The Oil Drum

Coal has been piped in the past, and there was some work on creating "coal logs" that were made of coal particles and a binder that would sensibly fill most of the volume of the pipe, thereby reducing water needs. The only operating unit at the moment that I am aware of is at Black Mesa. There has been some talk about using air as a conveying fluid, but I am not sure how well that would work at longer distances.

I just did a quick Google, and found this :

Several utilities and consultants are proposing the coal-slurry pipeline as a far cheaper alternate to unit trains.^It has been estimated that a slurry pipeline will be $14 billion cheaper than unit trains for a 1400-mile haul from Wyoming to a 1400-MW generating station in Arkansas.^This estimate of savings is from Larry Grundmann, engineering manager for Middle South Utilities` (MSU) fuel subsidiary.^MSU is building two coal-fired units--scheduled for operation in 1979 and 1981 at a site near White Bluff, Arkansas.^

(Obviously it is quite old, and was not implemented).

There are varying reports on how much water a pipeline would use - and sometimes it is difficult to separate out the facts, since the railways, for some obscure reason, seem to be dead set against them. There is more information on the coal log idea at this site.