Regarding the load issue of the Lurgi furnace

Our unit has encountered this problem as well. First, it’s necessary to consider the type of coal used; since Lurgi furnaces use coal fed through conveyors, and the feeding rate is fixed, the low calorific value of lignite results in a decrease in output. If there are no restrictions on the type of coal used, then blending different types of coal could be an option, or the lignite could be dried to some extent. I’m new to this topic, so I’m not sure if this is correct. I also have another question: we use lignite here, and the yield of tar is very low. Is this related to the low outlet temperature? How can we increase the tar yield?

When lignite is gasified in a Ruhrgas furnace, the inability to increase the load is closely related to the composition and particle size of the coal; too low a fixed carbon content leads to frequent coal feeding, and the time required for this coal feeding limits the increase in load. At the same time, if the particle size is too fine or uneven, it can also lead to an excessively fast local reaction rate, causing the flame layer to rise and resulting in high temperatures at the upper flange, which in turn affects the increase in load. Here, the maximum load per furnace can reach 8500–8800 NM3/h; however, the tar production is very low. It is likely due to the low volatile content in your coal – this has little to do with the low outlet temperature. When the temperature of the coal exceeds 100°C, the moisture in the coal evaporates ； When the temperature rises above 200°C, the bound water in coal is released ； Above 350°C, cohesive coals begin to soften and further form viscous colloids (this phenomenon does not occur in peat and lignite, etc.) ； At 400–500°C, most of the gas and tar are distilled out; there must be a space within the vaporization furnace at a temperature of 400–500°C with oxygen exclusion.

The load cannot be increased; the main reason is the quality of the coal. The poor operating conditions are only temporary, and adjustments can be made through various measures. If the conditions remain stable but then suddenly deteriorate, it’s usually due to changes in the coal quality. Another issue is that the purpose of gasification is to produce qualified gas – so what’s the need for so much tar? Great!

The inability to increase the load is largely due to coal quality issues; if the coal fed into the furnace is not suitable for combustion, the coal feeding rate will not be able to keep up, which will certainly affect the load. One option to consider is increasing the pressure in the gasification furnace, or enlarging the volume of the coal lock (though this approach is not very ideal).

Many current Luchie furnaces increase their load by enlarging the coal lock volume.