METHOD FOR MELTING ROCK MATERIAL FOR MINERAL FIBRE PRODUCTION

Abstract: The invention is related to a method of melting rock material for the manufacture of mineral fiber. In the method, the crushed rock material and the amount of fuel, proportionated according to the quantity of the rock material, together with a possible introduction of additive ingredients, are introduced into a shaft furnace, and combustion air possibly complemented with auxiliary fuel is introduced into the bottom part of the furnace in order to create a melting zone. The melted rock material is discharged from the furnace bottom. According to the method, at least a portion of said additive ingredients is introduced along with a carrier medium directly into the melting zone or its immediate vicinity.

Description: Method for melting rock material for mineral fibre production The present invention relates to a method of melting rock material into a smelt used for manufacturing mineral fiber. The method according to the invention is implemented by performing the melting in a shaft furnace in which the rock material and the amount of fuel proportionated according to the quantity of the rock material is fed into the furnace via an inlet at the top thereof . The rock material is crushed to a proper particle size. Also the particle size of coke conventionally used as the fuel is selected appropriately. Typically, the rock material and coke are charged into this type of furnace in layers, whereby the pile of layered raw materials sinks in the furnace downward as the lower end of the pile melts in the melting zone formed in the bottom part of the furnace and is discharged from the furnace bottom. To maintain the melt zone at the bottom of the furnace, air is injected upward at a suitable height from the furnace bottom into the mixture of rock material and fuel. The flue gases formed in the fuel combustion process rise through the pile of rock material and fuel until reaching the top of the furnace to be discharged therefrom. To ensure an unobstructed passage of flue gases through the pile, the particle size in the pile must be sufficiently large to provide an appropriate free space about the particles. To feed the combustion air into the melting zone, injection nozzles of a special construction are used. The melt formed is collected on the furnace bottom into a pool of suitable height by allowing the excess melt to discharge over a weir disposed slightly above the level of the furnace bottom. This pool formation serves to equalize the short-term fluctuations of the melt qualities. However, 2 the average composition of the melt must be controlled by adjusting the composition of the raw materials to be melted, that is, by adding suitable ingredients to the in- feed material mix. In conventional techniques, the composition of materials being melted is controlled by sampling the melt, and based thereon, adding the required raw material components to the top of the furnace, into the infeed mix of rock material and fuel. Such a melt control technique is primarily hampered by the finite transport delay of the added component along with the rock material to the bottom of the furnace. This delay brings about a significant uncertainty factor to the material composition control and, in spite of predictive calculations and estimations, inaccuracy of control results. Hence, the composition of the melt is difficult to keep within the set limits. In the view of present knowledge, however, it is most essential for certain properties of manufactured fiber to keep the mutual proportions of prescribed raw material components within tight limits. It may be required from a fiber with a composition falling within these limits to provide, e.g., such physiological compatibility require- ents that are set for the fiber by authorities as a prerequisite for its use in some specific application. These properties are generally controlled by complementing the rock material to be melted with additive ingredients such as bauxite for adjusting the aluminium compound content, apatite for adjusting the phosphorus compound content, boron compounds and titanium compounds. The introduction of these additive ingredients at the top of the furnace into the mix of rock material and fuel causes problems of a different type. Firstly, the additive ingredients tra- veiling downward in the raw material pile will be subjected to a relatively long period in contact with the hot flue gases, which leads to loss of additive ingredients 3 through evaporation. Particularly apatite and boron compounds are problematic in this respect. On the other hand, some of the additive ingredients such as bauxite and titanium compounds are slowly melting requiring their grinding to a substantially smaller particle size than the rock material and the fuel . When mixed into the pile of coarser materials, the fine particulate matter causes problems to the passage of flue gases through the material pile as well as loss of material due to entrained transport of material dust, whereby the elimination of these problems necessitates briquetting of additive ingredients into sufficiently large agglomerates. An essential improvement regarding the above-described problems associated with the introduction of additive ingredients has been found by virtue of the present method according to which at least a portion of said additives is introduced along with a carrier medium directly into the melting zone or its immediate vicinity. Then, the additive ingredient can be introduced into the furnace along with the combustion air. Alternatively, the additive ingredient can be mixed with an auxiliary fuel which may be a gaseous, liquid or fine-ground solid fuel. Also the combinations of the above carriers can be used for introducing the additive ingredient. In the method according to the invention, a change in the feed rate of an additive ingredient will affect the melt composition with a substantially shorter delay, which obviously offers an improved control precision over the prior art. Also the other problems mentioned above in regard to evaporation, dusting and slow melting rate are better controlled by virtue of the present invention. In the method according to the invention, the melt composition can be primarily controlled using conventional coarse control techniques, so that the initial charge of 4 basic materials known beforehand to be in short supply in the melt and also known to behave rather unproblematical- ly in the melting process, are added slightly undercompensated into the melting furnace. Then, the special cha- racter of the present invention can be utilized for fine control of the melt composition and the introduction of hard-to-melt additive ingredients. According to a specific embodiment of the invention, the introduction of the additive ingredient along with its carrier medium can be complemented by feeding enriching oxygen into the melting zone, whereby the feed rate of oxygen addition is adjusted compatible with the actual composition of additive ingredients thus creating advan- tageous conditions for the melting thereof in melting zone. Due to the presence of carbon, the overall conditions in the melting zone are reducing. The degree of reducing conditions can be decreased by the oxygen addition, or even reversed into oxidizing conditions if the excess amount of oxygen addition is sufficiently large. The introduction of the enriching oxygen is advantageously carried out separately from the introduction of additive ingredients and also is provided with an independent control facility. This can be accomplished by different types of injection nozzle constructions having separate channels on one hand for the additive ingredient (s) and its carrier and on the other hand for the enriching oxygen. One problematic issue particularly concerning the preparation of melt for the manufacture of mineral wool deals with the physical properties of the melt. The most important of these is the viscosity of the incoming melt at the fiberizing unit. The melt viscosity is primarily affected by the melt composition and temperature. For instance, the available raw material and/or the raw material 5 mix giving the desired melt composition may be such that melts at a high temperature requiring the melt to kept at a high melt temperature, too. This melt pool temperature, however, may be excessively high to maintain the optimal viscosity, which subsequently causes problems in the fi- berizing stage. The method according to the invention can offer a solution to problem by allowing the introduction of such an additive ingredient that has no significant effect on the melt composition. Advantageously, the mel- ting of such an additive ingredient binds heat thus lowering the melt temperature. One useable additive for this purpose is recycled fiber, preferably in milled form. The control of melt composition by virtue of the method according to the invention may also be used for controlling the composition-dependent viscosity of the melt. The implementation of the invention may be accomplished by means of conventional infeed equipment based on, e.g., the use a carrier gas flow into which solid particulate matter is introduced with the help of a separate feed apparatus . The feed apparatus in an embodiment of such equipment comprises a rotating compartmental feeder adapted centrally in a cylindrical container, said feeder having its compartments bordered by the cylindrical shell of the container and its end surfaces. The carrier gas flow is provided with opposite aligned inlet and outlet nozzles, respectively, at the opposite ends of the cylindrical container thus permitting the carrier gas flow to entrain the solid particulate matter loaded in the com- partments as they sequentially meet the opposed nozzles.

