EP0676465B1 - Process for gasification of wastes in a circulating fluidized bed - Google Patents

Description

The invention relates to a method for gasifying waste materials containing combustible components in the circulating fluidized bed, taking out the waste materials in a gasification reactor with the addition of Gasified gas in the swirl state, from upper area of the gasification reactor Gas-solid mixture feeds a separator from which Separator removes dusty gas and separates it separated solids and the solids at least partially in the gasification reactor leads back.

In U.S. Patent 4,469,050, combustion or Gasification of carbonaceous material or of Waste described in the circulating fluidized bed. The reaction takes place in the vortex state with air supply in a reactor instead of a cyclone separator connects. The separated ones are separated from the cyclone Solids at least partially in the lower range of the reactor.

The invention has for its object to ensure in waste gasification that the formation of highly toxic substances, such as especially dioxins and furans, is avoided as far as possible. At the same time, the amount of exhaust gas formed should be kept low. According to the invention, this is achieved in the process mentioned at the outset by carrying out the gasification in the gasification reactor at temperatures in the range from 800 to 1100 ° C. with the supply of gaseous gasification agent which consists of 20 to 90% by volume of oxygen by leaving the separator draws off a dust-containing gas, the content of free O _{2 of which is} at most 0.5% by volume, that the gas drawn off from the separator is partially burned in a cracking reactor which is at the same time from 70 to 100% by volume of oxygen-rich O ₂ existing gas is supplied, that temperatures in the range of 1200 to 1600 ° C are maintained in the cracking reactor and liquid slag is generated which is discharged from the cracking reactor, and that the cracking gas formed in the cracking reactor is cooled in at least one cooler with a cooling rate of at least 100 Cools down to a maximum temperature of 300 ° C per second. A gaseous gasification agent is understood to mean all gases supplied to the gasification reactor, but with the exception of H ₂ O in liquid form or in vapor form. The O ₂ content of the total amount of gaseous gasifying agent is preferably at least 50% by volume.

In the method of the invention, it is possible to achieve solid Inert gasification residues through slagging. Preferred vortex media in the gasification reactor ground slag, own ash, sand or another inert granules in question. When gassing municipal waste is usually before the Gasification initially pre-sorted, in particular Metal and glass parts are discarded. Of the The remaining waste is then shredded, e.g. to piece sizes of at most 70 mm before it gasifies becomes.

The oxygen necessary for the partial oxidation in the gasification reactor is supplied by the gaseous gasification agent preferably in the form of air enriched with oxygen or technically pure oxygen. In this way, the amount of inert gas which leaves the gasification reactor in the gas-solid mixture is kept low and the dust-containing gas drawn off from the separator has a calorific value of approximately 4000 to 8000 kJ / Nm ³ . If the calorific value of this gas is high enough, there is no need to add additional fuel in the cracking reactor.

To the formation of dioxins and furans as possible suppress, it is necessary that from the cleavage reactor withdrawn fission gas, especially when walking through the Temperature range between 800 ° C and 300 ° C, if possible to cool down in shock. One is recommended Cooling rate of at least 100 ° C per second and preferably at least 200 ° C per second.

For the rapid cooling of the from the gap reactor drawn off cracked gas come in two main ways questionable, on the one hand, the direct spraying of a Excess amount of cooling water and so on the other inject metered amount of cooling water into the cracked gas, that there is no waste water.

The further treatment of the cooled cracked gas that still Pollutants such as Mercury, sulfur compounds, and contains chlorine and nitrogen compounds in a known manner. Gas cleaning is made easier then when you have the cooled cracked gas of an existing Incinerator, e.g. a power plant can, whose gas cleaning devices in this case be shared.

Fig. 1

das Fließschema der Abfallvergasung mit angeschlossener Kühleinrichtung und

Fig. 2

eine zweite Variante der Kühleinrichtung.

Design options of the method are explained with the aid of the drawing. It shows:

Fig. 1

the flow diagram of the waste gasification with connected cooling device and

Fig. 2

a second variant of the cooling device.

The waste materials to be gasified, which can be, for example, municipal or industrial waste, are fed in line (1) to a gasification reactor (2), where they come into contact with hot gases and particles in the state of the circulating fluidized bed. Oxygen-containing fluidizing gas is introduced in line (3) and passed through a distribution chamber (4) with a grate (5) into the fluidized bed of the reactor (2). Through the secondary gas line (3a), additional oxygen-rich gas is added to the fluidized bed above the grate (5), the O ₂ content of this gas being higher than in the gas in line (3). Based on the total amount of gas fed to the reactor (2), the O ₂ content in the gas is 50 to 90% by volume (calculated as anhydrous).

