Dual-Point pH Control for Cooling Water Circuits
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Solution Overview
Problem
Existing methods for preventing mineral deposits in cooling water circuits using carbon dioxide face challenges in maintaining a stable pH value due to CO2 stripping in cooling towers, leading to increased risk of limescale formation and corrosion, especially in the cooling tower packing and pipe sections.
Innovation Solution
The method involves measuring the pH value at two points within the cooling water circuit, allowing independent regulation of carbon dioxide and mineral acid addition to maintain a stable pH range, with carbon dioxide added upstream of the process heat exchanger and mineral acid added upstream of the cooling tower, ensuring uniform pH reduction and minimizing deposit and corrosion risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon dioxide is added to cooling water to regulate pH value, then corrosion risk is reduced and salt content increase is minimized, but pH value becomes unstable due to CO2 stripping in cooling tower
Solution Approach 1:
The patent changes the pH control strategy by introducing a second measuring point upstream of the cooling tower and using mineral acid addition to compensate for CO2 stripping effects. This parameter change stabilizes the pH value despite the dynamic CO2 loss in the cooling tower, resolving the contradiction between corrosion protection and pH stability.
Solution Approach 2:
The patent implements a feedback control system with two pH measuring points (upstream and downstream of the cooling tower) that independently regulate CO2 and mineral acid addition. This dual feedback mechanism allows the system to respond to pH changes caused by CO2 stripping and maintain stable pH while preserving the corrosion protection benefits of CO2 regulation.
2Reliability
If pH value is kept high to prevent corrosion, then corrosion risk is reduced, but limescale deposits form due to increased CO3 ion concentration
Solution Approach 1:
The patent maintains pH in the optimal range of 7.4-7.6 through dual regulation, preventing both the high pH conditions that cause limescale formation and the low pH conditions that cause corrosion. By precisely controlling pH within this narrow window, the system avoids both harmful effects simultaneously.
3Measurement precision
If mineral acid is added to regulate pH, then pH control is effective, but handling risks and corrosion risk increase
Solution Approach 1:
The patent uses mineral acid as an intermediary substance to indirectly control pH without directly introducing large amounts of corrosive acid into the entire cooling water circuit. The acid is added upstream of the cooling tower in controlled amounts to compensate for CO2 stripping, achieving pH regulation while minimizing handling risks and corrosion effects compared to traditional mineral acid dosing methods.
4Measurement precision
If CO2 is added upstream of process heat exchanger, then pH regulation is effective, but CO2 stripping in cooling tower causes pH increase downstream
Solution Approach 1:
The patent segments the pH control into two independent zones: CO2 addition upstream of the process heat exchanger for initial pH reduction, and mineral acid addition upstream of the cooling tower to compensate for CO2 stripping. This segmentation allows each substance to perform its function in the appropriate location, maintaining pH uniformity throughout the entire circuit despite the stripping effect.
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 maintains a pH range that prevents limescale and corrosion throughout the cooling water circuit, including the cooling tower packing, by ensuring uniform pH reduction and minimizing CO2 stripping effects, thus reducing the formation of deposits and corrosion risks.
Implementation Method 1
carbon dioxide is fed to the cooling water, the carbon dioxide being fed upstream to the process heat exchanger, but downstream to the cooling tower
Implementation Method 2
cooling water is fed from a process heat exchanger to a cooling tower, where it is cooled in contact with ambient air
Implementation Method 3
cooling water is fed from a process heat exchanger to a cooling tower
Data Source
Figure 1
AI summary
To prevent deposits, such as limescale, in cooling water circuits, state-of-the-art technology employs mineral acids or carbon dioxide to control the pH value of the circulating water. Acid is added, depending on the pH value measured at a specific point in the circuit, until a predetermined target value is reached. However, this type of control using mineral acids is inadequate and leads to a high salt concentration due to the acid used, with correspondingly negative consequences for the durability of the circulating pipes and for the environment. Similarly, control using carbon dioxide leads to increased CO2 consumption due to stripping effects in the cooling tower, as well as to zones in the circuit with elevated pH values.According to the invention, the pH value of the cooling water is regulated at two points spaced apart in the cooling water circuit, once by adding carbon dioxide and once by adding a mineral acid. A first pH measurement and the addition of carbon dioxide required to reach a first target pH value take place downstream of a second pH measurement and the controlled addition of the mineral acid to reach a second target pH value, the second target pH value being chosen to be higher than the first target pH value.