Nitric Acid Tail Gas Beds for Startup NOx Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing nitric acid plants face high NOx emissions during transitory events like startup and shutdown due to inadequate catalyst activity at low temperatures, leading to visible plume stacks and environmental concerns, without requiring expensive additional heating equipment.
Innovation Solution
Temporarily modify the operation of the catalytic beds in the nitric acid plant's treatment section by adding a reducing agent, such as ammonia, to the catalytic bed designed for N2O removal, allowing it to function as an additional bed for NOx reduction during transitory events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the catalytic bed for N2O removal is used during transitory events, then N2O removal is maintained, but NOx reduction is insufficient due to low temperature
Solution Approach 1:
The catalytic bed designed for N2O removal is made multi-functional by introducing a reducing agent (ammonia or hydrocarbon) that enables it to simultaneously reduce NOx during transitory events. The catalyst maintains its N2O removal capability while gaining NOx reduction functionality through the added reducing agent, allowing one bed to perform both functions during low-temperature operation.
Solution Approach 2:
The introduction of a reducing agent changes the chemical environment and reaction parameters in the catalytic bed. This parameter change enables the catalyst to perform NOx reduction in addition to its original N2O removal function, effectively expanding its operational capability at low temperatures without requiring temperature increase.
2Object-generated harmful factors
If additional heating equipment is installed to increase tail gas temperature during startup, then NOx reduction is improved, but equipment complexity and cost increase
Solution Approach 1:
The system uses the reducing agent (ammonia or hydrocarbon) to provide both chemical reduction of NOx and thermal contribution to the catalytic bed. The reducing agent serves dual purposes: chemically reducing NOx and thermally assisting the low-temperature catalytic reactions, eliminating the need for separate heating equipment.
Solution Approach 2:
Instead of changing the physical temperature parameter through external heating, the invention changes the chemical parameters by introducing a reducing agent. This chemical parameter change enables NOx reduction to occur effectively at low temperatures, avoiding the need for thermal heating equipment.
3Loss of energy
If the catalytic bed operates at low temperature during transitory events, then energy consumption is reduced, but catalytic activity is insufficient for adequate NOx reduction
Solution Approach 1:
The reducing agent acts as an intermediary substance that facilitates NOx reduction at low temperatures. It provides an alternative reaction pathway that is less temperature-dependent, enabling the catalytic bed to maintain effective NOx reduction activity during transitory events without requiring high temperature operation.
Solution Approach 2:
The introduction of the reducing agent changes the reaction kinetics and catalytic behavior, allowing the bed to maintain adequate activity at low temperatures. This parameter change in the chemical environment enables reliable NOx reduction without sacrificing energy efficiency.
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
Enhances NOx reduction capacity by up to 50% during transitory events, reduces the risk of ammonia slip, and minimizes catalyst downtime, while avoiding the need for costly additional heating equipment.
Implementation Method 1
the first catalytic bed is exploited for the catalytic decomposition of N2O into nitrogen and oxygen and in the temperature range of 300° C. to 600° C.
Implementation Method 2
in the second catalytic bed nitrogen oxides NOx are reduced in the presence of a suitable reducing agent into nitrogen and water
Implementation Method 3
Commonly used reducing agents are ammonia and hydrocarbons
Data Source
AI summary
A method for reducing the NOx emission during start-up and shutdown events of a nitric acid plant, wherein the nitric acid plant comprises a tail gas treatment section including a first catalytic bed for removal of N2O followed by a second catalytic bed for removal of NOx, wherein during a start-up or shutdown the operation of said treatment section (10) is temporarily modified by adding a NOx reducing agent upstream of said first catalytic bed, so that said first catalytic bed provides reduction of NOx.