Claims:We Claim:

1. A gas fired burner for igniting solid fuel at grate level in grate-fired boilers comprising
a horizontal outer tube with nozzle for air supply;
a concentric inner tube with nozzle for supplying of fuel gas; and
a flame stabilizer disc on inner nozzle for creating turbulence in air stream,
wherein said tubes and nozzles for gas and air supply can be interchanged, configured to supply required amount of gaseous fuel with air and create a condition of rapid mixing therefore produce sustained long flame which can impose a high intensity heat flux on solid fuel spread on the grate of a grate-fired boiler.

2. The gas fired burner as claimed in claim 1 is adapted to be configured for different fuel gases of calorific value 1,200 Kcal/Nm3 and above.

3. The gas fired burner as claimed in anyone of claims 1 or 2 which is capable to create long flame of more than 1 meter length.

4. The gas fired burner as claimed in anyone of claims 1 to 3 having a turn down ratio of at least 1: 10 so that the burners can work even at fuel gas flow rate of one-tenth of its rated capacity.

5. An improved ignition system for combusting solid fuel for grate-fired boilers wherein each grate fired boiler is associated with a plurality of gas fired burners as claimed in claims 1 to 4, having the head of said burners comprising of a central tube with nozzle for supplying of fuel gas and a co-axially disposed cylindrical air tube around the said gas tube for supplying air and a flame stabilizer disc on inner nozzle for creating turbulence in air stream, or vice-versa, and mounted on the side walls at a location just above the grate level configured for igniting the uppermost layer of the solid fuel on the grate, imposing long flame with high intensity heat flux, particularly when the calorific value of the solid fuel is low.

6. The ignition system as claimed in claim 5 wherein the burners are configured/ retrofitted and mounted at the side(s) of the grate-fired boiler just above the grate level, preferably tilted downwards to direct the flame thus generated to reach near the top layer of solid fuel spread on the grate.

7. The ignition system as claimed in anyone of claims 5 or 6 wherein said burners are lighted up with the help of the flame either from the solid fuel on grate or from a portable gaseous/liquid fuel-fired lance or with the help of electrical spark from an ignitor; and may be kept in lighted-up condition during the normal process.

8. The ignition system as claimed in anyone of claims 5 to 7 that enable combustion of solid fuel spread on the grate by imposing high intensity radiative and/or convective heat flux thus improving the completeness of combustion of the solid fuel as well as the spontaneous ignition of solid fuel, layer after layer as it is spread over grate.

9. The ignition system as claimed in anyone of claims 5 to 8 that ensure burning of solid fuel as complete as possible; thereby reducing the loss-on-ignition of ash generated and reducing specific energy consumption.

Dated this the 20th day of March, 2017
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

, Description:FIELD OF THE INVENTION
The present invention relates to gas fired burner for igniting solid fuel at grate level in grate-fired boilers and an improved ignition system of solid fuel for grate-fired boilers involving a plurality of such burners. More particularly, the present invention is directed to provide gas-fired burners that are designed, fabricated and introduced in-between the boiler tubes at grate-level of Grate-fired Boilers. The burners of the present invention determine the mixing rate and pattern of air and gaseous fuel directly affecting the flame stability, shape and emission. The new burners not only help in sustaining the flame, but also favour burning of solid fuel as complete as possible; thereby reducing the loss-on-ignition of ash generated and reducing specific energy consumption and therefore having prospects for wide scale application in grate-fired boilers in different industries with significant economic advantage.

BACKGROUND OF THE INVENTION

It is well known that in a boiler, water or other liquid is heated, steam or vapour is generated which may also be superheated, under pressure or vacuum, for use external to itself, by the direct application of energy from the combustion of fuels, from electricity or nuclear energy. The act of combustion of solid fuels consists of three relatively distinct but overlapping phases:
(I) Preheating phase, when the unburned fuel is heated up to its flash point (i.e. the lowest temperature at which there is a flammable vapour / air mixture at the surface) and then fire point (i.e. a slightly higher temperature than flash point where sufficient flow of vapours are produced to support a diffusion flame) to cause chemical decomposition of the fuel, breaking large polymeric molecules into smaller fragments which can vaporize and escape from the surface. Flammable gases start being evolved in a process similar to dry distillation.
(II) Distillation phase or gaseous phase, when the mix of evolved flammable gases with oxygen is ignited. For successful ignition, an ignition source must be capable of raising not only the surface temperature to the fire point, or above, but it must also cause the vapours to ignite. Energy is produced in the form of heat and light. Flames are often visible. Heat transfer from the combustion to the solid maintains the evolution of flammable vapours.
(III) Charcoal phase or solid phase, when the output of flammable gases from the material is too low for persistent presence of flame and the charred fuel does not burn rapidly and just glows and later only smoulders.

