type combustion chamber Flexible for any type 4 Must be designed to withstand high vibration level Casing & frame are will fixed to the ground 5 Weight & size is very important in design Weight & size is not important 6 Cannot burn any fuel (liquid fuel only) Can burn natural gas or fuel oil 7 Turbine is designed to handle fan & compressor work only where part of energy is accelerated in nozzle to provide thrust Turbine is design to handle Compressor work & extra mechanical power to the load(shaft power, electric power) 8 The aim is to produce thrust The aim is to produce mechanical power 9 Turbine & compressor size is much smaller Turbine & compressor size is larger 10 cycle modification cannot be added (weight) Any cycle modification can be added
  35. 35. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 35 Rolls Royce Gas turbine used in jet aircraft
  36. 36. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 36 GAS TURBINE AIR INTAKE SYSTEMGAS TURBINE AIR INTAKE SYSTEMGAS TURBINE AIR INTAKE SYSTEMGAS TURBINE AIR INTAKE SYSTEM ‫ز‬ ‫ا‬ ‫ر‬ ‫اء‬ ‫ـ‬ ‫ا‬ ‫م‬ M6001B-G.E.
  37. 37. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 37 17-‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫م‬ ‫ح‬‫؟‬ 17-Explain air intake filter house in details? Air Intake system in gas turbines: Gas turbines consume large mass of air (a 125 MW machine has compressor inlet flow of 438 kilograms of air per second for 50ºC ambient temperature), thus careful design of the intake system is needed to ensure that frictional losses are a minimum, and that the noise of the air entering the machine is kept to an acceptable limit. Figure (29) Side view of medium side land base gas turbine (SIEMENS-V94.2) Figure (30) Air intake filter house from inside showing air filter elements before & after installation & the hole behind each filter is for filtered air exit)
  38. 38. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 38 Air intake main parts: a- Air intake filter house Filter house normally designed to have large shape so to make sure that the pressure drop across it will minimized (each 10 mbar pressure drop will reduce turbine power by 1%), it contains air filters, air entrance guide vanes & the implosion doors. b- Filter element Air entering compressor must be filtered from any dust or residues that may enter & cause fouling to the which reduce compressor blades efficiency, the use of series of filters in stead of one big filter is more practical because design & erection complexity are reduced, also if pressure drop in air intake increases, a set of small filters can easily be removed in stead of removing the hall big filter. Figure (31) Air intake filter house Fig(32) Compressed air lines for filters purging & pulse air outlet can be seen Pulse air header pressure is 7.5 bar & each pulse has a pressure of 3 bar
  39. 39. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 39 c- Air intake silencer Due to the high speed of air entering air intake filter house, a large noise level will produced & silencer must be used to reduce noise level. The silencer contain sound absorbent baffles & these baffles are covered with perforated sheets & filled with high quality heat & moisture resistance mineral wool, this mineral wool is covered by a glass fiber which gives an additional mechanical protection for the absorbent material. d- Filter element purging system As air passes through filter elements for a long period, the filters become dirty & thus the pressure drop across them will increase, to overcome rapid increase in pressure drop either filter elements is replaced with new elements or air filter must be purged. *The filter purging system is compressed air that provided from separate air compressor, if the pressure drop across any one of the filters raw increase to more than normal limit, this compressor will start to provide compressed air for cleaning these filters. *-The compressed air will released via small holes on the air lines located behind each filter ,there are solenoid valves that operate with respect to each raw of filters to release that compressed air. *-Compressed air releasing process will done by pulsing ,so some time filters cleaning system may named as pulse air system ,complete purging process may take 84 pulses (30 minutes duration ) & the cleaning process will start from top of the air intake to the bottom so that we avoid dust to sucked again by upper filter raw. Activation of pulse air system (Example from SIEMENS V94.2 Gas Turbine): Pulse air system aim is to clean the dirty filters & to do so there are two ways to activate this system which are: a- high pressure drop across filters raw signal b- High ambient air relative humidity signal (humidity > 80% signal) a- high pressure drop across filters raw signal During gas turbine on load, the control system will monitor air intake filter house pressure drop via two pressure sensors:
  40. 40. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 40 First sensor is to measure air pressure before & after filters raw (this sensor activates pulse air system). Second sensor is to measure air pressure drop across air intake filter house (this sensor not activates pulse air system & it is associated with gas turbine protection only). Figure (33) Schematic diagram of pulse air system If the second sensor indicate very high pressure drop, a gas turbine trip will initiated by the following steps: 1-As air intake pressure drop increases, the air pressure after silencer decreases, this will create a local vacuum area, 2-Due to the vacuum inside air intake filter house, the implosion doors (4 to 6 doors) will be sucked in 3-There are limit switch on each door so for any door reach full open position, this mean that the limit switch will send open signal which will initiate gas turbine trip to protect gas turbine from operating with air intake filter house is blocked. Implosion doors are designed to make sure that the pressure inside air filter house is equalized to the atmospheric pressure to avoid air intake damage. * If the gas turbine on load, normally pulse air system will activated only due to pressure drop signal
  41. 41. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 41 Figure (34) Pressure sensors used in air intake filter house b- High ambient air relative humidity signal (humidity > 80% signal) *There is humidity sensor on air intake filter house entrance to measure ambient humidity, if humidity is raise to 80%, a signal will go to activate pulse air system, and complete purging process may take 168 pulses (1 hour duration), this is to insure dry filter & avoid condensation which may block the filters during gas turbine operation. *Normally pulse air system activated by humidity sensor only when the unit is off load, pressure drop sensor will not sense any pressure drop because air is not entering inside filter house at high speed (no pressure difference).
