JPS60216950A - Reconditioning method of molding sand - Google Patents

Abstract

PURPOSE:To maintain the inside of a fluidized roasting furnace in a natural roasting state in the stage of making molding sand roast naturally in said furnace by adding a powdery or granular combustible material to the molding sand or the fluidized bed in the furnace when the content of the combustible material in the molding sand is low or zero. CONSTITUTION:The molding sand a2 is roasted in the fluidized bed 11 in the furnace 1 and is then allowed to flow into a fluidizing air heating part 4 right under said bed to heat the fluidizing air up to about the roasting temp. by a heat exchanger 10 in the heating part 4. The heated fluidizing air is blown from fluidizing air nozzles 8 into the bed 11 so that the molding sand a2 is maintained in the natural roasting state by utilizing the heat energy of the combustible material contained by the binder of said sand. The molding sand a1 is thus reconditioned. The powdery or granular combustible material such as coke powder or carbon dust is added to the sand a1 or is added by direct blowing to the bed 11 if the content of the combustible material in the sand a1 is low or zero. The maintenance of the natural roasting state and the reduction of the fuel cost are thus realized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating foundry sand, and in particular to a method for efficiently roasting foundry sand in a natural state by utilizing the thermal energy of combustible materials contained in the binder of old sand. This invention relates to a method for recycling recycled foundry sand.

Conventionally, many mechanical methods have been proposed and widely used for regenerating this type of foundry sand 1, such as organic self-hardening sand. However, in the case of green sand, it is difficult to use only mechanical methods, so the old sand is first roasted in a fluidized roasting furnace and then recycled using mechanical methods. Although high-quality recycled sand can be obtained, the thermal efficiency of fluidized torrefaction furnaces is generally low, resulting in huge fuel costs.

Therefore, it is unprofitable, there are few examples of this practice outside of large-scale factories, and there is no more economical method, so the reality is that most factories simply dispose of old sand.

In addition, various proposals have been made for improving the thermal efficiency of fluidized torrefaction furnaces in order to reduce the cost of recycling the old sand, but these methods are far from resulting in significant fuel cost savings. Naturally, there were limits to energy conservation.

In view of these shortcomings in the conventional art, the inventors thoroughly investigated the combustion action of fluidized torrefaction furnaces and discovered the following new technology, which they filed earlier (Japanese Patent Application No. 58).
-90519).

In other words, this effectively recovers the combustion heat of the foundry sand roasted in the fluidized bed and reduces the combustion heat to fluidized air that is blown onto the fluidized bed, thereby reducing the temperature of the fluidized air as much as possible. This is to cause the carbon combustibles contained in the foundry sand to self-combust in the fluidized bed.

By self-combusting in this way, there is no need to constantly supply heat to the fluidized torrefaction furnace to roast the foundry sand, resulting in a significant reduction in fuel costs, which is useful not only in large-scale foundries. In particular, it is possible to regenerate foundry sand at low cost even in medium and small-scale foundries, and it can greatly contribute to resource and energy savings.

However, in this self-combusting molding sand regeneration method, it is true that good results can be obtained if the foundry sand contains a relatively large amount of combustible binder, but for example, if the foundry sand contains a relatively large amount of combustible binder, In the case of foundry sand that does not contain too much, if a large amount is introduced into the fluidized bed, there is a risk that the self-combustion roasting state will stop.

In other words, if foundry sand that does not contain much combustible binder is added in large quantities or intermittently, in the fluidized bed,
Since there is not enough thermal energy to roast the combustibles of the molding sand that is subsequently introduced, the self-combustion roasting state inside the fluidized fluidized roasting furnace gradually stops.

Therefore, in order to avoid stopping the self-combustion roasting state, it is necessary to efficiently recover the exhaust heat of the roasted foundry sand to raise the temperature of the fluidized air as much as possible, or to take measures in addition to keeping the furnace wall warm. However, there is a practical limit to this, especially when a large amount or continuous use of foundry sand that does not contain IT (fired products) inevitably results in self-combustion roasting.
The output will stop.

Therefore, in order to prevent such a situation, when the self-combustion roasting state shows a tendency to stop, the inside of the fluidized bed is heated and replenished in eight steps.

However, when heating with a burner, the fuel cost does not increase so much if it is heated temporarily, but when molding sand containing only a small amount or no combustible binder is continuously input. However, since the burner must be constantly heated, the fuel cost increases significantly, and the method of recycling foundry sand, which involves self-combustion roasting, has been abandoned.

The present invention was made in view of these circumstances, and even when foundry sand containing only a small amount of combustibles or no combustibles is put into the fluidized torrefaction furnace, it is possible to heat the inside of the fluidized torrefaction furnace. It is an object of the present invention to provide a method for regenerating foundry sand that can be configured to a self-combusting roasting state without replenishment, thereby significantly reducing fuel costs.

Hereinafter, one embodiment of the method of the present invention will be described in detail with reference to FIG.

FIG. 2 shows a schematic configuration of a fluidized roasting furnace to which this embodiment method is applied.

In FIG. 2, a preheating section 2. A fluidized roasting section 3 and a fluidized air heating section 4 are formed in sequence, and an input hopper 5 is provided above the preheating section 2.
A burner 6 is provided on the furnace wall of the fluidized roasting section 3 toward the inside of the furnace, and a take-out lower is provided at the bottom of the lower furnace of the fluidized air heating section 4. The air heating section 4 is partially partitioned by a fluidized air nozzle 8, and there are no chutes or other additional means between the two parts 3.4, and the fluidized air nozzle 8 and the outside of the lower part of the furnace body are A pipe connecting the blower 9 to the other blower 9 is located within the fluidized air heating section 4 and forms a heat exchanger 10.

