A flare system for recovery of energy in a flow of residual gas generated in an industrial process, the system including: a flare stack, connected to the flow of residue gas and arranged to perform open combustion of said residue gas, and at least one modular flare unit connected to said flow of residue gas in parallel with the flare stack, said modular flare unit being arranged to recover energy in said residue gas, each modular flare unit including: a frame; at least two energy conversion modules detachably supported by the frame; a fuel manifold connected to receive the flow of residue gas; an air manifold connected to receive air from the ambient; an exhaust manifold connected to receive exhaust from the energy conversion modules; and an electric generator, each energy conversion module including: a combustion chamber having a fuel inlet selectively connectable to said fuel manifold via a fuel valve, an air inlet selectively connectable to said air manifold via an air valve, and an exhaust outlet connected to said exhaust manifold, said combustion chamber configured to receive a flow of residue gas through the fuel inlet for combustion in the chamber at close to atmospheric pressure, and a Stirling engine configured to convert heat from the combustion chamber into mechanical energy, said Stirling engine having a heat engine heat exchanger including a set of tubes conducting a compressible working fluid, a portion of said heat engine heat exchanger extending into the combustion chamber, and one or several cylinders each having a piston connected to an output shaft, wherein said electric generator is connected to the output shaft and is configured to generate electric power from said mechanical energy. a flare stack, connected to the flow of residue gas and arranged to perform open combustion of said residue gas, and at least one modular flare unit connected to said flow of residue gas in parallel with the flare stack, said modular flare unit being arranged to recover energy in said residue gas, each modular flare unit including: a frame; at least two energy conversion modules detachably supported by the frame; a fuel manifold connected to receive the flow of residue gas; an air manifold connected to receive air from the ambient; an exhaust manifold connected to receive exhaust from the energy conversion modules; and an electric generator, a frame; at least two energy conversion modules detachably supported by the frame; a fuel manifold connected to receive the flow of residue gas; an air manifold connected to receive air from the ambient; an exhaust manifold connected to receive exhaust from the energy conversion modules; and an electric generator, each energy conversion module including: a combustion chamber having a fuel inlet selectively connectable to said fuel manifold via a fuel valve, an air inlet selectively connectable to said air manifold via an air valve, and an exhaust outlet connected to said exhaust manifold, said combustion chamber configured to receive a flow of residue gas through the fuel inlet for combustion in the chamber at close to atmospheric pressure, and a Stirling engine configured to convert heat from the combustion chamber into mechanical energy, said Stirling engine having a heat engine heat exchanger including a set of tubes conducting a compressible working fluid, a portion of said heat engine heat exchanger extending into the combustion chamber, and one or several cylinders each having a piston connected to an output shaft, a combustion chamber having a fuel inlet selectively connectable to said fuel manifold via a fuel valve, an air inlet selectively connectable to said air manifold via an air valve, and an exhaust outlet connected to said exhaust manifold, said combustion chamber configured to receive a flow of residue gas through the fuel inlet for combustion in the chamber at close to atmospheric pressure, and a Stirling engine configured to convert heat from the combustion chamber into mechanical energy, said Stirling engine having a heat engine heat exchanger including a set of tubes conducting a compressible working fluid, a portion of said heat engine heat exchanger extending into the combustion chamber, and one or several cylinders each having a piston connected to an output shaft, wherein said electric generator is connected to the output shaft and is configured to generate electric power from said mechanical energy.