WO2001029149A1

WO2001029149A1 - Process for the selective recovery of residual gases from a pyrolysis reaction of solid carbonizable material

Info

Publication number: WO2001029149A1
Application number: PCT/CA1999/000979
Authority: WO
Inventors: Jean-Pierre Lamothe; Paul Hebert
Original assignee: Hebco International Inc.
Priority date: 1999-10-21
Filing date: 1999-10-21
Publication date: 2001-04-26
Also published as: AU6321999A; CA2232015A1

Abstract

Process for safe recovery of gases produced during a pyrolytic treatment comprising the steps of introducing a solid carbonizable material into a pyrolysis reactor (1), making vacuum in the pyrolysis reactor (1) by means of a first pumping system (5, 6), stopping the first pumping system (5, 6) when the pressure is between 1 and 2.5 Psi, heating the pyrolysis reactor (1), recovering oils-containing combusted gases from the pyrolysis reactor (1), and when the rate of THC is lower or equal to 60 %, stopping the second pumping system (7), the first pumping system (5, 6) being mounted on a first derivation of the line (10) connecting the separator and the gas storage enclosure, and the second pumping system (7) being mounted on a second derivation of the line (10).

Description

PROCESS FOR THE SELECTI VE RECOVERY OF RESIDUAL GASES FROM A PYROLYSIS REACTION

OF SOLID CARBONIZABLE MATERIAL

Background of the invention;

1. Field of the invention 0

The invention relates to a process for the selective and safe recovery of residual gases produced in a reactor during pyrolysis of solid carbonizable material, such as wood chips, sawdust and similar wood particles, car fluff, coal, coal residues, plastics, soils contaminated with hydrocarbons, tires and any material rich in polymerized hydrocarbons .

2. Brief description of the prior art 0

The concept of selective recovery of combustible gaseous, liquid hydrocarbons and usable carbonaceous solid residues from coal and from domestic and industrial wastes has received increased attention with the rising costs of solid, liquid and gaseous fossil fuels and problems inherent with conventional disposal of solid wastes.

Elements which are contained in a solid carbonizable material, such as carbon black and steel and which remain solid even during pyrolysis in a reactor can easily be

30 recovered in the lower part of the reactor after completion of the pyrolysis reaction. Due to the complex and fluctuating composition of the gases produced in the reactor during the pyrolysis reaction, over-dimensioned condensers and separators are necessary in order to adequately separate the condensable fraction generally designed as "oils" and the non condensable fraction generally designated as "gaseous hydrocarbons". Otherwise, the gaseous hydrocarbons are loaded with a significant rate Of oils which accumulate in equipments located downstream the reactor and in contact with the gaseous hydrocarbons. Such may cause "contaminations" and damages the pumps (stripping), compressors and the like. If the contaminated equipments are not quickly disconnected and decontaminated before further use, fire and explosion may occur with the inherent risk of a complete destruction of the unit.

A number of processes currently exist for recovering oils and gases produced during the pyrolysis of solid material rich in polymerized hydrocarbons.

CA-A-1, 149, 134 discloses a process for recovering carbon black and hydrocarbons from used tires, wherein the gases produced in a pyrolysis reactor are first treated in an oil condenser then in an oil separator to lower the amount of oils, present in the gases. Then, with the help of a vacuum pump placed after the oil separator, the gases are sent to a second separator which reduces the amount of gaseous water present in the gases. As mentioned hereinabove, the vacuum pump may be damaged by the oils still present in a substantial amount in the gases.

US-A-4, 740, 270 discloses a process wherein in a first stage, a subatmospheric pressure of less than about 35 mm Hg is generated. In a second stage, a vacuum pump is used to fill a storage gas tank with the generated gases. In this process, all the condensable hydrocarbons have preliminary are first extracted in a complex condensating and separating system. This process enables to increase the yield of the liquid hydrocarbons and to lower the yield of the gaseous hydrocarbons present in the gases resulting from the pyrolysis reaction of rubber tires. Due to the sophisticated condensation apparatus used in this process, the amount of recovered oils is increased and the amount of oils in the residual gases is reduced to such an extent that the risks of stripping and of explosion of the vacuum pump are reduced. Costs for such an advanced purification are high and there is a limited commercial need for a gas with high purity, particularly since the recovered gases are commonly used to heat the pyrolysis reactor.

