Producing synthetic gas

A apparatus for cooling a gas, the system comprising:

• a pressure vessel with a diameter between 2.5 meters and 3.1 meters, the pressure vessel having a body with a first portion and a second portion, wherein the pressure vessel is rated to contain pressures up to at least 133 bar, the pressure vessel comprising:
• a gas inlet arranged in the second portion of the pressure vessel, and
• a gas outlet arranged in the second portion of the pressure vessel, wherein the gas outlet is fluidly connected to the gas inlet;
• an evaporator disposed in the pressure vessel;
• a coil disposed in the pressure vessel and releasably engaged with the pressure vessel;
• and
• a tongue-and-groove flange assembly comprising:
• a first flange with a raised ring extending from a face of the first flange, the first flange attached to the first portion of the body;
• a second flange with a groove defined in a face of the second flange, the second flange attached to the second portion of the body wherein the raised ring extending from the face of the first flange is positioned in the groove defined in the face of the second flange.