EP0626988B1 - Method and device for heating a low-temperature distillation drum - Google Patents

Abstract

To heat a drum (4) designed to generate low-temperature distillation gases (s), a heating gas (g) which passes round a heating-gas circuit (70, 72) is used. In order to enable the distillation plant (1) to be operated particularly efficiently, and also autonomously, the invention calls for the heating gas (g) to be produced by burning a part (t1?) of the distillation gases (s). In a distillation/combustion plant, in particular a combustion plant (2) retrofitted with a distillation plant (1), the remainder (t2?) of the distillation gases (s) produced is fed to the combustion chamber (34) of the combustion plant (2).

Description

The invention relates to a method for heating a smoldering drum according to the preamble of claim 1. The invention further relates to a device for carrying out the method and also to a smoldering and firing system operating according to this method.

The charring of waste at a low temperature is an endothermic process. The heat required for the reaction is fed indirectly to the waste via heat exchanger heating surfaces which are arranged in the form of tubes in the wall of a rotating drum or smoldering drum.

In a method for thermal waste disposal known from European Patent Specification 0 340 537, a heating gas is fed to the smoldering drum, which is conducted in a heating gas circuit. The heating gas circuit in a smoldering-firing system operating according to this method comprises a heat exchanger which is arranged on a combustion chamber of the firing system and absorbs thermal energy from the hot flue gas there. The carbonization system is practically always operated together with the combustion system, the carbonization gas generated being burned in the combustion system to produce steam.

An independently heatable smoldering system is known from DE-OS 30 18 572. In the smoldering or pyrolysis plant described there, a partial stream of the smoldering gas generated is burned in a combustion chamber. The resulting flue gas is used as heating gas for the smoldering drum and is released into the environment after flowing through a heat exchanger.

A self-sufficient smoldering system is also from the publication "Pyrolysis of waste" by Karl J. Thomé-Kozmiensky, EF-Verlag für Energie- und Umwelttechnik GmbH, 1985, pages 97 to 120, especially picture 2 on page 101 and text on page 103. In the known system, the entire carbonization gas generated is converted into a clean gas in a gas converter with a downstream scrubber. Part of this clean gas is burned in a combustion chamber. The resulting flue gas is conducted in an essentially open circuit and used as heating gas for the smoldering drum. However, this process is particularly complex and uneconomical, especially since an already economically usable clean gas is used to generate heating gas.

The invention is therefore based on the object of specifying an economical method for heating a smoldering drum, with the heating gas always being used to introduce a sufficient amount of heat into the smoldering drum. This is to be achieved with a largely simplified device that ensures the provision of a heating gas required for the autonomous operation of the carbonization system.

With regard to the method, the stated object is achieved according to the invention by the features of claim 1.

In order to adjust the temperature of the heating gas, which is generated by combustion of a partial stream of the carbonization gas, a controllable partial stream of the heating gas flowing out of the carbonization drum and thus cooled is returned to the carbonization drum in a closed partial circuit and mixed with the hot heating gas again.

Since the partial flow of the carbonization gas is expediently dedusted before the combustion, there is the possibility that dust will be deposited in the heating gas circuit, in particular in the carbonization drum, during operation of the carbonization system. The amount of dust deposited can be reduced by reducing the partial flow of the carbonization gas to be burned. However, this leads to a reduction in the amount of heat introduced into the smoldering drum with the heating gas. In order to supply the heating gas with the missing amount of heat, the cooled heating gas flowing out of the carbonization drum is first preheated.

The preheated heating gas is then fed back to the carbonization drum together with the burned partial stream of the carbonization gas. A partial flow of the heating gas flowing out of the smoldering drum is branched off from the heating gas circuit before or after preheating.

The partial flow of the carbonization gas is expediently carried out in the presence of negative pressure in the heating gas circuit. This measure serves on the one hand to promote the partial flow of the carbonization gas and the heating gas generated in the heating gas circuit. On the other hand, escape of carbonization gas or heating gas into the environment in the event of a leak is avoided.

The cooled heating gas is advantageously preheated by indirect heat exchange with steam. The cooled heating gas is expediently dedusted before preheating.

With regard to the device, the stated object is achieved according to the invention by the features of claim 6.

Advantageous refinements are specified in subclaims 7 to 11.

In a carbonization plant with a carbonization drum for generating carbonization gas, which operates according to the method of the invention, a partial stream, preferably 20 to 50%, of the carbonization gas generated can be fed to a first combustion chamber for generating the heating gas for the carbonization drum. The residual stream of the carbonization gas generated can be fed to a second combustion chamber of the combustion system for steam generation. Steam generated in the combustion system is fed to a heat exchanger connected upstream in the heating gas circuit of the first combustion chamber. As a result, the cooled heating gas is preheated by indirect heat exchange with the steam.

