Line / FIFO Inventory Methods

For the Line method, pipelines with significant capacity can be modeled. A line inventory can use up to 20 different packets of material in the line in any one calculation. Each packet of material comes out in the same order as it went in. No mixing of material occurs between the separate packets. The volume of the inventory Element does not change over the case.

A FIFO inventory represents a first-in, first-out tank without mixing.

LINE and FIFO Inventories have identical methodology, except that for FIFO the material quantity is the exiting transfer, and for LINE, the material quantity is the entering transfer.

Line and FIFO Inventory Methods Example

A line has volume 2000 bbl and initially holds a mixture of 50%A:50%B. There are three time slices during the accounting period. During time slice 1 a quantity of 2000 bbl 40%B:60%C enters. During time slice 2 a quantity of 3000 bbl 33.3%B:66.7%C enters. During time slice 3 500 bbl 100%A are added. The packet number signifies the order the packets entered into the inventory.

The calculation procedure is described below.

• Add the quantities of each material entering the inventory in new columns to the right.
• Take the quantity in packet 1 from the quantity entering/exiting the inventory.
• If the result is positive, then move the values in Col. 2, Col. 3 … Col. n, left by one column.
• Take the new quantity in Col. 1 from the result to give a new result.
• If this new result is positive, then move the columns left again.
• Continue until the result is negative.
• When the result is negative make it positive and copy this over the original value in Col. 1.
• Assume that the volume entering must leave. Products must be listed in the order that they enter the pipe.
• Add the quantities of each material entering the inventory in new columns to the right.
• Total the quantities in packet 1.
• Take the quantity of packet 1 from the quantity entering the LINE.
• If the result is positive, then delete packet 1, move all entries left, and renumber the packets.
• Sum the new quantities for packet 1 and subtract from the result to give a new result.
• If this result is positive, follow the steps above.
• If the result is negative, then prorate the result across all entries in packet 1 and save over the original values.

The results are illustrated in the tables below.

Inventory has an opening volume of 2000 bbl and a starting composition of 50%A;50%B.

The Col 1, Col 2, …column syntax is Packet number.; material; quantity (bbl).

Initial Inventory Reading

Inventory	Col 1	Col 2
101	1;A;1000	1;B;1000

Time Slice 1 Add the Input of 800 bbl B, 1200 bbl C

Inventory	Col 1	Col 2	Col 3	Col 4
101	1;A;1000	1;B;1000	2;B;800	2;C;1200

Time Slice 1 Remove the material (same volume as Input starting with packet 1)

Inventory	Col 1	Col 2	Col 3	Col 4
101	2;B;800	2;C;1200

Time Slice 1 index packets

Inventory	Col 1	Col 2	Col 3	Col 4
101	1;B;800	1;C;1200

Time Slice 2 Add the Input of 1000 bbl B, 2000 bbl C

Inventory	Col 1	Col 2	Col 3	Col 4
101	1;B;800	1;B;800	2;B;1000	2;C;2000

Time Slice 2 Remove the material (same volume as Input starting with packet 1)

Inventory	Col 1	Col 2	Col 3	Col 4
101	2;B;1000	2;C;2000

Time Slice 2 (Can only have 2000 bbl in the line. Input volume greater than packet 1 volume; remove from packet 2, packet 3…)

Inventory	Col 1	Col 2	Col 3	Col 4
101	2;B;667	2;C;1333

Time Slice 2 index packets

Inventory	Col 1	Col 2	Col 3	Col 4
101	1;B;667	1;C;1333

Time Slice 3 Add the Input of 500 bbl A

Inventory	Col 1	Col 2	Col 3	Col 4
101	1;B;667	1;C;1333	2;A;500

Time Slice 3 Remove the material (same volume as input starting with packet 1) – Ending Result

Inventory	Col 1	Col 2	Col 3	Col 4
101	1;B;500	1;C;1000	2;A;500

Inventory has an ending volume of 2000 bbl and a composition of 25%A:25%B:50%C.