NOVELTY - A gasifier (18) comprises first gasification zone for gasifying high-calorific-value (HCV) feedstock (22) with oxidant, which is consumed within the zone; and second gasification zone for gasifying low-calorific-value, high-oxygen-content feedstock (32). The gasifier further comprises injector (60) for steam, in the first zone; a third gasification zone, where the calorific value of the feedstock injected in the third gasification zone is lower than the calorific value of feedstock injected in the first gasification zone; at least one oxidant injector in at least one gasification zone.    USE - As multi-fuel gasifier for gasifying multiple fuels such as coal and biomass (claimed) to generate energy.    ADVANTAGE - The gasification system is capable of gasifying both coal and biomass, without having to face the problems encountered by the prior art system; can gasify multiple fuels without operational problems. The gasification system can retrofit existing coal gasifiers to achieve fuel flexibility. The system has two separate injection points for coal and biomass thereby avoiding operational issues and effectively gasifying both coal and biomass. The system allows injection of at least two different fuels into the gasifier designed and operated in a manner to effectively utilize the differences in composition of characteristics of both. The reduced oxygen requirement corresponds to smaller size of the air separation unit that produces pure oxygen supplied to the gasifier. Lesser amount of pure oxygen can be produced from the air separation unit, while still meeting the requirements of the gasifier unit. This results in operational and capital cost saving of the overall gasification system (due to saving on the air separation unit). The system accomplishes higher conversion of HCV char by producing reactive species from devolatilization of LCV HOC feedstock. Thus the need for injecting higher amount of oxygen is eliminated. The system provide for firing of the high-calorific-value and low-calorific-value feedstocks separately in separate zones. Thus problems of common injection such as layering are avoided. Separate injectors and feed preparation arrangements are made for the two feedstocks that again eliminate the problems of a single injector feeding in both the feedstocks. Since the feed preparation sections are separate for each fuel, appropriate equipment such as size reduction equipment may be employed depending upon characteristics such as brittleness, fibrous nature etc. of the feedstock. The particle size of LCV HOC feedstock can be optimized to minimize fuel-processing requirements while achieving high conversion efficiency. The LCV HOC feedstock particle size is chosen to provide desired mixing of low-calorific-value feedstock particles with the gases in the gasifier reactor during injection. Thus by controlling the particle size of the feedstock fed to the gasifier, levels of mixing with the gasifier and the conversion efficiencies are controlled. The moisture and oxygen content of the low-calorific-value feedstock, which otherwise lead to problems during gasifier operation, are effectively made use of by the system.    DETAILED DESCRIPTION - A gasifier (18) comprises a first gasification zone for gasifying a high-calorific-value (HCV) feedstock (22) with an oxidant, which oxidant is consumed within the first gasification zone; and a second gasification zone for gasifying a low-calorific-value, high-oxygen-content feedstock (32). The low-calorific-value, high-oxygen-content feedstock further comprises moisture in a quantity to generate steam to effectively gasify the low-calorific-value, high-oxygen-content feedstock. The gasifier further comprises at least one injector (60) for steam, in the first gasification zone; a third gasification zone, where the calorific value of the feedstock injected in the third gasification zone is lower than the calorific value of feedstock injected in the first gasification zone; at least one oxidant injector in at least one gasification zone. The high-calorific-value feedstock comprises at least one carbonaceous fuel selected from high rank coal, medium rank coal, oil and natural gas. The low-calorific-value, high-oxygen-content feedstock comprises biomass or low rank coal. The high-calorific-value feedstock is injected as a dry feed or as slurry feed. The system contains at least one injector for injecting HCV feedstock into the first zone and at least one injector for injecting HCV feedstock into second zone. The first zone is configured to devolatilize the high-calorific-value feedstock to form volatile matter and a char (HCV char). The second zone is configured to produce oxygen containing compounds by devolatilizing the low-calorific-value, high-oxygen-content feedstock and gasifying the char produced from the high-calorific-value feedstock using the oxygen containing compounds.    DESCRIPTION OF DRAWING(S) - The figure shows schematic drawing of a multi-zone gasifier.    Gasifier (18)    High-calorific-value feedstock (22)    low-calorific value, higher oxygen content feedstock (32)    Injector (60)    Carrier gas (114)    Syngas (300)