WO1982000460A1

WO1982000460A1 - A method and an apparatus for the production of a melt

Info

Publication number: WO1982000460A1
Application number: PCT/SE1981/000213
Authority: WO
Inventors: L Bjoerklund; I Faeldt
Original assignee: L Bjoerklund; I Faeldt
Priority date: 1980-07-25
Filing date: 1981-07-10
Publication date: 1982-02-18
Also published as: SE8005400L; EP0057195A1; SE8101701L

Abstract

A method and an apparatus for the production of a melt (42) from minerals and/or raw materials preferably for mineral wool. The method is performed in a process furnace (10, 26) that at a first place is equipped with an adjustable feed opening (24) for the lumped raw material (18) and at a second place (26) with an inlet opening for a process gas that is heated by a plasma in a plasma generator (32) to a high temperature. A mixing chamber (38) is arranged to receive the process gas before it is let into the furnace. To the mixing chamber (38) a number of feed devices (45, 46, 48) are conducted and through which a fine particle fraction of the material, solid fuel resp. waste material can be introduced into the mixing chamber. Further there is a recirculation pipe (50) for the recovery of process exhaust gases from the upper part of the process furnace (16) to the plasma generator (32).

Description

A method and an apparatus for the production of a melt

This invention concerns a method for tiie production of a melt from minerals and/or raw materials, especially for mineral wool. At the procedure the basic energy generating properties of a plasma are used in order to perform a number of very important improvements regarding both the flexibility in the choise of energy and material efficiency and further by simple means governing an efficient emiss ion control during the operation. The invention also concerns an apparatus to perform the new method.

Methods for melting the mentioned material are in itself known and are comprising of simple and well-established technology. So melting of lumps of raw material in a cupola furnace by using coke as a fuel may be mentioned.

Also electric melting using either resistance heating or arc/resistance heating is practiced in a certain amount.

The drawbacks of the methods mentioned are regarding now existing opportunities and requirements however numerous and partly decisive.

The main purpose of the invention is to bring about a method and an apparatus as was mentioned in the introauction, so simplifying the well-known technology and the production of the mentioned melt can be performed in many ways in order to get a cheap and competative final product. This is achieved by the invented method, primarely by feeding the material as lumps at a first place of a process furnace, and a high temperature process gas heated by a plasma generated in a plasma generator is introduced at a second place and so supplying at least part of the energy required for the melting of the raw material feed.

In order to perform the very sensitive process in a cupola furnace shaft the feed must be restricted to a very limited particle fraction and all the fines produced by the milling operation can not be used in the process without a very expensive additional agglomeration process. Alternatively a costly dumping must be accepted.

By using the invented method the whole fine particle fraction can be utilized by being injection charged and brought together with the high temperature process gas generated in the plasma generator. The fine particle fraction will in this way also contribute to the temperature control at this process stage. A further advantage of the invention is the reuse of practically all process waste as slag granules, fibrous material and/or waste material and so contributing to the over all process economy and the mentioned fine particle fraction can be used either as a raw material substitute or as an energy carrier.

One of the more pronounced drawbacks of the cupola furnace is its requirement of high grade metallurgical coke as an expensive and. abating fuel. The method using metallurgical coke, with applications as an advanced reductant in large blast furnaces, only as a fuel for just melting the oxidic material is of course something very doubtful.

By the invention new and unique opportunities are created in order to use fuels characterized by accessibility as well as cheapness. This is achieved by the ability of the invented method of using plasma technique characterized by giving a very high energy concentration in the plasma formed by the carrier gas, coke gas, recirculated gas and/or some waste gas which at the very high temperature in the plasma generator do not form a gas aggressive to the construction material. In connecion with the necessary temperature drop in the process chamber immediately in front of the entrance into the reaction chamber solid, liquid and gaseous fuel can be introduced into the expanding plasma and so forming a process gas. This process gas can according to the process requirements be given a varying content of carbon monoxide and hydrogen. Among the potentials fuel coal and lignite are according to their low price of the lower qualities that can be utilized in the new procedure very interesting fuel alternatives.

If the process of various reasons should call for a smooth temperature profile, the gas temperature in the front of the reaction chamber can be lowered by converting part of the fuel's carbon content by a recycled process gas rich in carbon dioxide and water vapour to carbon monoxide and hydrogen and so being able to generate energy by the final combustion further in the process.

The central process step in order to produce a melt has been given an increased interest by the opportunity to use the high temperature region of the furnace in decomposing various waste materials formed both in the following process steps and in other processes within a plant. The method of using the plasma technique for melting the actual material is according to the generated high temperature and reaction intensity giving unique opportunities by a simultaneous recovery of the waste bound energy.

