JPS59252B2 - Firing method for powder raw materials such as alumina - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for firing powdery raw materials such as alumina.

Generally, granular raw materials, such as alumina raw material cake, are
It has a moisture content of 14%, which requires a large amount of heat to burn, and it is also necessary to maintain the inlet gas temperature of the electrostatic precipitator at the final stage of the plant above the dew point. requires a large amount of heat.

For this reason, in one example of the conventional method, as shown in Figure 1, the raw material is dried in a dryer with its path indicated by the broken line, then separated from the gas in a dry raw material separator, and then the raw material is passed through a floating heater. It was partially dehydrated and finally introduced into a kiln where the remaining majority was dehydrated and fired. The heated gas from the kiln is guided through the floating heater to the hot blast furnace as shown by the solid line, where it is further heated by a burner, and then passed through a dryer and separated from the raw material by a dry raw material separation device. It is designed to escape into the atmosphere through an electrostatic precipitator. This example had the following drawbacks.
(i.e.) Installing a hot-air stove increases equipment costs; this hot-air stove requires dilution air in consideration of the heat resistance of the dryer installed following it, which increases heat loss; ←→ Floating heater In general, the system consists of a cyclone and a connecting duct, and there is a large pressure drop, and the power consumption of the fan that sends the gas is large. Another example of the conventional method, as shown in Figure 2, is to introduce the raw material into a floating heater with auxiliary combustion (cyclone type), dry it, dehydrate most of it, separate it from gas, and then introduce it into a kiln. In this case, the dehydration process is almost completed in the sliding heater, so the exhaust gas temperature of the heater easily fluctuates due to fluctuations in heat input, and Fluctuations in the amount of raw material input into the kiln or the amount of moisture attached to the kiln directly affect the kiln, making it complicated to change the ratio of the firing amount between the auxiliary furnace and the kiln in order to ensure stable operation. The gas after the process has a temperature of 400-500C.
Since the gas induction fan has poor heat resistance and cannot withstand use, it must be installed before and after the electrostatic precipitator at the rear, making it difficult to control combustion, such as the amount of oxygen supplied to the kiln. (c) The cake is put into the floating heater as a lump, and it passes through the heater without any problem, and a large amount of attached moisture enters, disturbing the steady state and making the kiln operation unstable (Ni) ) Floating heaters generally consist of a cyclone and a connecting duct, and have drawbacks such as the pressure loss of the cyclone and the power consumption of the fan, and (e) the risk of excessive dehydration and clogging of the cyclone chute.

The present invention is a method for firing a powder raw material such as alumina, which aims to eliminate the above-mentioned drawbacks, and one embodiment thereof will be described below in detail with reference to the drawings, taking alumina firing as an example.

Referring to FIGS. 3 and 4, the entire firing apparatus will first be described.

A is a food pin for supplying raw materials, B is a shaft drum that is the main part of the raw material drying section for drying the moisture attached to the raw materials, and C is a cyclone type dryer for separating dry raw materials from gas. Raw material separation device, D is the first floating heater for heating the raw material gas, E is the second floating heater
Heater, F is an auxiliary combustion furnace for assisting and promoting the above heating, G
This is a five-port kiln for dehydrating and firing most of the raw materials. H is an electrostatic precipitator which separates and collects the dust remaining in the gas separated by the cyclone type dry raw material separator C again. J is a multi-tube cooler for cooling the dehydrated and fired raw materials, K and L are suction fans, and M is a cyclone for mixing the dehydrated and fired raw materials with cooling air for cooling and separation. This is a floating cooling separator. All of the above devices except the first and second floating heaters D and E are known, and the details of the floating heaters D and 4E are as follows.

That is, as shown in FIGS. 5 to 7, it is a heater that separates powder and granular materials by inertial force, and is composed of a separation chamber 1 having a rectangular horizontal cross section, a gas/powder mixture inflow passage 3, and an outflow passage 4. The separation chamber 1 is formed by a vertically erected side wall 1a, a horizontal ceiling wall 1b, and a bottom 2 having a funnel-shaped cross section in one direction. An opening is connected to one side of the separation chamber 1 so as to allow the flow of water into the separation chamber 1. Further, the outflow passage 4 is mounted on the separation chamber on the opposite side of the inflow passage 3, has a rectangular cross section, and is opened upward. A plurality of dust outlets 5 are provided at the bottom of the funnel-shaped bottom 2. A collision plate 6 is installed vertically penetrating the ceiling wall 1b slightly closer to the separation chamber 1 at the connecting portion between the flow passageway 3 and the separation chamber 1, and extends along the entire width in the width direction. It has a length sufficient to prevent the introduced airflow from flowing horizontally as it refracts and advances along the ceiling wall 1b. A rectangular box-shaped cover 7 for storing the collision plate 6 is provided on the upper side of the ceiling wall 1b to cover the collision plate 6. An adjustment rod 8 is rotatably connected to the upper end surface of the collision plate 6 in an upright manner. A handle 9 for rotating the adjustment rod is fixed to the upper end of the adjustment rod 8. An internal screw member 7 fixed to the upper wall of the cover 7 is located in the middle of the adjustment rod 8.
It is screwed onto a. A cover 11, an internal threaded member 11a, and an adjustment rod 12 similar to those described above are provided near the entrance of the outflow passage 4 on the vertical wall 1a facing the opening of the inflow passage 3, and a collision plate 10 equipped with a handle 13 is provided. These handles 9 and 13 are attached so that they can be adjusted horizontally forward and backward.
By rotating the colliding plates 6 and 10, the advance and retreat of the collision plates 6, 10 is adjusted, and the gas flow (solid line arrow) is bent to separate the gas flow from the powder raw material indicated by the broken line arrow, in other words, the outflow passage. 4 can be freely controlled. A powder inlet 1 is installed on the upper side of the ceiling wall of the separation chamber 1, and if necessary, on the outer wall of the inflow passage.
4 and 15 are provided. Incidentally, one of the above-mentioned collision plates 6 and 10 may be omitted depending on the degree of raw material separation rate. Incidentally, alumina sintering can be broadly divided into the following reaction processes.

