JPS61228087A - Method for removing deposit in ammonia recovery equipment - Google Patents

Abstract

PURPOSE:To remove deposits with the maintained operation state, by making an ammonia absorption system and ammonia distillation system respectively and independently operable and leading a dilute aqueous solution of caustic soda to a heat exchanger, contactor, distillation column condenser and distillation column one after another. CONSTITUTION:An absorbing solution consisting of a phosphoric acid solution is first taken out of an absorption column 2 into a blow tank 4, and the phosphoric acid solution in a reduced amount of the taken out solution is filled in the absorption column 2. The absorption system and distillation system are temporarily cut off by valves 16 and 17 to carry out the separate respective operation thereof. In the absorption system, the supply of steam 10 to the distillation column 9 is stopped to keep the distillation column 9 in the pressure holding and reduced pressure state. Caustic soda and water are then respectively fed from lines 13 and 14 into a washing tank 12 to adjust the concentration to 5%. The resultant washing solution is then passed through a heat exchanger 6, contactor 7, distillation condenser 8, distillation column 9, heat exchanger 6, and cooler 10 and then returned to the washing tank 12. The above-mentioned operation is repeated and the solution is partially blown from the tank 12.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention efficiently removes deposits from ammonia recovery equipment (J2i-cho, Foursome equipment) from coke oven gas while maintaining the operating state of the equipment. It is about the method.

[Conventional technology]

In the foursome process, which recovers ammonia in coke oven gas as liquid ammonia, an aqueous phosphoric acid solution is used as an absorbent to absorb ammonia, and the aqueous phosphoric acid solution that has absorbed ammonia is then steam-distilled under high pressure to finalize Collect liquid ammonia automatically.

Phosphoric acid and ammonia coexist in a certain ratio in the absorption liquid used in such operations, and are used while being circulated within the system.

This absorption liquid is commonly called a rich/lean liquid.

Ammonium dihydrogen phosphate aqueous solution ((NH4)f(,P
O- is sprayed as an absorption liquid in an absorption tower.

It absorbs ammonia and is extracted as an aqueous solution of ammonium monohydrogen phosphate ((NH4)!HPO4).

The ratio of the number of moles of NH3 and PO4 in this lIi collected liquid is generally referred to as the molar ratio.

[Problem that the invention seeks to solve]

By the way, when recovering ammonia from coke oven gas, crystals will precipitate if the molar ratio changes and goes out of the range for proper operation. Therefore, when operating for ammonia recovery, NH5/PO.

Appropriate control of the molar ratio is an important factor in operation, but in addition, coke oven gas contains oil such as tar, which causes carbonization during the thermal history process and causes a chemical reaction with the phosphoric acid solution. It adheres to the inner walls of equipment such as heat exchangers, lowering thermal efficiency, and in some cases, it becomes necessary to stop the entire process and clean it.

``To remove oil such as tar.

Separation methods such as flotation using air bubbles and filtration have been adopted, but the oil is not completely separated, and usually only a few ppm remains.

In addition, the reaction between components (such as silica) contained in the seal water and make-up water in each pump and phosphoric acid
:Thus, adhesion due to the compound formed is also considered,
Improving the quality of such make-up water requires extra equipment and a large amount of cost, and it is not possible to provide sufficient equipment due to the need for ammonia recovery, which is the original equipment.

Therefore, after operating the foursome facility.

In order to remove the crystals that have precipitated and adhered to the equipment as mentioned above, as well as oil-based scale and other sludge, we shut down all equipment and removed the piping of each part.
The drawback is that it is necessary to open the heat exchanger and clean it using various physical or chemical means, and the repair costs are prohibitive.

[Means for solving problems]

The present invention was arrived at as a result of studies on the above-mentioned problems in foursome equipment, and after making it possible to operate the ammonia absorption system and the ammonia distillation system independently in the foursome equipment.

A heat exchanger that distills a dilute caustic soda solution.

A method for removing deposits characterized by conducting the conductor% distillation column conductor, the distillation column sequentially, and returning to the cleaning tank (2).

, [Work, Use] Analysis of the deposits inside the heat exchanger in the foursome equipment targeted by the present invention revealed that the solid content consists of a mixture of iron, phosphorus, ammonia, cyanide, silica, carbon, etc., and is bound by a high oil content. It turned out that it was.

Therefore, it is thought that the above-mentioned solid content can be easily dispersed by decomposing or dissolving the oil content as a binding medium.

From this point of view, we performed treatments using various chemicals and obtained the following results.

It is clear from the results in the above table that by treatment with a caustic soda solution, the oil content can be decomposed or dissolved, and the strong and large scale can be reduced to fine particles and atomized.

