Hot gas quench systems

The gas and the liquid flow in co-current mode through the apparatus. Water is injected in surplus to quench (= rapidly cool) the hot feed gas. The quench system typically comprises of three nozzle layers, from top downwards: 

• 1st layer: Tangential nozzles: Form a liquid wall film on the inner wall of the apparatus to protect the equipment from thermal damage and fouling by deposition of dust or other components
  
  
• 2nd layer: Flat jet nozzles: Form a liquid spray curtain across the cross-sectional area of the apparatus to carry out the initial quenching and to prevent back-spray of liquid droplets
  
  
• 3rd layer: Main spray nozzles: Are oriented in a 45° angle to the gas flow and spray water into the gas stream (co-currently) to cool the gas to the thermodynamic equilibrium temperature

The thermodynamic equilibrium temperature results from the energy balance of the system. The enthalpy of the hot gas stream entering the system is absorbed by the quench medium. This energy uptake must be compensated, typically, this is by evaporation of water. The temperature of the quench liquid defines the max. partial pressure of water vapor in the gas phase. At the equilibrium temperature of the system the partial pressure of water (and therefore the amount of evaporated water) is just as high that the enthalpy of evaporation covers the energy uptake from the hot feed gases. 

In the event of a malfunction or failure of the nozzle system in case the equipment is made of plastic materials, an emergency water system is used to provide the nozzle system with water to ensure that the liquid wall film and the quenching function is maintained in order to protect downstream-arranged equipment against thermal damage.