Digester Downcomer Insulating Region Heat Transfer
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Solution Overview
Problem
The existing digester apparatuses experience inefficiencies due to undesirable heat transfer between the wash and cooking downcomers, which affects the overall process efficiency and effectiveness in delignifying wood chips to form pulp.
Innovation Solution
The digester apparatus incorporates a structure that defines an insulating region between the first and third downcomers, preventing continuous liquid flow through the second downcomer, which can be filled with stagnant liquid or air to reduce heat transfer between the cold blow filtrate and cooking liquor, thereby minimizing heat exchange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the wash and cooking downcomers are directly adjacent to one another, then the device complexity is reduced, but undesirable heat transfer occurs between the two downcomers which makes the overall process less efficient and effective
Solution Approach 1:
A second downcomer is introduced as an intermediary element positioned between the first (wash) downcomer and the third (cooking) downcomer. This intermediate downcomer acts as a thermal barrier that prevents direct heat transfer between the cold wash liquor and hot cooking liquor, thereby reducing energy loss while maintaining a relatively simple concentric pipe structure.
2Loss of energy
If structure is added to prevent continuous liquid flow through the second downcomer, then heat transfer between downcomers is reduced, but the device complexity increases
Solution Approach 1:
The second downcomer is segmented into multiple sections: an upper section, a middle section that forms the insulating region, and a lower section. The flow prevention structure divides the second downcomer into functional zones, with the middle section serving as a stagnant liquid or air-filled insulating barrier that prevents continuous liquid flow through the entire downcomer while maintaining structural integrity.
3Loss of energy
If the second downcomer is used as an insulating region with stagnant liquid or air, then heat transfer is minimized, but the device complexity increases
Solution Approach 1:
The insulating effectiveness of the second downcomer is achieved by changing the physical state and flow characteristics of the liquid within it. By preventing continuous flow and creating stagnant liquid or air-filled regions, the thermal conductivity parameter is reduced, transforming the second downcomer into an effective thermal insulator without requiring additional insulating materials or complex structures.
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 design enhances the operational efficiency of the digester apparatus by reducing energy input requirements, improving pulp washing, and enhancing pulp strength and quality by minimizing heat transfer between the cooking liquor and cold blow filtrate.
Implementation Method 1
the second downcomer defines an insulating region between the first and third downcomers so as to reduce heat transfer between the first and third downcomers
Data Source
AI summary
A digester apparatus is provided for delignifying wood chips to form wood pulp comprising: a vessel, a first downcomer, an outer fluid supply downcomer and structure defining an insulating region between the first and outer downcomers. The first downcomer extends into the vessel for delivering a first fluid into the vessel. The first fluid is generally at a first temperature when passing into the first downcomer. The outer fluid supply downcomer extends into the vessel and may be located about the first downcomer for supplying a second fluid into the vessel. The second fluid may be generally at a second temperature different from the first temperature when passing into the outer downcomer. The structure defining an insulating region between the first and outer downcomers functions to reduce heat transfer between the first and outer downcomers.