JP2539443B2 - A method for separating and recovering CO 2 under 2 with high purity from exhaust gas from a steel mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a blast furnace gas (hereinafter referred to as BF
CO ₂ such as converter gas (hereinafter referred to as LDG) etc.
The present invention relates to a method for separating and recovering CO ₂ with high purity by applying a pressure swing method (hereinafter referred to as PSA method) to exhaust gas containing 5 to 40%.

[Prior Art] The main uses of CO ₂ are for welding shields, soft drinks, dry ice, and bottom blowing converters. The CO ₂ sources conventionally used for these are mainly those recovered from the by-product gas during ammonia synthesis and off-gas during oil refining.
It will occupy more than 80% of ₂ . A liquid absorption method such as an alkanolamine method, a potassium carbonate method, or a catacarb method is used as a method for recovering the same.

[Problems to be Solved by the Invention] However, all of the above-mentioned methods are liquid absorption methods, and the equipment cost is high, and a large amount of steam or electric power is required for regeneration and circulation of the absorption liquid, resulting in running costs. There are problems such as high cost and complicated handling due to being a liquid.

Further, in recent years, ammonia synthesis plants and oil refining plants have tended to shrink with changes in the industrial structure, and it has become necessary to secure new CO ₂ sources. In this way, BFG and LDG, which are produced as a large amount by-products from steel mills, have been paid attention to. If CO ₂ can be separated and recovered with high purity from these CO ₂ -containing gases, it will be of great industrial benefit.

The present invention has been studied under such an environment, and the object of the present invention is to separate CO ₂ in the exhaust gas of a manufacturing plant containing 15 to 40% CO ₂ with high purity and at low cost by the PSA method. It is to provide a method that can be recovered.

[Means for Solving the Problems] The present invention, which was able to solve the above problems, has a pressure swing adsorption device in which two or more adsorption towers are arranged in parallel, and the amount is 15 to 40%.
In introducing CO ₂ -containing steel plant exhaust gas to recover CO _{2 in} this exhaust gas, the adsorbent filling structure in the adsorption tower is as follows: (1) Zeolite in the upper stage, activated carbon in the middle stage, activated alumina or silica gel in the lower stage. (2) Zeolite is used in the upper stage and activated alumina or silica gel is used in the lower stage, and the exhaust gas containing moisture and S is CO ₂ partial pressure 1
After introducing from below into the CO ₂ adsorption tower at 20 mmHg or more, the pressure inside the adsorption tower is reduced to atmospheric pressure, and the impure gas component filling the dead space in the adsorption tower is exhausted, and further 700 to 100 torr Vacuum is applied to desorb the impure components adsorbed on the adsorbent,
With the recovery of high purity CO ₂ by then to further desorb evacuated to a CO ₂ to 100～30Torr, other adsorption with the moisture and S content adsorbed, performing the vacuum in the adsorption column In the adsorption cycle of the column, the gas passing through the adsorption column is introduced from above to desorb the gas, thereby regenerating the adsorbent and improving the CO ₂ recovery rate.

[Function] Hereinafter, the case of BFG will be described as a typical example of the exhaust gas from a steel mill containing 15 to 40% CO ₂ .

The main part for carrying out the method of the present invention is shown in FIG.
As shown in (e), a compressor 2 for compressing and introducing BFG into the adsorption tower 1, an adsorption tower 1 filled with an adsorbent for selectively adsorbing CO ₂ [in FIG. 1, three towers (1A , 1B, 1C), but those in which two or more columns are arranged in parallel are all included in the present invention], and a pressure reducer 3 for desorbing the selectively adsorbed CO ₂ under reduced pressure. Connected.

The adsorbent may be packed in the adsorption tower 1 as follows: (1) Zeolite in the upper stage, activated carbon in the middle stage, activated alumina or silica gel in the lower stage, or (2) zeolite in the upper stage, activated alumina in the lower stage or It is desired that any one or more kinds of silica gel and the zeolite packed in the adsorption tower 1 have a pore diameter of 10 Å or more and a large pore volume. An example of this is X-type zeolite NoX. As is clear from the adsorption / desorption pressure-adsorption / desorption amount diagram under isothermal conditions shown in FIG.
Although the amount of CO ₂ adsorbed is large, the amount of CO, N ₂ and H ₂ adsorbed is small, and desorption is easy, which indicates that the adsorbent is suitable for pressure swing. The main components of BFG are as shown in Table 1, which contains moisture (H ₂ O) and a trace amount of S in addition to N ₂ , CO ₂ , CO and H ₂ , and the middle and / or The activated carbon, activated alumina, and silica gel packed in the lower stage have excellent adsorption capacity for moisture and S in the gas. Therefore, when the raw material gas is introduced from the bottom of the tower, they reach the upper zeolite packed bed. These components are preferentially adsorbed. Since the BFG in from Table 1 CO ₂ are contained in a large amount CO ₂
It can be seen that it is useful as a recovery resource.

