GB2416583A

GB2416583A - A torodial reactor for converting carbonaceous material to a mixture of gases and particles for combustion

Info

Publication number: GB2416583A
Application number: GB0415268A
Authority: GB
Inventors: Christopher Edward Dodson; Martin Alexander Groszek
Original assignee: Mortimer Technology Holdings Ltd
Current assignee: Mortimer Technology Holdings Ltd
Priority date: 2004-07-07
Filing date: 2004-07-07
Publication date: 2006-02-01
Also published as: GB0415268D0; WO2006003454A1

Abstract

In a process for the combustion of a carbonaceous material containing volatiles (e.g. waste coal 45), the material is introduced into a toroidal bed reactor 1 which has a circumferentially directed flow of air and heated within the reactor to transform it into a mixture comprising a volatile gaseous component and fine particulates, the mixture is then removed from the reactor 1 and combusted in a conventional pulverised burner (figs 2 &3). The airflow may be preheated, can be caused to rotate about a vertical axis by radial vanes 20,25, and in an embodiment there is a bed of particles 30. The reactor is heated to between 600{C and 700{C. The material may be supplied without drying or milling by a venturi 40 using compressed air injection, and swirls in the reactor 1 until it shatters from coal lumps as big as 25mm to dust of less than 50 m. A cyclone may remove the fine particulates before the burner.

Description

Process for treating a carbonaceous material The present invention relates

to a process for treating a carbonaceous material such as waste coal or low grade coal to produce a mixture comprising volatiles and char particles, which can then be combusted.

A toroidal bed (TORBED (RTM)) reactor and process is described in European Patent No. 0 068 853 and US Patent No. 4 479 920. In the process, a particulate material to be treated is embedded and centrifugally retained within a compact, but turbulent, toroidally circulating bed of particles which circulate about an axis of the processing chamber. Specifically, the particles within the bed are circulated above a plurality of fluid inlets arranged around the base of the processing chamber. The fluid inlets are preferably arranged in overlapping relationship and the particles are caused to circulate around the bed by the action of a processing fluid, for example a gas injected into the processing chamber from beneath and through the fluid inlets. The fluid inlets may, for example, be a plurality of outwardly radiating, inclined vanes arranged around the base of the processing chamber.

The toroidal bed reactor provides a rapidly mixing bed which can be used to circulate particulates toroidally through a zone in a process chamber where an interaction occurs with a gas stream.

Waste coal (a term that also encompasses low grade coal) is generally considered to have little or no commercial value. It is therefore treated as a waste material and is therefore often disposed.

We have now developed a process and apparatus that makes it possible to treat a carbonaceous material such as, for example, waste coal so that it can be combusted in a burner, for example a pulverised fuel burner.

Accordingly, in a first aspect the present invention provides a process for the combustion of carbonaceous material containing volatiles, the process comprising: (i) providing a toroidal bed reactor comprising a chamber having an inlet and an outlet; (ii) providing a burner having an inlet coupled either directly or indirectly to the outlet of the chamber of the toroidal bed reactor; (iii) introducing carbonaceous material into the chamber of the toroidal bed reactor through the inlet thereof; (iv) generating a substantially circumferentially directed flow of fluid within the chamber to cause the carbonaceous material to circulate rapidly about an axis of the chamber in a toroidal band, and heating the carbonaceous material whereby it transforms into a mixture comprising a gaseous component and a fine particulate component; (v) removing said mixture from the chamber through the outlet thereof and passing said mixture either directly or indirectly to the burner through the inlet thereof; and (vi) effecting combustion in said burner.

The carbonaceous material will typically comprise waste coal, a term that also encompasses low grade coal. All types of coal from lignite to anthracite are encompassed.

The carbonaceous material is pyrolysed in the toroidal reactor to result in a mixture comprising a gaseous component and a fine particulate component.

The fine particulate component comprises at least partially devolatised particles of the carbonaceous material, for example carbonaceous char particles. The particles preferably have a d50 particle size of 100 microns or less, more preferably 50 microns or less.

