Brian M Igoe & Michael J Welch Fuels, Combustion and Environmental Considerations in Industrial Gas Turbines - Introduction and Overview Restricted © Siemens AG 20XX All rights reserved. siemens.com/answers AGENDA Fuels, Combustion and Emissions • Introduction • Environmental Impact • Combustion Systems • Fuel Types Restricted © Siemens AG 2013 All rights reserved. Page 2 2013-Nov BMI / MJW SITL AGENDA Fuels, Combustion and Emissions • Introduction • Environmental Impact • Combustion Systems • Fuel Types Restricted © Siemens AG 2013 All rights reserved. Page 3 2013-Nov BMI / MJW SITL Introduction Industry requires Energy • Electricity • Mechanical Power • Heat • Most commonly provided through the combustion of fossil fuels • Number of technologies can be used • Gas Turbines • Boiler / Steam Turbines • Reciprocating Engines For this Symposium subjects covered include Fuels and Emissions issues surrounding Gas Turbines Restricted © Siemens AG 2013 All rights reserved. Page 4 2013-Nov BMI / MJW SITL Fluids / Gases Turbine Entry / Exit Some of the fluids entering or exiting the gas turbine core or package Exhaust Gas Combustion Air Compressed Air Ventilation Air Lubricating Oil – through cooler Gas and Liquid Fuels Restricted © Siemens AG 2013 All rights reserved. Page 5 2013-Nov BMI / MJW SITL AGENDA Fuels, Combustion and Emissions • Introduction • Environmental Impact • Combustion Systems • Fuel Types Restricted © Siemens AG 2013 All rights reserved. Page 6 2013-Nov BMI / MJW SITL Environmental Impact Pollutant Effect Method of Control Carbon Dioxide Greenhouse Gas Cycle Efficiency Sulphur Oxides Acid Rain Fuel Treatment Nitrogen Oxides Ozone Depletion Smog Combustion System Carbon Monoxide Poisonous Combustion System Hydrocarbons Poisonous Greenhouse Gas Combustion system Smoke Visible Pollution Combustion System Restricted © Siemens AG 2013 All rights reserved. Page 7 2013-Nov BMI / MJW SITL Environmental Impact DLE - Introduction / Drivers • Improve the environmental impact • More stringent environmental limits • Customer goals and requirements • Improved operational reliability • Simple design with simple operating philosophy required • Minimal impact of product cost • Easy to understand • Easy to maintain • Wide fuel range coverage • Part load capable Restricted © Siemens AG 2013 All rights reserved. Page 8 2013-Nov BMI / MJW SITL NOx Formation 2200 1600 1400 1200 1000 TV2 = 400°C = 20 ms NOX real mixing NOx [ppm] T [°C] 1800 PV2 = 16 bar Combustor GT Diffusion Combustor GT Lean Pre-mix 2000 Flame temperature NOX stoichiometric mixing 800 0 0 0,5 2 Equivalence ratio 1 1 2 0,5 3 0,3 = 1/excess air ratio Restricted © Siemens AG 2013 All rights reserved. Page 9 2013-Nov BMI / MJW SITL Emission Abatement Options Emissions Abatement Dry Low Emissions Diffusion Flame SSI WI PSI Wet Injection Methods: WI = Water Injection PSI = Primary Steam Injection SSI = Secondary Steam Injection Restricted © Siemens AG 2013 All rights reserved. Page 10 2013-Nov BMI / MJW SITL Combustion 1000 NOx Impact • Diffusion flame • Produces high combustor primary zone temperatures • NOx is a function of temperature • Results in high thermal NOx formation • Use of wet injection (Water or Steam) directly into the primary zone • Lowers combustion temperature • Reduced NOx formation NOx Formation Rate [ ppm/ms ] 100 10 1 0 .1 0 .0 1 Diffusion Flame 0 .0 0 1 0 .0 0 0 1 Lean Pre-mix 0 .0 0 0 0 1 0 .0 0 0 0 0 1 1300 1500 1700 1900 2100 2300 2500 F la m e T e m p e r a tu re [ K ] Flame Temperature as a function of Air/Fuel ratio Lean burn Flame temperature • Dry Low Emissions • Lean pre-mixed combustion • Results in low combustion temperature • Low NOx formation • Low NOx across a wide load and ambient range Diffusion flame reaction zone temperature Diffusion flame Lean Pre-mixed (DLE/DLN) Lean Stoichiometric Fuel Air Ratio Rich Restricted © Siemens