Two-stage quench tower for use with oxygenate conversion process

A process using a two-stage quench for recovering heat and removing impurities from a reactor effluent stream withdrawn from a fluidized exothermic reaction zone, said process comprising:

• a) passing a preheated feedstream comprising an oxygenate to an intercondenser to at least partially vaporize the preheated feedstream by indirect heat exchange to provide a partially vaporized feedstream;
• b) passing the partially vaporized feedstream to a feed vaporizer to fully vaporize the partially vaporized feedstream to provide a vaporized feedstream;
• c) passing the vaporized feedstream to a feed side of a feed superheater having a feed side and an effluent side to raise the vaporized feedstream to conversion conditions by indirect heat exchange with a reactor effluent stream to provide a superheated feedstream;
• d) passing the superheated feedstream to the fluidized exothermic reaction zone at conversion conditions and therein contacting the superheated feedstream with a particulate catalyst to at least partially convert the oxygenate to produce the reactor effluent stream comprising light olefins, impurities, water and catalyst particles;
• e) passing the reactor effluent stream to the effluent side of the feed superheater to cool the reactor effluent stream to provide a desuperheated vapor effluent stream;
• f) passing the desuperheated vapor effluent stream to a first stage tower of a two-stage quench zone comprising the first stage tower and a second stage tower and recovering an overhead stream comprising the light olefins and a first stage bottoms stream comprising impurities, catalyst particles, and water, returning a first portion of the first stage bottoms stream and a neutralization stream to an upper portion of the first stage tower, and withdrawing at least a second portion of the first stage bottoms stream from the process as a drag stream;
• g) passing the overhead stream to the intercondenser to cool the overhead stream by indirect heat exchange with the preheated feedstream to provide a cooled overhead stream;
• h) passing the cooled overhead stream to the second stage tower to separate the light olefins and water to provide a vapor product stream comprising light olefins and a purified water stream;
• i) returning a first portion of the purified water stream to the upper portion of the first stage tower, cooling a second portion of the purified water stream in a product heat exchanger to provide a cooled purified water stream and returning the cooled purified water stream to an upper portion of the second stage tower;
• j) passing a third portion of the purified water stream to a water stripper column to provide a water stripper overhead stream and a highly purified water stream;
• and
• k) preheating a feedstream in a feed preheater by indirect heat exchange with the highly purified water stream to produce the preheated feedstream.