Energy Balance and Benchmarking Questions and Answers

Answer: A

It is the first law applied to a boundary drawn round the plant, and nothing may be created or destroyed within it. Every term must be quantified for the balance to close, which is what forces the auditor to find the losses nobody had measured.

Answer: B

The law cannot be wrong, so the discrepancy is the auditor's own: an unmetered feeder, a forgotten vent, a wrong meter constant or an instrument reading low. Chasing it down often locates the largest single opportunity on the site.

Answer: C

Whether the boundary is a furnace, a department or the site decides which streams are inputs, which are outputs and which are internal, and a stream counted twice or not at all follows from leaving it vague. Losses necessarily cross it, which is the point.

Answer: D

Correct answer: the mass flows carry the energy and must be consistent with it

Energy enters and leaves a process largely inside the material streams, so the two balances share the same numbers. A mass balance that does not close means a stream has been missed or mismeasured, and the energy balance built on it will be wrong in the same place - which is why the two are drawn together and each checks the other.

Answer: A

Making the width carry the quantity is what lets a reader see at a glance that a third of the input leaves up the stack. Omitting the losses would defeat the whole purpose, since they are what the diagram exists to expose.

Answer: B

Correct answer: the diagram is a picture of the energy balance

A Sankey diagram is the first law drawn to scale: the widths are proportional to the flows, so what enters must equal what leaves in useful output and losses together. If the widths do not balance, the diagram is reporting an incomplete balance rather than a drafting error.

Answer: C

Expressing consumption per tonne, per piece or per litre removes the effect of how much was made and leaves a figure that can be compared over time and between plants. It is the basis of the targets under the trading scheme.

Answer: D

Fixed loads such as lighting, ventilation and idling compressors run whatever the output, so a plant at half capacity spends more per tonne while spending less in total. It is why the two figures must always be read together.

Answer: A

Lighting, ventilation, standby heating and idling machinery continue through a shift in which nothing is made, and on many sites they are a surprisingly large share. Finding the figure is usually the most valuable single result of a regression.

Answer: B

The slope is the marginal energy per unit of output and the intercept is what the plant consumes when producing nothing, which is the base load. Measuring consumption on a non-production day confirms the figure independently.