Flue gas heat recovery systems – for bakeries

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Recent studies have shown that ovens and space heating are the two most energy intense processes in a bakery.

Achieve energy efficient baking

Cutting carbon emissionsThe 2008 Climate Change Act made Britain the first country in the world to set legally binding ‘carbon budgets’, aiming to cut UK greenhouse gas emissions by 34 % by 2020, compared to 1990 levels, and at least 80 % by 2050.

This is truly a very challenging target for all, including British industry which accounts for approximately 25 % of UK’s emissions.

Bakeries can take the leadEvery bakery is in the ideal position to actively contribute to massive savings and work towards achieving set targets whilst increasing its own profitability.

The bakery ovens are the largest users of energy in any bakery, and the sophisticated controls supplied by the oven manufacturer do a fantastic job, but much of the energy used is discharged to the atmosphere through the ovens’ chimneys.

Up to 15 % recovery of lost heat & energyBy installing a compact stainless steel heat exchanger directly behind the burner or bed of the oven, or integrating it into the exhaust gas line or flue, a bakery can typically recover around 10 % or even more of the heat in the oven’s exhaust gas.

This recovered heat can be used to provide a constant supply of hot water for cleaning and for heating the building in the cold months.

Alternatively the recovered heat can be used to preheat the water in steam boilers or to provide cooling for both baking trays and mixing areas.

Apart from the use of a heat exchanger there are substantial savings to be made by ensuring the burners operate at their optimum efficiency.

But there is a catch!

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Energy use in Bakeries

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Annual variations in the chimney draughtAt maximum and minimum outdoor temperature and an average flue gas temperature of 180 C.

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The Fig. shows temperature fluctuations that are dependent on the time of year

What is the catch? Modern bakery systems control just about everything that happens inside the bakery. Time, temperature, humidity – everything needed to make perfect bread, cakes or pastry.

But the bakery system cannot control the atmosphere.

The atmospheric pressure, the outdoor temperature, the season, even the wind have major influences on the draught in the chimney into which the flue gases from the ovens are discharged. If the weather and the flue conditions are working against it, the sophisticated controls of the oven will cause it to burn more fuel or even worse result in an uneven bake as flunctuating draught conditions results in variable burner output.

Installing a heat exchanger into the chimney from the oven creates a resistance in the flue and as it cools down the flue gases it makes the natural draught practically impossible.

Even without a heat exchanger, the variation of natural draught will have a negative effect on the energy performance of the oven. Burner performance, in terms of optimal combustion and flame conformity, is essential for high efficiency.

There is a solution!An exodraft flue gas heat recovery system can ensure that the needed draught is available to ensure energy efficient baking results every day throughtout the year irrespective of any external influences or changes in the required output.

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exodraft fanThe purpose-designed exodraft chimney fan modulates the speed to maintain the optimum pressure in the flue for the ovens whether the system is in bypass mode or in heat recovery mode. The exodraft fans are heat resistant up to 250 °C on continuous operation.

The controllerThe EBC is an “on-demand” controller that maintains a precise draught by constantly monitoring the pressure in the flue for the burner and signaling the fan to adjust the speed ensuring a constant and optimum pressure level for the bakery ovens.

The XTP sensorThe XTP sensor reads the pressure and signals the EBC controller to obtain constant optimum pressure in the flue for the efficient operation of the ovens.The dampers

The EKG Dampers are used for balancing the air from fume vents.

How it works

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Heating

Cooling

Hot water

Steam/proofing

The heat exchangerThe heat exchanger allows for selective heat extraction from bakery ovens and their flues. When no heat is required from the system, you are able to bypass the heat exchanger. Usually 10-15% of the heat from the oven extract can be recovered, thereby saving energy.

The XTP sensorThe XTP sensor reads the pressure and signals the EBC controller to obtain constant optimum pressure in the flue for the efficient operation of the ovens.

Many possibilitiesThe exodraft chimney draft system can be used in different configurations for bakeries:

y To achieve a constant and optimum pressure in the chimney for single bakery ovens or for multiple bakery ovens connected to one chimney stack.

y To achieve design flexibility in the flue/chimney system.

y In connection with a heat exchanger to provide heat recovery and optimum performance of single or multiple bakery ovens.

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The exodraft chimney draft system is a well-tested concept in mechanical venting of commercial boilers and water heaters. The princi-ple has been transferred to industrial bakery ovens.

