JPS6026561B2 - Mechanical vapor compression evaporation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vapor compression evaporation method using a mechanical compression method.

One method of energy economy for evaporators is a mechanical compression method in which evaporated steam is mechanically recompressed to increase its pressure and used as heating steam to repeatedly use the latent heat of the steam.

This mechanical compression method has traditionally been mainly used in salt production equipment, but recently it has become more popular from the perspective of energy conservation, and because cooling water is not required, the only wastewater from the equipment is condensed water from heated pine trees, making it an effective wastewater treatment method. Since then, people are beginning to reconsider.

The compressors conventionally used in these devices are of the types shown in the table below.

The compressors in the table above have been selected to have better mechanical efficiency than liquid ring pumps, but because they are entrained by droplets from evaporated coins, solid objects may adhere to the casing, rotor, blades, etc. Efficiency decreases in a short period of time due to wear, corrosion, etc.

Furthermore, since they are used in high temperature ranges, consideration must be given to the thermal expansion of the rotor and casing, as well as surging prevention, which makes the compressors of the types listed above extremely expensive. Therefore, the conventional vapor compression type evaporator using the mechanical compression method employing these compressors is extremely disadvantageous economically, as it requires high construction costs and a large amount of maintenance costs.

The present invention solves these drawbacks, has low construction costs, and
It is an object of the present invention to provide a vapor compression evaporation method using a mechanical compression method that has low maintenance costs and extremely good energy efficiency.

In a vapor compression type evaporator, the present invention uses a liquid that does not mix with water and has a higher boiling point than water as a sealing liquid, such as a petroleum-based high bran fraction (lubricating oil, heat transfer oil, etc.), silicone oil, etc. ,
A liquid-ring pump using a water ring is used as a vertical compaction machine, and the water vapor generated from the steamed eagle does not mix with water.
In addition, a liquid with a higher boiling point than water is sucked and compressed using a liquid ring pump as a sealing liquid, and the thermal energy of the water vapor and sealing liquid discharged from the liquid ring pump is used as a heating source for the liquid to be evaporated. This is a characteristic feature.

Next, the present invention will be explained based on the drawings.

The first diagram shows the first embodiment of the present invention, which is a process for concentrating an aqueous sodium bromide solution.

-It is a sheet. First, a dilute aqueous solution of sodium bromide (N
(containing around 2.7% aBr) is sent at a constant flow rate using a flow meter 2 from FIG. Indirect heat exchange is performed to provide heat recovery and to cool the concentrate to a temperature suitable for handling. Next, the liquid to be concentrated is transferred to the oil/water scale tank 5.
A corrugated tube heat exchanger 6 and a double tube heat exchanger 7 installed inside
After indirect heat exchange with the drain from the heated bonito 9, which will be described later, and waste heat recovery, the downtake 8
After that, it is heated in a heating oven 9 and supplied to an evaporator hammer 10. The type of evaporator shown in FIG. 1 is a so-called natural circulation type, but any type such as a forced circulation system, a liquid film rising type, a liquid film descending type, a plate type, etc. can be used. The evaporated liquid is compressed by a liquid ring pump 14 (to be described later) in the heated bonito 9.
The concentrated liquid whose temperature has increased by exchanging heat with the evaporated steam from 0 is supplied to the evaporating rock 101 and boiled and evaporated, and the concentrated liquid whose temperature has decreased passes through the downtake 8 and enters the heating moth 9 again and is heated by compressed steam. After that, it is recycled to the evaporation key 10. In this embodiment, the heated bonito 9 is of the so-called shell-and-tube indirect heat exchange type, but other types can also be used. The aqueous sodium bromide solution thus concentrated to the required concentration (30%) passes through the overflow pipe 11 and accumulates in the concentrate storage tank 3, and is taken out of the system by the concentrate pump 12.

On the other hand, the evaporated water vapor is separated into droplets by a mist separator 13, sucked and compressed by a liquid ring pump 14 that uses lubricating oil as a sealing liquid, and passes through a gas-liquid separator 15 to separate a sealing liquid. After that, it is condensed by exchanging heat with the liquid to be concentrated in a heating fabric 9, and then transferred to a drain trap 16 and a double pipe heat exchanger 7.
The water passes through the water, collects in the acid tank 5, and is discharged to the drain via the water overflow pipe 17.