Therefore, in the case of this configuration, first of all, molding sand a containing a combustible binder is charged from the hopper 5 to a predetermined level and then stopped, and air blowing from the blower 9 is started to blow the molding sand. After a fluidized bed 11 is formed in the lower part of the fluidized roasting section 3 above the air nozzle 8, the burner 6 is ignited to heat and roast the foundry sand a forming the fluidized bed 11. Waiting for the fluidized bed 11 to rise to the roasting temperature,
The removal lower is opened, and at the same time, the injection of the foundry sand a1 is restarted.The foundry sand a1 is charged into the preheating section 12, dried and preheated by the exhaust gas, and then descends in the roasting section 3 to form a fluidized bed. 11, and the foundry sand a that has reached this fluidized bed 11
, is roasted by the burner 6 and heated to the maximum temperature in the furnace.

The thus roasted foundry sand a flows down through the fluidized air heating section 4 with almost no temperature drop, and its sensible heat is exchanged with the fluidized air passing through the heat exchanger lO. , and is eventually discharged to the outside from the take-out lower.

As this process is repeated, the average temperature of the fluidized air heating section 4 also rises, and at the same time, the temperature of the fluidized air with which heat is exchanged also gradually increases. The temperature of the fluidized bed 11 from which the fluidized air is blown out by the vJ lever also shows an increasing tendency, but in order to keep the roasting temperature constant, the burner 6 is gradually throttled down, and eventually the burner 6 is completely stopped. The roasting temperature is maintained for a while, and the state automatically shifts to the self-combustion roasting state.

Therefore, in the fluidized roasting furnace 1 that has shifted to the self-combustion roasting state in this way, for example, foundry sand that does not contain much combustible binder or foundry sand that does not contain any combustible matter (for example, molding sand that does not contain inorganic binder) If a large amount of molding sand (molding sand) is added continuously, the molding sand contains only a small amount or no combustible material, so thermal energy gradually becomes insufficient in the fluidized bed 11, and the fluidized bed 11 In this case, coke powder or carbon-based dust generated in a foundry may be mixed and added to the foundry sand, or it may be added by direct injection into the fluidized bed 11. , thermal energy shortage and temperature drop in the fluidized bed II can be effectively prevented.

Therefore, even if foundry sand containing only a small amount or no combustible materials is put into the fluidized roasting furnace I in a self-combustion roasting state, the coke powder or dust generated in the factory will not be produced. By adding powdered or granular combustible materials, the self-combusting roasting state can be maintained continuously.However, powdery granular combustible materials such as coke powder or dust generated in factories are extremely Since it is inexpensive, the fuel cost is significantly reduced compared to the case where the inside of the fluidized bed is auxiliary heated with the burner 6, and especially when the above-mentioned foundry sand is continuously introduced, the fuel cost can be significantly reduced. .

By the way, in the above embodiment, the case where foundry sand that does not contain much or no combustible material is introduced into the fluidized roasting furnace l, which is already undergoing self-combustion roasting, has been described. Of course, the invention is not necessarily limited to such a case; for example, even if self-combustion roasting has not yet been carried out and the interior of the fluidized roasting furnace is to be subjected to self-combustion roasting, the above-mentioned powdery single grain By adding a combustible substance to the foundry sand in an amount of N, self-combustion roasting can be carried out in the same operating procedure as in the above embodiment. Therefore, by mixing and adding such powdery 9-granular combustibles to the above-mentioned foundry sand, even foundry sand that does not contain any combustibles can lead to a self-combusting roasted 1 g in a fluidized roasting furnace. It means something.

As can be easily understood from the above explanation, the method for regenerating foundry sand of the present invention is effective when the foundry sand contains little combustible matter or no combustible matter at all. By adding extremely cheap powdered combustible particles such as coke powder or carbon-based dust to the foundry sand or to the fluidized bed, fluidized roasting of sheet metal can be achieved even with such foundry sand. Since the inside of the furnace can be maintained in a self-combusting roasting state, fuel costs can be significantly reduced compared to the conventional method of heating and replenishing the inside of the fluidized bed with a burner. By adding combustible materials, we can bring the benefits of self-combustible roasting to foundry sands that have a low combustible content or that do not contain any combustible materials, which have not been possible until now. without any loss,
The method of regenerating foundry sand by self-combustion roasting can provide a very useful method for regenerating foundry sand.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the general structure of a fluidized roasting furnace used in an embodiment of the method of the present invention. l...Fluidized roasting furnace 2...Preheating section 3...Fluidized roasting section 4...Fluidized air heating section lO...Heat exchanger 11...Fluidized bed patent applicant Nippon Steel Pipe Fitting Co., Ltd. Company Representative Patent Attorney Takashi Suzue - #J1 Diagram

Claims (1)

[Claims] The foundry sand that has been roasted in the fluidized bed in the fluidized roasting furnace is flowed down to the fluidized air heating section directly below the fluidized bed, and the fluidized air is heated to around the roasting temperature by heat exchange in this heating section. Blowing out this heated fluidized air into the fluidized bed,
A method for regenerating foundry sand in which foundry sand is naturally roasted, and when the foundry sand contains little or no combustibles, coke powder or A method for regenerating foundry sand, characterized in that a powdery two-grain combustible material such as carbon-based dust is added to the foundry sand or to the fluidized bed.