An important point which is often not appreci-ated about any type of heating system is that the flue has not only to exhaust the waste gas to the atmosphere, but also to provide a stable operating pressure at the oven flue outlet, often under vari-ous levels of loading, to ensure that the air ratio to the combustion is optimal.

The exodraft chimney draft system guarantees the pressure is kept at the required level at any given time - irrespective of changes in heat loads or external influences.

A stable and optimum pressure in the flue and chimney increases the efficiency of the oven, the performance of the bakery oven and allows for consistent baking results, independent of weather conditions, amount of piping or flue diameter.

Even without utilizing the saving possibilities of a heat exchanger, a stand alone exodraft chimney draft system offers great opportunities to save energy and waste.

Controlling the draught

7Design flexibility and cost savings in new installations

y No need for individual flue gas chimneys. y Long horizontal flue runs are possible. y Flexibility of design allows for placement of ovens where you want them and

placement of chimneys where you want them. y The height of the chimney can be reduced if needed, improving the

aesthetics of the building. y The chimney diameter can be reduced whilst guaranteeing the draught.

Minimal flue size = optimum utilization of floor space and dramatic reduction in the area of the roof being penetrated.

Reduce operating cost

y Modulating system keeps running costs very low. y High quality components ensure long life and low maintenance costs. y The only system that guarantees the energy efficiency of the oven whilst

recovering the heat. y Reduced waste due to even bake.

Enables heat recovery

y Savings of up to 15 % on heating costs can be made through heat recovery and mechanical draught systems.

y Recovered heat can be used for heating, cooling, a constant supply of hot water for cleaning or to preheat the water in the steam boilers thereby increasing the savings.

Enabling Quick Return On Investment

y Technology one of the focus areas in stage 2 of the “Industrial Energy Efficiency Accelerator” under Carbon Trust (Bakeries).

y Payback usually within 3-4 years depending on operational characteristics of the bakery.

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exodraft’s extensive product range is based on more than 50 years of experience and knowledge in the field of combustion and chimney draft technology.Our products are known for high safety and quality and we’re helping to set the standards and requirements for draft technology.

exodraft products are all fully documented in accordance with current national and international standards and are sold in more than 40 countries – to small domestic fireplaces in private homes to larger commercial and industrial boiler installations.

exodraft Ltd.Unit 3, Lancaster Ct., Cressex Business Park , GB-High Wycombe HP12 3TDTel: +44 1494 465 166, Fax: +44 1494 465 163, info@exodraft.co.uk, www.exodraft.co.uk

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Frequently asked questions

Is there a system for my bakery machine?There are exodraft Flue Gas Heat Recovery Systems available for every manufacturer’s bakery ovens and systems, new or old and the systems are suitable for all types of fuel.

What about the design of the system?Based on the oven type and size(s), the operational characteristics of the bakery and the flue design, the Flue Gas Heat Recovery System is calculated to match the exact requirements of the entire system.

Is the fan system heat resistant?The fan and the control technology can be used at temperatures of up to 250 °C. In the case of the special high-temperature version, the maximum temperature is 350 °C – in this case, it is not the temperature of the oven that is the relevant factor, but the temperature of the exhaust gases at the top of the chimney stack. This is usually approximately 60 % of the baking temperature. The temperatures are checked in all circumstances at the design stage.

Can I extract flue gases and baking fumes through the same stack?Technically you can collect flue gasses and baking fumes through the same stack, but attention must be payed to the content of the baking fumes in order to prevent a build up of oils and acids. This also depends on the local customs regarding recipes and breads being baked. In the UK it is widely concluded that it is safest only to recover from the flue gases.

How do I clean the system?The fan unit is equipped with a fully hinged cover for simple maintenance and cleaning. The heat exchanger is easily opened and is cleaned by means of high pressure water.

What about fat and oil in the flue gases?If needed, we use our grease fans expecially designed for easy discharge of oil through the bottom of the fan.

What happens if the system breaks down?The exodraft Chimney Fans are extremely safe to operate and breakdowns are very rare. If a breakdown should occur, the burner is switched off by the fail-safe mechanism built into the automated control.

The installation of a bypass fan in the top of a parallel chimney can be done to ensure constant operation in case of fan failure.

In the unlikely event of overheating the water vessel, the overpressure valve will bring the steam or hot water out of the system.

Where have these systems been installed?The last 3-5 years have seen a dramatic increase in installations in single oven bakeries and multiple oven bakeries, primarily in Mainland Europe.