EP1318351B1 - Solid fuel combustion device and method of supplying air to such a device - Google Patents

Description

The invention relates to a method for supplying air to a combustion plant according to the preamble of claim 1 and a solid fuel incineration plant according to the preamble of claim 7. The method and plant of the aforementioned type are made EP 0 952 398 A2 known.

In the known system of the rotary grate is frustoconical, which is why it is called "fuel cone", and rotated about an approximately 35 ° to the horizontal inclined axis, so that the fuel located in the fuel cone is circulated by the orbital motion of the firing cone. The firing cone consists of radial, hollow support arms facing inwards, i. have bores facing the fuel, and support rings carrying grate bars that form the grate surface. The firing cone is surrounded by a housing, and its mouth is opposite to a secondary combustion chamber in which the flame gases emerging from the firing cone are burned out.

In the known system according to the known method for supplying combustion air, a first part of the combustion air supplied to the hollow support arms and blown through the holes directly into the interior of the firing cone under the fuel located there. A second part of the combustion air is supplied to the afterburner chamber at the end remote from the firing cone via radial guide vanes, flows there helically along the wall in the direction of the firing cone and then centrally back again. In this case, usually 20 to 30% of the total amount of air required for combustion is supplied as primary air via the hollow support arms, while the rest, d. H. 80 to 70% of the total amount of air to be supplied as secondary air of the afterburner.

The upper limit of the primary air quantity must not be exceeded, because otherwise slag forms on the grate bars of the firing cone, which can clog the firing cone with time. On the other hand, resulting in secondary air quantities of the order of 70 to 80% of the total amount of air necessary to avoid a lack of air at the given primary air quantities, on the support arms and support rings material temperatures of more than 900 ° C, resulting in high material stresses leads. Namely, between the end of the afterburner chamber and the outlet opening of the firing cone there is an annular gap for discharging ash into the housing surrounding the firing cone, and through this annular gap hot air from the afterburner chamber enters the housing, which leads to the overheating of the firing cone.

Reducing the secondary air quantity, while the mentioned material temperatures of support arms and support rings decrease, but the combustion is thereby brought to a lack of air, which leads to exhaust gases that do not comply with the regulations on the clean air.

The invention is therefore based on the object of specifying a method and an incinerator of the type mentioned above, with which a combustion according to the exhaust gas regulations can be achieved without overheating of the rotary grate.

This object is achieved by the features contained in claims 1 and 7. Advantageous embodiments of the invention are the subject of the respective dependent claims.

The described problem is solved according to the invention in that in the housing of the rotary grate an air inlet is arranged, is sucked by the prevailing in the housing during operation negative pressure, a third amount of air whose volume is suitably regulated by a valve disposed in the inlet flap in that the total amount of air supplied to the combustion corresponds to the quantity of air required for the combustion.

$$\mathrm{Sekundärluftmenge\; L}2\mathrm{=}\mathrm{ca}\mathrm{.}\mathrm{30}\mathrm{\%}\mathrm{+}\mathrm{/}\mathrm{-}\mathrm{ca}\mathrm{.}\mathrm{10}\mathrm{\%}$$

$$\mathrm{Tertiärluftmenge\; L}3\mathrm{=}\mathrm{ca}\mathrm{.}50\mathrm{\%}\mathrm{+}\mathrm{/}\mathrm{-}\mathrm{ca}\mathrm{.}15\mathrm{\%}\mathrm{.}$$

Favorable values result for: $$\mathrm{Primary\; air\; quantity\; L}\mathrm{1}\mathrm{=}\mathrm{ca}\mathrm{,}\mathrm{20}\mathrm{\%}\mathrm{+}\mathrm{/}\mathrm{-}\mathrm{ca}\mathrm{,}\mathrm{8th}\mathrm{\%}$$

$$\mathrm{Secondary\; air\; quantity\; L}2\mathrm{=}\mathrm{ca}\mathrm{,}\mathrm{30}\mathrm{\%}\mathrm{+}\mathrm{/}\mathrm{-}\mathrm{ca}\mathrm{,}\mathrm{10}\mathrm{\%}$$

$$\mathrm{Tertiary\; air\; quantity\; L}3\mathrm{=}\mathrm{ca}\mathrm{,}50\mathrm{\%}\mathrm{+}\mathrm{/}\mathrm{-}\mathrm{ca}\mathrm{,}15\mathrm{\%}\mathrm{,}$$

Investigations have shown that the material temperature dropped at a firing cone as an exemplary rotary grate of about 900 ° C with supply of primary and secondary air to about 650 to 700 ° C, according to the invention, the third air quantity (tertiary air) was fed into the Brennkegelgehäuse. This temperature is also sufficient far below the ash melting point of wood or biomass, slagging is avoided.

The entry for the tertiary air into the housing of the rotary grate may be at any point, but particularly effective for the reduction of the material temperature is an arrangement of the inlet such that the tertiary air blows directly against the back of the rotary grate, d. H. the side facing away from the bearing surface for the fuel.

Even with an arbitrary arrangement of the inlet for the tertiary air at the housing, the CO values of the exhaust gas remain well below 50 mg / m ³ even with small O ₂ contents in the exhaust gas of only 3 to 4%, which means that the tertiary air completely at the Combustion takes part. This is a very amazing fact that was not expected.

