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21 Landfill gas

21 Landfill gas. 1. “Landfill gas is an explosive topic” (J.Jacobs, 2006). 21 Landfill gas Overview. 21.1 Landfil gas production 21.2 Prognosis of landfill gas production 21.3 Extraction systems 21.4 Production monitoring 21.5 Flaring, electricity and heat production. 21.1 LFG production.

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21 Landfill gas

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  1. 21 Landfill gas 1

  2. “Landfill gas is an explosive topic” (J.Jacobs, 2006)

  3. 21 Landfill gas Overview 21.1 Landfil gas production 21.2 Prognosis of landfill gas production 21.3 Extraction systems 21.4 Production monitoring 21.5 Flaring, electricity and heat production

  4. 21.1 LFG production Waste contains a certain amount of degradable organic matter Microbiological processes result in the formation of landfill gas (LFG) 21.1 – Landfill gas Biological processes

  5. 21.1 Landfill gas production Degradation follows 4 biological stages during waste disposal: Hydrolosis Acidogenesis Acetogenesis Methanogenesis 21.1 – Landfill gasproduction

  6. Biological processes 21.1 – Landfill gasproduction

  7. Hydrolosis In the first stage complex solid organic material is solubilized by enzymes excreted by hydrolytic micro-organisms 21.1 – Landfill gasproduction

  8. Acidogenesis In the second stage soluble organic components including the products of hydrolysis are converted into organic acids and alcohols 21.1 – Landfill gasproduction

  9. Acetogenesis In the third stage the products of acidogenesis are converted into acetic acid, hydrogen and carbon dioxide 21.1 – Landfill gasproduction

  10. Methanogenesis In the fourth and final stage methane is formed mainly from acetic acid or from hydrogen and carbon dioxide. Methane can also be formed directly from products of the acidogenesis such as formic acid and methanol 21.1 – Landfill gasproduction

  11. Composition LFG primarily consists out of methane (CH4) and carbondioxide (CO2) Ratio CH4:CO2 = 50:50 (theoretically) CH3COOH (Acetic acid) --> CH4 + CO2 CO2 is more soluble in water, ratio shifts to 60:40 21.1 – Landfill gasproduction

  12. Composition (cont’d) CH4 is a green house gas (GHG) with a GHG potential of 21 times that of CO2 1 ton of CH4 has an equivalent of 21 ton of CO2 LFG can contain traces of hydrocarbons, halogenated hydrocarbons and sulphur compounds 21.1 – Landfill gasproduction

  13. 21.2 Prognosis of LFG production Modelling with LFG production models Only two models are validated First order model Multi phase first order model 21.2 – Prognosis of landfill gasproduction

  14. First order model 21.2 – Prognosis of landfill gasproduction

  15. First order model – organic content 21.2 – Prognosis of landfill gasproduction

  16. Multi phase first order 21.2 – Prognosis of landfill gasproduction

  17. Multi phase first order – organic content 21.2 – Prognosis of landfill gasproduction

  18. Organic matter and Organic C 21.2 – Prognosis of landfill gasproduction

  19. Prognosis of LFG production 21.2 – Prognosis of landfill gasproduction

  20. Prognosis of LFG production Only two models are validated Uncertainty depending on: Waste composition Degree of pre-treatment Type and degree of compaction, method of operation, type and thickness of cover material Quantity of refuse, geometry and hydrogeolocic properties of landfill Climatic conditions 21.2 – Prognosis of landfill gasproduction

  21. 21.3 Extraction systems Lay out of an extraction system Various types of extraction systems Recovery efficiency 21.3 – Extraction systems

  22. Lay out emission oxidation extraction production flaring and/or utilisation 21.3 – Extraction systems

  23. Various types of extraction systems Vertical Horizontal Slope Point 21.3 – Extraction systems

  24. Vertical 21.3 – Extraction systems Cell wise Conventional HDPE piping (non -perforated) GRAVEL Build up Build up + early extraction HDPE piping (perforated)

  25. Horizontal 21.3 – Extraction systems

  26. Slope 21.3 – Extraction systems

  27. Point 21.3 – Extraction systems

  28. Gas well connection 21.3 – Extraction systems RULE OF THUMB: 4 GAS WELLS PER HA

  29. Gas well connection 21.3 – Extraction systems

  30. Recovery efficiency 21.3 – Extraction systems

  31. 21.4 Production monitoring Monitoring equipment 21.4 – Production monitoring Anemo meter Digital mano meter Gas analyser

  32. Gas analyser can measure: CH4 CO2 O2 N2 (= 100% - CH4% - CO2% - O2%) 21.4 – Production monitoring

  33. If CH4 and O2 concentration respectively in a gas well is: > 50% and < 1% then more extraction < 50% and > 1% then less extraction 21.4 – Production monitoring

  34. If N2:O2 ratio is: > 5 indicator suction of ambient air < 4 indicator leakage piping extraction system 21.4 – Production monitoring

  35. 21.5 Flaring, electricity and heat production A suitable nearby use for LFG must be identified The landfill must have a depth of at least 5 m. and preferably 10 m. of unsaturated biodegradable waste Amount of waste deposited: 0.5 Million tonnes Waste should not be too old (between 5 – 10 years, less if mainly food and vegetable wastes) Leachate level should be at least 5 m. below the landfill surface 21.5 – Flaring, electricity and heat production

  36. Flaring 21.5 – Flaring, electricity and heat production Open flare Passive flare Enclosed flares

  37. Heat production 21.5 – Flaring, electricity and heat production Heat exchangers WWTP LFG fired boilers

  38. 21.5 – Flaring, electricity and heat production Electricity production

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