The cupola furnace is in connection with melting basalt known to give a very unsatisfactory combustion of the various gases as carbon monoxide, hydrogen sulphide, carbonoxy sulphide, carbon disulphide and other sulphur compounds. This fact is on the other hand easy to understand according to the badly defined mass transfer at the solid/gas contact between the charged coke and the oxygen in the process gas. According to the invention the final combustion is completed in a turbulent gas/gas contact in the charge column also giving a well defined oxidation potential due to a well defined reaction system. The decisive effect of the invention regarding a heavily decreased emission is however the opportunities of the plasma technique to generate a process gas of a high energy density. So it is possible to produce immediately after the plasma generator a process gas with an energy content of 3-4 kWh/Nm³ with for instance a corresponding value at the combustion of coal and coke of only 0,3-0,4 kWh/Nm³. The greater part of the total energy generated by plasma energy the lower amount of process gases - and simpler and cheaper gas cleaning work is required.

The selected partition of energy between on one side plasma energy and on the other side combustion energy from the carrier gas and coal or other solid fuels is finally determined by the balance between energy cost, process requirements related to as for instance the temperature profile and the cost of the exhaust gas cleaning. As distinguished from for instance the cupola operation great opportunities for the control of the total energy supply as well as the temperature profile and oxygen potential are at hand according to this invention. Especially the oxygen potential is important in order to avoid or at the best strongly eliminate the risks for the reduction of iron that is a serious draw-back at the traditional cupola operation used for the melting of basalt.

The developed process according to the invention can in order to melting materials be performed in a process furnace of a type shown in the drawing. The furnace is illustrated in a simplified way and in a side projection.

The combustion or process furnace comprises of a vertical chamber of shaft 10, comprising a sintering/melting zone 12, a secondary zone 14 and an aftercombustion zone 16. In the secondary zone 14 as well as in the after-combustion zone 16 the temperature control regarding the material 18 being charged in to the upper part of the shaft is maintained by an adjustable lock 24. For this purpose in itself well-known but not shown in the drawing air feed equipment is used. The material 18 either as a primary material as lumps of suitable size or a material in advance crushed to lumps, are stored in a material storage 20 with a control device 22 for charging through the above mentioned charging lock 24.

At the lower part of the shaft 10 there is a horizontal en larged part 26, comprising of a conditioning zone 28, where an eventual tapping of formed metal 30 is taking place. A plasma generator 32 with parts 34, 36 for the supply of electric energy and water cooling is connected with a mixing zone 38. The produced melt 42 is discharged at the discharging devices 40 and is further spun with conventional devices 44 in a conventional way to produce stone wool, glass wool or the like. In the mixing zone 38 that is directly connected to the conditioning zone 28 process gas is fed from the plasma generator 32. Over separate feed pipes 45, 46, 48 it is further possible to feed a fine fraction of the material 18, solid fuels resp. waste into the mixing chamber 38. There is further a recirculation system 50, through which exhaust gases from the sintering and melting zone 12 are withdrawn above the charge level in the shaft 10 and are recirculated to the plasma generator 32 over scrubbers and filtering devices 52 resp. 54 in order to be utilized in the process gas. In connection with the exhaust gas system 50 there are close to the afterccmbustion zone 16 devices 56 for the disharge of sludge. In connection to this (at 58) the flow control is taking place. Close to the filtering devices 54 is also a cyclone 60 connected in a traditional way.

At the operation of the new process the material 18 in the form of lumps is fed over the lock 24 into the brick-lined shaft 10. The escaping process gas is finally burnt in the aftercombustion zone 16 before the entry into the gas cleaning section. The charge is passing downwards under a temperature increase by burning of process gas at different levels in such a way that the charge column will start melting at the intended place in the shaft and from the charge formed gases are burnt as intended.

A correct control of temperature and oxygen content is regulating the combustion. The charge column reaches the final melting at the brick-lined horizontal part of the furnace 26 and is exposed to the superheated melt as well as hot process gases. The melt is overheated to a suitable temperature for the subsequent manufacturing process by heat transfer from the hot gases immediately after the plasma generator 32 and by heat radiation from the furnace surfaces. Eventually formed iron is collected in the furnace bottom and is tapped in a convenient manner through the tap hole 62. The melt is tapped continuously. Close in the front of the opening of the plasma generator a mixture of fine material, waste fibres or waste and different fuels like fossile fuels are injected. At the same place also different so called non-process waste may be injected for a total decomposition in the hot part of the furnace. In order to achieve a more even temperature profile and to form a process gas for the final combustion in the shaft 10 recirculated and fully burnt process gas can be introduced at this stage. The exhaust gas cleaning may take place in the simplest way by a primary SO₂-absorption in a quasi-dry slurry scrubber 52. The neutralized product formed is separated either in a combination of the cyclone 60 and in the filtering devices 54 or alone in the filtering devices , and the clean exhaust gases are conducted to a stack 64 over a fan (not shown) .

The combustion furnace may of cource be modified in many different ways. This is especially actual for the lower part of the furnace. It is thus also possible to exclude that part of furnace 26 and to arrange for the feed of the process gas at the lower part of the shaft. In this case it is convenient to use a special feeder located at the lower part of the process furnace and that is equipped with temperature control instruments for the regulation of the final melt temperature.

