Non-Condensable Gas Injection for Lime Kiln Ring Reduction

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Solution Overview

Problem

Elongate rotary calcination kilns, such as lime kilns, face issues with mid-kiln ring formation due to temperature fluctuations and the generation of nitrogen oxides (NOx) from combustion processes, which affect the calcining reaction efficiency and contribute to environmental pollution.

Innovation Solution

Introducing non-condensable gases (NCGs) into the kiln chamber at a specific temperature range, typically between 212°F to 2,200°F, downstream of the burner end, to reduce sporadic flame activity, lower temperatures, and mitigate NOx generation, while using a plenum system to convey NCGs into the pre-heating or calcining zone.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If combustion processes are used to heat the kiln chamber, then the calcining reaction can proceed, but nitrogen oxides (NOx) are generated causing environmental pollution

Engineering Contradiction:

Improvekiln chamber temperatureVSAvoidnitrogen oxides emissions

Core Design Contradiction:

TemperatureVSObject-generated harmful factors

Solution Approach 1:

The patent introduces non-condensable gases (NCGs) containing sulfur compounds into the kiln chamber to convert harmful NOx into beneficial sulfates through chemical reaction. The NCGs act as a sacrificial reagent that reacts with NOx to form stable sulfate compounds, thereby eliminating the harmful emissions while maintaining the calcining process

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the chemical composition parameters of the kiln atmosphere by introducing NCGs with specific sulfur compound concentrations. This parameter change alters the chemical reactions occurring in the kiln, shifting from NOx formation to sulfate formation, thereby reducing emissions while maintaining thermal conditions for calcining

Inventive Principle:

Principle #35Parameter changes

2Productivity

If high temperatures are maintained in the kiln chamber, then the calcining reaction efficiency is improved, but temperature fluctuations cause mid-kiln ring formation

Engineering Contradiction:

Improvecalcining reaction efficiencyVSAvoidtemperature stability

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The patent implements a feedback mechanism where the introduction of NCGs creates a self-regulating chemical environment. The sulfur compounds in NCGs react with NOx and participate in thermal reactions that help stabilize the temperature profile along the kiln, preventing the extreme fluctuations that lead to ring formation while maintaining sufficient heat for efficient calcining

Inventive Principle:

Principle #23Feedback

3Object-generated harmful factors

If non-condensable gases (NCGs) are introduced into the kiln chamber, then NOx emissions are reduced and temperature fluctuations are minimized, but additional equipment and process complexity are required

Engineering Contradiction:

Improvenitrogen oxides emissionsVSAvoidplenum system and gas introduction equipment

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The patent makes the introduced NCGs serve multiple functions simultaneously: they act as a NOx scavenger, a temperature stabilizer, and a reactant for sulfate formation. This multi-functionality reduces the need for additional separate equipment, as the NCG introduction system performs multiple emission control and process optimization roles in one integrated approach

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces mid-kiln ring formation by minimizing temperature fluctuations and lowers NOx emissions, allowing for more precise temperature regulation and improved calcining reaction efficiency within the kiln.

Implementation Method 1

introducing non-condensable gases (NCGs) into the kiln chamber at a specific temperature range, typically between 212°F to 2,200°F, downstream of the burner end, to reduce sporadic flame activity, lower temperatures, and mitigate NOx generation

Methodology Applied

Scientific EffectTemperature reduction: Cooling

Implementation Method 2

using a plenum system to convey NCGs into the pre-heating or calcining zone

Methodology Applied

Scientific EffectGas flow: Convection

Implementation Method 3

combustion processes, which affect the calcining reaction efficiency

Methodology Applied

Scientific EffectCombustion: Combustion

Implementation Method 4

lime kilns, used for chemical recovery in the pulp and paper industry... conversion back into quicklime (i.e. calcium oxide (CaO))

Methodology Applied

Scientific EffectThermal decomposition: Pyrolysis

Data Source

PatentUS10995991B2Process for reducing ringing in lime kilns

Publication Date: 2021.05.04 ANDRITZ INC

AI summary

This application discloses exemplary processes and systems for reducing mineral ring accumulation in calcination kiln. The processes and systems comprise inserting non-condensable gases (“NCGs”) in a preheating zone of a calcination kiln, upstream of the burner end. The pre-heating zone may be characterized by temperatures ranging from 1,300° F. to 1,750° F. The system may desirably comprise a plenum for inserting the NCGs into the rotating calcination kiln at the pre-heating zone.