A syngas reforming reactor has a shell-and-tube configuration wherein the shell-side fluid flow path through the tube bundle has a longitudinal configuration. The reactor can include a shell-side inlet fluid distributor plate below the lower end of the tube bundle, and a flow sleeve in an enlarged-diameter discharge annulus at an upper end adjacent the tube sheet to prevent short-circuiting of the shell-side fluid into the shell-side fluid outlet. The tube bundle can include a plurality of ring baffles and lattice baffles. The longitudinal flow configuration can provide a lower shell-side pressure drop and lower cost compared to a conventional cross-flow reforming exchanger
