Material Insights · Understanding the Material World

Boiler heat recovery: Impact and additionality

Saving fuel, water and chemicals in one move

What this tab covers The impact and additionality lens: direct emission cuts, side benefits for water and air, and the risk of prolonging the life of a polluting host plant.

Each measure cuts on-site fuel burn directly, and condensate and blowdown recovery also save water and treatment chemicals.

Direct Scope 1 and Scope 2 abatement

Favourable

DOE's economiser example recovers about 38,600 MMBtu of heat a year; at 80% boiler efficiency that is about 48,300 MMBtu of gas, or roughly 2,560 t CO2 a year at 0.0053 t CO2 per therm (calculated). The blowdown example saves 8,500 MMBtu a year, about 450 t CO2 (calculated). Skyven's California Dairies projects had avoided over 3,500 t CO2 and over 65,000 MMBtu of gas by early 2024, with over 7,000 t a year projected.1389

CO2 avoided, DOE economiser example about 2,560 t/yr (calculated)18 CO2 avoided, DOE blowdown example about 450 t/yr (calculated)38 California Dairies projected abatement over 7,000 t CO2 a year9

Water and air synergy

Favourable

Returning condensate cuts makeup water, sewage and treatment chemicals: a US specialty paper plant cut makeup water from about 35% of steam output to 14 to 20% and saved over USD 300,000 a year. Reducing blowdown from 8% to 6% on a 45 t/h (100,000 lb/h) boiler saves about 1 t/h (2,300 lb/h) of makeup water. Condensing units also pull water out of flue gas (about 85% of the humidity for direct-contact and 35% for indirect designs), though this water is acidic.524

Paper plant makeup water from about 35% to 14 to 20% of steam5 Flue gas humidity removed, direct-contact about 85%2 Makeup water saved, 8% to 6% blowdown about 2,300 lb/h on a 100,000 lb/h boiler4

Avoided lock-in

Mixed

Economisers and condensing units make existing gas or coal boilers cheaper to run and can delay a switch to heat pumps or electric boilers. The capital is small, though, and condensate return and blowdown recovery reduce heat demand whatever the future heat source, so they are no-regret. Investors should favour these water-side measures and treat flue-side upgrades on coal boilers with more caution.5

Share of steam energy left in condensate more than 10%5

Sources

  1. Use Feedwater Economizers for Waste Heat Recovery, Steam Tip Sheet #3 (DOE/GO-102012-3412) US DOE Advanced Manufacturing Office, 2012
  2. Considerations When Selecting a Condensing Economizer, Steam Tip Sheet #26B (DOE/GO-102012-3397) US DOE Advanced Manufacturing Office, 2012
  3. Recover Heat from Boiler Blowdown, Steam Tip Sheet #10 (DOE/GO-102012-3408) US DOE Advanced Manufacturing Office, 2012
  4. Install an Automatic Blowdown-Control System, Steam Tip Sheet #23 (DOE/GO-102012-3402) US DOE Advanced Manufacturing Office, 2012
  5. Return Condensate to the Boiler, Steam Tip Sheet #8 (DOE/GO-102012-3410) US DOE Advanced Manufacturing Office, 2012
  6. Not Just Hot Air: Low-Cost Decarbonization through Heat Recovery (Zahlan and Talan, Cadmus), ACEEE Summer Study on Energy Efficiency in Industry ACEEE, 2021
  7. Skyven Technologies: Decarbonizing Industrial Process Heat through Public-Private Partnerships (implementation model) US DOE Better Buildings Solution Center, 2024