JPS6211502A - Method for recovering solvent in circulation type closed spray dryer - Google Patents

Abstract

PURPOSE:To obtain a device capable of recovering solvent used for spray drying in the form of clean liquid contg. no nonvolatile material by providing a moisture increasing stage and a cooling stage prior to a condensation stage. CONSTITUTION:Solvent in the feed liquid fed through a feed liquid feeding pipe 1 is evaporated in a main body 2 of a dryer, and evaporated solvent is fed to a moisture increasing and cooling device 11 in the vapor state through a solid/gas separator 3 and a blower 4. The moisture increasing and cooling device 11 serves to control the temp. of the discharged gas to near the dew point of the exhaust gas of a blower by means of a pump 12 and a first outside cooler 13. The gas is then introduced into a condenser 5, and the solvent contained in the exhaust gas of the blower 4 is condensed and discharged out of the system from a liquid drain pipe 8. Accordingly, the solvent is not condensed in the moisture increasing and cooling device 11 due to contacting effect of gas with liquid, but only powder accompanying the exhaust gas is removed. Therefore, recovered solvent being clear and contg. no powder is obtd. in the condenser 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a closed-circuit system for recovering a solvent-containing stock solution as a clean liquid free of non-volatile substances when spray-drying the solvent-containing stock solution. This invention relates to a method for recovering solvent in a spray dryer.

Conventional technology Generally, when spray drying a liquid containing a solvent, a large amount of solvent is contained in the vapor state in the dryer outlet gas (hereinafter referred to as exhaust gas) and cannot be released into the air. , a closed circulation spray dryer that cools the exhaust gas to below the condensation temperature using a condenser, condenses and removes the solvent vapor in the exhaust gas, reheats the exhaust gas, and uses the treated exhaust air as hot air for drying. is used.

Usually, the condenser cools the condensate with an external cooler,
A direct contact type condenser is used in which the solvent vapor in the exhaust gas is cooled by returning it to the condenser and bringing it into direct contact with the exhaust gas to condense the solvent vapor in the exhaust gas.

What is shown in FIG. 2 is a system diagram of a conventional circulating closed type spray drying apparatus. According to this diagram, the solvent in the stock solution supplied through the stock solution supply pipe 1 evaporates within the dryer main body 2, and vaporizes. The solid state is introduced directly into the condenser 5 via the solid gas separator 3 and the exhaust fan 4. The condenser 5 is equipped with a pump 6 and an outer cooler 7, in which the liquid is cooled below the condensing temperature and returned to the condenser 5, where it cools the exhaust gas by direct contact with the exhaust gas and cools the exhaust gas. #14-
1 /Fl # *II L m m + -w
-m + mow, color (taken out to the outside. The gas leaving the condenser 5 is heated by the heater 10 via the blower 9, and returned to the dryer main body 2 as hot air.

The embodiments of the present invention, which will be described later, also basically follow this conventional format.

This method has the advantage that, at the same time as recovering the solvent, powder in the circulating gas can also be removed by the gas-liquid contact action.

Problems to be Solved by the Invention However, despite the advantages of the conventional method, powder is mixed or dissolved in the recovered solvent. Furthermore, if the mixed powder is highly toxic, it is necessary to take great care in refining the solvent and handling it, which is really troublesome.

The present invention was devised to eliminate these problems, and its purpose is to directly recover clean solvent without the need for repurification.

Means for Solving the Problems Figure 3 is a temperature and humidity chart for explaining the present invention in detail, with humidity on the vertical axis and temperature on the horizontal axis, and the curves A-F shown in the chart. -E-D represents a saturation curve, and curve B-C-D represents an isenthalpy line.

To explain each point in Fig. 3 in parallel with Fig. 2 showing the conventional type, point A shows the state of gas at the outlet of the condenser 5, and point B shows the state of the gas from the condenser 5 through the blower 9. State of hot air heated by heater IO and supplied to dryer main body 2, point C
shows the state of exhaust air at the outlet of the dryer main body 2.

That is, the state of the gas at the outlet of the condenser 5 is at a temperature T1.
It is indicated by point A, which is at humidity H1.

Even if this gas is heated to a temperature T2, the humidity in the gas does not change, so the state of the gas after heating is at a temperature T2.
- Indicated by point B, where the humidity is H1.

Inside the dryer main body 2, the temperature and humidity move to the left in the figure on the isenthalpy line (FIG. 3 B-D) due to the evaporation of the solvent in the stock solution, and the humidity increases as the temperature decreases.

The state of the gas at the outlet of the dryer main body 2 is represented by the intersection C between the temperature T3 of the exhaust gas and the isenthalpy line (B-D), and the humidity of the gas at this time is H2.

The difference between the humidity H2 at point C and the humidity H1 at point B indicates the amount of evaporation of the solvent in the stock solution.

