CA2281131A1

CA2281131A1 - Process and apparatus for producing fuel gas

Info

Publication number: CA2281131A1
Application number: CA002281131A
Authority: CA
Inventors: Andreas Schieber; Wilhelm Mottitschka; Dieter Eidner; Peter Modde; Klaus-Dieter Witthauer; Peter Wolowski; Xaver Neubert; Alfred Escherle
Original assignee: Dbi Deutsches Brennstoffinstitut Rohstoff- & Anglagentechnik GmbH
Current assignee: Dbi Deutsches Brennstoffinstitut Rohstoff- & Anglagentechnik GmbH
Priority date: 1998-08-28
Filing date: 1999-08-30
Publication date: 2000-02-28
Also published as: KR20000017431A; JP2000080375A; EP0982389A1

Abstract

In a process for producing fuel gas from domestic and industrial waste, old tires, plastic scrap, paint and varnish sludges, light shredded automobile scrap and the like, the waste is pyrolyzed in the absence of air in a pyrolysis device. The volatile pyrolysis products formed in the pyrolysis are gasified with addition of air or oxygen-enriched air to form the fuel gas. The volatile pyrolysis products are introduced into a free space reactor by means of subatmospheric pressure. The gasification of the volatile pyrolysis products is carried out in the free space reactor. The volatile pyrolysis products are gasified using their own heat of reaction.

Description

PROCESS AND APPARATUS FOR PRODUCING FUEL GAS
The invention relates to a process for producing fuel gas from domestic and industrial waste, old tires, plastic scrap, paint and varnish sludges, light shredded automobile scrap and the like. In addition, the invention relates to an apparatus for carrying out such a process.
A process of the above type and an associated apparatus are known from German Patent No. 2,432,504. Developments of the process described to therein and the apparatus are described in German Patent No. 3,347,554 and Published European Patent Application No. 126,408.
In all these processes, the gasification of the volatile pyrolysis products is carried out over a bed of glowing coke.
However, the use of coke for the gasification has some disadvantages.
Thus, the reaction of the glowing coke with the oxygen fed in and with the water vapor present in the volatile pyrolysis products consumes a very large part of the coke in a manner which is unnecessary per se. This greatly ao reduces the economic viability of the processes described.
In addition, the strongly endothermic reaction of water vapor and carbon dioxide with the glowing coke very quickly reduces the temperature in that region of the apparatus in which the volatile pyrolysis products are gasified, which prevents complete gasification of the volatile pyrolysis products, in particular the oil vapors present therein. This incomplete gasification of the oil vapors leads to formation of chemical compounds such as aromatics and naphthenes which can at a later point in time of the process be converted into harmless substances only with difficulty, if at all.
It is therefore an object of the present invention to provide a process and an associated apparatus for producing fuel gas from domestic and -~ 2 -industrial waste, old tires, plastic scrap and the like, in which process volatile pyrolysis products are gasified in an economical way to form fuel gas, without resulting in the formation of harmful materials.
According to one aspect of the invention, there is provided a process for producing fuel gas from domestic and industrial waste wherein the waste is pyrolysed in the absence of air in a pyrolysis device and volatile pyrolysis products formed in the pyrolysis are gasified with addition of air or oxygen enriched air to form the fuel gas. The process of the invention is characterized ~o in that:
the volatile pyrolysis products are introduced by means of subatmospheric pressure into at least one free space reactor;
15 gasification of the volatile pyrolysis products is carried out in the free space reactor; and the volatile pyrolysis products are gasified using their own heat of reaction.
The present invention also provides, in another aspect thereof, an apparatus for carrying out a process as defined above. The apparatus of the invention comprises:

2 s a pyrolysis device;
at least one space reactor connected to the pyrolysis device for the gasification of the volatile pyrolysis products;
so a device for generating subatmospheric pressure in the free space reactor;

