CO2 Injection for Alkaline Effluent Desalination
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Solution Overview
Problem
Direct injection of CO2 into highly alkaline effluents in the steel industry is challenging due to the formation of encrusting calcium carbonate, which clogs injection systems and is difficult to manage, especially when high concentrations of calcium ions are present, leading to inefficiencies and maintenance issues.
Innovation Solution
The process involves diverting a portion of the effluent post-decantation to a high-pressure zone where CO2 is dissolved, reducing the pH and preventing carbonate formation, and using a secondary CO2 injection point upstream to manage clogging risks, allowing for continuous operation and reduced maintenance needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CO2 is directly injected into highly alkaline effluent, then calcium carbonate precipitation occurs, but injection system clogging occurs
Solution Approach 1:
The effluent flow is divided into two separate streams: one stream receives CO2 injection for pH reduction, while the other stream contains calcium ions. These streams are mixed downstream, allowing calcium precipitation to occur in a controlled environment away from the injection system, thus preventing encrustation and clogging.
Solution Approach 2:
The CO2 injection step is extracted and performed separately from the calcium precipitation step. By injecting CO2 into a portion of the effluent before mixing with the calcium-containing stream, the harmful precipitation reaction is separated from the injection point, eliminating the clogging problem while maintaining treatment effectiveness.
2Object-affected harmful factors
If CO2 is injected to reduce pH and prevent encrustation, then calcium precipitation efficiency decreases
Solution Approach 1:
A portion of the effluent is pre-treated with CO2 injection to reduce its pH and increase carbonate content before mixing with the calcium-containing stream. This preliminary action ensures that when the streams combine, calcium precipitation occurs efficiently without forming encrusting deposits in the injection system.
Solution Approach 2:
The CO2-treated effluent stream acts as an intermediary that carries dissolved CO2 and carbonate ions. When mixed with the calcium-containing effluent, this intermediary stream provides the necessary carbonate ions for calcium precipitation while maintaining conditions that prevent encrustation in the injection system.
3Reliability
If sodium carbonate is used to introduce carbonate ions, then calcium precipitation occurs, but water consumption and salinity increase
Solution Approach 1:
The effluent itself is used as the source of carbonate ions through CO2 injection, eliminating the need for external carbonate sources like sodium carbonate. The CO2 reacts with water and hydroxide ions already present in the effluent to form carbonate, achieving self-sufficient carbonate generation without additional water consumption or salt addition.
Solution Approach 2:
Instead of adding chemical substances to introduce carbonate ions, the method changes the pH parameter of a portion of the effluent through CO2 injection. This parameter change transforms the chemical equilibrium to generate carbonate ions in situ, avoiding the need for additional reagents and reducing water and base consumption.
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 effectively prevents clogging, maintains system performance, and allows for efficient calcium precipitation and removal, reducing the risk of blockages and extending maintenance intervals.
Implementation Method 1
at least one injection of gaseous CO2 is carried out in the diverted stream, thus achieving a reduction of the pH of the diverted stream in the range of 4 to 6.8
Implementation Method 2
the principle of precipitation of calcium contained in an alkaline solution (limed for example, i.e. by adding slaked lime CaOH 2 or quicklime CaO) with CO 2
Data Source
Figure 1~2
Figure 3~4
AI summary
A method for treating an industrial effluent loaded with calcium in order to remove all or part of the calcium, comprising the implementation of the following measures: - the effluent (10) to be treated is directed to an area equipped with a settling tank (12); - a portion of the effluent is diverted (13), taken from the outlet of the settling tank, a portion between 3 and 25% of the flow leaving the settling tank, preferably between 5 and 10% of the flow leaving the settling tank, taken downstream of a high-pressure pump (9), operating at a pressure typically between 8 and 10 bar; - at least one injection (15) of gaseous CO2 is carried out in the diverted stream, thereby reducing the pH of the diverted stream to the range of 4 to 6.8, preferably to the range of 4.5 to 6; - the diverted stream thus treated is returned to the initial effluent before its arrival in the settling tank or in the settling tank itself.