Styrene Reactor Feed Preheating via Waste Heat Recovery
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Solution Overview
Problem
The existing styrene production processes through ethylbenzene dehydrogenation require high amounts of energy in the form of steam, leading to increased utility costs and inefficiencies, particularly in heating the reactor feed to the required temperature for efficient conversion, which exceeds the mechanical limits of steam transfer lines and mixing devices, necessitating higher reaction steam ratios.
Innovation Solution
A method and system that involve preheating a reactor feed stream using a combination of reheating steam streams, where the steam is initially heated against flue gas from fired heaters, then indirectly transferred to the reactor feed, and finally mixed with the hydrocarbon stream before entering the reactor, reducing the overall steam-to-ethylbenzene ratio while practicing azeotropic heat recovery without the need for expensive alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If large amounts of steam are used to heat reactor feed to required temperature, then efficient dehydrogenation conversion is achieved, but energy consumption and utility costs increase significantly
Solution Approach 1:
The reactor feed is preheated before entering the reactor using heat from the product stream. This preliminary heating action reduces the amount of steam needed for heating, thereby decreasing energy consumption while maintaining the required temperature for efficient dehydrogenation conversion
Solution Approach 2:
The hot product stream exiting the reactor, which would normally be a waste heat source, is utilized to preheat the incoming reactor feed. This converts the harmful waste heat into a beneficial heating source, reducing the overall steam requirement and energy consumption
2Use of energy by moving object
If steam temperature is increased to supply heat at lower steam-to-oil ratios, then energy efficiency improves, but costly special metallurgy is required
Solution Approach 1:
Instead of increasing steam temperature to improve energy efficiency, the process changes parameters by implementing heat recovery from the product stream to preheat the feed. This maintains steam temperature within standard metallurgical limits while achieving energy efficiency through improved heat utilization
3Use of energy by moving object
If reaction steam ratio is reduced to lower energy consumption, then utility costs decrease, but heating the reactor feed to required temperature becomes insufficient
Solution Approach 1:
The reactor feed receives preliminary heating from the hot product stream before entering the reactor. This preliminary temperature increase ensures that even with reduced reaction steam ratio, the feed achieves the required temperature for effective dehydrogenation, thus lowering utility costs without compromising temperature requirements
4Loss of energy
If heat is recovered from product stream to preheat feed, then steam requirement decreases, but additional heat exchange equipment complexity increases
Solution Approach 1:
The hot product stream, representing wasted energy, is directed through a heat exchange unit to preheat the incoming feed. This converts the harmful waste heat loss into a beneficial heating source, reducing steam requirements while adding only one heat exchange unit to the system
Data Source
AI summary
Methods and systems for heating a reactor feed in a multi reactor hydrocarbon dehydrogenation process. The methods and systems are advantageously employed for the production of styrene by the catalytic dehydrogenation of ethylbenzene. The catalytic dehydrogenation process employs heating steam operating at a steam to oil ratio of about 1.0 or less and relatively low steam superheater furnace temperature, such that all components exposed to steam in the process (outside of the fired heaters) can be constructed with standard metallurgy.