Friction Loss of Pulp Suspensions in Pipe Section 2

To determine the pipe friction loss component for a specified design basis (usually daily mass flow rate), the following parameters must be defined:

a) Pulp Type - Chemical or mechanical pulp, long or short fibered, never dried or dried and reslurried, etc. This is required to choose the proper coefficients which define the pulp friction curve.

b) Consistency, C (oven-dried) - Often a design constraint in an existing systemNOTE: If air-dried consistency is known, multiply by 0.9 to convert to oven-dried consistency.

c) Internal pipe diameter, D - Lowering D reduces initial capital investment, but increases pump operating costs. Once the pipe diameter is selected. it fixes the velocity for a prespecified mass flow rate.

d) Bulk velocity, V - Usually based on a pre-specified daily mass flow rate. Note that both V and D are interdependent for a constant mass flow rate.

e) Stock temperature, T - Required to adjust for the effect of changes in viscosity of water (the suspending medium) on pipe friction loss.

f) Freeness- Used to indicate the degree of refining or to define the pulp for comparison purposes.

g) Pipe material - Important to specify design correlations and compare design values

The bulk velocity (V) will depend on the daily mass flow rate and the pipe diameter (D) selected. The final value of V can be optimized to give the lowest capital investment and operating cost with due consideration of future demands or possible system expansion. The bulk velocity will fall into one of the regions pre-viously discussed. Once it has been determined in which region the design velocity will occur, the appro-priate correlations for determining pipe friction loss value(s) may be selected. The following describes the procedure to be used for estimating pipe friction loss in each of the regions.