Emissions to Air from Landfill and Landfill Gas Engines. Alan Rosevear Environment Agency Science Group

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1 Emissions to Air from Landfill and Landfill Gas Engines Alan Rosevear Environment Agency Science Group

2 Typical Landfill Operation

3 Post Landfill Directive Required to Control, Collect and Treat landfill gas. Where possible utilise the gas, the remainder to be flared. A step change in management of landfill gas at permitted sites. Combustion of methane reduces greenhouse gas potential Renewable fuels obligation (10% electricity from renewables such as landfill gas by 2010)

4 The Regulatory Framework Old Legacy sites - pre CoPA with no control, little monitoring but probably low gas production. Now Contaminated Land under Part IIA Old Waste Management Licensed sites - some control and monitoring - significant gas Sites permitted under PPC - well engineered, contained, gas utilised

5 The Holistic View Source - Pathway - Receptor GASSIM provides a conceptual model

6 Raw Gas Emission Rates Each tonne of waste will generate 6 cubic metres of landfill gas a year over first 10 years A modern permitted site contains several million tonnes of waste Passive venting no longer acceptable Gas collection efficiency 85% on capped/controlled areas

7 Fugitive emissions of raw gas the capped surface lateral migration leaks & failures in collection system active tipping area uncapped active cells

8 Surface Emissions Monitoring 1. identify high permeability area 2. Rectify faults 3. Quantify with an array of flux boxes

9 Standards for Emission of Raw Gas Surface emissions of raw gas - from permanently capped area 10-3 mg methane per m 2 per sec. Only achieved with a well engineered cap and good gas management.

10 Raw Gas Methane Carbon dioxide Trace Components (less than 1% in total) Air (oxygen depleted) Global warming potential and calorific value from methane (ca 60% v/v in source gas) Odour and potential health impact from a few of the 550 trace components

11 Median and mean conc n s of trace components - recent typical sites Mean Concentration Median Concentration Concentration (mg.m -3 ) Hydrogen Sulphide Chloroethene m -Xyle n e + p -Xyle n e Be n ze n e Carbon Disulfide To lu e n e EthylBenzene Limonene Ethyl Butyra te 1-Pe nte ne p-ethyltoluene cis-1,2- Dichloroethene Te tra c hlo ro e the ne Tric h lo ro e th e n e Fu ra n Dimethyl sulfid e 1,1-Dichloroethene 1,1-Dichloroethane tra ns-1,2- Dichloroethene Dimethyl d isulfid e Bu tyric Ac id Chloroetha ne 1,2-Dichloroethane 1-Pro p a ne thio l Etha nethiol Tetra chlorometha ne Diethylsulfide 1-Buta ne thio l 2-ButoxyEtha nol Me tha ne thio l 1,3-Buta d ie ne

12 Potential impacts of raw gas Acute - explosive risk from methane accumulation in voids (lateral migration) Acute - odour due to trace components in the gas; principally sulphur compounds Global - methane as greenhouse gas Chronic - potential health impact from trace components such as chlorethene, carbon disulphide and benzene.

13 Combustion Products - Engines & Flares Carbon dioxide and water diluted with excess air Products of incomplete combustion of methane (Carbon monoxide, unburnt methane, VOCs such as formaldehyde, dioxins?) Products from combustion of traces in raw gas (sulphur dioxide, hydrogen chloride, hydrogen fluoride) Products of high temperature (nitrogen oxides) Impact is on local air quality

14 Gas Utilisation in Engines Gas use may be in an adjacent compound and managed separately from the landfill

15 Central facility - variation in scale Single Unit with balancing flare Multiple units with single, high stack

16 Enclosed Landfill Gas Flares

17 Stack Emissions Monitoring

18 Principal Standards Emissions to be Assessed for Compliance Emission Engine (mg/nm 3 ) Typical Uncertainty Flare (mg/nm 3 ) NOx % % Typical Uncertainty CO % % Total VOC % 10 40% NMVOC % 5 40%

19 Impact of Combustion on Local Air Quality Landfills often near major transport corridors NOx background already close to annual mean AQ objective of 40 micrograms/ m 3 Flares and engines are point sources with relatively low velocity at small height (low plume rise), close to site boundary Compliant engines and flares must also take account of local air quality

20 Air Quality Objectives NOx from Combustion - additional contribution from two compliant engines may breach air quality objectives at nearest receptor (2005) and even more likely at site boundary (2010) less significant - site specific Benzene in Raw Gas - surface emission has potential to breach air quality objectives at nearest receptor (2005) and site boundary (2010) SO 2 from Combustion - small potential on some sites for breach at nearest receptor

21 In Conclusion Landfill Gas emission from permitted landfills is controlled and relatively low; less control at older landfills. Raw Gas: global warming potential of methane; risk of explosion from gas migration and risk of odour or health impact from aerial emission of trace components. Combustion Products: engines could impact local air quality, particularly for NOx.