The process for recovering high-purity CO ₂ from BFG will be specifically described below with reference to FIGS. 1 (a) to 1 (e).

(1) Adsorption step: The raw material BFG is compressed by the compressor 2, the temperature is adjusted by the aftercooler 4, and then introduced into the adsorption tower 1A to raise the pressure to a predetermined pressure. At this time, the CO ₂ concentration in the passing exhaust gas discharged from the gas discharge part of the adsorption tower 1A was measured, and the BFG was measured until it became almost the same as the CO ₂ concentration in the raw material BFG at the gas inlet part of the adsorption tower 1A. It is introduced and CO ₂ is adsorbed on the adsorbent [Fig. 1 (a) Thick line raw material BFG to adsorption tower 1A].

Here, CO ₂ in BFG is mainly adsorbed on the zeolite packed in the upper stage of the adsorption tower 1, and moisture and S are adsorbed on the activated carbon, activated alumina or silica gel packed in the middle stage and / or the lower stage. As the adsorption pressure becomes clearer from the adsorption / desorption tower temperature curve shown in Fig. 2, the CO ₂ partial pressure becomes higher and the CO ₂ adsorption amount increases on the higher pressure side. However, increasing the adsorption pressure is necessary for gas compression. Energy costs are high,
Based on the fact that the CO ₂ content is 15 to 40% and the relationship between the CO ₂ adsorption and desorption isotherm and the adsorption amount, the CO ₂ partial pressure is 120 mmHg or more, and the total pressure is 0.2 to ² kgf / cm ² · G. It is desirable.

The gas that has passed through the adsorption tower is discharged (or recovered, the same applies hereinafter) as rest gas through a pressure regeneration step (described later) of the other tower [Fig. 1 (a) Thick line adsorption tower 1A to 1B to rest gas].

(2) Depressurization step: After the adsorption step is completed, the pressure is reduced to atmospheric pressure and the impure gas component filling the dead space in the adsorption tower 1A is discharged from the adsorption tower 1A [Fig. 1 (b) thick line]. This step can be omitted if the adsorption pressure is low.

(3) Initial vacuum desorption process: After the decompression process is completed, the pressure is reduced to 700 to 100 torr by the decompressor 3, but the gas desorbed by this initial vacuum desorption (containing a large amount of CO ₂ , N ₂ as impurities,
The gas containing CO, H ₂ , S, etc.) is discharged from the inside of the adsorption tower 1A [thick line in FIG. 1 (c)].

(4) Vacuum desorption process: The pressure inside the adsorption tower is further reduced by the decompressor 3, and CO ₂ adsorbed on the adsorbent is desorbed and recovered as a product. At this time, the degree of vacuum is preferably 100 to 30 torr in consideration of CO ₂ purity and recoverability [thick line in FIG. 1 (d)].

(5) Step-up regeneration step: Most of the moisture and S adsorbed in the lower part of the adsorption tower by the desorption during the initial vacuum desorption step and the vacuum desorption step are also desorbed, but are discharged in the adsorption step of the other tower 1C. The adsorbent passing gas is introduced from above the adsorbing tower 1A, that is, from the passing gas outlet side, and the moisture and S remaining in the BFG inlet part of the adsorbing tower are desorbed to regenerate the adsorbent. The pressure inside the tower is increased to prepare for the next adsorption step. Also,
The gas passing through the adsorption tower 1C contains CO ₂ that has not passed through the adsorption column, and by collecting this gas, the CO ₂ recovery rate as a whole is also improved. The gas that has passed through the adsorption tower for pressurization regeneration is exhausted or recovered as rest gas [Fig. 1 (e) Thick line adsorption tower 1C through adsorption tower 1A to rest gas], but this rest gas contains little CO _2. Since it does not contain calories per unit amount, it can be separately collected as having high calories.

