GB2090609A - Carbonaceous material heat- treatment system - Google Patents

Abstract

The invention relates to heat treatment systems for the production of useful products from carbonaceous materials. Such feedstock normally requires a plurality of treatment stages which should be accurately monitored for good results. The present invention comprises a system in which a single heat source (2) is used to supply each of the plurality of stages (10, 18) which are separately controlled, by monitoring the respective heat transfer systems (12, 20). The source (2) is normally a hot gas generator and the control preferably effected by selective mixing of gas from the generator with recycled gas from downstream of the treatment stages (10, 18). <IMAGE>

Description

SPECIFICATION Pyrolysis system This invention relates to heat treatment systems for the production of useful products from carbonaceous materials particularly those having a moisture content. Typical feedstock comprise biomass substances such as agricultural and animal waste, forest waste, energy crops, tree bark, straw, corn husks, algal and other aquatic growth. The feedstock can also include more general refuse and industrial waste such as plastics and rubbers.

Known treatments of the kind to which the invention relates utilise heat to break down the feedstock material, with or without combustion.

Prior to this treatment stage the feedstock should be dried and this is either accomplished quite separately or as part of a total processing operation in which the respective treatment stages are carried out in a common retort. All known processes suffer from the disadvantage that the treatment cannot be controlled accurately and thus the nature and quality of the products cannot be predicted with any confidence.

The present invention seeks to integrate the essential component stages of such treatment in a system using a single heat source which is tapped to serve a plurality of treatment stages. In a system according to the invention, a single source provides heat energy for a plurality of treatment stages of which one is a heat reactor, the respective heat transfer systems including monitoring means enabling the amount of heat transfer and the operation of each stage to be controlled.

A typical heat source in a system of the invention is a hot gas generator. The discharge gases from one or more of the treatment stages can be recycled to the heat source (as fuel), or to one or more other treatment stages, or to itself or themselves. By this means, the temperature in each treatment stage can be accurately monitored and the composition of the reaction products; solid, liquid and gaseous, can be predicted.

Pyrolysis reactions, to which systems of the invention are particularly suited, generate different products at different temperatures, flow rates, and feedstock, and accordingly, the present invention enables a plurality of different reactions to be carried out simultaneously in a single overall system. Capital outlay is minimized by the use of a single primary heat source.

Three systems according to the invention will now be described by way of example and with reference to the accompanying block diagram drawings wherein: Figure 1 is a flow diagram of a pyrolysis plant wherein the output from a single hot gas generator, is fed in parallel to a dryer and a reactor; Figure 2 is a flow diagram of a pyrolysis plant wherein the output from a single hot gas generator is fed in parallel to a dryer and two reactors; and Figure 3 is a flow diagram of a pyrolysis plant adapted for particular feedstocks wherein the output from a single hot gas generator is fed in parallel to two reactors.

In each of the plants illustrated, a hot gas generator 2 is used to provide hot gases for at least two treatment processes. In Figure 1, a feedstock passes along conveyors 4 through a shredder 6 and a lock hopper 8 to a dryer 10. The dryer 10 receives hot gases from the generator 2 along line 1 2. The dried feedstock then passes via a conveyor 14 and elevator 1 6 to a pyrolysis reactor 18, which also receives hot gases from the generator 2, but along line 20. Gases discharged from the dryer 10 pass to a first scrubber 22 and a cleaned gass is recycled therefrom to the generator along line 24 by a recirculation fan 26.

Liquid (normally water) is circulated through the scrubber via a filter 28, a pump 30 and an air cooler 32.

Gases discharged from the reactor 1 8 pass to a second scrubber 34 and the cleaned gas is also recycled to the generator 2 along line 24 by fan 26. The liquid fraction from the scrubber 34 is filtered at 36 and returned to the scrubber 34 by a pump 38 and the air cooler 32. Any oil product from the liquid fraction can be extracted downstream of the pump 38 at 40. The solids discharge from the reactor 1 8 is passed along a cooled conveyor 42 to a product lock hopper 44.

