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HMRC internal manual

Oils Technical Manual

Computer systems: refinery mass balance systems

A Mass Balance is a means of accounting for the operations/activities of a refinery over a period of time in units of mass. It provides assurance that a balance exists between stock levels, receipts and deliveries. At its highest level the balance is reported for the whole of a refinery but it is prepared from balances obtained at process and storage item level. The Mass Balance is not concerned with duty liabilities or duty accounting.

Data concerning processes, storage plant and the connections between processes and plants is defined.

The balance is produced by a computer system which models a refinery’s plant and production processes. Each item of refinery plant which stores, receives and delivers product is defined. The system is provided with details of every movement in the specified period and by reference to the definitions a balance for each process and storage location can be established.

No refinery will produce a mass balance which has no losses or gains. The principal discrepancies will arise through the tolerances in measurement devices. With the measurement tolerances of each storage tank and meter defined the system, having identified a discrepancy, will attempt to remove the discrepancy by attributing the loss to measurement tolerances and correct the amounts moved.