Downer Reactor End Cap for Extended Vapor Residence Time
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Solution Overview
Problem
Conventional downer reactors face challenges in extending vapor residence time beyond 1 second without increasing capital expenditure (CAPEX) or operational expenses (OPEX), which is necessary for maximizing olefin production under severe operating conditions.
Innovation Solution
The introduction of a mushroom-shaped distributor end cap at the lower end of downer reactors, submerged in a catalyst bed, allows for additional vapor residence time in a fluidized bed, achieving minutes-long residence times without altering the reactor's diameter or height, combined with a close-coupled cyclone system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the downer height or diameter is increased to extend vapor residence time beyond 1 second, then the residence time is improved, but the capital expenditure (CAPEX) and overall system height increase
Solution Approach 1:
The patent introduces a fluidized catalyst bed at the bottom of the downer reactor, creating a new dimensional space for vapor-catalyst contact. This allows extension of residence time from the downer section into the fluidized bed section, achieving total residence times of 2-5 seconds without increasing downer height or diameter. The fluidized bed operates as a separate reaction zone that supplements the downer reactor's functionality.
2Duration of action of moving object
If the downer diameter is increased to extend vapor residence time, then the residence time is improved, but the capital expenditure (CAPEX) and catalyst-feed contacting performance deteriorate
Solution Approach 1:
The patent segments the reaction system into two distinct zones: a downer reactor section for initial cracking reactions and a fluidized catalyst bed section for extended residence time. This segmentation allows each zone to be optimized independently - the downer maintains its efficient contacting characteristics while the fluidized bed provides the additional residence time needed, avoiding the need to increase downer diameter.
3Productivity
If severe operating conditions (longer residence time, higher temperature, higher catalyst-to-oil ratio) are applied to light paraffinic feedstock, then olefin production is maximized, but the operational expenses (OPEX) and equipment requirements increase
Solution Approach 1:
The patent introduces a fluidized catalyst bed as an intermediary zone between the downer reactor and the separator. This intermediary allows vapors to undergo additional cracking reactions at moderate temperatures while in contact with circulating catalyst, achieving high olefin production without requiring excessively high temperatures or catalyst-to-oil ratios in the main downer reactor, thus reducing operational expenses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances hydrocarbon feedstock conversion and selectivity towards propylene production while maintaining cost-effectiveness by controlling vapor residence time and reducing catalyst bypassing.
Implementation Method 1
allows for additional vapor residence time in a fluidized bed, achieving minutes-long residence times
Implementation Method 2
The vapors with entrained catalyst exiting the separator are further separated in a close-coupled cyclone system
Implementation Method 3
The separated catalyst falls through the respective diplegs into a reactor/stripper
Data Source
AI summary
A downer reactor assembly includes an outer disengager vessel, at least one downer reactor extending vertically from a top end to a lower end within the outer disengager vessel, and a mushroom-shaped distributor end cap positioned at the lower end of the at least one downer reactor. A process for cracking a hydrocarbon feedstock includes providing a catalyst feed to at least one downer reactor assembly. Discharging the catalyst feed at a lower end of at least one downer reactor underneath a mushroom-shaped distributor cap. The process includes separating hydrocarbon vapors from the catalyst feed under gravity and distributing upward flowing hydrocarbon vapors separated from the catalyst feed through nozzle holes in the mushroom-shaped distributor cap.