Rotary Kiln Thermal Control for Lime Deposition

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Solution Overview

Problem

Rotary kilns used for burning lime-containing mixtures face issues with ring formation on the inner perimeter, leading to uneven burning, energy inefficiency, and production interruptions due to high alkali content and mud ball formation, which existing methods struggle to prevent effectively.

Innovation Solution

A method that collects temperature data along the kiln's axis, predicts the temperature gradient, and uses a control strategy to manage lime deposition by adjusting the temperature gradient, set-point values for lime and fuel supply, and controlling alkali content to reduce ring formation and ensure consistent burning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If temperature is increased to prevent lime deposition, then deposition resistance improves, but energy consumption increases and risk of sintering increases

Engineering Contradiction:

Improvelime depositionVSAvoidenergy consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The system dynamically adjusts temperature parameters along the kiln length based on real-time deposition detection. Instead of uniformly high temperature, the control system modifies local temperature parameters only where deposition occurs, reducing overall energy consumption while preventing harmful deposition.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces mechanical ring removal methods (shooting rings away using guns) with a thermal control system that uses temperature gradients to prevent deposition. This substitution eliminates production interruptions and reduces energy waste associated with mechanical removal operations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-affected harmful factors

If temperature is increased to prevent lime deposition, then deposition resistance improves, but risk of sintering increases

Engineering Contradiction:

Improvelime depositionVSAvoidsintering risk

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The system applies different temperature conditions to different locations along the kiln. Temperature is increased only in areas where deposition is detected, while maintaining lower temperatures in other zones. This localized approach prevents deposition without causing sintering in the overall system.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If ring formation occurs and is removed by shooting, then deposition is cleared, but production is interrupted

Engineering Contradiction:

Improvering formationVSAvoidproduction continuity

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The system performs preliminary detection of deposition using sensors that monitor temperature and other parameters along the kiln. By detecting deposition early, the control system can adjust temperature gradients proactively to prevent ring formation from reaching problematic sizes that would require shutdown for removal.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Object-affected harmful factors

If temperature gradient is controlled to prevent deposition, then deposition is reduced, but control complexity increases

Engineering Contradiction:

Improvelime depositionVSAvoidcontrol system complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The system uses sensors to continuously monitor temperature and deposition conditions along the kiln, feeding this information back to the control system. Based on this feedback, the control system automatically adjusts fuel supply and air flow to maintain optimal temperature gradients, preventing deposition without requiring complex manual intervention.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The control system automatically adjusts temperature gradients based on sensor feedback without requiring external intervention. The system serves itself by detecting deposition conditions and autonomously modifying operational parameters to prevent ring formation, simplifying the overall control architecture.

Inventive Principle:

Principle #25Self-service

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 effectively reduces lime deposition issues, preventing ring formation and mud balls, ensuring consistent product quality and minimizing production interruptions by controlling where and how lime deposits within the kiln, thereby optimizing energy use and product quality.

Implementation Method 1

a thermal model describing the temperature along the cavity of the kiln

Methodology Applied

Scientific EffectHeat conduction: Conduction (thermal)

Implementation Method 2

predicting the actual temperature gradient along the longitudinal axis of the cavity based at least on the measurement data of the temperature in the wall

Methodology Applied

Scientific EffectThermal diffusion: Diffusion

Implementation Method 3

the area of deposition of lime on the inside of the walls of the kiln is controlled

Methodology Applied

Scientific EffectDeposition: Deposition (physical)

Implementation Method 4

The chemical process in the kiln is described as: CaCO3 + heat → CaO + CO2

Methodology Applied

Scientific EffectThermal decomposition: Pyrolysis

Data Source

PatentEP2449329B1Method for controlling a process for burning a lime containing mixture to burnt lime

Publication Date: 2014.12.03 ABB AB

Figure 1
Figure 2a~2b

AI summary

A method and a device (1 ) for controlling a process for burning lime containing mixture (CaCO3) and converting it to calcinated lime (CaO) in a rotary kiln (2), said rotary kiln (2) having an elongated cavity (3) surrounded by a wall (4) and a burner (5) arranged to heat the cavity (3). The method comprises collecting measurement data of the temperature in the wall (4) at a plurality of measuring points along the longitudinal axis (20) of said cavity (3), predicting the actual temperature gradient along the longitudinal axis (20) of said cavity (3) based at least on said measurement data of the temperature in the wall (4), and by means of a thermal model describing the temperature along the cavity (3) of the kiln (2), determining a desired temperature gradient along the cavity (3) based on the predicted temperature gradient along the cavity (3) and a predetermined control strategy controlling the temperature in the kiln (2) so that the area of deposition of lime on the inside of the walls (4) of the kiln (2) is controlled and the drawbacks of the lime deposition is reduced.