Claims: 6 Claims 1. Method of melting rock material for the manufacture of mineral fiber, in which method the crushed rock mate- rial and the amount of fuel, such as coke, proportionated according to the quantity of the rock material, together with a possible addition of additive ingredients, are introduced into a shaft furnace, combustion air possibly complemented with auxiliary fuel is introduced into the bottom part of the furnace in order to create a melting zone, and the melted rock material is discharged from the furnace bottom, characterized in that at least a portion of said additive ingredients is introduced along with a carrier medium directly into the melting zone or its im- mediate vicinity. 2. Method according to claim 1, characterized in that the combustion air and/or the auxiliary fuel is used as the carrier medium. 3. Method according to claim 1 or 2 , characterized in that the feed rate of the additive ingredient (s) is controlled by monitoring the melt qualities such as its composition and/or temperature. 4. Method according to any of foregoing claims, characterized in that besides the introduction of the additive ingredient along with the carrier medium, also enriching oxygen is fed into the melting zone. 5. Method according to claim 4, characterized in that the feed rate of enriching oxygen is controlled based on the composition of the additive ingredient (s) .

Inventors: LAUREN PETER, PERANDER MICHAEL, TAMMINEN KIMMO, LAUREN, PETER, PERANDER, MICHAEL, TAMMINEN, KIMMO
Applicants: LAUREN PETER, PARTEK PAROC OY AB, PERANDER MICHAEL, TAMMINEN KIMMO, LAUREN, PETER, PERANDER, MICHAEL, TAMMINEN, KIMMO
Application year: 1999
Main classification: C03B5
IPC codes: C03B3, C03B5