Flash Steam Pressure Boost for Chip Pretreatment
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Solution Overview
Problem
Existing methods for generating steam in chemical pulp mills using black liquor often result in steam containing volatile compounds, leading to odor and explosion risks, and inefficient energy use, particularly due to the need for additional low-pressure steam in chip bins.
Innovation Solution
A method involving a flash tank where the pressure of black liquor is decreased to produce flash steam, which is then used in an indirect heat exchange with clean liquid in a reboiler to generate steam, and a compressor or fan is used to increase the steam pressure for chip pretreatment, optimizing steam production and reducing volatile compound introduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If flash steam is used for chip preheating, then energy efficiency is improved, but volatile compounds and sulfur compounds are introduced causing odor and explosion risks
Solution Approach 1:
The invention extracts and removes volatile compounds and sulfur compounds from the black liquor before steam generation. A gas-liquid separator is used to separate non-condensable gases, and a scrubbing system with caustic soda solution is employed to remove sulfur compounds, thereby producing clean steam without harmful substances while maintaining energy efficiency
Solution Approach 2:
The invention introduces an intermediary scrubbing system using caustic soda solution that acts as a mediator between the black liquor and the steam generation process. This intermediary substance chemically reacts with and removes sulfur compounds, preventing them from entering the steam stream while allowing the steam generation to proceed efficiently
2Device complexity
If flash steam is used in chip bins, then steam generation is simplified, but explosion risk increases due to concentrated gases in low concentration gases
Solution Approach 1:
The invention extracts and removes concentrated gases from the black liquor before steam generation. A gas-liquid separator is used to separate non-condensable gases, and a scrubbing system with caustic soda solution is employed to remove sulfur compounds, thereby producing clean steam without harmful substances while maintaining energy efficiency
Solution Approach 2:
The invention converts the potentially harmful concentrated gases into a beneficial process by using them to drive the steam generation process. The gases are separated and their energy content is utilized to generate steam, transforming the explosion risk into a useful energy source while maintaining safety through proper separation and scrubbing
3Object-affected harmful factors
If reboiler systems are used to produce clean steam, then volatile compounds are minimized, but steam pressure is insufficient requiring additional low-pressure steam
Solution Approach 1:
The invention merges the flash steam generation system with the reboiler system. Flash steam is generated from hot black liquor in a flash tank, then combined with steam from the reboiler in a common steam line. This combination allows the system to benefit from both the clean steam production of the reboiler and the high pressure/temperature of flash steam, eliminating the need for additional low-pressure steam
Solution Approach 2:
The invention creates a multi-functional steam generation system where the flash tank serves both as a pressure reduction device and a steam generation device, while the reboiler serves both as a heating device and a steam purification device. The combined system can produce steam with varying pressures and purities for different process requirements, making the system universally applicable to various steam needs
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 increases steam production by up to 40% and reduces steam temperature by at least 5°C, minimizing the need for live steam, improving energy economy, and reducing odor and explosion risks while maintaining higher dry solids content in black liquor for further treatment.
Implementation Method 1
the pressure of black liquor is decreased to produce flash steam
Implementation Method 2
flash steam is then used in an indirect heat exchange with clean liquid in a reboiler to generate steam
Implementation Method 3
a compressor or fan is used to increase the steam pressure for chip pretreatment
Data Source
AI summary
The present invention relates to a method of producing steam at a digester plant of a chemical pulp mill. Black liquor is discharged from the digester at a first temperature and pressure. The black liquor is treated in a flash tank for generating flashed black liquor and flash steam at a second temperature and a second pressure, which are lower than the first temperature and pressure. The flashed black liquor is taken for further treatment to the evaporation plant. The flash steam is led to an indirect heat exchange contact with clean liquid in the reboiler for boiling the liquid and for generating steam. The steam is led from the reboiler into a fan or compressor for increasing the steam pressure to a third pressure, which is higher than the second pressure and for adjusting the pressure of the steam in the flash tank. Steam at a third pressure is used for pretreating comminuted cellulosic fiber material, such as chips, prior to cooking.