EP0573756B1 - Method for the incineration of refuse and incinerator - Google Patents

Description

The invention relates to a method for incinerating waste according to the preamble of claim 1 and a waste incineration plant for carrying out the method according to claim 1 according to the preamble of claim 6.

When waste is burned in a grate furnace, the waste is placed on a combustion grate, conveyed through the grate over the grate with the supply of combustion air and thereby burned to ashes and flue gas. Known incineration grates are moving grates, sliding grates, traveling grates and roller grates.

Because of the inhomogeneity of waste, the problem with burning it on a grate is to achieve a good burnout of both the ash and the flue gas. The burnout of ash and flue gas is improved in each case by the long residence time at high temperature and by thorough mixing.

From DE-OS 33 45 867 it is known to promote the waste by mechanically transporting grids from a pre-drying zone through a combustion zone into a burnout zone. Since the flue gas originating from the individual zones flows directly into the evaporator, good burnout, at least of the flue gas, can occur from the smoldering zone, but also from the burnout zone, i.e. that is, cannot be obtained from the low temperature zones. The low temperature in the burnout zone also prevents, according to today's standards, good ash burnout.

The device described in DE-OS 1 955 035 has a combustion grate and a burnout grate, both of which are supplied with compressed air. The air supply through the burnout grate leads to a better burnout of the ashes. In addition, air nozzles for blowing in part of the combustion air are set up as secondary air. Secondary air is used for secondary combustion and thus better combustion of the flue gas.

There are limits to the additional supply of combustion air, be it as primary air through additional grates or as secondary air. To minimize the CO content of the flue gas, the O₂ content of the flue gas leaving the waste incineration plant is between 6% and 10.5%. This corresponds to an excess of air of n = 1.4 to 2.0. However, the excess air should be as low as possible to maintain high combustion chamber temperatures.

A further improvement of the burnout enables the z. B. in the DE-Z garbage and waste, 22. Jg. (1990), page 288-295, described direct current firing. In this generic method and the generic waste incineration plant, the flue gas is converted to the firing material in cocurrent. that is, waste and ashes. The flue gas from the gasification area is also led through the hot combustion area. A good burnout of the flue gas is also caused by the supply of secondary air above the combustion bed, here called upper air, and at the beginning of the first flue gas draft. The intense flame radiation that acts on the ash from the start of the grate to the end of the grate improves its burnout quality. Another improvement in ash burnout, e.g. B. due to larger rust areas, is not possible due to the limited excess air. In particular, not because the primary air portion of the combustion air, also called underwind, cools the combustion grate and therefore cannot be reduced. A reduction in the proportion of secondary air would worsen the combustion of the flue gas.

To improve the ash burnout, DE-Z VDI Bildungswerke, Seminar 16.03. to 17.03.92, BW 1389, special device for treating the ash, called slag there, known as a downstream slag generator or a downstream rotary kiln. However, these devices are very complex to install and operate. In the case of a rotary tube, the turned parts working at high temperature must be serviced. In addition, the refractory lining of the rotary tube is subject to increased wear. The capacity of a rotary tube is also limited.

The object of the invention is therefore to further develop the method according to the preamble of claim 1 so that the burnout of the ashes without affecting the burnout of the flue gas and without great effort.

Another object is to further develop the waste incineration plant according to the preamble of claim 6 so that it is suitable for carrying out the method according to claim 1.

The objects are solved by the characteristics of claims 1 and 6.

According to the invention, the additional burnout of the ashes is brought about in a simple manner without any effort using the hot flue gas containing oxygen in a waste incineration plant. The flue gas should have temperatures of 800 ° C to 1200 ° C and an oxygen content of 6% to 11%.

The ash is conveyed via an ash burn-out device connected to the combustion grate and, above all, is kept at a high temperature by the radiation effect of the flue gas guided through the ash burn-out device. At these temperatures, the oxygen present in the flue gas is completely sufficient to burn carbon still present in the ashes. The additional burnout therefore takes place without the supply of additional combustion air. 65% to 85% of the combustion air is supplied as primary air or underwind through the combustion grate and the remaining combustion air as secondary air.

The contact between ash and hot, oxygen-containing flue gas on the ash burn-out device is ensured in that the flue gas in the conveying direction of the waste and the ash is first passed through the combustion grate and the ash burn-out device and only above the ash burn-out device into the first flue gas duct. The supply of secondary air above the combustion grate, but also at the beginning of the first flue gas flue, promotes the exhaust gas burnout by supplying oxygen and by improving the mixture due to the impulse of the air jets and thus increases the radiation effect of the exhaust gas on the ash.

