Lime Mud Scrubbing for Kraft Mill Flue Gas
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Solution Overview
Problem
Current methods for processing flue gases from kraft pulp mills are costly and inefficient, as they require significant sodium hydroxide usage and result in harmful sodium and sulfur emissions, with no simple method to control the Na/S balance and reduce environmental discharge.
Innovation Solution
The method involves using lime mud from the calcium circulation loop in a kraft pulp mill as a calcium compound to scrub flue gases, reducing the need for caustic makeup and minimizing sodium and sulfur emissions by utilizing calcium compounds already destined for discharge, which are free and environmentally harmless.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If sodium hydroxide solution is used in a caustic scrubber to bind sulphur dioxide, then sulphur emissions are minimized, but chemical costs increase significantly due to the need for caustic makeup
Solution Approach 1:
The patent replaces expensive sodium hydroxide with cheap calcium compounds (limestone, calcined clay, or other calcium-based materials) that can be easily disposed of or discharged. The calcium compound reacts with sulphur dioxide to form calcium sulphate, which is then discharged with the waste water, eliminating the need for costly caustic makeup while maintaining effective sulphur removal.
Solution Approach 2:
The patent changes the chemical parameter from sodium-based to calcium-based scrubbing agents. This parameter change fundamentally alters the chemistry of the scrubbing process, allowing for effective sulphur dioxide removal without the economic drawbacks of sodium hydroxide consumption and caustic makeup requirements.
2Loss of substance
If fly ash is dissolved and discharged to control Na/S balance, then sodium emissions are reduced, but environmental harm increases due to harmful substance discharge into water systems
Solution Approach 1:
The patent uses calcium compounds that are already part of the waste disposal stream in the kraft pulp mill. The calcium compound reacts with sulphur dioxide and the resulting calcium sulphate is discharged with the waste water, combining two disposal functions into one and eliminating the need for separate fly ash dissolution and sodium control processes.
Solution Approach 2:
The patent merges the sulphur removal function with the existing waste water discharge system. By using calcium compounds that are discharged with the waste water, the process combines sulphur dioxide removal with the disposal of harmful substances, eliminating the need for separate treatment streams and reducing overall environmental impact.
3Object-affected harmful factors
If a dual alkali process with calcium oxide and sodium bisulphite is used, then sulphur emissions are controlled, but device complexity increases due to multiple process steps
Solution Approach 1:
The patent extracts the essential function of sulphur removal from the complex dual alkali process and implements it using a single calcium compound in a simplified scrubbing system. By taking out the need for sodium bisulphite regeneration and calcium oxide handling, the process is reduced to a simple one-step reaction where calcium compound reacts with sulphur dioxide and the product is discharged with waste water.
Solution Approach 2:
The patent segments the complex dual alkali process into a single, simple stage using calcium compounds. Instead of the multi-step process involving sodium bisulphite regeneration and calcium oxide treatment, the invention uses a direct reaction between calcium compound and sulphur dioxide, followed by discharge of the reaction product with waste water, thereby simplifying the overall process architecture.
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 reduces chemical costs and environmental harm by utilizing free lime mud for scrubbing, allowing for effective control of the Na/S balance and minimizing harmful discharges, while eliminating the need for costly caustic makeup and fly ash handling.
Implementation Method 1
the calcium compound is lime mud which is obtained from the calcium circulation between causticization and lime reburning in the chemical recirculation loop of the kraft pulp mill and which is used as a substance reacting with sulphur dioxide in gas scrubbing
Data Source
AI summary
In a method for processing flue gases, flue gases from an incineration plant for non-condensable gases of a kraft pulp mill are scrubbed by means of a calcium compound. The calcium compound is lime mud taken from the chemical recirculation of the kraft pulp mill after causticization and before a lime reburning kiln, and it is used in the scrubbing of gas as a substance reacting with sulphur dioxide.