Nitric Acid Process Tail Gas Splitting for Ammonia Synthesis
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Solution Overview
Problem
The nitric acid production process faces inefficiencies in power consumption and nitrogen waste due to the expansion of tail gas, which contains residual nitrogen oxides, and the need for separate units for nitrogen and oxygen supply, leading to high energy costs and emissions.
Innovation Solution
The process integrates the use of NOx-depleted tail gas as a nitrogen source for ammonia synthesis, eliminating the need for an air separation unit and nitrogen compressor, by splitting the tail gas into portions where one is work-expanded for power generation and the other used directly as a nitrogen source, reducing oxygen content and avoiding additional purification steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If tail gas is work-expanded in an expander to generate power, then power consumption is reduced, but nitrogen is lost to the atmosphere
Solution Approach 1:
The patent recovers nitrogen from the tail gas that would otherwise be discarded to the atmosphere. The tail gas is split into two streams: one is work-expanded to generate power, and the other is routed to the ammonia synthesis unit as a nitrogen source, thereby recovering the nitrogen resource.
Solution Approach 2:
The tail gas serves multiple functions: it is used for power generation through work-expansion and simultaneously serves as a nitrogen source for ammonia synthesis. This multi-functional use resolves the contradiction between energy recovery and nitrogen conservation.
2Reliability
If an air separation unit and nitrogen compressor are used to supply nitrogen for ammonia synthesis, then nitrogen supply is ensured, but device complexity and energy consumption increase
Solution Approach 1:
The nitric acid production process itself provides the nitrogen needed for ammonia synthesis by routing tail gas to the ammonia synthesis unit. This self-service approach eliminates the need for separate air separation units and nitrogen compressors, reducing device complexity while ensuring reliable nitrogen supply.
Solution Approach 2:
The patent merges the nitrogen supply function into the existing nitric acid production process by utilizing tail gas. This integration eliminates the need for separate nitrogen generation equipment, simplifying the overall system while maintaining reliable nitrogen supply for ammonia synthesis.
3Use of energy by moving object
If tail gas is completely work-expanded to maximize power generation, then energy efficiency is improved, but nitrogen oxides are emitted to the atmosphere
Solution Approach 1:
The tail gas stream is segmented into two separate streams: one portion is directed to the expander for power generation, and the other portion is routed to the ammonia synthesis unit. This segmentation allows simultaneous power generation and nitrogen oxide removal, resolving the contradiction between energy efficiency and emission control.
Solution Approach 2:
The tail gas containing nitrogen oxides is converted into a beneficial resource by routing it to the ammonia synthesis unit, where the nitrogen is utilized. This transforms the harmful nitrogen oxide emission into a useful nitrogen source, eliminating emissions while maintaining energy efficiency through partial work-expansion.
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 integration reduces energy consumption, minimizes nitrogen emissions, and allows for independent operation of ammonia and nitric acid processes, while avoiding costly air separation and nitrogen compression, resulting in a more efficient and cost-effective production method.
Implementation Method 1
the tail gas is commonly work-expanded in a proper expander from the absorption tower overhead pressure to the atmospheric pressure
Implementation Method 2
The most widely used family of NOx control techniques is the catalytic reduction
Implementation Method 3
comprising a synthesis of ammonia by catalytic conversion of a make-up gas comprising hydrogen and nitrogen in an ammonia synthesis loop
Implementation Method 4
catalytic oxidation of ammonia with atmospheric oxygen to yield nitrogen monoxide (NO); oxidation of the nitrogen monoxide product to nitrogen dioxide (NO2)
Data Source
AI summary
Integrated process for the synthesis of ammonia and nitric acid, comprising a synthesis of nitric acid including the following steps: a) subjecting a stream of ammonia (10) to catalytic oxidation, obtaining a gaseous stream containing nitrogen oxides (13); b) subjecting said gaseous stream to a process of absorption of nitrogen oxides, providing nitric acid (16) and a tail gas (17) containing nitrogen and residual nitrogen oxides; c) subjecting at least a portion of said first tail gas (17) to a process of removal of nitrogen oxides, providing a nitrogen oxides-depleted tail gas (18), and comprising a synthesis of ammonia by catalytic conversion of a make-up gas (126, 226) comprising hydrogen and nitrogen in an ammonia synthesis loop, wherein at least a portion (18b, 18d, 21) of said second tail gas is used as nitrogen source for obtaining said make-up gas (126, 226).