JPH05345115A - Recovery of co2 from exhaust gas of limekiln - Google Patents

Abstract

PURPOSE:To inexpensively recover CO2 in the exhaust gas discharged from a limekiln. CONSTITUTION:When quick lime 8 is produced by baking limestone in a limekiln 4 consisting of a preheating zone 3, a baking zone 2 and a cooling zone 1, cooling air 7 is blown in the lower part of the cooling zone 1 to be drawn out of the upper part of the cooling zone 1 or the lower part of the baking zone 3 and mixed gas 11 of CO2 and O2 is blown in the lower part of the baking zone 2 to burn coke to bake and preheat limestone and the exhaust gas 12 with high CO2 concn. discharged from the upper part of the preheating zone 3 is introduced into a CO2 liquefying and purifying device 14 to recover liquefied CO2 15. Therefore, the CO2 concn. in the exhaust gas discharged from the limekiln can remarkably be raised to concn. introducible into the CO2 liquefying and purifying device and liquefied CO2 can inexpensively be recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering CO ₂ from exhaust gas from a lime furnace which produces quicklime by burning limestone.

[0002]

2. Description of the Related Art Quick lime used for applications such as carbides, auxiliary raw materials for iron making, and agricultural chemicals is produced by firing limestone in a lime furnace such as a shaft kiln or a rotary kiln. As the firing reaction, CaCO ₃ = CaO + CO ₂ , and 40% or more of the total weight is released as CO ₂ gas. As shown in FIG. 2, for example, a conventional lime furnace has a vertical lime furnace 24 including a cooling zone 21, a firing zone 22, and a pretropical zone 23.
3. Limestone 25 is charged from the upper part, and combustion air 27 pressurized by a blower 26 is blown from the lower part of the cooling zone 21. The calcined quicklime 28 is cooled by exchanging heat with the combustion air 27 in the cooling zone 21, and taken out from the lower part of the cooling zone 21.
Combustion air 27 that has exchanged heat with quicklime 28 in the cooling zone 21
Next, the coke or the like is burned in the calcining zone 22 to calcinate the preheated limestone, and the limestone 25 charged from the upper portion in the pretropical zone 23 is preheated together with the CO ₂ generated by the calcining reaction. Is exhausted as exhaust gas 29 from.

Therefore, most of the exhaust gas 29 of the lime furnace 24 is occupied by nitrogen in the combustion air 27, and the CO ₂ concentration is about 20 to 40%. CO _{2 in} this exhaust gas 29
For the recovery of the exhaust gas 29, after the pressure of the exhaust gas 29 is increased by the compressor 30,
It is introduced into a CO ₂ recovery device 31 of PSA or absorption method to separate and recover CO ₂ , and the recovered CO ₂ is liquefied and refined device 32.
Was liquefied and purified to obtain liquefied CO ₂ 33. Incidentally, 34 is a waste gas from which CO ₂ has been separated.

[0004]

Recently, from the viewpoint of preventing global warming and protecting the environment, it has been desired to reduce CO ₂ emission as much as possible, and CO ₂ is contained in a large amount of 20 to 40%. The recovery of CO ₂ from the exhaust gas of a lime kiln is extremely important. However, the recovery of CO ₂ in the exhaust gas from the conventional lime kiln as described above, the CO ₂ separated and recovered by introducing the CO ₂ recovery apparatus PSA or absorption method,
Since it is necessary to introduce the recovered CO ₂ into the liquefaction purification apparatus for liquefaction purification, not only the equipment cost becomes high, but also the running cost is high.

An object of the present invention is to provide a method for recovering CO ₂ from exhaust gas of a lime furnace which solves the above-mentioned drawbacks of the conventional method and can recover CO ₂ in exhaust gas discharged from a lime furnace at low cost. It is in.

