JPH0545460U - Lime firing kiln exhaust gas treatment equipment - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an apparatus for treating exhaust gas of a lime-baking kiln used for a carbonation reaction. [Structure] An apparatus that combines a wet scrubber 3 and a shell-and-tube heat exchanger 4, and uses exhaust gas from the wet scrubber 3 as a shell-and-tube heat exchanger 4.
Of the lime firing kiln, which introduces cooling water into a large number of small-diameter tubes 8 that are introduced in the shell 7 of the heat exchanger 4 and connected in parallel in the heat exchanger 4 in the horizontal direction. .

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is an apparatus for treating exhaust gas from a lime-baking kiln, and more specifically, the exhaust gas from a lime-baking kiln in a pulp manufacturing plant is used to process the exhaust gas from a lime-baking kiln used for producing light calcium carbonate. The present invention relates to a treatment device capable of improving the heat exchange efficiency of a heat exchanger without adhering to dust in exhaust gas.

[0002]

[Prior Art]

 Calcium carbonate is widely used as a white filler for pigments and paints, a filler for composite plastics and the like. In particular, in recent years, talc, which has been used as a filler for papermaking, is often used to produce neutral paper using calcium carbonate.

Conventionally, calcium carbonate used as a filler for neutral paper was heavy calcium carbonate, but since the wear of paper machine wires, especially plastic wires is large, light calcium carbonate is increasingly used. ing. The light calcium carbonate is generally known to have a spindle shape, a columnar shape, a cubic shape or the like, and various particle diameters have been obtained by changing reaction conditions.

A typical industrial production method of this light calcium carbonate is to bubble carbon dioxide gas into a suspension by bubbling carbon dioxide gas from a jetting outlet such as a nozzle or a straight pipe from the bottom of the carbonation reaction tank. It is allowed to react by contacting with calcium hydroxide in the suspension while floating.

Conventionally, the exhaust gas of a lime firing kiln (hereinafter abbreviated as lime kiln) used in the production of light calcium carbonate is the exhaust gas of the lime kiln sent to a scrubber by a blower to perform primary cooling and dust removal, and then a packed tower. After that, fine mist dust is removed by a mist filter, and then it is sent to a carbonation reaction tank through a secondary cooler via a blower.

[0006]

[Problems to be solved by the device]

 Conventionally, the production method of light calcium carbonate is equipped with various equipments for removing the dust contained in the exhaust gas from the kiln, but it is not sufficient yet and there are many problems. First, since dust particles adhered to the blower that sends the exhaust gas to the carbonation reaction tank, a positive displacement blower with a small clearance, such as a Roots blower, could not be used, resulting in high power consumption.

Secondly, the mist filter for removing fine soot and dust is frequently clogged and has a large pressure loss, which contradicts power saving and causes operational troubles.

Thirdly, a heat exchanger for cooling exhaust gas is used, but when a shell-and-tube heat exchanger is used for this heat exchanger, it is included in the exhaust gas. The soot dust adheres and needs to pass through a tube that can be cleaned to remove it, so the thermal efficiency is inevitably low, and the overall heat transfer coefficient is as low as 10 to 50 Kcal / m ² · hr · ° C. There was a flaw.

An object of the present invention is to provide a processing apparatus which improves the above-mentioned conventional drawbacks, has less adherence of soot and dust in exhaust gas, and has good heat efficiency of a heat exchanger.

[0010]

[Means for Solving the Problems]

 The present invention comprises a wet scrubber and a shell-and-tube heat exchanger combined in a lime kiln exhaust gas treatment device, wherein the exhaust gas processed by the wet scrubber is a shell-and-tube heat exchanger. The heat exchanger is configured to be conducted to the shell side of the exchanger, and the cooling medium is conducted to a large number of tubes inside the shell-and-tube heat exchanger.

[0011]

[Action]

 The lime kiln exhaust gas contains a carbon dioxide concentration of about 19.6%, which is primarily cooled by a wet scrubber from about 210 ° C to about 60 ° C, and the soot and dust contained in the exhaust gas is removed (the exhaust gas When releasing into the atmosphere, remove dust with an electric precipitator). Since this exhaust gas is treated by the wet scrubber, the relative humidity is about 100%, and the soot dust is not completely removed.

The present invention treats exhaust gas with an apparatus combining a wet scrubber and a shell-and-tube heat exchanger, and the shell-and-tube heat exchanger is about 60 ° C to about 40 ° C. Cool to a degree. However, the cooling temperature at this time is one of the requirements for the quality design of calcium carbonate, and may be appropriately changed according to the quality design.

The shell-and-tube heat exchanger of the present invention conducts the lime kiln exhaust gas to the shell side, while conducting the cooling medium to a large number of tubes mounted inside the heat exchanger. ..

That is, the exhaust gas introduced into the heat exchanger of the present invention is cooled by coming into contact with many tube outer surfaces through which the cooling medium is conducted, but the relative humidity is about 100%. The moisture in the exhaust gas contacts the tube, condenses and condenses, and the progress of this condensation causes the entire outer surface of the tube to become wet, causing it to drop as drops. At this time, the soot and dust contained in the exhaust gas from the ash kiln is captured by the moisture that has condensed on the outer surface of the tube, and the soot and dust is removed.

