Mercury Removal from Distillation Overheads via Complexation
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Solution Overview
Problem
Current methods for removing mercury from hydrocarbon fluids in crude oil refineries, such as mercury removal units (MRUs), are limited in capacity and ineffective against particulate mercury forms, leading to accumulation in distillation column overhead sections and light products, necessitating improved control and reduction techniques.
Innovation Solution
A method involving the use of a complexing agent, such as polysulfides, to convert elemental mercury in the overhead vapor fractions into water-soluble mercury compounds, which are then removed from the distillation unit, reducing mercury concentrations in light naphtha products and eliminating the need for multiple MRUs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If mercury removal units (MRUs) are used to remove mercury from light products, then mercury content in light products is reduced, but the units have limited capacity and cannot handle high mercury content crude
Solution Approach 1:
The invention changes the chemical form of mercury from elemental to water-soluble complex compounds by adjusting chemical parameters (adding complexing agents like polysulfides). This transformation allows the mercury to be removed through phase separation rather than chemical reaction, dramatically increasing the removal capacity and enabling handling of high mercury content crude (at least 50 ppbw).
Solution Approach 2:
The invention introduces complexing agents (polysulfides, thiocyanates, etc.) as intermediaries that convert elemental mercury into water-soluble complexes. These intermediaries enable the mercury to transfer from the hydrocarbon phase to the aqueous phase, allowing efficient removal without requiring multiple MRUs with limited capacity.
2Object-affected harmful factors
If multiple MRUs are placed on different light product streams, then mercury removal coverage is improved, but device complexity and cost increase
Solution Approach 1:
The invention creates a universal mercury removal method that can be applied to all light product streams simultaneously. By using complexing agents that work across different hydrocarbon matrices and targeting a single overhead stream rather than multiple product streams, the system achieves comprehensive mercury removal coverage with a single integrated approach, reducing device complexity and eliminating the need for multiple separate MRUs.
Solution Approach 2:
The invention merges the mercury removal function into a single process step applied to the overhead stream. Instead of placing separate MRUs on multiple light product streams (fuel gas, LPG, light naphthas), the complexing agent treatment combines and consolidates the removal function into one unified process, simplifying the overall system architecture.
3Object-affected harmful factors
If adsorbents are used to chemically react with elemental mercury, then mercury is removed from light products, but particulate mercury forms like fine HgS pass through without being removed
Solution Approach 1:
The invention changes the chemical parameter of mercury from elemental form to water-soluble complex form. This transformation makes mercury removable through phase separation regardless of its original particulate or elemental form, ensuring reliable removal of all mercury species including fine HgS particles that would pass through adsorbent-based MRUs.
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 effectively reduces mercury levels in light products by up to 75% and increases mercury concentration in sour water, allowing for efficient disposal and treatment, thereby addressing the limitations of existing mercury removal technologies.
Implementation Method 1
contacting the overhead vapor fractions with a complexing agent to convert at least a portion of the mercury into water soluble mercury in solution
Implementation Method 2
fractionally distilling a crude product containing at least 50 ppbw mercury to form overhead vapor fractions comprising light naphtha
Data Source
AI summary
Mercury in distilled products from a distillation column is removed and extracted as soluble mercury compounds with the injection of a complexing agent into the overhead sections of the column. Examples of complexing agents include polysulfides such as sodium polysulfide or ammonium polysulfide. In one embodiment, the complexing agent is injected into the inlet pipe just before the overhead condenser, converting the volatile elemental mercury into a species that is soluble in the sour water stream that collected in the overhead sections.