JPH10118440A - Treatment of gas containing methanol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating a gas containing methanol by controlling the newly replenished amount of water to scrubbers and maintaining the efficiency to remove the methanol at a high level. SOLUTION: In a method for treating a gas containing methanol using water scrubbers, two units of water scrubber 1A, 1B are arranged in series. Further, part 15 of a circulating water 5B in the rear stage water scrubber 1B is used in part of the front stage water scrubber 1A to sequentially treat the gas containing methanol. In addition, this treating method is used for treating the gas to be treated by adsorption and removing an organic solvent from the gas in the upstream side or the downstream side of the treatment process employing the water scrubbers 1A, 1B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating a gas containing an organic solvent, and more particularly to a method for treating a gas containing methanol which is difficult to treat by an adsorption method.

[0002]

2. Description of the Related Art Conventionally, the treatment of organic solvent gas involves adsorption and absorption.
Desorption, combustion, and biological treatment methods are commonly used.
In the adsorption / desorption method, activated carbon, synthetic zeolite, or the like is used as an adsorbent, and after the adsorption layer is saturated with a solvent, the adsorbed layer is desorbed with water vapor or air and collected. The combustion method includes a direct combustion method and a contact combustion method.The direct combustion method is a method of decomposing an organic solvent gas at a high temperature to make it harmless.The catalytic combustion method uses an organic solvent gas heated to a catalyst such as alumina. This is a method of contacting and decomposing at lower temperature than the direct combustion method. The biological treatment method utilizes a decomposition by microorganisms and uses a scrubber-type cleaning device to perform treatment, and has been used for deodorization in many cases. Further, as a method of treating a gas containing methanol, the present inventors,
First, Japanese Patent Application Nos. 5-163313 and 5-237.
No. 290. Among them, in the former, after adsorbing methanol with a scrubber, the adsorbed solution is decomposed by aerobic biological treatment, and solvent gases other than methanol are adsorbed by an adsorbent. At this time, alcohols other than methanol,
Other water-soluble solvents are also notably absorbed by the scrubber.

In the latter, a cooler, a water replenishment line and a water discharge line are provided in a water circulating section or a circulating water tank of a scrubber. This method utilizes the fact that the lower the temperature, the higher the rate of absorption of methanol into water. doing. By the way, when treating a methanol-containing gas by the adsorption method, methanol having a small molecular weight has a small adsorption capacity of the adsorbent and is not economical. On the other hand, instead of being hardly adsorbed by the adsorbent, methanol is soluble in water and can be removed by a water scrubber, and the above two applications use this. Water scrubbers are a simple way to remove methanol, but increasing the rate of methanol removal requires an increase in fresh make-up water, and an increase in make-up water after removing methanol. The amount of wastewater discharged out of the system is increased, and as a result, there is a problem in that the water treatment load on the wastewater treatment equipment in factories and business establishments is increased.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and reduces the amount of new replenishment water for a scrubber.
An object of the present invention is to provide a method for treating a methanol-containing gas while maintaining the methanol removal efficiency.

[0005]

In order to solve the above-mentioned problems, the present invention provides a method for treating a methanol-containing gas using a water scrubber, wherein the two water scrubbers are arranged in series to circulate a water scrubber in a subsequent stage. A part of the water is used for a part of the water scrubber in the preceding stage to sequentially treat the methanol-containing gas. In the treatment method, the treatment gas may be subjected to an adsorption treatment on an upstream side or a downstream side of the treatment using the water scrubber to remove an organic solvent in the gas.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the use of two water scrubbers can reduce the concentration of methanol in the processing gas without increasing the amount of external replenishment water, thereby reducing the amount of discharge from the circulating water tank. This contributes to reducing the burden of wastewater treatment at factories and offices. First, FIG. 2 shows a mass balance diagram focusing on the aqueous phase of the water scrubber, and the methanol concentration in each aqueous phase will be described using this diagram. In FIG. 2, the flow rate of makeup water is F ₁ ,
The methanol concentration in the makeup water is C ₁ , the circulating water flow rate is F ₂ ,
The methanol concentration of F ₂ is C ₂ , and the methanol concentration of spray water at a flow rate of F ₁ + F ₂ is C ₃ . Further, assuming that the mass flow rate at which methanol dissolves from the exhaust gas into the aqueous phase is M, the following two equations are derived. C ₁ F ₁ + M = F ₁ C ₂ (1) C ₃ + M / (F ₁ + F ₂ ) = C ₂ (2)

