A heat exchanger, comprising:
- an elongated pressure vessel shell having an axial dimension with a removable head at one end of the axial dimension, a primary fluid inlet, a primary fluid outlet, a secondary fluid inlet, a drain outlet and a heat transfer assembly comprising:
- a primary fluid inlet conduit extending into the pressure vessel from the primary fluid inlet;
- a primary fluid outlet conduit extending into the pressure vessel from the primary fluid outlet;
- a plurality of pairs of heat transfer plates supported in tandem with each of the pairs of plates sealed around a periphery to define a primary fluid flow channel in between a first and second heat transfer plate of each pair, with each pair having a heat transfer plate inlet opening fluidly connected either directly or indirectly to the primary fluid inlet conduit and a heat transfer plate outlet opening fluidly connected either directly or indirectly to the primary fluid outlet conduit to form a parallel flow path with flow in the same direction as the parallel flow path through each of the other pairs of heat transfer plates in a direction orthogonal to the axial dimension of the pressure vessel shell;
- and
- a spacer module configured to preserve room for later adding heat transfer capacity, the spacer module comprising a first support plate, a second support plate spaced from and disposed opposite the first support plate, and at least one support extending between the first and second support plates,
- wherein the plurality of pairs of heat transfer plates are arranged in modules with at least one of the modules, including at least one of the pairs of heat transfer plates, connected in tandem with an adjacent module or the primary fluid inlet or the primary fluid outlet with a nondestructively removable mechanical coupling,
- wherein the spacer module has substantially less heat transfer capacity than the modules of pairs of heat transfer plates, the spacer module being connected in tandem with the modules of pairs of heat transfer plates, the spacer module being at least as long in the axial dimension as the modules of the pairs of heat transfer plates and having an inlet duct passing axially therethrough, fluidly connected either directly or indirectly to the primary fluid inlet conduit and an outlet duct passing axially therethrough, fluidly connected either directly or indirectly to the primary fluid outlet conduit,
- wherein the inlet duct comprises a first pipe and the outlet duct comprises a second pipe each spanning between said first support plate and said second support plate and
- wherein the first pipe forms a portion of the primary fluid inlet conduit;
- and wherein the second pipe forms a portion of the primary fluid outlet conduit.