and a burner device for introducing the volatile pyrolysis products into the free space reactor and for heating the volatile pyrolysis products.
As a result of the introduction of the volatile pyrolysis products into a free space reactor by means of subatmospheric pressure, i:e. by suction, the volatile pyrolysis products are subjected to continual motion while passing through the free space reactor, so that the gasification of these proceeds very much more quickly.
to As a result of the gasification according to the invention of the volatile pyrolysis products in the free space reactor, the use of coke can be dispensed with, which brings considerable economic advantages with it.
Furthermore, the free space reactor makes available a considerably greater volume for the gasification of the volatile pyrolysis products, as a result of ~5 which the latter are exposed to high temperatures for a significantly longer time. Thus, very much purer gasification products, also referred to as cracking gases, are obtained after passage through the free space reactor. In particular, a reduction in the concentration of undesired hydrocarbons in the combustible cracking gases can be achieved.
According to the invention, coke can be completely dispensed with since exclusive use is made of the volatile pyrolysis products themselves for heating and thus for continuing the gasification reaction after a certain heating-up phase.
A further advantage of the process of the invention is that the use of pure oxygen is not necessary.
The apparatus of the invention is very well suited to carrying out the 3 o process and, as a result of the burner device provided in the free space reactor, ensures immediate commencement of the reactions necessary for the gasification. The free space reactor can advantageously be made exactly as large as necessary for the gasification reactions to proceed to completion.
Further features and advantages of the invention will become more s readily apparent from the following description of prefered embodiments as illustrated by way of examples in the accompanying drawings, in which:
Fig. 1 schematically illustrates an apparatus according to the invention for producing fuel gas;
io Fig. 2 is a cross section of a part of the free space reactor used in the apparatus of the invention and having a burner device fitted thereto; and Fig. 3 is an enlargement of the burner device shown in Fig. 2.
is Fig. 1 shows an apparatus 1 for producing fuel gas from domestic and industrial waste, old tires, plastic scrap, paint and varnish sludges, light shredded automobile scrap and the like.
zo The waste is located in a hopper 2 from where it passes through a line 3 and is introduced via an attached transport screw 4 into a pyrolysis device configured as a pyrolysis drum 5. In the pyrolysis drum 5, the waste is pyrolyzed in a manner known per se by indirect heating in a temperature range from 300°C to 650°C. The doubly-walled pyrolysis drum 5 is heated by as means of a combustible gas supplied via a line 6, which will be discussed in more detail at a later point.
The pyrolysis in the pyrolysis drum 5 forms firstly pyrolysis coke and secondly volatile pyrolysis products such as long-chain and cyclic 3 o hydrocarbons, water vapor, pyrolysis oils and also mineralized solids in the form of dust and ash. The pyrolysis coke is discharged from the pyrolysis drum 5 via a discharge device 7 and is passed to a further use. The volatile pyrolysis products are discharged from the pyrolysis drum 5 via a line 8.
From the line 8, the volatile pyrolysis products go via a burner device 9 into a free space reactor 10. A line 11 via which air or air mixed with oxygen is passed into the free space reactor 10 also opens into the burner device 9, which is shown in great detail in Fig. 3, located in the upper region of the side wall of the free space reactor 10. The volatile pyrolysis products are introduced by means of subatmospheric pressure, i.e. by suction, into the free io space reactor 10. For this purpose, a device not shown in the figure for generating subatmospheric pressure, for example a fan, is located in a region downstream of the free space reactor 10 at a particularly suitable point.
The burner device 9 is arranged tangentially to the inner wall of the first i5 individual free space reactor 10a, as a result of which cyclone-like flow is achieved in the latter and thus good utilization of the volume of the free space reactor 10 is obtained. A different arrangement of the burner device 9, e.g.
vertically in the free space reactor 10, is likewise possible, but the tangential arrangement has been found to be advantageous.
The free space reactor 10 is, in the present embodiment, built up of two individual, cylindrical free space reactors 10a and 10b which are joined to one another at their lower ends by means of a passage 12. Below the passage 12 there is located a discharge device 13 which runs through the entire length of the free space reactor 10 or across the two diameters of the individual free space reactors 10a and 10b and also through the passage 12.
Instead of the free space reactor 10 being built up of two individual free space reactors 10a and 10b, it is of course also possible for only a single free space reactor 10 or a larger number of free space reactors 10 to be provided. The 3o cylindrical configuration of the two individual free space reactors 10a and 10b can be replaced by any other geometric shape, but the cylindrical shape has been found to be most suitable for the reactions described below.