  42. 42. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 42 GAS TURBINEGAS TURBINEGAS TURBINEGAS TURBINE ----AIR COMPRESSORAIR COMPRESSORAIR COMPRESSORAIR COMPRESSOR ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ MS6001B-G.E.
  43. 43. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 43 18-‫؟‬ ‫و‬ ‫ه‬ ‫و‬ ‫ا‬ ‫ه‬ 18-What is the main purpose of a compressor? The compressor is located at the front behind the air intake. It consists of a spinning fan with a number of fixed blades arranged in several rows. Air is drawn into the engine from its surroundings by using compressor fans. These fans are driven from the turbine by a shaft. This air is heated by being compressed and is led into one of several combustion chambers. The Compressor can reach typical pressures up to 40 times higher than atmospheric pressure. ‫؟‬ ‫ر‬ ‫ا‬ ‫ا‬ ‫و‬ ‫اق‬ ‫ا‬ ‫ف‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫ا‬ ‫ج‬ ‫ذا‬ -19 19-Why do we need to compress air before it is enter to the combustion chamber? Gas turbine efficiency will increase whenever pressure ratio increases. Refer to Fig (29). Figure (35) Pressure ratio versus gas turbine efficiency 20-‫اء‬ ‫ا‬ ‫ا‬ ‫اع‬ ‫أ‬ ‫ه‬‫ا‬‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬‫؟‬ 20-What are the main types of compressors which are used in gas turbine engines? In general compressors are classified in two main groups: 1-Positive displacement compressors (in which air pressure is increased by reducing its volume)
  44. 44. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 44 2-Dynamic compressors (in which air pressure is increased by increasing its speed) The following table summarizes compressors classification. Figure (36) Compressors Classification *Most common compressors used in gas turbine are: 1- Centrifugal Compressor. 2- Axial Compressor. Note that both of them are of dynamic type. 21-‫ز‬ ‫ا‬ ‫ت‬ ‫ر‬ ‫ا‬ ‫دد‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫م‬ ‫ذا‬‫؟‬ 21-Why reciprocating compressors are not used in gas turbine engines? Reciprocating compressors are not used in gas turbine due to: a- They have higher vibration level due to pulsation (coming from changing rotary motion reciprocal motion to rotary motion. b- They produce very high pressure c- As gas turbine size increase, the size of reciprocating compressor must be increased & due to its heavy parts it will require larger power. d- They provide small air flow compare to centrifugal or axial compressors. e- They have a lot of moving parts (pistons, connecting arms, crank shaft, and intake & discharge valves). f- Relatively inefficient (20% - 45%).
  45. 45. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 45 g- High power consumption. h- High maintenance requirement since more moving parts are involved compared to other types of compressors. I -Good for service air application. Figure (37) Reciprocating Compressor ‫؟‬Centrifugal Compressor ‫ي‬ ‫آ‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ذو‬ ‫ا‬ ‫ه‬- - 22 22-What are the operating principals of Centrifugal Compressor? Figure (38) Centrifugal Compressor
  46. 46. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 46 Centrifugal Compressor is a dynamic compressor, it increases air pressure by accelerate it, the air enter centrifugal compressor at the center of compressor impellers & thrown out by centrifugal force to compressor discharge which is located at compressor casing arc (Direction of air flow discharge is perpendicular to the axis of rotation). Acceleration of the air is obtained through the action of one or more rotating impellers; the discharge air is free from pulsation. Figure (39) Centrifugal Compressor Diffuser Figure (40) Multistage Centrifugal Compressor Figure (41) Multistage Centrifugal Compressor ‫؟‬Axial compressor ‫ري‬ ‫ا‬ ‫ا‬ ‫ه‬- -23 23-What are the operating principals of axial compressor? All modern high output gas turbines use axial flow compressors, the principles of operation are shown in
  47. 47. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 47 Figure (43). The air enters at the left and is speeded up by a set of revolving blades. The air leaves the first set of revolving blades and enters a set of stationary blades, where the air is slowed down and its kinetic energy converted to pressure energy. This process is repeated by a lot of stages depend on the desired output pressure. (The direction of flow is parallel to the direction of the rotation). Figure (42) Axial Compressor, the lower picture showing axial compressor of SEMENS -V94.2 gas turbine & the first six stages are coated with Aluminum Pigment