By substituting equation (2) into equation (1), C ₂ is eliminated. _{F 1 (C 3 + M /} (F 1 + F 2)) = C 1 F 1 + M C 3 + M / (F 1 + F 2) = C 1 + M / F 1 C 3 = C 1 + (F 1 + F 2 -F ₁ ) / F ₁ (F ₁ + F ₂ ) × MC ₃ = C ₁ + F ₂ M / F ₁ (F ₁ + F ₂ ) (3) Formula (3) is fresh as makeup water. C ₁ = 0 if pure water is used, but if the second-stage circulating water is used as a part of spray water as in the first stage of the present invention, the methanol concentration of the second-stage circulating water will be reduced. It can be seen that the spray water concentration is added as it is. Based on this fact, it will be examined how much the amount of methanol absorbed and discharged when trying to obtain the same processing gas concentration is different between the scrubber system of the present invention and the conventional water scrubber system.

FIG. 1 shows a flow configuration diagram of a two-stage in-line water scrubber which is a scrubber system of the present invention. In FIG. 1, reference symbol A indicates a first-stage scrubber, and B indicates a second-stage scrubber.
1 is a scrubber main body, 1A is a first stage, 1B is a second stage, and similarly, 2 is a packed bed, 3 is a spray, 4 is an eliminator, 5 is a circulating water tank, 6 is a circulating pump, and 7 is a discharge line. , 8 indicates a blow, 9 indicates a circulating water line, 10 indicates a spray water transfer pump, 11 indicates an exhaust gas inlet line, 12 indicates a line between scrubbers, 13 indicates an exhaust gas outlet line, and 14 indicates an injection water line. ing. The exhaust gas to be treated is introduced from the line 11 to the first-stage scrubber 1A, passes through the packed layer 2A, the eliminator 4A, and is introduced from the line 12 to the second-stage scrubber 1B, passes through the filled layer 2B, the eliminator 4B. The exhaust gas from which the contained methanol is absorbed and removed is discharged from the line 13.

On the other hand, water is introduced from the line 14 through the line 9B to the scrubber 1B of the second stage by spray 3B, reaches the water storage tank 5B through the packed bed 2B, and is partially discharged from the line 9B by the circulation pump 6B. Circulated to spray 3B. The remainder is sprayed 3A from the line 15 through the line 9A by the transfer pump 10 to the first stage scrubber 1A.
, And reaches the water storage tank 5A through the packed bed 2A, and partly sprays 3A from the line 9A by the circulating water pump 6A.
And the remainder is discharged from line 7A. Also,
The spray water transfer pump 10 transfers the circulating liquid in the circulating water storage tank 5B to the transfer line 1 by controlling the level of the circulating water storage tank 5B.
5 into the circulating water line 9A. FIG. 3 shows a flow diagram of a conventional one-stage water scrubber. The reference numerals are all the same as those in FIG. 1, and the exhaust gas is treated in only one stage of the water scrubber.

Next, referring to FIGS. 1 and 3, the treatment of the exhaust gas containing methanol was performed under the following conditions. The size of one is the same for both.

Table 1 shows the amount of circulating water and the amount of fresh makeup water.

