In one aspect, the invention relates to a system for producing direct reduced iron wherein a portion of the top gas from a first module for reducing iron oxide by a direct reduction process is utilized as fuel in the thermal equipment of a second module for reducing iron oxide by a direct reduction process, wherein the second module comprises a process gas heating unit. In various aspects, the thermal equipment of the second module is a reducing gas heater and/or a steam boiler. In a further aspect, the top gas from multiple instances of the first module can be utilized collectively as fuel in the thermal equipment of the second module. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.