  An online cryogenic distillation system for the removal of krypton and radon
from xenon was designed and constructed for PandaX-4T, a highly sensitive dark
matter detection experiment. The krypton content in a commercial xenon product
is expected to be reduced by 7 orders of magnitude with 99% xenon collection
efficiency at a flow rate of 10 kg/h by design. The same system can reduce
radon content in xenon by reversed operation, with an expected radon reduction
factor of about 1.8 in PandaX-4T under a flow rate of 56.5 kg/h. The
commissioning of this system was completed, with krypton and radon operations
tested under respective working conditions. The krypton concentration of the
product xenon was measured with an upper limit of 8.0 ppt.
