JPH0415180B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for firing powdery lime, etc., and more specifically, a method for fluidized bed firing of powdery lime, etc. in which fine powder is scattered. and regarding equipment.

[Prior art]

Limestone, which is an auxiliary raw material input into blast furnaces, steelmaking furnaces, etc., is fired to produce products with decarbonization, desilication, and desulfurization functions. When limestone is collected, it may be a large lump, but it is made into a desired granular shape in advance so that it has a size suitable for firing. In order to calcinate such lime, a vertical furnace, a rotary kiln, a fluidized bed furnace, etc. are conventionally used.
Due to the rise in the price of heavy oil, the fuel used for calcination has been replaced by cheaper coal, and the above-mentioned vertical furnaces and fluidized bed furnaces are increasingly being used as lime calcination furnaces. By the way, in a vertical furnace, since the height of the filled bed of lime becomes large, in order to ensure air permeability, lime cannot be fired unless it has a certain particle size or more. Therefore, the fine powder produced when the collected limestone is crushed is not used in consideration of clogging, and is sent to a separate landfill, making it impossible to increase the utilization rate of the collected amount. Furthermore, since firing in a vertical furnace takes time, firing in a fluidized bed furnace has recently come to be performed. For example, Jikko 58-
No. 55215 proposes an apparatus for calcining lime using a fluidized bed furnace. This type of fluidized bed furnace not only has the advantage of being able to shorten the firing time, but also allows for the input of fine powder, which was not subject to firing as described above, and can be fired in the same manner as granular lime. This has the advantage of significantly increasing the utilization rate of extracted resources.

[Problem that the invention seeks to solve]

Lime that has been crushed to a certain level is fed into the fluidized bed furnace, but as mentioned above, it also contains lime that has become powder during crushing, and the lime that has passed through the fluidized bed during firing. It floats or scatters on the freeboard in the oxidized air. Therefore, when the exhaust gas discharged from the fluidized bed furnace is released into the atmosphere or sent to a separately provided suspension preheater, it is necessary to remove fine powder contained in the exhaust gas. Therefore, a cyclone must be attached to the fluidized bed furnace to collect the fine powder from the exhaust gas. An example in which a cyclone is provided in a fluidized bed furnace as described above is described in JP-A-53-110624. In this device, the fine powder collected by the cyclone is introduced into a cooling device which is a post-process of the firing furnace, so that the fired fine powder is also cooled as a product.

By the way, powdered lime is burned while flowing in a fluidized bed, but the fine powder is often immediately scattered from the fluidized bed. Fine powder suspended on free boards above the fluidized bed is only exposed to the heat of the exhaust gas and is not directly affected by the combustion heat of the fluidized bed.Furthermore, the fine powder is collected by the cyclone, which may result in insufficient firing of the fine powder. There is a tendency to To achieve this, the furnace must be raised to increase the residence time of the fine powder in the furnace, and the firing temperature in the fluidized bed may be set at 950 to 1000°C, for example, to allow firing even if the residence time is short. Must be kept high. As a result, the temperature of the exhaust gas from the kiln and the temperature of the product discharged from the cooling device increase, resulting in a problem of poor fuel consumption. Moreover, if the amount of fuel to be supplied is large, a large amount of fluidizing air is also required, which in turn necessitates an increase in the size of the furnace body and the capacity of ancillary equipment such as a blower. There is also the problem that the degree of calcination of the fine powder is not constant, making it difficult to maintain the calcination rate of the calcined lime discharged from the cooling device at a desired value.

The present invention was made to solve the above-mentioned problems, and its purpose is to lower the temperature of the fluidized bed as much as possible to improve the fuel consumption rate, thereby realizing downsizing of the furnace equipment and To provide a method for calcination of powdery granular lime, etc., and an apparatus thereof, which can produce lime with a high calcination rate, even if it contains fine powder or is crystalline lime that is severely pulverized during decarboxylation. It is.

[Means for solving problems]

To explain the characteristics of the method for firing powdery lime, etc. of the present invention, when powdery lime, etc. is fired in a fluidized bed, the fine powder that is scattered is collected, and all or part of the fine powder is returned to the fluidized bed and fired again. That's what I would do. Further, to describe the features of the device with reference to FIG. 1, it is composed of a fluidized bed furnace 3 that burns powdery lime, etc., and a cyclone 12 that collects fine powder scattered from the fluidized bed furnace 37. A product chute 14 for discharging part of the fine powder collected by the cyclone 12 as a product, and a return chute 15 for returning the remaining fine powder to the fluidized bed furnace 3 are installed.