IS The gaseous component comprises the volatiles from the carbonaceous material. The combustible volatile gas typically comprises one or more of carbon monoxide, hydrogen, and low molecular weight hydrocarbons, the proportions varying between different sources.

It has surprisingly been found that the effect of a toroidal bed reactor not only effects pyrolysis but also results in the carbonaceous material being thermally shattered or comminuted so as to result in a fine carbonaceous powder.

The carbonaceous material, for example waste coal, can be introduced into the chamber of the toroidal bed reactor in a non-dry state, in other words while it is still wet or damp. Thus, no initial drying step is required.

The carbonaceous material typically has a particle sieve size distribution of 90-100% less than 25 mm, preferably less than 10 mm, more preferably less than 5 mm.

An important feature of the present invention is that the carbonaceous material, for example waste coal, can be introduced into the chamber of the toroidal bed reactor in a non-milled state. Thus, no initial milling step is required.

lO The carbonaceous material, for example waste coal, typically has a Calorific Value of 5000 to 35000 kJ/kg, preferably 8000 to 29000 kJ/kg. Waste coal is usually relatively finely divided and often arises as a byproduct of coal cleaning or beneficiation processes that are used in ]S the production of a marketable coal product.

The flow of fluid within the chamber will typically have a horizontal and a vertical velocity component.

The chamber will typically comprise a plurality of fluid inlets at or adjacent a base thereof. A fluid is directed through the fluid inlets at the base of the chamber to generate the substantially circumferentially directed flow of fluid within the chamber. The fluid inlets will typically impart both a horizontal and vertical velocity component to the fluid. The fluid inlets may comprise, for example, a plurality of outwardly radiating, inclined vanes at or adjacent the base of the chamber.

The fluid may be heated before and/or after entry into the chamber. This allows for thermal transfer between the fluid and the carbonaceous material. The fluid temperature measured in the reactor may be in the range of from 500 to 800 C, preferably from 550 to 750 C, still more preferably from 600 to 700 C, still more preferably from 630 to670 C, still more preferably approximately 650 C. Alternatively, S or in conjunction, the carbonaceous material may be heated by combustion of a part thereof in the chamber.

The fluid may comprise, for example, air or an oxygen- containing gas such as, for example, an exhaust gas from a I() combustion process. A restricted oxygen supply allows just enough combustion to occur to provide the heat needed for pyrolysis. If a non-oxygen containing fluid is used, then it is preferably heated to a temperature of from 750 to 1000 C to provide the necessary heat energy for the Is pyrolysis.

The fluid preferably has an oxygen content in the range of from 2 to 21% by volume, preferably from 3 to 10% by volume.

Advantageously, the oxygen content of the process gas stream entering the toroidal reactor is controlled so that just sufficient carbonaceous material and/or volatiles are combusted to maintain the reactor temperature at 600 to 700 C.

Depending upon the nature of the fluid and the processing conditions, the fluid may react chemically with the carbonaceous material.

A reactant may be added to the toroidally circulating bed of particles to effect reduction of any gaseous emissions such as, for example, sulphur dioxide or oxides of nitrogen from the reactor. Examples of reactants include one or more of calcium carbonate, calcium oxide and ammonia.

In one embodiment, the processing chamber contains a bed of particulate material which circulates about an axis of the chamber when the flow of fluid is generated, wherein the carbonaceous material interacts with the fluid. The circulating bed particles will typically define substantially uniform tortuous paths along which particles of the carbonaceous material travel. The mean terminal velocity of the particles of the bed may preferably be such that there is little or substantially no migration thereof to the outlet until such time as sufficient comminution of the particles has occurred. The circulating bed particles provide a turbulent environment within which gas/particles heat and mass transfer properties are enhanced. This consequently enhances heat transfer to or from the carbonaceous material. A tortuous/labyrinthine flow type path is provided, which increases the effective residence time of the carbonaceous material in the processing chamber, hence increasing the time for heat and/or mass transfer between the fluid and particles. The circulating bed of particles may also act as a heat-sink. The carbonaceous material will generally enter the chamber below and/or adjacent to the circulating bed particles in order to contact therewith. Alternatively, if the inlet is vertically spaced above the fluid inlets at the base of the chamber and the circulating bed, then the carbonaceous material will fall down through the chamber, under the action of gravity, on to the circulating bed. This may be achieved by, for example, a gravity feed mechanism provided in a vertical wall of the chamber.