The gasification in the reactor (2) takes place at temperatures of 800 to 1100 ° C and mostly at temperatures in the range from 850 to 1000 ° C. Ash is removed through the line (6) withdrawn and a separating device (60), e.g. one Sieve. Rough ash parts are drawn in the Line (61) and the fine ash parts are passed through the line (62) to a grinding (63), in order to then if desired, on the transport route (12a) To be able to give up the gap reactor (13).

At the upper end of the reactor (2), a gas-solid mixture leaves the reactor through the channel (8) and flows into a cyclone separator (9), from which dust-containing gas with a free O ₂ content of at most 0.5 Vol .-% is withdrawn through line (10). Separated solids are returned from the lower area of the separator (9) through line (11) to the reactor (2). The line (11) can also have a side draw (12) for removing an excess of solids. This excess of solids can also be passed into the gap reactor (13) on the transport path (12a).

The dust-containing gas drawn off in the line (10) from the separator (9) is fed to the cracking reactor (13), where partial combustion takes place at temperatures in the range from 1200 to 1600 ° C. and preferably 1250 to 1500 ° C. In line (14), oxygen-rich gas containing 70 to 100% by volume of O ₂ is introduced, which can also be technically pure oxygen. A line (15) for additional fuel, for example natural gas, is also provided. Partial combustion in the cracking reactor (13) produces liquid slag that flows downwards. Hot cracked gas leaves the reactor (13) together with liquid slag through the channel (17).

The cracking reactor (13) can be, for example, a combustion chamber, a melting cyclone or a hearth furnace. In the reactor (13), many pollutants introduced in line (10) are destroyed at the high temperatures reached there, and in particular also higher hydrocarbons are split, so that the cracked gas in channel (17) is practically free of hydrocarbons with more than 4 carbon atoms per Molecule is. For economical splitting in the splitting reactor (13), it is advantageous if only little or practically no additional fuel is used. This is achieved by feeding a gas with a calorific value of 3000 to 8000 kJ / Nm ³ and preferably of at least 5000 kJ / Nm ³ to the reactor (13) through line (10). It is important for this that the gasification reactor (2), together with the gasification agent, is fed with as little inert gas as possible. Solids that get into the reactor (13) on the transport path (12a) are melted there.

1 the shock-like cooling of the hot takes place Fission gas, which leaves the reactor (13) in the channel (17), in the cooler (18) by excess cooling water injected, which is introduced in line (19). Doing so at the same time the slag solidifies into granules. in the Cooler (18) one reaches cooling speeds, especially in the temperature range between 800 ° C and 300 ° C, from 100 to 300 ° C per second and more. The cooled cracked gas saturated with water vapor Cooler leaves in the line (20), usually has a temperature in the range of 60 to 95 ° C.

Water that carries slag granules with it arrives through the line (21) in the lock container (22) and thence into the separation container (23), from which one can pass through the Line (24) pulls out slag granules. The severed Water is returned in line (19), where in the line (25) water to add losses admits.

The cooled gas from line (20) is now still further cleaned by washing water, taking it down through a jet washer (28) up through the channel (29) in an aerosol washer (30) through line (31) a venturi washer (32), down there to the channel (33) and then flows up through the spray tower (34). The Spray tower (34) is led through line (35) Fresh water to which you also add sodium hydroxide solution can, in particular, chlorine in the gas to be treated tie. It is useful to have one in the spray tower (34) Pack (36) for intensifying the Provide gas-liquid contact. The gas that the Leaves spray tower (34) through line (37) is through an activated carbon filter (38) passed to mercury remove before it is in line (39) further, per se known cleaning stages or a combustion, e.g. in a power plant. Another Possibility is to gas the line (37) first of all to a known desulfurization undergo before passing it through the filter (38), however this possibility was not shown in the drawing considered.

In Fig. 1 are water supply lines with the Reference number (40) and cooler with reference number (41) Mistake. Used water in the pipes (42) and (43) runs, gets into the settling container (44). Out partially clarified water is fed to this container Reuse in the jet washer (28) and Aerosol washer (30) pulls wastewater through the Line (45) and removes sludge through the Line (46). Mud and sewage are not in shown further processed separately.

