Method and apparatus for purifying gases containing volatile organic compounds, and for recovering and concentrating volatile organic compounds

Abstract

PROBLEM TO BE SOLVED: To provide a method for cleaning, recovering and concentrating an exhaust gas which contains volatile organic compounds, the method making effective use of energy to the maximum; and to provide a device therefor. SOLUTION: In cleaning volatile organic compound gases and a volatile organic compound-recovering and concentrating method for making effective use, to the maximum, of the energy of a volatile organic compound-containing exhaust gas emitted from drying facilities, a necessary temperature (thermal energy) of the exhaust gas is determined by the temperature and humidity of air (or an inert gas such as nitrogen) before being heated, which is the origin of the exhaust gas, and the energy of the exhaust gas, which exceeds the determined temperature, is used for the pre-heating of the air (or an inert gas such as nitrogen) before being heated, which is the origin of the exhaust gas, or the like.

Description

[Technical field]

[0001] The present invention is a method for producing a volatile organic compound (VOC) that can utilize the thermal energy of exhaust gas to the maximum extent possible. Contains Gas purification, volatile organic compound recovery and concentration method and equipment Place Regarding. [Background technology]

[0002] In April 2006, emission regulations for volatile organic compounds based on the revised Air Pollution Control Law came into force, and emission standards for volatile organic compounds contained in exhaust gases have been established. At present, in most cases, these are applied when the air volume of a blower or exhaust fan is above a certain level, but it is inevitable that further voluntary efforts to reduce emissions will be required, and from the perspective of making effective use of limited resources, the reuse of these resources is one of the major issues for future technological development.

[0003] Currently, most of the methods generally used for purifying exhaust gases containing volatile organic compounds emitted from hot air dryers and the like and recovering and reusing these volatile organic compounds are cooling methods or a combination of cooling and adsorption methods (see, for example, Patent Documents 1, 2, and 3). Taking N-methyl-2-pyrrolidone (hereinafter referred to as NMP) as an example of a volatile organic compound, the method involves first cooling the exhaust gas, liquefying and recovering as much NMP as possible that can be condensed, and then adsorbing and removing the remaining NMP by an adsorption method. The adsorbed NMP is desorbed by applying heat with a small amount of high-temperature gas, and the condensed gas is further cooled to increase the recovery rate. In the above method, cold and hot energy is provided from the outside, and a heat exchanger is used to effectively utilize the energy and reduce the amount of energy used. However, in most cases, the carrier gas that is the source of the exhaust gas is clean air that has been filtered from the atmosphere, and the energy required to heat the clean air as a drying gas is very large. The specific heat of air is 0.24kcal / kg°C, the temperature to be heated is 100°C, and the specific gravity of atmospheric air is 1.28kg / Nm 3 , air temperature 20℃, drying gas flow rate 240Nm 3 / min. In that case, 240Nm 3 / min×60min / hr×1.28kg / Nm 3 × 0.24 kcal / kg·℃ × (100℃-20℃) = 353,894 kcal of heat is required. This is equivalent to more than 412 kW of electricity, or more than 655 kg / hr of steam (assuming the latent heat of vaporization of water is 540 kcal / kg). In this method that combines the cooling method and the adsorption method, from the viewpoint of reducing the required energy, heat exchange with clean air is carried out to cool the gas, and the first preheating is carried out, and in order to lower the temperature of the concentrated gas after desorption, heat exchange with air that has been first preheated and second preheating is carried out, thereby achieving a saving in the energy required to heat the clean air.

