Title of Invention

"PROCESS FOR RECYCLING A FINE-PARTICULATE SOLID AND AN APPARATUS FOR CARRYING OUT THE PROCESS"

Abstract

ABSTRACT Process for recycling a fine-particulate solid, such as coal and iron particles, discharged from a reactor vessel (1), in particular a melter gasifier, by means of a carrier gas at a discharge point (at 2) of the reactor vessel (1), at a recycling point (at 15) of the reactor vessel (1), wherein the solid is separated in a solids separator (4), in particular a cyclone, and subsequently recycled into the reactor vessel (1) by means of a carrier gas, maintaining a pressure difference between the solids separator (4) and the recycling point (at 15), and at least partially gasified and/or burnt upon entry into the reactor vessel (1) under the supply of oxygen, characterized in that the separated solid is directly and continuously exhausted from the solids separator (4) by means of a propellant gas under injector action, accelerated, and conveyed to the reactor vessel (1).

Full Text

The present invention relates to a process for recycling a fine-particulate solid and an apparatus for carrying out the process. The invention relates to a process for recycling a fine-particulate solid, such as coal and iron particles, discharged from a reactor vessel, in particular a melter gasifier, by means of a carrier gas at a discharge point of a reactor vessel, at a recycling point of the reactor vessel, wherein the solid is separated in a solids separator, in particular a cyclone, and subsequently recycled into the reactor vessel by means of a carrier gas, maintaining a pressure difference between the solids separator and the recycling point, and at least partially gasified and/or burnt upon entry into the reactor vessel under the supply of oxygen, as well as an arrangement for carrying out the process. A process of the aforementioned type is known from EP-A - 0 493 752. In this process, hot dusts from a melter gasifier are separated in a hot, cyclone and recycled into the melter gasifier via a burner. To overcome a pressure difference between the hot cyclone and the melter gasifier, recycling is accomplished via a sluice system with several bins provided between two sluices each. The reducing gas withdrawn from the melter gasifier has a temperature of approx. 1050°C and carries considerable amounts of powdered solids. The dust load is approx. 150 g/m3 reducing gas. Immediately after exiting, the temperature of reducing gas is adjusted to approx. 850°C by adding cooling gas, mostly cospecific cooling gas. The solid, which mainly consists of a mixture of coal and iron particles, is continuously separated in the hot cyclone. As this solid is highly abrasive the known sluice system not only requires an expensive design but is also subjected to a high degree of wear. The solid is discontinuously conveyed to the injector, i.e. batchwise, so a continuous operating mode of the dust burner is not ensured and the effectiveness of the dust burner is impaired. The solid may settle on filling up a bin, and the dust flow may get blocked. A process for recycling a fine-particulate solid discharged from a reactor vessel by means of a carrier gas is known from. EP-B - 0 278 287. In this process, the solid accumulating in the solids separator is conveyed into a collecting tank and collected there. The collecting tank serves as compensation tank in this case, from which the solid is withdrawn by means of a hot reactor gas directly withdrawn from the reactor vessel and is directly recycled into the reactor vessel via an injector. In the collecting tank the solid may settle and the solids flow get blocked, in particular due to the hot carrier gas directly withdrawn from the reactor vessel, which may cause caking and partial melting of the solid. In the known process, the injector opens directly into the reactor vessel. The object of the invention is to prevent these disadvantages and difficulties and to solve the technical problem of creating a process 'as well as an arrangement for carrying out the process, which allow recycling of the sblid without moving parts - which would thus , be-subjected to a high degree of abrasion and alternating thermal stress -, wherein in particular recycling "is to be performed continuously and in a controlled manner and the pressure difference between the outlet of the solids separator and the reactor vessel is overcome without any problems. Moreover, a troublefree continuous solids flow has to be ensured with a high degree of certainty. According to the present invention there is provided a process for recycling a fine-particulate