A particularly good additional burn-out of the ash on the ash burn-out device is achieved if the combustion air according to claim 2 is supplied with the primary air in at least three stages in the conveying direction of the waste. First, an average amount of air per grate surface is supplied in the drying stage, a higher amount of air per grate surface in the combustion stage and finally a smaller amount of air per grate surface in the burnout stage. If the waste is incinerated in these three stages, drying, incineration and burnout, the additional ash burnout on the ash burnout device leads to a further improved burnout quality.

With this method it is possible to safely reduce the carbon content of the ash to values below 1%.

According to claim 3, the dwell time of the ash on the ash burn-out device is one fifth to half the time that the waste takes to pass through the combustion grate. With shorter dwell times, only a little additional ash burnout is achieved. Longer dwell times than the specified one have hardly any additional effect.

The dwell time is initially set according to claim 4 depending on the waste composition and preferably changed during operation depending on the burnout quality of the ash and / or the flue gas. The dwell time of the ash can e.g. B. can be increased by increasing the layer height of the ash on the ash burn-out device by damming the ash.

An equalization of the layer height of the ash on the ash burnout device according to claim 5, for. B. by shaking, improves the burnout of the ashes. This is particularly advantageous when using combustion grates with low stoking effect.

In the case of waste incineration according to the invention, in which the furnace is designed as a grate and direct current furnace, an ash burn-out device arranged next to the combustion grate in front of the ash removal device, according to the characterizing part of claim 6, provides an additional burnout of the ash without impairing the burnout of the flue gas and without great structural effort. In some cases, the combustion grate can also be made a little smaller.

The ash burn-out device has a conveyor device for conveying the ash to the ash removal device. To support ash extraction, the conveying surface can also be inclined at a small angle to the horizontal to the ash removal.

The ash burn-out device should have a flat conveying surface. The conveying surface can also not have channels or troughs that are too deep. It is important that the entire ash is exposed to the heat radiation of the flue gas as evenly as possible.

The ash burnout device advantageously has a width corresponding to the width of the combustion grate, so that the ash can be easily conveyed from the combustion grill to the ash burnout device.

It is free of combustion air supply devices. As a result, the entire primary air portion of the combustion air can be used to cool the combustion grate.

The arrangement of the inflow opening of the first flue gas flue above the ash burn-out device, in conjunction with the combustion chamber ceiling projecting over the combustion grate, enables the hot, oxygen-containing flue gas to be passed over the ash burn-out device and brought into contact with the ash for additional burnout. In addition, a space with hot flue gas is formed by this arrangement above the ash burn-out device. The heat radiation from the hot flue gas increases the temperature of the ash on the ash burnout device and thus its burnout.

The feature of claim 7 is particularly suitable for achieving the residence time of the ashes described in claim 3 on the burnout device.

A reduction in the width of the ash burn-out device according to claim 8 enables a ash removal device with a smaller width.

In the formation of the ash burn-out device as a vibratory conveyor according to claim 9, the layer height of the ash conveyed above it is simultaneously made uniform by shaking.

Since the conveying surface of the ash burn-out device is exposed to heat radiation and the oxygen from the flue gas, it is advantageously provided with interchangeable wear parts.

Another advantageous equipment against wear are cooling devices according to claim 11.

The invention will be further explained using an example shown schematically in the drawing. Figure 1 shows a waste incineration plant and Figure 2 shows an ash burn-out device.

A waste incineration plant has a combustion chamber 1 and several flue gas flues 2, in which heating surfaces 3 for the generation of steam and possibly for preheating combustion air are arranged. A flue gas cleaning system, not shown, is connected to the last flue gas flue.

The direction of flow of the flue gas is represented by arrows 4 and the direction of conveyance of the waste by arrows 5.

The combustion chamber 1 is equipped with a feed device for waste, a roller grate with five rollers 6, an ash burnout device 7 and a, e.g. B. designed as a plunger, ash removal 8.

The feed device consists of a chute 11 provided with a funnel 9 and a slide 10, which is open in the region of its base 12 to the roller grate and on the base 12 of which there is a ram feeder 13 for conveying the waste onto the roller grate. Under each of the five rollers 6 of the roller grate there is an airtight ash hopper 14 for the ash falling through the grate. The ash funnels 14 open into a collecting device 15.

