Reverse-Flow Condensing Economizer for Flue Gas Heat Recovery

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Solution Overview

Problem

Existing condensing heat recovery systems in flue gas stacks suffer from inefficient heat transfer and condensate drainage issues, where condensate is re-evaporated by hot flue gas and often drains into the boiler or heat source, affecting equipment and efficiency.

Innovation Solution

The system redirects upwardly flowing flue gas to flow downward across a heat exchanger tube bundle, allowing condensate to drain downward and using a damper to redirect cooled flue gas upward, while a tertiary flow passage ensures condensate is drained out of the stack, enhancing heat transfer efficiency and preventing condensate from reaching the boiler.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If flue gas flows upward across the heat exchanger tubes with condensate draining downward, then heat transfer occurs, but condensate is re-evaporated by hot flue gas reducing heat transfer efficiency

Engineering Contradiction:

Improveheat transfer efficiencyVSAvoidenergy recovery efficiency

Core Design Contradiction:

Loss of energyVSProductivity

Solution Approach 1:

The patent inverts the conventional flow arrangement by directing flue gas downward across the heat exchanger tubes instead of upward. This reversal ensures that condensate drains downward without being re-evaporated by the flue gas, eliminating the energy loss associated with re-evaporation and improving overall heat transfer efficiency.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent extracts the condensate re-evaporation problem from the system by separating the condensate drainage path from the flue gas flow path. The downward-flowing flue gas and downward-draining condensate are arranged to prevent interaction, effectively removing the harmful re-evaporation effect from the heat exchange process.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If exchanger tubes are arranged in line with upward traveling exhaust gas and downward draining water, then heat exchange occurs, but condensate drainage into the boiler or heat source equipment becomes very difficult to prevent

Engineering Contradiction:

Improveequipment protectionVSAvoidcondensate drainage control

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent inverts the flue gas flow direction to downward flow, which naturally aligns with the condensate drainage direction. This inversion creates a gravity-assisted system where condensate drains downward away from the heat source equipment without requiring complex control mechanisms, thereby improving reliability while minimizing device complexity.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent creates a gravitational equipotential arrangement where both flue gas and condensate flow in the same downward direction. This alignment with gravity eliminates the need for additional control mechanisms to prevent condensate from reaching the boiler, as the natural flow paths keep condensate separated from the heat source equipment.

Inventive Principle:

Principle #12Equipotentiality

3Productivity

If larger economizers are used to achieve sufficient energy recovery, then heat transfer efficiency improves, but manufacturing cost and size increase

Engineering Contradiction:

Improveenergy recovery amountVSAvoideconomizer size and cost

Core Design Contradiction:

ProductivityVSEase of manufacture

Solution Approach 1:

The patent inverts the flow arrangement to eliminate condensate re-evaporation, which significantly improves the effectiveness of each unit of heat exchange surface area. This allows smaller economizers to achieve the same energy recovery as much larger conventional units, reducing manufacturing costs and installation space requirements while maintaining high productivity.

Inventive Principle:

Principle #13The other way round (Inversion)

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 configuration improves heat transfer efficiency, allows for smaller and less expensive economizers, and prevents corrosive condensate from draining into the boiler, thereby enhancing energy recovery and equipment protection.

Implementation Method 1

the flue gas interacts with the bundle of heat exchange tubes as the flue gas travels downwardly through the secondary flow passage such that condensate is formed

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

Condensing heat recovery involves the removal of a significant quantity of heat from waste exhaust gases, to the point where the exhaust gas actually condenses and water vapor drops out as condensate

Methodology Applied

Scientific EffectCondensation: Condensation

Implementation Method 3

As condensate forms on the tubes, it drains downward across any lower tubes carrying colder medium

Methodology Applied

Scientific EffectGravity: Gravitation

Data Source

PatentUS8006651B2Reverse-flow condensing economizer and heat recovery method

Publication Date: 2011.08.30 COMBUSTION & ENERGY SYSTEMS LTD

AI summary

A condensing heat exchange economizer wherein upwardly flowing hot flue gas is redirected to flow in a downward direction over a bundle of heat exchange tubes carrying a counter-flowing heat exchange medium to form condensate and cool the flue gas, and the condensate is forced by gravity to flow in the downward direction. The economizer may be in the form of a cylindrical economizer adapted for insertion in an exhaust stack for flue gas. The cooled flue gas may be redirected to flow in an upward direction and merged with a primary flow passage leading to the stack.