The temperature of the gases fed to the dryer 10 and the reactor 1 8 is of course critical to the plant operation. These temperatures can be carefully monitored by bleeding selected portions of the recycled gases in line 24 into the respective feed lines 12 and 20 along lines 46 and 48.A typical gas temperature from the generator is in the range 800-1 000C, and recycled gas at lower temperatures, for example, 1 200C can be used to cool the feed to the dryer to a typical temperature in the range 100-1 500 C. Similarly, the feed to the reactor 1 8 can be cooled to for example 500 to 8000 C. Valves 50 are included in the various gas flow lines to enable the respective temperatures and flow rates to be controlled and the generator 2 itself can be controlled by fuel delivery from 52 and its draughting by fan 54. The plant illustrated enables each stage in the treatment process to be controlled and hence, the products therefrom can be predetermined with accuracy.Each of the dryer 10 and reactor 18 can be a cross flow unit, but this is not necessary.

The advantage of the system shown in Figure 1 is that vapourised moisture emerging from the dryer 10 may be independently recovered for disposal thus reducing the overall effluent disposal problem. If drying the pyrolysis reactions were to be undertaken in a single reactor, in the case of carbonaceous material containing, for example, cellulose, the effluent stream would be contaminated with pyroligneous acids which are partially solubilised into the aqueous phase. A further advantage is that the condensible organic fraction emerging from the pyrolysis reactor is generated in a more concentrated form. Also, by placing the dryer in parallel accepting hot gas from a single generator, economy on capital plant is obtained.

The plant shown in Figure 2 broadly adds to that of Figure 1 a second pyrolysis reactor 56 for a second feedstock and associated components which are each incorporated in the plant.

Additionally, the first scrubber (22) of Figure 1 has been replaced by a cyclone separator 58. In other respects, the treatment process for the first feedstock is similar to that described with reference to Figure 1.

The second reactor 56 receives a second feedstock from conveyor 4', shredder 6' and lock hopper 8', and the solids discharge is passed along a cooled conveyor 42' to a product lock hopper 44'. The feed of hot gases to the reactor 56 is along line 60 from the hot gas generator 2 which in this case is not modified by any bled recycled gases. The reactor 56 thus operates at the generator output temperature and is suitable for the treatment of feedstock which requires higher temperatures than the first. The gases discharged from the reactor 56 are fed to a second scrubber 62 and cleaned gas therefrom is passed along line 64 to join the recirculation system for the dryer 10 and first reactor 1 8 upstream of the fan 26. The liquid fraction from the scrubber 62 is filtered at 66 and recycled via pump 68 and heat exchanger 70. The liquid flow may be adjusted by addition or extraction at 72.

The generator 2 of Figure 2 is supplemented by a primary air heater 74 which exchanges heat from the exhaust gases with a supplementary air intake from the air cooler 32 along line 76 via primary air fan 78.

The plant of Figure 2 is then operable to pyrolyse two feedstocks at different temperature using the same hot gas generator. The respective temperatures are controllable as in the embodiment of Figure 1 and the respective products can also thus be predetermined. For example, wet carbonaceous material could be fed through the dryer 10 and reactor 18, and shredded rubber tyres could be fed through the second reactor 56. The advantages of this are as described above in relation to Figure 1, but additionally, this arrangement permits energy derived from, for example, one feedstock to supplement the energy requirements for drying of the other, all product gases being passed back into the hot gas generator 2 where they are combusted to generate the necessary drying and pyrolysis gases.In this manner it can be possible to pyrolyse high moisture content material without a requirement for importing significant quantities of prime fuel. The system described allows for separate solid product removal which would be important in terms of product marketing vs.

product purity. The condensible oil fraction from the reactors (18, 56) could be collected separately.

