JP2007130622A - Mercury removal apparatus of waste fluorescent lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems of a devolatization method of mercury in a waste fluorescent lamp by vacuum high temperature heating, wherein an apparatus can be made in the smallest and simplest structure, obtaining high vacuum by making crushed glass pieces of the waste fluorescent lamp a stationary packed layer, but a space between packed layers obstructs heat transfer to a central part of the layer. <P>SOLUTION: After evacuating inside the packed layers, only a small amount hydrogen or helium of high heat conductivity is charged into the layer during heating period of the packed layers; thus heat transfer is promoted and temperature raising time can be shortened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a mercury removal apparatus for waste fluorescent tubes. Specifically, the present invention relates to a method for evaporating and removing mercury from a crushed glass of a waste fluorescent tube by vacuum high temperature heating.

Mercury contamination is well known in Minamata Bay and the Agano River basin, and it is also known that even inorganic mercury can be converted to organic mercury, the causative agent of Minamata disease.
Fluorescent tubes widely used in homes and factories also contain a very small amount of mercury, and waste fluorescent tubes have been hardly treated and disposed of as difficult-to-treat materials for a long time. Therefore, there is a need for an inexpensive method for recovering and processing mercury from this waste fluorescent tube.
Traditionally, there is no lack of waste fluorescent tube processing technology. The method is shown below.
1) End cutting machine for straight pipes (both ends cutting, base removal) → separation (fluorescent powder, glass) → crushing → (fluorescent powder) mercury recovery distillation equipment (glass) attached mercury removal equipment (wet method: glass cleaning equipment → drying, Cleaning liquid processing equipment)
(Dry method: Rotating high temperature vacuum heating device)
2) Sealed crusher → Low-temperature indirect heating mercury recovery device → Magnetic separator for separation (base, glass, fluorescent powder)
The former is a method in which mercury can be removed almost completely because glass, a base, and fluorescent powder are separated, mercury is recovered from the fluorescent powder, and adhering mercury is also removed from the glass.
However, it is necessary to have a straight pipe, round pipe, broken pipe cutting machine and crusher, crusher and magnetic separator for the cap part, dust exhaust treatment equipment, etc., and to collect and remove mercury for both fluorescent powder and glass In particular, the wet method for removing mercury adhering to glass requires more steps such as washing, drying, and waste liquid treatment. Equipment costs are also very large.
Since most of the mercury is on the fluorescent powder side and the amount of glass cullet is much larger, a method using only a mercury recovery device from fluorescent powder is also used. The remaining process is incomplete and is not a method to be adopted in the future.
Since the latter is processed by a rotary kiln type mercury recovery apparatus without separation, mercury can be removed from all parts.
However, since the internal pressure of the apparatus is normal pressure, the processing temperature is as low as 300 ° C., and the temperature is lower than the boiling point of mercury, the removal cannot be performed efficiently and completely.

  Thus, the removal of mercury from the waste fluorescent tube requires large-scale equipment and processes, which is a cause of difficulty in processing. For this reason, there is a need for a waste fluorescent tube processing method that can completely process the entire amount of waste fluorescent tubes with a very simple device and achieve the environmental standard of 0.0005 mg / l for mercury elution.

