There are mainly 2 type degasser used in oilfield, vacuum degasser and poor boy degasser.
Vacuum degasser is used in drilling solids control system to remove the gas such as methane, H2S and CO2 from the gas-cut mud, there are horizontal vacuum degasser, vertical vacuum degasser and atmospheric degasser. 
Poor boy degasser is well control equipments, it is used to separate dangerous gas, and the vacuum degasser is used only when we need more effective and more efficient results.