Hydraulic Digester Steam Injector Design for Uniform Heating
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Solution Overview
Problem
In single-vessel hydraulic digesters, there is a significant temperature difference between the impregnation and cooking zones, leading to uneven heating of chips and liquor, resulting in poor pulp quality due to the inability to directly add steam to the top of the digester without causing hammering or shell damage.
Innovation Solution
Direct steam is safely introduced into the liquor phase above the chip level using steam injectors with small bubble-forming openings, which increase the impregnation zone temperature, reducing the temperature difference and enhancing even heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If direct steam is added to the top of the hydraulic digester, then the impregnation zone temperature increases, but hammering and shell cracks occur
Solution Approach 1:
The steam injection system is segmented into multiple injectors distributed across the digester wall rather than a single large steam input. Each injector contains multiple small openings (0.5-2.0 mm diameter) that break the steam into fine bubbles, distributing the phase change energy throughout the liquor phase and avoiding localized hammering forces that could damage the shell.
Solution Approach 2:
The steam injection creates localized heating zones around each injector opening, with steam condensing in the surrounding liquor phase. This distributed local heating approach raises the overall impregnation zone temperature gradually and uniformly, preventing the sudden temperature spikes and pressure surges that cause hammering while still achieving the desired temperature increase.
2Manufacturing precision
If steam is added to increase impregnation zone temperature, then heating uniformity improves, but the system complexity increases
Solution Approach 1:
The liquor phase acts as an intermediary medium between the steam and the chips. Steam is injected into the liquor phase where it condenses and transfers heat through the liquid, which then distributes the heat uniformly to the chips during circulation. This indirect heat transfer through the liquor intermediary achieves uniform heating without requiring direct steam-chip contact, simplifying the overall system design.
Solution Approach 2:
The existing liquor circulation system within the hydraulic digester serves the dual function of both transporting chips and distributing heat. The same circulation loops that move chips through the digester automatically distribute the heat from steam-injected zones throughout the entire chip mass, eliminating the need for separate heating mechanisms and reducing system complexity.
3Use of energy by moving object
If atmospheric steaming is used in the feed system, then the temperature difference between impregnation and cooking zones increases, but the energy consumption decreases
Solution Approach 1:
Steam is injected into the impregnation zone at the top of the digester before the chips enter the cooking zone. This preliminary heating action raises the impregnation zone temperature closer to the cooking zone temperature, reducing the temperature differential that would otherwise require additional energy input during the cooking phase to achieve uniform chip heating.
Solution Approach 2:
The steam injection system operates continuously during the impregnation stage, maintaining a steady temperature in the impregnation zone. This continuous heating action ensures that chips are pre-heated consistently as they move through the impregnation zone, reducing the energy required in subsequent cooking stages and eliminating the need for intermittent high-energy heating inputs.
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 method allows for a controlled temperature increase of 1-40 °C in the impregnation zone, improving heating uniformity and pulp quality, especially in systems with only atmospheric steaming, by avoiding hammering and shell damage, and is more economical for heating.
Implementation Method 1
Direct steam is safely introduced into the liquor phase above the chip level using steam injectors with small bubble-forming openings, which increase the impregnation zone temperature
Implementation Method 2
the steam condensing into liquor would have caused hammering
Data Source
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AI summary
The present invention relates to a method of heating a hydraulic digester, such as a single-vessel hydraulic digester, which has a top separator, a level of chips and a liquid phase above the level of chips. The method comprises at least the following steps: a. entraining chips in liquor to produce a slurry having a first temperature, b. feeding the slurry of chips to the digester through the top separator, c. supplying direct steam to the liquid phase between the level of chips and the top separator to heat the slurry to a second temperature for the impregnation stage, wherein the steam is fed by using at least one steam injector having a plurality of steam discharge openings; and d. heating the slurry to a third temperature and cooking the chips in a cooking zone, and withdrawing the cooked pulp from the bottom of the digester. The invention relates also to a digester system.