A vessel for use in a gasification system is provided. The vessel includes a shell and a heat exchange structure positioned within the shell. The heat exchange structure defines a central cavity configured to receive and to direct a syngas to a quenching portion positioned downstream of the central cavity along a syngas path. A passageway is disposed between the shell and the heat exchange structure. A liquid seal is positioned upstream of the quenching portion, and the liquid seal is configured to block transport of at least one of the syngas between from the quenching portion into the passageway and inert gas from the passageway into the quenching portion.