solid, such as coal and iron particles, discharged from a reactor vessel, in particular a melter gasifier, by a carrier gas at a discharge point of the reactor vessel, at a recycling point of the reactor vessel, wherein the solid is separated in a solids separator, in particular a cyclone, and subsequently recycled into the reactor vessel by a carrier gas such as herein described, maintaining a pressure difference between the solids separator and the recycling point, and at least partially gasified and/ or burnt upon entry into the reactor vessel under the supply of oxygen, characterized in that the separated solid is directly and continuously exhausted from the solids separator by a propellant gas under injector action, accelerated, and conveyed to the reactor vessel. In a 'process of the aforementioned type, this problem is solved by directly and continuously exhausting the separated sblid by means of a propellant gas under injector action, by accelerating-it and by conveying it to the reactor vessel. According to the invention, a completely open line is thus provided between the solids separator and the reactor vessel in normal operating condition, without any retaining zones and storage baffles. The propellant gas sucks the solid directly from the solids separator along with a small part of the carrier gas which the solids separator is dispersed with. This ensures that the solid is constantly in motion and is not allowed to settle. The danger of sticking particles and, consequently, blocking of the dust flow is thus reliably prevented. The flow velocity of the propellant gas should be preferably equal to or greater than sound velocity (in a supercritical pressure ratio) in order to ensure a high operational stability of solids recycling. It is advantageous to use nitrogen and/or cooled and cleaned process gas as propellant gas. According to a preferred embodiment, the cooled and cleaned process gas is formed by a reducing gas containing CO and H2. An arrangement for carrying out the process according to the invention with a reactor vessel, in particular a melter gasifier, a gas discharge duct departing from the reactor vessel and leading to a solids separator, in particular a cyclone, from which a solids discharge duct conveying the separated solid to an injector departs, and with a solids recycling duct leading from the injector to the reactor vessel and opening into the latter via a dust burner, is characterized in that the solids separator is connected with the solids recycling duct and, thus, with the dust burner via the injector by a continuous line. The set-up of the arrangement according to the invention is simple and uncomplicated and allows a completely free solids flow during normal operation and, as the solids are directly and continuously exhausted, an improved efficiency of the solids separator, resulting in greatly reduced dust losses. The simple set-up of the arrangement according to the invention ensures a very low maintenance expenditure and a high availability and performance of the arrangement. To separate large particles, for example coarse coal and coke lumps, a coarse filter is advantageously connected downstream of the solids separator. In order not to directly impede the solids separation in case of disturbances in the dust recycling line, a solids tank is connected downstream of the solids separator according to a preferred embodiment, which is provided with a fluidization element on transition into the solids discharge duct. This solids tank is not working during normal operation, i.e. the solid is freely dispersed in this tank by free fall. In order to be able to discharge large particles originating e.g. from a refractory lining of the solids discharge duct without impeding the solids flow, the injector is expediently comprised of a solids collecting tank designed as bag tank, which is provided with a drain opening that can be closed with a shut-off element, with the solids collecting tank expediently provided with a fluidization element in the area of the bottom. In the following, the invention is explained in greater detail by the embodiments shown in the drawing, Fig. 1 showing a general layout of a state-of-the-art solids recycling system, and Fig. 2 schematically representing solids recycling according to the invention. According to the state of the art illustrated in Fig. 1, the off-gas generated by coal gasification and subsequently used as reducing gas is discharged from a reactor vessel designed as melter gasifier 1, serving for sponge iron melting and simultaneous generation of a reducing gas from carbon-containing