FCC Riser Injection Zones for Propylene Yield
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Solution Overview
Problem
Current fluid catalytic cracking (FCC) processes for producing propylene and ethylene face challenges in achieving high yields without increasing unit capacity or altering hardware, while also dealing with catalyst deactivation and water formation issues.
Innovation Solution
The process involves cracking an olefinic naphtha stream and main hydrocarbon stock in combination with an olefinic C4 hydrocarbon stream in an FCC unit with a mixed catalyst comprising pentasil zeolite and Y zeolite, where the olefinic C4 hydrocarbon stream is injected in the lift zone and the main hydrocarbon stock is cracked above, optimizing conditions such as temperature, pressure, and weight hourly space velocity to enhance propylene and ethylene yields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If steam is used as lift medium in the FCC riser, then catalyst is kept above choking velocity, but catalyst deactivation and attrition increase due to contact with steam at high temperature
Solution Approach 1:
The patent removes steam from the lift medium composition entirely, replacing it with inert gases (nitrogen, carbon dioxide, or recycled flue gas). This extraction of the harmful component (steam) eliminates the cause of catalyst deactivation and attrition while maintaining the lift function through alternative gases that do not cause hydrothermal damage to the catalyst structure.
Solution Approach 2:
The patent introduces inert gases as intermediary substances to perform the lift function without causing catalyst damage. These intermediary gases (nitrogen, carbon dioxide, recycled flue gas) serve as the mediating medium between the catalyst particles, providing the necessary velocity and fluidization without the harmful effects of steam contact at high temperatures.
2Productivity
If ZSM-5 catalyst is added to increase propylene yield, then propylene production increases, but catalyst deactivation occurs due to coke formation
Solution Approach 1:
The patent implements periodic regeneration of the ZSM-5 catalyst by cycling it between the cracking riser and regenerator. The catalyst is periodically removed from the riser, regenerated in the regenerator to burn off accumulated coke, and returned to the riser. This periodic action maintains catalyst activity and propylene production capability over extended operation periods.
Solution Approach 2:
The patent discards the deactivated catalyst portion in the regenerator where coke is burned off, and recovers the regenerated catalyst for continued use in the cracking riser. This discarding and recovering cycle allows the ZSM-5 catalyst to maintain high propylene yield capability by continuously removing deactivating coke deposits.
3Productivity
If reaction temperature is increased to improve propylene and ethylene yield, then conversion increases, but water formation increases and catalyst deactivation accelerates
Solution Approach 1:
The patent removes water from the reaction system by eliminating steam as a lift medium and operating with reduced moisture content. This extraction of water source prevents water-gas shift reactions and hydrothermal catalyst deactivation, allowing higher reaction temperatures to be used for improved olefin yield without the penalty of increased water formation and catalyst damage.
4Productivity
If FCC unit capacity is increased to meet propylene demand, then propylene production increases, but investment cost and hardware complexity increase
Solution Approach 1:
The patent changes key operating parameters including eliminating steam as lift medium, using inert gases instead, optimizing riser residence time, and adjusting regeneration conditions. These parameter changes enable existing FCC units to produce significantly more propylene without any hardware modifications or capacity expansions, thereby avoiding increased investment costs and device complexity.
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 approach increases propylene and ethylene yields without hardware changes, reduces catalyst deactivation and water formation, and improves catalyst activity, achieving incremental yields of propylene by 0.5 to 3 wt% and ethylene by 0.3 to 0.8 wt%.
Implementation Method 1
contacting the hydrocarbon feedstock with a ZSM-5 catalyst in a fluidized bed reactor
Implementation Method 2
cracking an olefinic naphtha stream and main hydrocarbon stock in combination with an olefinic C4 hydrocarbon stream
Implementation Method 3
contacting the hydrocarbon feedstock with a ZSM-5 catalyst in a fluidized bed reactor
Implementation Method 4
combustion of appropriate fuel hydrocarbon in a fluidized regenerator zone
Implementation Method 5
combustion of appropriate fuel hydrocarbon
Implementation Method 6
heat necessary to maintain the reaction is to be provided by separately heating the catalyst particles in a fluidized regeneration zone
Data Source
Figure 1
AI summary
A fluid catalytic cracking (FCC) process for manufacturing propylene and ethylene in increased yield. The process comprises cracking an olefinic naphtha stream and main hydrocarbon stock in combination with an olefinic C4 hydrocarbon stream in different zones of one or more risers of an FCC unit. Each FCC riser comprises an acceleration zone at the lower portion thereof, a lift stream feed nozzle at the bottom of the acceleration zone, a main hydrocarbon stock feed nozzle above the acceleration zone and an olefinic naphtha feed nozzle at a location along the acceleration zone between the lift stream feed nozzle and main hydrocarbon stock feed nozzle. The cracking is carried out on a mixed FCC catalyst comprising atleast 2 percent by weight pentasil zeolite and at least 10 percent by weight Y- zeolite. The catalyst is injected at the bottom of each FCC riser, the olefinic naptha is injected through the olefinic feed nozzle, the main hydrocarbon stock is injected through the main hydrocarbon stock feed nozzle and the lift stream is injected through the lift stream feed nozzle at the bottom of the acceleration zone. The lift stream comprises the olefinic C4 hydrocarbon stream with or without steam and/or a fuel gas. The olefinic C4 hydrcarbon steam is cracked in the acceleration zone at 600 to 8000°C and pressure of 0.8 to 5 kg/cm up 2 (gauge) and weight hourly space velocity (WHSV) of 0.2 to 100 hr up 1 and vapour residence time of 0.2 to 5 seconds.