[0006]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies and conducted test studies in order to achieve the above object. As a result, in the conventional lime furnace, the product quick lime is cooled in the cooling zone by the combustion air, the limestone is burned in the firing zone, and the limestone is preheated in the pre-tropical zone. Focusing on the fact that CO ₂ and nitrogen in the combustion air are mixed and the CO ₂ concentration decreases, cooling air is blown in from the lower part of the cooling zone to extract cooling air from the upper part of the cooling zone, and CO ₂ and O The inventors have found that the CO ₂ concentration in the exhaust gas released from the upper part of the pre-tropical zone is dramatically increased by blowing the mixed gas of ₂ and withdrawing it from the upper part of the pre-tropical zone, and reached the present invention.

That is, according to the present invention, when limestone is manufactured by calcining limestone in a lime furnace composed of a pre-tropical zone, a calcination zone and a cooling zone, cooling air is blown from the lower part of the cooling zone and extracted from the upper part of the cooling zone or the lower part of the calcination zone. , From the bottom of the firing zone to C
CO ₂ discharged from the upper part of the pretropical zone by injecting a mixed gas of O ₂ and O ₂ to burn coke to burn and preheat limestone
Exhaust gas having a high concentration is introduced into the CO ₂ liquefaction refining apparatus to recover the liquefied CO ₂ .

When limestone is calcined in a lime furnace consisting of a pre-tropical zone, a calcination zone and a cooling zone, quicklime is produced,
The mixed gas of CO ₂ and O ₂ and the hot air extracted from the upper portion of the cooling zone or the lower portion of the firing zone are heat-exchanged by blowing the cooling air from the lower portion of the cooling zone to raise the temperature of the mixed gas of CO ₂ and O _{2 to} the lower portion of the firing zone. after the combustion of coke by blowing firing limestone, preheated, circulated a portion of the high exhaust gas of the CO ₂ concentration discharged from the preheating zone the upper as the CO ₂ mixing gas CO ₂ in O _2, balance the introduced into CO ₂ liquefier purifier liquefied CO ₂
Is recovered.

[0009]

In the present invention, cooling air is blown from the lower part of the cooling zone to be withdrawn from the upper part of the cooling zone or the lower part of the firing zone, and a mixed gas of CO ₂ and O ₂ is blown from the lower side of the firing zone to burn coke and burn limestone. Since it is preheated, the cooling air blown from the lower part of the cooling zone is used only for cooling the product quicklime in the cooling zone, and is extracted from the upper part of the cooling zone or the lower part of the firing zone. In addition, CO ₂ and O ₂ blown from the bottom of the firing zone
The mixed gas of (1) is extracted from the upper part of the pre-tropical zone after burning coke in the firing zone, firing limestone, preheating limestone in the pre-tropical zone. As a result, the exhaust gas withdrawn from the preheating zone top, because the CO ₂ in the mixed gas with CO ₂ generated by burning reaction of coke combustion and limestone are discharged are mixed, CO in the exhaust gas ₂ The concentration is dramatically improved to 90 to 100%. Therefore, this CO ₂ concentration is 90-100%
The exhaust gas of the above can be recovered as liquefied CO ₂ by directly introducing it into the CO ₂ liquefaction purification apparatus.

Further, a mixed gas of by blowing air from the cooling zone to bottom withdrawn from the cooling zone upper or firing zone lower hot air CO ₂ and O ₂ were heat exchange, a mixed gas of preheated CO ₂ and O ₂ C blows from the bottom of the firing zone, burns coke and fires limestone, preheats, and discharges from the top of the pretropical zone.
Since a part of the high O ₂ concentration exhaust gas circulates as CO ₂ in the mixed gas, the preheating of the mixed gas of CO ₂ and O ₂ can be effectively utilized product quicklime heat, moreover, the CO ₂ and O ₂ As part of the CO ₂ -rich exhaust gas discharged from the upper pretropical zone is circulated as a CO ₂ source for the mixed gas, CO
There is no need to supply ₂ .