  48. 48. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 48 Figure (43) Axial Compressor pressure & speed curves Refer to Fig (43): a- Moving blades accelerate air. b- Fixed blades slow down air & hence change kinetic energy of air into pressure energy. c- Discharge velocity should equal suction velocity. *-The design of compressor blades are different than turbine blades, compressor blades divergent profile which works as diffuser to increase air pressure, while turbine blades have convergent profile which is works as nozzle since turbine is reducing air pressure by changing its pressure energy into kinetic energy. Refer to Fig (44) Figure (44) Turbine & Compressor blades profile
  49. 49. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 49 *-Note that compressor blades are suffer from high stress but with lower temperature while combustion chamber suffer from high temperature but with relatively lower stress. *-In axial compressor, design of moving blades are significance to provide aerodynamic shape with minimum losses, also blade tip clearance must be as minimum as possible to improve moving blade efficiency &avoid blade tip leakage. Normally compressor moving blades have blade clearance of 7 mm to minimize blade tip losses. *-During humid weather, high humidity may occur only on the first sex stages of compressor because air is heated so rapidly & condensate may occur. To overcome pitting damage to compressor blades, the first six stages are coated with Aluminum pigment. *-Air enter compressor may contain dust or dirt (even if its passes through air intake system) & such dust or contaminations will stick into compressor blades which will affect compressor performance because: a- It will reduce compressor stage efficiency since accumulation of dirt on the moving blade will cause change in discharge angle of blade by 7º which will result in changing output velocity direction to the next stage & hence reduce blade efficiency. b- Dirt or dust when stick on compressor blades will form a hot spots, recall that compressor blades will be heated during compressor operation due to friction coming from high rotation. Dirt or dust will generate high temperature spots on the blade because they have different thermal conductivity than steel,(compressor blades are made from steel),so these hot spots will produce thermal stresses on the blade which will result on blade failure if the dirt is not removed or washed. c- Compressor blades fouling may produce turbulence to the flow; produce vibration & increase discharge temperature which will result in reduce blade efficiency. *-Most of gas turbine compressors have compressor washing unit in which compressor blades are washed with a mixture of demineralized water & special agent to remove any dirt or dust on compressor blades, washing process can be performed either when the gas turbine is running(on-line washing) or when gas turbine is stand by (off- line washing).
  50. 50. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 50 Figure (45) Compressor blade fouling ‫؟‬ ‫ا‬ ‫ه‬ -24 24-What is compressor washing process? *-The aim of compressor cleaning process is to remove deposits from blades that have caused a decline in output and efficiency of Gas Turbines. *-Pollution of the ambient air cannot be completely removed by the air intake filter system. *-compressor washing are mainly two types online & off line washing. *-Compressor washing is carried out by using detergent solution and demineralized water for the final flushing. Both fluids are sprayed onto the compressor blades through two types of nozzles: a- Jett nozzles which are consisting of two jet nozzles which inject water at high speed Jet nozzles are used for off load washing only since them inject high speed water jet which will be harmful to the blades of compressor which are rotating at synchronizing speed-3000 rpm. The effect of one droplet of water will become like a bullet. b- Spray nozzles which are uniformly spaced around the circumference of compressor inlet, upstream of the variable compressor inlet guide vanes, each producing a gentle jet of water. *-Compressor cleaning skid is consisting from a tank & pumping unit, a centrifugal pump draws the cleaning solution and demineralized water from portable tank and feeds it through a hose to the jet or spray nozzles. The cleaning solution / demineralized water are delivered at a pressure of about 10 bars. Isolation valves are used to change over from the jet nozzles to the spray nozzles and vice versa. Refer to Fig(48).
  51. 51. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 51 Figure (46) Compressor washing nozzles Figure (47) Compressor Washing Skid ‫؟‬ ‫ا‬ ‫ا‬ ‫ى‬ ‫ا‬ ‫ق‬ ‫ا‬ ‫ه‬ -25 25-What are the alternative methods used for compressor cleaning? *-Alternative methods for compressor cleaning include: a- Dissemble the compressor partially to clean the blades of the rotor, this method gives excellent result but it required long time outage. b- Injection of crushed walnut shells, Injection of rice & Injection of concentrated carbon. The second method should not be used in modern gas turbines because: a- Fire hazard.
