Summary of Fully Automatic Filter Cleaning and Pre filming for Circulating Cooling Water System

Fully automatic filters clean and pre film the system, and master the process control and monitoring requirements for cleaning and pre film.

1.0 Introduction
To ensure the long-term stable operation of the two sets of circulating cooling water systems for synthetic ammonia and urea after annual overhaul and start-up, they mainly supply cooling water for the production of synthetic ammonia and composite fertilizers, with carbon steel as the main water equipment. The circulating water volume of the urea system is 1500t/h, with a retained water volume of about 750t. It is mainly used for cooling water in urea production, and the water equipment is mainly made of stainless steel.

2.0 Cleaning process
2.1 Water flushing
Before chemical cleaning, start flushing the two systems with water. After the circulating water is connected, the turbidity significantly increases. Wait until the water tank is filled and the pump is started for chemical cleaning.

2.2 Oil removal and cleaning
The two systems of synthetic ammonia and urea operate synchronously. When a large amount of foam is produced in the pool, JC-863 defoamer is added. After dosing, the turbidity of the synthetic ammonia system increased from 34.02mg/L to 53.24mg/L, and the urea system increased from 31.06mg/L to 72.47mg/L.

2.3 Mud peeling and cleaning
JC-863 defoamer is added to the two systems when a large amount of foam is produced in the pool. After dosing, the turbidity of the synthetic ammonia system increased to 78.39mg/L, and there was no significant increase in the turbidity of the urea system. After running for 24 hours, when the turbidity of the two systems no longer significantly increases, the second drainage replacement will begin, emptying the system and pool water, and cleaning the pool. After the pool is filled with water, the pump is started to circulate, and the turbidity is basically qualified when the water is discharged and supplemented. Since the turbidity is mostly analyzed by sampling from the pump, and a large amount of slimy dirt in the water is carried to the surface by foam, the measured turbidity does not rise but fall. However, the turbidity is as high as 106mg/L after defoaming the sample taken from the pool surface of the cooling tower of the synthesis system. During the entire stripping period, through water quality analysis and visual observation during tank cleaning, the stripping effect was obvious and the expected goal was achieved.

2.4 Rust removal and scale cleaning
Due to the qualified turbidity of the pumped effluent, a large amount of water change was not carried out. The synthesis system was only replenished with water until it overflowed for 3 hours, and the third drainage replacement was carried out after continuing to operate for 6 hours. The system and pool water were drained and cleaned.

3.0 Pre film process
After the water change is qualified, ensure the total phosphorus content in the circulating water and control the pH between 6.0 and 7.0. In order to ensure the pre film effect, JC-326 scale inhibitor and dispersant are added in batches during the pre film process. The synthesis system uses a small amount of concentrated H2SO4 for pH regulation due to water replenishment and fan operation. When there is a clear blue halo observed in the pre film hanging piece in the water tank, the pre film is completed and the pre film time is 34 hours.

Pre film effect inspection:

After pre coating, there is a clear blue color halo visible to the naked eye, especially for the urea system water tank coating, which forms a film on the surface

Very uniform and dense. Using CuSO4 solution for inspection, the time difference between the appearance of red dots, synthesis>20 seconds, and urea>45 seconds, indicates that the pre film effect is very ideal.

4.0 Problems in the cleaning and pre film process
a. Due to the closure of the downstream hydropower station of the Shaxi River, the water flow fluidity has decreased, and there is direct flow drainage from the upstream power plant. The alkalinity of the supplementary water may increase. In addition to the increase in system equipment, this cleaning has not been able to reduce the pH below 3.0. Therefore, an increase in the amount of cleaning agent should be considered next time.
b. The turbidity of the synthesis system during pre filming is relatively high, and there is a phenomenon of water leakage. Regular water replenishment is necessary, which has an impact on the pre filming effect.

5.0 Conclusion
The cleaning and pre coating work, including mud stripping, acid washing, and pre coating treatment, achieved the expected results, laying a good foundation for the water treatment work after the production of synthetic ammonia, composite fertilizer, and urea.