The pressure drop through the chamber of the toroidal reactor is typically less than 400 Pa.

The process temperature in the chamber is typically in the range of from 550 to 750 C, more typically from 600 to 700 C, still more typically from 630 to 670 C.

The burner is preferably a pulverized fuel burner and is a conventional piece of apparatus that is known in the art. Commercial suppliers such as Saacke of Germany and Coen of the United States provide such pulverized fuel Is burners. Typically they comprise double vortex mixing between pneumatically conveyed coal particles and the requisite combustion air.

The burner combustion zone(s) or 'flame' is preferably operated at a temperature in excess of 900 C, more preferably in excess of 1000 C, still more preferably in excess of 1100 C.

The combustion step or steps in the burner preferably results in the production of pozzolanic fly ash.

After the mixture comprising the gaseous component and the fine particulate component is removed from the chamber through the outlet thereof, at least a portion of the fine particulate component may be removed from the mixture before the combustion step in the burner. This may be achieved using, for example, a cyclone fluidly connected to the outlet of the chamber and the inlet of the burner, whereby after said mixture is removed from the chamber through the outlet thereof it passes to the cyclone, wherein at least a portion of the fine particulate component is separated from the gaseous component, and wherein the gaseous component and any residual fine particulate is then passed to the burner through the inlet thereof.

The fine particulate component thus removed is preferably substantially free of volatiles and may therefore be used as an environmentally friendly fuel. The fine particulate may be supplied in any suitable form such as, for example, briquettes.

In a second aspect the present invention provides an apparatus for carrying out a process as herein described, the apparatus comprising: (a) a toroidal bed reactor comprising (i) a chamber having an inlet for introducing carbonaceous material into the chamber, (ii) means for heating the contents of the chamber, and (iii) means for generating a substantially circumferentially directed flow of fluid within the chamber to cause, in use, the carbonaceous material to circulate rapidly about an axis of the chamber in a toroidal band, whereby the carbonaceous material is pyrolysed and thermally decrepitated to result in a mixture comprising a gaseous component and a fine particulate component, and (iv) an outlet for exhausting the said mixture from the chamber; and (b) a burner having an inlet coupled either directly or indirectly to the outlet of the chamber of the toroidal bed reactor. - 9 -

The apparatus may further comprise a cyclone in fluid communication with the outlet of the chamber and the inlet of the burner. Accordingly, after the mixture is exhausted from the chamber it passes to the cyclone, wherein at least a portion of the fine particulate component is separated from the gaseous component, and wherein the gaseous component and any residual fine particulate is then injected into the burner through the inlet thereof.

All aspects of the invention described herein in relation to the process are also applicable to the apparatus either singularly or in any combination. Similarly, all aspects of the invention described herein in relation to the apparatus are applicable to the process either singularly or in any combination.

The inlet for the carbonaceous material may be located adjacent a base of the chamber and the outlet will generally be spaced downstream from the inlet. The inlet is preferably located at a position above the fluid inlets of the chamber. The outlet will generally be vertically spaced above the inlet of the processing chamber, although the inlet may be located adjacent thereto. Both the inlet and the outlet may be provided in a top portion of the chamber.

The carbonaceous material may be introduced into the processing chamber by injecting it through the inlet under the influence of a compressed gas such as compressed air and/or an inert gas such as nitrogen, CFC and other noble/mono-atomic gases. In a preferred embodiment of the present invention, the inlet is located above the fluid l inlets at the base of the chamber and the carbonaceous material is introduced into the chamber by a gravity feed mechanism, for example using an air lock device such as a rotary valve. The gravity feed mechanism may be provided in a vertical wall of the chamber.

