The invention relates to a pump (1) having a pump guide tube (13) for the
transport of a heat-exchange medium (6) for a reactor having a bundle of
catalyst tubes (2), where the pump (1) has a casing (14) which surrounds
the pump guide tube (13), having an aperture (15) in the lower part of
the casing (14) via which the heat-exchange medium (6) discharged from
the lower region of the reactor by means of the pump (1) flows into the
casing (14), flows upward in the region between the inner wall of the
casing (14) and the outer wall of the pump guide tube (13), if desired
via a heat exchanger (18), flows into the interior of the pump guide tube
(13) via an aperture (16) in the upper region of the pump guide tube
(13), flows through the pump guide tube (13) from top to bottom and flows
via an aperture (17) in the lower region of the pump guide tube (13) into
the reactor, into the upper region of the interspace between the catalyst
tubes (2).