GB2348482A

GB2348482A - Flare for burning combustible gas

Info

Publication number: GB2348482A
Application number: GB9827705A
Authority: GB
Inventors: Stephen Carswell
Original assignee: Shanks and Mcewan Ltd; Shanks Waste Services Ltd
Current assignee: Shanks and Mcewan Ltd; FCC Waste Services UK Ltd
Priority date: 1998-12-16
Filing date: 1998-12-16
Publication date: 2000-10-04
Also published as: GB9827705D0

Abstract

A flare (1) suitable for burning landfill gas is supplied with the landfill gas via a supply pipe (2). The supply pipe (2) feeds separate burners (3,4,5) via respective control valves (6,7,8). As supplied, the flare is designed to meet current regulatory standards and may typically be designed to replace a combustion temperature of approximately 85% degrees centigrade and a retention time of 0.3 seconds over a turndown ratio of 5:1. With a view to allowing more precise control of the flare operating conditions to meet subsequently imposed regulatory standards the flare is designed to be modified after installation to provide combustion air control. Combustion air control may conveniently be provided in response to combustion monitors and may involve the use of force draught primary and secondary air admission.

Description

FLARE FOR BURNING COMBUSTIBLE GAS This invention relates to a flare for burning combustible gas and, in the preferred embodiment, provides a flare which can be constructed economically to meet existing regulations for the combustion of surplus landfill gas but which can readily be upgraded to meet future potentially more rigorous environmental standards.

As will be understood by those skilled in the art, when waste materials decompose in a landfill site a combustible gas is produced. This gas, which is commonly known as"landfill gas"or"LFG"consists largely of methane but may contain traces of other combustible or non-combustible gases or vapours.

Operating regulations imposed on some landfill sites require the extraction of the LFG for safe disposal. In other cases, even if no requirement for extraction of LFG exists, the LFG is regarded as a valuable by-product of operating the landfill site and is extracted, for example to power electrical generators. In either event, there can be circumstances when the landfill gas must be burnt either as a regular means of disposal or as a means of disposal when power generation equipment is not working. In order to ensure safe disposal of LFG under these circumstances purpose built flares are used.

According to one aspect of the present invention a flare for burning a combustible gas comprises a plurality of burners each selectively connectable to a source of landfill gas; ignition means for igniting the or each burner ; a combustion chamber for burning combustible gas emanating from the or each burner ; means for admitting combustion air to the combustion chamber; and means facilitating subsequent connection to the incinerator of automatic control devices for automatic control of the amount of combustion air admitted to the combustion chamber.

Preferably, means are provided for separately admitting primary and secondary combustion air and both the primary and secondary combustion air inlets are adapted for subsequent modification to allow automatic control.

Preferably, the flare is adapted for subsequent modification allowing forced draught primary and/or secondary air admission. Preferably, the flare is adapted to receive one or more flue gas monitors to determine combustion conditions and permit automatic control of combustion air in light of sensed combustion conditions.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only reference being had to the accompanying drawings wherein: Figure 1 illustrates schematically an embodiment of flare according to the present invention; Figure 2 illustrates the flare of Figure 1 after modification to permit automatic control of combustion air; and Figure 3 illustrates the flare of Figure 2 modified to permit forced air operation.

Referring firstly to Figure 1 there is illustrated schematically a flare 1 suitable for burning LFG. The LFG is supplied to the flare by a supply pipe 2 and is typically supplied at low pressure. The supply pipe 2 supplies three separate burners 3,4,5 via respective control valves 6,7,8. The control valves 6,7,8 are preferably automatic valves which operate to provide gas flow to only one burner when low gas flow rates are present. If the gas flow rate increases the remaining burners are progressively brought into operation in order to ensure proper combustion over a wide range of flow volumes. The valve 6,7,8 can conveniently be pressure sensitive valves or can be controlled by a pressure sensor so that at low supply pressures only one burner operates and as supply pressure increases (indicating an increase in flow) further burners are automatically brought into action. Pilot lights supplied by a pilot line 9 are associated with each burner. The pilot lights can conveniently burn LFG.

The flare has a body comprising a steel shell 10 having suitable refractory linings. Each burner 3,4,5 has associated therewith a respective combustion air inlet 11, 12,13, the air inlets having associated therewith manually operable control valves. Ports 14,15 provided on the flare body permit entry of secondary combustion/dilution air. If desired, the ports 14,15 can be closed by blanking plates.

A flare of the general type described above can be constructed to meet current regulatory standards. These typically require a combustion temperature of 850 C and a retention time of 0.3 seconds over a turndown ratio of 5: 1.

