CA2678169A1

CA2678169A1 - Method and apparatus for preparing a slag melt in a medium frequency induction furnace for producing slag wool fiber materials

Info

Publication number: CA2678169A1
Application number: CA 2678169
Authority: CA
Inventors: Yongqiang Guo
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-09-03
Filing date: 2009-09-03
Publication date: 2011-03-03

Abstract

A medium frequency induction furnace, in particular directly employed blast furnace slag in molten state as raw materials. The induction furnace includes an induction coil attached with refractory material tamped inner chamber as upper piece of furnace; and a non-magnetic inductive hollow member dispose below the upper chamber of furnace as lower piece of furnace.
The upper piece of furnace and lower piece together consist of furnace chamber for further heating and regulating the molten slag materials. An electromagnetic conductive member disposed within furnace chamber and a cover on the top of furnace to further improve heating efficiency. Along with an outside furnace shell, a bottom of furnace, water cooling system, feeding charges system and associated power supply system. The induction furnace feeding with molten slag for further heating and regulating in order to meet the required temperatures, composition and viscosity for producing the slag fiber materials.

Description

Description of the invention Summary of the invention This invention relates to a method for producing slag wool fibre materials, in particular directly employed blast furnace slag in molten state which obtained from Blast furnace and feeding into the medium frequency induction heated furnace as raw material to further heat and regulating. More particularly, the present invention relates to methods and process to manufacture slag wool fibers material in energy efficient and environment friendly manner.

Background of the invention Slag wool or mineral wool counts among the most frequently employed materials in thermal protection, noise control and fire-proofing applications. The base material used for slag wool is blast furnace slag.

The common way of producing mineral wool or slag wool fibres is mixed iron slag, correction materials and coke in a cupola furnace where the coke is burn in order to melting of slag or rock material at temperature around 1500 degree C. This traditional method has been used for over 100 years basically produced in two stages. In the first stage transport the air cooled or water cooled slag which occurs in the blast furnace by-products to the slag wool manufacturer's working field. In the second stage mixed slag, coke and other materials into a cupola furnace. The fibre is produced by melting a mixture of blast furnace slag and other minerals in a coke-fired cupola. The additional correction minerals, such as silica creek gravel or granite, are added to the raw material to control the melt chemistry and the viscosity of the melt. The molten slag is directed to a spinner where the fibre forming takes place. The final products are commonly insulating boards used for thermal insulation, sound and fire-proofing purposes.

The manufacture of slag wool fibres does involve high energy expenditures.
During the production process cupola furnace use coke to melt the air cooled blast furnace slag and other materials in the c *pola furnace. Thus melting of the raw materials at melting temperatures between approx 1350 degree C and 1650 degree C requires considerable energy expenditure. About 80%
of energy required for the melting process; meanwhile the carbon dioxide emission and dust problems is associated with the melting process.

In addition, the traditional method melting of slag or rock materials in a cupola furnace is connected with a series of problems, the formation of carbon monoxide from carbon dioxide has the effect that the heat content of the coke is only partly used and usually the fuel economy is poor. The traditional methods are also associated with carbon dioxide emissions that are not environmentally friendly.
Moreover, cupola furnaces have only a small productive capacity, because the general trend has been to avoid long transporting of the material which requires a lot of space.
Because of the structure of cupola furnace, the molten period in the material production becomes fairly short, which makes quality control difficult, and thus the final product easily becomes non-homogenous.

This invention is significantly reducing the energy consumption for preparing slag wool fibres materials by using molten slag as base materials that are delivered by slag car, in particular when blast furnace tapping slag during operation. Blast furnace slag as "the non-metallic product consisting essentially of silicates and alumina silicates of calcium and other bases for slag fiber manufacture, is developed in a molten condition simultaneously with iron in a blast furnace. It comes from the furnace in a molten state with temperatures exceeding 1480 C
(2700 F). Blast furnace slag typical chemical constituents are silica 32%-42%, alumina 7%-16%, calcium 32%-45%, Magnesia 5%-15%, sulfur 1%-2%, iron oxide 1%-1.5%.

It is to be noticed here that it is advantage if those high temperature slag are employed as raw materials for slag fibers manufacture. Starting out from the prior described at the outset, it was therefore an object of the present invention to allow the use of molten slag from blast furnace in the manufacture of slag wool fiber materials.