In Figure 3, the plant illustrated is especially suited to the simultaneous treatment of tyre and peat/shale. It is a dual feed input to a parallel reactor system which does not incorporate the stage drying section. Essentially the tyre feedstock is acting as a source of energy to pyrolyse the peat and recover the kerogen from the shale. In the case of the kerogen recovery it is probable that temperatures of 500-6000C would be used. The tyre feedstock passes via conveyors 4", shredder 6" and lock hopper 8" to the tyre reactor 80. The pyrolysed product is discharged along cooled conveyor 42" to product lock hopper 4". The peat/shale feedstock is first dried in dryer 82 and then passed via conveyor 84, screen 86 (where shale fines are separated), and lock hopper 88 to the reactor 90.The pyrolysed product from reactor 90 is discharged along cooled conveyor 42" to product lock hopper 44".

The gaseous outputs from the reactors 80 and 90 are treated as are those from the dryer 10 and reactor 1 6 of Figure 1 with the exception that provision is made for the extraction of oil product at 92 from the recycled liquid fraction in the scrubber 22. As the shale/peat reactor 90 must operate at a higher temperature than the tyre reactor 80, it is fed directly with unblended hot gases from the generator 2. The dryer 82 also operates with gas directly from the generator 2 although a portion of the gas from the dryer 82 may be recycled thereto by fan 94. As in the plants of Figures 1 and 2, primary air is fed to the generator 2 from the cooler 32.

It should be appreciated that, although not shown in any of the drawings described above, it is possible to locate one reactor immediately downstream of another reactor; i.e., reactors could be placed in series with one or more drying stages being incorporated as necessary. In the case of a series reactor, the objective would be to obtain distinctly separate solid products which would be suitable for different markets. The pyrolysis gases plus pyrolysis gas stream from the upstream reactor would pass from the upstream reactor into the downstream reactor at a lower temperature.

This system might operate, for example, with a carbonaceous material such as domestic waste being pyrolysed in the upstream reactor at 8000C plus, the emerging product would have a temperature of 500 to 6000 C. At this temperature oil yield from a rubber pyrolysis is maximized.

Thus, if the feed to the downstream reactor is rubber tyres, oil yield would be maximised whilst retaining the separate quality of the recovered carbon black from the tyre pyrolysis reaction.

Claims (14)

1. An heat treatment system for carbonaceous material wherein a single source provides heat energy for a plyrality of treatment stages of which one is heat reactor, the resepective heat transfer systems including monitoring means enabling the amount of heat transfer and the operation of each stage to be controlled.

2. A system according to Claim 1 wherein the single source is a hot gas generator, the heat transfer systems comprising gas ducts for carrying hot gas to the respective stages.

3. A system according to Claim 2 including means for recycling gases from downstream of the treatment stages to the transfer systems to control the gas temperature in the ducts.

4. A system according to Claim 3 including means for cleaning gases downstream of at least one of the treatment stages before recycling.

5. A system according to Claim 4 wherein the cleaning means comprises at least one scrubber including means for circulating water therethrough.

6. A system according to Claim 5 including means for extracting oil from the liquid fraction generated in said at least one scrubber.

7. A system according to Claims 3 to 6 wherein the recycling means is coupled to the transfer systems enabling recycled gases to mix with gas from the generator in the respective systems.

8. A system according to any of Claims 2 to 7 including means for recycling gases from downstream of the treatment stages to the generator.

9. A system according to Claim 3 or Claim 8 including means for mixing gases downstream of the respective stages before recycling.

10. A system according to any preceding Claim wherein one of the treatment stages is a dryer for the carbonaceous material prior to its delivery to the reactor.

11. A system according to any preceding Claim wherein the treatment stages comprise at least two pyrolysis reactors.

12. A system according to Claim 11 including a separate feedstock delivery mechanism for each reactor.

13. A system according to Claim 11 or Claim 1 2 wherein said two reactors are adapted to operate at different temperatures.

14. An heat treatment system for carbonaceous materials substantially as described herein with reference to Figure 1; Figure 2, or Figure 3 of the accompanying drawings.