Timber Drying Process Using Exhaust Air Recirculation

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Solution Overview

Problem

The timber drying process in sawmills is inefficient, with approximately 80% of added heating energy being lost due to venting out hot air without recovery, leading to high energy costs and suboptimal product quality.

Innovation Solution

The process involves recirculating moist hot air generated during the drying operation to pre-heat incoming batches of timber, using it to maintain moist heat conditions, and subsequently drying under dry heat conditions, reducing the need for external heat and optimizing energy use.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If hot air is vented out during drying operation, then drying efficiency is improved, but energy loss increases significantly

Engineering Contradiction:

Improvedrying efficiencyVSAvoidenergy loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent recovers the exhaust air containing residual heat and moisture from the drying chamber and reuses it in the heating chamber. This prevents the energy that would otherwise be lost with the vented air from being wasted, while still maintaining adequate air exchange for effective drying.

Inventive Principle:

Principle #34Discarding and recovering

Solution Approach 2:

The exhaust air that carries away energy is converted from a harmful waste stream into a beneficial resource. The residual heat and moisture in the exhaust air are utilized to pre-heat and humidify the incoming timber batch, turning what was previously a loss into a valuable energy source.

Inventive Principle:

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

2Temperature

If external heat is continuously supplied, then timber heating is maintained, but energy costs increase

Engineering Contradiction:

Improvetimber heating temperatureVSAvoidenergy cost

Core Design Contradiction:

TemperatureVSUse of energy by moving object

Solution Approach 1:

The system maintains continuous utilization of thermal energy by creating a closed-loop air circulation where exhaust air is continuously recovered and reused. This continuous action eliminates idle energy loss and ensures that heat energy remains productive throughout the drying cycle.

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The exhaust air from the drying chamber is used to pre-heat the timber batch before it enters the drying chamber. This preliminary heating action reduces the amount of additional energy needed to bring the timber up to the required drying temperature.

Inventive Principle:

Principle #10Preliminary action

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 significantly reduces external heat requirements by up to 100% and enhances energy efficiency, allowing for faster drying times while maintaining high product quality.

Implementation Method 1

an exhaust stream of moist hot air is removed from a chamber containing a first batch of timber and is passed into a chamber containing a following second batch of timber for heating said second batch of timber under conditions of moist heat

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentEP3667218B1Timber drying process

Publication Date: 2021.06.09 VALUTEC AB

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AI summary

The present invention relates to a process for drying of timber comprising a heating step under conditions of moist heat and a subsequent drying step under conditions of dry heat.