Setting Up Pump Circuits

Table of Contents

1. Purpose

This procedure explains how to create a hydraulic circuit for a single process pump that supplies two discharge services and two centrifugal pumps in series. It also provides guidance on selecting the control valve which acts as the floating element in the hydraulic circuit.

2. Single Pump Supplying Two Discharge Services Example

Consider using a single pump for two discharge services when both services have similar head requirements, or when the flow rate of the low head service is much smaller than the flow rate of the high head services. If a clear choice is not apparent, a capital cost estimate for the installation of a single set of pumps should be compared against the installation cost of two separate sets of pumps. Determine if the utility savings with separate services will pay out the additional installation cost for the second set of pumps in a reasonable time period. The Cost Estimating group or the Pump Specialist can be consulted for capital cost information.

When a single pump supplies more than one discharge service and the design flow factor differs for each service, the design flow factor for the pump supplying both services is the weighted average of the two design flow factors. For example, Inflection Point Engineering uses a design flow factor of 110 percent for a net overhead product but in some special cases (difficult split, customer request, etc.) may opt to use a higher design flow factor (e.g. 120 percent) for a column reflux.

a. Include the pump in the net overhead and reflux circuits.

b. Use a split node to identify where the split in flow between two discharge services causes circuit flow rate changes.

c. Calculate the design flow factor for the circuit definition by dividing the pump design flow rate by the normal pump flow rate and multiplying by 100 percent.

Design Flow Factor =

d. Calculate the design flow factor for the circuit as follows:

• Normal Flow Rates:

Net Overhead = 605.8 gpm

Reflux Rate = 742.7 gpm

Pump Rate = 1348.5 gpm

• Design Flow Factors:

Net Overhead = 110 percent

Reflux Rate = 120 percent (special case or customer request)

• Pump Design Flow Rate = (1.1 x 605.8 gpm) + (1.2 x 742.7 gpm)

• Pump Design Flow Rate = 1557.6 gpm

• Design Flow Factor = 1557.6*100/1348.5

• Design Flow Factor = 115.5 percent

Enter the calculated design flow factor on both circuit forms and copy to all the equipment and pipes in the circuit. NHP will only accept whole numbers for the flow scenario factors currently. Enter a value of 116%.

e. Set the design flow factor for all equipment, lines, orifices, exchangers, etc. after the split node equal to the design flow factor for that discharge service (110 percent for net overhead in example). The design flow factor for the individual equipment will override the design flow factor in the circuit definition. The equipment design flow factor (110 percent) adjusts the design flow scenario pressure drop after the split.

f. The Hydraulic Tabulation Report identifies all circuit items after the split node that have an overridden design flow factor that differs from that of the circuit definition.

g. The reflux equipment would be run with a Design Flow Factor of 120% after the splitter.

h. See Attachment 1 for a Hydraulic Report example.

3. Pumps in Series

The recommended work process to generate hydraulic tabulation in NHP when there are two pumps in series in one circuit, such as the lean solvent line from the Regenerator to the CO2 Absorber with LP and HP Lean Solvent Pumps and Flow Control Valve, is outlined below. Since NHP cannot handle two pumps and one control valve in a single circuit, there is some trial and error involved.

a. Create Circuit 1 starting from an equipment with a known pressure with start pressure as “Previous” and ending downstream of the first pump with one value entered for the normal flow scenario end pressure (only one process case). The end pressure instruction should be set to “Calculated”. See the Circuits section 22.7 in TD-510-01 for more detailed instructions. The design engineer will have to determine this value. There may be some trial and error until a final value is accepted.

b. Create Circuit 2 starting from the final equipment in Circuit 1 with start pressure as “Previous” and ending at an equipment with a known pressure with end pressure as “Previous” – including the second pump and Flow Control Valve. The control valve should be set as “Hydraulic Balance”.

c. Run these two circuits and send the results to the pump specialist to review Pump Selection and pump curves. The pump specialist may make a manual pump selection.

d. Manually enter the pump selection and pump head curves in NHP for both pumps if required. Lock the Pump Type and Pump Curve if manually entered.

e. If the pump curve was manually entered and locked for the pump in circuit 1, keep the end pressure instruction to “Calculated” for Circuit 1. Clear the port pressures for the end equipment in the circuit in order to remove the manually entered pressure from Step a above.

f. Rerun both circuits.

g. Both pumps follow the normal calculations for maximum suction pressure, shutoff pressure and NPSHA except that the maximum suction pressure for the second pump in series is equal to the first pump’s shutoff pressure. These calculations are automatic within NHP.