Fixed grate firing was the first combustion system used for solid fuels. Later, travelling, reciprocating and vibrating grates were introduced for combusting solid fuels, followed by other modes like fluidized bed and pulverized solid fuel burners. When solid fuels are combusted in boilers with the help of air or oxygen enriched air, by spreading the solid fuel over grates near the bottom of the boiler and passing the air over / through the solid fuel layer, they get ignited from the radiation of the flame generated due to combustion of other fuels present in the boiler.
Boiler burners are the functional component of boilers that provide the heat input by combustion of a fossil fuel with air or oxygen. They are supplied either as part of the boiler package from the manufacturer, as stand-alone products for custom installations, or as replacement products.

Once, the solid fuel ignites, it releases heat, which not only helps in converting the liquid to vapour, but also helps to sustain the combustion process by igniting the next layer of solid fuel fed to the boiler.

Thus, for the economical production of steam or vapour in a grate-fired boiler, it is important, with regard to the ignition, that the an ignition source must be capable of raising not only the solid fuel surface temperature to above the fire point, but it must also cause the vapours from the solid fuel to ignite. This is to be attained with the smallest possible fuel input.

The economics of the process is substantially influenced by the possible un-burnt carbon being rejected along with ash which, in turn, is decisively dependent upon the quality of sustained ignition of the solid fuel. An imposed low intensity radiative heat flux from a remote source (like a burner located much above the grate level) or a near source (like low calorific value solid fuels) sometimes lead to the solid fuels not igniting. It results in insufficient heat release, hampering steam production.

There has been, therefore, a need in the art to develop a new design of a gas burner devices, suitably located and tilted, that supply required amount of gaseous fuel with air or oxygen enriched air and create a condition of rapid mixing and produce a stable, long flame which can impose a high intensity heat flux adequate for complete combustion of solid fuels reducing the loss-on-ignition of ash generated and reducing specific energy consumption.

OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to provide a gas fired burner at grate level for igniting solid fuel or sustaining ignition of solid fuel in grate-fired boilers and an improved ignition system of solid fuel for grate-fired boilers involving a plurality of such burners for imposing high intensity heat flux on solid fuel spread on the grate of a grate-fired boiler and thereby improving the completeness of combustion of the solid fuel.

A further object of the present invention is directed to provide an improved gas burner device for imposing high intensity heat flux on solid fuel, spread on the grate of a grate-fired boiler and thereby improving the spontaneous ignition of solid fuel, layer after layer as it is spread over grate reducing the loss-on-ignition of ash generated and reducing specific energy consumption.

Another object of the present invention is directed to developing a gas burner device for imposing radiative and/or convective high intensity heat flux on solid fuel, spread on the grate of a grate-fired boiler.

Yet another object of the present invention is directed to provide an improved gas burner device such that it can supply required amount of gaseous fuel with air and create a condition of rapid mixing and produce sustained and stable long flame for imposing high intensity heat flux on solid fuel.

A still further object of the present invention is directed to provide an improved gas burner device which is selectively located and directed in relation to the solid fuel on grate such that it can impose high intensity heat flux on solid fuel that is spread on the grate of a grate-fired boiler.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a gas fired burner for igniting solid fuel at grate level in grate-fired boilers comprising
a horizontal outer tube with nozzle for air supply; and
a concentric inner tube with nozzle for supplying of fuel gas, wherein said tubes and nozzles for gas and air supply can be interchanged, configured to supply required amount of gaseous fuel with air and create a condition of rapid mixing therefore produce sustained and stable long flame which can impose a high intensity heat flux on solid fuel spread on the grate of a grate-fired boiler.

A further aspect of the present invention is directed to developing a gas fired burner system for grate-fired boilers wherein a stabiliser disc on the outer side of the concentric inner nozzle is provided in order to create sufficient turbulence in air stream emerging out of the burner to anchor the flame thus generated in front of the burner mouth without any refractory quarl, even though the flame is slightly detached from the burner mouth to protect the boiler tubes nearby from localized heating.

A further aspect of the present invention is directed to said gas fired burner which is adapted to be configured for different fuel gases of calorific value 1,200 Kcal/Nm3 and above.

A still further aspect of the present invention is directed to said gas fired burner which is capable to create long flame of more than 1 meter length.

A further aspect of the present invention is directed to said gas fired burner having a turn down ratio of at least 1: 10 so that the burners can work even at fuel gas flow rate of one-tenth of its rated capacity.

Another aspect of the present invention is directed to an improved ignition system for combusting solid fuel for grate-fired boilers wherein each grate fired boiler is associated with a plurality of gas fired burners as described above, having the head of said burners comprising of a central tube with nozzle for supplying of fuel gas and a co-axially disposed cylindrical air tube around the said gas tube for supplying air, or vice-versa, and mounted on the side walls at a location just above the grate level configured for igniting the uppermost layer of the solid fuel on the grate, imposing long flame with high intensity heat flux, particularly when the calorific value of the solid fuel is low.

