This is regarding vertical retorts, specifically those used in "distillation" of coal to produce coal (town) gas, tar and other by products. It is understood that the distillation of coal is done by heating coal in an air (oxygen) free container (ie in a retort). The vertical retort is, apparently, a fairly large vertically oriented open topped cylinder with a narrowing body at the bottom of the cylinder to form a relatively small opening to allow discharge of coke (and some tar). Now, with regard to a "continuous" feed vertical retort, it is understood that coal is loaded into the top of retorts, and as it makes its way down the retort under the influence of gravity, the coal is converted to coke while the retorts are heated (using coke, gas, or oil fuel as the heat source). And the size of coke produced is maybe slightly smaller than the coal. So coke is still a fair sized "lump". There are several questions regarding this process. 1) How is the continuous feed of coal achieved in an air (oxygen) free environment? If air (oxygen) is admitted to the retort, surely the coal would burn instead of being broken down by distillation(?) 2) Small lumps of coal would presumably fall straight through the retort without being distilled(?) So how is coal prevented from falling through the retort without being "processed" first? 3) The narrow(ing) discharge at the bottom of the retort would surely tend to cause clumping of coal/coke and prevent discharge(?) So how is this overcome?