Coal Cleaning and Air Flow Reduction for NOx Control
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Solution Overview
Problem
Current methods for reducing NOx emissions during coal combustion are either expensive or impractical, particularly when dealing with varying coal quality, and there is a need for technologies that can effectively lower NOx emissions across different types of coal feedstocks.
Innovation Solution
The method involves cleaning coal to reduce its ash content, pulverizing it, and then using a reduced amount of primary combustion air while compensating with secondary and tertiary air to maintain burn efficiency, thereby lowering the air/fuel ratio and reducing NOx formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If selective catalytic reduction (SCR) is used to remove NOx from flue gas, then NOx emissions are reduced, but capital investment cost increases significantly
Solution Approach 1:
The invention applies iron-based catalysts to coal before combustion to promote nitrogen release in advance. This preliminary catalytic action occurs during coal preparation, converting fuel nitrogen to N2 before it enters the combustion zone, thereby preventing NOx formation at its source rather than treating it after combustion
Solution Approach 2:
The invention converts the harmful effect of fuel nitrogen (which would form NOx) into a beneficial outcome by using iron catalysts to transform it into inert N2 gas during the combustion process. The catalyst promotes the reaction of fuel nitrogen with carbon to form N2, turning a pollution source into a harmless product
2Object-generated harmful factors
If iron-based catalysts are applied to coal using conventional methods (Ohtsuka method), then fuel nitrogen is released more rapidly, but ash content increases and water must be added for washing
Solution Approach 1:
The invention uses inexpensive iron-based catalysts (such as iron oxide, ferrocyanide, or ferricyanide) that can be applied directly to coal without requiring complex preparation or removal processes. These catalysts perform their function during combustion and do not require washing or removal, avoiding the ash increase and water addition problems of conventional methods
Solution Approach 2:
The invention extracts and eliminates the problematic steps of conventional catalyst application (washing with water to remove chloride salts). By using iron-based catalysts that do not require washing, the method removes the source of additional ash and water content while retaining the nitrogen release enhancement benefit
3Object-generated harmful factors
If primary combustion air is reduced to lower air/fuel ratio, then NOx formation is reduced, but burn efficiency may decrease
Solution Approach 1:
The invention changes the chemical parameters of the combustion process by introducing iron-based catalysts that alter the reaction pathways. The catalysts promote alternative reactions that release fuel nitrogen as N2 instead of NOx, allowing the system to maintain burn efficiency while operating at lower air/fuel ratios that would otherwise produce NOx
Solution Approach 2:
The iron-based catalysts act as intermediaries in the combustion process, facilitating the conversion of fuel nitrogen to N2 through intermediate reaction steps. The catalyst provides an alternative reaction pathway that bypasses NOx formation, enabling efficient combustion with reduced primary air while maintaining energy release
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 approach results in significant NOx reductions, with pilot-scale testing showing reductions of up to 50% or more, depending on the initial ash content of the coal, and improves the economic value of waste coal feedstocks by making them usable without increasing NOx emissions.
Implementation Method 1
Researchers have discovered that iron-based catalysts can assist in releasing fuel nitrogen from coal. Ohtsuka and coworkers at Tohoku University (Sendai, Japan) describe methods for producing an iron-based catalyst which, when combined with coal and placed in an pyrolysis environment, causes nitrogen compounds in coal to be released more rapidly, thus causing a decrease in the amount of nitrogen remaining in the char material
Implementation Method 2
Coal combustion is a major source of energy for the production of electricity throughout the world
Implementation Method 3
Ohtsuka and coworkers at Tohoku University (Sendai, Japan) describe methods for producing an iron-based catalyst which, when combined with coal and placed in an pyrolysis environment, causes nitrogen compounds in coal to be released more rapidly
Data Source
AI summary
An initial coal is cleaned to reduce ash content by ≧20% and yield refined coal that optimizes combustion air flow through a coal burner. This permits conveyance of pulverized refined coal in suspended condition through feeder pipes of the coal burner using reduced air flow compared to the quantity of air required to convey pulverized initial coal in suspended condition through the feeder pipes. This reduces oxygen in the primary combustion zone, lowering conversion of fuel nitrogen into NOx and instead converting it into N2 using the refined coal product. Reduced primary combustion air also reduces core flame temperature, reducing thermal NOx formation using the refined coal product. Increasing secondary and/or tertiary combustion air compensates for reduced primary combustion air and result in overall decrease in NOx formation (e.g., thermal NOx formation is reduced when combustion completed in cooler secondary and/or tertiary combustion zones).