Clean Steam Generation via Flash Steam Merging in Digester Systems
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Solution Overview
Problem
Continuous digester systems face challenges in generating sufficient clean steam, especially in cold climates where the demand exceeds the supply from black liquor reboilers and steam-to-steam converters, leading to inefficiencies and increased costs.
Innovation Solution
A method where dirty flash steam and vent gases from the steaming vessel are combined and fed into a common steam-to-steam converter, allowing for the production of clean steam through indirect heating, which increases clean steam output by 40-50% and reduces reliance on the steam net, optimizing the use of existing infrastructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If black liquor reboilers and steam-to-steam converters are used for clean steam generation, then clean steam can be produced, but the supply is insufficient in cold climates where demand exceeds supply
Solution Approach 1:
The patent combines multiple steam sources (black liquor reboiler, steam-to-steam converter, and flash steam system) into a unified steam generation network. The flash steam from black liquor extraction is merged with the steam-to-steam converter output to create a hybrid system that increases total clean steam supply beyond what any single system could provide individually.
Solution Approach 2:
The steam-to-steam converter is designed to handle multiple functions: it converts both process steam and flash steam into clean steam, serving as both a steam generator and a steam purifier. This multi-functionality allows the system to maximize clean steam production from available heat sources while maintaining steam quality requirements.
2Quantity of substance
If additional steam-to-steam converters are installed to increase clean steam production, then clean steam supply increases, but investment costs increase
Solution Approach 1:
Instead of adding separate steam-to-steam converters, the patent merges the flash steam system with the existing steam-to-steam converter. This integration allows the single converter to process multiple steam sources simultaneously, achieving increased clean steam production without the capital cost of additional converters.
Solution Approach 2:
The flash steam system generates its own steam from black liquor extraction heat, which then feeds into the steam-to-steam converter. This self-service approach uses waste heat that would otherwise be lost, converting it into useful clean steam without requiring additional external energy input or expensive equipment.
3Quantity of substance
If flash steam is used for steaming, then clean steam production increases, but malodorous gases may leak against the flow of cellulose material
Solution Approach 1:
The patent extracts malodorous gases from the flash steam before it contacts the cellulose material. A dedicated gas extraction system removes these harmful components from the steam stream, allowing the flash steam to be used for steaming without the risk of malodorous gas contamination or leakage against the material flow.
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 increases clean steam production, reduces investment costs for additional steam-to-steam converters, and allows for more efficient energy use, enabling the generation of clean steam sufficient for both chip pre-steaming and cooking processes.
Implementation Method 1
a clean steam is evaporated from clean water fed to the steam-to-steam converter by indirect heating from the dirty flash steam as well as the stream of vent gases from the steaming vessel
Implementation Method 2
a series of flash tanks receiving the extracted liquor, that reduce the pressure of the extracted liquor and generates dirty flash steam from the extracted liquor
Data Source
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AI summary
The invention relates to an improved method for generating clean steam in a digester plant of a chemical pulp mill. By feeding a steam-to-steam converter (SSC) with venting steam from a black liquor flash tank (FT) as well as venting steam from chip steaming (SV) could the volume of clean steam produced be increased by over 40-50%, and to such an extent that the volume of clean steam covers the needs for preheating of chips in the digester system also in severe operational conditions. The total consumption of clean steam from the steam net of the mill may be reduced and used for other purposes such as electricity production, which meets the requirements for converting the pulp mill to an environmental friendly pulp mill.