In particular, the invention relates to using medium frequency induction heated furnace to further heating and regulating the molten slag with correction materials in low cost and environment friendly manner. Because of the medium frequency induction heated furnace do not use coke as heating energy resources therefore the carbon dioxide emission and dust problems are not occurred.
Furthermore, the cost for energy is reduced significantly. Using the medium frequency induction heated furnace, large feed batches can be treated at the same time, the manufacturing process becomes quicker, the manufacturing costs are reduced significantly and quality control can be arranged more easily than before. In addition to this, the molten volume within medium frequency induction heated furnace can be advantageously adjusted. This induction furnace are capable of producing a continuous heating and melting in an energy efficient manner, especially for slag wool fibres materials production.

Brief description of the drawings The accompanying drawings illustrate various embodiments of the present invention together with the description, further serve to explain the principles the invention.

FIG1 is a cross sectional elevation view of top cover of the induction furnace.

FIG 2 is a perspective view of a schematic diagram upper inner chamber and lower inner piece of furnace connected together. An induction coil of copper tubes around the upper chamber that heating the furnace rapidly.

FIG 3 is a perspective view of lower inner piece of furnace that is hollow and allowing cooling water go through.

FIG 4 is a sectional view of inner chamber of induction furnace and shows a cylinder shape of conductive member is made from molybdenum disposed on inside wall of upper inner chamber fixed with a support structure.

FIG. I shows a sectional elevation view of top cover of the induction furnace.
The top cover comprises a layer of refractory materials 3 which can prevent the high temperature from the induction furnace chamber. An insulation layer 2 to reduce the heat leakage, the top cover is water cooled equipment therefore, the cooling water go through I a hollow space.

FIG. 2 shows a perspective view of a schematic diagram of the induction furnace. The tamped refractory materials as inner wall I and induction coil 2 attached with it as upper chamber of furnace. The upper piece of furnace, hollow lower piece of furnace and bottom wall consist of the melt chamber of furnace.

FIG. 3 shows a perspective view of lower inner piece of furnace. This diagrammatic perspective view shows clearly that the water inflow from I and out flow at the 2 in order to cool down the lower piece of chamber of furnace that is a hollow and made of stainless. The residual iron which generated during production can be outflow at 4. When the melt chemistry and the viscosity of the slag materials met the requirements, the molten slag go through to 3 the tapping launder to the centrifugally spinner where the fibres are produced. Top edge of lower piece of furnace there are support structure 5 for conductive member.

FIG. 4 shows a sectional view of cylinder shape inner chamber of induction furnace. An induction coil 6 attached with tamped refractory inner wall 5, at the inside of inner wall there is a conductive member 4 for absorb induction energy and further improve heating efficiency.
In between the lower piece of furnace 7 there is an insulation layer 3 to prevent the electromagnetic effect on the lower piece of furnace. A bottom of furnace comprising of electrically non-conductive refractory insulation material 2 usually magnesium brick on plate base 1. On the top of chamber of furnace there is a water cooled support part 9 for the top cover of furnace; the arrow shows the water inflow at inflow hole 8.

Detailed description The present invention is described herein in detail an illustrative embodiment with the understanding that the present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the illustrated embodiment. This invention is particularly useful for slag melting and made to slag fibre materials production, this should not be deemed to limit the scope of the invention. The induction furnace may also be used with non- metallic materials, such as silicon, zirconia and magnesium; heating and melt small sizes solid materials is also an option.

The present invention provides an medium frequency induction furnace comprising an electromagnetic non-conductive tamped inner upper piece of furnace and water cooled hollow lower piece of furnace together defining a furnace chamber; an electromagnetic conductive member disposed on the inside wall of upper piece of chamber for initially absorb induction energy heating slag materials and correction materials within the furnace chamber; and enforce electromagnetic stir power when other correction materials via a feeding system added into furnace chamber; a top cover with cooling system and refractory lining to further prevent heat leakage; an non-electromagnetic conductive outside shell.

The induction furnace upper chamber comprising an induction coil for creating an electromagnetic field to inductively heat slag materials and other correction materials within the melting chamber.
An upper piece of furnace and a lower piece comprising a melting chamber; an electromagnetic conductive member disposed inside of melting chamber; the conductive member and the slag materials within the melting chamber absorbing energy simultaneously from the electromagnetic field together, therefore slag materials and other correction materials are heated rapidly, the furnace is more efficiency.

