Combustion Chemistry / Environmental Aspects of Power Generation

1. CCGT Operations Principles Combustion Chemistry / Environmental Aspects of Power Generation

2. OBJECTIVES OF THE SESSION: • Identify the common elements by their chemical symbols and appreciate the use of those symbols to depict chemical compounds and chemical reactions. • Define the basic terms used in the chemistry of combustion. • Be able to carry out simple equations relating to combustion. • Identify the principal chemical constituents of Fuel Oil, and Natural Gas. • Define the primary constituents of air giving their percentage by weight and volume.

3. OBJECTIVES OF THE SESSION: • Know what the products of combustion are for fuels used within the power industry, the expected values of these products and the effects of poor combustion, including ‘humming’. • Understand how NOx is produced and how it can be controlled. • Understand the importance of operating within NOx and CO emission limits • Discuss flame stochiometry, and premix/diffusion burning • Show awareness of organisational and regulatory environmental requirements relating to power station operation.

4. The Hydrogen Atom Electron One proton, No neutrons One electron Atomic weight = 1 Proton

5. The Helium Atom Two protons, Two neutrons Two electrons Atomic weight = 4

6. The Carbon Atom Six protons, Six neutrons Six electrons Atomic weight = 12

7. Table of Chemicals Commonly Found in the Combustion Process

8. The Hydrogen Molecule Electron Electron Proton Electrons are no longer dedicated to each nucleus, but are shared in the combined orbital.

9. Exercise 1 For example, below are listed a number of molecules, using table 1 calculate the molecular weight of the compounds below.

10. Combustion Chemistry • C + O2 = CO2 • 12+32 = 44 • 2C + O2 = 2CO • 24 + 32 = 2 x 28 • S + O2 = SO2 • 32+32 = 64 All these reactions use stoichiometric quantities of fuel and oxygen, i.e. exactly the right amount of each element

11. Basic Combustion Chemistry • N2 + O2 = 2NO • 28 + 32 = 2 x 30 = 60 • 2NO + O2 = 2NO2 • 2x30 + 32 = 2 x 46 = 92 • CH4 + 2O2 = CO2 + 2H2O • 16 + (2 x 32) = 44 + (2 x 18) = 80 ? ? ?

12. Production of Pollutants - Air • Coal consists of approximately • 60% Carbon • 18% Ash • 15% Water • 4% Hydrogen • 2% Sulphur • 1% Chlorine

13. Production of Pollutants - Air • One thousand tonnes of coal contains: • 600 tonnes of Carbon • 180 tonnes of ash • 150 tonnes of Water • 40 tonnes of Hydrogen • 20 tonnes of Sulphur • 10 tonnes of Chlorine • 0.4 tonnes of Nitrogen

14. Production of Pollutants - Air • Burning a thousand tonnes of coal produces • 2200 tonnes of Carbon dioxide. • C + O2 = CO2 • 12 + 32 = 44 Molecular weight • 600 + 1600 = 2200 Weight in tonnes

15. Production of Pollutants - Air • Burning a thousand tonnes of coal produces • 2200 tonnes of Carbon dioxide • (180 tonnes of ash, 0.1% emitted to air) • 510 tonnes of water vapour • 40 tonnes of Sulphur dioxide • 10 tonne of Hydrochloric acid • 8 tonnes of Nitrogen oxides

16. Production of Pollutants - Air • Oil consists of approximately • 85% Carbon • 11% Hydrogen • 4% Sulphur • 0.1% ash

17. Production of Pollutants - Air • One thousand tonnes of oil contains • 850 tonnes of Carbon • 110 tonnes of Hydrogen • 40 tonnes of Sulphur • 1 tonne of ash

18. Production of Pollutants - Air • Burning a thousand tonnes of oil produces • 3120 tonnes of Carbon dioxide • 990 tonnes of water vapour • 80 tonnes of Sulphur dioxide • 12 tonnes of Nitrogen oxides • 1 tonne of ash

19. Production of Pollutants - Air • Natural gas is about 90% methane with traces of ethane, hydrogen, carbon monoxide and nitrogen (and a very small amount of sulphur compounds) • METHANE IS APPROXIMATELY: - • 75% Carbon • 25% Hydrogen

20. Production of Pollutants - Air • One thousand tonnes of methane contains • 750 tonnes of Carbon • 250 tonnes of Hydrogen • How much CO2 and water are produced when this thousand tonnes is burnt?

