JPH0131458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing by-product ammonium sulfate by improving the method of heating ammonium sulfate mother liquor when recovering ammonia in coke oven gas (hereinafter referred to as COG) as ammonium sulfate.

In the method of producing by-product ammonium sulfate by bringing COG into contact with dilute sulfuric acid in a saturator, ammonium sulfate crystals adhere to the inside of the saturator, so it is necessary to periodically wash the inside of the container with water, and the COG Since the water vapor entrained in the sulfuric acid and the moisture etc. that accompany the sulfuric acid also enter the vessel, if the operation continues as it is, the amount of liquid in the vessel will increase over time. For this reason, conventionally, a heater is installed in the ammonium sulfate mother liquor circulation line of the saturator to heat the ammonium sulfate mother liquor, and a part of the water in the ammonium sulfate mother liquor is evaporated in the saturator and transferred to the COG to be discharged to maintain the water balance. methods are being implemented.
In this case, when the ammonium sulfate mother liquor is heated, the tar contained in the mother liquor polymerizes and adheres to the heating surface, reducing heat transfer efficiency, so a corrugated tube heat exchanger, which has a simple structure and is easy to clean, is used as a heater. has been done. However, the overall heat transfer coefficient of the corrugated tube heat exchanger is 300~
Since it is small at around 500 Kcal/m ² ·hr ·°C, it has the drawbacks of poor thermal efficiency and large-sized equipment.

Therefore, in order to use a plate heat exchanger or a shell-and-tube heat exchanger with a large heat transfer coefficient, the inventors of the present invention conducted intensive studies on the method for removing the deposits mentioned above, and as a result, they decided to carbonize the coal. By using the coke oven gas liquid (hereinafter simply referred to as gas liquid) obtained when manufacturing coke, and by cleaning the heat exchanger intermittently, it is possible to use the plate type, multi-tube type, etc. The present invention was achieved by discovering that even if a heat exchanger is used, operation is possible without trouble.

That is, the gist of the present invention is a method of bringing coke oven gas into contact with dilute sulfuric acid in a saturator and recovering ammonia in the gas as ammonium sulfate, in which an ammonium sulfate mother liquor from which ammonium sulfate has been separated from an ammonium sulfate slurry produced in a saturator, It is heated by a heat exchanger and circulated to the saturator,
Part of the moisture in the liquid is evaporated in a saturator and discharged along with the coke oven gas to maintain the liquid level at a nearly constant level. The present invention relates to a method for producing by-product ammonium sulfate, which is characterized by intermittent cleaning with coke oven gas liquid.

The present invention will be described in detail below. The method for producing by-product ammonium sulfate to which the present invention is applied is a well-known method,
They are roughly divided into bubble type, an example of which is shown in FIG. 1, and spray type, an example of which is shown in FIG. In Figure 1, 1
is a saturation tank, 8 is a flow path switching mechanism, 9 is a heat exchanger, 1
1 is a crystal separation tank, and 13 is a centrifugal separator. COG containing ammonia (hereinafter referred to as NH ₃ ) is continuously introduced into the saturation tank 1 through a conduit 5 , comes into contact with dilute sulfuric acid in the tank, absorbs NH ₃ , and is then led out through a conduit 4 . . Fresh sulfuric acid is introduced through conduit 3 and is uniformly distributed over the liquid surface in the tank through a ring-shaped pipe (not shown).

The ammonium sulfate mother liquor in the saturation tank 1 is introduced into the crystal separation tank 11 through the conduit 2 together with the generated ammonium sulfate crystals,
It overflows from the conduit 10 and is introduced into the storage tank 18. The ammonium sulfate crystals in the crystal separation tank 11 are supplied through a conduit 12 to a centrifugal separator 13, where the mother liquor is separated and washed with water, and then transferred through a conduit 14 to a drying process where they are made into a product. The separated mother liquor and the water used for washing are connected to conduit 15.
The liquid is then introduced into the storage tank 18.

