SK177498A3 - Method and arrangement for burning gas in a furnace - Google Patents

Abstract

The invention relates to a method and arrangement for burning fuel gas in a furnace (2), particularly for burning gases of low heating value in a boiler (1) principally fired with a main fuel. The invention is based on feeding the product gas of a gasifier (5) or other combustible gas into air-deficient conditions of the lower part (10) of the furnace (2) and the gas is combusted upper in the furnace (2) at a desired level of combustion air infeed, or alternatively, at multiple infeed levels of the combustion air.

Description

Technical field

The present invention relates to a method according to the preamble of claim 1 for burning fuel gas in a furnace, in particular for burning low-calorific gases in a boiler in principle heated by yet another, main fuel. The invention also relates to a device suitable for carrying out the method.

The invention is particularly suitable for heating with gases produced by gasification of air, blast furnace gas and other low calorific value gases. The invention is used in, for example, making fuel variations in the boiler heating and can also be used to burn gases with a high calorific value such as natural gas.

BACKGROUND OF THE INVENTION

Traditionally, the produced ("heating") gas, obtained from a separate gasifier, is supplied to the furnace by means of burners. If this gas has a low calorific value, these burners must be designed for a low axial velocity to ensure reliable ignition, making the burner dimensions very large. With low calorific gases, such as those produced by gasification of the air, the amount of gas supply volume becomes extremely large, which complicates the fuel supply at low speed and increases the burner size. Furthermore, treating larger burners in an existing furnace is technically difficult, and moreover, the refurbishment (i.e., refinement) of an old boiler by means of multiple burners substantially limits the usable heat transfer surface. Difficulties in achieving a sufficient residence time in the combustion of the fuel gas and constraining the structure may also cause complications in the arrangement of the additional burners. Since high-calorific fuel gases can be supplied at higher axial speeds, adapting the new burners in an existing boiler is no less difficult. Because boilers are generally designed for a particular fuel and air flow rate, additional burners can cause fouling problems and flow failures because introducing new boiler flow rates changes the furnace flow patterns, thus changing the fuel combustion pattern of the flue gas flame and heat transfer on the inside surfaces of the boiler.

It is an object of the present invention to provide a method suitable for burning low-calorific gas, especially in existing boilers designed for another type of main fuel, without any need for major design changes in these boilers.

SUMMARY OF THE INVENTION

The object of the present invention is achieved by supplying combustion gas from a gasifier or other combustion gas to the bottom of the boiler under oxygen-depleted conditions and then burning the gas at the top of the boiler at desirable combustion air supply levels or a plurality of combustion air supply levels. .

More particularly, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1. In addition, the device according to the invention is characterized by what is set forth in the characterizing part of claim 7.

The present invention provides significant advantages.

Based on the present invention, existing boiler designs, using minor modifications therein, can very advantageously use gases of fairly low calorific value. The heat transfer area of the steam generator need not be limited, and boilers equipped with combustion gas recirculation can use an existing recirculation system to supply additional heating gas to the bottom of the boiler. The invention achieves stable combustion (combustion) and causes only minor changes in the furnace internal flow pattern. In this method the flame radiation stabilizes the ignition and combustion of the additional fuel gas. In addition, the new inlet arrangement offers an easier remodeling of the existing boiler, as the gas inlet openings are easier to adjust in the furnace than large burners.

The new method is more adaptable with respect to the type of fuel and provides wider possibilities than the prior art to reduce the amount of nitrogen oxides in the flue gas (flue gas) by the combustion control means. Since this method achieves a firm separation into the furnace stages by means of a properly timed air supply scheme, the boiler can be operated as stepped burners with a low nitrogen oxide content.

The advantages of this method will be most pronounced when the combustion of the combustion gas is connected as a supplementary fuel supply to an existing boiler. Due to the supply of the fuel gas through nozzles adapted to the bottom of the furnace or through openings through the eventual combustion exhaust gas recirculation system, instead of using burners, the changes required on the heat transfer surfaces remain substantially less than when the boiler is equipped to burn fuel gas by burners. Additionally, the advantages of the above-described combustion process are achieved. In addition, if a new boiler is specifically designed for the use of mixed fuel, particularly advantageous conditions depending on the composition of the fuel gas, re-firing can be achieved, reducing the emission of nitrogen oxides. Here, the hydrocarbon radicals formed from the fuel reduce the nitrogen monoxide back to molecular nitrogen, thus reducing the total amount of nitrogen oxide emissions.

The process of the present invention can be applied to the combustion of all types of gaseous fuels. However, the advantages of the method relating to boiler construction are best utilized in the combustion of low calorific gases such as gas produced by gasification of air, blast furnace gas and waste gases. Nothing less, the above-described advantages of improved combustion can also be used when high calorific gases such as natural gas are burned. In addition, the fuel gas may be combusted as the main fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be examined in more detail with reference to the accompanying drawing, FIG. 1 in which an embodiment of the present invention is shown schematically.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the aforementioned scheme, the heating gas is supplied to the air deficiency zone (reducing) in the lower part 10 of the furnace 2, thus ensuring sufficient residence time therein and to prevent explosions in the furnace. Since no combustion air is supplied to this zone, the gas is ignited and burned only in the combustion air streams that are supplied to the upper zones of the furnace. The air can be supplied to the boiler via burners 8 supplying other fuels and / or through the air supply nozzles themselves 9. Instead of combustion and thereby further distribution of heat transfer within the steam generating circuit of the boiler 1 can be effectively controlled by vertical air supply distribution, The distribution of the air supply also offers an effective means for controlling and forming the nitrogen oxide chain in the furnace 2, by means of which a properly stepped air supply arrangement can achieve a substantial reduction in harmful mixtures.

