Coloured Cardboard Production Using Carbon Dioxide Acidification
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Solution Overview
Problem
The use of sulphur dyes in cardboard production leads to environmental problems due to the acidification process, which results in the release of toxic and explosive chemicals, as well as excessive acid radicals in wastewater.
Innovation Solution
A process involving a pulp colouring apparatus that uses carbon dioxide injection to acidify the pulp and sulphur dye mixture, achieving a pH value between 6.5 and 7.0, thereby preventing environmental issues associated with traditional acidification methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If hydrochloric acid is used to acidify the pulp, then the pH-value is decreased effectively, but toxic and explosive H2S is released
Solution Approach 1:
Carbon dioxide is introduced as an intermediary substance to acidify the pulp instead of using hydrochloric acid directly. The CO2 dissolves in the alkaline pulp to form carbonic acid, which gradually decreases the pH-value to the required range. This intermediary approach avoids the direct release of toxic H2S gas while achieving the necessary acidification for proper dye precipitation.
Solution Approach 2:
The invention changes the chemical parameter of acidification from strong mineral acids to weak carbonic acid formed by CO2 dissolution. By controlling the amount and pressure of CO2 injection, the pH-value is adjusted in a controlled manner from alkaline (pH 10-11) to the target range (pH 6.5-7.0), preventing excessive H2S release while maintaining effective dye precipitation.
2Temperature
If alum or acetic acid is used to acidify the pulp, then the pH-value is decreased, but acid radicals remain in the waste water causing purification problems
Solution Approach 1:
Carbon dioxide serves as a clean intermediary acidifying agent that decomposes into water and CO2, leaving no harmful acid radicals in the waste water. Unlike alum which leaves sulphate radicals or acetic acid which leaves acetate radicals, CO2 acidification produces only carbonic acid that decomposes harmlessly, simplifying waste water purification.
Solution Approach 2:
The invention extracts the harmful acid radicals (sulphate from alum, acetate from acetic acid) from the acidification process entirely by replacing them with CO2. The only substances remaining in the waste water are water, dissolved CO2, and the original pulp components, eliminating the need for complex removal of acid radicals during waste water treatment.
3Productivity
If carbon dioxide is injected at high pressure, then the acidification efficiency is improved, but the equipment complexity increases
Solution Approach 1:
The invention uses pneumatic injection of carbon dioxide gas into the pulp flow under controlled pressure (above 200 kPa). The high pressure forces CO2 to dissolve efficiently in the alkaline pulp, creating carbonic acid rapidly. The system uses a simple injection nozzle or diffuser integrated into the existing pulp duct, avoiding complex equipment while achieving fast and uniform acidification.
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
The process effectively precipitates the sulphur dye on the pulp fibers, achieving excellent colouring results while avoiding environmental problems, as the carbon dioxide dissolves under pressure and the acid radical is environmentally non-troublesome.
Implementation Method 1
injecting, by the carbon dioxide injection means, carbon dioxide into the pulp duct structure, in such manner that in the pulp duct structure the carbon dioxide is mixed with the pulp and the sulphur dye mixed with the pulp which are being pumped out of the first pulp reservoir towards the second pulp reservoir
Implementation Method 2
wherein a residence time of the carbon dioxide in the pulp duct structure is longer than 20 seconds, so that the pulp and the sulphur dye mixed with the pulp, by the carbon dioxide injected and dissolved therein, in the pulp duct structure is being acidified to become an acidified coloured pulp mixture having a pH-value between 6.5 and 7.0
Implementation Method 3
wherein, at the location of injecting the acidified coloured pulp mixture, the acidified coloured pulp mixture to be injected has a static pressure in the pulp duct structure which is higher than 150 kPa, and wherein said injecting the acidified coloured pulp mixture takes place at a distance of at least 2 meters below a level of the acidified coloured pulp mixture in the second pulp reservoir
Data Source
AI summary
According to the invention, in producing coloured cardboard, carbon dioxide is injected and dissolved in a mixture of pulp and at least a sulphur dye, while the mixture is pumped with a delivery pressure higher than 200 kPa out of a first pulp reservoir (11) towards a second pulp reservoir (12), and in such manner that the mixture is acidified by the carbon dioxide to become an acidified coloured pulp mixture (14) with a pH-value between 6.5 and 7.0. The acidified coloured pulp is injected under high pressure out of a pulp duct structure (7) into the second pulp reservoir (12) at a distance of at least 2 meter below a level (15) of the acidified coloured pulp mixture (14) in the second pulp reservoir (12). Accordingly, the invention provides a high-quality colouring of cardboard, wherein environmental problems are prevented.