[0004] In addition, there is a method and device (see Patent Document 4) developed by the applicant, which uses water to absorb volatile organic compounds in exhaust gas, and evaporates the water in the aqueous solution absorbed by thermal energy to concentrate the recovered liquid. With this method and device, the recovery rate of volatile organic compounds in exhaust gas is 99% or more, and the greatest feature is that the liquefied volatile organic compounds can be concentrated without external energy other than the thermal energy of exhaust gas at 45°C or more. In the case of NMP, the volatile organic compound is concentrated to 80wt% or more and recovered as a concentrated liquid. (Note that the value of 80, which is 80wt% or more, is usually adopted because, in the case of distillation purification, a process of removing water from the recovered liquid is always required due to the cost of regeneration, but if the concentrated liquid is 80wt% or more, there is no significant difference in the additional cost (energy) required for water removal, and if it is 85wt% or less (water content is 15wt% or more), there is no flash point and it can be treated as a non-hazardous material, so it is safe.) However, the greatest feature of the gas recovery method (apparatus) of this prior patent was that it only used the thermal energy of the exhaust gas, but there was a lower limit to that thermal energy, and as described in Patent Document 4, "it is intended for exhaust gases of 45°C or higher, and if the exhaust gas is below 45°C, thermal energy must be applied from the outside." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-38144 A [Patent Document 2] JP 2007-44595 A [Patent Document 3] JP 2007-83238 A [Patent Document 4] JP 2008-114203 A Summary of the Invention [Problem to be solved by the invention]

[0006] The Applicant Person in charge In the above-mentioned prior patent, as mentioned above, a method for recovering and concentrating exhaust gas by water absorption was proposed. However, this proposal requires the addition of heat energy when the exhaust gas temperature is below 45°C. Amount For efficient gas-liquid contact with water Is decoration In addition, the other prior patents mentioned above had problems such as excessive size. , exclusion Since external thermal energy is required in addition to the thermal energy of the gas, there is a limit to how much energy can be reduced. In order to solve these problems, the present invention has been developed as a result of extensive research and development, and has developed a system that can purify and concentrate exhaust gas at a temperature lower than the temperature of the original exhaust gas even with the use of a small amount of water, and can be used to power pumps, blowers, etc. Energy Providing a purification, recovery and concentration method that does not use any other energy The purpose is For example, exhaust gas below 45°C of In this case, steam etc. By In the past, it was necessary to supplement heat energy from outside, but with the system of the present invention, it is possible to determine the necessary exhaust gas temperature based only on the temperature of the air taken in for drying. Even when the temperature of the air taken in is low in winter, or high in summer, Exhaust gas temperature Higher than intake temperature However If this is done, the excess heat can be put to other effective use, achieving further energy savings. can . [Means for solving the problem]

[0007] The first aspect of the present invention relates to a method for purifying gases containing volatile organic compounds and recovering and concentrating volatile organic compounds, which comprises measuring the temperature and humidity of a drying carrier gas consisting of air or an inert gas, introducing it through a filter into a heat exchanger to preheat it, introducing it into a drying facility and heating it, evaporating and drying materials to be dried that contain volatile organic compounds that have a higher boiling point than water and are soluble in water, which have been separately introduced into the drying facility, and discharging the exhaust gas containing the volatile organic compounds, introducing the exhaust gas into a heat exchanger to raise the temperature to a temperature equal to or higher than the dew point determined by the temperature and humidity of the drying carrier gas, and then liquefying, concentrating and recovering the volatile organic compounds using water as an absorption medium. The second aspect of the present invention relates to a method for purifying a gas containing volatile organic compounds and recovering and concentrating the volatile organic compounds described in the first aspect, characterized in that the supply control of the water used as the absorption medium is performed by measuring the concentration and liquid level of the recovery liquid that liquefies, concentrates and recovers the volatile organic compounds. The third aspect of the present invention is a means for introducing a drying carrier gas consisting of air or an inert gas into a heat exchanger through a filter, preheating the gas and then introducing the gas into a drying facility; a measuring means for measuring the temperature and humidity of the drying carrier gas provided upstream of the heat exchanger; Drying Facility the concentration and recovery section; means for introducing exhaust gas containing volatile organic compounds from a drying facility through a heat exchange section at a temperature equal to or higher than the dew point determined by the temperature and humidity of a drying carrier gas; means for supplying an absorption medium (water) for volatile organic compounds, a purified gas discharge means, and a means for storing a volatile organic compound-containing treatment liquid in a storage section, all of which are provided in the concentration and recovery section; means for circulating and supplying the stored treatment liquid to the concentration and recovery section; and means for measuring a liquid level, a means for measuring the concentration of volatile organic compounds in the treatment liquid, and a discharge means for discharging the volatile organic compounds to the outside of the system as a recovered concentrated liquid, all of which are provided in the storage section. The fourth aspect of the present invention relates to an apparatus for purifying volatile organic compound-containing gases and recovering and concentrating volatile organic compounds, as described in the third aspect, characterized in that a means for spraying water used as an absorption medium is provided above the concentration and recovery section. Effect of the Invention

