JP2004067922A - Process for treating de-ammoniacal liquor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for avoiding some troubles based on a waste-water treatment for a de-ammoniacal liquor formed as a byproduct from a coke oven and for effectively utilizing a heat generated therefrom. <P>SOLUTION: The method comprises a step for removing ammonia by steam stripping an excessive ammoniacal liquor formed as a byproduct from the coke oven to obtain a de-ammoniacal liquor, a step for utilizing steam vapor generated by flashing the de-ammoniacal liquor into the first reduced pressure region to primarily cool it to 80-90°C, a step for utilizing a vapor generated by flashing the primarily cooled de-ammoniacal liquor into the second reduced pressure region to make it secondarily cool to 55-65°C and a step for an activated sludge processing after flashing the secondarily cooled de-ammoniacal liquor into the third reduced pressure region to cool it or after mixing it with another waste water, to make up a temperature of_≤40°C. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for avoiding troubles due to the treatment of dewatered dewatered water produced as a by-product from a coke oven and effectively utilizing the amount of heat.
[0002]
[Prior art]
2. Description of the Related Art In a coke plant attached to a steel mill or the like, many devices are provided for purifying gas generated from a coke oven and collecting by-products. As a matter of course, it is important to produce high value-added products from the generated gas and to minimize costs related to the operation of the apparatus.
[0003]
Regarding hydrogen sulfide and ammonia generated in large quantities from a coke oven, hydrogen sulfide is often used for producing sulfur, sulfuric acid, ammonium sulfate (ammonium sulfate), and ammonia is used for producing ammonium sulfate. In each step of the coke oven gas treatment, the wastewater containing the ammonia compound is collected and treated as low-temperature water. In the treatment of the surplus water, the ammonia is removed as a gas component by steam stripping and the waste water is incinerated in a combustion furnace. On the other hand, deoxidized water obtained by stripping ammonia is activated sludge treatment and discharged outside the factory.
[0004]
Since the deaerated water obtained from the ammonia stripper has a temperature around 100 ° C., it must be cooled to about 40 ° C. or less in order to prevent bacteria in the sludge from being killed in the activated sludge treatment. For this reason, for example, the deaerated water is flushed under a low-pressure area to generate steam and cooled to about 80 ° C., and the generated steam is heated and heated to serve both as cooling of the deaerated water and effective use as a heat source. While being used for steam stripping by pressurization, a processing method has been adopted in which the deaerated water that has been cooled is further cooled to about 40 ° C. or less by external cooling and then subjected to activated sludge treatment. However, according to this treatment method, sludge contained in the dewatered water contaminates the heat exchanger for external cooling and causes clogging, so that it is necessary to periodically clean the heat exchanger. Was.
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for treating de-aerated water that avoids such troubles and that can effectively utilize the amount of heat of the de-aerated water.
[0006]
[Means for Solving the Problems]
That is, the first invention is a step of removing excess ammonia from the coke oven by steam stripping to remove ammonia, obtaining deaerated water, flushing the deaerated water to a primary depressurized region to 80 to 90 ° C. Primary cooling, using the generated steam, flashing the decooled water that has been primarily cooled to the secondary decompression region, secondary cooling to 55 to 65 ° C., and using the generated steam, decooling using the secondary cooling. This is a method for treating deoxidized water, comprising the step of flushing the dehydrated water to a tertiary depressurized region and cooling it, or mixing with other wastewater to reduce the temperature to 40 ° C. or lower to activate sludge.
[0007]
A second invention uses the steam generated by secondary cooling as a heating source for concentrating ammonium sulphate solution in a crystallization tank at 35 to 45 ° C. for production of ammonium sulphate for bulk blending in the above method for treating deammonified water. It is.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a drawing showing an example of a method for treating deammonified water and using the waste heat as a heat source for concentrating ammonium sulphate liquid in a crystallization tank for producing ammonium sulfate for bulk blending.
[0009]
In FIG. 1, while the excess low-water produced as a by-product from the coke oven is supplied to the ammonia stripper 1 from a pipe 41, steam having a temperature of about 100 to 110 ° C. and a pressure of about 0.10 to 0.15 MPa is supplied from a pipe 43. To vaporize the volatile components of the ammonia tower in the surplus water. The volatile components such as vaporized ammonia are discharged from the top of the stripper 1 through a pipe 44, sent to an incinerator (not shown), and incinerated.
[0010]
Dewatered water is extracted from the bottom of the stripper 1 by the pump 2 and supplied to the thermocompressor 3 via the pipe 45. The upper part of the thermo-compressor 3 is connected to the Venturi tube 4, and the high-pressure steam (temperature of about 170 to 180 ° C., pressure of about 0.8 to 1.0 MPa) from the pipe 42 is passed through the Venturi pipe 4 to reach a temperature of 80 to 400 V. It is in a reduced pressure state of about 90 ° C. and a pressure of about 0.05 to 0.07 MPa. Therefore, the deaerated water from the pipe 45 is flushed by the thermo-compressor 3 to generate steam which is entrained by the high-pressure steam via the pipe 46 and the venturi pipe 4 and used as a part of steam in the stripper 1. Is done.