  52. 52. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 52 b- Oil system contamination & blockage. c- Result in blade cooling system fouling. d- Early hot component failure. Figure (48) Types of compressor washing nozzles ‫ري؟‬ ‫ا‬ ‫وا‬ ‫ي‬ ‫آ‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ذو‬ ‫ا‬ ‫ر‬ ‫ا‬ ‫و‬ ‫ه‬ -26 26-What is the difference between axial & centrifugal compressors? ‫ري‬ ‫ا‬ ‫ا‬ Axial Compressor ‫ي‬ ‫آ‬ ‫ا‬ ‫د‬ ‫ا‬ ‫ذو‬ ‫ا‬ Centrifugal Compressor 1 Higher efficiency (82% - 90%) Lower efficiency (72%-82%) 2 Larger in size Smaller in size 3 Has higher isentropic efficiency Has lower isentropic efficiency 4 Longer in size Shorter in size 5 Good for medium pressure/flow application Good for low pressure / large flow application 6 Used in higher speed application (aircraft engines) Used in high speed application (land base gas turbines) 7 Its performance will reduces as dirt is contaminated on its blades surface Not liable to loss its performance due build up of dirt on its blades surface 8 Multistage configuration is done with no pressure losses As number of stages increases pressure losses will increases 9 More expensive Less expensive
  53. 53. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 53 Figure (49) Compressors operating range ‫؟‬Axial Compressor Design ‫ري‬ ‫ا‬ ‫ا‬ ‫ح‬- -27 27-Explain Axial Compressor in details? Axial compressor consists of: 1-Stator & Guide Blade Carrier 2-Rotor 5-Blow off Lines 3-Inlet Guide Vanes 4-Exhaust Diffuser Figure (50) SIEMENS-V94.2 Gas Turbine Longitudinal section (Compressor section)
  54. 54. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 54 1-Stator & Guide Blade Carrier: *-Compressor stator consists of three guide blade carrier, they are separated from each other to provide good control in blade tip clearance, guide blade carrier position can be adjusted using eccentric bolt which provide flexibility to guide blade carrier movement in all direction except axial direction by 3 mm. *-There are gaps on compressor stator which provide passages to blow off air. *-Blade tip clearance is measured by six peep holes located on compressor stator. *-There are carbon rings fitted in segments around the shaft to protect moving blades from rubbing compressor stator on the event of rotor misalignment. *-Usually compressor stator is made up from steel alloys. 2-Compressor rotor: *-The rotor is consisting of a serious of rotor disks which are joined to gather by Hirth Coupling, refer to Fig(50) & Fig(51) .Rotor disk is holding the moving blades of the compressor. *-Rotor disks are hollow from inside & there are central tie bolt which insure that they are hold into position, note that there is a gap between rotor disks ( about 3 mm) & central tie bolts, this gap is to provide passages for extracted air from compressor to cool down hot components (combustor & turbines). *-Damper rings are used to reduce vibration of central tie bolt by supporting it with rotor disks. *-Rotor is supported by radial & axial bearings (journal bearings). *-Compressor rotor is made up from steel alloys & its blades generally made by machining process. Figure (51) Compressor Rotor Disk
  55. 55. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 55 Figure (52) Hirth Coupling 3-Compressor variable inlet guide vanes (I.G.V.): *-Most of modern gas turbine contain Variable Inlet Guide Vanes, They normally set to be open for 40% when the unit is stand by, once the gas turbine starts they put under control to being used to provide the air necessary for the given load & also to control turbine outlet temperature & avoid increase in temperature by increase I.G.V. opening position to increase compressor flow to cool down turbine. *- I.G.V. is used to control compressor flow for a given load & to control boiler inlet temperature in combined cycle, also I.G.V. is set at 40% open during gas turbine start up to reduce compressor inlet flow which will reduce stresses on first stage moving blade of compressor (longest moving blade in compressor) during start up. The movement of inlet guide vane is done via electric motor which is attached to guide vane mechanism see Fig(53). *-As the gas turbine load increases, IGV opening position will increase until it reach 100% open & at this time the unit is said to be under base load operation (i.e. compressor flow is maximum) ,note that additional fuel input to the gas turbine will increase turbine inlet temperature to higher value & extra power can be supplied but in this case the unit is said to be under Peak load operation since turbine outlet temperature is higher than in case of base load operation due to I.G.V. cannot open more (100% already) to provide necessary cool down to the turbine.
  56. 56. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 56 Figure (53) Compressor variable inlet guide vanes (I.G.V.) 4-Exhaust Diffuser: *- Exhaust Diffuser is used to provide further increase in air pressure also to remove vortices from air & make it more laminar since air direction is being changed along the entire compressor stages & hence its turbulence increased. *-Number of compressor stages is more than turbine stages since increasing air pressure from axial compressor (dynamic compressor) required either increasing the size of stages or increase number of stages to produce the desired pressure. 5-Blow off Lines: *-Blow-Off Systems are designed to Control the Pressure / Flow Ratio, During Low Speed Running, such as star up period. *-Axial flow compressor contain blow off line (or bleed lines) to blow out some of the air entering the compressors during start up to the exhaust (by pass the combustion chamber & turbine), this help to eliminate
  57. 57. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 57 compressor surge during low speed operation (start up).On each of this lines there are blow off valve normally butterfly type & its operates by compressed air from compressor extraction. *-Blow off lines usually placed at 30% & 60% through the compressor, For axial compressor having 10 stages, one blow off valves are required & large axial compressor need three lines, not that compressor surge associated only with dynamic compressors & positive displacement compressor do not need blow off valve. Figure (54) Compressor Blow off Lines
  58. 58. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 58 28-‫؟‬ ‫ا‬ ‫ه‬ ‫و‬ ‫ا‬ ‫ط‬ ‫أه‬ ‫ه‬ 28-What are the advantages of using blow off lines in axial compressor? *-Advantages of blow off lines: 1- They blow off air is used as anti icing to prevent blockage due icing in air intake filter house in cold weather, this bleed air (warmer than outside air) is re circulated to compressor inlet again. 2- Bleed air is used as purge air for furnace in combined cycle. 3- Blow off lines Dissipate Energy in Event of Trip, Preventing Over-speed. 4-If the speed is reduced to less than under frequency limit, blow off valves will open to prevent compressor surge. *-Refer to Fig(54) There are two blow off lines on 30% of compressor length (stage#5) & one blow off line on 60% of compressor length (stage#10),the reason why there are two blow off line at 30% of compressor length is because the air pressure at this stage is not high so its volume is bigger, this means that we need to blow a lot of air out ,but in 60% length of compressor (stage#10) air is pressurized so only little amount of air must be sent out & hence one blow off line is enough. *-Note that: Blow off valves of at stage #5 will closed at 38Hz (2280rpm) Blow of valve at stage #10 will closed at 49Hz (2940 rpm) Fig(55) Blow off lines *-Compressor must supply two types of air: 1- Air that discharge from last stage of compressor & enter combustion chamber to being utilized for combustion. 2- Air that is extracted from compressor at different location via hidden passages & sent to provide film cooling for the hot component of gas turbine (combustion chamber & turbine section).