In carrying out the present method using such a reaction process and apparatus, the alumina raw material fed into the feed pin A is guided to the shaft dryer B via a lattice conveyor, etc., as shown in FIGS. The gas is separated from the gas in the next cyclone-type dry raw material separation device C.

Then, it is guided to a first floating heater D, a second floating heater E,
Heating and separation are performed by gas from kiln G and auxiliary furnace F, and part of the raw material (0.3-2Ky/Ky-Al2O3)
is returned to the cyclone-type dry raw material separation device C together with the gas through the heater fan K and the dryer B. The raw material separated and collected in the first floating heater D is led to the auxiliary combustion furnace F, where it is heated and undergoes a part of the dehydration process, and then introduced together with the heated gas into the second floating heater E, where it is further heated and undergoes the dehydration process. Most of the raw material is sent from the outlet E2 to the kiln G, where the remaining dehydration process is carried out and then fired. The fired raw material is cooled and separated through a multi-tube cooler J and a cyclone floating cooling separator M, and then sent out as a product. In addition to the raw materials returned from the electric precipitator H and the cyclone type floating cooling separator M being introduced into the auxiliary combustion furnace F, the combustion exhaust gas from the kiln G is also returned.

Particularly noteworthy points here are the dryer B1, the dry raw material separator C1, as mentioned above and indicated by the dashed line in FIG.
Part of the raw material is circulated in the order of floating heaters D and E. Therefore, the exhaust gas that has completed part or most of the dehydration process and a portion of the heated raw materials are used as a heat source for the next drying process, so even if the exhaust gas temperature after the dehydration process is low, there is enough heat for the drying process. Obtainable. Note that one or both of the shaft dryer B1 and the auxiliary combustion furnace F may be omitted depending on the degree of necessity.

However, if the dryer B is omitted, a space such as a duct is required in which the heating gas and the raw material can come into contact for an appropriate period of time.
Furthermore, the floating heaters D and E are not limited to two stages, but may be one stage or several stages. Furthermore, the present invention is also applicable to the firing of other granular raw materials such as cement and lime. The following table shows an example of alumina firing.

As explained above, the method according to the present invention includes an input raw material drying section that dries adhering moisture on powder raw materials such as alumina in an air stream, a dry raw material separation device, and a preheated raw material dehydration process that has low pressure drop and can adjust the collection rate. In combination with a floating heater, which performs some or most of the This makes it possible to stabilize and reduce the exhaust gas temperature during the dehydration process, eliminating the need for a hot air oven for the drying process and eliminating the need for a heat-resistant structure for the subsequent drying process. A fan can be installed before the drying process, making operation control easier.
Equipment costs are low, and because a floating heater with a low separation rate is used, there is little pressure loss and power consumption is reduced.

Furthermore, since a part or most of the dehydration process is carried out in a floating heater, the reaction temperature here is approximately constant, there is no inconvenience caused by excessive dehydration, there is little fluctuation in the temperature of the exhaust gas, and as mentioned above, the temperature of the exhaust gas is small. Since the pressure loss is small, the negative pressure of the entire system is small, and there is little air intrusion into the system, resulting in stable operating conditions and low heat consumption.

[Brief explanation of drawings]

Figures 1 and 2 are process diagrams of the conventional method, Figure 3 is a process diagram showing an embodiment of the present invention, Figure 4 is a flow sheet of the present invention, and Figure 5 is a longitudinal section of the floating heater. FIG. 6 is a plan view of the same, and FIG. 7 is a side view of the same.

Claims (1)

[Claims] 1. Leading a powder raw material such as alumina to an input raw material drying section, mixing it with heated gas from a kiln to remove attached moisture, and leading the raw material and gas to a dry raw material separation device to separate the gas and raw material, The feedstock is then introduced into a floating heater and heated by mixing with heated gas from the kiln to perform part or most of the dehydration process of the feedstock and to separate most of the feedstock from the gas. The separated raw material is led to a kiln to perform the remaining dehydration process and then fired, the fired raw material is cooled, and a part of the raw material from the floating heater is led together with gas to the input raw material drying section and charged. A method for firing a powder raw material such as alumina, which comprises drying the raw material and then introducing the raw material to the dry raw material separation device.