Fired Heater Reboiler Hydraulics

1. Table of Contents

2. Purpose

This procedure provides guidelines for creating a hydraulic circuit for a fired heater reboiler system.

3. General

The fired heater reboiler detailed hydraulics is calculated based upon input provided to the hydraulics program.

4. Inflection Point Engineering Practices

Consider the following general guidelines in the creation of a hydraulics circuit for a fired heater reboiler system.

4.1 Flow Rate

The flow rate (lb/h) to a heater shall be the same for all simulation cases and flow scenarios (normal, turndown, alternate, etc.). Once the highest flow rate is determined, use it for all cases. The Process Engineer is responsible for representing the same flow rate and correct vaporization in all heat and weight balance files.

The flow rate to a heater being revamped shall be equal to the original flow specified in the vendor’s heater data sheets. If the Process Engineer determines that the flow cannot remain equal to the original design value, the Heater Specialist will be notified as soon as possible.

4.2 Suction Line

Size reboiler pump suction line using standard guidelines for pump suction lines (maximum ΔP/100' = 0.15 psi).

4.3 Reboiler Circulation Pump

The maximum flow rate available for a single Reboiler Circulation Pump is

13,000 gpm with 60 Hz power

10,800 gpm with 50 Hz power**

** - If the electrical system available is 50 Hz power and desired flow rate is between 10,800 gpm and 13,000 gpm, consult with Rotating Equipment Specialist to explore possibility of specifying a gear speed increaser to maximize pump performance by increasing the operating speed by 20% (60 Hz/50Hz).

For 60 Hz electrical system, a given pump’s performance range is greater due to the electric motor’s higher operating speed (1750 rpm vs. 1450 rpm).

At flow rates above the maximum, three 50% capacity pumps may be required. Consult with Rotating Equipment Specialist and/or Process Specialist. Use Tool to confirm pump availability at desired flow rate and head.

Specify the reboiler circulation pump with the rated, design and alternate flows set equal to the normal flow.

The design flow factor specified for the pump normally should be set at 100%. However, if the column bottoms pump is a multiple service pump (net bottoms and reboiler circulation), add contingency (design flow) only for the net bottoms portion of the total flow. Be sure to add the flow scenario factors on the pump not just the suction and discharge pipes.

4.4 Pump Discharge Line to Heater

Size reboiler pump discharge line using standard guidelines for pump discharge lines (max ΔP 1.5 psi/100')

Static Head – Consider the static head required to get into the heater inlet nozzle. Use Attachment 1 for determining inlet nozzle elevation of the heater.

The feed to the fired heater reboiler may split to a number of branches depending on the number of heater passes. If the heater specification is not complete, estimate the number of passes by assuming a maximum flow of 12000 barrels per day per pass. Complete the hydraulics on a per pass basis in order to obtain correct CV and orifice information. For a Project Specification 201 heater, confirm that the number of passes in hydraulics and project spec are consistent.

Note: The number of tube passes for a vertical cylindrical heater is based upon guideline of 12,000 BPD/pass. If the calculated number of passes is an odd number and the heater is a box or cabin type, increase the number of passes by one.

4.5 Control Valve

The minimum control valve pressure drop should follow Inflection Point Engineering’s typical guidelines. The CV pressure drop guideline will allow for heater operation at 110% of heater duty at design flow rate. The CV also has a minimum flow stop to prevent a no flow situation.

4.6 Heater Pressure Drop

Typically for Project Specification 202, set the inlet nozzle to outlet nozzle heater pressure drop at 50 psi (3.5 kg/cm2) for the governing normal process case (Design Duty). If the Heater Specialist specifies anything different than "Pressure Drop (allowable) – 50 psi," they will advise the Process Engineer as soon as possible. Large duty heaters (>150MMBtu/hr) such as Xylene Column reboilers may be specified with a lower pressure drop (30-35 psi). Consult with the Heater Specialist.

The Heater Specialist shall calculate the heater pressure drop using both the design and normal operating cases when generating a 201 Project Specification.

