Application of citric acid

[Technical index] GB/T8269-2006 citric acid

[Application] Citric acid has a strong chelating effect, can remove iron, copper and other metal oxide scales, easy and safe to operate, suitable for a wide range of materials (it can be used for titanium, carbon steel, stainless steel and other materials), and is corrosive to metals It has low performance, because it does not contain CI ^{-in the} molecule, it will not cause stress corrosion of the equipment.

Commonly used 3% citric acid (adjust pH 3-4 with ammonia water, add 0.

Citric acid cannot eliminate calcium magnesium scale and silicate scale.

The main corrosion inhibitor added to the citric acid cleaning solution is thiourea, with a concentration of 0.

Another major use of citric acid in chemical cleaning is as a neutralizing pretreatment agent or rinsing agent

Mu Yongzhi and others studied the chemical cleaning technology of the steam turbine oil system of a 200MW unit.

Among them, the citric acid pickling control process conditions are: corrosion inhibitor (Ningmong No.

During the pickling process, tests are carried out according to the specified chemical supervision items.

When the citric acid waste liquid is discharged, add NaOH solution, adjust the pH of the waste liquid to 6-9, add NaCIO for stirring and neutralization, and discharge after CODMn<150mg/L and pH 6-9 are qualified

The rinsing process is: 0.

After rinsing, if the rinsing solution TFe<300mg/L, directly adjust the pH value to passivation, if the rinsing solution TFe>300mg/L, take the replacement method and switch to passivation when the rinsing solution Tre<300mg/L

After the operation of the oil system after this chemical cleaning, the oil particle size decreased from 10 to 11 of the US Aerospace Standard before cleaning to 7 to 9

The characteristics of using citric acid as a cleaning medium and the matters needing attention are as follows:

(1) Citric acid can dissolve iron and copper rust.

(2) Citric acid is a polybasic acid with fractional ionization, and the concentration of citrate in its aqueous solution is greatly affected by the pH value

(3) Citrate has the ability to cooperate with multiple metals

In citric acid pickling, when the concentration of iron ions in the pickling solution is too large and the pH value is greater than 4, precipitation of iron citrate may be formed, which will affect the cleaning effect

Technical measures to prevent the formation of ferric citrate precipitation: Keep the pickling temperature above 80°C without causing a sudden drop in temperature.
Generally, it should be maintained at 90-105°C.
At the same time, the cleaning speed should be ensured, and the cleaning time should be shortened to 3~4h.
After internal cleaning, generally no more than 6h; appropriately increase the flow rate, generally 0.
5m/s, or even 1~1.
5m/s; because ferric citrate is insoluble in citric acid, but can be dissolved in hot water, when the The concentration of iron ions increases rapidly, and when the pH of the solution is higher than 4.
5, hot water should be used to replace the citric acid solution.
After the precipitation of iron citrate occurs, wash with hot water circulation; in the citric acid solution, add ammonia to make the pH of the solution The value is increased to 3.
0-3.
5 to become a cleaning solution of monoammonium citrate, and then an appropriate penetrant can be added to effectively reduce the precipitation of ferric citrate
.

(4) The surface of the boiler cleaned with hydrochloric acid can be rinsed with a dilute citric acid solution.
Using its ability to cooperate with iron ions, remove the residual iron salt, which is beneficial to the passivation treatment of the surface after cleaning
.

(5) The acidity of citric acid is relatively weak.
In order to ensure a certain cleaning speed, generally a higher cleaning temperature should be maintained
.

(6) The price of citric acid is relatively high, so in general cleaning, try to choose other pickling solutions first instead of using citric acid casually
.

(7) Citric acid has low toxicity, but its concentrated solution stimulates mucous membranes
.

Citric acid is mainly used to clean oxide scale on the surface of relatively expensive equipment, and it can also dissolve carbonate scale
.

Related link: How to prepare citric acid