In addition, if the concentration of the caustic soda aqueous solution used is high, it may cause another problem of corrosion of the equipment, so a diluted solution is preferable.On the other hand, based on the results in the table above, It is desirable to use a substance with a concentration of this level, since a relatively diluted substance such as chlorine has a considerable effect.

The present invention will be further explained below with reference to Examples.

〔Example〕

A coke oven gas liquid was treated using the foursome equipment shown in FIG. In the figure, 1 is coke oven gas, 2 is an ammonia absorption tower, and 3 is a phosphoric acid solution.

4 is a blow tank, 5 is a tar separation tank, 6 is a heat exchanger,
7 is a conductor, 8 is a distillation column condenser, 9 is a distillation column,
10 is a steam introduction line, 12 is a washing tank, 13 is a caustic soda introduction line, 14 is water, and 15 is a concentrated ammonia water takeout line.

During normal operation in a foursome facility with such a configuration, coke oven gas 1 is transferred to absorption tower 2.
The ammonia in the gas is absorbed by the phosphoric acid solution here, and the absorbent liquid that has absorbed the ammonia is separated and removed from the oil in the tar separation tank 5.

The absorbent liquid from which the oil has been removed in this way.

After being heated to a predetermined temperature in a heat exchanger 6, it is introduced into a contactor 7, where acidic gas is removed. It then passes through a distillation column condenser 8 and enters a distillation column 9.

Ammonia is separated and removed from the absorption liquid by steam distillation, and this absorption liquid is passed through a heat exchanger 6. It is circulated and used in the absorption tower 2 via the cooler 11.

While such normal operation continues, if scale or sludge adheres or accumulates on the heat exchanger, distillation column condenser, distillation column, piping, etc., efficiency in heat transfer will decrease.

In order to remove the deposits, first, the absorption liquid is extracted from the blow tank 4+ so that the ammonia in the coke oven gas 1 can be absorbed within the cleaning time, and the reduced amount of the extracted liquid is filled with phosphoric acid solution. : The absorption system and distillation system are temporarily shut off by pulp 16 and 17 and operated separately.

In the absorption system, the supply of steam 10 to the distillation column 9 is stopped to maintain pressure or reduce the pressure.

After this condition is reached, caustic soda and water are supplied to the cleaning tank 12 from the caustic soda supply line 13 and the industrial water line 14, respectively, and the degree of a is adjusted to 5 degrees. Vessel 6, Conctaph, Distillation Column Condan +8
．． Distillation column9. Island exchanger9. The operation of passing through the cooler 1°0 and returning to the cleaning tank is repeated several times, up to about 10 times if necessary, and a portion of the liquid is blown out from the cleaning tank soil 2.

The time required for this cleaning process and the frequency of cleaning are not constant depending on the degree of dirt inside the device.

Generally, 1-2 times per 20-50 days of operation.
It is sufficient to spend several hours cleaning.

After the cleaning operation is completed as described above, soft water is circulated through the system two or three times to remove caustic soda, the cleaning line is stopped, and the pulp 16.17 is opened for normal operation. Return twice.

According to this method, it is possible to carry out the process without sufficiently lowering the temperature of the iIA distillation column 9, and therefore the amount of steam used when normal operation is resumed can be reduced.

The relationship between the two is shown in Figure 2.

〔Effect of the invention〕

According to the present invention, by simply installing a cleaning tank and accompanying simple piping and pulp, it becomes possible to easily clean the fornum equipment as needed or after a preset period of time has elapsed. Not only does the operation itself require less time, but the overall operating cost can be reduced compared to conventional methods, and it has the effect of reducing the frequency of equipment changeovers.

[Brief explanation of drawings]

FIG. 1 is an overall explanatory diagram of the apparatus constructed according to the present invention (2);
FIG. 2 is a graph showing the behavior of the temperature of the distillation column and the required amount of steam. 1... Coke oven gas, 2... Ammonia absorption tower. 6... Phosphoric acid solution, 5... Tar separation tank, 7...
Contactor, 8... Distillation column condenser, 9... Distillation column, 10... Steam, 12... Washing tank, 15
...Caustic soda, 14...Industrial water, 15...Concentrated ammonia, 16゜17...Pulp

Claims (1)

[Claims] In equipment for recovering ammonia from coke oven gas, after enabling the ammonia absorption system and ammonia distillation system to operate independently, a dilute aqueous solution of caustic soda is distilled into a heat exchanger, a conductor, a distillation column condenser, and a distillation column. A method for removing deposits in an ammonia recovery facility, characterized by sequentially introducing ammonia into a cleaning tank and returning it to a cleaning tank.