Calcium Bicarbonate Crystallization for RO Concentrate Hardness Removal
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Solution Overview
Problem
Existing methods for treating reverse-osmosis (RO) concentrated water with high temporary hardness, such as lime softening, face challenges with high reagent consumption and operating costs, and are inefficient in removing calcium bicarbonate due to its solubility and formation of autogenous nuclei.
Innovation Solution
A system and method utilizing calcium bicarbonate crystallization, comprising a crystallization unit, precipitation unit, and dewatering unit connected in series, with a programmable logic controller (PLC) system to control the process, ensuring precise pH control and hydraulic retention time for effective crystallization and separation of calcium bicarbonate crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lime softening method is used to remove temporary hardness, then the removal efficiency is improved, but reagent consumption and operating costs increase
Solution Approach 1:
The patent changes the chemical parameters by controlling pH within a specific range (7.5-8.5) and adjusting the molar ratio of calcium hydroxide to bicarbonate ions (0.4-0.6), creating optimal conditions for calcium bicarbonate crystallization that reduces reagent consumption while maintaining removal efficiency
Solution Approach 2:
The system enables self-service by generating autogenous nuclei from the concentrated water itself, which then serve as crystal seeds for continuous calcium bicarbonate precipitation, eliminating the need for external reagents and reducing operating costs
2Reliability
If calcium bicarbonate concentration exceeds solubility limit, then autogenous nuclei formation is promoted, but control precision becomes difficult
Solution Approach 1:
The patent implements feedback control by continuously monitoring pH and adjusting calcium hydroxide dosing accordingly, maintaining pH within 7.5-8.5 to control the saturation state and prevent uncontrolled precipitation while promoting reliable nucleus formation
Solution Approach 2:
The system performs preliminary action by pre-generating autogenous nuclei in the concentrated water before main precipitation occurs, creating a controlled population of crystal seeds that guide subsequent calcium bicarbonate deposition and improve overall process control
3Reliability
If RO concentrated water with high temporary hardness is treated, then the treatment effectiveness is improved, but the complexity of the treatment system increases
Solution Approach 1:
The patent merges multiple functions into a single integrated system where the crystallization reactor performs both nucleation and crystal growth, the centrifugal separator combines solid-liquid separation with crystal discharge, and the system operates as a unified automated process controlled by PLC, reducing overall complexity while maintaining high effectiveness
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
The system achieves a removal rate of temporary hardness exceeding 85% with reduced calcium hydroxide consumption by 14-32% compared to lime softening, avoids the use of auxiliary reagents, and recycles high-purity calcium bicarbonate crystals for economic benefits, while being integrated and easy to operate.
Implementation Method 1
introduce an alkaline reagent (such as calcium hydroxide and sodium hydroxide) to raw water to cause an increase in the pH, so as to promote the hydrolysis of carbonate salts, thereby forming the calcium carbonate precipitate
Implementation Method 2
it is promising to lower the temporary hardness of the RO concentrated water by utilizing calcium bicarbonate crystallization
Implementation Method 3
the dewatering unit comprises a horizontal spiral centrifuge
Data Source
AI summary
A system and method for treating reverse-osmosis (RO) concentrated water with high temporary hardness. The system includes a crystallization unit, a precipitation unit, a dewatering unit, and a programmable logic controller (PLC) system. The crystallization unit, precipitation unit and dewatering unit are connected in series, and the PLC system is configured to control pumps, valves, and displays in the crystallization unit, precipitation unit and dewatering unit. The crystallization unit includes a storage tank and a crystallization reactor communicated therewith. The crystallization reactor is provided with a pH meter, a liquid-level gauge, and a stirrer. A connection pipe between the crystallization reactor and the RO concentrated water is provided with an inlet pump and a inlet valve. A connection pipe between the crystallization reactor and the storage tank is provided with a feeding pump and a feeding valve.