What is a flux?

Flux: Generally refers to a substance that can lower the softening, melting, or liquefaction temperature of another material. 　　In chemical analysis, its main function is to convert insoluble substances into soluble ones to facilitate analysis. Such as sodium carbonate, potassium carbonate, mixtures of sodium carbonate and potassium nitrate, etc. 　　In metallurgy, its main function is to combine with impurities in minerals to form slag, thereby separating them from the metal, in order to achieve melting or refining. 　　Based on their chemical properties, they can be classified as: (1) basic fluxes with calcium oxide and magnesium oxide as their main components ； 　　(2) Acidic flux with silica as the main component ； 　　(3) A central flux with fluorite and alumina as its main components.

But why is it called limestone instead of quicklime? You know, limestone is just CaCO3. CaO is quicklime. I don’t get it – surely everyone doesn’t keep getting these basic facts wrong for such a long time?

Limestone is added, but when calculating the ash melting point (the basic components in the ash), it is calculated based on the amount of calcium oxide

So it’s CaCO3. Is there any CaO added?

My personal opinion on the OP’s question: 1. First, limestone CaCO3 is added, not quicklime CaO； 2. Limestone is added to lower the ash melting point of raw coal, thereby preventing premature coking of the ash from causing problems in production; MgCO3 can also be used, as long as it is a substance that becomes alkaline after pyrolysis ； 3. Why cannot quicklime CaO be added? It is because during the production of water-coal slurry, CaO reacts with H2O to form Ca(OH)2, thereby rendering CaO ineffective ； 4. Why is CaO used in the calculations? This is because CaCO3 decomposes at high temperatures to form CaO. When CaO is present in the ash, it can lower the ash fusion point. The ash fusion point is determined by the ratio of acidic substances such as Al2O3 and SiO2 to basic substances such as CaO, MgO, and Fe2O3 in the ash; the higher this ratio, the higher the ash fusion point ； 5. The amount of limestone to be added must be determined based on calculations; it cannot be added in unlimited quantities, as an excess will instead lead to an increase in the melting point of the ash. I wonder if the original poster is satisfied with the above answer?

CaCO3, right? At high temperatures, it splits into CaO and CO2

CaCO3 is generally adjusted using limestone or quartz sand, right? I think CaO should work too. One reason is that the amount added is generally not much, and the other is that CaO is a bit harder to grind. I thought of it myself

Could CaO form Ca(OH)2 in the mill and pipelines, causing it to adhere to the pipe walls? Furthermore, if CaO is added, then why is it necessary to add NaOH to adjust the pH value? Why do people have different opinions on such a simple matter? It’s really confusing. I’m becoming more and more confused! ! !

So what you’re saying is that the flux must be CaCO3 and not CaO. As for what role it plays, no further explanation is needed; I can also understand the effective value in CaCO3 in terms of the CaO content. We are a new factory, and there are different opinions among everyone regarding what kind of flux should be used. From my personal understanding, it must be powdered CaCO3; it’s just a matter of seeing if anyone has used powdered CaO.

Either one will work; whether CaO or CaCO3 is used, it is CaO that serves as the active ingredient. Iron oxide can also be used, but the cost is slightly higher!

I learned it! Thank you all, guys!