Energy recovery through a flue gas condenser

The flue gas condenser stands at the center of a number of initiatives aiming at implementing energy recovery in various industries and sectors. Imperatives such as improving energy efficiency and reducing operational costs have become strong motivators for the development of new technologies. Among these solutions, flue gas condensers stand out as a particularly effective solution for capturing waste heat and maximizing energy recovery.

The working principle behind a flue gas condensing heat exchanger allows it to extract heat from the exhaust gasses of combustion processes, which would otherwise be lost to the atmosphere. Instead, they can now be used for a number of applications . By harnessing this otherwise wasted energy, flue gas condensers help industries optimize their processes and reduce dependency on primary energy sources.

The rise of this approach has been powered by the increasing use of biomass as fuel, as opposed to non-renewable fossil fuels. Because biomass presents a high water content, its fuel gas can add up to 30-50% water, allowing for great efficiencies to recover and treat thermal energy from the gas.

At a time when recovering energy and environmental sustainability have become paramount, the flue gas condenser has become a key solution to a number of processes and industries.  

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What is a flue gas condenser

A flue gas condenser is a technology used to recover heat from exhaust gasses produced by combustion processes in industrial plants or power stations. 

At its core, it’s a type of heat exchanger, a device designed to efficiently transfer heat from one medium to another. In this case, it facilitates the transfer of heat from hot flue gasses to a cooling medium (such as water).

The flue gas condensation process involves the cooling down of flue gasses below their dew point, which causes water vapor and other components to condense into liquid form. Through this condensation, latent heat is released, which is then recovered and used for a number of purposes.

As such, the process not only recovers heat that would otherwise be lost, but also reduces the emissions of harmful pollutants by capturing them in the condensed liquid.

How does a flue gas condensing heat exchanger work

  1. Hot flue gasses, generated from combustion processes, enter the flue gas condenser through an inlet port. These gasses typically contain water vapor and other combustion by-products (carbon dioxide, nitrogen oxides, sulfur dioxide, particulate matter…)
  2. Inside the flue gas condenser, the hot flue gasses pass through a series of heat exchange surfaces (such as tubes or plates) that maximize contact with a cooling medium (which can be water, air, or another fluid). 
  3. This contact causes heat to be transferred from the gasses to the cooling medium through conduction, which in turn causes the temperature of the flue gasses to decrease below their dew point. As a result, the water vapor and other components in the flue gasses start to condense into liquid form.
  4. The condensed water vapor, along with any other liquid by-products, accumulates on the surfaces of the heat exchanger and drips down into a collection system. This collected condensate may contain dissolved acidic gasses, such as sulfur dioxide and nitrogen oxides, which were present in the flue gasses and will require proper treatment. 
  5. The heat energy has now been transferred to the cooling medium and can be used for various purposes.
  6. The cooled and partially dehumidified flue gasses exit the condenser through an outlet port at a reduced temperature.

flue gas condensing heat exchanger

Applications of flue gas condensation

Various industries and energy facilities are successfully incorporating the flue gas condenser model into their operations, including:

  • Power plants, increasing overall efficiency and using this recovered heat to preheat water or air before it enters the combustion chamber, thereby reducing fuel consumption and lowering emissions.
  • Industrial Processes where hot exhaust gasses are generated can use flue gas condensers. This includes chemical manufacturing, steel production, cement manufacturing, and food processing, where recovered heat energy can be used to preheat processed fluids or for other heating purposes.
  • Waste incineration plants, so that heat is recovered in a waste-to-energy scheme: the heat from the combustion of municipal solid waste or hazardous waste, it is repurposed for district heating, steam generation, or other industrial processes.
  • Cogeneration systems or Combined Heat and Power systems, where flue gas condensers can be integrated to capture additional heat from the exhaust gasses, increasing  overall efficiency. In this context, the recovered heat can then be employed to power steam turbines for electricity generation, among other uses.
  • District Heating initiatives employ flue gas condensers to recover heat from the exhaust gasses to then provide space heating and hot water for residential, commercial, and institutional buildings.

Benefits of a flue gas condenser

Increased energy efficiency

By recovering heat from exhaust gasses that would otherwise be lost to the atmosphere, flue gas condensers improve the overall energy efficiency of combustion processes. As such, it reduces the need for additional energy inputs and lowers fuel consumption.

Cost savings

The use of captured heat can offset the need for additional fuel to achieve the same heating, resulting in lower operational costs. This adds to the improved energy efficiency that the flue gas condensing heat exchanger facilitates, thus leading to lower operational costs over the long term.

Lower emissions and environmental impact

Incorporating a flue gas condenser lowers greenhouse gas emissions and other pollutants, as it captures and repurposes heat that would otherwise contribute to air pollution. As such, it’s a solid strategy for companies looking for significant emissions reductions for regulatory compliance and sustainability initiatives.

Additionally, the reduced energy consumption also contributes to less environmental pollution.

A versatile technology 

Flue gas condensers can be customized to suit specific project requirements. They can also be retrofitted to existing combustion systems or integrated into new installations.

flue gas condenser

The role of flue gas condenser in energy efficiency

The role of a flue gas condenser in energy recovery and efficiency is proving to be extremely important. This is especially true in industrial settings and power generation plants where operators might be looking for a significant transformation towards sustainability.

Its working principle towards circularity and a waste-to-energy paradigm is particularly appealing, as it extracts valuable heat energy that would otherwise be lost to the atmosphere. 

At a time when decarbonization and energy efficiency are more important than ever, flue gas condensers offer an opportunity to significantly improve the overall energy efficiency of certain processes and systems.

Additionally, the adaptability of this approach ensures flue gas condensers can be integrated into various types of combustion systems, thus being a useful alternative for a wide variety of industries and energy systems.

The promising field of energy recovery through flue gas condensers goes one step further when purposefully designed for each individual project. For instance, seawater heat exchanger technologies can bring a number of benefits to the table when such a resource is available. At the same time, district heating systems designed for direct condensation can represent an additional aid in reducing energy consumption.

At ARANER, we put our thermal engineering expertise to work to help companies implement  environmentally friendly practices into industrial processes and energy generation. From our district heating solutions to picking the right heat exchanger in industrial environments, we focus on each project’s needs to guarantee optimized processes and cost efficiencies.

Want to learn more about our work and the potential of flue gas condensers? Get in touch with us and speak to our team about your project and how we can help you realize it.

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