EP0307764B1 - Device for supplying gases to combustion spaces and method to reduce pollutants in combustion processes - Google Patents

Description

The present invention relates to a combustion chamber with at least one gas collection tube for introducing aerosols, gases and / or gas-solid mixtures and a method for reducing the pollutants or pollutants occurring in the combustion of gases, aerosols and / or gas-solid mixtures in a combustion chamber.

Usually, an exhaust gas containing nitrogen compounds is disposed of in a 2-stage combustion chamber, the first combustion chamber being operated with a lack of oxygen and the second with a corresponding excess of oxygen. In addition, in order to minimize the thermal NO _x formation, a heat exchanger is placed between the two combustion chambers. Plants with 2-stage combustion are from R. Römer, W. Leukel, A. Stoeckel, G. Hemmer: Influencing nitrogen oxide formation from fuel-bound nitrogen by means of firing measures, Chem.-Ing.-Techn. MS 875/81 or 0. Carlowitz, H. Wiebe, U. Gravemeier Combustion of vapors containing ammonia and nitrogen oxides in a swirl combustor system, VDI reports No. 423/81, known.

These incinerators are primarily used to reduce pollutants, although a significantly lower amount of flue gas is under discussion compared to power plant firing systems. An upstream connection of a pre-combustion chamber operated with insufficient air to a steam boiler with forced circulation is ruled out due to the changed heat release and the associated change in the local heat transfer.

The use of suitable burners can reduce NO _x emissions. Targeted air and fuel supply create zones within the burner flame in which there is a lack of air and accordingly the CO that is suitable for NO _x reduction is created. The effect of these burners is further increased in that the addition of oxygen-depleted combustion air, which is usually available as a mixture of fresh air and recirculated flue gas, both reduces the flame temperature and the oxygen supply at a suitable point.

From VDI reports 574, pages 443 et seq., It is known to minimize the NO _x content in flue gas of nitrogenous fuel in furnaces equipped with several burners to adjust the fuel concentration and air volume at the individual burners.

This technology can only be used for small volume flows of exhaust gas containing nitrogen compounds. This exhaust gas would have to be supplied in the primary region of the flame, since otherwise there is no or only very incomplete mixing with the reducing agent required for reducing the NO _x resulting from the exhaust gas.

A self-stabilized burner is known from FR-A-2456285. In this, the fuel gases are released against the pre-combustion chamber through an umbrella-like attachment after leaving a gas collecting tube. The flame then leaves the burner at a free jet angle.

The object of the invention was therefore to provide a device which makes it possible to easily reduce the NO _x generated in the combustion of exhaust gases in combustion chambers.

Surprisingly, it has now been found that a change in the supply of the exhaust gas in conventional burners can significantly improve the exhaust gas values. The changed supply is done by an umbrella-like attachment at the end of the gas collection tube. The numbering used below refers to FIG. 1, in which a preferred embodiment of the device according to the invention is shown.

• ― daß am Austritt des Gassammelrohres (1) ein schirmartiger Aufsatz (2) so installiert ist, daß das einzutragende Gas, Aerosol und/oder die Gas-/Feststoffmischung ringförmig mit einem Öffnungswinkel von 90° bis 180°, bevorzugt von 120° bis 150° in den Brennraum eingetragen werden kann,
• ― daß das Gassammelrohr (1) eine ringförmige Erweiterung (3) aufweist und
• ― daß am und/oder oberhalb des schirmartigen Aufsatzes (2) eine Kühlvorrichtung (4) angeordnet ist.

The subject of this invention is a combustion chamber with at least one gas collection tube for the introduction of arosols, gases and / or gas-solid mixtures, characterized in that

• - That at the outlet of the gas collecting tube (1) an umbrella-like attachment (2) is installed so that the gas, aerosol and / or the gas / solid mixture to be entered in a ring with an opening angle of 90 ° to 180 °, preferably from 120 ° to 150 ° can be entered in the combustion chamber,
• - That the gas collection tube (1) has an annular extension (3) and
• - That a cooling device (4) is arranged on and / or above the umbrella-like attachment (2).

The guidance of the gas flow can be optimized by the annular extension (3). This cooling device protects the device according to the invention against incident heat. It can consist of cooling coils through which liquid flows, which are preferably designed in a meandering shape. Furthermore, a particularly preferred embodiment of the combustion chamber according to the invention consists in that one or more entry elements (5) are fitted in the gas collecting tube (1). Additional gas flows, such as air or oxygen, can be introduced here. One or more fuel gas introduction elements (6) can also be attached to the gas samel tube (1) in such a way that the fuel gas can reach the outlet area (7) of the gas collection tube (1).

