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Thermodynamics and engines (A-level only)

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Question 1

The National Grid is supplied mainly from thermal power stations which have overall efficiencies of up to about 38%38\%38%.

Table 1 shows the average power requirements of a large-scale industrial distillery.

Table 1

RequirementAverage power / MW
For driving grain mills, mash tun stirrers, centrifuges, and refrigeration compressors19
For boiling wort, steam distillation, and bottle sterilization62
For running automation systems, office services, and warehouse lighting5

The distillery can either:

  • purchase all of its electrical power from the National Grid and burn gas locally in boilers to meet its heating demand, or
  • install an on-site biogas-driven turbine as part of a combined heat and power (CHP) scheme. The turbine has a maximum electrical generator output of 28 MW28\text{ MW}28 MW and an electrical efficiency of 30%30\%30%. High-temperature exhaust gases from the turbine are captured to produce steam for the heating requirements.

The directors of the distillery are evaluating whether to proceed with the CHP installation.

Explain, with reference to the provided data and physical principles, the advice you would give them.

In your answer you should:

  • explain why the maximum theoretical efficiency of any heat engine is fundamentally limited to well below 100%100\%100%
  • use the numerical data to quantitatively compare the two operating options.
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Markscheme

Thermodynamics and engines (A-level only) Questions

  1. A Level
  2. /Physics
  3. /Thermodynamics and engines (A-level only)

29 exam-style questions on AQA A Level Physics Thermodynamics and engines (A-level only), covering First law of thermodynamics (A-level only), Non-flow processes (A-level only), The $p$ - $V$ diagram (A-level only), Engine cycles (A-level only), Second Law and engines (A-level only), and Reversed heat engines (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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