  59. 59. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 59 *-Each 1% of air extraction from compressor will reduce turbine power by 2% because extracted air is used to cool down hot component but not as air for combustion. ‫؟‬Axial Compressor ‫ري‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ا‬ ‫ه‬ -29 29-What are the main design considerations in axial compressor? 1-Back Work Ratio (B.W.R.): It is the ratio of compressor work (Wc) to turbine work (Wt) B.W.R.= Wc/Wt Compressor mechanical power required to compress air is supplied by the turbine, for large gas turbines back work ratio greater than 0.5 can be found. The gas turbine must provide additional mechanical power to drive its compressor. Therefore, the turbine used in gas turbine is larger than those used in steam turbine for the same net power output. Fig (56) Back Work Ratio 2-Pressure Ratio(rp): Pressure ratio is the compressor discharge pressure over compressor inlet pressure, for modern gas turbines this ratio exceeds 20. Fig (57) for a fixed value of compressor inlet &turbine inlet temperatures, an increase in pressure ratio will result in increasing turbine work to maximum then it will decrease
  60. 60. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 60 3-Hub/Tip Ratio: This is the ratio of the diameter of the hub into which the blades are fitted (Stator) to the diameter over the tips of the blades (the outside diameter of the whole rotor at that section). Hub/Tip Ratio= R1/R2 Fig(58) Hub/Tip Ratio *-Hub/tip ratio has an effect on compressor design. A low value permits a slightly smaller overall compressor diameter, but increases the blade height. *- At the intake end the hub/tip ratio is not normally less than about 0.5, while at the exit end of the compressor its value is 0.9 (i.e. blade length is minimum). 4-Aspect Ratio: The aspect ratio of the blade is given by
  61. 61. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 61 Fig(59) Terms Used in Describing Compressor Blade design A high value of aspect ratio gives a higher efficiency of the compressor. However, the blade height is fixed by the mass flow of air at the stage being considered, and changes in the aspect ratio can only be made by changing the chord length, so to increase aspect ratio we have to lower chord width. The disadvantage is that the blades are thinner and hence blade vibration problems will occur. 5-Mean Blade Diameter: As the air passes along the length of the compressor, its specific volume decreases, and since the flow velocity parallel to the longitudinal axis remains approximately constant (land base gas turbine have constant speed (synchronizing speed at all load intervals), it follows that the cross-sectional area needed to reduce to compensate decreasing in air volume. Methods to reduce area is tapering down the inside diameter of the outer casing. Also, increasing the rotor outside diameter while holding the stator inside diameter constant. Furthermore, these two methods can be combined by increasing the rotor diameter & reducing the diameter of the casing. *-Note that axial flow compressor is design to have constant flow speed if its shaft speed is constant from no- load to full load. However, this is not the case in gas generator & power turbine configuration. *-the speed of two spools (HP & LP shafts) are mechanically independent but a strong aerodynamic coupling exists.
  62. 62. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 62 Fig(60) Methods of Decreasing Compressor Cross-sectional Area to Compensate for Decrease in Specific Volume of Air as Pressure Increases Along Length of Compressor Hint: The above notes are simplification about compressor design; major compressor design will be determined by a lot of complex factors. *-Refer to Fig(60) which shows three types of reducing compressor cross-sectional area. In (a) the mean diameter decreases as the air moves through the compressor. In (b) the mean diameter increases and in (c) the mean diameter remains constant. Generally the effects of blades mean diameter are that: (a) Can generate very high pressure ratios (b) limited to pressure ratios of about 14(c) Offers a useful solution since it can handle pressure ratios up to about 24. 6-Compresosr blade twist: Compressor blade must be twisted in order to maintain same blade velocity vector (blade speed is maximum at tip & minimum at root), the velocity vector will be different at each radius of the blades &
  63. 63. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 63 hence the angles of the blade necessary to meet the air stream correctly will vary at each radius of the blade which will represent poor design to the blade, so compressor blades must be twisted to obtain correct angle for all blade radii. you can see clearly blade twist on Fig(61) Fig(61)Compressor blade twist *-Note that compressor blade twist decrease as we move along compressor length since at these stages compressor blade length is decreasing so blade twisting is reduced. *-Compressor blade airfoil is vary in shape depend on air speed inside compressor, refer to Fig(63). ‫؟‬ Axial Compressor 30-‫ري‬ ‫ا‬ ‫ا‬ ‫ط‬ ‫ا‬ ‫ء‬ ‫أ‬ ‫اء‬ ‫ا‬ ‫ات‬ ‫ه‬ 30-What are the types of air effects during compression process in axial compressor?