It will be appreciated that the flow of fluid may be generated either before or after the carbonaceous material is introduced into the chamber. Alternatively, the flow of fluid may be generated at the same time as the carbonaceous material is introduced into the chamber.

Air, for example, may be used as the fluid. The fluid may optionally be heated. Heating may be achieved by any suitable means. Alternatively, or in conjunction, separate heating means may be provided for heating the processing chamber and its contents. In other words, the means for heating the carbonaceous material can be the fluid itself and/or separate heating means for heating the processing chamber. Combustion of a portion of the carbonaceous material may also be relied on to heat the material.

The flow of the fluid through the chamber may be generated in a manner as described in EP-B-O 382 769 and EP B-O 068 853, i.e. by supplying a flow of fluid into and through the processing chamber and directing the flow by means of the plurality of outwardly radiating and preferably overlapping fluid inlets arranged in the form of a disc and located at or adjacent to the base of the processing chamber. The fluid inlets are inclined relative to the base of the chamber so as to impart rotational motion to the heating fluid entering the chamber, hence causing the heating fluid to circulate about a substantially vertical axis of the chamber as it rises. The fluid inlets may comprise, for example, a plurality of outwardly radiating vanes at or adjacent the base of the chamber. The vanes are S typically inclined relative the base and preferably disposed in overlapping arrangement.

The present invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a TORBED process reactor for use in the process and apparatus according to the present invention; Figure 2 illustrates an arrangement for a TORBED process reactor combined with a conventional pulverised fuel burner.

Figure 3 illustrates another arrangement for a TORBED process reactor combined with a conventional pulverised fuel burner.

In Figure 1, a generally cylindrical TORBED process chamber 1 has an inlet 5 and an outlet 10 spaced downstream therefrom. At the base 15 of the chamber 1 there is provided a circular arrangement of overlapping fluid inlets, for example vanes, wherein each inlet is inclined relative to the base. Two fluid inlets are shown at 20 and 25. The fluid inlets 20, 25 radiate outwardly from a central point towards the vertical wall of the chamber 1 and form part of a circular disc. A flow of a fluid, for example air, enters the chamber 1 via an inlet 7 and passes through the fluid inlets 20, 25 at the base 15 of the chamber 1. The arrangement of the fluid inlets 20, 25 imparts rotational motion to the fluid entering the chamber 1 so that the fluid circulates about a substantially vertical axis of the chamber 1 as it rises. By this process, the fluid swirls around the chamber 1 in a turbulent fashion and then exhausts from the chamber via outlet 10.

JO As shown, a bed of particles 30 is in the chamber 1.

This is an optional feature.

A feed hopper 35 and venturi arrangement 40 are provided, for example, to supply a carbonaceous material such as waste coal 45 to be treated, under compressed air injection, through the inlet 5 into the chamber 1. As the flow of fluid is generated through the fluid inlets 20, 25 at the base 15 of the chamber 1, the bed particles 30 circulate about a substantially vertical axis of the chamber 1 in an annular region thereof. The waste coal 45 is then injected into the chamber 1 and contacts immediately or almost immediately with the (optional) circulating bed particles 30. Because of their size, density and terminal velocity, there is little or substantially no migration of the bed particles 30 to the outlet 10 until such time as sufficient comminution of the particles has occurred. The fluid may be pre-heated if desired. Alternatively, or in combination, means may be provided to heat the contents of the chamber 1.

The contents of the TORBED reactor chamber l are typically maintained at a temperature in the range of from 600 to 700 C.

Irrespective of whether or not there is a bed 30, the effect of the TORBED reactor is to thermally shatter and devolatise the waste coal 45, thereby converting it into a fine particulate component, for example char, and a gaseous component made up of the volatiles in the waste coal.

The resulting mixture comprising the fine particulate component and the gaseous component may then be exhausted from the outlet lo and then injected directly into a conventional pulverized fuel burner. Alternatively, some or all of the fine particulate component may be removed by means of, for example, a cyclone disposed between the TORBED reactor and the pulverised fuel burner and fluidly connected therewith. This is illustrated in Figures 2 and 3. The pulverised fuel burners can achieve a temperature of at least ll00 C.

