NOVELTY - Hot flue gas obtained by combustion of combustible gas, is passed through a heat storing unit (1) that contains a bed of heat resistant inorganic material capable of catalyzing cracking of high molecular weight substances, to heat the heat storing unit to an elevated temperature to form synthesis gas. After heating the heat storing unit, gaseous medium is circulated through the heat storing unit, the biomass and back to the heat storing unit.    USE - For production of synthesis gas for synthesis of chemicals e.g. methanol and fuel for internal combustion engines and fuel cells (all claimed), from biomass such as wood, straw, waste paper, municipal solid waste.    ADVANTAGE - As the gaseous medium passes through and is in direct contact with the biomass, the biomass is directly heated and no thermal energy is lost in the heating process. Any contaminants such as tar and other high molecular weight substances present in the synthesis gas may be catalytically cracked to remove the contaminants.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for    (1) apparatus for producing synthesis gas, comprising a combustion chamber (4) in which hot flue gas is produced for heating the heat storing unit. A conduit (6) and gas transport pipe (7) circulate gaseous medium through the heat storing unit, biomass in two vertically mounted biomass reactors and back to the heat storing unit. The biomass reactors communicate at their lower end with a combustion chamber communicating with an auxiliary heat storing unit, and at their upper end with gaseous medium transport unit;    (2) use of synthesis gas for synthesis of chemicals such as methanol, and fuel for internal combustion engines and fuel cells;    (3) computer program product comprising program code to cause a processing unit to control the step of circulating gaseous medium through the heat storing unit, the biomass and back to the heat storing unit; and    (4) processing unit for controlling the step of circulating gaseous medium through the heat storing unit, the biomass and back to the heat storing unit.    DESCRIPTION OF DRAWING(S) - The figure explains the process of producing synthesis gas from biomass.    Heat storing unit (1)    Biomass reactor (2)    Gas storing unit (3)    Combustion chamber (4)    Pump (5)    Conduit (6)    Gas transport pipe (7)    Outlet (10)    Valve (11)    By-products (13)    Supply conduit (14)