  64. 64. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 64 Fig (62) Types of air circulation in axial compressor Fig(63)Compressor blade airfoil Design Z=Chord thickness/Chord length (a)-Subsonic Blades (M<0.7; Z=45%) (b)-Transonic Blades (1.3 >M >0.7; Z=65%) (c)-Supersonic Blades (M >1; Z=85%) Air flow effects on axial compressor: *-We think that air passing in a steady stream through the blades, and not deviating from its path, this is not correct. Even between the root and tip of a blade considerable differences can occur. One test on a good performance compressor using special instrumentation show a difference in air temperature between the root and the tip of 5 °C, change in temperature will affect air properties. *-Fig (62) shows some of the flows which can occur between two blades. Point (a) show the eddies produced by air leaking between the stator blades and the rotor, point (b) shows vortices arising from the trailing edges of blades. These are similar in type to the vortices which can sometimes be seen at the wing tips of aircraft in damp weather (High humidity). Point (c) shows the circulation patterns which arise due to the Coriolis acceleration acting on the airflow. (Coriolis acceleration arises when a body moves radially outward while
  65. 65. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 65 rotating circumferentially). All these flow components cause losses which reduce the efficiency of the compressor. ‫؟‬Axial Compressor 31-‫ة‬ ‫ه‬ ‫ه‬‫ري‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ 31-What is the definition of compressor surge? Compressor Surge/Stall: *-Compressor surge is a phenomena occur on axial flow compressor, this phenomena occur when compressor operates at incorrect pressure ratio & mass flow rate (i.e. they are not matching to gather) & the result is compressor flow instability & reversed air flow which will produce high vibration on the blades (extremely at the last stages blades) which may result in blade failure. Refer to Fig(64) which shows compressor flow instability, Fig(64) Compressor flow instability (a)Full stall [chocked] (b) Leading edge tip stall (c) Trailing edge root stall (d) Full flow (e) Trailing edge tip stall *-Axial compressor is designed to run at a design point at which it will operate most efficiently, with the air flow in each stage approaching the blades at the correct angle throughout the machine, and the flow velocity parallel to the axis of the machine will be constant along the length of the machine, and at a maximum value. *-Most of the compressor running should be at, or near, this point (design point). If at a given speed, the mass flow or the pressure ratio is changed, the balance of flow will be disturbed. *-If the pressure ratio increases to more than a certain point, the axial velocity of the air will fall and the blades will stall because the flow will now approach the blades at an incorrect angle. The compressor will then probably surge, with flow alternatively building up and breaking down, and with a possible complete of air delivery. This situation may be notes on the machine by high noise, and in bad cases, by physical damage to the
  66. 66. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 66 machine. Similarly, if the pressure ratio is reduced too far, the axial velocity will increase and the blades will again stall. *-The first condition described is referred to as positive shock stall and the second as negative shock stall. Operation under both these conditions must be avoided. If pressure ratio is plotted against mass flow a curve named as "compressor operating curve" will be obtained. Refer to Fig(65). Fig(65) Compressor operating curve ‫؟‬Axial Compressor 32-‫ري‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ ‫ب‬ ‫أ‬ ‫ه‬ 32-What are the main reasons of compressor surge? *-Reasons of compressor surge could be: 1- Drop on the speed of rotation while compressor is operating at its rated flow. 2- Blow off valves are closed two early (before rated speed is reached). 3- Blockage on compressor discharge lines which increase compressor discharge suddenly. 4- Sudden drop of compressor discharge pressure. *-Since compressor surge must be avoided, compressor surge protection must be installed.
  67. 67. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 67 Fig(66) Compressor surge is a result on excessive angle of attack ‫؟‬ Axial Compressor 33-‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ ‫ا‬ ‫ق‬ ‫آ‬‫ري‬ ‫ا‬ 33-How can compressor surge be avoided by improving compressor design? Compressor surge can be avoided by using the following methods: (a) Install variable inlet guide vane to control the angle of the incoming flow to the required angle so that it matches the angle of the first row of moving blades. (b) Make the angle of the first few rows of static guide vanes variable. This can be controlled automatically, and ensures that the blade angle matches the flow angle so that stalling does not occur. (c) Provide controlled air bleed off from the compressor so that the stages after the bleed off point receive less air, and the velocity is relatively reduced. In many cases all three of the above solutions are being used together.