On each of the five ash funnels 14 there is a separately meterable air supply line 16, through which the respective primary air portion is supplied to the corresponding roller 6.

The ash burn-out device 7 is connected directly to the fifth roller 6 of the roller grate and ends via an ash shaft 17 opening into the ash removal device 8.

A combustion chamber ceiling 18 which extends over the roller grate has approximately the shape of a pointed roof, one leg of the combustion chamber ceiling 18 projecting approximately beyond the fifth roller 6. This leg of the combustion chamber ceiling 18 separates the combustion chamber 1 from the first flue gas duct 2, which runs obliquely upwards in such a way that its inflow opening 19 is arranged exactly above the ash burnout device 7.

A plurality of air supply devices 20 for secondary air, also referred to as upper air, are attached to the firebox ceiling 18. Air supply devices 21 for secondary air are also located in the area of the inflow opening 19 of the first flue gas flue 2. Additional lines for returning flue gas to the various air supply devices for secondary air or primary air or to their supply lines can also be provided. In this example, at least lines are provided to the air supply devices 21 (not shown).

The ash burnout device 7 is designed as a vibratory conveyor. It has a plate 22 with a flat conveying surface, which is mounted on four elastic elements 23 and with an eccentric drive 24, for. B. a push crank drive is connected. A vibrating motor with internal unbalance can also be used as the drive. It is possible to manufacture the plate 22 from a heat-resistant material. The conveying surface is preferably provided with a layer 25 of heat-insulating material. As shown in FIG. 2, this layer 25 can consist of wear plates 26, but it could also be a stamped-on clay. Boundary walls 27 are attached to the sides of the conveying surface parallel to the conveying direction. In addition, the ash burnout device 7 with a cooling device, e.g. B. with a water cooling system with a feed line 28 and a discharge line 29.

With a length of the roller grate with five rollers 6 of 9 m, the length of the ash burn-out device 7 is preferably 2 m to 6 m. In this example it is 4 m. The width of the honeycomb grate, that of the ash burn-out device 7 and that of the ash removal device 8 is in each case 3 m. A roller grate with six or seven rollers can be used in particular to burn waste with a low calorific value.

In one embodiment of the invention, the width of the ash burn-out device 7, starting from the width of the roller grate, takes on a width corresponding to the ash removal device 8, e.g. B. 10% to 20% smaller width, from.

In a waste incineration plant with a roller grate with a width, e.g. B. of 8 m, three ash burnout devices 7 are arranged parallel to each other in the conveying direction.

In operation, the waste, e.g. B. household waste, bulky waste, sewage sludge or industrial waste, through the funnel 9 in the chute 11 and distributed with the ram feeder 13 on the first roller 6. By rotating the rollers 6 at about three to five revolutions per hour, the waste is conveyed through the roller grate, possibly with the supply of primary air and from recirculated flue gas, and burned to ash and flue gas.

The flue gas produced during the combustion is supplied with secondary air and possibly recirculated flue gas above the roller grate through the air inlets 20 in the combustion chamber ceiling 18 and secondary air and / or recirculated flue gas in the area of the inflow opening 19 of the first flue gas duct 2 through the air supply 21.

The excess air n of the total combustion air supplied is 1.4 to 2.0, which corresponds to an oxygen content of 6% to 11% of the flue gas leaving the flue gas flues.

In this example, an excess air of n = 1.6 and a primary air share of 80% are set for the combustion of household waste with a calorific value of 10,000 kJ / kg.

The secondary air portion of 20% is supplied through the air inlets 20 in the combustion chamber ceiling 18. Returned flue gas is supplied through the air supply lines 21 in the region of the inflow opening 19 of the first flue gas train.

The primary air is supplied in a drying stage, a combustion stage and a burnout stage.

In the drying stage, an average amount of air per grate surface is created by the first roller 6, in the combustion stage by a second and third roller 6 an amount of air per grate surface increased by a factor of 1.1 to 2 and in the burnout stage by the fourth and fifth roller 6 by a 0.1 to 0.9 lower amount of air per grate area.

The combustion and burnout stages are further subdivided.

The supply of primary air through the individual rollers 6 is set to the values listed in the following table:

The grading of the supply of primary air, but also the proportion of primary air, is regulated depending on the combustion behavior, combustion chamber and / or flue gas temperatures and the pollutant content of the flue gas.

The gradual supply of primary air means that the waste is first dried and possibly carbonized before it is burned and finally burned out.

