Elevated Pressure Steam Cracking Coil Tar Management
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Solution Overview
Problem
Conventional steam cracking processes for producing olefins require low coil outlet pressure to achieve high conversion of ethane to ethylene, leading to increased compressor stages and high operational costs, but increasing pressure results in elevated tar production and fouling issues.
Innovation Solution
A steam cracking process with elevated coil outlet pressure (200 kPa-gauge to 700 kPa-gauge) is implemented, where ethane-containing hydrocarbon feed is mixed with dilution steam, heated, and cracked in a radiant tube, followed by cooling and quenching to manage tar production through coke separation and recycling, allowing for reduced compressor stages and effective olefin recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If low coil outlet pressure is used to achieve high ethane conversion to ethylene, then conversion efficiency is improved, but the number of compressor stages increases leading to higher operational costs
Solution Approach 1:
The patent changes the pressure parameter from conventional low pressure (≤170 kPa-gauge) to elevated pressure (200-700 kPa-gauge) in the radiant coils. This parameter change simultaneously achieves high ethane conversion efficiency and reduces the number of compressor stages required, resolving the contradiction between productivity and device complexity
2Device complexity
If elevated coil outlet pressure is used to reduce compressor stages, then operational costs are reduced, but tar production increases causing fouling issues
Solution Approach 1:
The patent converts the harmful effect of elevated tar production into a beneficial process by introducing a quench tower that condenses and separates tar from the gas stream. The tar is then removed in a separate section, allowing elevated pressure operation to reduce compressor stages while managing fouling through systematic tar removal
Solution Approach 2:
The quench tower acts as an intermediary device between the elevated pressure cracking section and the product recovery section. It mediates the harmful tar production by condensing tar in the quench zone and separating it from the olefin product stream, enabling elevated pressure operation without excessive fouling
3Device complexity
If elevated coil outlet pressure is used to reduce compressor stages, then operational costs are reduced, but separation devices such as water quench tower face technical challenges
Solution Approach 1:
The water quench tower is segmented into distinct functional zones: a quench zone for condensing tar, a separation zone for separating tar from gas, and a product withdrawal zone. This segmentation allows each zone to handle specific challenges of elevated pressure operation, maintaining separation device reliability while enabling compressor stage reduction
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 process reduces the number of compressor stages required, effectively managing tar production and fouling, while maintaining high ethane conversion to olefins, resulting in cost savings and improved operational efficiency.
Implementation Method 1
cracking the heated feed-steam mixture in a radiant tube located in a radiant section of the steam cracking furnace under pyrolysis conditions to produce a radiant effluent
Implementation Method 2
The chemical reactions involved in the pyrolysis of the hydrocarbon feed in the steam cracker are highly endothermic and results in a net molar increase of gaseous species
Implementation Method 3
cooling the radiant effluent to obtain a cooled effluent; feeding a quench water stream into the quench tower to contact the cooled effluent in the quench tower
Data Source
AI summary
A process for producing a C2-C4 olefin product from an ethane-containing hydrocarbon feed can be carried out using a steam cracker operated with an elevated coil-outlet pressure, thereby reducing the number of stages of compression required for recovering products from the steam cracker effluent. Coke can be effectively managed in the processes of this disclosure.