Fluid Bed Calciner Linked to Combustor for Lime Mud Processing
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Solution Overview
Problem
The existing rotary kiln/LMD calcination process in pulp mills is inefficient in using low-cost, carbon-neutral fuels like biomass and WWTP sludge due to contamination issues and high energy consumption, leading to increased fossil fuel use and greenhouse gas emissions, while also facing challenges in separating combustion products from calcination reaction products to recover excess heat effectively.
Innovation Solution
A process utilizing a bubbling fluid bed calciner thermally linked by moving media heat transfer (MMHT) to a circulating fluid bed combustor, allowing low-cost fuels to be used without contaminating the calcine, and separating combustion and calcination stages to recover excess heat as steam, thereby reducing fossil fuel consumption and emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If low-cost fuels like biomass and WWTP sludge are used in the conventional rotary kiln/LMD calcination process, then fuel cost is reduced, but the calcine becomes contaminated and energy consumption increases
Solution Approach 1:
The invention divides the calcination system into two separate vessels: a combustor for burning low-cost fuels and a calciner for processing lime mud. This segmentation prevents fuel ash from contaminating the calcine while maintaining the ability to use inexpensive fuels like biomass and WWTP sludge in the combustor, thereby resolving the contradiction between fuel cost reduction and calcine quality maintenance.
Solution Approach 2:
The invention introduces a heat transfer medium (solid particles) that circulates between the combustor and calciner, transferring thermal energy without transferring contaminants. This intermediary enables heat transfer from the fuel combustion zone to the calcination zone while preventing direct contact between fuel ash and the lime mud, thus maintaining calcine quality while using low-cost fuels.
2Quantity of substance
If low-cost fuels like biomass and WWTP sludge are used in the conventional rotary kiln/LMD calcination process, then fuel cost is reduced, but energy consumption increases
Solution Approach 1:
By separating the combustion and calcination processes into distinct vessels with optimized functions, the system achieves more efficient energy utilization. The combustor can operate at optimal combustion conditions while the calciner receives pre-heated feed and operates at optimal calcination conditions, reducing overall energy consumption compared to the conventional single-vessel approach.
Solution Approach 2:
The circulating heat transfer medium creates a continuous energy transfer loop between the combustor and calciner, ensuring that thermal energy is continuously and efficiently transferred. This continuous action eliminates energy losses associated with intermittent heating and maintains optimal temperatures throughout the process, reducing total energy consumption.
3Device complexity
If combustion and calcination stages are combined in a single vessel, then system complexity is reduced, but excess heat cannot be effectively recovered
Solution Approach 1:
The invention separates combustion and calcination into different vessels, enabling independent optimization of each process and effective heat recovery through the circulating medium system. Although this increases structural complexity, it allows for efficient heat extraction from combustion gases to pre-heat feed and maintain calcination temperatures, significantly reducing energy losses.
Solution Approach 2:
The circulating heat transfer medium acts as an intermediary that enables efficient heat transfer from the combustor to the calciner. This intermediary system allows for controlled heat exchange and effective recovery of excess heat from combustion, which would be difficult to achieve in a combined single-vessel system where heat transfer paths are less controllable.
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 enables the production of high-quality CO2 and re-burned lime using low-cost fuels, reducing fossil fuel consumption by 30-50% and achieving energy efficiency through the separation of combustion and calcination stages, while also providing a compact and efficient system for pulp mills.
Implementation Method 1
A process utilizing a bubbling fluid bed calciner thermally linked by moving media heat transfer (MMHT) to a circulating fluid bed combustor
Implementation Method 2
separating combustion and calcination stages to recover excess heat as steam
Implementation Method 3
bubbling fluid bed calciner thermally linked by moving media heat transfer (MMHT) to a circulating fluid bed combustor
Data Source
AI summary
The invention features methods and systems for producing commercial quality carbon dioxide (CO2) of 90% to +99% purity using, wet calcium carbonate lime mud produced in a manufacturing operation, for instance, Kraft pulp mill lime mud (a.k.a., “lime mud”) as a feedstock to a multi-stage lime mud calcination process. This process may be fueled with waste water treatment plant (WWTP), sludge biomass, precipitated lignins, coal, or other low cost solid fuels. High reactivity “soft-burned” lime product (“calcine”) required in the mill's chemical recovery circuit is also produced, and steam and heated boiler feed-water is generated and exported to the mill's steam distribution and generation system as well as hot process water for use in the mill's boiler house and manufacturing operation. The system for calcining calcium carbonate lime mud produced from a re-causticizing manufacturing operation and converting it to re-burned lime and CO2 comprises a calciner and a combustor linked by a moving media heat transfer (MMHT) system or apparatus. The MMHT system or apparatus thermally links separate fluid bed combustion (exothermic) and calcination (endothermic) stages with a solid particulate media. The system further comprises a flash dryer or spray dryer that utilizes exhausted heat from the calcination stage.