A hydroprocessing system having a processing vessel that discharges a high temperature effluent that must be cooled prior to collection in a reflux drum. One or more gas assisted spray nozzle are provided that utilize light atomizing gas having a density of 8-15 times less than air, such as hydrogen, which preferably is the processing or recycle gas of the system. The spray nozzles are designed for the efficient atomization and direction of cooling water into a micron sized droplet distribution utilizing the light atomizing gas for affecting higher mass and heat transfer from the effluent. The spray nozzles each include a unique atomizing gas and cooling liquid passageway systems, a downstream impingement post, and a plurality of discharge orifices which sequentially breakdown the liquid into micron sized droplets as low as 500 microns and less.