AG 2013 All rights reserved. Page 11 2013-Nov BMI / MJW SITL Environmental Aspects Pollutant Effect Method of Control Carbon Dioxide Greenhouse gas Cycle Efficiency Carbon Monoxide Poisonous DLE System Sulphur Oxides Acid Rain Fuel Treatment Nitrogen Oxides Ozone Depletion Smog Poisonous Greenhouse gas Visible pollution DLE System Hydrocarbons Smoke 16750C DLE System DLE System DLE combustion Emissions level NOx/CO TRADE-OFF Optimum Temperature Combustion Aspects Diffusion Flame Lean Pre-mix Operability 21750C Diffusion Flame (Pressure Jet burner) Reactor temp Excessive CO Excessive NOx Restricted © Siemens AG 2013 All rights reserved. Page 12 2013-Nov BMI / MJW SITL Introduction Fuels, Combustion and Emissions Introduction Fuels Types Combustion Systems Environmental Impact Restricted © Siemens AG 2013 All rights reserved. Page 13 2013-Nov BMI / MJW SITL Combustion Combustion Systems Available ANNULAR Used on aero engines Used on medium and large gas turbines Tends not to be site serviceable Requires major engine disassembly CAN-ANNULAR Versatile Can be changed out at site Does not require engine disassembly SILO Used in some medium and large gas turbines Can be single or dual combustors DLE Combustion Conventional Combustion Restricted © Siemens AG 2013 All rights reserved. Page 14 2013-Nov BMI / MJW SITL Combustion Arrangements Reverse Flow In-Line Flow Restricted © Siemens AG 2013 All rights reserved. Page 15 2013-Nov BMI / MJW SITL Dry Low Emissions Gas Fuel Injection/Mixing Restricted © Siemens AG 2013 All rights reserved. Page 16 2013-Nov BMI / MJW SITL Combustion Properties and “flashback” Flame speed Flame speed is determined by the combustion reaction rates and those rates depend on: Equivalence ratio Fuel type Flow regime (laminar or turbulent) Flame speed Flame Speed v Fuel Type Laminar Flame Speed If Air flow velocity > Flame speed (SL) Blow off If Air flow velocity < Flame speed (SL) Flashback Laminar Flame Stability Restricted © Siemens AG 2013 All rights reserved. Page 17 2013-Nov BMI / MJW SITL Combustion Combustion Types More pilot means greater diffusion flame Higher emissions and pilot temperature Less pilot means more premix Pilot Burner less NOx but higher dynamics 80 70 Main burner Pilot Split (%) 60 High Pilot => High Pilot tip temperature 50 40 30 20 10 0 900 Low Pilot => High Combustion Dynamics – “Instability” 1000 1100 1200 1300 1400 1500 1600 Contr ol Param e te r Restricted © Siemens AG 2013 All rights reserved. Page 18 2013-Nov BMI / MJW SITL AGENDA Fuels, Combustion and Emissions • Introduction • Environmental Impact • Combustion Systems • Fuel Types Restricted © Siemens AG 2013 All rights reserved. Page 19 2013-Nov BMI / MJW SITL Fuel Type Various fuel types - Gaseous Fuels 100% 80% vol % 60% 40% 20% CO2 N2 CO H2 C3H8 C2H6 CH4 0% Restricted © Siemens AG 2013 All rights reserved. Page 20 2013-Nov BMI / MJW SITL Fuel Parameters - gaseous fuel Assessment requirements Fuel Placement • Fuel composition • Include contamination • Supply conditions Air Placement • Environmental requirements Combustion Products Restricted © Siemens AG 2013 All rights reserved. Page 21 2013-Nov BMI / MJW SITL Evaluation W ater Vapour Oxygen Carbon Dioxide Carbon Monoxide Hydrogen Methane Ethane Propane i-Butane n-Butane i-Pentane n-Pentane n-Hexane n-Heptane n-Octane n-Nonane n-Decane Hydrogen Sulphide Nitrogen Ethene Propene Total H2O O2 CO2 CO H2 CH4 C2H6 C3H8 i-C4H10 n-C4H10 i-C5H12 n-C5H12 n-C6H14 n-C7H16 n-C8H18 n-C9H20 n-C10H22 H2S N2 C2H4 C3H6 Density kg/m3 (ISO conditions) Molecular Mass 0.00 0.00 0.50 0.00 0.00 94.00 3.50 1.