A wastewater-free process for cooling the hot Cracked gas that is generated in the reactor (13) is with the help the schematic representation of FIG. 2 explained. Here becomes the hot gas that together with liquid slag leaves the reactor (13) in the channel (17), cf. Fig. 1, in a spray tower (50) initiated from above, in which one at the same time spraying water into the line (51) is introduced. The amount of water is so on Temperature and the amount of gas matched that the all of the water along with the chilled gas in the form of Water vapor is drawn off through line (52). Solids that dry out at the bottom of the spray tower (50) collect, are removed through line (48). The Gas of the line containing water vapor and dust (52) is passed through a filter device (53) in which e.g. around a bag filter or an electrostatic filter can act; you can also have several here Combine filter types. Dust-free gas flows in the Line (54) and is the other, known per se Gas cleaning supplied, which is not shown here.

The variant of the described here together with FIG Treatment of the exhaust gas of the line (20) can by such Known measures are modified, how to get them out Knows plants for waste incineration.

example

In a plant according to FIG. 1, but without the separating device (60), the grinding (63) and the transport route (12a), 7500 kg of waste are gasified per hour with the following analysis: C. 32.7% by weight H 5.0% by weight O 19.0% by weight N 0.8% by weight S 0.1% by weight Cl + F 0.8% by weight H ₂ O 26.0% by weight ash 15.6% by weight

Gasification takes place at 900 ° C, the temperature in the cracking reactor is 1450 ° C. The following data was partially calculated: material management amount Temperature (° C) air 3rd 1540 kg / h 140 air 3a 1540 kg / h 140 O ₂ 3rd 420 kg / h 140 O ₂ 3a 2240 kg / h 140 O ₂ 14 1490 kg / h 50 Heating oil 13 100 kg / h 30th Gas mixture 10th 12500 kg / h 900 water 19th 150 t / h 75 slag 24th 1170 kg / h 20th

After dewatering the sludge from line (46), a heavy cake containing heavy metals is obtained in an amount of 50 kg / h. The gas in line (20), which is produced in an amount of 10800 kg / h, has a calorific value of 5.7 MJ / Nm ³ . The slag drawn off in the line (24) is glazed by the pretreatment and can therefore be deposited without any problems.

Claims (7)

1. A method for gasification of waste substances containing combustible constituents in a circulating fluidised bed, wherein the waste substances are gasified in a gasification reactor in the fluidised state with oxygen-containing gas being supplied, from the upper region of the gasification reactor a gas/solids mixture is fed to a separator, dust-containing gas is removed from the separator and separately therefrom solids separated off are discharged and the solids are returned at least in part to the gasification reactor, characterised in that the gasification in the gasification reactor is effected at temperatures in the range from 800 to 1100°C with gaseous gasification agent being supplied which consists of 20 to 90% by volume oxygen, that a dust-containing gas, the content of free O₂ of which is at most 0.5% by volume, is withdrawn from the separator, that the gas withdrawn from the separator is partially burned in a cracking reactor to which an oxygen-rich gas consisting of 70 to 100% by volume of O₂ is simultaneously fed, that temperatures in the range from 1200 to 1600°C are maintained in the cracking reactor and liquid slag is produced which is discharged from the cracking reactor, and that the cracked gas formed in the cracking reactor is cooled to a temperature of at most 300°C in at least one cooler at a cooling rate of at least 100°C per second.
2. A method according to Claim 1, characterised in that the cracked gas formed in the cracking reactor is cooled in at least one cooler in direct contact with excess water sprayed in, and waste water is removed from the cooler.
3. A method according to Claim 1, characterised in that the cracked gas formed in the cracking reactor is cooled in at least one cooling means with cooling water sprayed in, and cooled cracked gas at a temperature of at most 300°C and containing the cooling water as water vapour is removed from the cooling means.
4. A method according to one of Claims 1 to 3,
   characterised in that the cracked gas is cooled in a cooler with an entry temperature of at least 800°C and an exit temperature of at most 300°C at a cooling rate of at least 100°C per second.
5. A method according to one of Claims 1 to 4,
   characterised in that the dust-containing gas removed from the separator has a calorific value of about 3000 to 8000 kJ/sm³.
6. A method according to one of Claims 1 to 5,
   characterised in that fuel is supplied to the cracking reactor.
7. A method according to one of Claims 1 to 6,
   characterised in that the cracking reactor is fed with solids removed from the gasification reactor.

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