[0008] According to the present invention, the following effects can be achieved. (1) The recovered liquid contains water, but the water content in the recovered liquid can be adjusted as desired. From the viewpoint of distillation regeneration, it is desirable for the liquid to contain 80 wt% or more of volatile organic compounds. (2) By installing multiple absorption devices, the gas concentration after purification is reduced to 0.1 x 10 -4 It can be less than vol.%. (3) Except for the method of adjusting the amount of water supplied, the system is the same as a multi-stage gas-liquid contactor and can be constructed with a simple mechanism. The number of stages required can be freely increased or decreased depending on the target values ​​for the type of volatile organic compounds to be treated, the recovery rate (purification rate), and the concentration rate. (4) It is possible to purify and concentrate exhaust gas at a lower temperature than the original exhaust gas temperature. In addition, since no energy other than that required for driving pumps, blowers, etc. is used, the surplus energy required for exhaust gas can be used for preheating the gas to be sucked in as a drying carrier gas. (5) The overall configuration of the device can be designed either vertically or horizontally depending on the installation location. (6) In the case of the vertical type, the methods and devices described in JP-A-2004-230265 and / or JP-A-2008-114203 can be used. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of the process flow of the present invention. [Diagram 2] FIG. 2 is a flow diagram when the plate heat exchanger of the present invention is used. [Diagram 3] FIG. 2 is a flow diagram when a plate fin type heat exchanger via a heat medium according to the present invention is used. [Figure 4] FIG. 2 is a flow diagram showing a purification and concentration operation using a tower-type apparatus according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The basic requirements for the present invention will be described below. The purification method for volatile organic compounds of the present invention is a method of absorption with water, and therefore, the premise is that the target volatile organic compounds are compounds that have a higher boiling point than water and are soluble in water. Na emissive organic compounds As is a solvent selected from the group consisting of NMP (N-methylpyrrolidone), NEP (N-ethyl-2-pyrrolidone), DMF (N,N-dimethylformamide), DMAc (N,N-dimethylacetamide), DMSO (dimethylsulfoxide), EG (ethylene glycol), DEG (diethylene glycol), TEG (triethylene glycol), PG (propylene glycol), BDG (butyl diglycol), 1,4-BD (1,4-butanediol), MEA (monoethanolamine), and DGME (diethylene glycol monomethyl ether). Examples include . In particular, such volatile organic compounds Gas Content occurs vinegar Drying facilities that are part of the manufacturing process for lithium-ion secondary batteries (targeting NMP and NEP), drying facilities that are part of the dry synthetic resin manufacturing process (targeting DMF and DMAc), facilities that are part of the liquid crystal manufacturing process (targeting BDG, MEA, and DMSO), and others. of Polymer (resin) drying facilities, etc. but Yes, this issue Ming is It is suitable for use in such facilities.