It also ought to be mentioned that the shown furnace after a simple modification can be arranged as a special waste decomposition furnace . In this operation no charge is fed into the shaft. The furnace shall instead have a more horizontal design and the feed of waste to be decomposed is located close to the plasma generator.

Below two different calculations concerning the operation with a varying portion of plasma energy will be given;

Example no 1:

Recalculated to one metric ton of molten basalt with the following analysis: SiO₂ 40-42 per cent, CaO 16-18 per cent, MgO 8-9 per cent, Feo 8-9 per cent, Al₂O₃ 14-16 per cent the following energy consumption is achieved: Electric energy to the plasma generator 410 kWh LPG 8,2 Kgs corresponding to 102 kWh Coal 152 Kgs corresponding to 505 kWh or per metric ton of molten basalt 1017 kWh

The produced exhaust gas is calculated to approx. 1700 Nm³

Example no 2:

In order to decrease the exhaust gas quantity from the combustion of coal considerably, exhaust gases are recirculated to such an amount that the supplied electric energy to the plasma generator - 850 kWh per metric ton of molten basalt - can be distributed to at least 150 Nm³ of carrier gas or with an energy content of approx. 6 kWh/Nm^3.

By this performance the exhaust gases from the combustion of 7,8 Kgs of LPG or approx. 50 Nm³ must be mixed with additionally approx. 100 Nm of recirculated process gas

The following figures per one metric ton of molten basalt are achieved:

Electric energy to the plasma generator 850 kWh LPG 7,8 Kgs corresponding to 97 kWh or per metric ton of molten basalt 947 kWh

Claims

1. A method for the production of a melt from minerals or raw materials, preferably for mineral wool, character ized in that the material (20) as lumps is charged at a first place (24) of a process furnace and that a process gas heated to a high temperature by a plasma in a plasma generator (32) is introduced at a second place (26) in order to supply at least part of the energy necessary to melt the material.

2. A method according to claim 1, characterized in that a present fine particle fraction of the material or a fine particle fraction formed at the crushing of the material and normally not fed at the first place of the process furnace without agglomeration, is before the entry into the process furnace mixed with a high temperature process gas from the plasma generator (32) .

3. A method according to claims 1 or 2, characterized in that waste - solid, liquid or gaseous - is introduced into the high speed process gas coming from the plasma generator (32) and the waste is melted and recovered and/or decomposed under the recovery of energy.

4. A method according to any of claims 1 to 3, characterized in that a solid fuel like coal, lignite, peat, chips or the like is introduced into the high temperature process gas from the plasma generator (32) .

5. A method according to any of claims 1 to 4, characterized in that the process gas at least partly is finally burnt in the upper part of the furnace (16) above the raw material level by adding tempered combustion air at different levels in the shaft.

6. A method according to any of claims 1 to 5, characterized in that at least part of the process exhaust gas is recirculated to the plasma generator (32) in order to form the carrier gas that also can include natural gas or the like.

7. A method according to any of claims 1 to 6, characterized in that solid fuels are separately gasified and that by this operation formed process gas is used as a carrier gas in the plasma generator (32) and/or as a process gas in the production procedure.

8. An apparatus for the production of a melt from minerals and/or raw materials, preferably for mineral wool according to the method mentioned in claim 1, characterized in that it comprises a process furnace (10, 26) that at a first place is equipped with an adjustable lock (24) for the particulate raw material (18) and at a second place (26) equipped with an inlet for a process gas heated to a high temperature by a plasma in a plasma generator (32) .

9. An apparatus according to claim 8, characterized in that a mixing chamber (38) is arranged to receive the process gas before the entry into the process furnace.

10. An apparatus according to claim 9, characterized in that a first feeding device (45) is leading to the mixing chamber (38) and through which a fine particle fraction of the material can be introduced into the chamber (38) .

11. An apparatus according to claim 9 or 10, characterized in that a second feeding device (48) is leading to the mixing chamber (38) for the feeding of waste material.

12. An apparatus according to claims 9, 10 or 11, characterized in that a third feeding device (46) is leading to the mixing chamber (38) for the feeding of solid fuel.

13. An apparatus according to claims 9 , 10 , 11 characterized, in that a third feeding device is leading to the process furnace (10, 26) for the feeding of solid fuel.

14. An apparatus according to any of claims 8 to 13, characterized in that it comprises a pipe (50) for recirculating process exhaust gases from the upper part of the process furnace (16) to the plasma generator (32) .

15. An apparatus according to any of claims 1 to 14, characterized in that the lower part of the furnace comprises a broadened part (25) .

16. An apparatus according to any of claims 1 to 15, characterized in that the place for the introduction of the process gases into the process furnace is adjustable depending on the material composition.

17. An apparatus according to any of claims 8 to 16, characterized in that a feeder at the lower part of the process furnace and equipped with temperature regulating devices is arranged in order to regulate the temperature of the melt at the tapping point.