It should be stressed that the waste coal can be introduced into the chamber l of the TORBED reactor without any pre-treatment steps. Thus, the waste coal can be provided while it is still wet or damp: no initial drying step is required.

The waste coal typically has an average size of from l to 25 mm, more typically from l to 15 mm. An important feature of the present invention is that the waste coal can be introduced into the chamber of the TORBED reactor in a non-milled state. Thus, no initial milling step is required.

The present invention involves the use of a toroidal bed reactor as herein described to devolatise low grade or waste coal. In the process, the waste coal is thermally comminuted to result in a dust, typically having a d50 of less than lOO,um, more typically less than 50 am.

The simultaneous pyrolysis and thermal decrepitation of the low grade or waste coal means that the resulting volatile laden gas stream, which contains the fine particulate coal char particles, can be passed directly to a conventional pulverised fuel burner.

The process of the present invention enables waste or low grade coal to be combusted at high temperatures (up to stoichiometric conditions) in a pulverised fuel burner without: (i) drying of the coal; and/or milling of the coal; and/or accretions within the combustion system. This differs from the known techniques in a number of respects.

In particular, in order to operate conventional pulverised fuel burners, the coal needs to be dry and milled to a fine particle size prior to injection into the burner. The present invention uses a rapid heat and mass transfer toroidal reactor to thermally shatter the coal so that neither drying nor milling is required.

In any combustion system, it is beneficial to operate at the highest possible temperature, normally at or around stoichiometric balance, to maximise the thermal efficiency of the subsequent heat usage. Under ideal conditions, pulverised fuel burners can achieve temperatures well in excess of 1100 C at which point the resulting fly ash is pozzolanic and has a value in the cement industry. The use of a fluidised bed, which can combust waste, wet and low CV coal, limits operating temperature to approximately 900 C to avoid accretions due to slagging of the ash particles in the bed of particles. Thus, the present invention allows waste, wet and low CV coals to be combusted at high temperatures, above the slagging point, producing pozzolanic fly ash and a high thermal efficiency.

