Techniques for the combustion of landfill gas have undergone many changes over the last fifteen years. From the initial "pipe-flares" of the early 1980's, where vertical tubes were simply forced into the surface of a site and the emitting landfill gas lit with a burning oily rag, the technology employed has advanced significantly. In many ways the combustion of landfill gas may be seen as leading waste-gas flaring technology in other industries.

This is largely because of the extremely difficult nature of landfill gas. As well as containing significant percentages of carbon dioxide and methane, landfill gas has been found to contain as many as three hundred and fifty trace substances, many of which are highly toxic. Higher standards demanded for the landfilling of wastes, including the need to control emissions, have added impetus for the flaring of landfill gas, where undertaken, to be done so in an acceptable manner.

It is a publicly stated aim of the current government to reduce green-house gas emissions in the United Kingdom. Methane emissions from landfill sites are recognised to make a significant contribution to this position. As a result, large-scale passive venting of landfill gas should no longer be considered an acceptable solution to possible offsite migration of landfill gas.

REGULATORY FRAMEWORK

 The introduction of the Environmental Protection Act (1990), the Framework Directive on Waste (75/442/EEC as amended by 91/156/EEC) and its associated regulations, extended the scope of waste regulation controls to a wider environment than before. These instruments also clarified that control of landfill gas flares is the responsibility of Waste Regulation Authorities, now part of the Environment Agency.  Waste Management Paper 4 (WMP 4) gives statutory guidance about the requirements to recover landfill gas in order to protect the global environment.

1.4              The Environment Agency now wishes to provide more guidance to regulators and others on landfill gas flaring and, with this objective, has prepared these Guidance Notes.  The main emphasis is to provide guidelines for landfill gas flare operation and monitoring, based on best practice, taking account of relevant draft and enacted EU Directives.

1.5              The review, upon which these Guidance Notes have been based, was carried out by staff of AEA Technology, mainly in the National Environmental Technology Centre (NETCEN), with support from the National Physical Laboratory (NPL).

The UK Environment Agency has prepared a set of Guidance Notes (still in draft form) in response to increasing demands from many diverse parties with interests in landfill gas flaring. They are primarily intended as an easy access document for Environment Agency officers required to inspect planned or existing flare installations. They have been prepared as an interim document, to be modified as other currently ongoing Agency sponsored projects make specific recommendations of relevance. The Guidance Notes have been drawn from a master document prepared by AEA Technology on behalf of the DoE "Guidance on the Emissions from Different Types of Landfill Gas Flare" They are organised into six Chapters and seven Appendices, as follows:

CHAPTER 1 provides a brief summary of landfill gas and summarises key aspects of landfill gas treatment and disposal.

CHAPTER 2 addresses definitions and concepts associated with combustion engineering and its application to the technologies involved in the flaring of landfill gas.

CHAPTER 3 considers the effects that a flare may have upon its surroundings.

CHAPTER 4 reviews the application to operational flares of the principles embodied within the DoE recommendations.

CHAPTER 5 summarises the types of instrumentation that may be employed to verify compliance.

CHAPTER 6 discusses standards in selected countries.

The APPENDIX contains information to be viewed in isolation. Topics covered include the DoE recommendations

(i); flare selection criteria
(ii); a typical flare maintenance checklist
(iii); a site visit checklist
(iv); sample combustion calculations
(v); flare siting criteria
(vi); and a glossary of terms
(vii). Acknowledgements

The Guidance Notes may be seen as the tip of an iceberg of effort from numerous parties. The source documents were prepared by Dr Richard Frost and Dr Jane Pearson of the National Environmental Technology Centre (NETCEN), in conjunction with Dr John Sykes of AEA Technology, Harwell.  The Guidance Notes were drafted by Dr Robert Eden of Organics, based upon the foregoing document and the guidance of the members of the Environment Agency Steering committee.
 