In the conventional case, the exhaust gas from the outlet of the dryer main body 2 at point C is cooled to point A in the condenser 5 that follows. Thereby,
An amount of solvent corresponding to the difference between the humidity H2 at point C and the humidity H1 of the exhaust gas at point A, that is, the outlet of the condenser 5, that is, an amount equal to the amount of solvent evaporated from the stock solution is condensed in the condenser 5. It will be liquefied and taken out of the system. However, as mentioned above, this condensate contains a considerable amount of powder.
It is molten and it is extremely difficult to reuse it as it is.

In the present invention, the process from point C to point A was studied in detail, and as a result, the exhaust temperature was maintained near the dew point of the exhaust gas cooled by the condenser 5, and powder was removed under this condition. It has been discovered that by carrying out this method, clean solvent can be recovered without reducing the amount of solvent recovered.

That is, a humidifying/cooling device is installed before the exhaust gas is sent to the condenser 5, and the exhaust air at point C in Fig. 3 is humidified once to the point where it reaches the point, and then cooled again to point E. If the solvent is sent to the condenser 5, the amount of solvent condensed in the condenser 5 will be the humidity H at point E.
2 and the humidity H1 at point A, and the amount of condensation should be the same as in the conventional method. If a scrubber-type humidifier/cooler with a powder removal function is used to remove powder almost completely, contamination in the condenser 5 can be prevented, and as a result, the condensation The solvent should also be extremely clean and should not require repurification.

Therefore, when we conducted an experiment by installing a humidifier/cooler that could control the exhaust air between points C and E, we obtained the expected results, and furthermore, the temperature at point E was T4.
If the temperature is adjusted to correspond to the temperature T5 at point F, it is possible to continuously draw out a liquid in which powder is dissolved in a high concentration, and the concentration can also be controlled by adjusting the temperature T4. There was found.

In accordance with the method of the present invention and based on these experimental results, we succeeded in designing a device that can be operated on a commercial basis.

Embodiment An embodiment according to the present invention is shown in FIG. 1, and as described above, its basic structure is the same as the conventional one, but its operation concept is as follows.

The solvent in the stock solution supplied through the stock solution supply pipe 1 evaporates within the dryer main body 2 and becomes a vapor state, which is transferred to the solid/gas separator 3.
The air is then sent to the humidifier/cooler 11 via the exhaust fan 4. The humidifier/cooler 11 includes a pump 12 and a first outer cooler 13, and serves to control the temperature of the gas at the outlet of the humidifier/cooler 11 to be near the dew point temperature of the exhaust gas. Gas from the humidifier/cooler 11 is introduced into the condenser 5. The condenser 5 is equipped with a pump 6 and an outer cooler 7, and the liquid is cooled to below the condensing temperature by the outer cooler 7, and the liquid is cooled to a temperature lower than the condensation temperature.
cooling the exhaust by direct contact with the exhaust,
Further, the solvent in the exhaust gas is condensed and taken out from the system through the liquid drain pipe 8. The gas exiting the condenser 5 passes through a blower 9, is heated by a heater 10, and is returned to the dryer body 2 as hot air.

By doing so, the humidity of the gas at the outlet of the humidifying e-cooler 11, that is, the concentration of the solvent in the gas, becomes almost the same as the composition of the gas at the outlet of the dryer main body 2. That is, the humidifier/cooler 11
In this case, due to the gas-liquid contact action, the solvent does not condense,
Only the powder entrained therein can be removed. The clean gas from which powder has been removed in this way is sent to the condenser 5 as described above, and the solvent vapor in the gas is condensed in the same manner as before with the aid of the pump 6 and the external cooler 7. The condensed liquid is taken out of the system from the drain pipe 8 as a clean solvent containing no powder.

On the other hand, when a liquid in which powder is dissolved in a high concentration is to be continuously extracted, a liquid drain pipe 14 is used.

In addition, the TC in FIG. 1 detects the temperature inside the humidifier/cooler 11,
This is a detection device for opening and closing a valve that controls the flow rate of the cooling medium to the first outer cooler 13.゛Effects of the Invention As described above, according to the present invention, by cooling the gas before it is sent to the condenser 5, only the powder accompanying the solvent is collected in the system without condensing the solvent itself. Since the solvent can be taken out, the solvent condensed in the condenser 5 in the next step will be clean and free of powder, and the re-purification step can be omitted to obtain a solvent that can be used as is. It also has the effect of omitting all the conventional complications in terms of pollution control and safety measures.

[Brief explanation of drawings]

FIG. 1 is a conceptual system diagram of equipment for carrying out the method of the present invention, and FIG. 3 is a chart showing the relationship between temperature and humidity for explaining the present invention in detail. No. ls stock solution supply pipe, 2. Dryer main body, 3. Solid/gas separator, 4. Exhaust fan, 5. Condenser, 6. Pump, 7. Outside cooler, 8. Liquid Extubation, 9...Blower, 1
0... Heater, 11ψ- Humidifier/cooler, 12- Pump, 13- First outer cooler, 14... Liquid drain pipe.

Claims (1)

[Claims] In a circulating closed spray dryer, humidification and
A method for recovering a solvent in a circulating closed spray dryer, characterized by providing a cooling step.