In NHP, the design engineer will have to manually enter the heater pressure drops for the design and alternate flow scenarios. In P9.8, the flow keys will be required to manually enter the design and alternate heater pressure drops. As shown in the examples, the design flow scenario heater pressure drop is equal to the normal pressure drop * discharge design flow % / normal flow %. The alternate case heater pressure drop is equal to the normal pressure drop * discharge alternate flow % / normal flow %.

4.7 Heater Transfer Line

Use Line Type Code 24.

4.8 Pressure Differential Controller (PDIC)

The ΔP for a PDIC orifice is 3 psi. Review the guidelines in Procedure for when to use PDIC and when to use TIC. Note there is no ΔP if a TIC is specified. Use a “Miscellaneous” equipment type in the Hydraulics Program for PDIC.

4.9 Column Inlet

Determine the column inlet velocity and compare against the recommended maximum allowable velocity. See Procedure Section 5.3. Typically the inlet piping (10 pipe diameters upstream of the column) and inlet nozzle size will need to be increased to be larger than the transfer line. Split the reboiler return into two column inlets when column has four-pass trays. Each pipe should be sized to meet the maximum reboiler return velocity criteria at half the reboiler return flow rate. Note: Only one inlet nozzle is required for MD Trays.

4.10 Stream Numbers

In general, identify stream numbers for each hydraulic segment. The heat and weight balance should report the heater outlet (outlet nozzle), PDIC outlet and the column inlet (inlet nozzle).

4.11 Equivalent Feet

Use the standard guidelines for equivalent feet. See Procedure IPE-TM-510-08, “Piping Equivalent Length Guidelines”. Be sure to add 100 to the “A” factor for the reboiler inlet line just upstream of the split to multiple heater passes. Reboiler heaters could be a considerable distance from column. Assume PDIC is located in pipe rack midway between heater and column.

	A	B	C
Heater Outlet Junction to PDIC	150	125	15
PDIC to Column	150	125	15
Heater Outlet Junction to Column (TIC)	300	250	25

4.12 Static Head

The heater outlet is two-phase and any static head would be small. The Hydraulics Program assumes heater outlet and column inlet are at same elevation for simplicity.

4.13 Design Pressure

The design pressure for fired reboilers without valves between the heater and the column is determined as follows:

a. Determine the column bottom pressure at relief conditions by adding the tray/packing pressure drop to the column design pressure.

b. Determine the transfer line design flow scenario pressure drop from the reboiler heater to the column.

c. Determine the heater design flow scenario pressure drop. This is normally the value determined in Section 4.6.

d. Set a design contingency of 10 psi. This is to account for the option of increasing the heat input by 10% over the normal since Inflection Point Engineering does not run the design flow scenario at 110%. Increased vaporization causes the pressure drop to increase.

e. The design pressure is the sum of the above calculated values.

The design pressure for fired reboilers with valves between the heater and the column is the pump blocked in pressure.

5. Other Considerations

5.1 If multiple heaters are required, the hydraulics should reflect the split to the multiple heaters as well as any split for multiple passes in each heater. If both multiple heaters and multiple pumps are required, consideration should be given to design completely separate circuits for each pump and heater combination.

5.2 Hydraulics for reboiler circuits are completed with the same flow rate for all process cases and flow scenarios. If hydraulics is done as per special request for alternate operations, use the following guidelines:

Additional Information

• Flow rate - same as governing normal operation.
• Heater ΔP - vary heater ΔP directly proportional with heater duty.
• Heater % Vap. - Vaporization will be dependent on duty with flow fixed.
• PDIC - For simplicity of design use 3 psi for all operations.
• Control valve - Control valve ΔP will float depending on circuit hydraulics.

5.3 The Heat and Weight Balance shall incorporate the latest and best guidelines for estimating equipment pressure drops. A good approximation of the column bottoms pressure is critical to having the correct percent vaporization information.

