Multi-layer steam grid for TSRU heat and mass transfer
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Solution Overview
Problem
Conventional solvent recovery units (TSRU) face inefficiencies in recovering hydrocarbon diluents from tailings containing paraffinic solvents and asphaltenes, due to poor heat transfer and mass transfer, leading to reduced solvent recovery and increased solvent loss, especially when operating at sub-atmospheric pressures and temperatures.
Innovation Solution
The use of a multi-layer steam grid within the TSRU vessel, where steam is conducted at a pressure greater than the vessel's operating pressure, is discharged at multiple locations throughout the internals, enhancing heat transfer and mass transfer by maintaining a low partial pressure and heating the internals to a higher temperature than conventional systems, facilitating the release of solvents from asphaltene agglomerates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If steam is introduced below shed decks in conventional TSRU, then heat transfer occurs, but the internals can only reach temperatures limited by steam condensation at vessel operating pressure, reducing heat transfer efficiency
Solution Approach 1:
The steam grid divides the steam introduction into multiple segments at different heights and locations throughout the vessel, allowing steam to be discharged at numerous points rather than from a single location below the shed decks. This segmentation enables more uniform heat distribution and allows the internals to reach higher temperatures by introducing steam at pressures greater than vessel operating pressure at multiple discrete locations.
Solution Approach 2:
The steam grid introduces steam at different locations with different properties (pressure, temperature, discharge direction) to create locally optimized heat transfer conditions. By discharging steam at multiple locations throughout the vessel at pressures greater than operating pressure, each local region receives steam at conditions optimized for that specific location, enabling the internals to reach temperatures higher than what would be achieved by single-point steam introduction at vessel pressure.
2Productivity
If conventional steam stripping is used at sub-atmospheric pressures, then solvent recovery is attempted, but mass transfer is poor leading to reduced solvent recovery efficiency
Solution Approach 1:
The steam grid introduces steam at pressures greater than vessel operating pressure before the steam reaches the tailings, allowing the steam to expand and discharge at high velocity at multiple locations throughout the vessel. This preliminary pressurization creates turbulent mixing and enhances mass transfer at each discharge point, improving overall solvent recovery efficiency by preparing the steam in a state that promotes better mass transfer when it contacts the tailings.
3Productivity
If steam is discharged at a single location, then the system is simple, but heat and mass transfer are insufficient leading to poor solvent recovery
Solution Approach 1:
The steam grid transitions from single-point (0D) or line (1D) steam introduction to a distributed three-dimensional network throughout the vessel. By adding spatial distribution in multiple dimensions (height, radial position, angular position), the system achieves superior heat and mass transfer without requiring excessively complex control systems, as the geometry itself provides the enhancement.
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 significantly enhances solvent recovery efficiency by maintaining a low partial pressure and elevated temperatures, promoting effective heat and mass transfer, which softens asphaltenes and facilitates the release of trapped solvents, thereby improving the overall solvent recovery process.
Implementation Method 1
steam being conducted through the steam grid at a pressure greater than a vessel operating pressure for heating the steam grid to a temperature greater than a vessel operating temperature
Implementation Method 2
resulting in a relatively low partial pressure substantially throughout the vessel for enhancing mass transfer
Implementation Method 3
enhancing mass transfer by maintaining a low partial pressure
Implementation Method 4
heating the internals to a higher temperature than conventional systems, facilitating the release of solvents from asphaltene agglomerates
Data Source
AI summary
A grid of pipes for conducting steam at a pressure greater than a vessels' operating pressure and delivering the steam throughout the grid forms the internals for a tailings solvent recovery unit. The delivery of steam throughout the grid aids in maintaining a relatively low partial pressure throughout the vessel to act as a driver for mass transfer. Conducting the steam at the higher pressure through the pipes in the grid permits a surface of the pipes to be heated to a temperature higher than possible in a conventional vessel, increasing the heat transfer to the feed stream which flows through the grid.