The liquid ring pump referred to in the present invention is a so-called Nash type pump.

For example, the structure is such that a sealing liquid is placed inside the pump casing.
The impeller is rotated by making it offset from the casing. Therefore, the sealing liquid flows along the inner wall of the casing due to centrifugal force, forming a circular flow and creating a crescent-shaped space inside. If the intake port is opened at a position where this crescent-shaped passage expands as it rotates, gas is sucked in, flows through the crescent-shaped passage together with the impeller, and enters an independent air chamber between the two blades, the case, and the inner surface of the sealing liquid circulation. You will be locked up. As the rotation progresses, the sealing liquid circulation inner surface of this air chamber approaches the root of the blade, and its volume decreases, compressing the gas inside. Therefore, the compressor pump has a structure in which the compressed gas is discharged by opening the discharge port at a position where the pressure reaches the required level.
That is, the liquid ring pump referred to in the present invention is a reciprocating compressor that is made to rotate continuously by using a sealing liquid in place of a piston. Furthermore, in a liquid ring pump, since the gas-liquid interface is disturbed, droplets are always ejected along with the compressed gas on the discharge side, and the amount of liquid must be replenished.

In this embodiment, lubricating oil was used as the sealing liquid, but it goes without saying that the sealing liquid should be selected depending on the properties of the droplets from the evaporated crab. Separation of droplets of sealing liquid (lubricating oil) discharged along with the water vapor is performed in a gas-liquid separator 15 installed on the discharge side of the liquid ring pump 14 in FIG. The liquid passes through the oil trap 18 and enters the oil sealing tank 19.
It accumulates in the liquid ring circulation pump 20' and the coiled pipe heat exchanger 2
1 for heat exchange, cooling, and recirculation for use. When a gas is compressed, externally applied mechanical energy is stored as internal energy, and the temperature of the compressed gas increases.

Although the mechanical efficiency of liquid ring pumps is lower than that of the various compressors described above by the amount equivalent to the rotational power of the sealing liquid, the temperature of the outlet steam and sealing liquid increases accordingly, and in the present invention, this temperature increase is Since it is used to supplement the sensible heat of the supply liquid and the heat radiated from the equipment, the decrease in mechanical efficiency is recovered as thermal efficiency, and there is no loss of energy. Therefore, if the sealing liquid is circulated as it is, the steam temperature on the discharge side of the liquid ring pump 14 will be extremely heated, resulting in a decrease in the overall heat transfer coefficient of the heating tower 9, decomposition and deterioration of the liquid to be concentrated due to overheating, and an increase in the partial pressure of the sealing oil. This causes a decrease in the amount of suction steam due to the increase. Therefore, in Fig. 1, the oil sealing tank 19
The sealing liquid inside is sent by a sealing liquid circulation pump 20 to a corrugated tube heat exchanger 21 installed in the evaporation tank system, where it is cooled by indirect heat exchange with the liquid to be concentrated, and then transferred to a liquid ring pump 14 as a sealing liquid. The thermal energy is used as a heating source for the liquid to be concentrated. In addition, since lubricating oil is used as the sealing liquid, a small amount of oil is entrained in the compressed steam due to the principle of oil filling and steam distillation, which cannot be separated in the gas-liquid separator 15. The oil overflow pipe 22 is condensed together with water vapor, passes through a drain trap 16 and a double-tube mature exchanger 7, is separated from water by gravity in an oil-water separation tank 5, and is installed slightly above the water overflow pipe 17. The oil is returned to the oil sealing tank 19 through the

At the time of starting, live steam is supplied from 23 to the heating moth 9.

The one shown in the second diagram is the second embodiment of the present invention, in which the sealing liquid discharged from the liquid ring pump is not separated from the water vapor, but is directly supplied to the heating key, and used as a heating source for the liquid to be concentrated. This is a flow sheet for concentrating an aqueous sodium bromide solution, similar to the one shown in Figure 1.

