Feed and Product Circuits (Including Storage)

Table of Contents

1. Table of Contents……… 1

2. Purpose 1

3. Geneal 1

4. Inflection Point Engineering Practice For Product to Storage 2

4.1 Steps to Enable Battery Limit Calculations 3

4.2 Upon hitting the "Add Battery Limit Equipments" button 3

4.3 Example 1 4

4.4 Example 2 7

5. Inflection Point Engineering Practice For Product to Battery Limits 10

5.1 Steps to Enable Battery Limit Calculations 10

5.2 Upon hitting the "OK" button 10

5.3 Example 3 11

5.4 Example 4 13

5.5 Example 5 15

5.6 Example 6 18

6. Inflection Point Engineering Practice For Feed from Storage 20

6.1 Example 7 20

7. Inflection Point Engineering Practice For Feed from Battery Limits 22

7.1 Example 8 22

8. Starting and Ending Circuits with same Storage Tank in NHP 25

2. Purpose

This procedure explains how to establish hydraulic circuits for lines going to/from battery limits. This includes battery limits to/from another process unit and to/from storage tank.

3. General

Hydraulic analyses are required at different flow rates--typically 100%, 110%, and 60% of normal--for control valve selection. The process unit battery limits pressure may change based on changes in the flow rate. These flow rate changes affect the frictional pressure drop in the circuit, including the rundown line from the battery limits to the storage tank.

Keep in mind that good engineering judgment is an important factor in these calculations as well. There may be exceptions to the general calculations listed below. As an example, let’s say that a vessel bottoms stream splits with the majority of the flow routed to a second vessel and a very small continuous flow going to storage with a battery limit pressure of 100 psig. Let’s also assume that the customer has requested that the line going to storage be sized to handle the full vessel bottoms flow before the split or 230% of the normal flow going to storage. How should the rundown line equivalent length be calculated? If the method above is used, the rundown line pressure drop will be very small for the normal flow scenario since the line size is based on the full bottoms flow which will give a very long rundown line equivalent length (20 miles). This is not a reasonable equivalent length and this will greatly increase the pump head in the circuit. In this case, it is suggested to match the battery limit pressure at the design flow scenario of 230% rather than the normal flow scenario.

4. Inflection Point Engineering Practice For Product to Storage

• The Hydraulic Tabulation Report must show changes in process unit battery limits pressures for changes in product flow rate. This is done by setting up the hydraulic circuit following a specific procedure. The hydraulic circuit, which includes the product to storage, begins with a vessel or node and includes all the equipment inside the battery limits (e.g., pumps, exchangers, flow elements, control valves, line segments, etc.), the line from the battery limits to storage, and the storage tank.

• The battery limits pressure is made up of three components: frictional pressure drop in the rundown line, static head between battery limits and the destination elevation of the storage tank and pressure in the storage tank at the inlet nozzle:

limits pressure = frictional P + static head pressure + tank P

• Use the following standard values for the tank pressure component (the tank dimensions are not known) of the battery limits pressure:

	Normal/Design, psig	Alternate, psig 3
Destination (storage) System Pressure provided in BEDQ	BEDQ value 1	10% of BEDQ value (2 min)
Atmospheric tanks (value not in BEDQ) 2	20 (full tank)	2 (empty tank)
Low pressure storage (VP at highest T < 15 psig) 2	10 + liquid VP @ highest T (operating or dry bulb)	2
Pressurized spherical storage (VP at highest T > 15 psig) 5	10 + liquid VP @ highest T (operating or dry bulb)	1 + liquid VP @ winterizing T 4

1 Assuming the value is for a liquid full tank

2 Assume that the battery limits and the storage tank are at the same elevation (grade). Therefore, the static head component between the battery limits and the storage tank will be zero

3 This case determines the maximum pressure drop case for the control valve

• 4 The pressure in the tank could go below atmospheric. Be aware that NHP and 4D will give warning messages for this case since the hydraulic pressure will be lower than the stream vapor pressure. Most likely this will not be anything to be concerned about as long as the normal and design hydraulic pressures are greater than the stream vapor pressure.
• 5 The elevation of a spherical tank will be based on pump NPSH.