The said flap in the inlet for the tertiary air is preferably an adjustable non-return valve, on the one hand, the volume flow can be influenced, but on the other hand closes automatically with a pressure increase in the housing and thereby prevents the blowing hot combustion gases into the environment.

The material temperature of the combustion grate can be lowered even further, if one in the secondary air return gas (cold exhaust gas from the chimney) initiates. Conveniently return gas quantities of 10 to 30%, preferably 15 to 20% of the total amount of air. Because the return gas is burned out gas and is oxygen lean or free, it can not contribute to the combustion and therefore acts as a cooling gas for the combustion process, even if it is warmer than the ambient air.

The invention will be explained in more detail below with reference to an exemplary embodiment shown in the drawing.

The drawing shows a total of 1 designated firing cone, which is surrounded by a housing 2. The housing 2 is expediently lined up inside, which can be seen in the drawing. The firing cone 1 has a frusto-conical and an adjoining cylindrical portion which narrows into a frusto-conical mouth. It is driven to rotate about an inclined axis O, wherein the drive means are not shown in the drawing for reasons of clarity. The inclination angle of the axis O is in the drawing indicated by α. At the mouth of the firing cone is axially followed by a conically narrowing afterburner chamber 3.

The firing cone 1 consists of radial, hollow support arms 4 and extending in the circumferential direction support rings 6. These bear grate bars, which form the grate surface, but are not shown here. The hollow support arms 4 have inwardly, d. H. in the interior of the firing cone 1 facing openings 5 and are connected to a device, not shown here for supplying primary air L1 in their interior. Details of this can be found in the aforementioned publication.

The afterburner 3 has at its end facing away from the fuel cone 1 means for supplying secondary air for afterburning, which is provided with vanes 7, which are directed so that the secondary air is a helical path near the peripheral wall 8 of the afterburner 3 in the direction of the Brennkegel 1 takes.

The housing 2 is provided with a shaft-shaped inlet 9 for the supply of a third amount of air or tertiary air L3, in which there is a check valve 10, with the aid of the opening cross-section of the shaft 9 can be adjusted, recognizable in the drawing on an adjusting screw 11. Wie it can be seen, the mouth of the shaft 9 located inside the housing 2 is directed directly to the back of the firing cone 1, d. H. on the side facing away from the fuel in the firing cone (not shown).

In operation, due to the nature of the supply of secondary air in a known manner, the already mentioned helical movement of the secondary air in the afterburner, which partially reverses due to the known physical conditions in the region of the larger diameter of the afterburner, which is close to the fuel cone, so that results in a central, directed towards the outlet of the afterburner flow, which entrains the escaping from the fuel cone 1 flame gases. Partly enters the near-wall flow but also through an annular gap between the secondary combustion chamber 3 and Brennkegelmündung in the housing 2, wherein entrained ash is ejected into the housing 2 (cyclone effect). In the area between this central flow and the near-wall flow, intensive mixing becomes fresher within the afterburner chamber in a known manner Combustion air with flame gases instead, which leads to an intensive burnout.

It should be noted that the invention is also applicable to other rotary grate designs, such as burners, drums and the like.

Claims (11)

1. A method of supplying air to an installation for the combustion of solid fuel, said installation comprising a rotatable grate (1) rotating around an axis which extends horizontally or inclined with respect to the horizontal and at the same time revolving said solid fuel, a housing (2) surrounding said rotatable grate (1), and an afterburner chamber (3) opposite to said rotatable grate (1), wherein a portion (L₁) of the air is blown as primary air directly below said fuel through hollow formed supporting arms (4) of said grate, said arms being provided with exit holes, and another portion (L₂) of the air is blown as secondary air into the afterburner chamber (3), characterized in that the amounts of air are partitioned as follows:

   a) air amount blown through the supporting arms (4): L₁ = 12 to 28% of the total air amount,

   b) air amount blown into the afterburner chamber (3): L₂ = 20 to 30% of the total air amount,

   c) air amount supplied into the housing (2): L₃ = 35 to 62% of the total air amount.
2. The method of claim 1, characterized in that L₁ = 20% of the total air amount.
3. The method of claim 1 or 2, characterized in that L₂ = 30% of the total air amount.
4. The method of claim 1 or 2, characterized in that L₃ = 50% of the total air amount.
5. The method of claim 1 or 3, characterized in that L₃ = 50% of the total air amount.
6. The method of any one of the preceding claims, characterized in that the portion of the air introduced into the housing (2) is directed towards the outer side of the rotating grate (1).
7. An installation for combusting solid, particulate fuel, comprising a rotating grate (1) which rotates around an axis (O) extending horizontally or inclined with respect to the horizontal and comprises hollow, air passing supporting arms (4), and further comprising a housing (2) surrounding said rotating grate and an afterburner chamber (3) opposing said rotating grate (1), characterized in that said housing is provided with an air supply opening (9) which disem-bogues into the air volume surrounding said rotating grate within said housing.
8. The installation according to claim 7, characterized in that the air supply opening (9) is formed as a shaft passing through the housing wall.
9. The installation according to claim 8, characterized in that the outlet of said shaft (9) is directed towards the outer side of said rotating grate (1).
10. The installation according to any one of claims 7 to 9, characterized in that an adjustable device (10, 11) for influencing the air volume flow is disposed within the air supply opening (9).
11. The installation according to any one of claims 7 to 10, characterized in that a check flap (10) is disposed within said air supply opening (9).

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