First, a dilute aqueous solution of sodium bromide is sent at a constant flow rate using a flowmeter 2 from FIG. Indirect heat exchange is carried out to recover heat and cool the concentrate to a temperature where it can be easily handled. Subsequently, the liquid to be concentrated is sent to a corrugated pipe heat exchanger 6a and a double-pipe heat exchanger 7a installed in the oil-water separation tank 5a, where indirect heat exchange is performed with the liquid discharged from the heating moth 9a, which will be described later. After heat recovery, the evaporative fabric 1 is heated by the heating key 9a through the downtake 8.
Supply to 0a. The evaporated bonito internal liquid exchanges heat with the evaporated steam from the evaporation tank 10a compressed by the liquid ring pump 14 (to be described later) and the sealing liquid of the liquid ring pump in the heating whisker 9a, resulting in a heated liquid to be concentrated. is supplied to the evaporator 10a and boiled and evaporated, and the concentrated liquid whose temperature has decreased passes through the downtake 8 and enters the heating mallet 9a again, where it is heated by compressed steam and the sealing liquid of the pump, and then recirculated to the evaporated bonito 10a. . The aqueous sodium bromide solution thus concentrated to the required concentration passes through the overflow pipe 11 and accumulates in the concentrate reservoir 3, and is taken out of the system by the concentrate pump 12. On the other hand, the water vapor evaporated in the evaporation key 10a having droplet separation performance is suctioned and compressed by the liquid ring pump 14 using lubricating oil as the sealing liquid, enters the heating plate 9a together with the pump sealing liquid, and exchanges heat. The condensed water passes through the drain trap 16a and the double-pipe heat exchanger 7a together with the pump sealing liquid, collects in the oil-water separation tank 5a, and is collected in the oil-water separation tank 5a. . On the other hand, the pump sealing liquid (lubricating oil) statically diluted in the oil-water separator tank 5a rises, is stored in the upper part of the oil-water separation tank, and is liquidized by the seal-liquid circulation pump 20 from the sealing liquid outlet provided in the middle of the oil layer. It is circulated and reused as a sealing liquid to the sealing pump 14. At the time of starting, live steam is supplied from 23 to the heating side 9a.

The present invention has been described above with reference to flow sheets of examples of concentrating an aqueous sodium bromide solution, but of course the present invention is not limited to aqueous sodium bromide solutions.

Next, examples of the present invention will be shown.

Example 1 An aqueous sodium bromide solution was concentrated according to the flow sheet shown in the figure.

The main data is shown below.

As is clear from the above explanation, the method of the present invention eliminates the adhesion, wear, and corrosion of solid objects to the casing and blades of liquid ring pumps due to entrainment of droplets from evaporated bonito; No decrease in mechanical efficiency was observed.

Therefore, the equipment maintenance cost is no different from that of a general single-effect evaporator and is very low. In addition, the driving sound of the liquid ring pump is 74 horns on the machine side 1, which is extremely low compared to other compressors, and the drainage from the adjacent tank for oil and water (see Figure 1 and The oil content in the overflow water from the overflow pipe 17 in Fig. 2 is less than 1 trace, and the COD is less than 5 traces, so there is no concern about secondary pollution. Also, the energy efficiency is 69.2%, which is 1% compared to a multiple effect evaporator.
Assuming that the utility is 80%, it is actually 8. It corresponds to the night effect. Moreover, since no cooling water is required, operating costs are reduced to an unimaginable level. In addition, equipment costs are approximately 20% compared to general single-effect evaporators because no condenser is required.
Stops up.

[Brief explanation of the drawing]

1 and 2 are flow sheets of an embodiment of the present invention. 3... Concentrated liquid storage tank, 5, 5a... Oil/water adjoining tank, 6, 6a... Corrugated tube heat exchanger, 7, 7a...
...Double pipe heat exchanger, 9,9a... Heating, 10,10a... Evaporation basket indigo, 13...
... Mist separator, 14 ... Liquid ring pump, 15 ... Gas-liquid separator, 20 ... Sealed liquid circulation pump. Fig. 1 Fig. 2

Claims (1)

[Claims] 1 The water vapor generated from the evaporation can is sucked and compressed by a liquid ring pump whose seal liquid is a liquid that does not mix with water and has a higher boiling point than water, and the water vapor discharged from the liquid ring pump and the seal are A mechanical vapor compression evaporation method characterized in that the thermal energy of the liquid is used as a heating source for the liquid to be concentrated, and the sealing liquid separated from water is recycled and reused.