[0011] The process flow of the present invention will be described with reference to Figure 1. Outside air taken in as "raw drying gas" is introduced into a heat exchanger through a filter, spare After heating, the "drying Career The gas is then introduced into the drying facility. The drying facility is also equipped with materials to be dried, including volatile organic compounds that have a higher boiling point than water and dissolve in water. drying Things Evaporative drying After Contains volatile organic compounds nothing This exhaust gas is purified by a heat exchanger and discharged as "exhaust gas". collect· It is introduced into the concentrator, Water as the absorption medium "Purification gases" and volatile organic compounds nothing "collect liquid " is obtained. Note that, as shown in Figure 1 Medium "Drying gas source" → "Drying gas Career Gas" → "Exhaust gas" → "Purified gas" of In the flow, the temperature, composition, and concentration of the gas change depending on the place it passes through. strange Bad For , and is expressed using such terms. In the process of the present invention, Drying carrier gas Temperature and Humidity in The dew point can be determined by knowing the temperature and humidity of the air being sucked in. 、 Water Vapor Pressure of calculation formula from The moisture content in the air can be calculated. The water If we know the water vapor pressure, we can determine how much the air needs to be cooled before moisture is exposed. Formula For example, if there is formula A for calculating the saturated water vapor pressure, Then, formula A The variables required are temperature T and humidity R%. the law of nature The vapor pressure at that time can be calculated by A(T) × R%. On the other hand, to determine the dew point T', it is sufficient to find T' where the vapor pressure calculated by A(T) × R% = A(T'). Ku , it is possible to calculate the dew point. The wet bulb temperature is the lowest temperature that can be achieved by purely evaporative cooling on a draught-wet (or ice-covered) surface. For air that does not reach 100% relative humidity, the wet bulb temperature is lower than the dry bulb temperature (thermometer), and the dew point is lower than the wet bulb temperature. There is a formula for estimating the wet bulb temperature, and it can be calculated if the water vapor pressure of the air and the temperature of the air (in this case, the exhaust gas) are known. Can do. The above filters include particulate removal filters, salt damage prevention filters, etc., and generally commercially available filters are sufficient. The heat exchanger may be any heat exchanger that can be used for heating, cooling, and heat exchange of gas, such as a plate-fin type heat exchanger, an aerofin type heat exchanger, a plate type heat exchanger, a multi-tube type heat exchanger, etc. A plate type heat exchanger is particularly preferred. In addition, the above exhaust gas purification and concentration device andA multi-stage water absorption type purifier can be used. The shape of the multi-stage water absorption type purifier is as described in the present invention. of Even in the horizontal type shown in the example, The above-mentioned special Open 2004-230265 Publication number and Patent Publication 2008-114203 Publication number Even with the tower type described in good . EXAMPLES

[0012] The present invention will be described in more detail below by way of examples, but the present invention is not limited to these examples.

