Technical Solutions for Emissions Reduction

Transcription

1 Genera 2015 Technical Solutions for Emissions Reduction Juan Nogales GE Power & Water Madrid, February 24, General Electric Company. All rights reserved. This material may not be copied or distributed in whole or in part without prior permission of the copyright owner. LM1600, LM2500, LM6000, LMS100 and LM5000 are registered trademarks of the General Electric Company (USA)

2 Combustion Principles Flame Types DIFFUSION FLAME PREMIXED FLAME (Yellow & Sooty) (Blue) Fuel and air (reactants) are not mixed, fuel and air are Fuel and air (reactants) are uniformly mixed injected separately into the combustion environment. to a molecular scale upstream of the flame. Air and fuel diffuse together at the boundaries. Flame occurs downstream of premixing. Application Examples candle flame torch diesel engine all types of furnaces standard combustors Application Examples spark ignition engine oxy-acetylene welding torch Dry Low NO x combustor

3 Combustion Principles Diffusion vs. Premixed Flame DIFFUSION PREMIXED Very Robust and Stable Flame Very Narrow Operating Window Typically Operable Over a 1100 C (2000 F) Temp. Rise Range Typically Operable Over a C ( F) Temp. Rise Range High NOx Emissions Without Diluent Can Achieve Very Low NOx Emissions Low CO Emissions Without Diluent Flame Temperature Diffusion Flame Temp. Range Diffusion Low CO Emissions Can Be Difficult Premixed Flame Temp. Range Lean Blow Out Lean Premixed ø = 1 Rich Blow Out Lean Fuel/Air ratio (f) Rich

4 Combustion Principles Combustion Chambers Primary Purpose To Ensure Flame Stability Througout All Operating Phases ANNULAR CHAMBER Axial development Direct Flow Low Aerodynamic Jet Derivative resistance CAN SYSTEM CHAMBER Radial developement Heavy Duty Reverse Flow Easier Maintenance

5 Can System Design Main Components Casing Liner Cover Cross Fire Tubes Fuel Nozzle Spark Plug

6 Aeroderivative combustors Single-Annular Combustor (SAC) Dry-Low-Emissions (DLE) Combusto

7 Flame Temperature Combustion Principles NO x Reduction: premixing Premixed combustors operate with lean mixture reducing the flame temperature down to the lower flammability limit (Lean Blow Out). Diffusion Standard Combustor Diffusion Standard Combustor NOx Lean Premixed Lean Blow Out Lean ø = 1 Fuel/Air ratio (f) Rich Blow Out Rich NO x DLN Comb Lean Premixed Flame Temperature Premixer example Fuel is injected into airstream Turning vanes swirl air to increase turbulence. DLN1 Combustor

8 Combustor Evolution: DLN Flame Temperature Lean Premixed Lean Blow Out Lean R L L Diffusion ø = 1 Fuel/Air R R Rich Blow Out L Rich NOx CO DLN Comb Lean Premixed Standard Comb Flame Temperature Diffusion CO NOx Standard Combustor Regions of Rich and Lean Reactions Turbine Inlet Fuel Air Fuel/Air Premixer Homogeneous Lean Premixed Flame Dry Low NOx Lean Premixed Combustor

9 Temperature Comparison of Diffusion & DLN Fuel/Air Premixers Tflame Diffusion Flame High Tflame High NOx Dilution Air Seal leakage Lean Premixed Flame Homogeneous F/A Low Tflame Low NOx Tflame Seal leakage Tfire CO Burnout Tfire Tcd Tcd Premixer Example Fuel injected into airstream Turning vanes swirl air Fuel and air mix before Entering flame zone

10 Technological Summary Standard combustors (Diffusion) -water/steam: NOx ~50 mg/nm3 CO ~ 30 mg/nm3 +5% heat rate increase vs dry, lower exhaust temp. -Combustor/HS wear/thermal stress DLE/DLN Combustors (Premix) -1.0/1.5/2.X: Nox mg/nm3 CO 30 mg/nm3 -DLE Commercial op.: 1995 / operating hours: ~15 MM -DLN Commercial op.: 1991 / operating hours: ~150 MM -Water source ~0.25 tons/hr/mwe