[0011]
Deaerated water at 80 to 90 ° C. in the thermocompressor 3 is withdrawn from the bottom of the thermocompressor by the pump 5 and introduced into the flash tank 6 through the pipe 47. The top of the flash tank 6 is connected to the vacuum pump 7 via a pipe 48 and a pipe 49, and is kept at a reduced pressure of about 0.017 to 0.020 MPa. Therefore, the deaerated water from the pipe 47 is decompressed in the flash tank 6 to generate steam, while being cooled to a temperature of about 55 to 65 ° C. The generated steam is used as a heating source of the heater 27.
[0012]
The deaerated water in the flash tank 6 is introduced into the secondary flash tank 8 through the pipe 50. The top of the secondary flash tank 8 is connected to the condenser 9 and the vacuum device 25 through a pipe 51, and is maintained at a pressure of 0.0070 MPa or less, so that the deaerated water is cooled to 40 ° C. or less, It is directly led to an activated sludge device (not shown) via the pipe 52. According to this method, it is not necessary to externally cool the deaerated water by the heat exchanger, and therefore, it is free from the clogging trouble of the heat exchanger.
[0013]
In winter or the like, when the temperature of the other wastewater is sufficiently low and can be mixed with the deaerated water from the flash tank 6 to make it 40 ° C. or less, the depressurized cooling in the secondary flash tank can be omitted.
[0014]
On the other hand, coke plants often produce ammonium sulfate from ammonia in coke oven gas, as described above. According to the particle size, ammonium sulfate is classified into chemical conversion (particle size of 2 mm or less), compounding (particle size of 2 to 4 mm), and bulk blending (BB) (particle size of about 4 mm). Of these, the demand for ammonium sulfate for BB has been rapidly increasing in recent years. In order to increase the amount of ammonium sulfate for BB, a method of dissolving ammonium sulfate for chemical formation or blending in water and recrystallizing the same is employed. This is an example of using as a heat source for concentration.
[0015]
In FIG. 1, ammonium sulfate for chemical formation or ammonium sulfate for compounding is dissolved in water in a dissolving tank 21 to prepare an aqueous solution having a concentration of about 40%. Next, this aqueous solution is supplied to the crystallization tank 23 through the pipe 61 by the pump 22. The crystallization tank 23 is provided with an evaporator 24, the top of which is connected to the condenser 26 and the vacuum device 25 by a pipe 64 and maintained at a pressure of 0.0045 to 0.0060 MPa. The aqueous solution in the crystallization tank is withdrawn from the pipe 62, introduced into the heater 27 by the circulation pump 28, heated, and circulated through the pipe 63 to the evaporating pipe 24 of the crystallization tank 23. In the heater, the aqueous solution is heated by the flash steam of 55 to 65 ° C. introduced from the flash tank 6 through the pipe 48, and the generated steam of 35 to 45 ° C. is condensed in the condenser 26 and discharged out of the system. . By this operation, the aqueous solution in the crystallizer is concentrated, and crystals are gradually generated and grow.
[0016]
When the grain size of the crystals becomes about 4 mm, it is withdrawn from the crystallization tank, introduced into the centrifugal separator 30 through the pipe 65 by the pump 29, separated therefrom, and then put into the dryer 31 through the pipe 66. ,dry. The dried crystals are then separated from the BB ammonium sulfate having a predetermined particle size by the screen 32, passed through a pipe 68, and formed into a product. Other dry crystals are supplied to the dissolving tank 21 through the tube 60 and reused. The filtrate in the centrifuge 30 enters a filtrate tank (not shown), and is supplied to the crystal tank by a pump (not shown) for reuse. By setting the pressure in the evaporator within the above range, water evaporates at 35 to 45 ° C., so that the flash steam can be used as a suitable heating source.
[0017]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, while the holding | maintenance calories of the de-aerated water obtained by the steam stripping of the surplus de-aerated water can be used effectively, the clogging trouble of the heat exchanger accompanying the treatment of the de-aerated water can be avoided.
[Brief description of the drawings]
FIG. 1 is a drawing showing a flow sheet in which the treatment of deammonated water and the production of ammonium sulfate for bulk blending are combined.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ammonia stripper 3 Thermo-compressor 4 Venturi tube 6 Flash tank 8 Secondary flash tank 21 Dissolution tank 23 Crystal tank 24 Evaporator 27 Heater 30 Centrifuge 31 Dryer 32 Screen

Claims (2)

A process of removing ammonia by steam stripping excess by-products from a coke oven to obtain deaerated water, flushing deaerated water to a primary depressurized region, primary cooling to 80 to 90 ° C., and generating steam The step of flashing the decooled water that has been primarily cooled in the secondary depressurized area and secondarily cooling it to 55 to 65 ° C., and using the generated steam; and the step of using the decooled water that has been secondarily cooled to the tertiary depressurized area. A method for treating deoxidized water, comprising the step of performing activated sludge treatment at a temperature of 40 ° C. or lower by flashing and cooling or mixing with other wastewater. 2. The method according to claim 1, wherein the steam generated by the secondary cooling is used as a heating source for concentrating an ammonium sulfate solution in a crystallization tank at 35 to 45 [deg.] C. for producing ammonium sulfate for bulk blending. .

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