Page 236 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

206 Applied Process Design for Chemical and Petrochemical Plants

(text contin ued from page 203) 7. Calculate Brake Horsepower for viscous liquid
water needs to be determined using Figure 3-56 or 3-57 in
order to rate pump selection from manufacturer's curves.
Qvi, H ,;, (SpGr)
Determine proper pump selection and specifications (BHP),.i, 3960(e vis ) (3- 35)
when pumping oil with SpGr of0.9 and viscosity of25 cen-
tipoise at the pumping temperature, if the pump must (125) (86) (0. 9)
deliver 125 GPM at 86 feet total head (calculated using ------ = 4. 3 B. horsepower
(3960) (0.568)
the viscous liquid).
Viscosity conversion: Example 3-17: Corrected Performance Curves for
Viscosity Effect

Centistokes = 25/0.9 = 27.8
When a pump performance is defined for water, the
corrected performance for a viscous fluid can be devel-
Referring to Figure 3-56: oped using Figure 3-56 or 3-57. In order to develop the
curves for viscosity conditions of 100 SSU or 1,000 SSU as
shown in Figure 3-58, the following general procedure is
1. Enter capacity at 125 GPM, follow vertically to 86 used [17].
feet of head, then to right to viscosity of 27.8 centi-
stokes, and up to correction factors:
1. Starting with performance curve based on pumping
water:
Efficiency, CE = 0.80 a. Read the water capacity and head at peak efficien-
Capacity, CQ = 0.99 cy. This capacity is the value of (1.0 Q.,w).
Head, CH= 0.96 (for 1.0 QN),
QN = head at best efficiency point b. Using this value of GPM, calculate 0.6, 0.8 and 1.2
times this value, giving 0.6 Qnw, 0.8 Qnw and 1.2
Qnw respectively, and read the corresponding
Note this represents a flow rate using water under maxi- heads and water efficiencies.
mum efficiency conditions [ 1 7].
2. Using Figure 3-56 or 3-57 enter GPM at value corre-
sponding to peak efficiency, 1.0 Qnw, and follow up
2. Calculate approximate water capacity: to the corresponding head value, Hw, then move to
the viscosity value of the liquid, and up to the cor-
Qw = Q.i,/CQ (3-32) rection factors CE, CQ, CH.
Qw = 125/0.99 = 126.3 3. Repeat step 2 using GPM and head values of step
(lb).
3. Calculate approximate water head: 4. Correct head values:

(3-33)
I-Iw = H,i,/CH = 86/0.96 = 89.6 ft (3-33)
5. Correct efficiency values:
4. A pump may now be selected using water as the
equivalent fluid with capacity of 126.3 GPM and (3-34)
head of 89.6 feet. The selection should be made at
or very near to the point ( or region) of peak perfor- 6. Correct capacity values:
mance as shown on the manufacturer's curves.
5. The pump described by the curves of Figure 3-36 fits (3-32)
these requirements. The peak efficiency is 71 per-
cent using water. 7. Calculate the viscous BHP as indicated in the previ-

6. Calculate the viscous fluid pumping efficiency: ous example.
8. Plot values as generally indicated on Figure 3-58 and
evi, = Cc(e,J (3-34) obtain the performance curves corresponding to
= (0.80) (71) = 56.8% the viscous liquid conditions.