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.80 0.00 0.00 100 35065 48468 941 Temperature corrected Wobbe Index kJ/m3 W obbe Index Calculation Temperature °C 46652 2.5 Temperature °C Pressure bara Minimum gas supply temperature °C Maximum gas supply temperature °C Gas Constant ft lbf/lb K Gamma Species Methane Ethane Propane Carbon Dioxide Nitrogen Formulae CH4 C2H6 C3 H8 CO2 N2 Mol % 94 3.5 1.2 0.5 0.8 Simple things: Visual Inspection Anything unusual? Wt%, Mol %, add to 100%, contaminants, …? INPUT DATA 0.7235 17.11 LCV kJ/m3 (ISO conditions) LCV kJ/Kg LCV Btu/scf Dewpoint Step 1: Start with a typical natural gas composition Step 2: Complete an assessment using gas analysis methods Can see other species that may be present in other fuels Calculations shown in lower section – OUTPUT, includes: Lower Calorific (Heating) Value (LCV or LHV) Wobbe Index (WI) Dewpoint Density < -20 20.0 2.5 120.0 162.47 1.294 OUTPUT DATA Specific Gravity (ISO conditions) Restricted © Siemens AG 2013 All rights reserved. Page 22 2013-Nov 0.591 BMI / MJW SITL Fuel Assessment Assessment requirements Wobbe Index (WI) parameter LCV sg WI Compares energy input of different gas fuel compositions, and indicates the inter-changeability of gas fuels Cv = Net Calorific Value sg = specific gravity Temperature Corrected Wobbe Index (TCWI) Gas may be heated e.g. due to dew point WI T WI 15 * T 15 TT WI T WI 15 * 288 TT Temp in Kelvin Restricted © Siemens AG 2013 All rights reserved. Page 23 2013-Nov BMI / MJW SITL Gaseous fuels- Assessment Restricted © Siemens AG 2013 All rights reserved. Page 24 2013-Nov BMI / MJW SITL Hydrocarbon Dew Point W ater Vapour Oxygen Carbon Dioxide Carbon Monoxide Hydrogen Methane Ethane Propane i-Butane n-Butane i-Pentane n-Pentane n-Hexane n-Heptane n-Octane n-Nonane n-Decane Hydrogen Sulphide Nitrogen Ethene Propene Total H2O O2 CO2 CO H2 CH4 C2H6 C3H8 i-C4H10 n-C4H10 i-C5H12 n-C5H12 n-C6H14 n-C7H16 n-C8H18 n-C9H20 n-C10H22 H2S N2 C2H4 C3H6 Density kg/m3 (ISO conditions) Molecular Mass 0.00 0.00 0.50 0.00 0.00 94.00 3.50 1.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.80 0.00 0.00 100 35065 48468 941 Temperature corrected Wobbe Index kJ/m3 W obbe Index Calculation Temperature °C 46652 2.5 Temperature °C Pressure bara Minimum gas supply temperature °C Maximum gas supply temperature °C Gas Constant ft lbf/lb K Gamma Let us look at the reasons for understanding dew point and the need to apply a margin of superheat < -20 20.0 2.5 120.0 162.47 1.294 Specific Gravity (ISO conditions) Restricted © Siemens AG 2013 All rights reserved. Page 25 Ensure fuel gas is maintained in vapour phase Normal to apply superheat margin 0.7235 17.11 LCV kJ/m3 (ISO conditions) LCV kJ/Kg LCV Btu/scf Dewpoint Importance of DEW Point 2013-Nov 0.591 BMI / MJW SITL Hydrocarbon Dew Point In the previous example the dew point for a typical pipeline gas fuel is very low so a minimum value is applied – this prevents freezing in the fuel system vent pipework. Replacing C5 with a representative breakdown: Parameter Mol % I propane N propane 0.5 0.5 Pentane 0.5 Mol % Heptane 0.25 Oxygen, O2 Nitrogen, N2 0.37 9.54 Octane 0.12 Nonane 0.06 Carbon Dioxide, CO2 8.00 Decane 0.03 Methane, C1 73.17 Ethane, C2 3.91 Propane, C3 1.91 Butane, C4 1.14 Propane+; C5+ 1.96 Take an example where the C5 species is defined as 1.9%+ Parameter Assume all is C5: Dew Point = 2.6OC Revised dew point 52.5OC This demonstrates the importance of providing and using the correct fuel composition. Incorrect dew point – hence incorrect supply conditions – results in gas condensate and impact on turbine operation. Restricted © Siemens AG 2013 All rights reserved. Page 26 2013-Nov BMI / MJW SITL Summary A brief overview in the use of fuels in a gas turbine and impact on the environment Method of assessment and why it is important to declare as early as possible the full details of the composition Combustion systems types and why DLE, DLN systems dominate new equipment sales Aspects of Siemens Energy standard combustion system detailed THANK YOU FOR YOUR ATTENTION Restricted © Siemens AG 2013 All rights reserved. Page 27 2013-Nov BMI / MJW SITL