[0013] Example 1 The process of the present invention will be described in more detail with reference to the flow chart of Figure 2. In this example, the case where the volatile organic compound is NMP will be described. Air from the atmosphere is taken into the blower through a particulate removal filter and a salt damage prevention filter, and then passed through a plate heat exchanger. Preheat with After that, dry it. Career It is introduced into the drying facility as gas. A separate NMP-containing gas is introduced into the drying facility and heated together with the drying carrier gas. NMP but evaporation death The resulting mixture is discharged as NMP-containing exhaust gas. In this embodiment, the gas flow rate is 200 kg / min (155 Nm 3 / min), from drying facility of Exclusion Start again Later Exclusion Gas temperature 100℃ , exclusion In gas of NMP concentration 0.1 vol%, source atmospheric air temperature 20°C, relative humidity 60%Rh, heat transfer area of ​​plate heat exchanger 200 m 2 , Overall heat transfer coefficient of the heat exchanger: 50 kcal / (m 2 In this embodiment, So, heat exchanger of Heat transfer area of ​​200m 2 Even if the temperature difference in heat exchange is increased, the temperature difference does not change significantly. 2 The manufacturing cost for a heat exchanger of the above but Rising, heat exchange Vessel The dimensions will also be larger. from , temperature difference, cost, dimensions consideration and the heat transfer area is 200m 2 It was decided. [Table 1] Heat transfer area: 200m 2 By using a heat exchanger, 20℃ air and 100℃ exhaust gas but Through heat exchange, the exhaust gas drops to 38°C, and because there is the same amount of 20°C air as the exhaust gas, it can be preheated to 20°C + (100°C - 38°C) = 82°C. The energy required to heat 200kg / min of gas to 100°C is 200kg / min × (100°C - 20°C) × 0.24kcal / (kg·°C) × 60min / hr = 230,400kcal / hr, and the energy required to heat 82°C air to 100°C is 200kg / min × (100°C - 82°C) × 0.24kcal / (kg·°C) × 60min / hr = 51,840kcal / hr, 、( Energy was reduced by 1-51840 / 230400) x 100 = 77.5%. The exhaust gas, whose temperature had dropped to 38°C, was purified and recovered. · The mixture is introduced into a concentrator. Uses water as the absorption medium So In order to concentrate the NMP after absorption, the water is evaporated. Let Considering the temperature and humidity of the original atmospheric air, To contains only 1.4 vol% moisture, and based on this moisture value and a temperature of 38°C, it is theoretically possible to discharge purified gas at the wet-bulb temperature of 21.2°C and relative humidity of 100% Rh. The moisture content of the purified gas at that time is 2.48 vol%, making it possible to evaporate the water sufficiently. Focusing only on the water mass balance, the absolute humidity at 20°C and 60% Rh is 0.0087 kg (moisture) / kg (dry air), so the moisture content of the original 200 kg / min of air is 200 x 0.0087 / (1.0087) = 1.72 kg / min. Absolute humidity can be found on a humidity chart or calculated using the water vapor pressure formula. Also , original air fromThe mass of dry air with moisture removed is 198.28 kg / min. On the other hand, the absolute humidity at 21.2°C and 100% Rh is 0.0158 kg (moisture) / kg (air), and the mass of the dry air does not change, so 198.28 x 0.0158 = 3.13 kg / min of water can be discharged into the purified gas. Therefore, in terms of time, (3.13 - 1.72) x 60 = 84.6 kg / hr of water is evaporated. Let It is possible to do this, and only by that amount, Absorption medium It is understood that it is possible to supply water. Like this To, Water The amount of supply is Theoretically It can be calculated from the temperature of the exhaust gas and the temperature and humidity of the original air. In actual operation, if you understand the theory, Resupply Decide on the amount thing In other words, because water evaporates sufficiently even at 38°C, gas purification and recovery using a multi-stage gas-liquid contact system is easy. · In the concentrator, the amount of circulating liquid decreases as water evaporates. The liquid level is controlled by level gauge 2 in Figure 2. When the liquid level falls below a certain level A, the liquid level is increased to a level higher than A. Liquid Side B Pay Absorbs like water medium The automatic valve 3 attached to the inlet of the exhaust gas inlet is opened and closed. Meanwhile, the gas-liquid contact part on the primary side where the exhaust gas enters is monitoring the concentration of the recovered liquid with a concentration meter, checking the decrease in the liquid level with a liquid level gauge 1, and teeth If the liquid level is low even though the concentration has reached 80wt%, or if the liquid concentration has not reached 80wt%, Also When the liquid level is low, the automatic valve 2 opens and closes to adjust the liquid level. Naturally, the liquid level in the second stage from the primary side is Go down However, because the liquid automatically flows from the third and fourth stages due to the difference in liquid level, the liquid level of each stage is monitored by the liquid level gauge 2. Decline can be confirmed. When the concentration of the recovered liquid from the first stage gas-liquid contact part on the primary side reaches 80 wt%, and the liquid level is above level C, automatic valve 1 opens and closes to extract 80 wt of concentrated liquid as the recovered liquid. Also, the liquid level on level gauge 1 is Go down Therefore, automatic valve 2 opens and water is supplied from the second stage. BeAs a result, the liquid level on the level gauge 2 drops, so the automatic valve 3 opens and closes to maintain the liquid level on the level gauge 2. Special Water can be replenished in batches without calculating the amount of water to be fed. Therefore, the amount of water evaporated is theoretically calculated based on the temperature and humidity of the air and the temperature after heat recovery. Let If it is possible to measure the temperature and humidity of the atmosphere, this method is valid. Pay If the result is no, the heat recovery rate can be lowered slightly to enable control. If not, the temperature on the thermometer will determine whether the bypass of the heat exchanger is required. Attached Open the control valve that is By The exhaust gas temperature can be increased, In the unlikely event Even if concentration is not possible at 38°C (for example, if a large amount of water is contained in the exhaust gas due to a problem), the bypass is adjusted and the inlet temperature of the device is monitored. If you do , purification and recovery · This does not cause any problems during concentration operations. By providing multiple gas-liquid contact sections, the NMP concentration in the purified gas can be of It is possible to make the concentration of NMP in the purified gas as close to zero as possible. -4 Theoretically, if each gas-liquid contact section can achieve the performance equivalent to one theoretical plate, then the -4 It is also possible to reduce it to less than vol%.

[0014] Example 2 FIG. 3 shows an example of an embodiment of the present invention in which a plate fin type heat exchanger is used instead of the plate type heat exchanger in FIG. 2 shown in Example 1. By adjusting the flow rate of the heat medium, it is possible to control the exhaust gas temperature.