Therefore, there is presently a need for a safe and economical process for the selective recovery of residual gases from a pyrolysis reactor without damaging of the equipments downstream the reactor, and in particular without damaging of the pumping apparatus used to fill the gas storage tank.

OBJECT AND SUMMARY OF THE INVENTION

A first object of the invention is to provide a process for the selective and safe recovery of residual gases from the pyrolysis of solid carbonizable material, which overcomes the disadvantages of the existing processes.

A second object of the invention is to provide a process which improves the overall productivity of pyrolysis plant of the batch type. The process according to the invention comprises the steps of: a process for selective and safe recovery of gases produced during a pyrolytic treatment of solid carbonizable material, which process comprises the steps of: a) introducing said solid carbonizable material into a pyrolysis reactor (1) ;

b) making vacuum in the pyrolysis reactor (1) by means of a first pumping system, so as to extract oxygen-containing gases present in said pyrolysis reactor and to exhaust said extracted gases in the air;

c) stopping the first pumping system when the subatmospheric pressure in the pyrolysis reactor (1) is between 1 and 2.5 Psi;

d) heating the pyrolysis reactor (1) with a burning combustion gas with a B.T.U of at least 1350 or with burning combustion oils with a B.T.U of at least 1800;

e) recovering oils-containing combusted gases from a heating zone of the pyrolysis reactor (1), condensing the oils present in said combusted gases in a condenser (2) , separately recovering the so condensed oils in a separator (3) and filling by means of a second pumping system a gas storage enclosure (8) connected to the separator (3) by a line (10) with said combusted gases recovered after condensation and separation of the oils; and

f) when the rate of total hydrocarbon content in the gases (THC) present in the gases after condensation and separation of the oils, is lower or equal to 60 , stopping the second pumping system and exhausting said combusted gases through at least one flare (9) ;

characterized in that:

the first pumping system is mounted on a first derivation of the line connecting the separator

(3) and the gas storage enclosure (8), said first derivation extending between the separator (3) and the gas storage enclosure (8); and

the second pumping system is mounted on a second derivation of the line connecting the separator (3) and the gas storage enclosure (8), said second derivation extending between the first derivation and the gas storage enclosure (8) .

BRIED DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described with reference to the appended drawings. It should be noted that the appended drawings illustrate only one typical embodiment of this invention and are therefore not to be considered as limiting of its scope since the invention may admit other equally effective embodiments.

Figure 1 which is identified as "prior art" illustrates a conventional equipment for the pyrolysis of tires.

Figure 2 illustrates a preferred embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

As exemplified in Figure 1 a prior art conventional equipment for the pyrolysis of tires comprises a pyrolysis reactor (1) connected to a condenser (2) . The condenser (2) is connected to a separator (3) and the separator (3) is connected to an oil filter (12) and to a water cleaning system (13). The water cleaning system is connected to the oil tank (4) and to the cooling system (15) . The separator (3) is connected by the line (10) to a gas tank (8) . The flare (9) is connected between the pump (7) and the gas tank (8) to the line (10) by the mean of the line (11) . Two pumps (5) and (6) are placed on a derivation of the pipe (10) . A third pump (7) is placed on the line (1)) after the derivation of the pumps (5) and (6) and before the gas tank (8) . Valves (VI) and (V3) are placed on the pipe (10) and a valve (V2) is placed on the line (11) . A THC counter (14) is placed on line (10) after the pump (7) and before the connection of line (11) to line (10).

