Make-Up-Purge Inventory Method
The Make-Up-Purge method is a representation of a balance tank, where the majority of the input goes direct to the output line, and only the excess is added to or taken from the tank.
In a Make-up-purge Inventory, if there is not enough input to supply the required outputs, the balance is supplied by the tank. The composition of the output stream is calculated by mixing the inputs with the contents of the tank at the start of the calculation interval. Any excess input material is purged to the tank, so the output has the same composition as the input. The excess input is mixed with the contents at the end of the calculation interval.
Make-Up-Purge Inventory Method Example
An inventory initially has 2000 bbl 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 and 1980 bbl are extracted. During time slice 2 a quantity of 1000 bbl is extracted and 3000 bbl 33.3%B:66.7%C enters. During time slice 3 1000 bbl are extracted and 500 bbl 100%A are added. Minimum tracking level is set such that any compositions less than or equal to 10 bbl are removed. The packet number signifies the order the packets entered into the inventory.
Make these assumptions:
- If there is not enough input material, the inventory supplies the balance.
- If the output quantity is more than the input quantity, then use the Well-Mixed method.
- If the input quantity is more than the output quantity, then use the Well-Mixed method.
- Add transfers entering the inventory in new columns on the right with a new packet number.
- Total the quantities in the last packet.
- Take the quantity of the last packet from the quantity leaving the inventory.
- If the result is positive, then delete the last packet.
- Force out all packets below the minimum tracking level first when the inventory supplies the balance.
- Sum the new quantities for all packets.
- Pro-rate the result for all packets and subtract from the values stored.
The results are illustrated in the tables below.
Inventory has opening volume of 2000 bbl and a starting composition of 50%A:50%B.
The Col 1, Col2, …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 After 2000 bbl Input of 40% B:60% 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 After 1980 bbl Output (Output less than Input)
| Inventory | Col 1 | Col 2 | Col 3 | Col 4 |
|---|---|---|---|---|
| 101 | 1;A;1000 | 1;B;1000 | 2;B;8 | 2;C;12 |
Time Slice 2 After 3000 bbl of 33.3% B:66.7%C
| Inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 |
|---|---|---|---|---|---|---|
| 101 | 1;A;1000 | 1;B;1000 | 2;B;8 | 2;C;12 | 3;B;1000 | 3;C;2000 |
Time Slice 2 After 1000 bbl Output (Output less than Input)
| Inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 |
|---|---|---|---|---|---|---|
| 101 | 1;A;1000 | 1;B;1000 | 2;B;8 | 2;C;12 | 3;B;667 | 3;C;1333 |
Time Slice 3 After 500 bbl Input of 100.0% A
| inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 | Col 7 |
|---|---|---|---|---|---|---|---|
| 101 | 1;A;1000 | 1;B;1000 | 2;B;8 | 2;C;12 | 3;B;667 | 3;C;1333 | 4;A;500 |
Time Slice 3 After Last Packet 1000 bbl Output (Output Greater than Input, Remove 500 bbl first)
| inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 | Col 7 |
|---|---|---|---|---|---|---|---|
| 101 | 1;A;1000 | 1;B;1000 | 2;B;8 | 2;C;12 | 3;B;667 | 3;C;1333 |
Time Slice 3 After Extraction of Remaining 500 bbl – Ending Result
| inventory | Col 1 | Col 2 | Col 3 | Col 4 | Col 5 | Col 6 | Col 7 |
|---|---|---|---|---|---|---|---|
| 101 | 1;A;875.6 | 1;B;875.6 | 2;B;7 | 2;C;10.5 | 3;B;584 | 3;C;1167.3 |
Inventory has an ending volume of 3520 bbl and a composition of 24.9%A:41.7%B:33.4%C.