11 DLE upgrades examples LM2500 SAC (diffusion): NOx: 383 mg/nm3 CO: 7 mg/nm3 LM2500 DLE (Premix): NOx: 50 mg/nm3 CO: 30 mg/nm GT hardware upgrade - Fuel System upgrade - Control systems upgrade - Engineering package - Installation - 12 months lead time (Order to Delivery) - Outage time: 28 days, 7 days start up

12 DLN upgrades examples Frame 6B (diffusion): NOx: 400 mg/nm3 CO: 7 mg/nm3 Frame 6B DLN (Premix): NOx: 50 mg/nm3 CO: 30 mg/nm GT hardware upgrade - Fuel System upgrade - Control systems upgrade - Engineering package - Installation - 12 months lead time (Order to Delivery) - Outage time: 49 days

13 Genera 2015 Technical Back up slides Juan Nogales GE Power & Water

14 DLN Fuel Staging DLN Operational Modes: Primary Mode Diffusion Flame 100% Primary Fuel Ignition - 19% Load Transfer Mode Diffusion Flame 100% Secondary Fuel 50% Load Diffusion Diff /Premix Lean-Lean Mode Diffusion Flame ~60% Primary / 40% Secondary Fuel 19% - 50% Load Diffusion Diffusion/Premix Premixed Mode Premixed Flame / Diffusion Pilot 81% Primary / 19% Secondary Fuel 50% - 100% Load F/A Mixing Premix Primary Zone Dual Purpose: 1. Low Load Diffusion Flame 2. High Load Premixing Chamber

15 Typical DLE Burner Modes Starting configuration B reaction zone (30 cups) Idle - 5% load BC/2 reaction zone (39) 5-25% load BC reaction zone (45) 25-35% load BC + 2A reaction zone (57 LM6000 only) 35-50% load AB reaction zone (60) 50% to full load ABC reaction zone (75)

16 Combustion Principles Flame Types PREMIXED FLAME (Blue) Fuel and air (reactants) are uniformly mixed to a molecular scale upstream of the flame. Flame occurs downstream of premixing. Application Examples spark ignition engine oxy-acetylene welding torch Dry Low NO x combustor DIFFUSION FLAME (Yellow & Sooty) Fuel and air (reactants) are not mixed, fuel and air are injected separately into the combustion environment. Air and fuel diffuse together at the boundaries. Application Examples candle flame torch diesel engine all types of furnaces standard combustors

17 Combustion Principles Diffusion vs. Premixed Flame DIFFUSION Very Robust and Stable Flame Typically Operable Over a 1100 C (2000 F) Temp. Rise Range High NOx Emissions Without Diluent Low CO Emissions Flame Temperature Diffusion Flame Temp. Range Diffusion PREMIXED Very Narrow Operating Window Typically Operable Over a C ( F) Temp. Rise Range Can Achieve Very Low NOx Emissions Without Diluent Low CO Emissions Can Be Difficult Premixed Flame Temp. Range Lean Blow Out Lean Premixed ø = 1 Rich Blow Out Lean Fuel/Air ratio (f) Rich

18 Combustion Principles Pollutants: Nitrogen Oxides Nitrogen oxides are to be limited by laws because their polluting effects include: lungs affecting and lower resistance to respiratory infections, greenhouse effect, photochemical smog, acid rains, depletion of stratospheric ozone. Nitrogen oxides (NO x ) usually refers to NO and NO 2. Since NO in contact with O 2 is quickly converted into NO 2, NO x measurements mainly consider NO 2 only. NO X Gas Characteristics NO: odorless and colorless gas. NO 2 : red-brown gas with strong odor, highly toxic and corrosive. NO x production is caused by 3 main mechanism: 1. Thermal NO 2. Prompt NO 3. Fuel bound NO

19 Combustion Principles Pollutants: Nitrogen Oxides The major part of NO produced during combustion processes belongs to the Thermal NO, produced by the Zeldovich mechanism. Thermal NO increases exponentially with the flame temperature and proportionally to the residence time. Solutions to reduce NO x content include: Temperature, K Temperature, K 1. premixed burner/combustor to assure lean combustion -> lower temperature; 2. steam/water/air injection to cool down combustion primary zone -> lower temperature; 3. short combustor -> lower residence time. NOx production rate f=1 Equivalence ratio

20 Combustion Principles Pollutants: Carbon Monoxides Carbon monoxide (CO) gas is a by-product of combustion systems; cars and trucks are the source of nearly two-thirds of this pollutant. When inhaled, CO blocks the transport of oxygen to the brain, heart, and other vital organs in the human body. Symptoms of mild poisoning include headaches and dizziness at concentrations less than 100 ppm. In the United States, OSHA limits long-term workplace exposure levels to 50 ppm. CO Gasses Characteristics CO : odorless and colorless gas. CO production is caused by 3 main mechanism: 1. Inadequate burning rates due to too low f/a ratio and/or insufficient residence time. 2. Inadequate mixing of fuel and air, which produce local rich regions that generate high local concentrations of CO. 3. Quenching of post flame products by entrainment with liner cooling air.

