Geothermal Brine pH Control via CO2 Recycle
Solution Overview
Problem
Geothermal power plants face operational issues due to scale deposition in binary heat exchangers and reinjection wells, which is costly to control using traditional inhibitors, and existing methods to decrease pH are either ineffective or increase corrosivity.
Innovation Solution
Separating a small amount of vapor rich in carbon dioxide from the geothermal brine before steam separation and combining it with the flashed brine to decrease pH, inhibiting scale deposition without the need for expensive inhibitors, while also reducing atmospheric emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicate inhibitors are added to control scale deposition in the binary heat exchanger, then scale deposition is controlled, but operating costs dramatically increase
Solution Approach 1:
The invention changes the pH parameter of the brine by adding acid to decrease it from neutral/alkaline levels to acidic levels (pH < 7). This parameter change fundamentally alters the chemical equilibrium, causing scale deposits to dissolve and preventing new deposits from forming, thereby eliminating the need for expensive silicate inhibitors while maintaining reliable scale control in the binary heat exchanger
Solution Approach 2:
The invention converts the harmful effect of acidification (which could increase corrosivity) into a beneficial effect by carefully controlling the acid addition to achieve the optimal pH range. The acidic conditions that might normally be considered harmful are instead utilized to dissolve and prevent scale deposits, transforming a potential harm into a beneficial scale control mechanism
2Reliability
If acid is added to decrease brine pH to control scale deposition, then scale deposition is controlled, but corrosivity increases
Solution Approach 1:
The invention precisely controls the pH parameter by adding acid to achieve a specific acidic range (pH < 7) that is sufficient to dissolve and prevent scale deposits. This controlled parameter change ensures that the brine becomes acidic enough to control scaling while avoiding excessive corrosion by maintaining the pH within an acceptable range rather than completely acidifying the brine
Solution Approach 2:
The invention applies partial acidification rather than complete acidification. By adding acid to achieve only the necessary degree of pH reduction (to below 7 but not to extremely low levels), the system achieves sufficient scale control while limiting the excessive action that would cause severe corrosion. This partial action is sufficient for the intended purpose while avoiding harmful side effects
3Power
If steam is separated from geothermal brine, then power generation is enabled, but pH increases causing scale precipitation
Solution Approach 1:
The invention applies preliminary acidification to the brine before steam separation and heat exchange operations. By pre-adjusting the pH to acidic levels (pH < 7) prior to steam separation, the brine is prepared in advance to prevent scale precipitation that would otherwise occur during the steam separation process and subsequent heat exchange operations
Solution Approach 2:
The invention applies preliminary anti-action by adding acid to counteract the alkaline shift that will occur during steam separation. Before the steam separation process begins, the brine is acidified to create a buffer that prevents the pH increase and subsequent scale precipitation, thereby preemptively neutralizing the harmful effect of the upcoming steam separation
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
Effectively controls scale deposition in binary heat exchangers and reinjection wells, reducing operational costs and environmental impact by using a cost-effective method that minimizes corrosivity and increases power output slightly.
Implementation Method 1
combining it with the flashed brine to decrease pH
Implementation Method 2
combining it with the flashed brine to decrease pH, inhibiting scale deposition
Implementation Method 3
Separating a small amount of vapor rich in carbon dioxide from the geothermal brine
Data Source
AI summary
Geothermal brine always contains some carbon dioxide in solution. Separating steam from geothermal brine removes the carbon dioxide, sharply increasing the pH of the brine and causing precipitation of pH sensitive minerals, including calcium carbonate, magnesium silicate and other metal silicates, clays, and metal sulfides. The binary heat exchanger in a steam-binary hybrid geothermal power plant is especially sensitive to scale deposition from flashed geothermal brine, and application of expensive scale inhibitors is required. Deposition of scale in the binary heat exchanger can be controlled by separating a small amount of gas-rich vapor from the brine before the main stage of steam separation, and combining this gas rich vapor with the flashed brine before in enters the binary heat exchanger. The carbon dioxide thus added to the brine will decrease pH, decreasing or completely blocking precipitation and deposition of pH sensitive minerals as scale.