To stabilize the flow and to improve the internal mixing action, the gas supply (5) and (6) can be carried out eccentrically or in another manner which improves the mixing. Furthermore, the device itself can be heated to 800 ° C to 1000 ° C by direct or indirect heating, e.g. electrical heating of the outer jacket of the device. This gives the possibility of pyrolyzing and thus cleaning products that bake in the device when the gas flow is switched off.

A preferred embodiment of the combustion chamber according to the invention thus consists in that a burner (8) for cleaning purposes is installed in the gas collecting tube (1).

This invention also relates to a method for reducing the pollutants resulting from the combustion of gases, aerosols and / or gas-solid mixtures in a combustion chamber according to one of claims 1 to 4, characterized in that the exit velocities of the gases, aerosols and / or Gas / solid mixtures are 18 m / s to 80 m / s, preferably 20 m / s to 40 m / s.

According to the method according to the invention it is possible, for example, to determine the conversion rate of a nitrogenous exhaust gas when it is disposed of in steam boilers or others To significantly reduce the boiler using waste heat. For this purpose, the exhaust gas upstream of the 1st burner level is introduced into the combustion chamber of a steam boiler by the device according to the invention in such a way that optimal mixing and residence time conditions are created. With the device according to the invention it is also possible to optimally adjust the exhaust gas to the combustion conditions even by admixing gaseous fuel and gaseous oxygen carriers.

Thus, according to the invention, it is possible to inject large quantities of low-calorific exhaust gas containing nitrogen compounds into a large combustion chamber, preferably into the cooled combustion chamber of boilers for generating steam. The amount of flue gas coming from the flue gas can be up to approx. 50% of the total flue gas amount if the flue gas has a corresponding calorific value. The exhaust gas itself can contain up to several 10,000 ppm of nitrogen compounds, for example HCN, which are thermally split and react to a considerable extent with oxygen to form NO or NO₂. In the first tests, the NO _x reduction was between 61% with a share of 13% and 48% with a share of the exhaust gas of 32% of the flue gas volume flow mentioned.

The invention is explained below by way of example, without any restriction being seen here.

example

Usually, the exhaust gas containing nitrogen compounds was introduced into the combustion chamber of a steam boiler with a cross section of 4 m × 4 m via 34 pipes of size DN 100 arranged in a central feed mushroom, about 2 m below the first burner level, consisting of 4 corner burners. The pipes in the feed mushroom formed an angle of 20 ° to the axis of the combustion chamber. The entry of the low calorific value exhaust gas with 0.8 MI / m³ to 1.2 MI / m³, typically up to 4% hydrocyanic acid and oxygen, 89% nitrogen and max. 2.2% carbon dioxide, water vapor and carbon monoxide and traces of various organic compounds, according to the invention by the device shown in Figure 1 such that the distributor mushroom was provided with an attachment, so that the exhaust gas at an opening angle of about 180 ° in streamed the firebox. The new type of distributor with an uncooled double heat shield was designed at the outlet in accordance with Figure 1 so that the exhaust gas could flow out of an annular gap of 100 mm with an average diameter of 1060 mm. Vs. measured by conventional mushroom-shaped distributor _NOx levels was m³ at a boiler part load and about 65,000 / h flue gas 8 installed in 2 burner planes gas burner of the NO _x content based and calculated according to GFAVO, with the inventive device at initiation of 10,000 m³ / h exhaust gas reduced by 61% and at 30,000 m³ / h by 48% under the same operating conditions. The residual oxygen content at the end of the furnace was 1%.

Claims (5)

1. Combustion space with at least one gas collecting pipe for feeding aerosols, gases and/or gas-solid mixtures, characterized in that

― at the outlet of the gas collecting pipe (1), an umbrella-like cap (2) is so installed that the gas, aerosol and/or gas/solid mixture to be fed can be fed annularly into the combustion space with an angular aperture of 90° to 180°, preferably of 120° to 150°,

― the gas collecting pipe (1) has a circular flaring (3) and

― a cooling device (4) is arranged on and/or above the umbrella-like cap (2).

2. Combustion space according to Claim 1, characterized in that one or several feeding elements (5) are mounted in the gas collecting pipe (1).

3. Combustion space according to one of Claims 1 or 2, characterized in that one or several combustible gas feeding elements (6) are mounted on the gas collecting pipe (1) in such a way that the combustible gas can reach the outlet region (7) of the gas collecting pipe (1).

4. Combustion space according to one or more of Claims 1 to 3, characterized in that a burner (8) for cleaning purposes is installed in the gas collecting pipe (1).

5. Process for reducing the pollutants arising during the combustion of gases, aerosols and/or gas-solid mixtures in a combustion space according to one of Claims 1 to 4, characterized in that the exhaust velocities of the gases, aerosols and/or gas/solid mixtures are 10 m/s to 80 m/s, preferably 20 m/s to 40 m/s.

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