In the present invention, C blown from the bottom of the firing zone
O ₂ concentration in the mixed gas of O ₂ and O ₂ is, O ₂ normal air
Concentration is sufficient. The temperature of the mixed gas of CO ₂ and O ₂ blown from the lower part of the firing zone is preferably as high as possible.
About 0 ° C is sufficient. CO used in this invention
_{As the two-} liquefaction refining apparatus, a known cryogenic method apparatus can be used as it is.

[0012]

【Example】

Example 1 Hereinafter, a method for recovering CO ₂ from lime furnace exhaust gas according to the present invention will be described in detail with reference to the example shown in FIG.
FIG. 1 is a system diagram of a method for recovering CO ₂ from lime furnace exhaust gas according to the present invention. In FIG. 1, a vertical lime furnace 4 comprising a cooling zone 1, a calcination zone 2 and a pre-tropical zone 3 is charged with limestone 5 from the upper part of the pre-tropical zone 3 and is cooled by a blower 6 from the lower part of the cooling zone 1. Blow 7 The quicklime calcined in the calcining zone 2 is cooled by exchanging heat with the cooling air 7 in the cooling zone 1 and taken out from the lower part of the cooling zone 1 as product quicklime 8. Hot air 9 heated in the cooling zone 1 by exchanging heat with quicklime 8
Is extracted from the upper part of the cooling zone 1 and introduced into the heat exchanger 10, where it exchanges heat with the mixed gas 11 of CO ₂ and O ₂ to produce CO ₂
After preheating the mixed gas 11 of C and O ₂ , it is released or used as combustion air for other combustion furnaces.
CO ₂ whose temperature has been increased by exchanging heat with the hot air 9 in the heat exchanger 10.
A mixed gas 11 of O ₂ and O ₂ is blown from the lower part of the firing zone 2, burns coke and the like in the firing zone 2 to burn the preheated limestone in the pretropical zone 3, and CO ₂ generated by the firing reaction.
At the same time, it is countercurrently contacted with the limestone 5 charged from the upper side in the pretropical zone 3 to be preheated, and is discharged from the upper portion of the pretropical zone 3 as the exhaust gas 12.

[0013] Therefore, the exhaust gas 12 of the lime kiln 4 is composed of CO ₂ and CO ₂ mixed gas 11 is consumed O ₂ by combustion generated by burning reaction of limestone generated by the combustion of the coke, CO ₂ Concentration reaches 90-100%. The CO _{2 in} the exhaust gas 12 is recovered by boosting the pressure of the exhaust gas 12 by the compressor 13 and then part of the CO ₂
Circulated as a mixed gas 11 of the O _2, the liquefied purified by introducing the remainder liquefied purification unit 14, the high-purity liquefied CO ₂
Collect 15. Note that 16 is O ₂ . Therefore, the CO _{2 in} the exhaust gas 12 of the lime furnace 4 as in the conventional method is
Does not need to be separated and collected by PSA or an absorption method and concentrated, and can be directly introduced into the liquefaction refining device 14 for liquefaction refining, so that not only the equipment cost is reduced by that much, but also the running cost is greatly reduced. Can be used at low cost
O ₂ can be recovered.

Example 2 A test furnace having an inner diameter of 180 mm and a height of 2000 mm was used as a lime furnace, cooling air was introduced at a rate of 200 Nl / min from the lower part of the test furnace, and hot air was extracted from a position 700 mm from the lower end of the test furnace. 800 mm from the bottom of the test furnace
From the position of CO ₂ 158 Nl / min, O ₂ 42 Nl / m
The mixed gas of in is heated to 600 ° C. with a heater and introduced, calcination of limestone is carried out, and product quicklime 4.3 kg / h
r was obtained. In addition, the composition of the waste gas discharged from the upper end of the test furnace was analyzed by gas chromatography. The results are shown in Table 1 in comparison with the case of the conventional method in which combustion air was blown at 200 Nl / min from the lower end of the test furnace to calcine limestone and exhaust gas was discharged from the upper end of the test furnace.