  68. 68. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 68 Fig(67) Methods of Controlling Axial Compressor surge ‫؟‬ Compressor Surge Protection 34-‫ري‬ ‫ا‬ ‫ا‬ ‫اء‬ ‫ا‬ ‫اب‬ ‫إ‬ ‫و‬ ‫ه‬ 34-What is compressor surge protection? *-Compressor surge protection provide excellent monitoring for surge phenomena in the compressor, This protection if activated will trip the gas turbine to avoid compressor blade damage which caused by reverse air flow due to surging. *-This protection is consist of differential pressure indicator & two pressure sensors, one of these sensor is placed at air intake filter house inlet to measure ambient pressure (point#1) & the other pressure sensor is placed just at compressor entrance before the inlet guide vanes (point#2) refer to Fig(68) Fig(68) Compressor Surge Protection
  69. 69. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 69 *-Note that total pressure is summation of static pressure & dynamic pressure, static pressure is the result of the force exerted by the of air when it is at rest & dynamic pressure is the result of the force exerted by t of air when it is moving (velocity pressure): Total Pressure (TP) = Static Pressure (ST) + Dynamic Pressure (DP) So total pressure at point (1): TP1= ST1 + DP1 Note that: Static pressure on point (1) is the ambient pressure. Dynamic pressure on point (1) is approximately equal zero since air speed is very slow. and total pressure at point (2) TP2= ST2 + DP2 Note that: *-Static pressure on point (2) is less than static pressure on point (1) due to vacuum created by compressor suction. *-Dynamic pressure on point (2) is much higher than Dynamic pressure on point (1) due to higher speed of air because of compressor suction. *-Now to put it clearly: Static pressure at point (1) at normal operating condition must be greater than static pressure at point(2),so Compressor surge protection is set so that: Differential Static Pressure (∆Ps)= SP1-SP2 must be at least greater than 40 mbar. i.e. Static pressure at point(1) must be at least grater than static pressure at point(2) by 40 mbar. *-Note that if (∆Ps) less than 40 mbar this means that static pressure at point(2) approach static pressure at point(1) which mean that compressor is no longer sucks air even if it is operating at its rated speed & flow(i.e. compressor is surged). *-Compressor surge differential pressure sensors is normally have three channels to provide redundancy, if two of these channels an out put signal that tells ∆Ps <40 mbar, then gas turbine trip will be initiated by gas turbine controller . *-If for any reason compressor surge protection is not activated during machine prepares to start, gas turbine start is blocked. *-Compressor surge protection is active only when the speed is (42 Hz, 2520 rpm) and above. *-If gas turbine speed is drop during its normal operation, then the following will happen: a-At turbine speed of (47.5 Hz 2850 rpm), compressor variable inlet guide vanes (I.G.V) will close to 75% to reduce compressor flow & hence avoid compressor surge due speed drop. b-At turbine speed of (47 Hz 2820 rpm), gas turbine will trip by under frequency protection.
  70. 70. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 70 Fig(69) Air flow through aircraft engines
  71. 71. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 71 GAS TURBINEGAS TURBINEGAS TURBINEGAS TURBINE----COMBUSTIONCOMBUSTIONCOMBUSTIONCOMBUSTION CHAMBERCHAMBERCHAMBERCHAMBER ‫اق‬ ‫ا‬ ‫ف‬ ‫ز‬ ‫ا‬ ‫ر‬ ‫ا‬ MS6001B-G.E.
  72. 72. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 72 35-‫ه‬‫ـــــ‬‫ا‬ ‫دئ‬‫ـــــــ‬‫اق؟‬ 35-What are the main principals for combustion? 1-Fuel: any material that can be burned (oxidized) to release energy is called fuel; most common fuels are consisting of hydrocarbon flues. Hydrocarbons exist in all phases (solid, liquid, gaseous) examples are coal, gasoline & natural gas. Most fuels are consists of mixture of hydrocarbons composites & exists as complex hydrocarbon nodes ,for simplicity most common fuels are treated as single hydrocarbon, for example: a-Gasoline is treated as Octane (C8 H18). b-Gas oil (Diesel) is treated as Dodecane (C12 H26). c-Kerosene is treated as (C12 H24 ) d-Natural Gas (mixture of 90% Methane CH4 & 10% Ethane C2 H6) is treated as Methane (CH4). Fig(70) Simplified distillate tower 2-Oxidizer: any material that is rich in oxygen is called oxidizer, most common oxidizer used in combustion processes is air because it is free oxidizer & located any where, Pure Oxygen however is used in special
  73. 73. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 73 applications such as cutting & welding were air cannot be used. 3-Combustion: a chemical reaction during which a fuel is oxidized & a large quantity of energy is released. 4-Combustion reactants: Components that exists before combustion. 5-Combustion products: Components that exists after combustion, any hydrocarbon fuel when it has complete combustion, it will produce Carbon dioxide, water vapor & Nitrogen. *-Note that Nitrogen is generally inert gas it is enter & exit from the reaction with out reacting with other chemical elements .However, as combustion temperature is increased to more than 1300ºC such as in internal combustion engines, Nitrogen start to react with other elements, most hazardous product of Nitrogen reactant is when it is react with Oxygen forming Nitric oxide (NO) &Nitrogen dioxide (NO2) . *-Note also that Nitrogen is represent 78% of air that is used for combustion ,so it is enter combustion chamber in large volume at low temperature & exit at a higher temperature & hence it will absorb a large portion of the chemical energy released during combustion. Fig(71) Combustion temperature vs. NOx & CO emission 6-NOx: an expression that represent the mixture of Nitrogen oxides (NO & NO2). 7-Sox: an expression that represent the mixture of Sulfur oxides (SO2 & SO3).