[0015] Example 3 FIG. 4 shows an example of an embodiment of the present invention in which the purification and concentration operation is performed using a tower-type apparatus shown in JP 2004-230265 A or JP 2008-114203 A in FIG. 2 shown in Example 1. By stacking the gas-liquid contacting sections vertically and by flowing the absorption water from the top of the tower and feeding the exhaust gas from the bottom of the tower, a multi-stage gas-liquid contact effect is obtained by countercurrent gas-liquid contact. Therefore, even if the amount of water as the absorption medium is small, NMP can be efficiently absorbed, and therefore the installation area and the number of devices can be reduced.

[0016] As described in detail in each of the above examples, in the present invention, the liquefied and recovered NMP is concentrated and dried without obtaining any heat energy from the outside. Career This achieves energy savings in gas heating. The energy saving effects are compared and summarized in the table below in relation to prior art. For comparison, Career Gas is atmospheric In The temperature is 20°C and the humidity is 60%Rh, and the temperature is raised to 100°C. The exhaust gas has an NMP concentration of 0.1 vol% and a temperature of 100°C, and the gas flow rate is 200 kg / min in both cases. Where It is a combination. In addition, see Table 2 below. Shown in The operating conditions for each method are described in Examples 1 and 2 of the present invention. of Conditions: cooling + adsorption method teeth Heat recovery from exhaust gas and heat recovery within the device raises air temperature from 20°C to 50°C. 、 The assumption is that the concentration of the recovered liquid is 80 wt%. ,single A pure scrubber reduces the concentration of purified gas to 20×10 without heat recovery. -4 In order to reduce the concentration to below vol%, it is assumed that the concentration of the circulating fluid will be controlled at 20 wt%. [Table 2]

Claims

1. A method for purifying a gas containing volatile organic compounds, and recovering and concentrating the volatile organic compounds, comprising the steps of: measuring the temperature and humidity of a drying carrier gas consisting of air or an inert gas; introducing the same through a filter into a heat exchanger to preheat it; introducing the same into a drying facility to heat it; evaporating and drying a material to be dried, which contains volatile organic compounds that have a higher boiling point than water and are soluble in water, and separately introduced into the drying facility; discharging the material as exhaust gas containing the volatile organic compounds; introducing the exhaust gas into a heat exchanger to raise the temperature to a temperature equal to or higher than the dew point determined by the temperature and humidity of the drying carrier gas; and then liquefying, concentrating and recovering the volatile organic compounds using water as an absorption medium.

2. A method for purifying a gas containing volatile organic compounds, recovering and concentrating volatile organic compounds, as described in claim 1, characterized in that the supply of water used as the absorption medium is controlled by measuring the concentration and liquid level of the recovery liquid that liquefies, concentrates and recovers the volatile organic compounds.

3. a means for introducing a drying carrier gas consisting of air or an inert gas into a heat exchange section through a filter, preheating the gas and then introducing the gas into a drying facility; a means for measuring the temperature and humidity of the drying carrier gas provided upstream of the heat exchange section; a means for introducing a material to be dried, which contains volatile organic compounds that have a boiling point higher than that of water and are soluble in water, into the drying facility; a means for introducing exhaust gas containing volatile organic compounds from the drying facility into the concentration / recovery section through the heat exchange section at a temperature equal to or higher than the dew point determined by the temperature and humidity of the drying carrier gas; a supply means for an absorption medium (water) for volatile organic compounds, a purification gas discharge means, and a means for storing a volatile organic compound-containing treatment liquid in a storage section, which are provided in the concentration / recovery section; a means for circulating and supplying the stored treatment liquid to the concentration / recovery section; and a liquid level measurement means, a means for measuring the concentration of volatile organic compounds in the treatment liquid, and a discharge means for discharging the volatile organic compounds to the outside of the system as a recovered concentrated liquid, all of which are provided in the storage section.

4. 4. The apparatus for purifying a gas containing volatile organic compounds, recovering and concentrating volatile organic compounds according to claim 3, characterized in that a means for spraying water used as an absorption medium is provided above the concentrating and recovering section.

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