The advantages achieved by the invention are, in particular, that by using a partial stream of the carbonization gas to generate the heating gas required for the carbonization, the carbonization system can be operated in a particularly economical manner. This carbonization system can therefore be used to retrofit an existing combustion or firing system, the excess carbonization gas and the residual material from the smoldering drum can be burned. In this case, no heat and mass transport with the cross connections required, for example, in the prior art according to EP-OS 0 340 537 between the existing combustion plant and the supplied or retrofitted smoldering plant for heating them are required.

An embodiment of the invention is explained in more detail with reference to a drawing. It shows a schematic representation of a smoldering-firing plant with a device for generating hot gas with a heat exchanger connected to two hot spots in a hot gas circuit.

The smoldering plant shown comprises a smoldering plant 1 with a downstream combustion plant 2. The smoldering plant 1 comprises a smoldering drum 4 with a feed device 6 for waste a and a discharge chamber 8 for separating the smoldering gas s produced from the outgassed residue r. In the smoldering drum 4, heating pipes 10 are arranged which are charged with a heating gas g. An inflow line 12 and an outflow line 14 are connected to the carbonization drum 4. The inflow line 12 is connected to a mixing chamber 16, which is preceded by a combustion chamber 18. A blower or suction draft 20 is located in the outflow line 14. A first branch 22 of the outflow line 14 is connected to the mixing chamber 16. A second branch 24 of the discharge line 14 is connected to the combustion chamber 18. In branches 22 and 24 there is a valve 23 and 25, respectively.

The discharge chamber 8 is connected via a line 26 to a device 28 for dust separation, for example a cyclone. The device 28 is connected to the combustion chamber 18 via a line 30. An outlet 27 of the device 28 is connected via a line 32 to a combustion chamber 34 of the combustion system 2.

The combustion chamber 34 is followed by a waste heat boiler or flue gas cooler 36 with heating surfaces 38. In a flue gas line 40, a device 42 for flue gas cleaning and a further fan or a suction 44 are connected. The flue gas line 40 opens into a chimney (not shown).

The outflow line 14 of the smoldering drum 4 opens into the flue gas line 40 via a valve 46 in the area between the waste heat boiler 36 and the cleaning device 42. A parallel branch 43 with a valve 45 ends in the waste heat boiler 36 in the area between adjacent heating surfaces 38. The flue gas line 40 is over a line 47 and valves 48 and 50 are connected to branch 22 and branch 24 of outflow line 14, respectively.

The smoldering drum 4 is fed the waste a via a conveyor 52. The waste a is pyrolyzed or carbonized in the smoldering drum 4 by the pipes 10 heated by hot flue gas or heating gas g. The resulting carbonization gas s and the outgassed residual material r are separated from one another in the discharge chamber 8. The residue r is fed to further processing via a discharge opening 54. He can e.g. be burned in the combustion chamber 34. The carbonization gas s is roughly cleaned by means of a sieve or filter 55 by separating fibers and large pieces and then sucked into the device 28 via the line 26. The carbonization gas s contains several% by weight of fine dust with a larger proportion of combustible material.

The carbonization gas s enters the device 28 at the top tangentially via an inlet opening 56, which is designed in the form of a relatively high narrow slot (not shown in any more detail). Due to the centrifugal force, dust particles become inside when deflected the device 28 pressed against the wall. As a result, dust is reduced in the center.

A low-dust partial stream t 1 of 20 to 50%, preferably 30%, of the carbonization gas s is removed from the device 28 via a suction pipe 62 extending far beyond the inlet opening 56 and fed to the combustion chamber 18 for combustion.

By different design of the suction tube 62, the dust content of the partial stream t₁ of the carbonization gas s can be further reduced. For example, Longitudinal slots in the suction pipe 62 have a positive influence on the dust separation, because the entry speed is thereby reduced and made more uniform.

The partial stream t₁ of the dedusted or dust-depleted carbonization gas s is used for heating gas generation. For this purpose, the partial stream t₁ of the carbonization gas s is burned in the combustion chamber 18 at a temperature T₁ of approximately 1250 ° C. The outflowing from the smoldering drum 4 and cooled to a temperature T₂ 'of about 250 ° C heating gas g is first preheated to a temperature T₂ "of about 360 ° C in a heat exchanger 80 connected to the discharge side of the blower 20 in the outflow line 14 Then an adjustable partial flow t₃ of the preheated heating gas g is fed via the branch 22 into the mixing chamber 16. There it is mixed with the heating gas g from the combustion chamber 18, so that a mixing temperature T₃ of approximately 520 ° when entering the carbonization drum 4 C. A partial flow t₄ of the preheated heating gas g that can be adjusted by means of the valve 25 can be fed directly to the combustion chamber 18. At least part of the heating gas g thus flows via the mixing chamber 16 and the inflow line 12 as well as through the heating pipes 10 and the heat exchanger 80 and above the branches 22, 24 of the outflow line 14 in a closed pitch circle 70.

The outlet opening 27 of the device 28 for the main or residual stream t₂ of the carbonization gas s is also tangential in the lower region of the device 28. The dust concentrated towards the wall reaches the residual stream t₂ via the line 32 to the combustion chamber 34. The direction of rotation of the flow is of the carbonization gas s after entering the device 28 and before leaving the device 28 the same. The bottom area 60 of the device 28 is raised conically or parabolically towards the center, so that no dust deposits can form there.

