Cleaner production in bread making

Buttercup Bakeries

By collaborating with a major tertiary research institution, RMIT University, Buttercup Bakeries has been able to apply new heat recovery technology suitable for bakery and other industrial applications. The initiative has resulted not only in cost and energy savings but more efficient oven heating boiler operations.

Background

Buttercup Bakeries is part of the Goodman Fielder Group of Companies, a major Australian conglomerate. Buttercup employs 5,000 people, operates 30 bakeries around Australia and produces 30 percent of the country's bread.

Bread production at Buttercup Bakeries in suburban Melbourne

Commercial bread baking generally involves a process called ëproofingí. In this process, loaf sized steel moulds containing the bread dough, pass through a low temperature proofing oven, triggering the yeast and other ingredients and making the dough soft and fluffy. The dough then passes through another very much hotter baking oven.

The temperature of the proofer oven is generally about 40 degrees Celsius with a relative humidity of 70-80 percent. Heat required for this part of bread baking is typically produced using steam from gas fired boilers. This is a high energy consuming and expensive way of heating the proofing oven. The energy consumption of a small size proofer at Buttercup Bakeries is about 5GJ per day (for one shift only) or almost 2000GJ per year. The cost of producing this heat using natural gas is about $10,000 per year. If oil or LPG were used the cost would be about $30,000 a year.

Loaves of bread are baked in the main oven at temperatures of 300 to 400 degrees Celsius. Excess oven exhaust gases are released into the atmosphere as wasted heat.

Buttercup realised their Clayton bakery in Melbourne was wasting exhaust gases from one oven and generating costly heat for another but was unsure as to how to overcome the situation.

Schematic of the oven and proofing oven with the heat pipe heat exchanger ducting systems

The company decided to collaborate with the Royal Melbourne Institute of Technology (RMIT) University in the development, installation and evaluation of a heat pipe waste recovery system to recycle wasted oven heat.

The RMIT group had developed considerable expertise in heat pipe heat exchanger technology and were in a position to demonstrate the suitability of heat exchangers to the Clayton bakery situation, notably good heat transfer characteristics, compactness, no moving parts, and no cross-contamination between fluid streams.

Heat pipes are devices which provide effective heat transfer. They operate by evacuating air and replacing it in part with a fluid such as water. When hot exhaust gases from the baking oven come in contact with the pipe containing the liquid, the liquid first boils and then condenses in cooler parts of the pipe, thereby transferring energy as latent heat. The heat extracted is fed directly into the proofer oven, conserving energy while providing air free of contamination.

The temperature range of the baking oven's flue gas ranges from 300 to 350 degrees Celsius. The waste heat available ranges from 70-80kW and the proofing oven requires energy between 20-45kW. With an air velocity for the system of 1. 5 metres per second and an heat exchanger effectiveness of around 65 percent, the waste heat recovery system was able to supply all the heat needed by the proofing oven, thus eliminating the need for any natural gas heating.

The predicted annual waste heat recovery from one eight hour shift working six days a week is estimated to be around 500GJ.

Buttercup's heat exchanger was manufactured locally from steel pipes charged with distilled water. The RMIT research team supervised the manufacturing process to ensure that the equipment would withstand the high temperature and corrosive environment of the baking oven's exhaust gases.

The total cost of manufacturing and constructing the 50kW prototype heat exchanger, excluding data monitoring operations, is estimated to be about $10,000.

Based on annual saving of 500GJ per year for one shift, cost of natural gas at $4 per GJ, and boiler efficiency of 70 percent, the pay back period is less than 3.5 years. For a three shift operation, the pay back period is reduced to 1.5 years.

Additional benefits resulted from the more efficient operation of the boilers in terms of lower steam requirement, less water to steam off, less gas used, less water treatment, and less maintenance on the boilers.

Following the success of the project at its Clayton plant, Buttercup has decided to install a second heat pipe heat exchanger system in a new baking plant just completed. This second heat recovery system employs a new arrangement - called a "split heat pipe heat exchanger" - in which the evaporator and condenser coils are located some distance apart, and connected with sections of heat pipes. This arrangement reduces the cost and complexity of ducting that would otherwise be required.

As part of the Goodman Fielder Group of Companies, Buttercup Bakeries is committed to pursuing an active program of cleaner production.

The initiative was made possible through the expertise and involvement of the RMIT. Collaboration was conducted under a major R&D project aimed at developing heat pipe exchange technology for industrial heat recovery applications.

Buttercup has plans to apply heat recovery technology using heat pipe exchangers to the companyís 30 other bakeries nationwide.

A barrier to the installation of heat pipe heat exchanger systems for heat recovery may be the very short payback period many companies seek on such investments (often less than two years). The payback period will vary from installation to installation, but in the present case the two year target is achievable provided the plant is operated for a sufficient number of shifts.

Mr Paul Matthews
Metro Engineering Manager
Buttercup Bakeries
18-52 Rosebank Avenue
CLAYTON VICTORIA 3169
Ph: 61 3 9549 3205
Fax: 61 3 9548 4346

For technical information:
Professor Akbarzadeh
Royal Melbourne Institute of Technology
Dept of Mechanical Engineering
124 LaTrobe Street
MELBOURNE VICTORIA 3000
Ph: 61 3 9407 6079
Fax: 61 3 9407 6108

For information on the heat exchanger used in this case study, contact:
Mr Alan Davis
Crossle McKee Pty. Ltd.
6 Capital Drive
Dandenong VICTORIA 3175
Ph: 61 3 9793 2588
Fax: 61 3 9794 8169

Heat pipe innovations at Buttercup Bakeries were published as IEA/OECD CADDET (Centre for the Analysis and Dissemination of Demonstrated Energy Technologies) Energy Efficiency ëResultí No. 277, March 1997.

Case study coordinated by the Environment Management Industry Association of Australia (EMIAA), May 1998.

The Cleaner Production Case Studies Directory is part of EnviroNET Australia.

For more information contact:

Environment Australia
Environment Protection Group
PO Box E305
KINGSTON ACT 2604
AUSTRALIA
Email: cproduction@ea.gov.au
URL: http://www.environment.gov.au/net/environet.html