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Abstract

A process is described for maximizing the FCC middle distillates comprising the use of two different converters, operating in a coordinated manner that seeks to maximize the production of LCO for diesel, generating a specified gasoline and reducing fuel oil production. Converter “A” operates with a low contact time in the riser, of 0.2 to 1.5 sec. (preferably from 0.5 to 1.0 sec.) making a higher reaction temperature possible even at low severity, from 510° C. to 560° C. (preferably from 530° C. to 550° C.) and with a catalyst suitable to the maximization of LCO. Converter “B” possesses a high activity catalytic system, suited to cracking naphtha and DO generated in the first converter. Preferably, converter “B” has two separate risers, allowing the reaction temperatures of each to be adjusted independently according to the range most recommended for maximizing the cracking of each of the streams: 530° C. to 560° C. for the DO riser and 540° C. to 600° C. for the naphtha riser. The high-quality LCO stream generated by cracking at low severity in converter “A” is not contaminated by the poorer quality LCO generated by re-cracking the DO in converter “B,” since each converter has its own fractionating tower. The use of low contact time as a route for reducing severity in converter “A” geared towards the production of better quality LCO allows it to operate with a higher reaction temperature for the same LCO conversion and quality level, entailing greater operating reliability for the unit, and providing benefits for the heat balance of the converter. In existing units, the improvement in the heat balance provides leeway to the air blower via increased batch temperature, and makes room for processing more residual batches.

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