The hot flue gas resulting from the combustion of the residual current t₂ of the carbonization gas s in the combustion chamber 34 is used in the waste heat boiler 36 to generate steam. The transport of this residual stream t₂ of the carbonization gas s from the carbonization drum 4 via the device 28 and the combustion chamber 30 as well as via the waste heat boiler 36 and the cleaning system 42 takes place via the suction fan 44.

The heating gas g not required for the heating gas generation flows in an open circuit 72 via the valve 46 and is mixed with the flue gas flowing out of the combustion chamber 34 in front of the cleaning device 42. In the cleaning device 42, therefore, only completely burned flue gas is cleaned.

Steam from the waste heat boiler 36 serves as the heat transfer medium for the heat exchanger 80. The steam is removed from the heating surfaces 38 at point A and fed to the heat exchanger 80 at an inlet temperature of approximately 390 ° C. The cooled steam exiting the heat exchanger 80 at point B flows back to the heating surfaces 38 at a temperature of approximately 330 ° C.

In order to achieve a further dust depletion of the heating gas g, a dust separator 82 is arranged on the suction side of the blower 20 in the outflow line 14.

When the valves 23 and 25 are closed, the heating gas g is led out of the carbonization drum 4 in the circuit 72 and is mixed with the flue gas via the valve 49 upstream and via the valve 46 downstream of the waste heat boiler 36. In this case, the gas mixture is cleaned solely in the device 42. The heating gas circuit 72 is now closed via the line 47 and the valves 48 and 50, the heat exchanger 80 ′ then being located in the line 47. In this case, clean flue gas is removed from the pressure side of the fan 44 and preheated in the heat exchanger 80 ′ arranged in the line 47. The preheated flue gas is then mixed into the heating gas g again.

The independently operated smoldering system 1 is particularly advantageously suitable for retrofitting an existing combustion system 2. For this purpose, essentially only a connection has to be made via the line 32.

Claims (13)

1. A method for heating a low temperature carbonization drum for generating a low temperature carbonization gas (s), wherein a heating gas (g) carried in a heating gas circuit (70, 72) is used which is generated by combusting a partial flow (t₁) of the low temperature carbonization gas (s),
   characterised in that
   a controllable partial flow (t₃, t₄) of the cooled heating gas (g) is returned to the low temperature carbonization drum (4) and re-admixed with the heating gas (g), after first preheating the cooled heating gas (g) flowing out of the low temperature carbonization drum (4).
2. A method according to claim 1, characterised in that the partial flow (t₁) of the low temperature carbonization gas (g) is carried at a reduced pressure prevailing in the heating gas circuit (70, 72).
3. A method according to claim 1 or claim 2, characterised in that dust is removed from the partial flow (t₁) of the low temperature carbonization gas (s) prior to the combustion.
4. A method according to one of claims 1 to 3, characterised in that the preheating of the cooled heating gas (g) is effected by indirect heat exchange with steam.
5. A method according to one of claims 1 to 4, characterised in that dust is removed from the cooled heating gas (g) prior to the preheating.
6. Apparatus for heating a low temperature carbonization drum (4) which is connected in a heating gas circuit (70, 72) through an inflow line (12) and an outflow line (14), the heating gas circuit (70, 72) having a combustion chamber (18) for generating the heating gas (g), wherein a partial flow (t₁) of the low temperature carbonization gas (s) produced in the low temperature carbonization drum (4) can be delivered to the combustion chamber (18),
   characterised by a heat exchanger (80, 80' incorporated in the heating gas circuit (70, 72) upstream of the combustion chamber (18) for preheating the cooled heating gas.
7. Apparatus according to claim 6, characterised in that a dust separation device (28) is incorporated upstream of the combustion chamber (18).
8. Apparatus according to claim 6 or claim 7, characterised in that an exhaust fan (20) is incorporated in the outflow line (14) of the heating gas circuit (70, 72).
9. Apparatus according to claim 8, characterised in that the pressure side of the exhaust fan (20) communicates with the combustion chamber (18).
10. Apparatus according to claim 8 or claim 9, characterised in that the pressure side of the exhaust fan (20) communicates with a mixing chamber (16) connected downstream of the combustion chamber (18).
11. Apparatus according to one of claims 6 to 10, characterised by a dust separation device (82) incorporated upstream of the heat exchanger (80, 80') in said outflow line (14).
12. A low temperature carbonization/combustion plant comprising apparatus according to one of claims 6 to 11, wherein the remaining flow (t₂) of the low temperature carbonization gas (s) generated is supplied to a combustion chamber (34) of the combustion system (2).
13. A low temperature carbonization/combustion plant comprising apparatus according to one of claims 6 to 11 wherein steam generated in the combustion system (2) can be supplied to the heat exchanger (80, 80').

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