Mercury Removal in CO2 Purification via Upstream Adsorption
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Solution Overview
Problem
Existing methods for purifying CO2 gas streams containing elemental mercury (Hg0) and nitrogen oxides (NOx) face challenges such as aluminum corrosion, adsorbent degradation, and limited scalability due to the harmful effects of NOx on adsorbents, particularly at high pressures and in cryogenic conditions.
Innovation Solution
A method involving sequential steps of cooling the gas stream, removing NOx, heating it, and then removing Hg0 using a brazed aluminum heat exchanger and an adsorption unit with specific adsorbents like sulfur-doped activated carbon or zeolite, ensuring the Hg0 deposition temperature is above the NOx separation temperature to prevent corrosion and optimize mercury capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If aluminum brazed plate heat exchangers are used for CO2 enrichment at cryogenic temperatures, then heat exchange efficiency and fluid arrangement are improved, but aluminum corrosion by elemental mercury occurs during heating phases
Solution Approach 1:
The invention extracts and removes elemental mercury from the gas stream upstream of the aluminum heat exchanger using an adsorption unit. This prevents mercury from reaching the heat exchanger and causing corrosion during heating phases, while allowing the aluminum heat exchanger to maintain its high heat exchange efficiency.
Solution Approach 2:
The invention performs preliminary mercury removal before the gas enters the aluminum heat exchanger. By installing an adsorption unit upstream that operates at temperatures above mercury's deposition point, mercury is captured in advance, preventing it from accumulating and corroding the aluminum equipment during subsequent heating cycles.
2Quantity of substance
If conventional adsorbents like sulfur-impregnated activated carbon are used to remove mercury, then mercury capture is improved, but adsorbent degradation by nitrogen oxides occurs
Solution Approach 1:
The invention changes the operating temperature parameter of the adsorption unit to be above the deposition temperature of elemental mercury. This parameter change allows the use of adsorbents that are more resistant to nitrogen oxide degradation while maintaining effective mercury capture, as the adsorption occurs in a temperature regime that prevents adsorbent damage.
Solution Approach 2:
The invention uses aluminum brazed plate heat exchangers and separator drums in the CO2 enrichment unit, copying the same material and design from the cryogenic unit. This creates a consistent system where aluminum components are protected from mercury corrosion through the upstream adsorption unit, allowing the use of efficient aluminum equipment throughout.
3Productivity
If the gas stream is cooled to cryogenic temperatures for CO2 separation, then CO2 enrichment efficiency is improved, but elemental mercury deposits and causes corrosion
Solution Approach 1:
The invention segments the purification process into two distinct temperature zones: an upstream adsorption unit operating above mercury's deposition temperature to capture mercury, and a downstream cryogenic CO2 enrichment unit that operates at low temperatures. This segmentation allows each unit to operate in its optimal temperature range without mercury causing corrosion.
Solution Approach 2:
The adsorption unit acts as an intermediary between the raw gas stream and the cryogenic CO2 enrichment unit. It mediates by removing elemental mercury from the gas stream before the gas enters the cryogenic equipment, preventing mercury from depositing and corroding the aluminum components during cooling and heating cycles.
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 method effectively removes Hg0 and NOx from CO2 gas streams without causing aluminum corrosion, enabling efficient CO2 enrichment and storage by using adsorbents that can handle high pressures and large volumes, thus addressing the limitations of prior art.
Implementation Method 1
a) a step of cooling the gas stream to a temperature T1 below the ambient temperature
Implementation Method 2
c) a step of heating the stream from step b), preferably to a temperature of between 5° C. and 150° C.
Implementation Method 3
d) a step of removing the elemental mercury (Hg0) from the gas stream from step c)
Data Source
AI summary
The present invention relates to a method for purifying a gas stream including CO2, elemental mercury (Hg0) and nitrogen oxides (NOx).