JPS5951358B2 - How to remove ammonia - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for removing ammonia.

More specifically, the present invention relates to an improved method for reducing corrosion of a blower used when removing ammonia from an ammonia-containing liquid by a stripping method.

Generally, when producing coke by carbonizing coal,
Gas liquid obtained by statically separating the condensate, which is a by-product of the condensation of moisture contained in coal, adhering water, and tar, in a tar treatment center, or tar such as wastewater discharged from other parts of a tar factory. In the factory wastewater, 2,000
~5. In addition to QQQppm of ammonia, the wastewater contains harmful components such as hydrogen cyanide and hydrogen sulfide, as well as tar-like substances, and the wastewater containing gas liquid has high COD and BOD, so it should not be directly discharged outside the system. is impossible due to environmental hygiene.

Therefore, in order to treat such wastewater, activated sludge treatment is usually performed to reduce COD and BOD.

However, when the ammonia concentration in wastewater is high, activated sludge cannot work effectively, which not only reduces the treatment efficiency but also makes the treatment capacity unstable.

Since ammonia itself is hardly removed by activated sludge treatment, it is said that discharging wastewater containing a large amount of ammonia into the sea causes eutrophication of the sea area and is one of the causes of so-called red tide.

Therefore, it is necessary to separate and remove ammonia from the ammonia-containing wastewater described above before treating it with activated sludge.

Furthermore, when producing acrylonitrile, methacrylonitrile, benzonitrile, phthalonitrile, etc. by ammoxidation of aliphatic hydrocarbons such as propylene and isobutylene, and aromatic hydrocarbons such as toluene and xylene, the exhaust gas contains Since it contains a large amount of ammonia and hydrogen cyanide, it is collected by water or other absorption liquid, but since this absorption liquid cannot be discharged as described above, it is necessary to separate and remove the ammonia.

In addition, in the case of urban sewage, most of it undergoes physical and chemical treatment, as well as biological secondary treatment, and most of the organic matter decomposes, but much of the nitrogen remains. There is 15-30 pIlrn ammonia in the secondary treatment water.

A method for removing ammonia and other activated sludge-inhibiting components from such ammonia-containing wastewater or ammonia-containing wastewater that has been pretreated by adding an alkaline agent to it is stripping with a gas such as steam or air. The law is known and widely practiced.

This method is the simplest method, and in addition to ammonia, low-boiling harmful components such as hydrogen cyanide and hydrogen sulfide can be removed at the same time. The removed ammonia can be used directly as a raw material for producing ammonium sulfate, or it can be thermally decomposed and converted into nitrogen. Can be rendered harmless.

In this type of ammonia stripping, ammonia-containing wastewater is usually introduced from near the top of the tower using a tray tower using perforated plates, a packed tower filled with materials such as Raschig rings, Belsaddle, Terraret, etc. as a stripper. Stripping is carried out by contacting with gas introduced from the bottom of the column.

As a stripping method, for example, JP-A-53-43
There is a wet gas circulation steam stripping method shown in No. 48, in which ammonia is stripped with a mixed gas of air and steam, and the ammonia-containing gas discharged from the top of the stripper column is pressurized with a blower, and then passed through the absorption column. In this method, the wet gas discharged from the absorption tower is recycled and reused as stripping gas, and the amount of steam used is reduced compared to the conventional steam stripping method, which consumes steam in one pass. It has the characteristic of being able to be significantly reduced.

When the stripping gas is circulated, the ammonia-containing wet gas that is stripped and discharged from the top of the stripper tower is pressurized and sent to the absorption tower, and the wet gas discharged from the absorption tower is further circulated through the stripper tower. It is necessary to use a blower to circulate to the ripper, but this blower
The disadvantage was that the casing, impeller, or discharge duct 1~ of the blower were severely corroded, and the life of the blower was extremely short.

The present inventors have investigated various metal materials, corrosion-resistant linings, paints, etc. to prevent corrosion of such blowers, but only high-grade materials such as titanium and Hastelloy have been used as the most important impeller component. It was found to be effective.

However, these materials are expensive and impractical.