4. Which Control Valve is the Floating Element?

This Procedure provides guidance to ensure that sufficient differential pressure and inlet pressure are available for control valves in pumped circuits. This procedure only applies to hydraulic circuits with new pumps. Hydraulic circuits which evaluate existing pumps for revamped operating conditions are not covered by this procedure.

The following figures provide guidance on selecting the control valve which acts as the floating element in the hydraulic circuit. In the following figures, frictional equipment refers to the cumulative result of piping losses, flow meters, heat exchangers, fired heater coils, guard beds, reactor beds, clay treaters, filters, and strainers.

4.1 Figure 1: Pump with Single Discharge Path, Immediately Followed by the Control Valve

Figure 1 provides the most common example. In this scenario, the floating element is obvious.

Figure 1

4.2 Figure 2: Pump with Multiple Discharge Paths, Followed by the Control Valves

Figure 2 provides another common example. In this scenario, the pump discharge piping splits into two flow paths. This scenario shall be modeled with two unique hydraulic circuits. Each circuit shall start at the suction vessel, include the pump and have its own floating element.

Figure 2

4.3 Figure 3: Pump with Single Discharge Path, Followed by a Back Pressure Control System

Figure 3 involves a pump whose discharge is flow controlled. The flow subsequently passes through some frictional equipment and then the back pressure is also controlled. In this scenario, the control valve at the pump discharge is the floating element in the hydraulic circuit that starts at the suction vessel and ends at the PIC.

Figure 3

4.4 Figure 4: Pump with Single Discharge Path and Pressure Differential Control which Diverts Flow to Other Areas of the Process Unit or Complex

Figure 4 involves a pump whose discharge is partially diverted under pressure differential control to other areas of the process unit or complex. The recombined flow is then flow controlled and subsequently passes through some frictional equipment. In this scenario, the final control valve is the floating element in the hydraulic circuit that starts at the suction vessel and flows through the pump, PDIC, FIC, control valve and frictional equipment.

In NHP, set the valve hydraulic function to “Fixedcv” and the pressure drop calc method to “Constant dP” for the PDIC. The differential pressure across this control valve shall not be included when calculating the total system frictional loss.

Another hydraulic circuit that starts at the splitter node upstream of the PDIC and ends at the mixer node downstream of the PDIC must be created for the flow that bypasses the pressure differential control valve; this hydraulic circuit must run after the hydraulic circuit that generates the pump curve. The control valve in this circuit must have the valve hydraulic function set as “hydraulic balance”.

Figure 4

4.5 Figure 5: Pump with Single Discharge Path and Flow Diversion through and bypassing a heat exchanger

In Figure 5, the pump discharge flow diverts through and around a heat exchanger. The flow subsequently passes through some frictional equipment and is then flow controlled. In this scenario, the final control valve is the floating element in the hydraulic circuit that starts at the suction vessel and flows through the pump, heat exchanger, control valve, frictional equipment, FIC and floating element control valve.

The control valve immediately downstream of the heat exchanger must have the valve hydraulic function set as ”Fixedcv” and assigned a pressure drop of 5 psi. Another hydraulic circuit that starts at the splitter node upstream of the heat exchanger and ends at the mixer node just upstream of the frictional equipment must be created for the heat exchanger bypass; this hydraulic circuit must run after the hydraulic circuit that generates the pump curve. The control valve in this circuit must have the valve hydraulic function set as “hydraulic balance”.

Figure 5

Attachment 1 Example of Hydraulic Summary Report

Platforming Process Unit NOTE - THE INFORMATION IN THIS DOCUMENT IS Date 31 Jul 13 14:08

Case 2 CONFIDENTIAL AND PROPERTY OF Inflection Point Engineering, AND Proj 500078-C.1.0

MUST NOT BE DISCLOSED TO OTHERS OR REPRODUCED By Pam Watkins

IN ANY MANNER OR USED FOR ANY PURPOSE

500078-Case2.usc WHATSOEVER WITHOUT ITS WRITTEN PERMISSION. Version 3.2.29

IPE-TM-510-11

Circuit 2 : Reformate Splitter Net Overhead

Normal Design Alternate

PRESS 100.0% 116.0% 60.0%

DROP ------------------- ------------------- -------------------

LINE 100 PER NOZL PRESS INLET PRESS INLET PRESS INLET

SIZE EQ 100ft ELEV DROP PRESS DROP PRESS DROP PRESS

EQUIPMENT IDENTIFICATION IN ft psi ft psi psig psi psig psi psig

Reformate Splitter Receiver 30.0 2.00 2.00 2.00

Liquid Level 1.0 -0.32 2.00 -0.32 2.00 -0.32 2.00

LN-XP309 12 5.77 0.10 0.59 2.32 0.79 2.32 0.21 2.32

Static Head 27.0 -8.53 1.73 -8.53 1.52 -8.53 2.10

Reformate Splitter Overhead Pumps *Gov* 3.0 -106.19 10.25 -99.88 10.05 -118.03 10.63

