Composite Heat Exchange Element Profile for Fouling Control
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Solution Overview
Problem
Rotary regenerative heat exchangers face challenges with fouling at both the cold and intermediate ends due to acid condensation and ammonium bisulphate formation, leading to reduced cleaning effectiveness and increased pressure drop, which limits the availability of the air preheater.
Innovation Solution
A composite heat transfer element profile is designed with a low-performance, low-fouling profile at the cold end and a higher-performance profile at the hot end, featuring a herringbone structure at the hot end and a notched flat profile at the cold end, along with a shallow transition zone to ensure smooth surface transition and continuity of sootblowing jets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-performance corrugated undulated elements are used throughout the full depth of the air preheater, then thermal performance is improved, but fouling occurs at the intermediate tier due to reduced sootblowing jet velocities
Solution Approach 1:
The element is divided into three distinct zones along its depth: a first zone with herringbone profile for high thermal performance, a second transition zone with flat profile, and a third zone with notched-flat profile for fouling resistance. This segmentation allows each zone to perform its specific function optimally.
Solution Approach 2:
Different profiles are applied at different locations along the element depth to address local fouling conditions. The herringbone profile (high performance) is used where thermal performance is critical, while the notched-flat profile (low fouling) is used where fouling resistance is needed, and the flat transition zone connects them smoothly.
2Object-affected harmful factors
If low-performance notched flat elements are used at the cold end to reduce fouling, then fouling resistance is improved, but thermal performance deteriorates and acid condensation temperature band shifts higher into the elements
Solution Approach 1:
The element is divided into three distinct zones along its depth: a first zone with herringbone profile for high thermal performance, a second transition zone with flat profile, and a third zone with notched-flat profile for fouling resistance. This segmentation allows each zone to perform its specific function optimally.
Solution Approach 2:
Different profiles are applied at different locations along the element depth to address local fouling conditions. The herringbone profile (high performance) is used where thermal performance is critical, while the notched-flat profile (low fouling) is used where fouling resistance is needed, and the flat transition zone connects them smoothly.
3Object-affected harmful factors
If deep tiers of uniform profile elements are used to control both cold end and intermediate fouling, then fouling control is improved, but cleaning effectiveness is reduced due to loss in sootblowing jet velocities
Solution Approach 1:
The element is divided into three distinct zones along its depth: a first zone with herringbone profile for high thermal performance, a second transition zone with flat profile, and a third zone with notched-flat profile for fouling resistance. This segmentation allows each zone to perform its specific function optimally.
Solution Approach 2:
Different profiles are applied at different locations along the element depth to address local fouling conditions. The herringbone profile (high performance) is used where thermal performance is critical, while the notched-flat profile (low fouling) is used where fouling resistance is needed, and the flat transition zone connects them smoothly.
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 design reduces fouling rates at the cold end, maintains effective cleaning across the element, and minimizes pressure drop, enhancing the operational availability of the air preheater by ensuring consistent sootblowing effectiveness and reducing energy losses.
Implementation Method 1
heat transfer elements used in rotary regenerative heat exchangers
Implementation Method 2
heat transfer, acid condensation and, consequently, associated solids deposition rates
Implementation Method 3
acid condensation and, consequently, associated solids deposition rates are at a maximum
Implementation Method 4
sootblowing devices that employ high energy cleaning jets consisting of pressurized steam or compressed air
Implementation Method 5
The effectiveness of such devices in cleaning areas further up the heat exchange elements is greatly hampered by the loss in energy and impact velocity of the cleaning jets
Implementation Method 6
selective catalytic reduction (SCR) processes for the reduction of nitrous and nitric oxides (NOx) produce the additional risk of ammonium bisulphate (ABS) fouling
Data Source
AI summary
A stack of heating surface elements includes a first heating surface element (4) having first (10), second (12) and third (14) zones arranged sequentially along a primary gas flow direction (A). The first zone (10) includes a herringbone structure, the second zone (12) includes a flat structure, and the third zone (14) includes a plurality of corrugations extending in the primary gas flow direction (A). The corrugations have flat peak and trough regions. The stack also includes a second heating surface element (36), where the second heating surface element includes a plurality of corrugations extending in the primary gas flow direction (A).