In a paper machine, removing water mechanically in the press section rather than thermally in the dryers is worth doing because evaporation
Answer: C
Evaporating a kilogram of water needs about 2.3 megajoules while pressing it out needs a tiny fraction of that, so a point of dryness gained at the press saves several per cent of the machine's steam. It is the first place to look on any dryer.
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The black liquor recovery boiler in a kraft pulp mill serves to
Answer: D
The organic fraction of the wood dissolved in pulping is burnt as fuel while the inorganic chemicals are recovered for reuse, which makes a well run mill nearly self sufficient in energy. It is both an energy and a chemical recovery plant.
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A regenerative glass furnace improves efficiency by using its waste gas to
Answer: A
The gases heat a brick chequerwork for twenty minutes, then the flow reverses and the incoming air is heated by it, giving combustion air at over a thousand degrees. Batch and cullet preheating are separate measures applied on top.
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Adding cullet to a glass furnace's batch reduces energy because cullet
Answer: B
Correct answer: needs no chemical decomposition
Batch materials must be heated and then chemically decomposed - soda ash and limestone giving off carbon dioxide - before any glass forms. Cullet is already glass, so it needs only to be melted, and each ten per cent of cullet in the charge saves roughly two and a half per cent of the furnace fuel.
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The membrane cell has displaced the mercury and diaphragm cells in chlor-alkali production because it
Answer: C
Correct answer: consumes less energy and avoids mercury
The membrane cell uses an ion exchange membrane in place of a mercury cathode or an asbestos diaphragm, and it consumes appreciably less electricity per tonne of chlorine while eliminating mercury from the process altogether. The two advantages together, one economic and one environmental, are what displaced the older cells.
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Modern ammonia plants approach the thermodynamic minimum energy per tonne chiefly through
Answer: D
Reforming, shift, synthesis and refrigeration are heat integrated so that one section's rejected heat drives another's requirement, and the compressors are steam driven from that heat. The best plants are within a third of the theoretical figure.
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Idle running of process equipment is worth attacking first in a conservation programme because it
Answer: A
A conveyor, an extraction fan or a hydraulic pack left running through a break consumes fully and produces nothing, and switching it off needs a procedure rather than a capital sanction. The saving is immediate and permanent if the discipline holds.
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Scheduling energy intensive operations into a single continuous run rather than several short ones saves energy by reducing
Answer: B
Correct answer: the number of heat-up and cool-down cycles
Every start from cold puts energy into the furnace, the fixtures and the surroundings that is then lost when the plant cools, and none of it appears in the product. Consolidating several short runs into one continuous run pays that cost once instead of several times, and the saving grows with the thermal mass of the equipment.
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Waste minimisation contributes to energy conservation because every unit of rejected product carries
Answer: C
Scrapping a tonne at the last operation wastes every kilowatt hour spent from the raw material onward, so yield improvement is an energy measure even when nobody calls it one. Rework doubles the energy in the affected units.
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Material efficiency reduces energy consumption most effectively when applied
Answer: D
Correct answer: at the design of the product
Design decides how much material the product contains, and every kilogram of material carries the energy of making it. Once the design is fixed, everything downstream can only trim the waste around it, so the largest leverage lies at the drawing board - the point at which the least has yet been spent.
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