〔Effect of the invention〕

In the present invention, the scattered fine powder is collected and all or part of the fine powder is returned to the fluidized bed, so that the fine powder with a low degree of firing is fired again, and the collected fine powder is fired. rate and product quality. As a result, it is no longer necessary to raise the temperature in the fluidized bed furnace for the purpose of sufficiently firing the fine powder, which tends to have a short residence time, and therefore, the fuel consumption rate is significantly improved. As the amount of fuel is reduced, the size of the furnace equipment can also be reduced. By collecting such fine powder and re-calcining it, it is possible to commercialize powdered lime, which makes it possible to use raw materials with a wide range of particle sizes and crystalline limestone that is highly pulverizable, thereby increasing the utilization rate relative to the amount collected. can be significantly improved.

〔Example〕

Hereinafter, the present invention will be explained in detail based on examples thereof. Fig. 1 is an overall configuration diagram of a granular lime calcination equipment 1, which mainly consists of a suspension preheater 2, a fluidized calcination furnace 3, and a cooling device 4. It manufactures raw materials, etc. The suspension preheater 2 is, for example, a floating heat exchanger consisting of a plurality of cyclones, in which powdery limestone introduced from the raw material input port 5 is sequentially passed through the cyclones C4, C4, and C4 while exchanging heat with the exhaust gas rising in each duct.
It is collected by C3, C2, and C1, falls, and is preheated to a predetermined temperature. The fluidized bed firing furnace 3 is a fluidized bed furnace in which preheated granular lime is fired in a fluidized bed 6, and air 7 that has passed through the cooling device 4 is introduced as fluidized air. This fluidized calcining furnace 3 is provided with a limestone supply chute 8 that supplies limestone collected by the cyclone C1 of the suspension preheater 2 to the fluidized bed 6, and a calcining furnace exhaust gas 9 in which fine powder is suspended is discharged onto the furnace. Exhaust gas outlet 1 for sending out to the cyclone 12 described later
0 is open.

The fluidized calcining furnace 3 in such a calcination equipment 1 for granular lime is equipped with a cyclone 12 that collects fine powder scattered from the fluidized bed 6. A preparative damper 13 is located at the bottom of the cyclone 12a installed on the cooling device 4 side of the cyclone 12.
A product chute 14 for discharging the collected fine powder as a product and a return chute 15 for returning the fine powder to the fluidized bed 6 are connected. The separation damper 13 has a built-in flapper that swings to switch paths, and by controlling the operation of the flapper, the firing rate of the fine powder can be adjusted to a desired value. Therefore, when the fine powder is discharged into the product chute 14 by the flapper, it is introduced into the cooling device 4 and cooled together with the calcined granular lime to form a product. When the fine powder is discharged to the return chute 15 by the flapper, it is returned to the fluidized fluidized firing furnace 3 again. As a result, part of the fine powder collected by the cyclone 12 is made into a product, and the remaining fine powder is refired. The operating time of the flapper is selected depending on the ratio of fine powder taken out as a product, but the firing rate of the fine powder is checked during operation, and the flapper operation is changed depending on the level of the firing rate to achieve even better quality. You can get lime. Incidentally, there is no problem in providing a plurality of cyclones equipped with a preparative damper 12, but if the amount of fine powder taken out as a product is small compared to the total amount of fine powder or there is a large amount of scattered fine powder, the cyclone does not have a preparative damper as shown by the imaginary line. An appropriate number of cyclones 12b may be added to speed up collection and circulation of fine powder or increase the number of circulations. Therefore, the number of cyclones attached to the fluidized fluidized firing furnace 3 can be arbitrarily selected, and in some cases, a large number of cyclones may be provided. In addition, in either cyclone, the exhaust gas separated from the fine powder is transferred to the cyclone.
Introduced in C1, suspension preheater 2
It is configured to be used for preheating the raw lime in the process.