The present invention was made to eliminate the various drawbacks of the conventional method as described above, and the ammonia-containing liquid is stripped in a stripper using gas, and the slip I/slip gas discharged from the top of the stripper is The gas discharged from the absorption tower is sent to an absorption tower where ammonia or at least a part of the other stripped components is absorbed and removed, and the gas discharged from the absorption tower is recycled and used as a stripping gas to be blown into the stripper to remove ammonia. In a method for removing ammonia from a liquid containing water, water is continuously or intermittently sprayed onto the gas on the suction side of a blower that circulates the gas in an amount equal to or higher than the water vapor pressure at the discharge side of the blower to reach the saturated water vapor pressure. This is an ammonia removal method characterized by:

The ammonia-containing liquid treated by the method of the present invention is a gas liquid (usually also called ammonium water) obtained by statically separating the condensate obtained by condensing gas discharged from a coke oven in a tarte counter. There is.

), other ammonia-containing wastewater discharged from tar factories, and mixed wastewater with these and gas liquids.

In addition, when producing acrylonitrile, methacrylonitrile, benzonitrile, phthalonitrile, etc. by ammoxidizing aliphatic hydrocarbons such as propylene and imbutylene, and aromatic hydrocarbons such as toluene and xylene, the exhaust gas is converted into water or other There are ammonia-containing liquids and the like that are collected by absorption liquids.

In addition, there are ammonia-containing liquids such as urban sewage treatment wastewater, and when the ammonia in the ammonia-containing liquid forms a stable salt, an alkali agent may be added.

Next, the method of the present invention will be explained in detail with reference to the drawings, taking a method of removing ammonia from a gas liquid as an example.

That is, as shown in the drawing, a gas liquid is introduced from a conduit 1 into a mixing tank 2, a flocculant such as ferrous sulfate or ferrous chloride is supplied to this from a conduit 3, and then introduced into a thickener 4. Oil or tar, hydrogen sulfide, hydrogen cyanide, etc. are separated to some extent by coagulation and sedimentation, and then discharged from the conduit 5.

The gas liquid is supplied from a pump 6 to a heat exchanger 7 and heated to a predetermined temperature, and then supplied to the top of a stripper 9 via a conduit 8.

A gas supplied from the second absorption tower is introduced into the stripper 9 via a gas conduit 10 to the bottom of the tower, and volatile substances such as ammonia, hydrogen cyanide, and hydrogen sulfide are stripped by countercurrent contact with the gas liquid.

The stripped ammonia-containing wet gas is discharged from the top of the column, passes through a mist separator 11, and is sent to a blower 13 through a conduit 12.

With this blower 13, the wet gas is about 500 to about 3000 mm.
Hydrogen cyanide, hydrogen sulfide, etc. are introduced into the lower part of the first absorption tower 14 and brought into countercurrent contact with an aqueous alkali solution such as sodium hydroxide, which is supplied from the alkali supply port 15 to the top of the tower via the conduit 16. of acid gas is removed.

After the alkaline aqueous solution is removed from the bottom of the column, it is circulated by the pump 17, but a portion of it is removed from the line through the conduit 18.

The gas that has been washed with the alkaline aqueous solution and contains a large amount of ammonia is introduced into the lower part of the second absorption tower 20 through a conduit 19, and is mixed with an acid aqueous solution such as a sulfuric acid aqueous solution that is supplied from an acid supply port 21 to the top of the tower via a conduit 22. Through countercurrent contact, ammonia is absorbed, recovered as a salt such as ammonium sulfate, and removed to the outside of the yarn through the conduit 23.

Note that unreacted acid is circulated and used by the pump 24.

The steam-containing gas discharged from the top of the second absorption tower 20 via the mist separator 25 is circulated through the conduit 10 to the stripper 9 for use.

This circulating wet gas is accompanied by heat and steam generated by the reaction between ammonia and sulfuric acid in the second absorption tower, contributing to the effective use of thermal energy. Preferably it is operated at a temperature of 70-90°C.

In addition, in some cases, the amount of acidic substances in the ammonia-containing liquid is not so large, especially when the ammonia-containing liquid is subjected to the coagulation and precipitation treatment as described above. May be omitted.

On the other hand, when the first absorption tower 14 is provided, the aggregation step can also be omitted.

On the other hand, the bottom liquid of the stripper 9 is discharged from the stripper, precooled in the heat exchanger 7, further cooled to a predetermined temperature (usually 40°C or less) in the cooler 26, and then passed through the conduit 27 to the activated sludge apparatus. (not shown) or other processing device for processing.