21 Temperature, K Combustion Principles Pollutants: Carbon Monoxides CO main zones of production are located: at high f (rich mixture) where lack of oxygen leads to incomplete reaction from CO to CO 2. at very low f (very lean mixture) combustion processes reaction rate is limited by low temperature and consequent no development from CO to CO 2. at stoichiometric condition the high temperature activates the equilibrium CO reactions. T,degrees K Relative NOx Production Rate Relative CO Production Rate 1.00E E-01 Solution to reduce CO include: CO NOx Equivalence Ratio 1.00E E E E E reducing of cold spots in the combustion chamber (film cooling, water injection). 2. use of mixing devices to reduce rich regions. 3. operation at adequate burning rates.

22 Combustion Principles Pollutants: UHC and VOC Un-burned HydroCarbons (UHCs) and Volatile Organic Compounds (VOCs) result from incomplete combustion, then some fuel and fuel derived compounds are present into combustion products. UHCs are toxic and react with NO to generate ozone (O 3 ) which, at ground level, is a pollutant element, causing eyes and respiratory issues and large ageing problems to plants. VOCs effect on environment is highly dependent on the type of compound, the most known and dangerous is benzene, which is carcinogenic. Typical emission trend for conventional gas turbine combustor UHCs production is normally associated with: 1. poor atomization of fuel 2. inadequate burning rate 3. chilling effects of film cooling. Then UHC production trend is similar to that of CO. Note: power is proportional to flame temperature

23 Combustion Principles Pollutants: Sulfure Dioxide Sulfur dioxide (SO 2 ) is caused mainly by the combustion of fuel containing sulfur compounds, like diesel, sour gas, etc. SO 2 acts as an acid. Inhalation results in laboured breathing, coughing, and/or a sore throat and may cause permanent pulmonary damage. When mixed with water and contacted by skin, frostbite may occur. When it makes contact with eyes, redness and pain will occur. SO 2 is also responsible for acid rains. Combustion reactions S O 2 8 SO 2 2 H 2 S(g) + 3 O 2 (g) 2 H 2 O(g) + 2 SO 2 (g) Solutions to reduce SO 2 emission include: fuel desulfurization flue gas desulfurization Typical desulfurization reaction SO NaOH Na 2 SO 3 + H 2 O

24 Combustion Principles Pollutants: Smoke and Particulate Smoke is a general term that refers to the black, impure carbon particles resulting from the incomplete combustion of a hydrocarbon fuels. Smoke is a product of incomplete combustion processes, it is primarily produced in region of high fuel concentration (f > 1) and high temperature which promotes pyrolysis and growth processes. Most of the smoke produced in the flame zone is destroyed in downstream zones with high oxygen unless some rich regions remain unmixed or are cooled prematurely. Liquid fuels Droplet size Equivalence ratio (f) If liquid fuel is not prevaporized, sprays tend to produce local zone of rich combustion, and consequent high production of smoke and particulate. Solutions include sprays with smaller droplet size in order to enhance vaporization and mixing.

25 Combustion Principles Pollutants: summary Modern combustors show many characteristics in order to reduce pollutant emissions and match nowadays restrictions. NO x CO UHC & VOC SO x Smoke &Particulate air injection steam/water injection premixed burner combustor design catalytic reduction combustor design control fuel sulfur content combustor design fuel composition liquid fuel atomization

26 Combustion Principles Pollutants: summary NO x and CO production trends versus equivalent ratio sets the operative window between 0.40 and A control of the effective flame fuel/air ratio can be obtained by use of premixed flame, where air/fuel proportion are set upstream combustion zone. Object of premixing is to maximize the amount of fuel burned at lean equivalence ratios where NOx is low, but flame is not cold enough to freeze the CO to CO2 reaction