Regarding the issue of low pH and weak acidity of the graywater in very large-scale gasification systems
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It is said that the graywater quality in many multi-nozzle vaporization systems with a capacity of over 3,000 tons is slightly acidic; in some cases, the pH is low at the beginning of operation but gradually returns to normal； Some remain weakly acidic at all times. The pH value of the gray water has always been between 6 and 7. Are there any companies that experience this situation? What is the reason for this problem? What are the common measures taken after this happens? I heard that with the same quality of coal, 1,000–2,000 ton vaporizers don’t have any problems, but 3,000 ton vaporizers do experience such issues. Some people attribute this to the production of by-product formic acid; I’m not sure if that’s accurate If alkali addition is not used, what effects does a low pH value have on the equipment in the system?
It’s not a matter of the size of the furnace, but rather the quality of the coal. In our facility’s 1,500-ton pulverized coal furnace, the pH level has dropped as low as 5.4 when the black water volume was low; currently it is generally between 5.8 and 6.1
The last edit to this post was made by shuker666 on 2019-6-18 at 13:39. Let me share my understanding: Regarding the reaction mechanism, ① coal gasification involves burning coal to provide energy, resulting in an incomplete combustion reaction that produces crude gas. This crude gas contains acidic gases such as hydrogen sulfide, carbon dioxide, and sulfur dioxide. After being washed in a quenching process, the crude gas, along with slag and water, enters the slag and water treatment system; hence, the slag and water have a weakly acidic nature； ②The composition of coal is very complex; all types of coal contain sulfur, in the form of organic and inorganic sulfur. After coal is burned or burned incompletely, the slag resulting from this process also contains sulfur, in the form of hydrogen sulfide, sulfur dioxide, and sulfate ions. Not to mention other ions such as carbonate ions, nitrate ions, chloride ions, and cyanide ions; therefore, the slag becomes weakly acidic when it enters the slag water ； Therefore, the intensity of acidity depends on the quality of the coal and is not affected by the equipment (since water and steam are of suitable quality and do not cause acidity). ③ For weak acidity, it is necessary to analyze through data whether there will be any impact on pipelines and equipment; for example, the accumulation of chloride ions can cause corrosion in the slag pipeline ； For example, alkali needs to be added to balance acidic scaling ； So pay attention to addressing clogging and corrosion issues ；