re preheater flow counter/parralell
Well The flow is neither perfectly parallel nor counter current,at the same time it is both. Seems bit complicated ? let me explain.
When material is fed it spreads more or less uniformly, from splash box, into gas (This is a example of counter current Gas-Solid mixing), When it raises to cyclone precipitation section (cylindrical section) Gas and material follows similar centrifugal trajectory towards cone (This is a example of co-current Gas-Solid mixing), but in so called 'Low Nox zone' or 'Reduction zone' of calciner where tertiary air is added flow pattern is more complex (due to addition of tertiary air tangentially, hot air from bottom and calcining material from last but one stage) to define with usual terms.