Water-coal slurry limestone problem!
Thread Content
Our coal ash has a high melting point; limestone is added during pulp production to lower this melting point. Why does adding limestone help to reduce the melting point? What is the principle?
The ash content in coal and the melting point of coal ash are also important indicators for coal pressurized gasification. Coal ash is an inert substance that does not participate in the reactions during coal gasification; its presence results in increased energy consumption, as energy is required for transporting the ash in coal, crushing it, and transporting and dumping the resulting ash waste ； It consumes more oxygen and raw coal, which is used for the melting of coal ash. When dealing with coal with a high ash melting point, limestone must be added as a flux during the preparation of the raw coal. The amount added, expressed in terms of CaO, is 5% to 20% of the ash content in the coal (CaO/A = 5% to 20%). This not only introduces an additional step for adding the flux, thereby complicating the process, but it also increases oxygen consumption, coal consumption, and energy consumption. Moreover, a high CaO content in the slag has a corrosive effect on refractory bricks. Based on experience, for every 5% increase in the ash content of coal, oxygen consumption increases by 3.5% to 5%, while coal consumption rises by 6.5% to 11%. When expressed on a moisture- and ash-free basis, coal consumption increases by 2% to 3.5%. Therefore, caution should be exercised when deciding to use coal with high ash content and high ash fusion point.
It mainly involves using limestone to reduce the acid-base ratio of the coal, thereby lowering its ash fusion point.
Current understanding of the underlying mechanisms is generally derived from triangular phase diagrams of ash composition; the effect of limestone in reducing the ash fusion point is not universal. For certain types of coal with a high content of CaO in their ash composition, adding more limestone will increase the ash fusion point, resulting in a situation where melting is facilitated. In such cases, to reduce the ash fusion point, it may be necessary to add Si or Fe. Limestone is a widely available, inexpensive flux; theoretically it may not be the most effective, but its low cost makes it commonly used. It also has side effects, such as sulfur absorption and formation of ash water
Although adding a small amount of limestone can lower the ash melting point, if too much limestone is added, it can cause severe erosion of the refractory bricks. The Luonai Institute has conducted specialized experiments on this; you can consult them for more information