Brick Kiln Cooling Air Recovery: Why Cooling Air Is Already Paid-For Energy
- Rapidflame Ltd
- Aug 14
- 5 min read
The most valuable unit of gas may be the one a brickworks does not need to burn.
Inside a tunnel kiln, gas is converted into thermal energy to fire the product. Some of that energy remains in the bricks as they enter the cooling zone and is transferred into the cooling air. When this warmed air leaves the kiln without performing another useful duty, part of the energy purchased by the manufacturer leaves with it.
For UK brick manufacturers facing high energy prices, weak demand and pressure to reduce carbon emissions, this deserves closer attention. Cooling air should not automatically be viewed as waste. It is an energy stream whose value depends on its temperature, volume, consistency and suitability for another process duty.
That changes the engineering question from “How can we burn less gas?” to “Where is useful heat already available before we burn more gas?”
Cooling air has both a temperature and a value
Not all recovered heat is equally useful. Air at a relatively modest temperature may be suitable for drying, while hotter air may have greater value as preheated combustion air. The best destination depends on matching the quality of the recovered heat to the temperature required by the receiving process.
This is sometimes described as heat cascading: using higher-temperature energy where temperature matters most, then considering lower-temperature duties further down the process.
In a cooling air recovery brick kiln project, the objective is not simply to capture the hottest possible air. The objective is to identify a usable supply that can be recovered without disturbing the cooling curve, kiln pressure or product quality.
Air temperature alone is not enough. A hot stream with insufficient flow may offer limited value. A large airflow that varies sharply with production may be difficult to use consistently. The recovered air must also be available when another part of the process
needs it.
Why recovered heat may reduce fresh gas demand
Imagine that combustion air enters a burner at the surrounding factory temperature. The burner must supply enough energy to heat that air, complete combustion and deliver the required heat to the kiln.
If suitable combustion-supporting air instead arrives already heated, some of that temperature rise has already taken place. The burner may therefore require less gas to achieve the same process duty.
This is the practical value of preheated combustion air. It does not create additional energy. It retains energy that would otherwise leave the system and returns it to a useful part of the process.
The result may be lower fuel demand and improved overall kiln energy performance. However, there is no universal saving figure. The outcome depends on the recovered-air temperature, airflow, burner duty, excess-air level, kiln operating pattern and losses within the recovery system.
Fans consume electricity, ductwork loses heat and additional equipment requires
maintenance. These factors must be included in the energy and commercial assessment.
Where should the recovered cooling air go?
Combustion-air preheating is one option, but it is not automatically the correct first choice.
A brickworks should compare possible uses according to temperature requirement, operating hours and physical distance from the recovery point. Potential destinations may include:
Preheated combustion air for suitable kiln burners
Green-brick drying
Space or make-up air heating
Another compatible thermal process on the site
Using recovered heat close to its source may reduce ducting costs and heat loss. Conversely, a more distant process may offer better utilisation if it operates continuously and has a stable demand.
The kiln must remain the priority. Removing or redirecting cooling air must not interfere with the required cooling curve, kiln draught, atmosphere or final product characteristics. Any proposed system requires assessment under the expected range of products and production rates.
How the Rapidflame Extflame Burner fits the strategy
The burner does not collect, move or recover cooling air. Those functions belong to the wider heat recovery system, which may include insulated ducts, fans, dampers, filtration, bypass arrangements and temperature and pressure controls.
The burner’s role is to use the available combustion-supporting air safely and controllably.
The Rapidflame Extflame Burner can accept combustion-supporting air at temperatures up to 300°C, so it can support heat recovery strategies involving preheated combustion air where suitable.
The range covers 2–400 kW and offers 50:1 turndown. Medium- and high-velocity versions are available, with a maximum flame/flue velocity of 150 m/s. The burner can operate on natural gas or LPG and is available with a customisable flame tube length. Other features include direct spark ignition and low CO and NOx performance when correctly selected, commissioned and operated.
These specifications provide application flexibility, but they do not remove the need to study the kiln. Burner capacity, velocity, mounting arrangement, control method and flame geometry must all be matched to the zone duty.
Heat recovery must continue to work at lower output
A recovery proposal based only on full production can give a misleading result.
When demand falls, a brickworks may reduce throughput, change its product mix or alter the firing curve. Cooling-air temperature and availability may then change at the same time as kiln-zone heat demand.
This is where burner turndown and combustion stability become important. The Extflame Burner’s 50:1 turndown can help a correctly engineered system follow a wide range of heat demands without relying on frequent on-off cycling.
Stable operation at lower firing rates can support temperature control when production schedules vary. It also helps ensure that recovered heat and gas input work together instead of competing through poorly coordinated controls.
Build an energy map before selecting equipment
Before deciding whether to reuse cooling air, the brickworks should build a simple operating map showing where heat is available and where it is required.
The assessment should record:
Cooling air temperature across different operating conditions
Available airflow, pressure and duration
Gas consumption against production output
Heat demand in each relevant kiln zone
Existing burner condition and combustion performance
Burner and kiln control capability
Product mix, firing curve and cooling requirements
Product quality and reject information
Potential heat users and their operating schedules
Installation cost, electrical demand, maintenance and payback
Measurements should cover representative production rather than a single favourable shift. This reveals whether the heat source and proposed heat user remain compatible as kiln conditions change.
Start with the heat, not the hardware
Brick kiln heat recovery should begin by following the energy through the process. Where does it enter? Where is it absorbed? Where does it leave? At what temperature could it still perform useful work?
Only after answering those questions should a brickworks decide on ductwork, controls and burner equipment.
Speak with Rapidflame about assessing whether recovered cooling air and preheated combustion air could support a practical fuel-efficiency project on your kiln. Rapidflame can review the available heat, combustion duty and operating range before recommending how an Extflame Burner could fit the wider system.
Frequently Asked Questions (FAQs)
Is all brick kiln cooling air suitable for recovery?
No. Its usefulness depends on temperature, flow, cleanliness, pressure and availability. Recovery must also avoid disrupting the kiln’s cooling curve, atmosphere and product quality.
Must recovered cooling air be used as combustion air?
No. Preheated combustion air is one possible use. Drying or another compatible heating duty may offer a better technical or commercial match at some sites.
Does an Extflame Burner recover heat from the kiln?
No. Heat recovery requires a separate engineered arrangement. The Extflame Burner can support the strategy by accepting combustion-supporting air at temperatures up to 300°C where suitable.
What happens to heat recovery when production falls?
Cooling-air availability and kiln heat demand may both change. The assessment should therefore cover reduced-throughput and different-product conditions rather than relying only on full-production data.
Why is heat recovery payback site-specific?
Payback depends on recoverable heat, operating hours, displaced gas use, ducting distance, electrical demand, installation cost, maintenance and production conditions. These factors differ between kilns and sites.