As exemplified in Figure 2, in a preferred embodiment, of the invention a pyrolysis reactor (1) is connected to a condenser (2) . The condenser (2) is connected to a separator (3) and the separator (3) is connected to an oil filter (12) and to a water cleaning system (13) . The water cleaning system is connected to the oil tank (4) and to the cooling system (15). The separator (3) is also connected by the line (10) to a gas tank (8) . The flare (9) is connected between the pump (7) and the gas tank (8) to the line (10) by means of the line (11) . Two pumps (5) and (6) are placed on a derivation of the pipe

(10). A third pump (7) is placed on a second derivation after the first derivation of the pumps (5) and (6) and before the gas tank (8) . The flare (9) is connected to the line (10) by the line (11), the connection is between the pump (7) and the gas tank (8) . A THC counter is placed on line (10) after the derivation of pump (7) and before the connection of line (11) with line (10) . Two valves (V2) and (V4) are placed on the line (10) . The valve (V2) is in the part of the line (10) limited by the second derivation bearing the pump (7) . The valve (V4) is between the gaz tank (8) and the connection of line (11) with line (10). A valve (VI) is placed in the first derivation just after the pumps (5) and (6) and a valve (V3) is placed on line (11) between the flare (9) and the connection of line (11) with line (10) .

The process according to the invention is preferably of a batch-type.

In a first step, the pyrolysis reactor is filled with a solid carbonizable material which is preferably in comminuted form. Such a solid carbonizable material can be selected in the group constituted by wood chips, shavings, sawdust and similar wood particles, car fluff, coal, coal residues, tires and the like. More preferably, the solid carbonizable material is a rubber based composite material containing polymeric hydrocarbons and carbon black and eventually metals, like steel. Particularly adapted are used tires in a shredded form.

In a second step, vacuum is made in the reactor so as to evacuate oxygen-containing gases present in the reactor and thus to reduce the risk to make the pyrolysis out of control. The pumping system used to evacuate the oxygen- containing gases is constituted of one or more pumps connected in series. Preferably, the pumping system is constituted of two pumps in series. The second pump is preferably started when the pressure in the reactor which was initially of 14.5 Psi, is ranging a value between 6.5 and 8.5 Psi, preferably about 7 Psi. The pumped gases which contain oxygen, are evacuated in the air without prejudice to the environment.

This primary pumping system is stopped as soon as the pressure in the reactor reaches a value between 1 and 2.5 Psi, and more preferably as soon as the pressure is about 1.4 Psi.

In a fourth step, the pyrolysis reactor is heated with a burning combustion gas with a B.T.U. of at least 1350 or burning combustion oils with a B.T.U of at least 1800. For this purpose, a train-gas (or burners) are preferably placed outside the walls and most preferably outside the bottom wall of the pyrolysis reactor which is horizontal and close to the ground. Preferably, the gas or oils are those recovered during a previous pyrolysis reaction carried out with the same equipment. In a preferred embodiment, the burning material is exclusively the gases recovered during a previous pyrolysis reaction. The heating of the pyrolysis reactor starts preferably immediately after the filling of the reactor with the solid carbonizable material is completed.

When the temperature in the material to be treated is about 475^{^}F, then the exothermic pyrolysis reaction starts. As a matter of illustration, this result is achieved in a 30 irr pyrolysis reactor feed with 12 000 pounds of used tires when the reactor is alimented with about 10 000 millions of B.T.U.

The composition and therefore the quality of the mixture of oils, gaseous water and hydrocarbon produced during the pyrolysis vary to a great extent according to advancement of the pyrolysis reaction. Preferably, the total hydrocarbon amount (THC) is continuously measured during the process with an apparatus of the type "Analyseur paramagnetique" commercialized by the company NOVA. A high THC expressed in percent value is an indication of valuable gases. A THC value of 100 % correspond to the best purity to be expected for gases recovered in such a process. However, a mixture of gases with a THC of 100% may contain gases which are not hydrocarbons .

At the beginning of the reaction, i.e during the heating step, the gases extracted from the reactor containing no oils have a THC which is lower than 60 ° and have a water content which lower than 5 % .