The dew condensation of water on the outer surface of the tube, the formation of drops, and the behavior of dropping are continuously performed, so that the dust is not fixed to the outer surface of the tube and the outer surface of the tube is always kept clean. It has a good cleaning effect. Furthermore, since the outer surfaces of many tubes through which the cooling medium is conducted are kept clean without soot sticking and are always kept in a wet state, the overall heat transfer coefficient is 400 Kcal / m ²・ Because it can be maintained at about hr · ° C, the heat exchange rate is extremely high and continuous operation is possible.

On the other hand, the lime kiln exhaust gas is sent to the carbonation reaction tank by a blower. Conventionally, a turbo blower having a large clearance and a large axial power is used due to the fixation of soot dust. Since the heat exchanger used for the has extremely high removal rate of soot and dust in lime exhaust gas, it is possible to use a roots blower and save electricity.

[0017]

【Example】

 FIG. 1 shows an embodiment of the present invention. Next, the structure and operation of the present invention will be specifically described with reference to the drawings. The exhaust gas of the lime kiln 1 is sent to the wet scrubber 3 by the blower 2, and this exhaust gas is further sent to the shell and tube heat exchanger 4 (hereinafter abbreviated as heat exchanger) which is combined with the wet scrubber 3. The exhaust gas is supplied to the carbonation reaction tank 6 by the blower 5.

As shown in FIG. 2, the shell-and-tube type heat exchanger 4 of the present invention is of a square pole type, and has a large number of small diameters arranged in parallel in the shell 7 inside the shell 7. The tube 8 is attached. As an example, the cross-sectional area of the shell is about 2.2 m ² , the tube diameter in this case is about 15.9 mm in outer diameter, and the number of tubes is 3120. When the capacity of the carbonation reaction tank 6 is 30 m ³ , the exhaust gas sent to the reaction tank 6 is 1600 m ³ / hr, and in this case, the exhaust gas supplied to the heat exchanger 4 is about 220 m ³ / min. is there. However, the present invention is not limited to the above-mentioned specifications, and it goes without saying that it can be appropriately changed depending on the capacity of the carbonation reaction tank.

An exhaust gas inlet 9 is formed on the lower side of the shell 7, and an exhaust gas outlet 10 is formed on the top of the shell 7, so that the exhaust gas is introduced to the shell 7 side of the heat exchanger 4. In addition, the small-diameter tube 8 is configured such that the cooling water is introduced from the cooling water inlet 11 and is sequentially sent to the many tubes 8 connected and arranged, and is discharged from the cooling water outlet 12. ing. Reference numeral 13 in FIG. 2 is a shower for cleaning the outer surface of the tube 8 when the heat exchanger 4 is stopped.

As shown in FIG. 1, the exhaust gas of the wet scrubber 3 is supplied from the exhaust gas inlet 9 of the heat exchanger 4 combined with the wet scrubber 3 into the inside of the shell 7 and into the tube 8 of the heat exchanger 4. It is cooled by the supplied cooling water. Since the exhaust gas supplied from the wet scrubber 3 has a relative humidity of 100%, the water in the exhaust gas comes into contact with the tube 8 to cause dew condensation, which drops as a drop. Therefore, the soot and dust contained in the exhaust gas is captured and removed by the dew condensation water, so that the soot and dust is remarkably reduced and is sent to the carbonation reaction tank 6 by the blower 5.

Since the exhaust gas is made even lower by removing soot and dust by the heat exchanger 4 of the present invention, the blower 5 for sending the exhaust gas to the carbonation reaction tank 6 is of a positive displacement type with small axial power. A roots blower can be used to save power.

Incidentally, calcium carbonate was produced by a plant using a combination of the wet scrubber of the present invention and a heat exchanger (calcium hydroxide concentration 15%, reaction time 4.5 hours, reaction temperature 45 ° C.). At this time, the whiteness of calcium carbonate (according to the test method of JISP.8123) is 97.5%, while the whiteness of calcium carbonate when only the wet scrubber is used without using the cooler of the present invention is It was bad at 90.0% due to the inclusion of soot and dust.

[0023]

[Effect of the device]

 As described above, the present invention uses a combination of a wet scrubber and a shell-and-tube heat exchanger when the carbonation reaction is carried out using the lime kiln exhaust gas, and the exhaust gas is heated by the heat exchanger. By introducing it to the shell side of the exchanger, the overall heat transfer coefficient can be greatly improved, and the soot and dust in the exhaust gas can be significantly reduced.

Further, according to the present invention, since the soot and dust in the exhaust gas sent to the carbonation reaction tank is remarkably reduced, the blower for sending the exhaust gas to the carbonation reaction tank can use a volume type roots blower with small axial power, which saves energy. Electrification is achieved.

[Brief description of drawings]

FIG. 1 is an example of the flow of a carbonation reaction according to the present invention using a lime kiln exhaust gas.

FIG. 2 is a side view of an example of a shell-and-tube heat exchanger.

[Explanation of symbols]

 1: Lime kiln 2, 5: Blower 3: Wet scrubber 4: Heat exchanger 6: Carbonation reaction tank 7: Shell 8: Tube 9: Exhaust gas inlet 10: Exhaust gas outlet 11: Cooling water inlet 12: Cooling water outlet 13: shower

Claims (1)

[Scope of utility model registration request] 1. A lime-calcining kiln exhaust gas treatment device comprising a wet scrubber and a shell-and-tube heat exchanger in combination, wherein the exhaust gas treated by the wet scrubber is shell-and-tube type. A lime calcination that is configured to be introduced to the shell side of a heat exchanger, and that a cooling medium is conducted through a large number of tubes inside the shell-and-tube heat exchanger. Kiln exhaust gas treatment equipment.