Whilst a flare meeting the above functional requirements can readily be built at relatively low cost, such flares cannot readily be modified if more rigorous environmental standards are imposed. As a result, any flare built to meet current standards at a competitive price will not be capable of easy upgrading to meet future more stringent environmental standards.

The object of the present invention is to provide an incinerator which can meet current standards and can be built at reasonable cost, and yet which can be readily upgraded to meet future standards.

To this end, although current standards require a combustion temperature of only 850 C the preferred embodiment of the present invention is built with a combustion chamber capable of operating at up to 1100 C. This will add slightly to the costs of construction but will not materially increase the overall costs of the flare. Further, the casing of the flare is preferably designed to operate over a substantial lifetime at an elevated operating temperature. For this reason, it is preferred that the case is constructed from stainless steel (304L), even though this is not strictly necessary for a flare operating at 850 C.

Referring now to Figure 2 there is illustrated the basic flare of Figure 1 after upgrading. It will be noted that the gas supply pipe 2 and valving arrangements 6,7,8 remain substantially unchanged. Similarly, the burners 3,4,5 are substantially unchanged although different injector designs may be used to produce a different flame pattern. The air inlets 11,12,13 are now automatically controlled by a control device 16. A secondary air controller 17 has been connected to the secondary air inlet 14 and is also controlled by the control device 16. One or more sensors 18 have been installed in the incinerator to provide control information to the control device 16. Using information supplied by the sensors 18 the control device 16 regulates combustion air flow automatically via both the primary and secondary combustion air inlets to achieve a combustion temperature of 1100 C and a 0.3 second retention time. Such an arrangement does not necessitate change to the casing of the flare or to the refractory lining-all that is necessary is to automate the air control valves, provide the necessary sensors, and to provide a control device responsive to the sensors for controlling the combustion air.

Figure 3 illustrates a further development of the invention. The control arrangements remain the same as in Figure 2 but in Figure 3 an air blower 19 has been added to provide for forced draught primary and secondary air. The use of forced draught arrangement and appropriate sensors, in combination with primary and secondary air control enables stoichiometric combustion to be obtained over a wide range of flow rates and enables flue gases to be diluted to meet appropriate standards (e. g. TA Luff).

It will be noted that the systems illustrated in Figures 1-3 include further provision for improvement in the form of a removable spool piece 20 in the gas supply pipe. If increased gas pressure is required the spool piece may be removed and a fan inserted in order to boost pressure supplied to the burners.

Claims

CLAIMS: 1. A flare for burning combustible gas comprising: a plurality of burners each selectively connectable to a source of landfill gas; ignition means for igniting the or each burner ; a combustion chamber for burning combustible gas emanating from the or each burner ; means for admitting combustion air to the combustion chamber; and means facilitating subsequent connection to the incinerator of automatic control devices for automatic control of the amount of combustion air admitted to the combustion chamber.
2. A flare according to claim I wherein means are provided for separately admitting primary and secondary combustion air and both primary and secondary combustion air inlets are adapted for subsequent modification to allow automatic control.
3. A flare according to claim 1 or claim 2 wherein the flare is adapted for subsequent modification to allow forced draught primary and/or secondary air admission.
4. A flare according to any preceding claim wherein the flare is adapted to receive one or more flue gas monitors to determine combustion conditions.
5. A flare according to claim 4 wherein the flare is adapted to permit automatic control of combustion air in light of combustion conditions sensed by the one or more flue gas monitors.
6. A method of providing a flare for burning a combustible gas comprising a plurality of burners each selectively connectable to a source of landfill gas; ignition means for igniting the or each burner ; a combustion chamber for burning combustible gas emanating from the or each burner; means for admitting combustion air into the combustion chamber and automatic control means for automatic control of the amount of combustion air admitted to the combustion chamber comprising providing a flare comprising a plurality of burners each selectively connectable to a source of landfill gas, ignition means for igniting the or each burner, a combustion chamber for burning combustible gas emanating from the or each burner and means for admitting combustion air to the combustion chamber; and subsequently providing automatic control means for automatic control of the amount of combustion air admitted to the combustion chamber.
7. A method according to claim 6 wherein the method includes providing automatic control of primary and secondary combustion air.
8. A method according to claim 6 including subsequently modifying the flare to allow forced draught primary and/or secondary air admission.
9. A method according to any of claims 6 to 8 comprising providing one or more flue gas monitors to determine the combustion conditions within the flare and providing automatic control means responsive to the sensors for control of combustion air.