Waste-heat power (steam Rankine)
Hot exhaust raising steam for a turbine in cement, steel, glass and acid plants, and in combined-cycle plants.
Recovery and reuse · Heat to power and cogeneration · No. 125
- Recovery and reuse
- Heat grade: Medium to high
A gas turbine alone turns about 43% of fuel into power; a steam cycle on its exhaust lifts that to 64%.
Chart: Illustration: Waste-heat power (steam Rankine)
Where it comes from
Chart: Map of where it comes from
Steady exhaust above about 230 C, from gas turbines, cement preheaters and big engines, can raise steam to spin a turbine. In combined-cycle plants the steam side supplies about a third of the output.
Three things to know
- Real steam cycles reach only 30-50% of the Carnot limit, so cement exhaust near 300 C yields roughly 14-24% as power.
- Cement kiln gas carries about 35-125 g of dust per cubic metre, so WHR boilers need hoppers and rapping to stay clean.
- One 13 MW Chinese cement unit makes 79.29 GWh a year and avoids 51,419 t of CO2.
The journey
- 1 Hot exhaustKiln, turbine or engine gas above 230 C
- 2 WHR boilerRaises steam from the exhaust heat
- 3 Steam turbineSpins a generator to make power
- 4 CondenserWater or air cools spent steam
- 5 Power usedUp to 25-30% of a cement plant's electricity