[0015]

[Table 1]

As shown in Table 1, according to the method of the present invention,
The CO ₂ concentration in the exhaust gas discharged from the upper part of the lime kiln, which was 30% in the conventional method, can be dramatically increased to 95% or more, and can be introduced as it is to the liquefied CO ₂ purification device by cryogenic separation. Met.

[0017]

As described above, according to the method of the present invention, the CO ₂ concentration in the exhaust gas discharged from the lime furnace is
The concentration can be dramatically increased to the level that can be introduced into the liquefied CO ₂ purification device, and the CO ₂ concentration / separation device becomes unnecessary,
Liquefied CO ₂ can be recovered at low cost.

[Brief description of drawings]

FIG. 1 is a system diagram of a method for recovering CO ₂ from lime furnace exhaust gas according to the present invention.

FIG. 2 is a system diagram of a conventional method for recovering CO ₂ from lime furnace exhaust gas.

[Explanation of symbols]

1,21 Cooling zone 2,22 Firing zone 3,23 Pretropical zone 4,24 Lime furnace 5,25 Limestone 6,26 Blower 7 Cooling air 8,28 Quicklime 9 Hot air 10 Heat exchanger 11 Mixed gas 12,29 Exhaust gas 13,30 Compressor 14,32 Liquefaction refining device 15,33 Liquefied CO ₂ 16 O ₂ 27 Combustion air 31 CO ₂ recovery device 34 Waste gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Noro 1 Kunomi-cho, Kokurakita-ku, Kitakyushu City, Fukuoka Prefecture Kyodo Oxygen Co., Ltd., inside the Kokura Factory (72) Inventor Shiro Komine 1 Konomi-cho, Kitakyushu, Kitakyushu, Fukuoka Address Kyodo Oxygen Co., Ltd. in the Ogura Factory (72) Inventor Takeshi Iida No. 1 Konomi-cho, Ogura Kita-ku, Kitakyushu, Fukuoka Prefecture Kyodo Oxygen Co., Ltd. in the Ogura Factory (72) Inventor Sozo Kawaguchi Kitahama, Chuo-ku, Osaka City, Osaka Prefecture 4-53-3 Sumitomo Metal Industries, Ltd. (72) Inventor Masanori Sugi 1-1-1 East Port, Kokurakita-ku, Kitakyushu City, Fukuoka Prefecture Sumikin Kokura Mineralization Co., Ltd.

Claims (2)

[Claims] 1. When calcining limestone in a lime furnace consisting of a pre-tropical zone, a calcination zone and a cooling zone to produce quicklime, cooling air is blown from the lower part of the cooling zone to extract it from the upper part of the cooling zone or the lower part of the calcination zone. A mixed gas of CO ₂ and O ₂ is blown from the lower part to burn coke to burn and preheat limestone, and the exhaust gas with a high CO ₂ concentration discharged from the upper part of the pretropical zone is introduced into the CO ₂ liquefaction refining device and liquefied. the method of recovering CO ₂ from the lime kiln exhaust gas and recovering the CO _2. 2. Hot air extracted from the upper part of the cooling zone or the lower part of the burning zone by blowing cooling air from the lower side of the cooling zone when manufacturing lime by firing limestone in a lime furnace consisting of a pre-tropical zone, a burning zone and a cooling zone. The mixed gas of CO ₂ and O ₂ is heat-exchanged, and the heated mixed gas of CO ₂ and O ₂ is blown from the lower part of the firing zone to burn coke to burn and preheat the limestone, which is discharged from the upper part of the pretropical zone. A part of the exhaust gas having a high CO ₂ concentration is circulated as a mixed gas of the CO ₂ and O ₂ ,
A method for recovering CO ₂ from lime furnace exhaust gas, characterized in that the remaining part is introduced into a CO ₂ liquefaction refining apparatus to recover liquefied CO ₂ .