The boiler 1 shown in the diagram is a traditional boiler designed, for example, to pair coal or peat. The burners 8 used for the solid fuel supply are arranged in rows on the wall of the furnace 2, whereby the combustion air required by these burners is supplied to the furnace via the air inlet nozzles adapted to the burners 8 and, if necessary, through the auxiliary air inlet nozzles located in the furnace. their proximity. In addition to the burner air inlet nozzles, the boiler 1 is equipped with at least one upper auxiliary air inlet nozzle 9 for supplying air to the upper portion of the furnace 2. A convenient upper portion of the boiler 1 comprises superheaters for heating the high steam temperature leaving the steam generator arranged to surround the furnace 2. , and a flue gas pipe outlet connection.

The fuel gas is fed to the lower part 10 of the furnace 2, under the burners 8, into a zone with no air supply, thus creating strongly reducing conditions therein. The gas is produced in a gasifier 5, which may be an air gasifier, a blast furnace or any other unit in which some combustible gas is produced or formed. The invention makes it possible to use gases with an exceptionally low calorific value, thereby exploiting their calorific value and simultaneously achieving an efficient and cost-effective reduction of harmful emissions, since the advanced combustion process of a large boiler with flue gas scrubbing connected thereto also performs efficient combustion / purification. gas produced in some gasifier. From the gasifier, the combustion gas is passed through a wide diameter channel 6 to the nozzles 7 located in the lower portion 10 of the furnace from where the gas can flow upwardly from the furnace. If this gas does not ignite at the bottom of the low air furnace, it will be heated and easily ignited in the upper zones by burning the flame of the furnace 2 (i.e., by thermal radiation of the combustion or combustion process) and oxygen introduced through the air nozzles of the burners. The combustion in the furnace is further subdivided into stages by supplying the remainder of the desired combustion air to the top of the furnace via the upper auxiliary air nozzles 9.

In addition to the above example, an alternative embodiment of the invention may be envisaged.

This method is also applicable to boilers adapted only to burn fuel gas, whereby separate burners are not necessarily required, but instead can only be replaced by air supply nozzles. However, in this case, it may be advisable to provide gas ignition and combustion using, for example, a natural gas burner or fuel oil. Furthermore, a single boiler can be used to burn fuel gases from several different gasifiers, which can find an advantageous use in gasification of waste to fuel.

Claims (12)

PATENT CLAIMS A method for burning gas in an oven, characterized in that: the combustion gas is supplied to the reduction zone in the lower part (10) of the furnace (2), and - the combustion air is supplied to the furnace (2) in at least one zone located above the gas supply zone (10) for combustion. Method according to claim 1, wherein the gas is burned in a boiler equipped with at least one burner (8) for burning some fuel other than the combustion gas, characterized in that the combustion gas is supplied to the furnace (2) under the burners. 8 /. Method according to claim 2, characterized in that a portion of the combustion air is supplied to the furnace (2) via the air nozzles of the burners (8) and another portion via at least one air supply nozzle (9) arranged above the burners. Method according to claim 1, characterized in that a portion of the combustion air is supplied to the furnace (2) in a first stage provided above the gas supply point and the auxiliary air is supplied to the furnace in at least one stage provided above the first air supply point . Method according to any one of the preceding claims, characterized in that the combustion gas is supplied to the furnace 121 via a combustion gas recirculation system. Method according to any one of the preceding claims, characterized in that the combustion gas is a gas produced by gasification of the air, a blast furnace gas, a waste gas or other gas with a low calorific value. 7. Apparatus for burning gas in an oven (2), characterized in that: - apertures (7) adapted to the reduction zone at the bottom (10) of said furnace 121 through which the gas is supplied to the furnace 121, and • at least one air supply nozzle for supplying combustion air to the furnace 121 in at least one zone located above the gas supply zone (10) for combustion. Ί Apparatus according to claim 7, comprising in their furnace at least one burner (8) for combustion of a fuel other than gas for combustion, characterized in that the openings Γ7! for supplying the gas for combustion to the furnace (2) are provided under the burners (8). Apparatus according to claim 8, characterized by burner air nozzles (8) through which a portion of the combustion air can be supplied to the furnace and at least one air nozzle (9) located above the burners (8) for supplying auxiliary air to the furnace (2). . Apparatus according to claim 7, characterized by air nozzles through which a portion of the combustion air can be supplied to the furnace 121 in a first stage arranged above the heating gas inlet point and at least one auxiliary air nozzle (9) located above the first air inlet point. for supplying auxiliary air in at least one stage to the furnace m. Apparatus according to any one of the preceding claims 7 - 10, characterized in that the combustion gas is supplied to the furnace H1 via a flue gas (flue gas) recirculation system. Device according to any one of the preceding claims 7 - 11, characterized in that it comprises a device (5) for generating fuel gas and at least one nozzle (6) for supplying the fuel gas to the furnace (2) for combustion therein.