• 4.1 Steps to Enable Battery Limit Calculations

• On the Product node, set the “Battery Limit Type” to “BL to storage”.
• Select the “Battery Limit” tab
• Enter the “Storage Tank Pressures” for all flow scenarios and process cases
• Enter the “Battery Limit Pressure” OR the “Storage Tank Elevation” and the “Distance BL to Tank”.
• Select the button “Add Battery Limit Equipments”.

• 4.2 Upon hitting the “Add Battery Limit Equipments” button, NHP will do the following steps automatically:

• Change the product node description to “Storage Tank”. Copy the storage tank pressures to the operating pressures at port for this node and the storage tank elevation to the elevation for this node.
• Copy the pipe connected to the inlet of the product node and number is with the same pipe number followed by an “R”.
• If “Distance BL to Tank” was entered by user, that value will copy to the pipe ending in “R”. However, the BEDQ typically does not provide the distance between storage tank and battery limit. The hydraulic analysis of the rundown line to storage must therefore make some general assumptions. NHP will calculate the “Equivalent Length” and insert it in the field on this pipe ending in “R”. NHP will calculate the minimum equivalent feet of the rundown line using the maximum (of all process cases) pressure drop per 100 Eq. ft for the normal (100%) flow case for the rundown line when sized using the standard line sizing guidelines:

Frictional P = battery limits pressure – normal tank pressure

• Create a splitter node with the same number as the product node followed by an “R”. The description is “Battery Limits”.
• Add 400 to the “A” factor for the pipe connected to the inlet of the product node.
• Edit the circuit. The new splitter and pipe will be inserted in the circuit immediately upstream of the destination node.
• The “End Pressure Instruction” is changed to “Previous”.

4.3 Example 1

Let’s take an example of bottoms material from a column going to atmospheric storage.

The BEDQ information lists 50 psig as the battery limits pressure without breaking down the frictional and static head P components.

Destination	Destination System Pressure: psig	Destination Elevation relative to Inflection Point Engineering Battery Limit: ft	Piping Distance from Inflection Point Engineering Limits to Destination: ft	Inflection Point Engineering Battery Limit Pressure: psig
Storage	Atmospheric			50

• On the Battery Limit tab, set the Storage Tank Pressures using the assumed values for tank pressure for atmospheric storage, 20 psig for the Normal and Design flow scenarios, and 2 psig for the Alternate flow scenario.
• Enter the Battery Limit Pressure of 50 psig.
• Running the circuit results in the tabulation indicated in Figure 1. The battery limits pressure for the normal case is 50 psig, but varies as a result of the change in rundown line pressure drop for the design and alternate cases. The battery limit pressure of 50 psig will only be calculated for one of the process cases (maximum volumetric flow). For the lower flow process cases, the normal case battery limit pressure will be less than 50 psig. The assumed terminal pressures of 2 psig for the Alternate case, and 20 psig for the Design case gives the widest range of pressure drop values for the control valve.

FIGURE 1

Example 1

Case 2:

Case 3:

4.4. Example 2

On revamps, or new units where the BEDQ provides the specific Destination Elevation and Piping Distance information for rundown to storage, use the available information to calculate the actual static head component and the rundown line pressure drops. In this case, the battery limit pressures for all flow cases will be calculated values, and will not be based on the nominal battery limit value set in the BEDQ.

Assume in the BEDQ that the “Outgoing Liquid Stream” data is:

Destination	Destination System Pressure: psig	Destination Elevation relative to Inflection Point Engineering Battery Limit: ft	Piping Distance from Inflection Point Engineering Limits to Destination: ft	Inflection Point Engineering Battery Limit Pressure: psig
Storage	Atmospheric	87.27	6562

• Set the circuit terminal pressures using the assumed values for tank pressure for atmospheric storage, 20 psig for the Normal and Design cases, and 2 psig for the Alternate Case.
• The rundown line equivalent length is 6562 ft. Note: This value will not be saved if “Add Battery Limit Equipments” button was not selected.
• Set the Storage Tank elevation to 87.27 ft.
• Running the circuit results in the tabulation indicated in Figure 2.