6. Examples

See Attachments 2, 3 and 4 for typical examples of fired heater reboiler hydraulic tabulation sheets and corresponding process flow scheme.

Attachment 1 Heater Inlet Nozzle Elevation vs. Heater Duty

Inflection Point Engineering

Hydraulic Tabulation

Nippon Petroleum Refining Co. Note - the information in this document is Page

confidential and the property of Inflection Point Engineering, and Date

Fractionation Unit must not be disclosed to others or reproduced in Proj XXXXXX

any manner or used for any purpose whatsoever By MAGRAF

without its written permission. EFID

Circuit 76: REFORMATE SPLITTER REBOILER WITH TIC Case Design Case Alternate

Press 100.0% 100.0% 100.0%

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 19 -6.96 56.2 -6.96 56.5 -6.96 55.3

Liquid Level 1 -0.15 63.2 -0.15 63.4 -0.15 62.3

Line 343 (Desgn%=102.2)(Alt.%= 91.4) 16 7.4 0.09 0.64 63.3 0.67 63.6 0.54 62.4

Static Head 16 -4.65 62.7 -4.65 62.9 -4.65 61.9

REFORMATE SPLITTER BOTTOMS PUMPS *Gov* 4 -105.1 67.3 -104.0 67.6 -108.7 66.5

Desgn%=102.2)(Alt.%= 91.4)

Pump head, feet 350.7 347.25 362.90

Pump capacity, gpm 2404 2457 2198

Flowing Specific Gravity 0.692

Operating Temperature, degF 389

Viscosity, cp 0.19

Line 344 (Desgn%=102.2)(Alt.%= 91.4) 10 4 0.74 2.96 172.4 3.09 171.6 2.47 175.2

JCT - REFORMATE BOTTOMS SPLIT 169.4 168.5 172.8

Line 351 10 3.3 0.46 1.50 169.4 1.50 168.5 1.50 172.8

JCT - SPLIT INTO 5 PASSES TO REBOILER 167.9 167.0 171.3

Line 352 (Flow %= 20.0) 6 .64 0.26 0.17 167.9 0.17 167.0 0.17 171.3

REBOILER FLOW METER (1789) 6 1.57 167.8 1.57 166.8 1.57 171.1

Line 353 (Flow %= 20.0) 6 1.3 0.26 0.33 166.2 0.33 165.3 0.33 169.5

REBOILER FLOW CONTROL VALVE (1689) 30.89 165.9 23.80 164.9 57.79 169.2

Line 354 (Flow %= 20.0) 6 1.9 0.26 0.50 135.0 0.50 141.1 0.50 111.4

Static Head 57 17.12 134.5 17.12 140.6 17.12 110.9

REFORMATE SPLITTER REBOILER 57 50.00 117.4 55.02 123.5 30.03 93.8

Line 55 (Desgn%=110.0)(Alt.%= 60.0) 18 6.9 0.60 4.15 67.4 5.03 68.5 1.50 63.8

Line 57 (Desgn%=110.0)(Alt.%= 60.0) 24 .19 0.14 0.03 63.2 0.03 63.5 0.01 62.3

REFORMATE SPLITTER 30 6.96 56.2 6.96 56.5 6.96 55.3

See following hydraulic circuit for notes, comments, and heater data.

IPE-TM-510-07

Attachment 2 Inflection Point Engineering Hydraulic Tabulation Example 1

Inflection Point Engineering Flow percentage reflect design flow of 110% on net flow and 100% on reboiler flow.

Hydraulic Tabulation For alternate case, percentage reflects 60% on net flow and 100% on reboiler flow.

