Dryer Exhaust Air Recirculation Control for Sheet Processing
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Solution Overview
Problem
Existing sheet-processing machines, particularly sheet-fed printing machines, face challenges in optimizing energy efficiency in dryers due to high energy consumption, with existing solutions being costly and inefficient in utilizing recycled exhaust air.
Innovation Solution
The solution involves controlling the proportion of recirculated exhaust air based on its absolute humidity, using sensors to measure temperature and relative humidity, and adjusting mixing flaps to optimize energy efficiency without stepless adjustment, while also utilizing waste heat in heat exchangers to preheat air and supply process heat to other machine components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If exhaust air is recirculated to the dryer supply air, then energy efficiency is improved, but drying performance deteriorates due to reduced moisture absorption capacity
Solution Approach 1:
A control unit continuously monitors the absolute humidity of exhaust air and adjusts the recirculation ratio accordingly. When exhaust air humidity is low (high moisture absorption capacity), the system increases recirculation to save energy. When humidity is high (low moisture absorption capacity), the system reduces recirculation to maintain drying performance. This closed-loop feedback control dynamically optimizes the trade-off between energy efficiency and drying effectiveness.
Solution Approach 2:
The system changes the recirculation ratio parameter based on the absolute humidity of exhaust air. By adjusting this parameter dynamically rather than using a fixed ratio, the system adapts to varying moisture absorption capacities of exhaust air, thereby maintaining optimal drying performance while maximizing energy recovery.
2Loss of energy
If a high proportion of exhaust air is recirculated, then energy efficiency is improved, but additional equipment complexity increases
Solution Approach 1:
The control unit automatically determines the optimal recirculation ratio based on measured exhaust air humidity without requiring manual intervention or complex external control systems. The system serves itself by using its own sensors and control logic to optimize operation, thereby achieving high energy efficiency with minimal additional complexity.
Solution Approach 2:
The patent replaces complex mechanical control systems with electronic sensing and control. Instead of using multiple mechanical dampers and manual adjustment mechanisms, the system uses electronic humidity sensors and an electronic control unit to automatically regulate the recirculation ratio, simplifying the overall device complexity while maintaining high energy efficiency.
3Ease of operation
If temperature measurement only is used, then measurement simplicity is maintained, but control precision deteriorates because absolute humidity cannot be determined
Solution Approach 1:
The control unit acts as an intermediary that processes temperature and relative humidity measurements to calculate absolute humidity. Rather than requiring direct absolute humidity sensing (which would add complexity), the system uses readily available temperature and RH sensors as intermediaries, combining their data mathematically to derive the precise absolute humidity value needed for optimal recirculation control.
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 energy consumption by optimizing the drying process, achieving a 50% increase in energy efficiency while maintaining effective drying performance, and allows for the reuse of exhaust air without significant deterioration in drying quality.
Implementation Method 1
sensors for measuring the temperature of the dryer exhaust air
Implementation Method 2
simultaneously measuring temperature and relative humidity, the amount of water vapor contained in the exhaust air can be determined
Implementation Method 3
heat exchangers through which the portions of the dryer exhaust air not directly fed into the dryer's supply air are routed
Implementation Method 4
waste heat from the non-recirculated portion of the dryer exhaust air is supplied to other, additional components within the machine
Implementation Method 5
one or more preferably motor-driven mixing flaps can be advantageously used, as are already partially available today
Implementation Method 6
Machine for processing sheets with one or more dryers
Implementation Method 7
the extent to which recirculated warm exhaust air can be reused to dry the moist sheet
Data Source
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AI summary
The machine has air supply devices provided in a drier unit i.e. infrared drier unit, and exhaust air channels discharging warm exhaust air. Mixing devices i.e. throttle flaps (29a, 29b), mix the warm dry exhaust air and drier supply air. Control-or regulating devices (28) control or regulate measure of mixing of the drier exhaust air and drier supply air based on measuring variables or adjusting values that are correlated with the moisture content of the exhaust air. An independent claim is also included for a method for drying printed and/or painted sheet in a sheet processing machine.