According to such an embodiment, the coarse particles of the preheated limestone are fired in the fluidized bed 6 for about one hour, and are discharged from the fluidized firing furnace 3 so as to overflow from the bottom or the fluidized bed 6. . The fine powder is scattered from the fluidized bed 6 and floats on the freeboard 16, or is carried on the fluidized air 17 and led to the cyclone 12. In each cyclone, fine powder is separated from the exhaust gas and collected. When the fine powder is to be discharged as a product and sent to the cooling device 4, the inclined position of the flap of the separation damper 13 is changed, and the fine powder flows through the product chute 14. After a certain amount of fine powder has been discharged to the product chute 14, the position of the flapper is changed, and the collected fine powder is then returned to the fluidized fluidized firing furnace 3 from the return chute 13. Since the fine powder that has remained in the furnace for a short time is fired again, there is no chance of under-firing. Of course, not all of the fine powder discharged as a product is completely fired, but since a lot of fine powder is fired while circulating through the cyclone, the fine powder collected by the cyclone cannot be fired. rate will be higher. Of course, the firing rate can be made even higher by measuring the firing rate of the discharged fine powder and controlling the amount of fine powder collected with the preparative damper 13 so as to achieve a predetermined firing rate. can. At that time, it is sufficient to understand the correspondence between the firing temperature and the firing rate of the fine powder, and to control the preparative damper 13 while detecting the firing temperature. If the configuration is such that all or part of the collected fine powder is returned to the fluidized fluidized firing furnace 3, it is necessary to discharge the entire amount of the fine powder that has undergone heat exchange only once in the fluidized fluidized fired furnace 3. 950〜
Compared to 1000°C, the firing temperature required to obtain a predetermined firing rate can be suppressed to about 850 to 900°C. Therefore, the amount of fuel consumed in the fluidized bed 6 can be reduced, and accordingly, the furnace can be made smaller.

FIG. 2 shows a different embodiment in which a plurality of cyclones 18 are attached to the fluidized firing furnace 3. When a large number of cyclones are provided, each cyclone itself can be used for collecting the product or for returning the product. Therefore, in this example, the product chute 1 is installed in the cyclone 18a.
4 is connected, and a return chute 15 is connected to the cyclones 18b and 18c. In addition, each cyclone is not equipped with a preparative damper,
The collected fine powder is primarily discharged to the cooling device 4 or returned to the fluidized fluidized kiln 3. By doing so, the precise control of the firing rate is somewhat inferior, but there are no moving parts in the device, so the occurrence of breakdowns and troubles is extremely low, and equipment costs can be reduced.

In each of the above embodiments, there is no need to adjust the particle size of the limestone to be charged, and even if it is heavily powdered such as crystalline limestone or even if there is a small amount of powder mixed in, it can be used over a wide range. It becomes possible to cool powdery lime having a particle size distribution, and the entire amount collected can be used as a raw material without discarding the powder as in the past, making it possible to use resources effectively. Furthermore, even when there is a large amount of fine powder, firing can be performed with high thermal efficiency.

[Brief explanation of drawings]

FIG. 1 is an overall view of a calcination equipment to which the method for calcination of powdery lime of the present invention is applied, and FIG. 2 is an overall view of a different embodiment. 3... Fluidized bed furnace (fluidized firing furnace), 12, 12a,
12b, 18, 18a-18c...Cyclone,
13... Preparative damper, 14... Product chute,
15...Chute for return.

Claims (1)

[Scope of Claims] 1. Powdered and granular lime, which is characterized in that when powdered lime, etc. is calcined in a fluidized bed, the fine powder that is scattered is collected, and all or part of the fine powder is returned to the fluidized bed and calcined again. etc. firing method. 2 For products consisting of a fluidized bed furnace that burns powdered lime, etc., and a cyclone that collects the fine powder scattered from the fluidized bed furnace, and a part of the fine powder collected by the cyclone is discharged as a product. 1. An apparatus for calcination of powdery lime, etc., characterized in that a chute and a return chute for returning the remaining fine powder to the fluidized bed furnace are installed. 3. The cyclone has a separation damper connected to a product chute and a return chute, and the amount of separation is adjusted so that the firing rate of fine powder or products becomes a desired value. An apparatus for burning powdery lime, etc., as set forth in claim 2, characterized by: 4. Calcining of granular lime, etc. as set forth in claim 2, wherein the plurality of cyclones are comprised of a cyclone exclusively for product discharge having a product chute and a cyclone exclusively for returning products having a return chute. Device.