The following method was used as the simplest processing step.
Sealed crusher → packed bed type mercury recovery device → magnetic separator for separation (base, glass, fluorescent powder)
First, waste fluorescent tubes, whether straight tubes, round tubes, or broken tubes, are crushed as they are by a closed crusher and filled into containers. The container is loaded into a mercury recovery device to remove mercury. Since there is no atmospheric exposure to the mercury crushed material so far, there is no need for an exhaust treatment facility for the work environment. Moreover, since it is a packed bed type mercury recovery device having no moving parts, it is the simplest and compact device. Since there is no sliding part, a high vacuum can be obtained. In addition, the existing crusher and the magnetic separator can use the existing inexpensive commercial apparatus.
In this method, the entire amount of the waste fluorescent tube is crushed independently of each part, the crushed material is filled in a packed bed, and this is heated in a vacuum to evaporate and separate mercury. The whole apparatus is shown in FIG.
An internal container (container) in which glass cullet is placed in a metal vacuum container is charged, and this is externally heated in an electric furnace. Since the flange portion of the vacuum vessel is sealed with water-cooled Viton O-rings, a high vacuum of about 0.133 Pa (0.001 Torr) can be easily achieved. The evaporated mercury vapor is recovered with a water-cooled condenser, and the exhaust gas is discharged from the vacuum pump through an activated carbon adsorption tank.
The boiling point of mercury is 357 ° C., but mercury is easier to remove at higher temperatures. Although this apparatus can easily raise the temperature to 1000 ° C., there is a limit to this temperature because of the mixed crushed material. Since the melting point of aluminum in the die is 660 ° C., it melts when the temperature is raised beyond this, and separation becomes difficult in the subsequent process. Therefore, the temperature is set below this temperature.
However, while the packed bed can be made extremely small, the biggest drawback of this packed bed type heating apparatus is the heat transfer rate limiting. In other words, since the thermal conductivity of the glass itself is low, heat transfer is hindered by the voids because of the cullet, and further vacuum insulation is added, so that the temperature rise inside the packed bed is slow. Therefore, hydrogen or helium is injected as the heat transfer medium gas.
As shown in FIG. 2, hydrogen and helium are unique gases having a thermal conductivity that is orders of magnitude higher than other general gases such as nitrogen and argon. Therefore, either hydrogen or helium is suitable as a heat medium. Hydrogen has a wide explosion range (4 to 75 vol% in air) and is dangerous, but it is inexpensive and easily available.
Further, if aluminum is oxidized even a little, it will be difficult to reuse because it generates noro at the time of dissolution. Therefore, it is convenient to raise the temperature in a reducing atmosphere with hydrogen.
As for mercury, it is stable at room temperature and does not oxidize and remains a metal. Even if mercury oxide is present in a broken fluorescent tube, it is thermally decomposed at 500 ° C. . Therefore, under such conditions, a reducing atmosphere with hydrogen gas is meaningless. In the experiment, mercury can be completely removed at 600 ° C. under vacuum regardless of whether the temperature is an oxidizing atmosphere or a reducing atmosphere.
Hydrogen has such a secondary effect, but its main purpose is a heat transfer medium. As can be seen from FIG. 2, as a general property of gas, the higher the temperature, the higher the thermal conductivity and the more advantageous, but on the other hand, there is almost no pressure dependence. This is shown in FIG. 3 for hydrogen gas. Therefore, the hydrogen to be added does not need to be at a high pressure at all, and the heat transfer effect is remarkable even at a low pressure.
As a result, the heating time is shortened in the hydrogenation heating as compared with the vacuum heating.
The mercury elution amount of cullet in packed bed heating decreases with increasing temperature, but under atmospheric pressure, the diffusion of mercury vapor in the gas is rate limiting and is incomplete. However, in vacuum packed bed heating, if the cullet temperature reaches 600 ° C. at 133 Pa (1 Torr) or less, the mercury elution amount is not only 0.005 mg / l of the waste treatment standard, but 0.0005 mg / l or less of the environmental standard. Thus, mercury is completely removed.

