In soda ash production, why does the soda ash product have high iron content?
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This post was last edited by mkp369 on 2013-12-25 18:03 In soda ash production, why does the soda ash product have high iron content? Where is it brought in? What is the iron content of the mother liquor that comes out of the cleaning tower? What about the alkali making tower? What about AII? Does the H2S in CO2 have any impact on this? How? Will the water in the compressor intercooler cause the iron content of the product to be high?
This post was last edited by mkp369 on 2013-12-25 18:04. I can only answer some of the questions.: Soda ash iron content is high because: It is caused by corrosion of iron equipment and pipelines, causing iron ions to mix into heavy alkali. H2S in CO2 has an impact on this because iron sulfide can be formed. Iron sulfide is easy and there is gray alkali or black alkali in the product. I don't know much about the rest. Looking forward to the answer.
This post was last posted by mkp369 on 2013-12-25 18:04 What the editor said on the second floor makes sense. The high iron content is indeed caused by corrosion of iron equipment and pipelines, causing iron ions to mix into heavy alkali. In order to reduce the corrosion of the inner wall of the equipment and ensure the quality of soda ash, you can add a certain amount of Na2S solution to the fine section of the ammonia distillation tower.
Normally, the iron content of the mother liquor coming out of the cleaning tower is 10 mg.
This post was last edited by mkp369 on 2013-12-25 18:06 The phenomenon of high-alkali iron accidents: Shortly after the system is shut down for inspection, deficiencies are eliminated and started, or shortly after the carbonization of a newly opened tower or the carbonization of a modified tower, a reddening color of the alkali is observed from the alkali outlet, alkali filter and finished soda ash, and the iron content of the soda ash is analyzed and detected to exceed the standard. Cause of accident: The liquid medium in the carbonization system is a strong electrolyte, which will corrode the equipment and cause iron to be corroded into the liquid. Normal production processes usually have a large circulation volume, and the corrosion rate is usually not enough to cause iron hyperalkali. However, if the inspection and elimination time is long, the accumulated iron content in the system will increase, which will lead to iron hyperalkali. ； Oxygen dissolves in the liquid medium and becomes a depolarizing agent, which will greatly promote and intensify the corrosion of the equipment. Therefore, if the inspection and elimination process is stopped, the equipment and pipelines of the carbonization system will be exposed to air, which will easily produce iron and high alkali. ； The corrosion of oxygen is very harmful, but the solubility of oxygen is very small. The corrosion of oxygen in the liquid phase is much weaker than that in the gas phase. If the liquid level control of the carbonization tower is low, it will inevitably lead to an increase in the iron content of the alkali solution. ； Generally, the speed of chemical reactions accelerates as the temperature increases. If the carbonization tower reaction moves upward and the temperature rises by 5°C, the corrosion rate of iron will double. ； Loss of alkali scar protection and excessive cleaning will increase Fe corrosion. ； The small amount of Na2S added is not enough to overcome the consumption of O2 content entering the system, and the FeS protective film cannot be formed. ； The newly opened carbonization tower was not thoroughly sulfur washed, the FeS protective film formed was not strong, and the load of the newly opened tower was not controlled. ； Carbonization changes the tower or the liquid level fluctuates, and the FeS protective film falls off ； Kiln gas and furnace gas have high oxygen content. Solution: Control the downtime of the carbonization system and reduce equipment maintenance time. ； When eliminating deficiencies or stopping inspections, raise the sulfur content of ammonia water to the highest limit in advance. ； Try to keep the tower liquid level as high as possible during shutdown and overhaul ； Control the oxygen content of the kiln gas and furnace gas well, and plug the negative pressure pipeline in front of the compressor inlet if there is any leakage. Pay special attention to the air pressure control during kiln maintenance and the leakage points of the furnace gas system. ； Newly opened carbonization towers need to be thoroughly sulfur washed, adhere to the qualification standard that the circulating liquid sulfur content does not change for two hours, and the load of the tower needs to be controlled. ； Maintain the liquid level of the alkali making tower and cleaning tower to avoid fluctuations or the FeS protective film falling off ； Try to be on time and do not disrupt the order of tower pouring, and add MgCl2 to the system as required to prevent excessive tower cleaning. ； During operation, it is necessary to prevent the temperature on the tower from being too high and try to increase the CO2 concentration of the neutralized water. ； The amount of Na2S should be added evenly as specified. When it is confirmed that the oxygen content of the furnace gas has increased, the amount of Na2S should be increased appropriately.
In addition to the opinions of the people above, there is also air leakage into the system. The oxygen in the air accelerates the oxidation of iron, so controlling the oxygen content in the raw gas is also an effective way to reduce the iron content in the finished product.
The main reason for high iron alkalinity is generally caused by poor sulfurization coating during cleaning of the carbonization tower, production fluctuations such as unstable liquid level in the carbonization tower, etc. Sometimes, excessive use of sodium sulfide, for example, causes the sulfide ion concentration after sulfur washing to be high. Iron high alkalinity will also occur. The amount of sodium sulfide added must be appropriate. Not more, the better. The intercooler carries water, which will not cause high iron alkalinity.
When excessive sodium sulfide is added, will the alkali and iron levels increase at the same time?
It should be that when the red alkali and iron are high, sodium sulfide is added excessively, and the gray alkali is iron sulfide.
This post was last edited by mkp369 on 2013-12-25 18:07. As far as I know, the slightly higher H2S content in CO2 has a certain impact on the color of heavy alkali (gray), but it does not have much impact on the quality of soda ash after calcination.； Moreover, a certain amount of H2S entering the carbonization tower has a positive effect on the vulcanization film on the tower wall. Of course, everything needs to have a degree, and too much is inappropriate.
Adding too much magnesium chloride will cause poor crystallization of heavy alkali. If the particle size is too small, the amount of dust in the calciner will be large. In the process of making heavy ash, alkali monohydrate does not crystallize well, and the water content is easily excessive, causing many post-system problems!