The ammonium sulfate mother liquor in the storage tank 18 is pumped to the conduit 1.
7. Introduced into the heat exchanger 9 via the flow path switching mechanism 8
After the temperature rises to 50~65℃, it is circulated to the saturation tank 1 via the flow path switching mechanism 8 and the conduit 6, and the mother liquor temperature in the tank is raised to 50~65℃.
Maintain a predetermined temperature within the range of °C. A portion of the mother liquor overflows from conduit 19 into reservoir 18 .

As the heat exchanger 9, well-known types such as plate type, shell-and-tube type, spiral type, jacket type, and spiral tube type are used, but plate type, shell-and-tube type, and spiral type are preferable because they have a large overall heat transfer coefficient. used. The heating medium may be any fluid having a temperature equal to or higher than the above-mentioned heating temperature, and hot water or steam of about 80°C or higher is usually used, but coke oven gas liquid (hereinafter referred to as gas liquid) for cleaning heat exchange surfaces, which will be described later, may be used as the heating medium. It is advantageous in terms of energy saving to use. The gas liquid is condensed from gas generated during carbonization of coal to produce coke, and usually has a temperature of 70 to 80°C. The gas liquid is supplied from the conduit 16, is normally introduced into the heating fluid side of the heat exchanger 9 by the flow path switching mechanism 8, and is led out from the conduit 7 after being used as a heating medium. When cleaning the heat exchange surface, the flow path is switched by the flow path switching mechanism 8, and the ammonium sulfate mother liquor is introduced into the flow side and led out from the conduit 7.

These relationships will be explained in more detail based on FIG. FIG. 2 is a system diagram showing an example of the flow path switching mechanism 8 and the heat exchanger 9. In the figure, 9 is a heat exchanger, 2
1, 23, 25, 29 and 31 are three-way switching valves. When heating the ammonium sulfate mother liquor, the three-way switching valve (hereinafter referred to as the valve) is connected to conduits 7 and 20 and conduits 17 and 24.
and 27, conduits 16 and 28, and conduits 6 and 32 are located at positions where they communicate with each other. Then, the ammonium sulfate mother liquor is introduced from the conduit 17 through the conduits 24 and 27 to the ammonium sulfate mother liquor distribution side 33 of the heat exchanger 9, and after being heated to a predetermined temperature, is led to the conduit 6 through the conduit 32. On the other hand, the gas liquid is introduced from conduit 16 through conduit 28 into the heating fluid side 34 of heat exchanger 9 and then through conduit 20 into conduit 7 .

Clean the heat exchange surface usually once a day, 10 times per time.
The cleaning may be carried out for about 20 minutes, but the frequency of cleaning and the cleaning time per cleaning may be shortened or extended as appropriate depending on the degree of dirt on the heat exchange surface. To perform the cleaning,
The valve 3 is placed in a position where the valve 25 communicates with the conduits 17 and 26.
1 at a position where conduits 30 and 32 communicate, valve 29 at a position where conduits 16 and 30 communicate, valve 21 at a position where conduits 7 and 22 communicate, and valve 23 at a position where conduits 22 and 27 communicate. , respectively. The valves are switched all at once automatically or manually using well-known electromagnetic, pressurized fluid, or mechanical means.
The steps may be performed sequentially according to the above order. When each valve is switched, ammonium sulfate mother liquor flows from conduit 17 to conduit 2.
6 to conduit 6, while the gaseous liquid is directed to conduit 1
6 is supplied to the ammonium sulfate mother liquor distribution side 33 of the heat exchanger 9 via conduits 30 and 32, and after cleaning the heat exchange surface (process side heat transfer surface), it is led to conduit 7 via conduits 27 and 22. After a predetermined period of time has elapsed, if the flow position of each valve is switched to the original position, the ammonium sulfate mother liquor will be introduced into the ammonium sulfate mother liquor side 33 of the heat exchanger 9, and the gas liquid will be introduced into the heating fluid side 34, so that the ammonium sulfate mother liquor will be introduced into the heating fluid side 34 again. The temperature of the mother liquor begins to increase.

The reason why a gas liquid is preferable as a cleaning agent is not clear, but it is thought that the tar acid contained in the gas liquid contributes to the dissolution of deposits.