In the mercury removing device from the cullet of the waste fluorescent tube, the vacuum packed bed type heating device is the smallest and can completely remove mercury reliably. However, the greatest drawback in practically scaling up this vacuum packed layer is the heat transfer rate limiting, and it takes time to raise the temperature to the center of the layer.
However, it has been found that by slightly injecting hydrogen or helium having high thermal conductivity into the packed bed during heating, the temperature rise time can be shortened and a sufficiently practical scale apparatus can be obtained.
Therefore, this device is given the following characteristics.
1) Since the mercury is removed in a vacuum at a temperature higher than the decomposition temperature of mercury oxide, it is completely removed. Since there is no sliding movable part, a high vacuum is obtained.
2) Since the treatment temperature is below the melting point of aluminum, it can be separated after treatment.
3) Despite the heat transfer rate limiting in the packed bed, the heating time is shortened by adding a small amount of hydrogen gas, and the productivity is high.
4) Due to the packed bed type, the device is extremely small.
5) Small energy consumption due to its small size and easy heat insulation structure.
6) No mercury exposure to the atmosphere. Mercury-adhered cullet is transferred from container to container and is not replaced in the atmosphere. For this reason, facilities such as environmental dust collection and exhaust treatment are not required.
7) It is not necessary to separate straight tubes, round tubes, broken tubes, etc. or fluorescent tube parts, and the entire amount can be crushed and processed.
In addition, the process is extremely simple and the equipment costs are low. Because it is dry, there is no need for waste liquid treatment.
8) Since the separation is after mercury removal, magnetic separation can be performed in the open air. Fluorescent powder recovery rate is low.
9) Since mercury is collected, it can be reused. If the magnetic separation is performed, the glass cullet is rendered harmless and can be reused as a raw material for foam glass and ballast. Because of heating in a reducing atmosphere, aluminum is not oxidized and can be reused. Rare earth elements can be recovered from the fluorescent powder and reused.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
The waste fluorescent tube is crushed with a closed crusher without separating the fluorescent tube, such as straight tube, round tube, broken tube, etc. or glass, fluorescent powder, cap, etc. This crushed material falls into the lower cylindrical container to form a packed bed.
This container is used as the inner container 2 and charged into the metal vacuum container 3.
After the vacuum pump 8 is operated and the inside of the vacuum chamber 3 is evacuated to 133 Pa (1 Torr) or less, the exhaust is stopped and hydrogen is charged to reach 10 kPa (76 Torr). Thereafter, the temperature is raised by an electric furnace (heater 4).
When the vacuum vessel surface temperature reaches 650 ° C., this temperature is maintained. In the inner container 4 having a diameter of 400 mm, the center temperature reaches 600 ° C. after 7.5 hours. Here, evacuation is performed again, and when the internal pressure of the container becomes 133 Pa (1 Torr) or less, evacuation is stopped and the pressure of the vacuum container is returned to normal pressure by the atmosphere. When the inside of the vacuum vessel 3 reaches normal pressure, the container 2 is taken out and allowed to cool in the atmosphere. When processing continuously, immediately insert the next container and perform the same operation.
Under this condition, no matter what part of the cullet in the cooled container is sampled, the mercury elution amount becomes 0.0005 mg / l or less of the environmental standard, and mercury is completely removed.
For comparison, when the temperature is raised while charging without adding hydrogen, it takes a long time of 10.5 h for the center to reach the same temperature of 600 ° C.
A water-cooled condenser 6 is provided in the exhaust pipe of the vacuum vessel 3 to condense and recover the evaporated mercury vapor.
In addition, since it is a crushed cullet of the waste fluorescent tube, a slight amount of plastic is mixed, but no particular adverse effect of carbonization or dry distillation was observed.
Here, when the cylindrical container has a diameter of 400 mm and a length of 1800 mm, the patch amount of the cullet is 250 kg. Since this apparatus can perform 3 batches / day, this processing capacity is 750 kg / day.
The production volume of fluorescent tubes in Japan is about 400 million per year. When this is divided by the population of 130 million, about 3 per year are used per person, including all households and workplaces. become. Since Toyama Prefecture has a population of about 1 million people, it is thought that 3 million waste fluorescent tubes are generated annually. Of the amount of waste fluorescent tubes generated, 70% are household (local government) and 30% are business (private). There are 1 million business lines per year, which are relatively easy to collect as industrial waste. Since the weight of one piece is 250 g with an average 40 W straight pipe, the weight is 250 t per year. Since this is about 700 kg per day, this total amount can be almost processed with the capacity of the apparatus shown here. Therefore, it can be said that this apparatus capacity is sufficiently practical.

1 is an overall view of the present invention. Indicates the thermal conductivity of the gas. The pressure dependence of the thermal conductivity of hydrogen gas is shown.

Explanation of symbols

1 Waste fluorescent tube crushed material 2 Internal container 3 Vacuum container 4 Heater 5 Cooling water 6 Condenser 7 Mercury reservoir 8 Vacuum pump 9 Oil liminator 10 Activated carbon adsorption tank 11 Hydrogen cylinder

Claims (7)

  In a method of evaporating and removing mercury from a crushed glass of a waste fluorescent tube by heating at high temperature in a vacuum, the crushed glass is made a stationary bed, and the inside of the packed bed is made into a hydrogen or helium atmosphere during heating. Equipment for removing mercury from waste fluorescent tubes.   2. The apparatus for removing mercury from a waste fluorescent tube according to claim 1, wherein the pressure is set to a vacuum of 133 Pa (1 Torr) or less.   2. The mercury removing apparatus for waste fluorescent tubes according to claim 1, wherein the inside of the vacuum vessel, that is, the inside of the packed bed is evacuated, then hydrogen or helium is charged, and the temperature is raised and then evacuated again.   The mercury removing device for a waste fluorescent tube according to claim 1, wherein a crushed material obtained by crushing the entire amount of the waste fluorescent tube without discrimination is used as a packed bed.   The mercury removal apparatus for waste fluorescent tubes according to claim 4, wherein the temperature in the packed bed is heated at a temperature not higher than the melting point (660 ° C) of aluminum.   The apparatus for removing mercury from a waste fluorescent tube according to claim 4, wherein the pressure of hydrogen or helium is 29300 Pa (220 Torr) or less when hydrogen or helium is charged.   The mercury removal device for waste fluorescent tubes according to claim 4, wherein the crushed material of the waste fluorescent tubes is filled in an inner container and is charged in a vacuum container.

Images