A further aspect of the present invention is directed to said ignition system wherein the burners are configured/ retrofitted and mounted at the side(s) of the grate-fired boiler just above the grate level, preferably tilted downwards to direct the flame thus generated to reach near the top layer of solid fuel spread on the grate.

A still further aspect of the present invention is directed to said ignition system wherein said burners are lighted up with the help of the flame either from the solid fuel on grate or from a portable gaseous/liquid fuel-fired lance or with the help of electrical spark from an ignitor; and may be kept in lighted-up condition during the normal process.

A further aspect of the present invention is directed to said ignition system that enable combustion of solid fuel spread on the grate by imposing high intensity radiative and/or convective heat flux thus improving the completeness of combustion of the solid fuel as well as the spontaneous ignition of solid fuel, layer after layer as it is spread over grate.

A further aspect of the present invention is directed to said ignition system that ensure burning of solid fuel as complete as possible; thereby reducing the loss-on-ignition of ash generated and reducing specific energy consumption.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawing.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1: illustrates the schematic cross-sectional view of the gas fired burner in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWING

The present invention is directed to provide a gas fired burner device and an improved ignition system using a plurality of such burners for imposing high intensity heat flux on solid fuel that is spread on the grate of a grate-fired boiler and thereby improving the completeness of combustion of the solid fuel as well as the spontaneous ignition of solid fuel, layer after layer as it is spread over grate. This device is directed to reducing the specific heat consumption in grate-fired boilers.

It has been found that the procedure for sustenance of solid fuel ignition is very cumbersome in grate-fired boilers; especially if the solid fuel is having low calorific value. Sometimes the flame of ignited solid fuel gets extinguished if air in proper ratio (within a narrow band) is not supplied. It takes lot of time for lighting up again. The conventional grate-fired boiler design is therefore not energy efficient and economical.

To eliminate the above problems and limitations of solid fuel ignition in grate fired boilers, the present invention attempts to provide an improved burner configuration and an improved ignition system for grate fired boilers that ensure long and sustained flame, complete combustion of solid fuel with improved energy efficiency as may be apparent from the following description of a preferred embodiment:

With reference to Figure 1, which illustrates the cross section of the burner as disclosed herein. The burner consists of a horizontal outer tube (3) with nozzle (1) for air supply, a concentric inner tube (4) with nozzle (2) for supplying of fuel gas and a flame stabiliser disc (5). The tubes and nozzles for gas and air supply can be interchanged. The burner design can be suitably modified for different fuel gases of calorific value 1,200 Kcal/Nm3 and above. It is proposed that the burners may be designed / retrofitted and mounted at the side(s) of the grate-fired boiler just above the grate level, preferably with a downward direction, such that the flame thus generated is directed towards the solid fuel on the grate. The burners are capable to create long flame of more than 1 meter length.

These burners are lighted up with the help of the flame either from the solid fuel on grate or from a portable gaseous / liquid fuel-fired lance or with the help of electrical spark from an ignitor; and may be kept in lighted-up condition during the normal process. By such an expedient, the advantages of the process according to the invention can be utilised at relatively low investment costs even in the case of pre-existing wall-mounted high-throughput burners, which are generally at a much higher level in the grate-fired boilers.

A particularly simple manner of construction of the burner and an attainment of particularly good completion of the solid fuel combustion process with the help of the burner, is particularly advantageous in the case of grate-fired boilers.

The solid fuel is loaded on the grate (fixed, travelling, reciprocating or vibrating) through a feeder. The top surface of the solid fuel is ignited through flames generated by these stationary burners. It is to be particularly stressed that the use of these burners to light up the soild fuels spread over the grate, confers an easy and quicker light-up of the grate-fired boilers.
The burners have a turn down ration of at least 1: 10. That means the burners can work even at fuel gas flow rate of one-tenth of its rated capacity.

In a manner similar to one of the known processes, it is also possible, in a process, according to the invention, according to a preferred embodiment thereof, to introduce in the inlet region of the solid fuel more flue gases at high temperatures from the burners operated.

Each grate fired boiler is associated with a number of such small burners, the head of which comprises of a central tube with nozzle for supplying of gas and a co-axially disposed cylindrical air tube around the said gas tube for supplying air and a flame stabilizer disc on inner nozzle for creating turbulence in air stream, or vice-versa, and mounted above the grate level. This arrangement is implemented based on the concept that for igniting the uppermost layer of the solid fuel on the grate, high intensity heat flux is required to be imposed, particularly when the calorific value of the solid fuel is low.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.