Rotary Kiln Heating System for Uniform Temperature Profile

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Solution Overview

Problem

Thermal processing of used foundry sand and road construction materials in rotary kilns faces challenges such as high carbon monoxide concentrations in flue gases, high temperature demands on kiln materials, and the need for afterburning to remove harmful emissions, which increase operating costs and pose environmental concerns due to the presence of polycyclic aromatic hydrocarbons (PAHs) in pitch-based road materials.

Innovation Solution

A method and system that combine direct heating of the drum chamber using a gas burner with indirect heating of the drum wall, allowing for a uniform temperature profile and reducing the need for afterburning by maintaining sufficient flue gas temperature through a heating system comprising a direct heating device and an indirect heating device, where the indirect heating medium flows counter to the material's conveying direction, ensuring a homogeneous temperature distribution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If direct heating with gas burner is used, then heating efficiency is improved, but flue gas temperature drops and CO concentration increases

Engineering Contradiction:

Improveheating efficiencyVSAvoidflue gas temperature

Core Design Contradiction:

Use of energy by moving objectVSTemperature

Solution Approach 1:

The patent combines direct heating (gas burner inside drum chamber) with indirect heating (heating medium flowing through conduits in the drum wall) to achieve both high heating efficiency and maintained flue gas temperature. The direct heating provides intense local heating while the indirect heating prevents overall temperature drop in the flue gases.

Inventive Principle:

Principle #5Merging (Combining)

2Manufacturing precision

If high starting temperature is used in direct flow operation, then material regeneration is improved, but temperature resistance demands on kiln material increase

Engineering Contradiction:

Improvematerial regeneration qualityVSAvoidtemperature resistance of kiln material

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The patent applies different heating qualities to different locations: direct heating with high temperature gas burner is applied locally where intense heating is needed for material regeneration, while indirect heating is applied to the drum wall to maintain overall temperature without requiring the kiln material to withstand extreme temperatures throughout.

Inventive Principle:

Principle #3Local quality

3Strength

If counterflow operation is used, then temperature demands on kiln material are reduced, but flue gas exit temperature drops causing condensation

Engineering Contradiction:

Improvetemperature resistance of kiln materialVSAvoidflue gas exit temperature

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

The patent merges direct and indirect heating methods to overcome the limitations of counterflow operation. The indirect heating through the drum wall prevents flue gas temperature drop and condensation, while the direct heating ensures adequate temperature for material processing, allowing counterflow operation without the usual temperature problems.

Inventive Principle:

Principle #5Merging (Combining)

4Object-generated harmful factors

If afterburning system is added, then CO concentration is reduced, but operating costs increase

Engineering Contradiction:

ImproveCO concentrationVSAvoidoperating costs

Core Design Contradiction:

Object-generated harmful factorsVSUse of energy by stationary object

Solution Approach 1:

The patent converts the harmful high CO concentration and low flue gas temperature into a benefit by using the indirect heating system to maintain flue gas temperature, which naturally supports complete combustion and reduces CO without requiring an additional afterburning system. The heating medium system serves dual purposes: heating the drum and preventing flue gas cooling.

Inventive Principle:

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

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 prevents cooling of flue gases, reduces the temperature requirements for kiln materials, eliminates the need for afterburning, and maintains high material exit temperatures, thereby lowering operational costs and ensuring effective removal of harmful emissions while maintaining a moderate and uniform operating temperature in the kiln drum.

Implementation Method 1

the drum chamber is heated directly by conducting a heating gas into the drum chamber

Methodology Applied

Scientific EffectDirect heating: Heating

Implementation Method 2

the drum chamber is heated indirectly by warming the drum wall at least in areas

Methodology Applied

Scientific EffectIndirect heating: Conduction (thermal)

Implementation Method 3

the indirect heating medium flows counter to the material's conveying direction

Methodology Applied

Scientific EffectCounterflow: Convection

Data Source

PatentUS10161680B2Method and system for the thermal processing of a material

Publication Date: 2018.12.25 EISENMANN SE

AI summary

A method and system for thermal processing of a material conveyed in a rotary kiln with a rotatable kiln drum, the drum wall of which delimits a heatable drum chamber, from a drum inlet to a drum outlet of the kiln drum. The drum chamber is heated directly by conducting a heating gas into the drum chamber. The drum chamber is also heated indirectly by warming the drum wall at least in areas.