The present invention as seen, in FIG 2, embodiments provide an unique heating improved medium frequency induction furnace for non-metallic materials melting, especially, for prepare slag wool fiber materials manufacture. The induction furnace inner chamber as a cylinder shape where the molten slag for further heating and regulating that consist of two pieces, the upper piece of chamber and the lower piece of chamber, the upper piece of chamber surrounded by an induction coil, the upper chamber shape as cylinder made of refractory materials; an tamped inner lining as inner wall.
An induction coil surrounds is helical and hollow, allowing the flow of cooling water or other coolants go through. The tamped inner lining is made of refractory material;
such liner is electrically non-conductive and thermally insulating. Because of an induction coil is cooled by water or other coolants and site the outside of tamped inner lining therefore, during operation within the chamber of furnace temperature are extremely high, inner lining are self lined by a thin slag layer of the chilled molten slag. This thin slag layer is perfect for both acid-proof lining and basic-proof lining.

A further heating improve arrangement employed in embodiments is the formation of electromagnetic conductive member made from molybdenum and shape as cylinder site on inner wall of chamber. Due to the less-conductive nature of slag material initially disposed within the furnace chamber at relative lower temperature, the induction coil generate electromagnetic field inductively heats the conductive member, which transfers heat to the slag material to heat a portion of the materials to molten point. Once the slag materials temperature is going up and the melting process has begun, inductive heating of the melt also occurs and the melt continues as a result of both inductive heating directly of the molten slag as well as transferred heat from the inductively heated conductive member. The slag becoming more susceptible the induction coils heating the slag materials rapidly.

In addition, the frequency applied to the coil is preferably initially at a relatively high frequency say at upper range of 1500Hz to 2000Hz and then once the molten slag materials temperature and viscosity meet the requirements the frequency is shifted to a relatively low frequency to better generated an electromagnetic stirring power in order to mix with other solid correction materials to regulate the raw molten slag materials.

The conductive member within the chamber of induction furnace is particularly useful when the induction furnace is temporary shutdown due to maintained or other reasons;
the slag is cool down or finally in solid state, the slag is becoming a less susceptible materials to inductive heating therefore the induction coil electromagnetic are less absorbed by the slag.
When the conductive member is inductively heated by the induction heating system, the heat is transferred to the slag through conduction; therefore, the slag materials are heated rapidly. The cylinder shape of molybdenum part preferably is site on the upper chamber inner sidewall.

With reference to FIG 2, the lower piece of furnace chamber includes a bottom wall and a hollow cylindrical sidewall. Sidewall is formed of a non magnetic susceptible material, such as stainless steel; sidewall has an inner surface with refractory materials attach on the surface. Because of the main function for lower piece of furnace chamber is tapping the molten slag materials to centrifuging spinner; when the melt chemistry and the viscosity of the slag materials met the requirements, the molten slag go through to the tapping launder to the centrifugally spinner where the fibres are produced. Due to there are no further heating required therefore,the lower piece of cylinder chamber account for no more than 30 per cent of total furnace in term of size. The lower piece of furnace chamber is hollow to allow the flow of cooling water go through to prevent the high temperature during operation.

The upper piece of furnace and lower piece of furnace is closely connected together as a furnace chamber in order to prevent the electromagnetic field affect on the lower piece of furnace, a non-electromagnetic conductive layer disposed in between the upper piece of furnace and the lower piece of furnace. As mention before the lower piece of furnace is hollow and in form of stainless steel that allow the water go through cooling the lower piece of furnace.

With reference to FIG 3, furnace includes a top cover and moveable with a lifting mechanism, due to high temperature on the furnace chamber, a top cover is hollow that cooled by a water cooling system; on its inner surface refractory lining is applied. While additional insulation material could be applied between the refractory lining and metal surface. During operation the raw materials and correction materials feeding into furnace chamber simultaneously, a top cover moves back so it's seal the entire chamber of furnace to substantially reduce heat leakage and enhance heating efficiency of the induction furnace. The top cover is releasable connected to the upper piece of the furnace chamber so that it can be easily removed thus providing a convenient mechanism for .-Lgzaw materials and correction materials.

An induction furnace includes a bottom wall and is formed of an electrically non-conductive refractory insulation material usually magnesium brick; in order to prevent attack by iron those magnesium bricks has a layer of clay material on surface. Moreover as mention above there are tap hold on the lower piece of furnace for tapping the residual iron.

