Process for multistage hydroprocessing in a single reactor

A reactor system for a single phase, multistage hydroprocessing of a liquid hydrocarbon feed pre-saturated with hydrogen, the reactor system comprising:

• a horizontal reactor with a feed inlet nozzle at one lateral end for an axial entry of a premixed mixture of the liquid hydrocarbon feed and gaseous hydrogen at a mixing point;
• a fixed bed catalyst loaded inside the horizontal reactor throughout length of the horizontal reactor, wherein the horizontal reactor is a fixed bed reactor;
• a longitudinal sparger running along a bottom portion of the horizontal reactor with a multitude of nozzles provided at a top periphery of the sparger to distribute the gaseous hydrogen;
• a multitude of vertically oriented gas separation and withdrawal vertical separation limbs provided at a top of the horizontal reactor acting as micro separation vessels and as a withdrawal assembly, integrated with the horizontal reactor for removal of product gases comprising hydrogen sulfide (H2S), ammonia (NH3) and dry gases that rise as bubbles against horizontally flowing liquid hydrocarbon feed, wherein the gas separation and withdrawal vertical separation limbs each are provided with pressure and level control devices to control pressure and levels of each portion, and wherein each vertical separation limb comprises a gas-liquid disengaging space and a gas withdrawal assembly;
• and
• an outlet product collector provided with outlet collectors distributed uniformly along a cross section of the horizontal reactor designed to avoid accumulation of liquids at other lateral end of the horizontal reactor and enable removal of a liquid product depleted of heteroatoms, wherein the liquid product is Ultra Low Sulfur Gasoline (ULSG) or Ultra Low Sulfur Diesel (ULSD).