Chromium Absorber Coating for High Temperature Heat Exchangers
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Solution Overview
Problem
High temperature plate heat exchangers face challenges with chromium evaporation at temperatures above 650°C, leading to contamination of fluids and environmental concerns due to the formation of toxic hexavalent chromium, which reduces the lifespan of heat exchangers and fuel cells, and poses environmental hazards.
Innovation Solution
A high temperature plate heat exchanger with chromium-containing alloy heat transfer plates coated with porous titanium dioxide, which acts as a chromium absorber, preventing hexavalent chromium from contaminating the fluid by reacting with it and reducing its presence to below 1 ppm in the gas leaving the exchanger.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromium-containing alloys are used for heat transfer plates, then heat transfer properties and oxidation resistance are improved, but chromium evaporation occurs at temperatures above 650°C causing fluid contamination and environmental harm
Solution Approach 1:
A porous titanium dioxide coating is applied as an intermediary layer between the chromium-containing alloy and the fluid. This coating acts as a mediator that allows heat transfer while preventing chromium evaporation into the fluid, thus resolving the contradiction between maintaining chromium-containing alloy benefits and preventing chromium contamination
Solution Approach 2:
The titanium dioxide coating is designed with porous structure that permits thermal energy transfer while physically blocking the evaporation of chromium compounds into the fluid stream. The porous nature allows heat conduction pathways while the material composition prevents chromium migration
2Object-generated harmful factors
If aluminum rich layers are applied to reduce chromium evaporation, then chromium evaporation is reduced, but the layer formation is laborious and expensive and micro-fissures form reducing effectiveness
Solution Approach 1:
The invention changes the material parameter from aluminum-rich alloy to titanium dioxide coating, which can be applied as a more manageable layer that forms a continuous protective film without the micro-fissure problems of aluminum-based layers, while maintaining chromium evaporation prevention capabilities
3Object-generated harmful factors
If impermeable alumina layer is formed to prevent chromium evaporation, then chromium evaporation is reduced, but micro-fissures form in the layer and the method is laborious and expensive
Solution Approach 1:
The invention uses porous titanium dioxide instead of impermeable alumina. The porous structure provides flexibility that prevents micro-fissure formation while maintaining effective chromium barrier properties, and the material is more amenable to application processes
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
The chromium absorber coating effectively minimizes chromium contamination in the fluid, extending the lifespan of heat exchangers and fuel cells while reducing environmental impact by maintaining low chromium levels in the gas, even at high temperatures, and allows for efficient heat transfer and catalytic oxidation of combustibles.
Implementation Method 1
a chromium absorber coating comprising porous titanium dioxide over at least a first portion of the length of said heat transfer surface
Implementation Method 2
reacting with it and reducing its presence to below 1 ppm in the gas leaving the exchanger
Implementation Method 3
high temperature plate heat exchanger for fluids above 550° C.
Implementation Method 4
catalytic oxidation of combustibles
Data Source
AI summary
A high temperature plate heat exchanger with low chromium rejection for fluids above 550° C. and a method of cooling a gas is suggested. The heat exchanger comprises a plurality of heat transfer plates made of a chromium-containing alloy, particularly high-temperature stainless steel or Ni-based chromium-containing alloy and having two heat transfer surfaces. The plurality of heat transfer plates comprise at least on one heat transfer surface of the heat transfer plates a chromium absorber coating comprising porous titanium dioxide over at least a first portion of the length of said heat transfer surface. The chromium absorber coatings of two adjacent heat transfer plates are facing each other.