After the RPC removes the particulates, the SRU squeezes the remaining energy out of the exhaust — recovering low-grade heat and clean, condensed water from gas that used to vanish into the sky.
The SRU retrofits directly onto existing boilers and furnaces — or integrates into new installations. As hot flue gas passes through, its heat transfers into your water or process loop, and the water vapor in the exhaust condenses into clean, usable water. Fuel bills drop, CO₂ drops, and the water meter slows down.
Captures rejected heat from exhaust and returns it to your process — cutting fuel input 8–10% at power plants.
Condenses clean water out of the flue gas — a resource, straight from your stack.
At coal plants, targets NOx, SOx, condensables and acid gases as the gas is cooled.
A flue gas condenser is a heat exchanger that cools boiler or furnace exhaust below its water dew point, about 135°F (57°C) for natural gas. When the water vapour in the exhaust condenses, it gives back the latent heat it took to boil it. A conventional economizer never reaches that heat, because it is designed to stop at around 250°F so nothing condenses.
That hidden heat is substantial. Burning natural gas produces roughly 10 to 12 gallons of water for every 1,000 cubic feet of gas, and it all leaves the stack as vapour. In one U.S. Department of Energy example, the latent heat in that vapour was about 9 percent of the boiler's firing rate. A flue gas condenser goes after that heat, plus the sensible heat in the hot gas, plus the water itself. See how much heat your boiler sends up the stack.
| Standard economizer | Flue gas condenser | |
|---|---|---|
| Heat recovered | Sensible heat only | Sensible and latent heat |
| Exhaust leaving | About 250°F or higher | Below about 135°F on natural gas |
| Water recovered | None, by design | Condensate collected for reuse |
| Materials | Carbon steel | Corrosion-resistant construction |
| Needs | Boiler feedwater | A cold water or process stream to absorb the heat |
The full comparison, including direct-contact and indirect designs, is in our guide to condensing vs. standard economizers.
The single deciding question is where the recovered heat goes. A condenser can only condense water if something cold is on the other side. These are the conditions that make a project worth a closer look:
Fuel type and annual use, stack temperature and oxygen, firing hours, and what cold water streams the site has. That data request leads to a metered baseline, and only then to a site-specific number. How a project starts.
E&J Gallo Winery, Darigold, Georgia Gulf, Mission Linen Supply, Harris Ranch Meats, Growers Transplanting — Sidel's condensing technology has been paying for itself in American industry since 1978.
"You will be 100% satisfied with the money saved, CO₂ emissions reduced, water conserved, and exceptional service — or we'll buy your unit back from you. Period."
A flue gas condenser is a heat exchanger that cools boiler or furnace exhaust below its water dew point, about 135 degrees F for natural gas, so the water vapour in the gas condenses. That recovers both the sensible heat in the hot gas and the latent heat in the vapour, plus liquid water, before the exhaust leaves the stack.
Hot exhaust passes over corrosion-resistant surfaces carrying cooler water. The gas gives up its heat to the water, and once it drops below the dew point the water vapour condenses and releases its latent heat into the same loop. The warmed water goes back to the process, and the condensate drains away for treatment and reuse.
A standard economizer heats boiler feedwater and keeps the exhaust above roughly 250 degrees F so nothing condenses. A flue gas condenser, also called a condensing economizer, deliberately goes below the dew point to recover the latent heat as well. That needs corrosion-resistant materials and a cold water stream to absorb the heat.
It depends on the fuel, the stack temperature and how cold the receiving water is. As a reference point, the U.S. Department of Energy estimates boiler efficiency rises about 1 percent for every 40 degrees F drop in flue gas temperature, and in one DOE example the latent heat alone was about 9 percent of a natural gas boiler's firing rate. Sidel CREN confirms site-specific numbers with a metered baseline before quoting anything.
Yes. The Sidel SRU is designed to retrofit onto existing boilers and furnaces as well as new installations. The key questions are space at the stack, a suitable cold water or process loop to take the heat, and a drain for the condensate.