Compressed air is one of the most expensive utilities in a plant, yet in gas cooling and quenching it is often part of the process. Two-fluid nozzles use it to turn liquid into fine droplets that evaporate quickly and cool the gas before it reaches downstream equipment. This article explains what drives compressed air consumption in gas cooling, and how newer nozzle designs, such as the 3D-printed FloMax® ECO, bring it down without giving up drop size.
Why gas cooling depends on compressed air
Gas cooling and conditioning controls the temperature, volume and humidity of a process gas. Done well, it protects equipment such as baghouses, electrostatic precipitators (ESPs) and heat exchangers, and helps a plant stay within its emission limits. Done poorly, droplets that do not evaporate in time cause wetting and sludge build-up. The process is common in cement, steel, chemical, power generation, waste incineration and pulp and paper plants.
The key is droplet size. Smaller drops have more surface area per volume of liquid, so they evaporate faster and absorb heat over a shorter distance. Two-fluid (air atomizing) nozzles create those small drops by using compressed air or steam to break up the liquid. That is also where the cost comes from. Compressing air takes a lot of electricity, and only a fraction of that energy ends up as useful work at the nozzle. Every cubic metre of air a nozzle does not need is energy the plant does not have to buy.
What drives compressed air use in a two-fluid nozzle
Air consumption is not fixed. Five factors have the biggest influence:
- Atomization efficiency: how much air the nozzle needs to reach a given drop size. The design of the internal air and liquid passages makes the difference.
- Turndown ratio: the ratio between maximum and minimum liquid flow. Gas cooling loads change with process conditions. A nozzle with a high turndown ratio can follow the load while the air pressure stays constant, so it does not waste air at partial load.
- Control strategy: closed-loop control that adjusts liquid and atomizing air flow based on gas temperature, such as the AutoJet® Gas Cooling System, avoids over-spraying.
- Placement and spray angle: droplets need enough distance and residence time to evaporate. Simulation such as CFD helps to position lances and injectors correctly. A DeNOx case in a glass plant in Pisa shows how a limited straight pipe length of 13 metres shaped the nozzle choice.
- Nozzle capacity: a larger flow rate per nozzle means fewer nozzles are needed for the same duty.
How 3D printing changes nozzle design
The FloMax® ECO is a hollow-cone air atomizing nozzle made by 3D printing. Additive manufacturing allows internal flow paths that are hard to machine in a conventional way, and the nozzle consists of a single piece plus a gasket. The goal is efficient use of compressed air while still producing the fine droplets that gas cooling needs. Key performance data:
- Drop size: 5 to 250 µm
- Air consumption: around 20% lower
- Turndown ratio: 10:1
- Spray pattern: hollow cone, 20° to 55° spray angle
For a wider look at the range, including anti-bearding, X and steam-atomized versions, see the FloMax® two-fluid nozzle bulletin.
Where lower air consumption matters most
Gas cooling and quenching run around the clock in many plants, so small savings per nozzle add up. Typical industries include:
- Cement and mining: gas cooling in conditioning towers and clinker coolers. See building materials.
- Steel and non-ferrous metals: off-gas cooling and conditioning. See the industrial spray applications overview.
- Chemical processing: quenching and evaporative cooling. See chemical processing.
- Power generation and waste incineration: flue gas quenching that protects fabric filters and heat exchangers. See process technologies spray applications.
- Pulp and paper: gas conditioning next to coating, cleaning and other mill operations. See pulp, paper and tissue.
A quick checklist to review your gas cooling system
- Log compressed air consumption per nozzle or lance at typical and minimum load.
- Check how much of the year the system runs at partial load, and whether the nozzles can follow it (turndown).
- Compare the drop size with the evaporation distance and residence time available in the duct.
- Look for signs of incomplete evaporation, such as wetting, sludge or build-up downstream.
- Validate any nozzle change with simulation or spray testing before it reaches the plant.
For more background on why droplet size and surface area matter, read why spray nozzles are essential for a performant cooling process.
Frequently asked questions
What is a two-fluid nozzle?
A two-fluid nozzle, also called an air atomizing nozzle, mixes a liquid with compressed air or steam to produce very fine droplets. It is widely used for gas cooling, gas conditioning and chemical injection.
Why does compressed air consumption matter in gas cooling?
Compressed air is costly to produce, and gas cooling systems often run continuously. Lower air use per nozzle reduces energy costs and supports sustainability targets.
What is a turndown ratio?
The turndown ratio is the ratio between the maximum and minimum flow a nozzle can handle. A 10:1 ratio means the liquid flow can be reduced to one tenth of the maximum while the nozzle keeps atomizing, which helps when process load varies.
Which industries use gas cooling nozzles?
Gas cooling nozzles are used in cement, steel, chemical processing, power generation, waste incineration and pulp and paper plants, among others.
Can a nozzle use less air without producing larger drops?
Yes. Nozzle design determines how efficiently air energy is turned into droplet break-up. The FloMax® ECO is designed to keep droplets fine, from 5 to 250 µm, with lower compressed air consumption.
Want to see what nozzle choice could mean for air consumption in your process? Talk to a local spray expert or browse more spray applications.