Modular plate and shell heat exchanger

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;
• and
• 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 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 through each of the pairs of heat transfer plates in a direction orthogonal to the elongated dimension of the pressure vessel shell;
• and
• wherein the plurality of pairs of heat transfer plates are arranged in tandem and at least some of the plurality of pairs of heat transfer plates are connected to an adjacent pair of heat transfer plates or the primary fluid inlet or the primary fluid outlet with a nondestructively removable mechanical coupling.