Pump Head,ft of fluid 335.85 315.89 373.29

Pump Capacity, gpm 1349 1565 810

Average Flowing ,SG 0.729

Operating Temperature,°F 169

Viscosity,cP 0.27

LN-XP310 8 3.93 0.82 3.21 116.44 4.32 109.93 1.16 128.66

Splitter Reflux Split 113.23 105.61 127.50

LN-XP313 (Des=110%) 6 1.94 0.70 1.35 113.23 1.64 105.61 0.49 127.50

Reformate Splitter Net Overhead C (Tube) 9.04 111.88 10.94 103.97 3.25 127.02

(Des=110%)

LN-317 (Des=110%) 6 1.94 0.68 1.31 102.84 1.59 93.03 0.47 123.76

Splitter Net Ovhd Liq Flow Orifice: FD-1 6 1.15 101.53 1.39 91.44 0.41 123.29

(Des=110%)

LN-319 (Des=110%) 6 1.94 0.68 1.31 100.38 1.59 90.06 0.47 122.88

Splitter Net Ovhd Liq CV: CV-1614 25.05 99.07 13.61 88.47 50.96 122.40

(Des=110%)

LN-XP321 (Des=110%) 6 5.94 0.68 4.02 74.02 4.86 74.86 1.45 71.45

Battery Limit 70.00 70.00 70.00

Platforming Process Unit NOTE - THE INFORMATION IN THIS DOCUMENT IS Date 31 Jul 13 14:08

Case 2 CONFIDENTIAL AND PROPERTY OF Inflection Point Engineering, AND Proj 500078-C.1.0

MUST NOT BE DISCLOSED TO OTHERS OR REPRODUCED By Pam Watkins

IN ANY MANNER OR USED FOR ANY PURPOSE

500078-Case2.usc WHATSOEVER WITHOUT ITS WRITTEN PERMISSION. Version 3.2.29

IPE-TM-510-11

Circuit 3 : Reformate Splitter Reflux

Normal Design Alternate

PRESS 100.0% 116.0% 60.0%

DROP ------------------- ------------------- -------------------

LINE 100 PER NOZL PRESS INLET PRESS INLET PRESS INLET

SIZE EQ 100ft ELEV DROP PRESS DROP PRESS DROP PRESS

EQUIPMENT IDENTIFICATION IN ft psi ft psi psig psi psig psi psig

Reformate Splitter Receiver 30.0 2.00 2.00 2.00

Liquid Level 1.0 -0.32 2.00 -0.32 2.00 -0.32 2.00

LN-XP309 12 5.77 0.10 0.59 2.32 0.79 2.32 0.21 2.32

Static Head 27.0 -8.53 1.73 -8.53 1.52 -8.53 2.10

Reformate Splitter Overhead Pumps *Gov* 3.0 -106.19 10.25 -99.88 10.05 -118.03 10.63

Pump Head,ft of fluid 335.85 315.89 373.29

Pump Capacity, gpm 1349 1565 810

Average Flowing ,SG 0.729

Operating Temperature,°F 169

Viscosity,cP 0.27

LN-XP310 8 3.93 0.82 3.21 116.44 4.32 109.93 1.16 128.66

Splitter Reflux Split 113.23 105.61 127.50

LN-311 (Des=120%) 6 1.94 1.04 2.01 113.23 2.90 105.61 0.72 127.50

Splitter Reflux Flow Orifice: FD *Swage* 8 1.48 111.22 2.13 102.71 0.53 126.78

(Des=120%)

LN-325 (Des=120%) 6 1.94 1.04 2.01 109.74 2.90 100.57 0.72 126.24

Splitter Reflux CV: CV-1616(Des=120%) 47.01 107.72 33.43 97.67 74.17 125.52

LN-XP327 (Des=120%) 6 3.34 1.04 3.47 60.71 4.99 64.24 1.25 51.35

Static Head -139.9 44.18 57.25 44.18 59.25 44.18 50.11

Reformate Splitter 139.9 -6.00 13.07 -6.00 15.07 -6.00 5.93