Steam Cracker Convection Segmentation for Thermally Unstable Feedstock
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Solution Overview
Problem
Steam crackers face challenges in processing thermally unstable feedstocks due to limited flexibility and fouling issues, which hinder efficient cracking and product yield, especially when handling unconventional feedstocks like hydrotreated plastic pyrolysis oil and crude oil.
Innovation Solution
A process involving preheating the feedstock to maintain it largely in a liquid phase, combining it with steam, and heating to produce a gasified feedstock without direct convection section heating, allowing for separate recovery and cooling of cracked gases, while using a dedicated heating fluid and easy maintenance access to minimize fouling and optimize energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If steam crackers are designed for conventional feedstocks with compact convection sections, then thermal efficiency and product yield are improved, but flexibility to process unconventional thermally unstable feedstocks deteriorates
Solution Approach 1:
The convection section is segmented into two distinct parts: a first convection bank for preheating feedstock in liquid phase, and a second convection bank for heating gasified feedstock. This segmentation allows each section to be optimized for its specific function, enabling the processing of thermally unstable feedstocks while maintaining overall thermal efficiency.
Solution Approach 2:
The invention changes the thermal parameters and phase state of the feedstock at different stages. The first convection bank operates at lower temperatures to preheat liquid feedstock, while the second convection bank operates at higher temperatures to heat the gasified feedstock before cracking, accommodating the thermal instability of unconventional feedstocks.
2Use of energy by moving object
If direct convection section heating is used for gasification, then heating efficiency is improved, but fouling in low-temperature sections increases
Solution Approach 1:
The feedstock is preheated in the first convection bank while still in liquid phase, and steam is added before the feedstock enters the second convection bank for gasification. This preliminary action prevents direct contact between hot convection surfaces and thermally unstable feedstock, reducing fouling while maintaining heating efficiency.
Solution Approach 2:
Steam acts as an intermediary medium in the process. Steam is added to the preheated liquid feedstock before it enters the second convection bank, facilitating gasification while preventing direct fouling of the convection surfaces. The steam also helps control the thermal environment during the gasification process.
3Productivity
If feedstock is heated to gasify before cracking, then cracking efficiency is improved, but fouling in preheating sections increases
Solution Approach 1:
The heating process is segmented into two stages: preheating of liquid feedstock in the first convection bank, and gasification heating in the second convection bank. This segmentation isolates the high-temperature gasification process from the preheating sections, reducing fouling while maintaining cracking efficiency.
Solution Approach 2:
The invention utilizes phase transition of the feedstock from liquid to gas state. The feedstock is preheated as liquid in the first convection bank, then steam is added and further heating in the second convection bank causes gasification. This controlled phase transition prevents fouling in preheating sections while enabling efficient cracking.
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 facilitates fouling cleanup in low-temperature sections, reduces fouling, and maintains efficient energy use, enabling the processing of thermally unstable feedstocks with improved flexibility and product quality.
Implementation Method 1
preheating is achieved using convection heat from a steam cracker furnace
Implementation Method 2
heating the heated feedstock of step (b) to produce a gasified feedstock and a residue
Implementation Method 3
heating the gasified feedstock of step (c) using convection heat to obtain a heated gasified feedstock
Data Source
AI summary
Process for steam cracking of thermally unstable feedstock such as plastic pyrolysis oil, or olefin rich hydrocarbon cuts such as cracked gasoline, coker naphtha or diesel. The invention is also about a heat exchanger suitable for that process.