During the exothermic phase of the reaction, the THC ranges between 60 and 100 °. The oils content ranges between 60 and 75 % and the water content is lower than 5 %. In the post exothermic phase, the THC is lower than 60 %, the oils content between 25 and 40 % and the water content lower than > •

The amount of oils and of hydrocarbons produced during the pyrolysis reaction is subject to unpredictable changes corresponding to a sudden acceleration of the exothermic process. Since at any time of the reaction, the concentration of oils present m the residual gases is over 25 %, condensation of the oils and separation of uncondensable hydrocarbons is unavoidable. For this purpose, a condenser and a separator are connected on the same line downstream the pyrolysis reactor. Thus, the gases exhausted from the reactor go through the condenser and separator. The amount of oils still present m the gases at this stage is about 5 % and the water amount is lower than 5 o. The oils are recovered m a suitable tank and can be commercialized without further chemical or physical treatment as fuel suitable for domestic or industrial heating systems. The gases substantially free of oils and of water are filled into the gas storage enclosure as long as the THC is better than 50 %, and more preferably as long as the THC is better than 60 %. For this purpose, a second pumping system is used. This pumping system consists of one or more pumps. Preferably, the pump is of the "blower" type. This secondary pumping system starts as soon as the first pumping system is disconnected and it is disconnected as soon as the critical THC value is reached. Then, the pyrolysis gases having a poor THC are sent to the flare where they are burned.

The primary pumping system is placed between the separator and the gas storage enclosure on a first derivation of the line connecting the separating system and the gas storage enclosure.

The secondary system is placed between the first pumping system and the gas storage enclosure, close to the gas storage enclosure, on a second derivation of the line connecting the separator system and the gas storage enclosure. Preferably, the pressure in the line connecting the pyrolysis reactor and the gas storage enclosure is modulated with the help of the second pumping system as a function the difference of pressure Δ = PT3-PT1, wherein PT3 is the pressure in Psi measured at a point between the pyrolysis reactor and the condenser and wherein PT1 is the pressure in Psi, measured in the gas storage enclosure. The second pumping system is in operation when Δ is ranging between 14.5 and 17.5 and is disconnected when Δ is lower than 14.5 or higher than 17.5.

The gas storage enclosure is preferably a gas storage tank.

One or more flares are branched on the line connecting the separator and the gas storage. Preferably, there is only one flare mounted between the second pumping system and the gas storage or between the pyrolysis reactor and the condenser.

In the process of the invention, the contaminated gases pass through the second pumping system during a limited period of time. Thus, accumulation of oil in the mechanical parts of the pump is limited, particularly since no gas goes trough the pump when the latter is in free flow. As a result no stripping of the pump occurs and therefore there is no need to dismantle the pump and to remove oil from the constituting parts in contact with the contaminated gases. More than one hour of maintenance is saved for each batch. A new batch process can be started immediately after the pyrolysis reaction is finished and the reactor discharged from the remaining solid parts. When carbon black is produced during the pyrolysis reaction, its recovery preferably takes place in the lower part of the reactor after the pyrolysis reaction is completed.

In the prior art processes it is not possible to start a new batch immediately since the time required for dismantling the pumps and cleaning the parts of the pump, is more than the time necessary to exhaust the gases having a THC lower than 60 % . Thus, a significant increase of the overall productivity of the plant is achieved with the process according to the present invention. Moreover, the modification that is so made to the flow sheet of the process eliminates high-pressure points, particularly in the condenser, and allows an overall stable pressure comprised between 14,5 and 17,5 Psi in all the plant. COMPARATIVE EXAMPLE 1

