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Direct Gas Fired Ovens

 

How to build a biscuit oven

Front Cover new

Publishing date to be announced

Description

The book enables a small team to build high quality Direct Gas Fired ovens. The Baker Pacific team of five engineers have manufactured a range of ovens for biscuits, crackers, cookies and cake with local contractors in China, India and Indonesia. Our experience, technical information and drawings are now available for companies who wish to build Direct Gas Fired biscuit ovens.

Our book describes the complete oven building process with photos, assembly drawings and parts lists, together with descriptions of the work in 15 stages.

In addition Baker Pacific can supply a complete set of manufacturing drawings together with all detail technical information and support.

This will allow small teams in biscuit bakeries and contract engineering companies to build ovens locally. The ovens can be built in a low cost environment with minimum shipping cost and requirement for hard currency.

Key features

  • Description of each stage of building and installing the oven with photos
  • All main assembly/layout drawings
  • All parts lists
  • Key component specifications and suppliers
  • Detail oven specifications

Readership

Senior management staff and engineers in contract engineering companies, biscuit manufacturers and companies supplying production and baking equipment in the food industry world – wide.

Author                                                                  

Iain DavidsonPhoto - Iain 1

Iain graduated from the School of Industrial Design (Engineering) at Royal College of Art in London in 1965 and joined Baker
Perkins Ltd. He was Industrial Design Engineer, working in the Technical Department on the design of new biscuit and bakery processing machines until 1975, gaining a thorough technical knowledge of the machines and processes.

In 1975, Iain was appointed Market Development Manager at Baker Perkins, involved in developing the Baker Perkins forward planning for new business, product development and acquisitions. In 1979 Iain became International Sales Manager with responsibility for the business in Asia and Africa.

In 1990 Iain was appointed Regional Manager Asia Pacific for Baker Perkins and re-located to Indonesia and later in 1997 to China. His appointments included Managing Director of Baker Perkins (Hong Kong) Ltd. and Director of Baker Perkins Japan KK.

Iain established a successful manufacturing facility for biscuit ovens in Dalian, China in 1990 for Baker Perkins and subsequently continued a manufacturing capability for Baker Pacific Ltd. in China, India and Indonesia.

Baker Pacific companies

Iain established PT Baker Pacific Mandiri in Indonesia in 2000. As the business outside Indonesia grew, Baker Pacific Ltd was established in Hong Kong in 2004 and is now our principal operating company, providing process technology and machinery for the biscuit, chocolate and candy industries.

Experience in the biscuit industry

  • Engineering design of biscuit process machines including a range of baking ovens
  • Biscuit baking oven manufacture in China, Indonesia and India
  • Sales and marketing in Europe, Asia, North America, Africa
  • Project management and service

 

Price for additional drawings on application to Baker Pacific Ltd.

To order or for more information:

Contact Baker Pacific Ltd. at our Contact Page or by email to: bakerman@bakerpacific.com.hk