In the free space reactor 10, the volatile pyrolysis products introduced via line 8 are gasified with the aid of air or oxygen-enriched air introduced via line 11. For this purpose, it is necessary for sufficiently high temperatures in s the range from 1000°C to 1200°C to be generated first by introduction of natural gas via the burner device 9. After these temperatures have been reached, the introduction of natural gas into the burner device 9 can be stopped, since the heat of reaction of the volatile pyrolysis products is sufficient to maintain the temperature in the free space reactor 10 and thus to ~o keep the gasification reaction going. In the gasification reaction, the cyclic and long-chain hydrocarbons of the volatile pyrolysis products (pyrolysis oil, tars, pyrolysis water, etc.) are cracked or dissociated to form permanent gases, i.e.
gases which cannot be dissociated further, for example carbon monoxide, hydrogen, carbon dioxide, methane or water vapor. During cracking, 15 pollutants such as nitrogen oxides are destroyed, with a dehydrogenation sometimes also taking place. The solids which are deposited in the form of dust or partially molten slag are discharged from the free space reactor 10 via the discharge device 13 and are conveyed to a further use. Of course, it is also conceivable for individual discharge devices 13 to be provided for each ao individual free space reactor 10a and 10b and for the passage 12.
The regulation of the introduction of air or oxygen-enriched air via line 11 into the free space reactor 10 makes it possible to ensure that the mineral material introduced in the form of dust and ash together with the volatile 25 pyrolysis products is melted only to such an extent that at the end of the gasification process it is present in the form of solid or at most paste-like particles together with soot formed. This enables the problems associated with the formation of liquid slag, for example the formation of solid slag, to be prevented. Usually, a substoichiometric proportion of air is set in the free 3 o space reactor 10.

All the dissociation or cracking reactions take place in the two individual free space reactors 10a and 10b, with turbulent flow of the volatile pyrolysis products being achieved by the deflection via the passage 12. As a result of this turbulence, the entire volume of the free space reactor 10 is s utilized. This ensures the necessary residence time of the volatile pyrolysis products in the free space reactor 10. In the free space reactor 10b, the volatile pyrolysis products are reacted almost to the thermodynamic equilibrium.
At the upper end of the second individual free space reactor 10b, the permanent gases formed in the reaction leave the individual free space reactor 10b via a line 14 and go to a cooling stage 15 in which they are cooled to below the softening point of the slag. A line 16 via which the cracking gases which are formed at a later point in time in the process and 15 have low temperatures are recirculated is connected to the cooling stage 15.
In this way, cooling of the gasified constituents of the volatile pyrolysis products to below the softening point of the mineral constituents is achieved and the paste-like particles are converted into the solid state.
2 o A waste heat boiler 17 in which the heat of the gasification gas is utilized is connected to the cooling stage 15. The gasification gas leaves the waste heat boiler 17 via a line 18. The waste heat boiler 17 and the line 18 are followed by a gas scrubber, a pure gas blower and various purification devices which are all not shown in the figure but which are known per se. The 25 line 18 is also followed by the above-mentioned device for generating subatmospheric pressure. After these devices, the line 6 to the pyrolysis drum and the line 16 to the cooling stage 15 are branched off. Thus, part of the cracking gas formed in the above-described gasification reaction is used for heating the pyrolysis drum 5 and another part is used for cooling in the 3o cooling stage 15; in the heating of the pyrolysis drum 5, the cracking gas used for this purpose does not come into contact with the waste to be pyrolyzed.
However, the two amounts of gas mentioned represent only a small proportion of the permanent gases formed. The major part is utilized as fuel gas.
Fig. 2 shows a cross section of the first individual free space reactor s 10a; a refractory lining 19 inside the outer wall of the reactor can be seen.
The lining 19 is present both in the free space reactor 10b and in the passage 12 and ensures good insulation of the entire free space reactor 10, thus enabling constant high temperatures to be maintained.
Fig. 2 also shows the burner device 9 with an ignition burner 20 provided for ignition and monitoring. The burner device 9 comprises the pyrolysis gas burner through which the pyrolysis gas is fed in and also a heating burner required for the initial heating. The ignition burner 20 and the heating burner are operated using natural gas. The heating burner can also 15 be employed when the calorific value of the volatile pyrolysis products is too low. At the lower end of the free space reactor 10, the discharge device 13 is shown in the form of a screw conveyor which is located in a recess 21 of the free space reactor 10 and is made of heat-resistant steel.
20 Fig. 3 shows a cross section of the burner device 9. This has, from the inside to the outside, an inner tube element formed by the line 8 for introducing the volatile pyrolysis products into the free space reactor 10.
Outside the line 8, there is a first annular slit 22 via which air or oxygen-enriched air from line 11 is introduced into the free space reactor 10. The first z5 annular slit 22 is arranged coaxially outside the inner annular element or the line 8.
Outside the first annular slit 22 and coaxially thereto, the burner device 9 has a second annular slit 23 which is connected to a feed line 24 around its 30 outer circumference. Natural gas is introduced into the free space reactor via the second annular slit 23 and is used for heating the gasification process.