[Table 1]

The results in Table 1 can be calculated as follows.
First, calculation is performed for the conventional method. Methanol concentration 200
It shall be reduced from 30 ppm to 30 ppm. Standard state gas amount = 50 × 273.15 / (273.15
+30) = 45.1 Nm ³ / min The amount of dry gas is 30.degree. C. and the saturated vapor pressure is 31.824 mmH.
g, dry gas amount in standard condition = 45.1 x $ (760-31.824) /
760｝ × 60 = 2592.7 Nm ³ / h Methanol collection amount = (200−30) × 10 ⁻⁶ × 2592.7 / 22.4
= 1.968 × 10 ^-2 kg · mol / h The amount of fresh makeup water is 2 m ³ / h and the amount of circulating water is 1 m ³ / h. Therefore, the shower amount of the scrubber is 2 + 1 = 3 m ³ /
h.

The amount of methanol in the shower at the top of the column is 1 × 1.968 × 10 ^-2 × 32 / (2 × 3) = 0.10
The amount of methanol increase in the 5 g / liter shower is 1.968 × 10 ⁻² × 32/3 = 0.210 g / liter. The amount of methanol in the shower at the bottom of the column is 0.105 + 0.210 = 0.315 g / liter. / Mol fraction) is calculated from the following empirical formula, where x is the mono fraction of methanol and t is the temperature. logE = 5.478- [1500 / (t + 230)] Here, x <0.1, t = 10 to 50 ° C. The Henry's constant at 30 ° C. is 0.3285 (atm / mol fraction).

From the above results, the molar fraction of methanol is converted, and the following results are obtained.

[Table 2] ^* Indicates equilibrium concentration.

[0015] From the above ^{(YY *) Lm = {(} Y 2 -Y 2 *) - (Y 1 -Y 1 *)} / In
{(Y ₂ −Y ₂ ^* ) / (Y ₁ −Y ₁ ^* )} = 5.060 × 10 ⁻⁵ Therefore, NTU (No. of Transfer Unit) is NTU = (Y ₂ −Y ₁ ). / a ^{(Y-Y *) Lm =} 3.36 scrubber of HTU (Height per Transfer Unit) and 0.6m. Assuming that the margin coefficient is 1.2, a packed bed height Z = 0.6 × 3.36 × 1.2 = 2.42 m, that is, a packed bed height of 2.5 m is sufficient.

Next, in the two-stage in-line water scrubber of the present invention, the following calculation can be made. The first part is 100 ppm from 200 ppm
ppm to 100 ppm to 30 ppm at the subsequent stage
Down to Rear part (second stage) Standard state gas amount = 50 x 273.15 / (273.15 + 30)
= 45.1 Nm ³ / min The amount of dry gas is 30.degree. C. and the saturated vapor pressure is 31.824 mmH.
g, dry gas amount in standard condition = 45.1 x ｛(760−31.824) / 7
60 ° × 60 = 2592.7 Nm ³ / h Methanol collection amount = (100−30) × 2592.7 / 22.4 = 8.
102 × 10 ⁻³ kg-mol / h The amount of fresh makeup water is 1 m ³ / h, and the amount of circulating water is 1 m ³ / h. Therefore, the shower amount of the scrubber is 1 + 1 = 2 m ³ /
h.

The amount of methanol in the shower at the top of the column is 1 × 8.102 × 10 ⁻³ × 32 / (1 × 2) = 0.13
0 g / liter The amount of methanol increase in the shower is 8.102 × 10 ⁻³ × 32/2 = 0.130 g / liter The amount of methanol in the shower at the bottom of the column is 0.130 + 0.130 = 0.260 g / liter As described above, 30 The Henry's law constant of methanol at 0 ° C is 0.
3285 (atm / mole fraction).

From the above results, conversion into methanol mole fraction is performed, and the following results are obtained.

[Table 3] ^* Indicates equilibrium concentration.

[0019] From the above ^{(YY *) Lm = {(} Y 2 -Y 2 *) - (Y 1 -Y 1 *)} / In
{(Y ₂ −Y ₂ ^* ) / (Y ₁ −Y ₁ ^* )} = 5.060 × 10 ⁻⁵ Therefore, NTU is NTU = (Y ₂ −Y ₁ ) / (Y−Y ^* ) Lm = 3. 29 The HTU of the scrubber is 0.6 m. The margin coefficient is 1.
Assuming that 2, the packed bed height Z = 0.6 × 3.29 × 1.2 = 2.37 m, that is, the packed bed height of 2.5 m is sufficient.

