The thermal diffusion enrichment system of the Quaternary Isotope Laboratory consists of 23 hot wire of 4 columns of 3m effective length combined to 2 separate systems of 3 and 3 separate systems of 4 columns at the top, each system in series with 1 bottom column. From roughly equal to 130 L NTP of CO (~65g of carbon) it produces roughly 8 L NTP of CO (~4g of carbon) enriched in 12C 18O by a factor 6 to 7 and in 14C16O by a factor 7 to 8 in about 5 weeks. For 12C 18O the system has a theoretical equilibrium separation factor of about 250 and a theoretical equilibrium enrichment of about 15. For 14C16O these values are 1300 and 16, respectively. The dependence of thermal diffusion transport on gas exchange between top and bottom section and between columns and reservoirs and on wire temperature is given. Forced gas exchange and a higher wire temperature gave a more rapidly increasing enrichment without substantially increasing its final value of 6 to 7 for 12C 18O. A comparison with the Groningen enrichment system shows that the two systems behave very similarly and that not the system geometry but individual column parameters and the ratio total sample mass/enriched sample mass are the dominant factors determining the enrichment.