FIGURE 2

Example 2

Case 2:

Case 3:

5. Inflection Point Engineering Practice For Product to Battery Limits

• 5.1 Steps to Enable Battery Limit Calculations

• On the Product node, set the “Battery Limit Type” to “Battery Limit”.
• Select the “Battery Limit” tab
• Enter one “Battery Limit Pressure” in the top left field if the value is the same for all flow scenarios and process cases OR enter the individual battery limit pressures in the grid for the different flow scenarios and process cases.

• 5.2 Upon hitting the “Ok” button, NHP will do the following steps automatically:

• Copy the battery limit pressures to the operating pressures at port for destination node.
• Add 400 to the “A” factor on the pipe connected upstream of the destination node.

5.3 Example 3

Let’s take an example of bottoms material from a column going to another process unit (out of Inflection Point Engineering scope).

The BEDQ information lists 50 psig as the battery limits pressure.

Destination	Destination System Pressure: psig	Destination Elevation relative to Inflection Point Engineering Battery Limit: ft	Piping Distance from Inflection Point Engineering Limits to Destination: ft	Inflection Point Engineering Battery Limit Pressure: psig
Product				50

• Enter the battery limit pressure of 50 psig.
• Running the circuit results in the tabulation indicated in Figure 3.

FIGURE 3

Example 3

Case 2:

Case 3:

5.4 Example 4

Let’s take an example of bottoms material from a column going to another Inflection Point Engineering process unit.

The Inflection Point Engineering design engineer provided the following battery limit pressures:

Process Case	Normal, psig	Design, psig	Alternate, psig
Case 2	50	55	45
Case 3	53	58	48

• Enter the battery limit pressures for all flow scenarios and process cases.
• Running the circuit results in the tabulation indicated in Figure 4.

FIGURE 4

Example 4

Case 2:

Case 3:

5.5 Example 5

Let’s take an example of bottoms material from a column going to another process unit (out of Inflection Point Engineering scope).

Assume in the BEDQ that the “Outgoing Liquid Stream” data is:

Destination	Destination System Pressure: psig	Destination Elevation relative to Inflection Point Engineering Battery Limit: ft	Piping Distance from Inflection Point Engineering Limits to Destination: ft	Inflection Point Engineering Battery Limit Pressure: psig
Process Unit	40	10	500

• For this example, set the “Battery Limit Type” to “BL to storage”.

• Enter the battery limit pressure of 40 psig for all flow scenarios and process cases.
• Enter the storage tank elevation (destination elevation) of 10 ft.
• Enter the distance from BL to tank (destination) of 500 ft. Note: This value will not be saved if “Add Battery Limit Equipments” button was not selected.
• Manually enter the product description indicating the final destination on the General tab.
• Running the circuit results in the tabulation indicated in Figure 5.

• FIGURE 5
• Example 5
• Case 2:

• Case 3:

5.6 Example 6

Let’s take an example of bottoms material pumped out of a column. The control valve is either out of Inflection Point Engineering’s scope or there is no control valve. We were given a battery limit pressure of 50 psig. For this situation, only include this pump in this circuit and no other circuit.

• Add 400 to the A factor on the line just upstream of the battery limit node.

• The terminal pressure for the Normal flow scenario (only one process case) must be specified and the terminal pressures for the Design and Alternate flow scenarios and Normal flow scenario for the remaining process cases must be left for the program to calculate. Set the End Pressure Instruction to “User Input”.
• Enter 50 psig for the normal flow scenario and governing process case only.
• Hit “Apply”.
• Change the End Pressure Instruction to “Calculated”.
• Running the circuit results in the tabulation indicated in Figure 6.
• FIGURE 6
• Example 6
• Case 2:

• Case 3:6. Inflection Point Engineering Practice For Feed from Storage

• For the tank pressure component of the battery limits pressure, all the values will be the same as the product to storage except the values are reversed.

	Normal/Design, psig	Alternate, psig
Destination (storage) System Pressure provided in BEDQ	10% of BEDQ value (2 min)	BEDQ value
Atmospheric tanks (value not in BEDQ)	2 (empty tank)	20 (full tank)
Low pressure storage (VP at highest T < 15 psig)	2	10 + liquid VP @ highest T (operating or dry bulb)
Pressurized spherical storage (VP at highest T > 15 psig)	1 + liquid VP @ winterizing T	10 + liquid VP @ highest T (operating or dry bulb)

6.1. Example 7

Let’s take an example of feed from an atmospheric storage tank going to a feed surge drum. Typically, the storage tank and feed pumps will be outside Inflection Point Engineering’s scope and the control valve will be within Inflection Point Engineerings scope. However, to more accurately calculate the control valve pressure drops, the feed circuit should start from the storage tank, include the feed pumps and end at the feed surge drum.

