A modular fluid processing architecture (10) is provided that consists of a matrix of nested tubes or processor modules (11A-D) secured between end block manifolds (12 & 13). Multiple chemical reactors may be housed in the annular spaces formed by the nesting of the tubes, and the processes may be integrated through flow splitting, mixing, switching and heat exchange in the manifolds. A flow switching system (5-9) may provide the ability to switch the flows on or off in individual processors or in banks of such processors. The switching may effect the operation of some or all of the processes. Such switching can facilitate rapid and close following of demand for the processor output while allowing each processor to run within a range of high efficiency, since processors may be turned off or on in response to falling or rising demand for the output.