material, via gas discharge duct 2 opening into melter gasifier 1 in an upper region of the latter. As fine-grained to powdered solid is entrained by the off-gas, the latter, serving as carrier gas for this solid, is supplied to solids separator 4, which is advantageously designed as hot cyclone. Immediately after the reducing gas has left melter gasifier 1, cospecific cooling gas is fed to the reducing gas via cooling gas duct 5 so that the reducing gas has a favorable temperature for the subsequent reduction of iron ore and an excessive temperature load on hot cyclone 4 is prevented. The solids separated in hot cyclone 4 subside and are collected in cyclone bin 6 integrated with the hot cyclone. The solid is further conveyed batchwise via a bin system connected downstream. For this purpose, slide valves 10 are arranged between bins 6, 7 and 8 in solids discharge pipe 9 connecting bins 6, 7 and 8. Finally, the solid is dosed to injector 12 as uniformly as possible by means of dosing element 11, for example a dosing valve or, according to another embodiment, a rotary valve (not represented here). Injector 12, which is operated e.g. with N2 as propellant gas - which is supplied via pipe 13 -, conveys the solid into melter gasifier 1 via solids recycling duct 14 opening into dust burner 15. Oxygen is supplied to dust burner 15 via oxygen supply duct 16. As the C-share of the dust is burned/gasified, the remaining inert shares of the solid (Fe, coal ash, CaO, SiO2, etc.) agglomerate. The agglomeration of the solid particles prevents the latter from being discharged by the gas exiting the reactor vessel. They subside towards the bottom of the reactor vessel and are e.g. melted or withdrawn as slag. This type of solids recycling involves a high maintenance expenditure. Particular problems in solids recycling are posed by the system of bins 6 to 10, i.e. batchwise dust conveyance, and by the dosing of the solid. Another disadvantage of the solids recycling system illustrated in Fig. 1 is that the individual solids bins 6 to 10 have to be valved off against the gas system of the process taking place in reactor vessel 1 time and again. As the system pressure, i.e. the pressure in melter gasifier 1 proper, and also in the following reduction vessel not represented, into which the reducing gas generated in the melter gasifier is fed, is subject to variations, large pressure differences occur time and again, which, in combination with gas flows, leads to heavy wear of slide valves 10. In order to keep these pressure differences in bounds, pressure compensation pipes not represented in greater detail are required in the known arrangement between solids bins 6, 7 and 8, on the one hand, and between the gas system of melter gasifier 1 and the reduction vessel, on the other hand. Fig. 2 shows the dust recycling system according to the invention. The solid separated in hot cyclone 4 is conveyed into vessel 18 integrated at cyclone outlet 17. In this vessel 18, which is provided with a refractory lining, a sloping grate 19 is installed, which serves to separate large particles such as coal or coke lumps, which are withdrawn from vessel 18 via tapping hole 20 in case of need. From hot cyclone 4, the solid which vessel 18 -which has no function during normal operation - is dispersed with by free fall is sucked by injector 12 via solids discharge pipe 9 designed as downpipe. Downpipe 9 is cylindrical or expediently tapered, expanding downwards in order to avoid clogging. Expediently, it is also provided with a refractory lining. From injector 12, solids recycling duct 14 leads to dust burner 15. Injector 12 is preferably operated at a supercritical pressure ratio, i.e. the velocity of the propellant gas fed via the injector via pipe 13 is equal to or greater than sound velocity. E.g. nitrogen or cooling gas, such as cooled reducing gas, can be used as propellant gas. Underneath propellant nozzle 22 proper, injector housing 21 changes into collecting tank 23, in which coarse-grained particles, such as flakes or pieces of the lining, which may lead to clogging, are caught. To be able to discharge coarse-grained particles, bottom 24 of collecting tank 23 is provided with an outlet with shut-off element 25 or a pressure sluice (not represented here). To facilitate the withdrawal of particles, fluidization elements 26, such as an annular nozzle, purging elements made of refractory material, elements of sintered material, nozzles in the form of self-closing valves, etc., may be provided in tank bottom 24. The fluidization gas may simultaneously act as secondary gas for injector 