High Temperature LC Refining Heat Recovery
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Solution Overview
Problem
The pulp refining process in the papermaking industry has poor energy efficiency, with mechanical pulping consuming a significant portion of global electric energy and converting most refining energy into heat, which is often wasted, leading to high energy demands and environmental concerns.
Innovation Solution
A system for low- and medium-consistency refining at temperatures above 100°C, where pressurized pulp slurry is expanded in a flash tank and heat is exchanged with water to generate low-pressure steam, which can be reused in the refining process, thereby simplifying the TMP flow sheet and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional TMP refining is used, then pulp production is achieved, but energy consumption is very high with most refining energy converted to waste heat
Solution Approach 1:
The invention converts the waste heat generated during refining into useful low-pressure steam through a flash tank. The hot pulp slurry (80-100°C) is discharged into the flash tank where pressure reduction causes immediate flashing of free water into steam, transforming the previously wasted thermal energy into a valuable process utility for heating dilution water and operating heat exchangers.
Solution Approach 2:
The invention utilizes the phase transition of water from liquid to vapor through flash evaporation. When hot pulp slurry enters the flash tank at reduced pressure, the free water undergoes rapid phase change to steam, which is then condensed in heat exchangers to heat process water, efficiently recovering the thermal energy.
2Use of energy by moving object
If low consistency refining at 70-90°C is applied, then some energy reduction (5-8%) is achieved, but fiber shortening and loss of tear strength occur
Solution Approach 1:
The invention changes the temperature parameter from conventional 70-90°C to elevated 80-100°C in the flash tank, which softens the lignin in chemo-mechanical pulps (CTMP) and makes fibers more flexible and resistant to mechanical degradation during subsequent refining, thereby maintaining tear strength while enabling higher energy reduction.
Solution Approach 2:
The invention performs preliminary heating and lignin softening in the flash tank before the pulp enters the low consistency refiner. This pre-treatment prepares the fibers to withstand harsher refining conditions without excessive shortening or strength loss, enabling more aggressive energy reduction strategies.
3Use of energy by moving object
If chemo-mechanical pulping is used, then higher energy savings potential is achieved, but lignin softening temperature control is required
Solution Approach 1:
The invention exploits the lower lignin softening temperature (<100°C) characteristic of chemo-mechanical pulps by operating the flash tank at 80-100°C, which flexibilizes the fibers and enables them to withstand higher refining intensity at low consistency, thereby achieving significant energy savings (potentially exceeding 5-8%) while maintaining pulp quality.
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 achieves significant energy savings, maintaining pulp quality while reducing electric energy consumption by up to 5-8% and allowing for the recovery of a high percentage of refining energy as low-pressure steam, improving the overall heat balance and reducing the need for additional energy inputs.
Implementation Method 1
introducing at least the liquid from the pressurized pulp slurry to a pressurized flash tank
Implementation Method 2
exchanging heat from the pressurized flash tank with water, such that the water is heated, and the pulp cooled
Data Source
Figure 1
Figure 2~3
AI summary
A method for recovering heat from a pulp refining process comprising: discharging pressurized pulp from a high pressure refiner, wherein the pressurized pulp comprises a pressurized slurry of fibers and liquid; introducing at least the liquid from the pressurized pulp slurry to a pressurized flash tank; exchanging heat from the pressurized flash tank with water, such that the water is heated, and using the heated water in the pulp refining process.