The residence time of the waste and the ashes on the roller grate is 20 minutes to 40 minutes. The ash is then conveyed through the ash burn-out device 7.

The supply of secondary air generates evenly hot and afterburned flue gas through the air inlets 20 in the combustion chamber ceiling 18 above the roller grate. Due to the shape of the combustion chamber ceiling 18 and the arrangement of the inflow opening 19 of the first flue gas duct 2 above the ash burnout device 7, this flue gas is guided over the roller grate to the ash burnout device 7 and via the ash burnout device 7 into the first flue gas flue 2. As a result, the ash lying on the ash burn-out device 7 is brought into contact with the hot, oxygen-containing flue gas and exposed to the heat radiation of the flue gas flowing into the first flue gas train 2, which is further mixed by the supply of recirculated flue gas, and burned out to a carbon content of less than 1%.

The dwell time of the ash on the ash burn-out device 7 is in the above. Household waste is set to 10 minutes to 30 minutes. The conveying speed of the ash and thus its dwell time on the ash burn-out device 7 is adjusted during operation by adjusting the shaking frequency, i.e. that is, by adjusting the angular velocity of the drive 24, or by adjusting the angle of the conveying surface to the horizontal depending on the burnout quality of the flue gas or the ash. As a result, the layer height of the ash on the ash burn-out device 7 is set. At the same time, the layer height is evened out by shaking the vibratory conveyor.

Claims (11)

1. A method of incinerating refuse, in which

   - the refuse is charged onto an incinerating grate, is fed over the incinerating grate and is burnt to form ash and flue gas while primary air is supplied through the incinerating grate,

   - the flue gas is conveyed over the incinerating grate in the feed direction of the refuse and the ash, and is then cooled in at least one gas flue, and

   - secondary air is supplied to the flue gas above the incinerating grate and/or at the beginning of the first gas flue,

   characterized in that

   - adjacent to the incinerating grate the ash is fed over an ash-burning-out device (7) with an approximately level feed surface and with a width corresponding to the width of the incinerating grate, and

   - the oxygen-containing flue gas is conveyed over the ash-burning-out device (7) and above the ash-burning-out device (7) to the first gas flue (2),

   - wherein the ash is further burnt out in the presence of the hot oxygen-containing flue gas without additional combustion air.
2. A method according to Claim 1, characterized in that the primary air is supplied to the incinerating grate in at least three stages: a drying stage, an incineration stage and a burning-out stage.
3. A method according to Claim 1 or 2, characterized in that the residence time of the ash on the ash-burning-out device (7) amounts to between a fifth and a half of the time for passing the incinerating grate.
4. A method according to one of Claims 1 to 3, characterized in that the residence time of the ash on the ash-burning-out device (7) is set as a function of the refuse supplied and/ or of the burnt-out quality of the ash and/or the flue gas.
5. A method according to one of Claims 1 to 3, characterized in that the height of the layer of ash on the ash-burning-out device (7) is made uniform.
6. A refuse-incinerating plant for performing the method according to Claim 1, having a grate firing means and at least one gas flue, wherein

   - the grate firing means comprises a charging device, at least one incineration grate and an ash-remover,

   - at least one supply device for combustion air is arranged below the incineration grate, and

   - an incineration-chamber cover projects over the incineration grate,

   characterized in that

   - the ash-burning-out device (7) is arranged adjacent to the incineration grate before the ash-remover (8), wherein

   - the ash-burning-out device (7) is provided with a feed device, has an approximately level feed surface with a width corresponding to the width of the incineration grate, and is free of supply devices for combustion air, and

   - the inflow opening (19) of the first gas flue (2) is arranged above the ash-burning-out device (7).
7. A refuse-incinerating plant according to Claim 6, characterized in that the length of the ash-burning-out device (7) amounts to between one third and two thirds, in particular between a quarter and a half, of the length of the incineration grate.
8. A refuse-incinerating plant according to Claim 6 or 7, characterized in that the width of the ash-burning-out device (7), starting from the width of the incineration grate, decreases in the feed direction of the ash.
9. A refuse-incinerating plant according to one of Claims 6 to 8, characterized in that the ash-burning-out device (7) is constructed in the form of a vibrating conveyor (22, 23, 24).
10. A refuse-incinerating plant according to one of Claims 6 to 9, characterized in that the feed surface of the ash-burning-out device (7) has exchangeable closure members (26).
11. A refuse-incinerating plant according to one of Claims 6 to 10, characterized in that the ash-burning-out device (7) comprises a cooling device (28, 29).

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