Claims

CLAIMS: 1. A process for the combustion of a carbonaceous material

containing volatiles, the process comprising: (i) providing a toroidal bed reactor comprising a chamber having an inlet and an outlet; (ii) providing a pulverized fuel burner having an inlet coupled either directly or indirectly to the outlet of the chamber of the toroidal bed reactor; (iii) introducing carbonaceous material into the chamber of the toroidal bed reactor through the inlet thereof; (iv) generating a substantially circumferentially directed flow of fluid within the chamber to cause the carbonaceous material to circulate rapidly about an axis of the chamber in a toroidal band, and heating the carbonaceous material, whereby it transforms into a mixture comprising a gaseous component and a fine particulate component; (v) removing said mixture from the chamber through the outlet thereof and passing said mixture either directly or indirectly to the burner through the inlet thereof; and (vi) effecting combustion in said burner.
2. A process as claimed in claim l, wherein the carbonaceous material comprises coal, preferably waste coal.
3. A process as claimed in claim l or claim 2, wherein the fine particulate component comprises char particles (devolatised coal particles), which preferably have a d50 particle size of 100 microns or less, more preferably 50 microns or less.
4. A process as claimed in any one of the preceding claims, wherein the carbonaceous material is introduced into the chamber of the toroidal bed reactor in a non-dry state.
5. A process as claimed in any one of the preceding claims, wherein the carbonaceous material is introduced into the chamber of the toroidal bed reactor in a non-milled state.
6. A process as claimed in any one of the preceding claims, wherein the carbonaceous material has a particle Is sieve size distribution of 100% less than 25 mm, preferably less than 10 mm, more preferably less than 5 mm.
7. A process as claimed in any one of the preceding claims, wherein the carbonaceous material has a Calorific Value of 5 to 35 MJ/kg, preferably 8 to 29 MJ/kg.
8. A process as claimed in any one of the preceding claims, wherein the flow of fluid within the chamber has a horizontal and a vertical velocity component.
9. A process as claimed in any one of the preceding claims, wherein the chamber comprises a plurality of outwardly radiating inclined fluid inlets at or adjacent a base thereof, and wherein fluid is directed through the fluid inlets at the base of the chamber to generate the circumferentially directed flow of fluid within the chamber.
10. A process as claimed in claim 8, wherein fluid directed through said fluid inlets is given both horizontal and vertical velocity components.
11. A process as claimed in any one of the preceding claims, wherein the fluid is heated before and/or after entry into the chamber.
12. A process as claimed in any one of the preceding claims, wherein the fluid is heated to a temperature in the range of from 500 to 800 C, preferably from 600 to 700 C, more preferably from 630 to 670 C.
13. A process as claimed in any one of the preceding claims, wherein the fluid comprises air or an oxygen- containing gas.
14. A process as claimed in claim 13, wherein the fluid comprises an exhaust gas from a combustion process.
15. A process as claimed in claim 13 or claim 14, wherein the fluid has an oxygen content in the range of from 2 to 21 % by volume.
16. A process as claimed in any one of the preceding claims, wherein there is heat or mass transfer between the fluid and the carbonaceous material.
17. A process as claimed in any one of the preceding claims, wherein the fluid reacts chemically with the carbonaceous material.
18. A process as claimed in any one of the preceding claims, wherein a reactant is added to the toroidally circulating bed of particles to effect reduction of any gaseous emissions from the reactor.
19. A process as claimed in any one of the preceding claims, wherein the processing chamber contains a bed of particulate material which circulates about an axis of the chamber when the flow of fluid is generated, and wherein the carbonaceous material interacts with said bed.
20. A process as claimed in claim 19, wherein there is heat or mass transfer between said bed and the carbonaceous material.
21 A process as claimed in claim 19 or claim 20, wherein the circulating bed particles define substantially uniform tortuous paths along which particles of the carbonaceous material travel.
22. A process as claimed in any one of the preceding claims, wherein the pressure drop through the chamber is less than 400 Pa.
23. A process as claimed in any one of the preceding claims, wherein the pulverized fuel burner is operated at a temperature in excess of 900 C, preferably in excess of 1000 C, more preferably in excess of 1100 C.
24. A process as claimed in any one of the preceding claims, wherein the combustion step in the burner results in the production of pozzolanic fly ash.
25. A process as claimed in any one of the preceding claims, wherein after said mixture is removed from the chamber through the outlet thereof, at least a portion of the fine particulate component is removed from the mixture before the combustion step in the burner.
26. A process as claimed in any one of the preceding claims, wherein a cyclone is provided in fluid communication with the outlet of the chamber and the inlet of the burner, whereby after said mixture is removed from the chamber through the outlet thereof it passes to the cyclone, wherein at least a portion of the fine particulate component is separated from the gaseous component, and wherein the gaseous component and any residual fine particulate is then passed to the burner through the inlet thereof.
27. An apparatus for the combustion of a carbonaceous material containing volatiles, the apparatus comprising: (a) a toroidal bed reactor comprising (i) a chamber having an inlet for introducing carbonaceous material into the chamber, (ii) means for heating the contents of the chamber, and (iii) means for generating a substantially circumferentially directed flow of fluid within the chamber to cause, in use, the carbonaceous material to circulate rapidly about an axis of the chamber in a toroidal band, whereby the carbonaceous material is pyrolysed and thermally decrepitated to result in a mixture comprising a gaseous component and a fine particulate component, and (iv) an outlet for exhausting the said mixture from the chamber; and (b) a pulverized fuel burner having an inlet coupled either directly or indirectly to the outlet of the chamber of the toroidal bed reactor.
28. An apparatus as claimed in claim 27, wherein a cyclone is provided in fluid communication with the outlet of the chamber and the inlet of the burner.
29. A process or apparatus substantially as hereinbefore described with reference to any one of the accompanying drawings.