12. Fluidization is adjusted in a way that fine particles can be exhausted by the injector and blown off and only coarse particles accumulate. In the arrangement according to the invention, shut-off elements 27 at the entry of downpipe 9 and upstream of dust burner 15 are only provided for repair and maintenance purposes. In case of any problems occurring during operation, vessel 18 connected downstream of hot cyclone 4 can thus also serve as buffer tank, with shut-off element 27 being closed. In order to prevent the solids from settling in this case of emergency, fluidization elements 26 are also provided at tank outlet 28, i.e. at the transition to downpipe 9. The invention is not limited to the described embodiment but can be modified in various respects. It is not only applicable to melter gasifiers but particularly to reactor vessels 1 of any type where solids are discharged by means of an off-gas. We Claim:- 1. Process for recycling a fine-particulate solid, such as coal and iron particles, discharged from a reactor vessel (1), in particular a melter gasifier, by a carrier gas at a discharge point (at 2) of the reactor vessel (1), at a recycling point (at 15) of the reactor vessel (1), wherein the solid is separated in a solids separator (4), in particular a cyclone, and subsequently recycled into the reactor vessel (1) by a carrier gas such as herein described, maintaining a pressure difference between the solids separator (4) and the recycling point (at 15), and - partially gasified and/ or burnt upon entry into the reactor vessel (1) under the supply of oxygen, characterized in that the separated solid is directly and continuously exhausted from the solids separator (4) by a propellant gas under injector action, accelerated, and conveyed to the reactor vessel (1). 2. A process as claimed in claim 1, wherein the velocity of the propellant gas flow is equal to or greater than sound velocity upon coming into contact with the solid. 3. A process as claimed in claim 1 or 2, wherein the solid is filtered after separation. 4. A process as claimed in one or several of claims 1 to 3, wherein the solid is fluidized after exiting the solid separator (4). 5. A process as claimed in one or several of claims 1 to 4, wherein nitrogen and/ or cooled and cleaned process gas is used as propellant gas. 6 An apparatus for carrying out the process as claimed in one or several of claims 1 to 6, with a reactor vessel (1), in particular a melter gasifier, a gas discharge duct (2) departing from a reactor vessel (1) and leading to a solids separator (4), in particular a cyclone, from which a solids discharge duct (9) conveying the separated solid to an injector (12) departs, and with a solids recycling duct (14) leading from the injector (12) to the reactor vessel (1) and opening into the latter via a dust burner (15), characterised in that the solids separator (4) is connected with the solids recycling duct (14) and, thus, with the dust burner (15) via the injector (12) by a continuous line. 7 An apparatus as claimed in claim 7, wherein a coarse filter (19) is connected downstream of the solids separator (4). 8. An apparatus as claimed in claim 7 or 8, wherein a solids tank (18) is connected downstream of the solids separator (4), said solids tank (18) being provided with a fluidization element (26) upon transition into the solids discharge duct. 9. An apparatus as claimed in one or several of claims 7 to 9, wherein the injector (12) is comprised of a solids collecting tank (23) designed as bag tank, which is provided with a drain hole that can be closed with a shut-off element (25). An apparatus as claimed in claim 10, wherein the solids collecting tank (23) is provided with a fluidization element (26) in the area of the bottom (24). An apparatus as claimed in one or several of claims 7 to 11, wherein the solids discharge duct (9) steadily expands from the solids tank (18) towards the injector (12). Process for recycling a fine-particulate solid substantially as herein described with reference to the accompanying drawings. 3. An apparatus for carrying out the process substantially as herein described with reference to the accompanying drawings.

Documents:

3130-del-1997-abstract.pdf

3130-del-1997-claims.pdf

3130-del-1997-correspondence-others.pdf

3130-del-1997-correspondence-po.pdf

3130-del-1997-description (complete).pdf

3130-del-1997-drawings.pdf

3130-del-1997-form-1.pdf

3130-del-1997-form-13.pdf

3130-del-1997-form-19.pdf

3130-del-1997-form-2.pdf

3130-del-1997-form-3.pdf

3130-del-1997-form-4.pdf

3130-del-1997-petition-137.pdf

3130-del-1997-petition-138.pdf