21. Production of Pollutants - Air • The theoretical combustion of pure methane is given by the equation • CH4 + 2O2 = CO2 + 2H2O • Burning a thousand tonnes of methane produces • 2750 tonnes of Carbon dioxide • 2250 tonnes of water vapour • 2.5 tonnes of Nitrogen oxides

22. Production of pollutants - Air • Sulphur dioxide emissions per 1000 tonnes of fuel

23. Production of pollutants - air • Nitrogen oxides emissions per 1000 tonnes of fuel

24. Production of pollutants - air • Carbon dioxide emissions per 1000 tonnes of fuel

25. Acid rain

26. SO2 Emissions in the UK

27. NOx Emissions in the UK

28. RWE npower renewables - Climate Change • Green house gas animation

29. CO2 Emissions in the UK Million tonnes

30. UK Environmental law • First offence = warning • Second offence = removal of furnace • Third offence (if furnace rebuilt) = death • “Burning of sea coal in open furnaces”, 1649

31. 1988 - The Large Combustion Plant Directive • Limits each Member State’s mass emissions of sulphur dioxide and nitrogen oxides. • Limits each Member State’s industrial plant’s emissions • Electricity industry given dispensation to transfer allowances between individual plants (the ‘bubble’ concept) • Limits each Member State’s mass emissions of sulphur dioxide and nitrogen oxides reducing over time.

32. Large Combustion Plant Directive 2004 • Options: • Emission Limit Values ELVs (concentration based) are: • For SO2, 400mg/m3 after Jan 2008 • For NOx, 500 mg/m3 after Jan 2008 and 200mg/m3 after Dec 2015 • For PM, 25mg/m3 after Jan 2008. • Or Annual mass-based National Emissions Reduction Plan trading • Or to Opt Out by taking the limited life Derogation.

33. Local air quality- NAQS • SO2, NOx, Volatile Organic Carbon (VOC) and ozone at ground level affect human health • VOC and NOx react in sunlight to form ‘smog’

34. European Union Emission Trading Scheme • Since 2005 a ‘Cap & Trade’ scheme used in EU for CO2 emissions • All installations of 20MWth or above must participate • 1 allowance = 1 tonne CO2 • Allowances based on previous measurements • If you exceed your allowance you must purchase more • You may sell any surplus you have

35. The Environmental Protection Act 1990 • All major industrial plants require an Authorisation • Operators had to demonstrate that • BATNEEC - Best Available Techniques Not Entailing Excessive Cost – were used, and • BPEO - Best Practicable Environmental Option was chosen for any modification, e.g. retrofits

36. International Environmental Law • 1989 – The Montreal Protocol. • Legislated for the phasing out of CFC Production & use. • 1997 – The Kyoto Protocol • Legislated for industrialised nations to reduce emissions of greenhouses gases by 5.2% of 1990 levels by 2012. • 2007 – Bali conference • 2009 – Copenhagen

37. NOx Emissions • The rate of formation of NO / NO2 is very temperature dependent • In a fuel-rich flame, NOx production is quite low • Towards stoichiometry, NOx production increases and with excess air gets higher up to a maximum, after which the excess air starts to cool the flame.

38. Bunsen Burner Flames

39. The Components of Air

40. Graph of CO v NOx Emissions

41. TYPICAL BURNER AIR FLOWS Cooling air Combustion air 20% cooling 20% mixing 40% mixing 80% 20% Primary zone Secondary zone Tertiary zone

42. Humming Damage

43. Corrosion in a Gas Turbine

44. FGD Absorber design

45. Carbon Capture & Storage