Nippon Petroleum Refining Co. Note - the information in this document is Page

confidential and the property of Inflection Point Engineering, and Date

Fractionation Unit must not be disclosed to others or reproduced in Proj XXXXXX

any manner or used for any purpose whatsoever By MAGRAF

without its written permission. EFID

Circuit 26: REFORMATE SPLITTER REBOILER WITH PDIC Case Design Case Alternate

Press 100.0% 100.0% 100.0%

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 19 -6.96 56.2 -6.96 56.5 -6.96 55.3

Liquid Level 1 -0.15 63.2 -0.15 63.4 -0.15 62.3

Line 343 (Desgn%=102.2)(Alt.%= 91.4) 16 7.4 0.09 0.64 63.3 0.67 63.6 0.54 62.4

Static Head 16 -4.65 62.7 -4.65 62.9 -4.65 61.9

REFORMATE SPLITTER BOTTOMS PUMPS *Gov* 4 -109.8 67.3 -108.7 67.6 -113.6 66.5

Desgn%=102.2)(Alt.%= 91.4)

Pump head, feet 366.4 362.78 379.13

Pump capacity, gpm 2404 2457 2198

Flowing Specific Gravity 0.692

Operating Temperature, degF 389

Viscosity, cp 0.19

Line 344 (Desgn%=102.2)(Alt.%= 91.4) 10 4 0.74 2.96 177.1 3.09 176.2 2.47 180.1

JCT - REFORMATE BOTTOMS SPLIT 174.1 173.2 177.6

Line 351 10 3.3 0.46 1.50 174.1 1.50 173.2 1.50 177.6

JCT - SPLIT INTO 5 PASSES TO REBOILER 172.6 171.7 176.1

Line 352 (Flow %= 20.0) 6 .64 0.26 0.17 172.6 0.17 171.7 0.17 176.1

REBOILER FLOW METER (1788) 6 1.57 172.5 1.57 171.5 1.57 176.0

Line 353 (Flow %= 20.0) 6 1.3 0.26 0.33 170.9 0.33 169.9 0.33 174.4

REBOILER FLOW CONTROL VALVE (1688) 32.45 170.6 25.29 169.6 59.60 174.1

Line 354 (Flow %= 20.0) 6 1.9 0.26 0.50 138.1 0.50 144.3 0.50 114.5

Static Head 57 17.12 137.6 17.12 143.8 17.12 114.0

REFORMATE SPLITTER REBOILER 57 50.00 120.5 55.02 126.7 30.03 96.8

Line 355 (Desgn%=110.0)(Alt.%= 60.0) 18 3.5 0.60 2.10 70.5 2.54 71.7 0.75 66.8

PDIC 30 3.00 68.4 3.00 69.1 3.00 66.1

Line 356 (Desgn%=110.0)(Alt.%= 60.0) 18 3.5 0.63 2.19 65.4 2.65 66.1 0.79 63.1

Line 357 (Desgn%=110.0)(Alt.%= 60.0) 24 .19 0.14 0.03 63.2 0.03 63.5 0.01 62.3

REFORMATE SPLITTER 30 6.96 56.2 6.96 56.5 6.96 55.3

Flow percentage to reflect 5 passes

Flow percentages reflect increase or decrease in vaporization (heat input) for design and turndown operation.

Line 357 is to limit maximum velocity into column, see section 4.9

Heater Data
Reboiler Duty …………………. 44.87 MMBTU/h
Flow Rate to Reboiler ………… 51,186 BPSD
Heater Type ……………………. Vertical, cylindrical
No. of Heater Passes = 51186/12000 = 4.27 Use 5 Passes

IPE-TM-510-07

Attachment 3 Inflection Point Engineering Hydraulic Tabulation Example 2

Attachment 4a Reboiler Hydraulics Diagram with PDIC

Attachment 4b Reboiler Hydraulics Diagram with TIC

Notes:

• Set the elevation of the PDIC equal to the elevation of the reboiler return nozzle on the column to eliminate any static head adjustments between the PDIC and the column. When TIC is used instead of PDIC, no pressure drop is required and element (TIC) is not included in hydraulic summary.

• The piping from the reboiler outlet to the common junction, for each heater pass, has minor impact on the hydraulics and is not included in the hydraulic tabulation.

• The piping into the column may need to be enlarged to meet the maximum velocity limitations for reboiler return nozzles (see Section 4.9).