Members of the Environment Agency who have been involved in assessing this report and working with ESTU to prepare the Guidance Notes were:
 

Ian Cowie (Chair) North East Region
John Keenlyside Anglian Region
Louise McGoochan Southern Region
Philip Taylor Thames Region
Jan Gronow Head Office
Peter Stanley Environment Agency, Wales
Catriona Bogan South West Region
Trevor Howard Midlands Region
Rowland Douglas SEPA, Arbroath
Richard Smith Head Office

The support and involvement of the following individuals is also acknowledged:

Jim Shaughnessy North East Region
Jonathan Atkinson Southern Region
Sheila Stevenson North West Region

Although open flares are popular with landfill operators, and are cheaper than enclosed flares, the differential cost is small, especially when considered in the context of the development of the landfill overall. Moreover, open flares are unable to achieve the level of emissions likely to be required in future permits and the environmental benefits of fully enclosed flares far outweighs their marginally greater cost. It is, therefore, recommended that:

1. No more open flares should be installed on UK landfills except for test and emergency purposes, and then only for limited periods of not greater than six months.

2. Existing waste management licences at landfill sites should be modified so as to effect the replacement of open flares with enclosed flares (or techniques offering equivalent performance) over a period of five years (by 31 December 2003), particularly at sites that:
• produce large amounts of landfill gas; and/or
• are close to population centres or other areas of environmental importance.

3. The combustion air supply should be controlled so as to achieve a minimum of 1,000^oC and 0.3 seconds retention time at this temperature whatever the landfill gas composition and throughput (within expected design limits). This is an indicative performance standard that is required to meet the emission standard. Alternative performance standards may be deemed more appropriate if compliance with the emission standard is suitably demonstrated.

4. To ensure that flare systems are operating correctly they should not exceed the following emission concentrations when referred to Normal Temperature and Pressure (NTP=0oC and 1013 mbar) and 3 % oxygen:
• Carbon monoxide (CO) - 50 mg/Nm³
• Oxides of nitrogen (NOx) - 150 mg/Nm³
• Unburned hydrocarbons - 10 mg/Nm³

5. Inlet gas concentrations should be analysed annually to determine trace gases. Guidance is given below as to the level of monitoring which should be recommended and the acceptable methods that may be employed. Easily accessible, safe and functional monitoring/sampling points should be retrofitted to enclosed flares as appropriate in situations where they are currently absent. This shall include a minimum of one emission representative monitoring location to be installed by 31 December 2000. All monitoring/sampling points should be provided in accordance with all relevant health and safety legislation.

 • First level monitoring should be carried out continuously since it provides the basic information needed for controlling the flare, checking the completeness of combustion and referencing the emissions to standard conditions.
• Second level monitoring should be carried out periodically or when there is some significant change in, for example, the composition of the LFG. It provides more information about the completeness of combustion, the main combustion products and the major emissions.
• Third level monitoring is likely to be infrequent but should be considered for large flares close to population centres or other environmentally sensitive areas since it is targeted at good indicators of potentially hazardous components in flare emissions.

6. Enclosure Enclosed flare design should:

• permit an homogeneous temperature distribution across the combustion chamber;
• be lined with refractory material on the interior;
• contain the flame within it; and
• be maintained in an effective condition.

7. Operators of landfill sites should undertake, or commission, an environmental assessment of the emissions from existing and proposed flares which: • should use either measured or reported emissions data, flow rate data and local meteorological data; • consider address the impacts of the dispersed emissions in the vicinity; • determine whether flaring is required for migration control and/or pollution prevention effectively controlling impacts of dispersed emissions; and • be approved in writing by the Environment Agency.

8. Flares should be positioned and sized so that potential health and environmental impacts are minimised. as a local planning issue.

9. Flares should be maintained in accordance with the manufacturers' recommendations. Full records should be available for inspection.

10. All results obtained by flare-system managers should be the subject of formal interpretation a formal review. Such reviews This interpretation and a copy of the flare maintenance log must accompany results and reports when communicated to Environment Agency officers, on at least a monthly basis.
 

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