The adsorption tower 1, the compressor 2, the decompressor 3, the heat exchangers 4, 5 and the on-off valve arranged between the pipes are operated so as to satisfy the above respective pressures.

FIG. 3 shows an example of a cycle pattern when CO ₂ recovery is performed using three adsorption towers.

As described above, the product CO ₂ gas can be continuously collected by arranging two or more adsorption towers in parallel and alternately adsorbing and desorbing them.

Further, in the present invention, since commercially available zeolite, activated carbon, activated alumina and silica gel are used as the adsorbent, the adsorbent can be easily obtained at low cost. Also in terms of equipment, the main part consists of a compressor, adsorption tower, decompressor,
Since there is no need to perform a pretreatment for removing impurities (particularly moisture and S content) as in the past, and there is no need to provide a cleaning step with a product gas to increase product purity, the equipment area can be reduced and construction The cost will be low.

Also, the adsorption pressure in the adsorption step is low, which is beneficial in terms of running cost, and the PSA method is used, which makes it easy to maintain operation.

Although BFG is used as the raw material gas in the method of the present invention, it can be applied to the converter gas and other CO ₂ -containing mixed gas.

[Example] High-purity CO ₂ was separated and recovered from CO ₂ -containing exhaust gas from a steelworks under the experimental conditions and methods described below.

Equipment: Two-column PSA adsorbent: Zeolite 480 cc in the upper stage, activated carbon 150 cc in the middle stage, activated alumina 80 cc in the lower stage Raw gas composition: CO ₂ : 22.0%, CO: 21.1%, H ₂ : 2.6%, H ₂ : 54.3%, COS: 33.6pp
m, H ₂ S: 12.0ppm, Moisture: Saturation Operating temperature: 20 ℃ Adsorption pressure: 1.0kgf / cm ² · G (CO ₂ partial pressure 330mmHg) Operation: Experimental results: As shown in Table 2, the product purity increases according to the amount of exhaust gas from the initial vacuum desorption, and the effect of the initial vacuum desorption is recognized.

Moisture and S are discharged in each step at the ratio shown in Table 3.

Even when the above operation was repeated 50 times or more, the gas passing through the activated carbon layer showed a dew point of −60 ° C. or lower, and S content was not detected in the gas passing through the activated carbon.

[Effects of the Invention] As described above, according to the method of the present invention, C including BFG
CO ₂ can be separated and recovered with high purity and at low cost from exhaust gas from a steel mill containing 15 to 40% of O ₂ .

[Brief description of drawings]

FIGS. 1 (a), (b), (c), (d), and (e) are examples of configuration diagrams for carrying out the method of the present invention, and FIG. 2 shows adsorption / desorption equilibrium partial pressure and adsorption / desorption amount at isothermal conditions. FIG. 3 is a diagram showing an example of a cycle pattern. 1 ... Adsorption tower, 2 ... Compressor 3 ... Decompressor, 4,5 ... Heat exchanger

Claims (1)

(57) [Claims] 1. An adsorption tower in which the exhaust gas from a steel mill containing 15 to 40% of CO ₂ is introduced into a pressure swing adsorption device in which two or more adsorption towers are arranged in parallel to collect CO ₂ in the exhaust gas. (1) Zeolite in the upper stage, activated carbon in the middle stage, activated alumina or silica gel in the lower stage, or (2) zeolite in the upper stage, activated alumina or silica gel in the lower stage CO ₂ partial pressure of the above exhaust gas in a state of containing at least one kind of moisture and S content
After introducing from below into the CO ₂ adsorption tower at 20 mmHg or more, the pressure inside the adsorption tower is reduced to atmospheric pressure, and the impure gas component filling the dead space in the adsorption tower is exhausted, and further 700 to 100 torr A vacuum is drawn to desorb and exhaust the raw material gas filled in the adsorption tower and the impure components adsorbed by the adsorbent, and then 100
With the recovery of high purity CO ₂ by desorbing evacuation to CO ₂ in ～30Torr, moisture and S component adsorbed in the adsorption tower, the other adsorption tower performs the evacuation suction The gas passing through the adsorption tower in the cycle is desorbed by introducing it from above to regenerate the adsorbent and CO
₂ A method for separating and recovering CO ₂ with high purity from exhaust gas from a steel plant, which is characterized by improving recovery rate.