[Gasification] cyclone sizing

[jim mason]

in the handbook on downdraft gasification, and the GATE small scall
gasification book, examples are given on how to size a cyclone
separator.  the examples suggest that for fine dust the gas speed must
not drop below 10m/s.  moderate dust 15m/s.  heavy stuff 25 m/s.

what is not clearly noted is the max velocity one can have at the
cyclone inlet or in the associated piping, nor what hearth load(s) we
should be concerned with for the min/max flow rates.  obviously we
should keep the speed as low as possible to keep drag and pressure
drop to a minimum, but what is "too fast"?  there is a line chart for
pipe pressure drops at various flow rates that i'm having a bit of
difficulty figuring out, but likely will figure out soon.  and i can
do the formula for cyclone pressure drop, though unclear on what i
should tolerate.  so i'm wondering if there are some other rules of
thumb for deciding what is "too fast".

the examples in the books figure velocity at the max gas rate for the
throat, and make sure that is above the "min" to keep the solids
entrained and have the cyclone work well (i.e. above 15m/s).  but how
are we to fudge with turndown in variable speed applications?  with
the examples in the book, half power or idle will have the gas
velocity well below the ideal pipe flow rate and cyclone rate.  yes,
as the gas slows down, there will be less dust, but i don't think this
is a linear reduction in dust.  the cyclone still has to work.  the
figures i'm getting here are suggesting a cyclone to be rather useless
at idle and other slow gas rates.

also, has anyone found a source for off the shelf purchased cyclones
in the size ranges and in the configurations that are suggested for
our application?  all the ones i can find are giant.  i can build, but
would also be interested in buying, done.

jim

ps- btw, for a 40hp application, i am getting that i want 2" pipe and
an 8" diameter cyclone.  the rest of the cyclone dimensions are by
ratio to the diameter, as suggested in the book.