In operation, the furnace function as follows, the furnace are being charged with raw material which refers to molten slag is placed into chamber of furnace. Normally slag cars carry that molten slag which as by-product from blast furnace. Due to the distance between the blast furnace and slag fibre materials production location the temperature of molten slag reduced meanwhile, a correction materials such as, silica creek gravel or granite has been added to chamber of furnace simultaneously. The mixed raw materials could be in a semi-liquid or liquid state, once material has been added to furnace chamber a top cover seal the chamber of furnace. The induction furnace is capable of producing a continuous heating and melt in an efficient manner; the chamber of furnace is preferred to keep proportion of molten slag materials and added the lower temperature slag materials and correction materials by dispersing heat over the initial heated raw materials. After relative lower temperature raw materials and solid correction materials are charged into the chamber of furnace. Electrical power is provided from power source to induction coil to create an electromagnetic field to heat raw materials and electromagnetic conductive member which within the chamber of furnace.

In order to expedite the transfer of heat from the coil induction furnace is capable of producing a continuous melt in an efficient manner. The molybdenum cylinder member is initially inductively heated by electromagnetic field whereby heat is connective transferred from the conductive member to raw material. Once the slag materials are heated to relative higher temperature range such as, above 1000 C, the less-conductive slag materials becoming electromagnetic conductive materials, therefore slag materials directly inductively heated by the medium frequency coil the melting and heating process is speed up.

Ow of advantages of the induction furnace is the temperature of slag materials can be controlled preaiion, by control the electric current that go through the induction coil, a better heating penetration and even temperature inside the melting slag can be achieved.

By selection of the frequencies employed in the induction coil, an electromotive or stir force can be created by the electromagnetic field stirring the melting pool to achieve better melting quality. For example frequencies in a range of from about 1500 KHz to about 2000 KHz, the relative lower frequency, the greater electromotive force are generated. This electromotive force push the molten slag materials literally moved with solid correction materials mixed together and helps produce a more uniform composition and temperature throughout the melt. The uniform composition and temperature are key factor for the final slag wool fibre products qualities.

Finally, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described. It will be appreciated that several of the above disclosed and other features and function may be desirable combined into many other different system or applications. Unforeseen from the invention or alternative, modifications or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the invention claims.

Claims

1. The medium frequency induction heated furnace for preparing slag melt for production slag fibres production, in particular molten slag directly employed as raw materials; in which method molten slag as by-products obtained from blast furnace;
delivering the molten state slag by a slag car to the induction furnace; correction materials for regulating the required composition and viscosity of the slag melt are added together via a feeding system. The medium frequency induction heated furnace comprising an upper piece of furnace that having an induction coil disposed outside wall of chamber. An induction coil generated the electromagnetic field to heat the electromagnetic conductive member which disposed within the upper chamber and slag materials simultaneously; the upper piece and lower piece of furnace consist of furnace chamber that contain the liquid slag material; the furnace has a cover that has a lifting mechanism to move the cover of furnace. A lower piece of furnace body have at least one tap-hole to drain the molten slag to the centrifuge; a bottom of furnace; a outside furnace shell, along with its associated power supply system and water cooling system as well as a feeding system for correction materials.

2. The medium frequency induction heated furnace as defined in claim 1, wherein upper inner chamber is comprising a tamped refractory liner defined as inner wall;
the shape of upper piece of induction furnace is cylindrical; an induction coil embodied with the tamped liner consist of inner upper piece of furnace that the induction coil helical turn lined as cylindrical in shape; the liner wall of upper piece of furnace are self lined by thin slag layer of the chilled molten slag particularly against the water cooled walls of the hearth area.

3. The medium frequency induction heated furnace as defined in claim 2, wherein an induction coil that made from copper or steel tubing with a 1/8" to 3/16"
diameter, cooled with water inside the tube, the size and shape of the coil single or multiple turn is reflect the shape of the upper piece of furnace and variables of volume process. The induction coil which generates the medium frequency electromagnetic field to heat raw materials and the electromagnetic conductive member that disposed on the inner wall of upper piece of furnace.

4. The medium frequency induction heated furnace as defined in claim 3, wherein the water cooled induction coil are multiple round turn and the distance between each coil is less than 15 millimetres; the distance between each coil at the range of 10 millimetres to 15 millimetres.

5. The medium frequency induction heated furnace according to claim 2, wherein the induction coil are bolted on a support structure that is fixed with the inner wall of outside shell of furnace.

6. The medium frequency induction heated furnace in claim 2, wherein the upper piece of furnace body further comprises of an electromagnetic conductive member disposed on inside wall of upper chamber; preferably the electromagnetic conductive member is made of molybdenum; the shape of the conductive member is cylinder; the conductive member is further improve the electromagnetic stirring effect when the molten slag material with other correction materials in order to control the melt component and the viscosity of the slag melt.

