Evaporative Gas Cooling
Cool hot flue gases prior to entering a baghouse or temperature-sensitive equipment
Evaporative Gas Cooling Process:
In many processes a gas is raised to temperatures that could easily damage downstream equipment. This can either be by direct combustion, as in the case of flue gas, or by secondary heating. The quickest and most effective way to cool a hot gas is through the evaporation of an injected liquid. Changing the phase of the liquid to gas consumes enormous amounts of energy compared to sensible cooling. As an example, heating water from 32 °F to 212 °F (0 °C to 100 °C) requires about 180 BTU/lbm (418 kJ/kg). Converting that same water from liquid at 212 °F (100 °C) to steam at 212 °F (100 °C) requires about 1000 BTU/lbm (2320 kJ/kg), or more than 5 times the energy. The energy used to vaporize the gas is taken from the hot gas, thus lowering its temperature.
In evaporative gas cooling, a mist of water is sprayed into the hot gas. In many cases this is flue gas from a combustion process. The water then evaporates, cooling the system rapidly as the energy is used to change the water from liquid to gas. When a volume of water is atomized into smaller droplets, more surface area is exposed, allowing the evaporation rate to increase.
Selecting an Evaporative Cooling Nozzle:
The rate of evaporation is often critical as the gas must reach its final temperature before a fixed point downstream. The evaporation rate is dependent on the droplet size, temperature differential, and partial pressure among other variables. It is important to note that since spray nozzles produce a droplet size spectrum rather than a single droplet size, expertise is needed to correctly choose between different types of nozzles.
Our applications engineers can confidently assess which nozzle to recommend with the information acquired through the BETE Gas Cooling/Quenching Application Data Sheet (PDF - 229 KB). This data will also allow the engineer to calculate the amount of water, pressure, and drop size that is necessary for your application.
Typical operating conditions for this application are listed for each nozzle