However, the blower 13 that increases the pressure of the ammonia-containing wet gas discharged from the stripper 9 has problems with the blower's casing, impeller, discharge duct, etc., probably because corrosive components or minute mist are mixed in the wet gas. If it is too early, severe pitting corrosion will occur approximately one week after operation, so water in an amount greater than the saturated vapor pressure is continuously or intermittently added to the gas on the suction side of the gas circulation blower 13 from the conduit 28. Spray.

Such water spraying completely solves the problem of blower corrosion.

The amount of water sprayed varies depending on the temperature of the gas, but is 1 to 5 times the amount at which the gas after pressurization reaches the saturated vapor pressure, preferably 1.5 times.
~2 times as much.

The water to be sprayed may be tap water, but preferably pure water.

The spraying method may be continuous or intermittent, but continuous supply is preferred.

By spraying water in this way, there is no need to use special expensive materials for the blower; instead, it is possible to use a blower made of ordinary stainless steel, etc., which has sufficient corrosion resistance and can be used for a long time. can.

Although the method for removing ammonia from a gas liquid has been mainly described above, it goes without saying that the method of the present invention can also be applied to other ammonia-containing liquids.

Next, the method of the present invention will be explained in more detail with reference to Examples.

Example The apparatus shown in the drawings (however, it does not include the first absorption tower 14).

) using C0D3.500 PTm, CN 11
00pp. SSCN380pI total ammonia 3,5
00 ppm The raw gas liquid containing 300 ppm of ferrous sulfate is sent to the mixing tank 2, and 6 oop of ferrous sulfate is added.
After adding pm and coagulating and precipitating, it is heated to about 80°C in a heat exchanger 7, and then transferred to the top of the column into a stripper 9, which is a tray column using a perforated plate with a hole diameter of 9 mm.
/hr.

The steam-containing gas from the second absorption tower 19 using an aqueous sulfuric acid solution as an absorbent is placed at the bottom of the stripper 9.
Stripping was carried out by blowing through the conduit 10 at a ratio of /G''-13 (1 mole).

After removing the mist from the ammonia-containing groove gas discharged from the top of the stripper 9, a mist separator 11 is sent to the reblower 13 through a conduit 12, and at the same time, pure water is added to the gas on the suction side of the blower 13 through a conduit 28. was continuously sprayed at a rate of 11.5 g/gas-1°00 ONm3.

The gas temperature at this time was 70'C.

Approximately 1 by blower 13 made of 5US316,
After increasing the pressure to 200 mmAQ, it was sent to the second absorption tower through conduit 19 and brought into countercurrent contact with an aqueous sulfuric acid solution to recover and remove ammonia as ammonium sulfate.

Further, the exhaust gas was circulated through the conduit 10 to the stripper 9 after removing the mist with the mist separator 25.

As a result, no significant corrosion was observed in the blower 13 even after two years had passed, and smooth operation continued.

Comparative Example When the same method as in the example was carried out except that the blower 13 was operated without any water spraying, the blower casing, impeller, and discharge duct were damaged one week after the start of operation. Severe pitting corrosion was observed in all of them, and they were no longer operable after four weeks.

[Brief explanation of drawings]

The drawings are flow sheets 1 to 1 showing an embodiment of the method of the present invention. 1... Raw gas liquid supply port, 4... Thickener,
7...Heat exchanger, 9...Stripper, 13...Blower-114...First absorption tower (
alkali cleaning tower), 20... second absorption tower (acid cleaning tower).

Claims (1)

[Claims] 1. An ammonia-containing liquid is stripped with a gas in a stripper, and the strip gas discharged from the top of the stripper is sent to an absorption tower to absorb at least ammonia or ammonia and other stripped components. In a method for removing ammonia from an ammonia-containing liquid by absorbing and removing a portion of the gas and using the gas discharged from the absorption tower as a stripping gas to be blown into the stripper, a blower for circulating the gas is used. - A method for removing ammonia, which comprises continuously or intermittently spraying water on the suction side of the gas in an amount equal to or higher than the water vapor pressure at the blower discharge side to a saturated water vapor pressure. 2. The method according to claim 1, wherein the amount of water sprayed is 1.5 to 3 times the amount at which the saturated water vapor pressure is reached. 3. The method according to claim 1 or 2, wherein the blower is provided for the exhaust gas of the stripper. 4. The method according to any one of claims 1 to 3, wherein the water to be sprayed is pure water or soft water.