Sludge Drying Process with Heat Recovery
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Solution Overview
Problem
Existing sludge drying processes are energy-intensive, structurally complex, and prone to faults, with inefficiencies in energy recovery and handling of sludges with fluctuating dry matter content.
Innovation Solution
A process involving predrying sludge on a drying hall floor followed by thermal drying, where air or water vapor is cooled to release heat, which is then reused for predrying, eliminating the need for vacuum and promoting energy-efficient drying with low structural expenditure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If vacuum drying is used to remove water from sludge, then drying efficiency is improved, but structural complexity and energy consumption increase
Solution Approach 1:
The drying process is divided into two distinct stages: predrying in a drying hall and main drying in a thermal dryer. This segmentation allows each stage to be optimized independently, with the predrying stage using simple ambient air circulation and the main drying stage using concentrated thermal energy, thereby avoiding the need for complex vacuum systems while maintaining high drying efficiency.
Solution Approach 2:
The predrying stage is implemented as a preliminary action before main drying. By removing a significant portion of moisture in the predrying hall using simple air circulation, the sludge is prepared for more efficient main drying in the thermal dryer. This preliminary action reduces the burden on the main drying system and eliminates the need for complex vacuum equipment.
2Productivity
If vacuum drying is used to remove water from sludge, then drying efficiency is improved, but energy consumption increases
Solution Approach 1:
The predrying stage is implemented as a preliminary action before main drying. By removing a significant portion of moisture in the predrying hall using simple air circulation, the sludge is prepared for more efficient main drying in the thermal dryer. This preliminary action reduces the burden on the main drying system and eliminates the need for complex vacuum equipment.
Solution Approach 2:
The process utilizes parameter changes by controlling the temperature and humidity conditions in the predrying hall versus the thermal dryer. The predrying hall operates at ambient or slightly elevated temperatures with controlled air circulation, while the thermal dryer uses high-temperature concentrated heat. This parameter optimization allows efficient drying without the high energy consumption associated with vacuum systems.
3Manufacturing precision
If continuous main drying under reduced pressure is implemented, then drying quality is improved, but operational complexity increases
Solution Approach 1:
The drying process is divided into two distinct stages: predrying in a drying hall and main drying in a thermal dryer. This segmentation allows each stage to be optimized independently, with the predrying stage using simple ambient air circulation and the main drying stage using concentrated thermal energy, thereby avoiding the need for complex vacuum systems while maintaining high drying efficiency.
Solution Approach 2:
The process accepts that the predried sludge will undergo further transformation in the thermal dryer. The predrying stage produces a semi-dried intermediate product that is then completed in the thermal dryer. This approach allows the use of simpler, less durable equipment in the predrying stage, reducing operational complexity while maintaining overall drying quality.
4Device complexity
If waste heat from thermal dryer is not recovered, then process simplicity is maintained, but energy efficiency deteriorates
Solution Approach 1:
The predrying stage is implemented as a preliminary action before main drying. By removing a significant portion of moisture in the predrying hall using simple air circulation, the sludge is prepared for more efficient main drying in the thermal dryer. This preliminary action reduces the burden on the main drying system and eliminates the need for complex vacuum equipment.
Solution Approach 2:
The process utilizes parameter changes by controlling the temperature and humidity conditions in the predrying hall versus the thermal dryer. The predrying hall operates at ambient or slightly elevated temperatures with controlled air circulation, while the thermal dryer uses high-temperature concentrated heat. This parameter optimization allows efficient drying without the high energy consumption associated with vacuum systems.
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 process achieves uninterrupted operation with high energy recovery, reduced energy consumption, and fault-free handling of sludges with varying dry matter content, utilizing a significant fraction of thermal dryer energy for drying while minimizing waste heat loss.
Implementation Method 1
air taking up moisture from the sludge flows over or through the sludge, wherein the air is brought to a temperature in a range from 70° C. to 160° C., or wherein, by heating the sludge, water vapor is liberated from the sludge
Implementation Method 2
passing the air heated in step d), or the water vapor, through a first region of a heat exchanger, through which, in a second region, ambient air or water or another liquid medium flows, wherein the air heated in step d) or the water vapor, with condensation of the moisture present therein, releases heat to the ambient air, or the water, or the other liquid medium
Implementation Method 3
The condensation of the water vapor can be promoted by compressing
Implementation Method 4
with condensation of the moisture present therein, releases heat to the ambient air, or the water, or the other liquid medium
Implementation Method 5
introducing the ambient air or the water or the other liquid medium heated in step e) into the drying hall, in such a manner that the ambient air flows on or above the surface of the sludge applied to the floor of the drying hall, or the water or the other liquid medium flows through at least one heating conduit in the floor of the drying hall and thereby heats the floor
Data Source
AI summary
The invention relates to a process for drying sludge having the following steps: a) applying a sludge having a dry matter content of 15% to 30% to a floor of a drying hall (10), or sludge already present, b) predrying the sludge in the drying hall (10), wherein the sludge is mixed, c) introducing at least a part of the predried sludge into a heated thermal dryer (12), wherein the sludge introduced in each case into the thermal dryer (12) is replaced in the drying hall (10), by carrying out the step a), by a sludge having a dry matter content of 15% to 30% which then likewise passes through step b), d) drying the sludge in the thermal dryer (12) to a dry matter content of 80% to 95%, wherein air (14) taking up moisture from the sludge flows over or through the sludge, wherein the air (14) is brought to a temperature in a range from 70° C. to 160° C., or wherein, by heating the sludge, water vapor is liberated from the sludge, wherein the sludge, after achieving the dry matter content of 80% to 95%, is discharged from the thermal dryer (12), wherein the sludge discharged from the thermal dryer in each case is replaced by predried sludge by carrying out step c), which predried sludge then likewise passes through step d), e) passing the air (14) heated in step d), or the water vapor through a first region of a heat exchanger (17), through which ambient air (16) passes in a second region, wherein the air (14) heated in step d) or the water vapor releases heat to the ambient air (16), with condensation of the moisture present in the heated air or in the water vapor, wherein the heated air (14) or the water vapor is cooled to a temperature in the range from 10° C. to 60° C., and the ambient air (16) is heated to a temperature at most 40 K above the ambient temperature and the former temperature is at most 50° C., and f) promoting the predrying according to step b) by introducing the ambient air (18) heated in step e) into the drying hall (10), in such a manner that the ambient air (16) flows onto or over the surface of the sludge applied to the floor of the drying hall (10).