Next, a case will be described in which a heat exchanger using steam as a heating medium is used to heat the circulating mother liquor of a spray type saturator. In Figure 3, 35 is an overflow tank;
8 is a spray tower, 45 is a heat exchanger, and 48 is a flow path switching mechanism. COG containing NH ₃ is transferred to conduit 42
The water is continuously introduced into the spray tower 38, which is a spray type saturator, and after coming into contact with the dilute sulfuric acid in the circulating mother liquor supplied from conduits 41 and 43 and sprayed into the tower to absorb NH _{3 , the NH 3} is passed through the conduit 39. derived. The circulating mother liquor in contact with COG is introduced into an overflow tank 35 together with ammonium sulfate crystals. Ammonium sulfate, which has relatively large crystals, is precipitated in the lower part, introduced into the crystal separation tank 11 through a conduit 36, separated by a centrifuge 13, and then transferred to a drying process through a conduit 14 to be made into a product.
The separated mother liquor is returned to the overflow tank 35.

The mother liquor containing ammonium sulfate with fine crystals extracted from the middle part of the overflow tank 35 is sprayed into the spray tower 38 from a lower nozzle through conduits 52 and 43. The mother liquor overflowing from the upper part of the overflow tank 35 is introduced into the storage tank 50 through the conduit 37, mixed with fresh acid supplied through the conduit 51, and then passed through the heat exchanger 45 into the storage tank 50.
After the temperature is raised to ~65°C, the spray tower 3 is sent from the conduit 41.
8 is sprayed into the tower from the upper nozzle.

The heat exchanger 45 is of a type that uses low-pressure steam as a heating medium, and the low-pressure steam is supplied and discharged through conduits 46 and 47. Flow path switching mechanism 4
8 indicates conduits 50 and 4 when heating the ammonium sulfate mother liquor.
1 is in communication with the ammonium sulfate mother liquor side of the heat exchanger 45, and when cleaning the heat exchange surface, the conduits 50 and 41 are in direct communication, and the ammonium sulfate mother liquor side of the heat exchanger 45 is connected to the gas liquid supply conduit 49 and the discharge conduit 44. It may be any device that has a flow function, and may be implemented, for example, by a slider valve, a six-way switching valve, or a combination of a four-way valve or a three-way valve. Cleaning inside the spray tower 38 is done through the conduit 40
This is done by spraying water supplied from

As detailed above, in the method of the present invention, deposits on the heat exchange surface can be easily removed by a simple operation of cleaning the heat exchange surface of the heat exchanger with a gas liquid for about 15 minutes once a day. , it is possible to use a heat exchanger with high heat transfer efficiency. Furthermore, since the heat exchange surface is easy to clean, a plate type or multi-tube type heat exchanger with a high overall heat transfer coefficient can be used. Furthermore, when a gas liquid is used as the heating medium, energy is saved, so the present invention is useful as a method for producing by-product ammonium sulfate from COG.

[Brief explanation of drawings]

Figure 1 is a system diagram of an example of using a bubble type as an ammonia saturator, Figure 2 is a system diagram of an example of a flow path switching mechanism, and Figure 3 is an example of a case of using a spray type as an ammonia saturator. This is a system diagram of 1: Saturation tank, 8, 48: Flow path switching mechanism, 9, 4
5: heat exchanger, 11: crystal separation tank, 13: centrifugal separator, 35: overflow tank, 38: spray tower.

Claims (1)

[Claims] 1 In a method in which coke oven gas is brought into contact with dilute sulfuric acid in a saturator and ammonia in the gas is recovered as ammonium sulfate, the ammonium sulfate mother liquor from which ammonium sulfate has been separated from the ammonium sulfate slurry produced in the saturator is heated with a heat exchanger. Some of the moisture in the liquid is evaporated in the saturator and discharged along with the coke oven gas, thereby maintaining the liquid level at a nearly constant level. Process side heat transfer surface,
A method for producing by-product ammonium sulfate, characterized by intermittent cleaning with coke oven gas liquid.