7. The medium frequency induction heated furnace in claim 6, wherein an electrical current passes through the induction coil to produce an electromagnetic field; the electromagnetic conductive member absorb energy from the electromagnetic field and transfer the heat to raw materials and correction materials.

8. The medium frequency induction heated furnace in claim 6, wherein the conductive cylindrical member is fixed on the inside wall of inner chamber of furnace;
prefer close to lower section of tamped inner chamber due to the furnace at least partly filled with liquid slag; and the level of liquid slag in furnace variable when the molten slag charged as raw materials by slag car.

9. The medium frequency induction heated furnace in claim 1, wherein the molten slag as raw materials is charged through the top of induction furnace; the cover of induction furnace inner lined with refractory material; a water cooling system applied on the hollow top cover; a lifting mechanism move the cover fully open when a slag car drop the molten slag into the induction furnace chamber or adding additional solid correction materials.

10. The medium frequency induction heated furnace in claim 9, wherein continuous and intermittent added correction material is provided by a feed mechanism for adding other solid correction materials to the melting chamber; the solid correction materials have a grain size of 0 to 30mm.

11. The medium frequency induction heated furnace according to claim 2, the working frequency in a range of from about 1500KHz to 2000KHz, the frequency is adjusted to enforce the electromagnetic stirring power, the lower the frequency the more stir power generated, therefore, the molten slag materials and other solid correction materials mixed together uniformed.

12. The medium frequency induction heated furnace in accordance with claim 11, wherein the induction coil has electromagnetic stirring effect which could be adjusted via the frequency that mixed with molten slag materials and other solid correction materials to meet the viscosity and composition requirements.

13. The medium frequency induction heated furnace in claims 2, further comprising temperature detecting element to monitor the temperature of molten slag in the chamber of furnace; the temperature of molten slag is adjusted by control the electronic current power through the induction coil; the temperature of molten slag in the chamber of furnace can be controlled within the range of ~ 5°C.

14. The medium frequency induction heated furnace according to claim 1, wherein the furnace is used for slag wool fibres material production further comprises a lower inner piece of furnace; the stainless steel lower piece of furnace is a hollow cylindrical in shape and the size match with upper inner piece of furnace body; the lower piece of furnace is located between the upper inner chamber and the furnace bottom; the lower piece of furnace has a water cooling system; and has at least one tapped hold for residual molten metals which collect in the center of the hearth and are periodically tapped from the tapped hole of the furnace.

15. The medium frequency induction heated furnace according to claim 14, wherein the lower inner piece of furnace at least has one tapping launder for the molten slag flow to the centrifuge where the fibres are formed; the tapping launder are water cooled;
the tapping launder is made from steel.

16. The medium frequency induction heated furnace according to claim 14, wherein the water cooled tapping launder has a control gate directing the flow and volume of molten slag to the centrifugally spinner.

17. The medium frequency induction heated furnace in claim 14, wherein the stainless steel lower inner piece of furnace and the upper inner chamber of furnace in between at the edge of the two piece of furnace have a layer of non-electrically conductive refractory insulator to prevent the electromagnetic field effect on the lower piece of furnace.

18. The medium frequency induction heated furnace in claim 14, wherein the lower inner piece of furnace is water cooled and has at least two change holes for cooling water inflow and out flow and has at least one hole for residual materials within the cooling water tapped outside.

19. The medium frequency induction heated furnace according to claim 1, further has comprising detector to monitor the temperature of the cooling water which coming from the induction coil; for the lower inner piece of furnace water cooled system and a cover of furnace water cooled system has separate temperature detector.

20. The medium frequency induction heated furnace in claim 1, wherein the bottom wall of the furnace is made of magnesium brick and has a layer of clay material applied on the surface of magnesium brick to protect the hearth from molten charge and particularly from attack by iron.

21. The medium frequency induction heated furnace according to claim 1, wherein the outside shell of furnace is made of non-magnetic material; commonly is aluminium. The shape of outside shell is cylindrical.

22. The medium frequency induction heated furnace in any of claims 1 to 15 in which the cooling system for the cover of furnace; the cooling system for the induction coil part; the cooling system for the lower piece of furnace; the cooling system operate separately for each pieces of furnace, and the each piece of cooling system has it's own temperature sensor to monitor the water temperature.