A recovery plant as shown in FIG. 1 was used to selectively recover gases produced in a pyrolysis reactor of the type used in a batch type process. The pressure within the reaction zone was generally maintained at ambient pressure with a negative pressure continuously applied to the gas-vapor outlet conduit to remove the gas-vapor stream from the reaction zone. At the start of the process, the reactor with a volume of 30 πø (1) was charged with 12 000 pounds of used car tires. Oxygen containing gases was first evacuated by closing the valve (V3) and by opening the valves (VI) and (V2) so that any air or other gas contained in the reactor (1) was sucked, via the line (10), by the first pumping system and then through the second pumping system prior to being finally exhausted in the atmosphere. When the pressure in the reactor (1) reached a value of 7 Psi, the second pump (6) was started. Both pumps worked until the pressure in the reactor (1) met a value 1.4 Psi. This value was reached approximately after 13 minutes. Then both pumps (5) and (6) were stopped. Simultaneously, the burners placed under the inferior wall of the pyrolysis reactor were fed with burning gases with a B.T.U. of 1475, recovered during a previous pyrolysis batch. Thus, the pyrolysis reactor was heated with 9 millions of B.T.U. Then, heating of the tires in the reactor started. About 15 minutes after the beginning of the pumping stopped, the pressure in the reactor was 1.4 Psi. Then the primary pumping system became free flowing and the second pumping system (7) started to work and to fill a gas storage tank which had a volume of 389 ir . Simultaneously, valves (VI) and (V3) were opened and the valve (V2) was closed. The residual gases going trough the condenser (2) had a THC which was equal to 50 % at the beginning of the reaction and which progressively increased up to 60 % after 1.40 hour. A this time the residual gases were sent to the gas storage tank. After 3.00 hours, when the THC was lower than 60 %, the valve (V3) was closed and the recovered gases were sent to the flare (9) .

After 4.30 hours, the exothermic phase of the pyrolysis was completed and the cleaning of the third pump was started. Then, the dismantling and the cleaning of the mechanical parts of the pump m contact with the oils was started. The time consuming cleaning, however, was not finished before the end of the process. Therefore, a delay arose for completing the process.

After 2.10 hours, the stripping of the pump (7) began. During 20 minutes it was necessary to divert valuables residual gases with a THC of about 90 % to the flare m order to avoid technical damages of the plant.

The overall productivity of the unit calculated on a week was of 50 tons (according to the English system) of carbon black. A stripping of the pump was required for each batch and the number of working hours for the maintenance of the pump was of 28 hours.

EXAMPLE 2

A recovery plant according to the invention as shown m FIG. 2 was used to recover selectively gases produced m a pyrolysis reactor of the type used m a batch type process. At the start of the process, the reactor which has a volume of 30 m^J (1) was charged with 1200 pounds of used car tires and was first evacuated by closing the valve (V4) and opening the valves (VI), (V2) and (V3) so that any air or other gas contained in the reactor (1) was sucked via the line (10) trough the vacuum pump (5) . When the pressure m the reactor (1) reached a value of 7 Psi, the second pump

(6) was started. Both pumps worked until the pressure m the reactor (1) met a value 1.4 Psi. This value was reached after approximately 13 minutes. Then both pumps (5) and (6) were stopped. Simultaneously, valves (V2) and (V3) were opened and the valves (VI) and (V4) were closed. Then, the heating of the reactor (1) started according to the same procedure as m previous example 1. The gas recovered after the condenser (2) had a THC (total hydrocarbon rate) which was 50° at the beginning of the reaction and which progressively increased to 60% after 1,40 hours. The gases were sent to the gas tank with the help of a pump (7) of the "blower" type commercialized under the name Hibon NX. 08 by the Company HIBON. After 3.00 hours and when the THC was lower than 60 %, the valve (V4) was closed and the recovered gases were sent to the flare. The latter pump was modulated during the filling of the gas tank (8). After 6.00 hours, the reaction of pyrolysis was completed. There was no accumulation of oil in the third pump and no cleaning was necessary.

The overall productivity of the unit calculated on a week was of 56 tons of carbon black. Since no stripping of pump (7) occurred and since no special maintenance of pump

(7) was necessary, it was possible to perform 3.5 batches more with the beneficial result of a win of 6 tones of carbon black.

