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Landfill Gas Flare Control – Stack Emission Monitoring or Design Criteria?
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Funded under the Environmental RTDI Programme 2000-2006, financed by the Irish Government under the National Development Plan and administered on behalf of the Department of the Environment and Local Government by the Environmental Protection Agency.
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Introduction
The operation and maintenance of landfill gas flares in Ireland varies significantly from site to site. Licence compliance assessment of flares based on stack emission monitoring results is not a satisfactory approach, as flare stack emission monitoring can seldom meet standardised monitoring protocols, as well as being extremely hazardous for monitoring personnel. This is due to the extreme temperatures of the stacks (~1000 °C) and the fluctuating volumetric flow encountered. There are also limitations of flare stack design and the presence of significant turbulence in stacks leading to non-uniform gas streams. 
Internationally, diverse approaches are being taken in the control and design of landfill gas flares, ranging from reliance on stack emission monitoring (UK) to control via strict design criteria (Germany, Netherlands and Switzerland). In the above European countries flare design criteria require manufacturers certification, ensuring that flares can meet combustion temperatures above 1000° C, and retention times of 0.3 seconds in the burner, as a means of effectively minimising emissions without undue reliance on flare stack monitoring.
In view of the fundamental difficulties inherent in extractive emissions sampling, and the feasibility of controlling the major flare emissions by system design as outlined in this small scale study, we consider a design certification and performance verification-based approach to be a preferred option for the control of emissions from flares in Ireland.
Figure 1 - Candle Flare
Photo: Summerleaze Re-Generation Ltd
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EPA Study Objectives 
Objective 1: To review the emission limit values that are achievable in landfill gas flares and to review the existing monitoring requirements and stack monitoring results for landfill gas flares in the Waste Licences.
Objective 2: To propose an approach that the EPA can adopt to ensure that emissions from flares are controlled.
Objective 3: To review the approach taken internationally by licensing authorities towards controlling emissions from landfill gas flares by design specification only.
Figure 2 - Open Flare
Photo: Summerleaze Re-Generation Ltd
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Recommendations
Flare Stack Monitoring Limitations
Stack monitoring can only be carried out on enclosed flares. Even then, emission monitoring of flares in general, and on Irish licensed landfill sites in particular, does not provide representative results which can be used for licence compliance assessment.
Figure 3 - Enclosed Flare Photo:Summerleaze Re-Generation Ltd
Control through Design Specification
If the temperature in the combustion chamber is between 1000oC and 1200oC , a minimum retention time of 0.3 seconds is observed (as per TA Luft 2001) and the flare is properly maintained and operated, enclosed landfill gas flares are capable of providing a destruction efficiency of nearly 98-99% for methane and VOCs. Where compounds of chlorine, fluorine and sulphur are present in the inlet gas it is inevitable that they, or compounds derived from them, will be present in the flare emissions. Their presence in the emissions is predictable and the only way in which they may be controlled is by attention to the quality of the inlet gas.
The following Emission Control Strategy is therefore proposed:
- Impose flare design and operations standards that can easily be assessed (temperature, retention time, inlet gas rate of input).
- Impose emission standards only on those compounds that can be safely monitored and that are controlled by design of the flare (CO, NOx and unburned hydrocarbons).
- Specify limits for key compounds to be monitored in the inlet gas (HCl, HF, SOx) which, if exceeded, require removal. Calculations based on mass balance can then be carried out to the assess exit emissions impacts.
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Conclusions:
In view of the fundamental difficulties inherent in extractive emissions sampling, a design and operational certification approach is proposed for the control of emissions from flares in Ireland. Proposed Design and Operational Certification Approach
Operational flare verification in Ireland could consist of a 2-stage approach. 1) Initial identification of the type of flare required for a particular site, based on a site specific survey or modelling of the key elements of the landfill gas in question; 2) followed by flare performance verification based on once-off sampling of the flare when it is commissioned at the site. If all requirements are met, a Verification of Operational Performance Certificate could then be issued to the Flare Operators.
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Table 1:Comparison between operations of the eight Enclosed Flare Stacks installed on licensed Landfill Sites in Ireland
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WL. Reg. & Name
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Flare installed
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Capacity m3/hr
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Stack Monitoring carried out
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Continuous exit CO and Temperature
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Inlet gas monitored CH4, CO2, O2
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Inlet Data provided routinely to EPA?
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Reason for occasional flare shut-down
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1-2 N. Kerry Landfill
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2001
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350
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Not yet
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Not yet
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Weekly
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Yes
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Teething problems
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Arthurstown
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June 2001
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1500
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2001 and 2002
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Yes
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Daily
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Yes
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No details provided
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Basketstown
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2002
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1000
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2001 and 2002
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Yes
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Weekly
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Some submitted, otherwise kept on site
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Fluctuating gas quality
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Ballymurtagh
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2001
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500
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2002
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Yes
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Continuous
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Yes
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Power failure
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17-1 Gortadroma
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April 2002
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750
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2002
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Not yet
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Continuous also H2S ,& mercaptan
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Yes
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Teething problems
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Derrynumera
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2001
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250
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Yes 2002
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Yes
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Continuous
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No, kept on site
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Fluctuating gas
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25-1 Powerstown
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2001 -2002
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500
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Yes, 2002 & 2002
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Not yet
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Daily
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Submitted, not routinely
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Thermocouple burn-out
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28-1 Ballydonagh
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2002
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250
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Not Yet
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No
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Weekly
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Yes
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Fluctuating gas quantity
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References & Interviewees
Refs: Guidance on Landfill Gas Flaring, UK EA 2002; Guidance on the Management of Landfill Gas (Draft), UK EA 2002; Landfill Gas Engine Exhaust and Flare Emissions LQM Ltd Sept.2002; Landfill Gas Flares and Engines Emissions Standards Shanks Int.Rpt 1999; Guidance on the Emissions from Types of Landfill Gas Flares, AEA Tech '97; TA.(Luft) 2001, Air Quality Guidelines, German Ministry of the Environment
Interviewees: Paul Glenister-Summerleaze Re-GenerationLtd; Andrew Leach- Renewable Power Systems; Norbert Salomon-German Ministry for the Environment; Edward Schokkar-Vereinigungs van Afvalverwerkehrs, Netherlands; Jörg Simon- Umweltanalytic RUK; Wolfgang Stachowitz- DAS-IB Gmbh; Graham White- Clarke Energy Ltd.
Funded work undertaken by ENVIROS staff:
Elisabeth Nagel, & Brian Latham.
Enviros Consulting Ltd., The Plaza, Swords, Co. Dublin. Tel: 01-8131020.
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