In a carbon constrained world it is desirable to use decarbonised fuels for electricity production. Hydrogen is the most attractive decarbonised fuel leaving only water after power generation. There is a need to progress research in hydrogen infrastructure in order to establish novel decarbonised fuels and technologies and investigate the viability of the related technologies over the short and long term. The production and recovery of hydrogen is especially challenging from the highly carbonaceous raw materials like heavy hydrocarbons (residues, fossil fuels), etc. Many parts of the world (such as China, India and USA etc.) are primarily dependent on the heavy hydrocarbons and the world has a supply of such raw materials for several years. This work aims to establish a novel methodology for the designing the process flowsheets from raw material to end products that utilise the light (e.g. natural gas) to heavy hydrocarbons for decarbonised energy generation. The key feature of this work is the exploitation of the poly-generation opportunities by capturing / removing carbon dioxide from the raw materials at the point of generation through the design of novel integrated / intensified processes, utilising pure hydrogen for power and heat generation (co-generation) and the sequestration of CO2 for geological formations and enhanced oil recovery from oil wells / reservoirs. The intensified process technologies include the auto thermal reactors that exploit partial oxidation, reforming and steam shift reactions with in-situ separation functions such as, membrane processes for hydrogen separation and sorption enhanced reaction processes for carbon dioxide capture leaving pure hydrogen as a product. The co-generation opportunities are exploited through the maximisation of the power generation via gas turbines while recovering the process heat via the direct heat exchange among streams and via the indirect heat recovery by steam. A three stage systematic methodology has been developed to assist the design of decarbonised energy generation flowsheets from the hydrocarbons. The first stage consists of the screening of the flowsheet options based on the poly-generation efficiency predicted for the various combinations from the hydrocarbon feeds. The poly-generation efficiency of a flowsheet that is calculated from the overall energy input and output balances of the flowsheet takes account of the cogeneration (power and heat generation) as well as the carbon dioxide utilisation efficiencies. The promising flowsheet design options screened from the first stage are subject to feasibility study in the second stage. In this stage, the various design tradeoffs (e.g. the direct heat exchange with maximum gas turbine power generation against the indirect heat exchange through steam at the cost of gas turbine power, but with better reliability-operability) and operating variables (e.g. temperature and pressure of the reactors and energy systems, minimum temperature approach, hydrogen dilution in the gas turbines and the auto thermal membrane reactors) are considered. Finally, a simultaneous optimisation study is carried out integrating the auto-thermal reactor design and the energy generation flowsheet options, for fine tuning the design and operation of the promising flowsheets. The methodology is effectively illustrated by the demonstration of an industrial case study that presents a systematic comparison and the tradeoffs between the sorption enhanced reaction processes and the membrane reactors for the decarbonised energy generation.