Claims

1. A process for selective and safe recovery of gases produced during a pyrolytic treatment of solid carbonizable material, which process comprises the steps of:

a) introducing said solid carbonizable material into a pyrolysis reactor (1) ;

b) making vacuum in the pyrolysis reactor (1) by means of a first pumping system, so as to extract oxygen- containing gases present in said pyrolysis reactor (1) and to exhaust said extracted gases in the air;

e) recovering oils-containing combusted gases from a heating zone of the pyrolysis reactor (1) , condensing the oils present in said combusted gases in a condenser (2) , separately recovering the so condensed oils in a separator (3) and filling by means of a second pumping system a gas storage enclosure (8) connected to the separator (3) by a line (10) with said combusted gases recovered after condensation and separation of the oils; and f) when the rate of total hydrocarbon content in the gases (THC) present in the gases after condensation and separation of the oils, is lower or equal to 60 %, stopping the second pumping system and exhausting said combusted gases through at least one flare (9) ;

characterized in that:

the first pumping system is mounted on a first derivation of the line connecting the separator (3) and the gas storage enclosure (8), said first derivation extending between the separator (3) and the gas storage enclosure (8) ; and

the second pumping system is mounted on a second derivation of the line connecting the separator (3) and the gas storage enclosure

(8), said second derivation extending between the first derivation and the gas storage enclosure (8) .

2. A process according to claim 1, characterized in that it comprises the additional step of modulating the pressure in the line connecting the pyrolysis reactor (1) and the gas storage enclosure (8) by means of said second pumping system as a function of the difference of pressure Δ = PT3-PT1 existing between the pyrolysis reactor (1) and the gas storage enclosure (8), wherein PT3 is the pressure in Psi measured at a point between the pyrolysis reactor (1) and the condenser (2) and PT1 is the pressure in Psi measured in the gas storage enclosure (8) .

3. A process according to claim 2, characterized in that it comprises the additional steps of activating the second pumping system when Δ is between 14.5 and 17.5 and deactivating said second pumping system when Δ is lower than 14,5 or higher than 17.5.

4. A process according to claim 1, 2 or 3, characterized in that said at least one flare (9) is connected between the second pumping system and the gas storage enclosure (8) .

5. A process according to claim 1, 2 or 3, characterized in that the said process is carried out with one flare (9) branched between the pyrolysis reactor (1) and the condensers .

6. A process according to any one of claims 1 to 5, characterized in that the solid carbonizable material is in a comminuted form.

7. A process according to any one of claims 1 to 6, characterized in that the solid carbonizable material is selected from the group consisting of wood chips, shavings, sawdust and similar wood particles, car fluff, plastics, soils contaminated with hydrocarbons, coal, coal residues and tires.

8. A process according to any one of claims 1 to 6, characterized in that the solid carbonizable material consists of rubber containing polymeric hydrocarbons and carbon black.

9. A process according to any one of claims 1 to 6, characterized in that the solid carbonizable material consists of shredded tires.

10. A process according to any one of claims 1 to 9, characterized in that the pyrolytic treatment is of a batch type.

11. A process according to any one of claims 1 to 10, characterized in that the first pumping system consists of a first and a second pump mounted in series, and wherein the second pump starts to work when the pressure in the pyrolysis reactor (1) is between 6.5 and 8.5 Psi.

12. A process according claim 11, characterized in that the second pump start to work when the pressure in the pyrolysis reactor (1) is equal to 7 Psi.

13. A process according to any one of claims 1 to 12 characterized in that the second pumping system consists of a pump of the "blower" type.

14. A process according to any one of claims 1 to 13 characterized in that step f) starts when the THC is lower than 50 %.

15. A process according to any one of claims 1 to 14, characterized in that the burning combustion gas consists of said gases recovered during the pyrolytic treatment of said solid carbonizable material.

16. A process according to any one of claims 1 to 15, characterized in that the burning combustion gas consists of a gas mixture having a B.T.U. ranging between 1350 and 1550.

17. A process according to any one of claims 1 to 16, characterized in that step c) takes place when the pressure in the pyrolysis reactor (1) is equal to 1.4 Psi.

18. A process according to any one of the claims 1 to 17, characterized in that a train-gas or burners are used in step d) for the heating of the pyrolysis reactor (1) .

19. A process according to any one of claims 1 to 18, characterized in that in step d) the burning of the combustion gas or of the combustion oils takes place outside the walls of the pyrolysis reactor (1) and under the bottom wall of the pyrolysis reactor (1) which is horizontal and close to the ground.