Precipitated Calcium Carbonate Production via Segmented Lime Addition
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Solution Overview
Problem
Existing processes for producing precipitated calcium carbonate (PCC) in low energy intensity reactors face challenges in achieving high dry matter content without increasing energy intensity, particle breakage, and non-uniform product morphology, especially when using unslaked lime directly in carbonation reactors.
Innovation Solution
A two-step process involving separate reaction vessels for contacting calcium hydroxide with CO2 and adding calcium oxide or dry calcium hydroxide to increase the dry matter content up to 75% without viscosity issues, using a recirculation loop to manage the addition of lime or calcium hydroxide, thereby avoiding particle breakage and maintaining product uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If unslaked lime is added directly to the carbonation reactor to increase dry matter content, then productivity is improved, but particle size distribution uniformity deteriorates and energy intensity increases
Solution Approach 1:
The process segments the addition of lime into two distinct stages: (1) initial carbonation with slaked lime to establish baseline conditions, and (2) subsequent addition of unslaked lime to the carbonated slurry to increase solids content. This segmentation allows the system to achieve high productivity while maintaining particle size uniformity by preventing direct contact between unslaked lime and the carbonation reaction zone.
Solution Approach 2:
The process performs preliminary carbonation of slaked lime to form a stable slurry before adding unslaked lime. This preliminary action creates a buffered environment that prevents abrupt pH changes and localized overheating, thereby maintaining particle size distribution uniformity while enabling high solids content production.
2Productivity
If unslaked lime is added directly to the carbonation reactor, then productivity is improved, but energy consumption increases
Solution Approach 1:
The process performs preliminary carbonation of slaked lime to form a stable slurry before adding unslaked lime. This preliminary action creates a buffered environment that prevents abrupt pH changes and localized overheating, thereby maintaining particle size distribution uniformity while enabling high solids content production.
Solution Approach 2:
The process uses carbonated slaked lime slurry as an intermediary medium to facilitate the addition of unslaked lime. This intermediary buffer zone absorbs the exothermic heat of unslaked lime carbonation and distributes it uniformly, preventing localized overheating and reducing overall energy intensity while maintaining high productivity.
3Productivity
If mechanical dewatering is used to increase solids content, then productivity is improved, but particle breakage occurs
Solution Approach 1:
The process performs preliminary carbonation of slaked lime to form a stable slurry before adding unslaked lime. This preliminary action creates a buffered environment that prevents abrupt pH changes and localized overheating, thereby maintaining particle size distribution uniformity while enabling high solids content production.
Solution Approach 2:
The process replaces mechanical dewatering systems (centrifuges, filters, presses) with a chemical approach using unslaked lime carbonation. This substitution eliminates mechanical particle breakage while achieving high solids content through controlled chemical precipitation and water consumption during the carbonation reaction.
4Manufacturing precision
If slaked lime is used to maintain homogeneous solution, then product uniformity is improved, but dry matter content is limited
Solution Approach 1:
The process segments the addition of lime into two distinct stages: (1) initial carbonation with slaked lime to establish baseline conditions, and (2) subsequent addition of unslaked lime to the carbonated slurry to increase solids content. This segmentation allows the system to achieve high productivity while maintaining particle size uniformity by preventing direct contact between unslaked lime and the carbonation reaction zone.
Solution Approach 2:
The process uses carbonated slaked lime slurry as an intermediary medium to facilitate the addition of unslaked lime. This intermediary buffer zone absorbs the exothermic heat of unslaked lime carbonation and distributes it uniformly, preventing localized overheating and reducing overall energy intensity while maintaining high productivity.
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 allows for the production of high-quality PCC with improved particle size distribution and reduced energy consumption, enabling the production of all commercially relevant morphologies at higher solids content without the need for dewatering, thus enhancing product quality and reducing manufacturing costs.
Implementation Method 1
contacting calcium hydroxide with a gas comprising carbon dioxide to allow formation of calcium carbonate
Implementation Method 2
using a recirculation loop to manage the addition of lime or calcium hydroxide
Implementation Method 3
adding calcium oxide, lime or dry calcium hydroxide to increase the dry matter content up to 75% without viscosity issues
Data Source
AI summary
The present invention relates to a process of preparing precipitated calcium carbonate (PCC) in a low energy intensity reactor in such a manner that the amount of solids in the PCC product can be raised to 35% or more without performing a dewatering step. The process comprises performing in parallel and in two or more separate reaction vessel the steps of contacting calcium hydroxide with a gas comprising carbon dioxide to allow formation of calcium carbonate, and adding calcium oxide, lime or dry calcium hydroxide or a combination of any of the three to a part of the resulting mixture of calcium hydroxide and calcium carbonate. The invention further provides a specialized reactor system as well as the use of this reactor system in the manufacture of PCC.