_ 9 _ A third annular slit 25 is located outside the second annular slit 23 coaxially thereto and is, like the first annular slit 22, connected to the line 11 for air or air mixed with oxygen. At the end nearest the free space reactor 10, the first annular slit 22 is connected to the third annular slit 25.
To cool the burner device 9, an annular slit element 26 is arranged outside the third annular slit 25; this annular slit element 26 comprises a fourth annular slit 27 and a fifth annular slit 28. The fifth annular slit 28 is connected to a feed line 29 for cooling water and the fourth annular slit 27, which is arranged inside the fifth annular slit 28, is provided with a discharge line 30 for the cooling water. All annular slits 22, 23, 25, 27 and 28 are thus arranged coaxially with one another, At the end nearest the free space reactor 10, the annular slit element 26 is provided with a gap 31 which connects the fourth annular slit 27 to the fifth annular slit 28. The gap 31 has a smaller cross section than the annular slits 27 and 28 and thus contributes to increasing the flow velocity of the cooling water in this region. As a result, cooling water is continually present at the outer wall of the annular slits 27 and 28, which leads to good cooling of the end of the burner device 9 nearest the free space reactor 10.
At the end nearest the free space reactor 10, the annular slits 22, 23 and 25 are inclined inward toward the line 8 in order to achieve an increase in the mixing intensity of the volatile pyrolysis products with the air or oxygen fed in. The second annular slit 23 is set back somewhat relative to the first is annular slit 22 and the third annular slit 25 and, at the end nearest the free space reactor 10, has drilled holes 32 through which the natural gas can exit.
Other structural configurations of the burner device 9 are of course also possible, but the present embodiment has been found to be useful.

Claims

1. A process for producing fuel gas from domestic and industrial waste, wherein the waste is pyrolyzed in the absence of air in a pyrolysis device and volatile pyrolysis products formed in the pyrolysis are gasified with addition of air or oxygen-enriched air to form the fuel gas, characterized in that:
the volatile pyrolysis products are introduced by means of subatmospheric pressure into at least one free space reactor;
gasification of the volatile pyrolysis products is carried out in the free space reactor; and the volatile pyrolysis products are gasified using their own heat of reaction.

2. A process as claimed in claim 1, wherein the air or oxygen-enriched air is fed into the free space reactor in such a way that mineral material introduced together with the volatile pyrolysis products into the free space reactor is melted only to such an extent that it is present in the form of solid or paste-like particles at the end of the gasification.

3. A process as claimed in claim 1, wherein the volatile pyrolysis products are cracked during their gasification.

4. A process as claimed in claim 1, wherein the volatile pyrolysis products and the air or oxygen-enriched air are introduced into the free space reactor via a burner device.

5. A process as claimed in claim 4, wherein the burner device is ignited by introduction of natural gas.

6. A process as claimed in claim 1, wherein the pyrolysis device is heated by means of the cracking gas formed in the gasification of the volatile pyrolysis products.

7. An apparatus for carrying out a process as defined in claim 1 comprising:
a pyrolysis device;
at least one free space reactor connected to the pyrolysis device for the gasification of the volatile pyrolysis products;
a device for generating subatmospheric pressure in the free space reactor; and a burner device for introducing the volatile pyrolysis products into the free space reactor and for heating the volatile pyrolysis products.

8. An apparatus as claimed in claim 7, wherein the burner device is arranged tangentially to an inner wall of the free space reactor in an upper region thereof.

9. An apparatus as claimed in claim 7, wherein two essentially cylindrical free space reactors are provided and area connected to one another by means of a passage.

10. An apparatus as claimed in claim 7, wherein a discharge device is located at a lower end of the free space reactor.

11. An apparatus as claimed in claim 7, wherein the free space reactor is provided with a refractory lining.

12. An apparatus as claimed in claim 7, wherein a cooling stage is located downstream of the free space reactor.

13. An apparatus as claimed in claim 7, wherein the burner device comprises:
an inner tubular element for feeding the volatile pyrolysis products into the free space reactor;
a first annular slit for feeding air or oxygen-enriched air into the free space reactor said first annular slit being arranged at least approximately coaxially outside the inner tubular element and being connected to a first feed line;
second annular slit for feeding natural gas into the free space reactor, said second annular slit being arranged at least approximately coaxially outside the inner tubular element and the first annular slit and being connected to a second feed line;
a third annular slit for feeding air or oxygen-enriched air into the free space reactor, said third annular slit being arranged at least approximately coaxially outside the inner tubular element, the first annular slit and the second annular slit and being connected to said first feed line; and an annular slit device for feeding in and discharging cooling water, said annular slit device being arranged at least approximately coaxially outside the inner tubular element, the first annular slit, the second annular slit and the third annular slit and being connected to a third feed line and a discharge line for cooling water.

14. An apparatus as claimed in claim 13, wherein the annular slit device for the cooling water is provided at an end of the burner device nearest the free space reactor with a gap for increasing the flow velocity of the cooling water.