Layered Catalyst for Simultaneous CO and NOx Removal
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Solution Overview
Problem
Current methods for removing carbon monoxide, volatile organic compounds, and nitrogen oxides from flue or exhaust gas require separate catalyst units, leading to increased reactor volume and efficiency losses due to the low SCR activity of combined catalysts, which affects power generation and heat flux in gas turbines.
Innovation Solution
A layered catalyst system is developed, comprising an upper oxidation catalyst layer of palladium, vanadium oxide, and titanium oxide, which does not react with ammonia, supported by a commercial NH3-SCR catalyst layer, allowing for simultaneous CO and VOC oxidation and NOx reduction without affecting ammonia, with enhanced pore structure and thickness to maintain SCR activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate catalyst units are used for CO oxidation and NOx reduction, then removal efficiency is improved, but reactor volume increases
Solution Approach 1:
The patent combines CO oxidation and NOx reduction functions into a single integrated catalyst unit with multiple layers. The first layer performs CO oxidation while the second layer performs NOx reduction, allowing both functions to operate simultaneously in one reactor, thereby reducing overall reactor volume while maintaining high removal efficiency for both pollutants.
Solution Approach 2:
The catalyst is segmented into distinct functional layers: a first layer for CO oxidation and a second layer for NOx reduction. This segmentation allows each layer to be optimized for its specific function while being integrated in a single reactor unit, resolving the contradiction between maintaining separate functions and reducing overall reactor volume.
2Volume of stationary object
If combined catalyst is used to reduce reactor volume, then reactor size is reduced, but SCR activity decreases
Solution Approach 1:
The catalyst is divided into functionally independent layers where the second layer is dedicated exclusively to NOx reduction via SCR. This segmentation ensures that the SCR activity is not compromised by the presence of the CO oxidation layer, as each layer operates independently with optimized catalyst composition for its specific function.
Solution Approach 2:
Each catalyst layer is designed with local quality optimized for its specific function: the first layer contains catalysts optimized for CO oxidation, while the second layer contains catalysts optimized for NOx reduction. This local optimization ensures high SCR activity in the second layer while maintaining effective CO oxidation in the first layer, within a compact integrated structure.
3Reliability
If oxidation catalyst is placed upstream of ammonia injection, then ammonia utilization is improved, but NH3 oxidation to NOx increases
Solution Approach 1:
The patent inverts the conventional arrangement by placing the oxidation catalyst layer first and the SCR catalyst layer second, but with ammonia injected before the SCR layer. This inversion ensures that ammonia is not exposed to oxidation catalyst activity, preventing NH3 oxidation to NOx, while still achieving high ammonia utilization efficiency in the SCR layer where it is needed.
Solution Approach 2:
The harmful function of ammonia oxidation is extracted and eliminated by ensuring ammonia does not contact the oxidation catalyst. Ammonia is injected directly into the gas stream positioned to contact only the SCR catalyst layer, thereby taking out the harmful NH3-to-NOx oxidation reaction from the system while preserving beneficial ammonia utilization for NOx reduction.
4Volume of stationary object
If oxidation catalyst is placed downstream of SCR catalyst, then reactor volume is reduced, but NH3 slip oxidation increases
Solution Approach 1:
The patent applies the inversion principle by positioning the oxidation catalyst layer upstream rather than downstream, but crucially positions ammonia injection between the two layers. This inverted arrangement with strategic ammonia injection prevents the oxidation catalyst from contacting ammonia, thereby eliminating NH3 slip oxidation while maintaining compact reactor volume through the integrated layered structure.
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 configuration reduces the total catalyst volume to that of the largest individual catalyst, achieving high CO, VOC, and NOx removal efficiencies while preserving SCR activity, thereby minimizing pressure drop and maximizing power generation efficiency.
Implementation Method 1
an upper first catalyst layer with an oxidation catalyst... oxidising at least part of the amounts of carbon monoxide and the volatile organic compounds
Implementation Method 2
an underlying second catalyst layer with an NH3-SCR catalyst... reducing the amounts of nitrogen oxides in the underlying second catalyst layer by reaction with the ammonia
Data Source
AI summary
A method in which flue gas or exhaust gas containing harmful carbon monoxide, organic compounds (VOC) and NOx is contacted with a layered catalyst. A first layer of the catalyst comprises an oxidation catalyst. An underlying layer of the catalyst comprises a NH3-SCR catalyst for the simultaneous removal of the carbon monoxide and NOx.