First stage (first stage) Standard state gas amount = 50 × 273.15 / (273.15)
+30) = 45.1 Nm ³ / min The amount of dry gas is 30.degree. C. and the saturated vapor pressure is 31.824 mmH.
g, dry gas amount in standard condition = 45.1 x (760-31.824) / 7
60 × 60 = 2592.7 Nm ³ / h Methanol collection amount = (200−100) × 2592.7 / 22.4 = 1.
157 × 10 ^-2 kg · mol / h Replenishment water uses part of the circulating water at the subsequent stage, 1 m ³ / h.
The amount of circulating water is 1 m ³ / h. Therefore, the shower amount of the scrubber is 1 + 1 = 2 m ³ / h.

The amount of methanol in the shower at the top of the tower is such that the methanol concentration of the circulating water in the latter stage is 0.260 g / liter, and the amount of methanol in the shower at the top of the tower can be obtained by simply adding 0.260 g / liter from the above formula. Because it is good 1 × 1.157 × 10 ^-2 × 32 / (1 × 2) + 0.260 = 0.44
5 g / liter The amount of methanol increase in the shower is 1.157 × 10 ^-2 × 32/2 = 0.185 g / liter. The amount of methanol in the bottom shower is 0.445 + 0.185 = 0.630 g / liter. The Henry's law constant of methanol at 0 ° C is 0.
3285 (atm / mole fraction).

From the above results, conversion into methanol mole fraction is performed, and the following results are obtained.

[Table 4] ^* Indicates equilibrium concentration.

[0023] From the above ^{(YY *) Lm = {(} Y 2 -Y 2 *) - (Y 1 -Y 1 *)} / In
{(Y ₂ −Y ₂ ^* ) / (Y ₁ −Y ₁ ^* )} = 4.262 × 10 ⁻⁵ Therefore, NTU is NTU = (Y ₂ −Y ₁ ) / (Y−Y ^* ) Lm = 2. 35 The HTU of the scrubber is 0.6 m. The margin coefficient is 1.
If it is set to 2, the packed bed height Z = 0.6 × 2.35 × 1.2 = 1.69 m, that is, the packed bed height 2.5 m is sufficient.

[0024]

According to the present invention, two scrubbers are required, and the initial cost increases, but the amount of discharged water is
For example, as described above, it is １ ／ compared to the conventional method,
Especially in the case of continuous operation, the effect is great. Further, by installing the two-stage in-line water scrubber of the present invention upstream or downstream of the organic solvent adsorption device, long-term continuous treatment of the adsorption device became possible.

[Brief description of the drawings]

FIG. 1 is a flow configuration diagram of a two-stage in-line water scrubber of the present invention.

FIG. 2 is a mass balance diagram of a methanol concentration in an aqueous phase of a water scrubber.

FIG. 3 is a flow configuration diagram of a conventional one-stage water scrubber.

[Explanation of symbols]

1, 1A, 1B: scrubber body, 2, 2A, 2B: packed bed, 3, 3A, 3B: spray, 4, 4, A, 4B: eliminator, 5, 5A, 5B: circulating water tank, 6, 6A,
6B: circulation pump, 7, 7A, 7B: discharge line, 8,
8A, 8B: blow, 9, 9A, 9B: circulating water line,
10: spray water transfer pump, 11: exhaust gas inlet line, 12: line between scrubbers, 13: exhaust gas outlet line, 14: injection water line, 15: spray water transfer line

Claims (2)

[Claims] In a method for treating a methanol-containing gas using a water scrubber, two of the water scrubbers are arranged in series, and a part of the circulating water of the latter water scrubber is used as a part of the former water scrubber. And treating the methanol-containing gas sequentially. 2. The method according to claim 1, wherein in the treatment method, the treatment gas is subjected to an adsorption treatment to remove an organic solvent in the gas at an upstream side or a downstream side of the treatment using the water scrubber. How to treat contained gas.