Standards Averages and Deviations

It is good practice for any energy balance to assume some standards for units like BTU, kcal, KJ, or MWh, any basic unit that is of common use for the personnel involved. It many cases it is good practice to comply also with some other physical significant package, like direct steam flow of tons per hour. For fuel, establishing a kind of currency, like an equivalent, in terms of mass or volume, of some common usage product, like a standard fuel oil barrel or natural gas 1000 cubic meter or feet. This helps communication and simplifies general evaluation of results and amounts for daily use on operational decisions.

Another standard that should be established is a kind of expected energy operational range. This means, considering the balance data series and its relations with processes and throughput for a certain operational mode, an expected reasonable range of consumption for each energy form should be complied with. An example, for a distillation column with a specific crude and campaign, for instance, maximization of diesel, the stripping steam flow must stay in between a determined minimum and maximum. Another sample would be establishing expected time patterns for pump operations and maintenance check. Reasons for noncompliance from that are to explained and recorded.

These values come from those same analyses performed over energy balances and benchmarking. It should express the proper manner in which the unit should be operated, and is a way to try to standardize operational and maintenance best practices. This procedure helps to spread knowledge and gage practices through the whole facility. Needless to say, now and then some argument about the practice, numbers and motivations of it will arise, but that is a good thing, if this movement shows that the standard might be either wrong or old-fashioned, and pushes improvement and awareness for the project.

As a natural consequence of instituting better practices by average numbers and model procedures, we must learn how to deal with deviations. Deviations can be tracked by historical comparison with usual dispersion ofvalues on energy balance, and it is possible to classify in two ways. One is the permitted and conceivable deviation, like numbers a little higher than expected average. An example: for steam consumption being higher than usual because of an asphalt campaign; since dealing with viscous oils demands more heating, an extra steam demand is justified. Relating operations and updating the records for these numbers increases knowledge about the process. The second one is trickier, when numbers are normally very far away from those expected with no apparent operational justification, but measurements confirm it. The chances are that it was a mistake and some improper operation was done. Trying to track down in which area the episode may have occurred is a good option. Investigating the reasons, but not pursuing the guilty. Once it is possible to determine where it might have happened, communicating the fact and its possible consequences, in terms of losses and lack of understanding, will eventually bring about the causes. Regis tering again on the balance all the facts will help the learning process and avoid its repetition in the future.

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