  74. 74. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 74 8-Dry air composition: dray air (on volume basis) consist of 20.9% Oxygen, 78.1% Nitrogen, 0.9% Argon & 0.1% is represent small amount of carbon dioxide, Helium, Neon and Hydrogen. 9-Theoretical air: minimum amount of air that is necessary for complete combustion. 10-Excess air: amount of extra air that is added to the combustion process to insure complete combustion or to cool down combustion chamber. 11-Complete Combustion: it is a combustion process in which all carbon on the fuel is burned (oxidized) to carbon dioxide (Co2) & all Hydrogen on the fuel is burned (oxidized) to water (H2O) & all Sulfur on the fuel (if any) is burned (oxidized) to Sulfur dioxide (SO2) in the product. 12-Incomplete Combustion: It is combustion in which combustion products contain unburned fuel or component such as carbon(C), Hydrogen (H2), Carbon Monoxide (CO) or Hydroxide (OH). *-Many reasons are responsible for incomplete combustion, major reasons are: a- Available air is not enough for complete combustion to take place (Insufficient Oxygen). b-Insufficient mixing in the combustion chamber burners during the limited time that the fuel & oxygen are in contact (even if the combustion is take place with excess air!). c-Dissociation which become important at high temperatures. At high temperatures, the main products of combustion will decompose or dissociate into other species. For example, complete combustion of hydrocarbons with air gives CO2, H2O, N2 (as products. But dissociation of these and reactions between the resultant species from the dissociation may lead to many other species, for example O, H, OH, N, NO, and others. *-Oxygen is more strongly attracted to Hydrogen than Carbon. Therefore, the Hydrogen in the fuel is normally burned completely & yet forming H2O even when these is less Oxygen than needed for complete combustion Some of the Carbon ends up as Carbon monoxide or just as Carbon particles in the products. 13-Flash Point Temperature: The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture with
  75. 75. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 75 oxygen. At this temperature, the vapor may continue to burn when the source of ignition is removed. Fire point is a slightly higher than flash point temperature. *-The flash point is used to describe the characteristics of liquid fuel, but it is also used to describe liquids that are not used intentionally as fuels (like lubrication & insulation oils). *-Petrol (gasoline) is used in spark ignition engines. The fuel should be premixed with air within its flammable limits and heated above its flash point, then ignited by the spark plug. The fuel should not pre-ignite in the hot engine. Therefore, gasoline is required to have a low flash point and a high auto-ignition temperature. *-Diesel is designed for use in compression ignition engines. Air is compressed until it has been heated above the auto-ignition temperature of diesel; then the fuel is injected as a high-pressure spray, keeping the fuel-air mixture within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a high flash point and a low auto-ignition temperature. Fuel Flash Point (ºC) Gasoline > -45 ºC Diesel > 62 ºC Jet fuel > 38 ºC Table (1) Flash Point Temperature for common fuels 14-Fire Point Temperature: The fire point of a fuel is the temperature at which the fuel continues to burn after ignition for at least 5 seconds. At the flash point, a lower temperature, a substance will ignite, but vapor might not be produced at a rate to hold the fire. Auto ignition temperature is always higher than flash point. 15-Auto-ignition Temperature: The lowest temperature at which the fuel will ignite in a normal atmosphere, without an external source of ignition, such as a flame or spark if mixed with Oxygen, note that in order to ignite a fuel, it must be exposed to higher temperature than its ignition temperature, note also that to ignite a fuel either we introduce a spark or flame, or we compress mixture of air & fuel to very high pressure until mixture temperature become above fuel ignition temperature. Some of famous fuels minimum ignition temperatures at atmospheric air pressure are shown in table below.
  76. 76. "Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894 76 Fuel Ignition Temperature ºC Gasoline 260 ºC Carbon 400 ºC Hydrogen 580 ºC Carbon monoxide (CO) 610 ºC Methane (CH4) 630 ºC Sulfur 243ºC Acetylene (C2H2) 482ºC Ethane (C2H6) 538ºC Diesel 210 ºC Jet Fuel 210 ºC Table (2) Ignition temperature for common fuels -Note: *-To start a combustion not only we have to perform spark or flame in a mixture of fuel & air, the percentage of the fuel into the air the must be in the proper range of combustion, for example natural gas will burn only if the ratio of the gas into the air is between 5% to 15% (by volume), for Hydrogen the ratio is 4% to 76% (by volume). 16-Adiabatic flame temperature: Maximum temperature that could be achieved in a combustion process if we assume that there is no heat losses from combustor to the surrounding. The table below shows some common fuels flame temperature. Fuel Flame Temperature ºC* Propane in air 1980 ºC Butane in air 1970 ºC Natural Gas in air 1950 ºC Acetylene in air 2500 ºC Acetylene in Oxygen 3100 ºC Methane in air 1950ºC *-assuming initial atmospheric conditions (1 bar and 20°C) *-Adiabatic flame temperature is affected by the percentage of air that used in the combustion, for example if Gasoline (Octane -C8 H18) is burned with: a-Theoretical amount of air ,then the resultant adiabatic flame temperature is 2122ºC. b-400% excess amount of air amount ,then the resultant adiabatic flame temperature is 689ºC.

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