Source	Inflection Point Engineering Unit Battery Limit pressure, psig
Tankage	UTS

• Build the circuit based on the connectivity in the flowsheet (most likely will not include storage tank or pumps).
• Rename the feed node to something like “Feed Storage Tank (By Others)” indicating where the feed is coming from.
• Create 2 pipes or copy the first pipe twice.
• Create a pump. Name it “Feed from Storage Pumps (By Others)”.
• Create splitter node and name it “Feed at Battery Limits”.
• Edit the circuit. Insert the following equipment after the feed node: pipe, pump, pipe, splitter.
• Set “Start Pressure Instruction” on circuit form to “User Input”. Enter the tank pressures as 2, 2, 20 psig.
• Go to Pump form, NPSH tab. Check on the box “Override Vapor Source”. Select “User Input” for the Vapor Pressure Source and Pump Suction Source.
• If the customer does not indicate the distance from the tank farm the unit’s battery limits, use a default distance of 10,000 ft. Enter an equivalent length of 10,000 ft for the line between the pump and the battery limit node.
• Enter an additional 400 ft to the A factor on the line coming from the battery limit node.
• When issuing the hydraulics in the EDI book, manually delete all the lines before “Feed at Battery Limits”.
• Running the circuit results in the tabulation indicated in Figure 7.

FIGURE 7

Example 7

7. Inflection Point Engineering Practice For Feed from Battery Limits

If the stream is a utility stream from a header (steam), use the normal pressure in the BEDQ for the normal battery limit pressure, minimum header pressure for the design flow scenario pressure and the maximum header pressure for the alternate flow scenario pressure. This would give the full range of control valve pressure drops. This circuit would be done manually and not use the automated battery limits functionality. Do not add 400 to the A factor for the line coming from the utility header.

7.1. Example 8

Let’s take an example of feed from another process unit outside of Inflection Point Engineering’s scope. The BEDQ lists the battery limit pressure.

Source	Inflection Point Engineering Unit Battery Limit pressure, psig
Process Unit	320

• Set the “Battery Limit Type” to “Battery Limit” on the Feed node.
• Enter a Battery Limit Pressure of 320 psig on the Battery Limit tab.
• Running the circuit results in the tabulation indicated in Figure 8.

FIGURE 8

Example 8

Case 2:

Case 2:

Case 3:8. Starting and Ending Circuits with same Storage Tank in NHP

There are situations when a circuit will end at the atmospheric storage tank and another circuit will start with the same atmospheric storage tank. In this situation, the starting and ending pressures for the tank are different. For the circuit feeding the storage tank, Inflection Point Engineering assumes that the tank is full for the normal and design flow scenarios (20 psig) and empty for the alternate flow scenario (2 psig). The opposite philosophy is used for the circuit downstream of the storage tank.

One option is to not use a vessel object. Start the circuit with a feed node and end the other circuit with a product node. In this situation, follow the examples listed above.

The other option is to keep both circuits connected to a vessel object for the storage tank. Follow the steps below to setup the circuits in NHP correctly for this second option.

a. For the feed circuit to the storage tank:

(1) Set the tank at zero elevation.

(2) Set the inlet pipe at an elevation of 0.01 ft and leave the outlet pipe at 0 ft elevation.

(3) Set the controlled pressure on the inlet nozzle at 20, 20 and 2 psig for the normal, design and alternate flow scenarios for all process cases.

(4) On the Pressure Drop Results and Delta P Frictional tabs, set the frictional pressure drop to -18, -18 and 18 psi for the section in between the inlet and outlet ports.

(5) Set the circuit End Pressure Instruction to “Previous”.

(6) For the inlet pipe to the storage tank, set the “Include Static Head?” to “No” on the Pressure Drop\Pressure Drop Data tab.

b. For the circuit downstream of the storage tank:

• Set the circuit Start Pressure Instruction to “Previous”.