The problem of producing water-coal slurry using methanol!
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Our coal ash has a high melting point, so limestone is added during pulping. I would like to ask: what would be the effect of adding a certain proportion of methanol instead of limestone? Could it help lower the ash melting point?
Methanol is a liquid fuel; when added, it contributes to increasing the calorific value, thereby indirectly reducing the amount of oxygen required by the slag. However, the ash melting point does not actually decrease. Moreover, the cost of methanol is relatively high, making it uneconomical.
It is feasible to incorporate methanol that needs to be discarded; this reduces environmental pollution and can also lower the specific oxygen consumption and specific coal consumption. Finding a type of coal whose components complement each other to form a new coal variety may help reduce the ash melting point, thereby making it suitable for use in furnaces lined with refractory bricks. :)
Typically, coal-based methanol plants are designed to utilize methanol wastewater in the pulp production process, and our plant does the same
In addition to adding limestone, iron ore can also be used to lower the ash fusion point, although the cost is higher. Methanol is added to the pulping process for environmental reasons; wastewater containing methanol cannot be discharged directly (due to the pollution factor COD).
Adding waste methanol to the coal slurry is likely a consideration from an environmental protection perspective. After all, it is quite difficult to completely remove methanol from wastewater, and it is also very uneconomical. However, it is necessary to analyze different types of coal to determine whether the addition of methanol will affect the slurry concentration, either increasing or decreasing it. Regarding the ash melting point, adding methanol should not cause any changes, as methanol would have already vaporized and decomposed at the temperature of the gasifier. Therefore, to reduce the ash fusion point, it is necessary to conduct an analysis based on the three-phase diagram of coal ash, and by selecting appropriate formulations (typically by adding alkaline substances such as CaO and FeO in controlled proportions), ensure that the ash remains in a liquid state at low temperatures.
Personally, I think this is merely a matter of waste utilization and has nothing to do with reducing the ash fusion point. The ash fusion point is determined solely by the type of coal; more precisely, it depends on the composition of the ash in the coal. The industry often uses a concept known as the ash acidity-alkalinity ratio to measure this value. It is a physical property of the coal type. Ordinary substances cannot penetrate deep into the coal to change this key factor—the ash acidity-alkalinity ratio; in other words, it is not possible to alter the ash composition, and thus the ash fusion point cannot be reduced. Methanol does not have this function!