Energy-efficient gasification-based multi-generation apparatus, facilities, or systems, and methods of modifying existing gasification-based multi-generation apparatus and the various conventional thermal coupling arrangements, are provided. Apparatus for managing waste heat recovery through integration of a gasification-based multi-generation facility or other multi-generation system with a hydrocarbon refining facility or other hydrocarbon refining system and methods of providing the respective integration are also provided. An exemplary apparatus includes an integrated site energy management system configured according to one or more process-based thermal coupling schemes comprising one or more thermal coupling arrangements between a gasification-based multi-generation system or facility and a hydrocarbon refining system or facility,. The gasification-based multi-generation system or facility can include an acid gas removal system or plant configured to remove acidic contaminants from a raw syngas feed to thereby provide a treated syngas feed, the acid gas removal system or plant containing a separation section including a solvent regenerator, and a gasification system configured to generate the raw syngas feed from a carbon-based feedstock. The hydrocarbon refining system or facility can include an aromatics system or plant containing a xylene products separation section including one or more of the following: an Extract column and a Raffinate column. The integrated site energy management system can include a hot-water system extending between the separation section of the acid gas removal system or plant and the xylene products separation section of the aromatics system or plant, and a plurality of added heat exchanger units providing various advanced thermal coupling arrangements.