A system, comprising: a gasifier configured to gasify a feedstock to produce a syngas; and a syngas cooler comprising a cooling chamber having a tapered configuration, wherein the cooling chamber comprises: a first annular section extending from a first central axial opening to a second central axial opening and defining a first passage through which the syngas flows, the first annular section being configured to separate particulates from the syngas wherein the first opening has a smaller width than the second opening; a second annular section surrounding the first annular section and in fluid communication with the first section, the second annular section comprising a plurality of tubes surrounding the first section, the plurality of tubes being circumferentially and radially spaced between an outer wall of the second section and an inner wall of the second section, wherein a first portion of the plurality of tubes is arranged parallel to a longitudinal axis of the cooling chamber, and a plurality of second passages defined between the plurality of tubes, wherein the plurality of tubes are configured to receive a coolant fluid and wherein the syngas flows from the first passage in the first annular section to the plurality of second passages in the second annular section and is cooled by indirect heat exchange with the coolant passing through the plurality of tubes; and a third passage configured to flow a seal gas between a shell of the radiant syngas cooler and the second section, wherein the shell encloses the cooling chamber, characterized in that a second portion of the plurality of tubes that coincides with the inner wall is arranged at an angle to radially diverge away from the axial axis in the direction of flow of the syngas through the first section such that the second portion of the plurality of tubes forms the tapered configuration in the first section, wherein the tapered configuration is configured to diffuse the syngas for decreasing the velocity of the syngas within the first annular section. a gasifier configured to gasify a feedstock to produce a syngas; and a syngas cooler comprising a cooling chamber having a tapered configuration, wherein the cooling chamber comprises: a first annular section extending from a first central axial opening to a second central axial opening and defining a first passage through which the syngas flows, the first annular section being configured to separate particulates from the syngas wherein the first opening has a smaller width than the second opening; a second annular section surrounding the first annular section and in fluid communication with the first section, the second annular section comprising a plurality of tubes surrounding the first section, the plurality of tubes being circumferentially and radially spaced between an outer wall of the second section and an inner wall of the second section, wherein a first portion of the plurality of tubes is arranged parallel to a longitudinal axis of the cooling chamber, and a plurality of second passages defined between the plurality of tubes, wherein the plurality of tubes are configured to receive a coolant fluid and wherein the syngas flows from the first passage in the first annular section to the plurality of second passages in the second annular section and is cooled by indirect heat exchange with the coolant passing through the plurality of tubes; and a third passage configured to flow a seal gas between a shell of the radiant syngas cooler and the second section, wherein the shell encloses the cooling chamber, a first annular section extending from a first central axial opening to a second central axial opening and defining a first passage through which the syngas flows, the first annular section being configured to separate particulates from the syngas wherein the first opening has a smaller width than the second opening; a second annular section surrounding the first annular section and in fluid communication with the first section, the second annular section comprising a plurality of tubes surrounding the first section, the plurality of tubes being circumferentially and radially spaced between an outer wall of the second section and an inner wall of the second section, wherein a first portion of the plurality of tubes is arranged parallel to a longitudinal axis of the cooling chamber, and a plurality of second passages defined between the plurality of tubes, wherein the plurality of tubes are configured to receive a coolant fluid and wherein the syngas flows from the first passage in the first annular section to the plurality of second passages in the second annular section and is cooled by indirect heat exchange with the coolant passing through the plurality of tubes; and a third passage configured to flow a seal gas between a shell of the radiant syngas cooler and the second section, wherein the shell encloses the cooling chamber, characterized in that a second portion of the plurality of tubes that coincides with the inner wall is arranged at an angle to radially diverge away from the axial axis in the direction of flow of the syngas through the first section such that the second portion of the plurality of tubes forms the tapered configuration in the first section, wherein the tapered configuration is configured to diffuse the syngas for decreasing the velocity of the syngas within the first annular section.