An apparatus for fluid catalytic cracking of hydrocarbon feed, comprising: (a) a regenerated catalyst holding vessel, an annular downer reactor concentric with an up-flow regenerator of circular cross section, an annular stripper concentric with the up-flow regenerator, and wherein the up-flow regenerator, the regenerated catalyst holding vessel, the annular downer reactor, and the annular stripper are in fluid connection with each other; (b) a radial catalyst distributor positioned concentric with the up-flow regenerator and located between the regenerated catalyst holding vessel and the annular downer reactor, the radial catalyst distributor comprising a plurality of stationary parts and a plurality of moving parts; the stationary part is a section of annulus having a shape of a circular sector with a particular vertex angle and the moving part is a section of an annulus having two parallel sides; the moving part being configured to move between edges of two stationary parts and to regulate catalyst flow from the regenerated catalyst holding vessel to the annular downer reactor and to create a variable flow area for the catalyst; a number of the moving parts being equal to a number of the stationary parts in the radial catalyst distributor; (c) an angular deflector plate with an angle of inclination varying between 30° to 80° with horizontal and located below the radial catalyst distributor and along an outer circumference of the up-flow regenerator, to generate a curtain flow of the catalyst from the regenerated catalyst holding vessel into the annular downer reactor; (d) feed injectors located circumferentially at equidistant locations at outer circumference of the annular downer reactor to inject a hydrocarbon feed along with a diluent preferably steam into the curtain flow of the catalyst just below the angular deflector plate; and (e) a plurality of conduits equipped with individual slide valve positioned between the annular stripper and the up-flow regenerator; and wherein: the regenerated catalyst holding vessel is positioned at top of the annular downer reactor and includes a regenerator termination device; and the annular downer reactor terminates in the annular stripper placed at the bottom to separate products from the catalyst. (a) a regenerated catalyst holding vessel, an annular downer reactor concentric with an up-flow regenerator of circular cross section, an annular stripper concentric with the up-flow regenerator, and wherein the up-flow regenerator, the regenerated catalyst holding vessel, the annular downer reactor, and the annular stripper are in fluid connection with each other; (b) a radial catalyst distributor positioned concentric with the up-flow regenerator and located between the regenerated catalyst holding vessel and the annular downer reactor, the radial catalyst distributor comprising a plurality of stationary parts and a plurality of moving parts; the stationary part is a section of annulus having a shape of a circular sector with a particular vertex angle and the moving part is a section of an annulus having two parallel sides; the moving part being configured to move between edges of two stationary parts and to regulate catalyst flow from the regenerated catalyst holding vessel to the annular downer reactor and to create a variable flow area for the catalyst; a number of the moving parts being equal to a number of the stationary parts in the radial catalyst distributor; (c) an angular deflector plate with an angle of inclination varying between 30° to 80° with horizontal and located below the radial catalyst distributor and along an outer circumference of the up-flow regenerator, to generate a curtain flow of the catalyst from the regenerated catalyst holding vessel into the annular downer reactor; (d) feed injectors located circumferentially at equidistant locations at outer circumference of the annular downer reactor to inject a hydrocarbon feed along with a diluent preferably steam into the curtain flow of the catalyst just below the angular deflector plate; and (e) a plurality of conduits equipped with individual slide valve positioned between the annular stripper and the up-flow regenerator; and wherein: the regenerated catalyst holding vessel is positioned at top of the annular downer reactor and includes a regenerator termination device; and the annular downer reactor terminates in the annular stripper placed at the bottom to separate products from the catalyst. the regenerated catalyst holding vessel is positioned at top of the annular downer reactor and includes a regenerator termination device; and the annular downer reactor terminates in the annular stripper placed at the bottom to separate products from the catalyst.