Table of Contents

1. Why build a biscuit oven?                                Page 1

1.1 Growing world-wide market for biscuits

1.2 Limited number of suppliers

1.3 Biscuit oven manufacture

1.4 Biscuit baking process

1.5 What is required?

2. What type of oven?                                                      7

3. Heat transfer and heat ratings                              10

3.1 Heat transfer

3.2 Radiation

3.3 Conduction

3.4 Convection

3.5 Oven designs

3.6 Heat rating

3.6.1 Crackers

3.6.2 Short doughs

3.7 Multi-purpose ovens

4. Direct Gas Fired Oven specifications                 18

4.1 Oven output

4.2 Calculation of oven zone lengths

4.3 Calculating the number and type of burners

4.4 Recommended burners

4.5 Technical specification for a multi-purpose oven

4.5.1 Oven feed end

4.5.2 Direct Gas Fired Oven 89.9m long, 7 zones

4.5.3 Direct Gas Fired burners and gas system

4.5.4 Automatic temperature control

4.5.5 Oven band

4.5.6 Oven band cleaner

4.5.7 Delivery end section

4.5.8 Emergency drive

4.5.9 Oven end extraction hood

4.5.10 Control panels

4.6 Oven safety systems

4.6.1 Oven band

4.6.2 Ignition

4.6.3 Purge system

4.6.4 Over temperature

4.6.5 Power failure

4.7 Electrical installation

4.8 Components

4.9 Finishes

4.10 Spare parts

5. Selecting the oven conveyor band                    28

5.1 Products

5.1.1 Crackers

5.1.2 Semi-sweet biscuits and short doughs

5.1.3 Cookies

5.2 Open wire mesh bands

5.3 Compound balanced weave belts (heavy mesh)

5.4 Steel bands

6. Purchasing and Shipping                                      33

6.1 Purchasing

6.1.1 Contractors for fabrication

6.1.2 Purchase of specialist components

6.2 Shipping

7. Manufacturing drawings                                    41

7.1 Design layout drawings

7.2 Oven construction

7.2.1 Modular construction and build on site

7.2.2 Manufacture and installation of the oven

7.3 Drawing numbers

7.4 Parts lists

7.5 Electrical drawings

7.6 Control panel fascias

8. Construction of the Direct Gas Fired Oven     52

8.1 Stage 1: Oven base structure

8.2 Stage 3: Baking chamber slides

8.3 Stage 4: Baking chambers

8.4 Stage 5: Crown sheets, explosion panels, extraction

8.4.1 Explosion panels

8.4.2 Extraction ducts

8.5 Stage 6: Frames for outer covers and fan supports

8.6 Stage 7: Clean out and inspection doors, wall sheets

8.6.1 Clean out doors

8.6.2 Inspection doors

8.6.3 Oven insulation

8.7 Stage 8: Extraction fans and dampers

8.8 Stage 9: Air header pipes

8.9 Stage 10: Gas header pipes

8.10 Stage 11: Outer covers for control side

8.10.1 Outer covers

8.11 Stage 12: Gas burners

8.11.1 Eratec MFB burners installation

8.11.2 Burner specification

8.11.3 Flynn burners and gas system

8.12 Stage 13: oven roof sheets

8.13 Stage 14: Outer covers on non-burner side

8.14 Stage 15: Oven extensions

9. Oven conveyor construction: feed/tension end  102

9.1 Oven band circuit

9.2 Conveyor feed / tension end

9.3 Feed end unit: Final assembly

9.4 Oven end drum and shaft assembly

9.5 Drum bearing and mount assembly

9.6 Oven feed end frame assembly

9.7 Pneumatic tension assembly

9.8 Plough assembly

9.9 Drum scraper assembly

9.10 Oven band tracking: band wander warning

9.11 Oven feed/tension end covers

10. Oven conveyor construction: delivery/drive end  125

10.1 Delivery/drive end arrangement

10.2 Drive end frame

10.3 Delivery end drum

10.4 Bearings, sprockets and drive train

10.5 Motor and gearbox

10.6 UPS Uninterruptible Power Supply

10.7 Stripping knife

10.8 Stripping conveyor

10.9 Drum scraper

10.10 Drive end band wander warning

10.11 Delivery end outer covers

10.12 Oven end hood design

10.13 Calculations for oven band drive

10.13.1 Calculation of oven band tension

10.13.2 Calculations of torque required for drive

11. Conveyor construction: oven bands                   159

11.1 Wire mesh bands

11.1.1 Skid bar supports

11.1.2 Return band supports

11.1.3 Wire mesh oven band cleaning

11.1.4 Wire mesh oven band tracking

11.1.5 Joining wire mesh bands

11.2 Compound balanced weave belts (heavy mesh)

11.2.1 Band support rollers

11.2.2 Heavy mesh band tracking

11.3 Steel bands

11.3.1 Steel band supports

11.3.2 Steel band tracking

12. Key Components                                                   180

12.1 Bearings

12.2 Burners

12.3 Clamping elements, chains, sprockets….

12.4 Electrical equipment

12.5 Electrical cable and trunking

12.6 Electric sensor and monitoring equipment

12.7 Fans and blowers

12.8 Gas equipment

12.9 Insulation and seals

12.10 Oven bands

12.11 Pneumatic equipment

12.12 Painting and coatings

12.13 Pressure switches

12.14 PLC equipment

12.15 Motors and gearboxes

12.16 Motors – DC

12.17 Thermocouples

12.18 Temperature controllers

12.19 UPS

13. Oven installation                                                    204

13.1 Factory layout drawings

13.2 Oven installation equipment

13.2.1 List of equipment required for the installation

13.2.2 Centre line

13.3 Oven installation

13.3.1 Installation stages

13.3.2 Stage 1: Oven support structure

13.3.3 Stage 3: Bottom oven sheets and slides

13.4 Stage 4: Baking chambers

13.4.1 Welding of the baking chambers

13.4.2 Installation of oven band supports

13.5 Crown sheets, explosion panels, extraction ducts

13.6 Frames for covers

13.7 Clean out doors, inspection doors

13.8 Extraction fans and dampers

13.9 Air header pipes

13.10 Gas header pipes

13.11 Outer covers, insulation, main air pipe

13.12 Gas burners and equipment

13.13 Roof sheets

13.14 Outer covers

13.15 Electrical installation

13.16 Oven band installation

13.16.1 Oven band tracking

13.16.2 Joining wire mesh oven bands

13.16.3 Joining compound balanced weave bands

13.16 4 Joining steel bands

13.16.5 Oven band cleaner

14. Disclaimer                                                                229

 APPENDIX: Operations and Maintenance Manual

_________________________________________________________________

 For more information:

Contact Baker Pacific Ltd. at our Contact Page or by email to: bakerman@bakerpacific.com.hk

LOGO 2014

 


 

 

 

 

Baking Process and Engineering Manual

A technical manual for senior technicians in the biscuit industry

 

282 pages including over 200 illustrations. Published in hard copy and e copy by Baker Pacific Ltd.

Engineering

  • Baking oven design and manufacture
  • Management of engineering and maintenance
  • Oven up-grades
  • Introduction of heat recovery system
  • Making and procuring spare parts

Production

  • Improved operation and maintenance
  • Oven efficiencies / reduced production cost
  •  Improved reliability / less downtime

Purchasing

  • Smart buying: oven designs, specifications, controls
  • Contracts: performance guarantees
  • Purchasing of spare parts and  components
  • Directory of  suppliers, including Asian manufacturers

A comprehensive manual that supports the principal activities of

purchasing, production and engineering, providing the basis for training

programs for all levels of management and staff

CONTENTS                                      Pic 1

1  The Biscuits

2  Baking Process

3  Biscuit Design and Output

4  Heat transfer

5  Oven designs

6 Oven specifications: hybrid ovens

7.1 Oven construction: Direct Gas Fired Ovens

7.2 Oven construction: Indirect Fired Ovens     Pic 2

8  Oven conveyor bands                      

9  Oven conveyor design

10 Oven control systems

11.1 Oven operation: Direct Gas Fired Oven

11.2 Oven operation: Indirect radiant Oven

12 Oven maintenance

13 Oven inspection and audit

14 Oven efficiency

APPENDIX 1: Combustion data

APPENDIX 2: Oven manufacturers

APPENDIX 3: Oven band manufacturers

APPENDIX 4: Key components

 

 

 

 

 

 baking by infrared

 

To order for the special price of USD 199.00 please request at our contact page

LOGO 2014

Training courses

Baking process and engineering – baking by infrared

  Individual company programs 

Button    The training programs are designed to suit each company’s requirements. Especially valuable for production management, engineering, maintenance staff  and oven operators.

Button    The programs include class work with Power Point presentations, discussion and  questionnaires. The training may also includes on-site training by our senior engineer. This can cover trouble shooting, oven operation, maintenance, planning oven up-grades and efficiency improvements

Button    Normally 2 – 3 modules are presented each day and the complete course is delivered in a 5 day week

Button    Each of our technicians has over 35 years experience as engineers in the biscuit industry in factories in Europe, Asia, North and South America

Post fig 1

 

 

 

 

 

Baker Pacific oven installations baking by infrared radiation

Training Modules

Complete course in one week

Day 1   Introduction / the biscuits / baking process / biscuit design and output

Day 2   Heat transfer / oven designs and specifications

Day 3   Oven bands and conveyor design

Day 4   Oven control / safety systems / oven operation

Day 5   Oven maintenance / inspection and audit / oven efficiency / heat recovery

 

Our training program has exclusive information on:

Button   All types of oven designs / direct and indirect fired / radiant / convection / re-circ ovens

Button   Specifying ovens for different applications for biscuits, cookies and crackers

Button   Setting standards and guarantees for suppliers

Button   Oven bands: types, tracking, cleaning, supporting on skids and rollers

Button   Oven efficiencies with actual data from trials

Button   Energy usage and energy loss

Button   Heat recovery system to save capital and operating costs

Button   Oven operation and maintenance

Button   Oven inspections and audits

 500 Power Point presentation slides

Post fig 2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Complete course given by a senior Baker Pacific engineer USD 4,500.00

(excluding travel and living expenses)

Alternative: complete course materials for in-house presentations USD 240.00

To order please contact Baker Pacific at bakerman@dircon.co.uk

 

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Crackers………………………..

Successful crackers from Europe, USA and Asia………………..

Cracker baking

A wide range of products characterised by crispy, open texture and savoury flavours. Crackers include soda and saltine crackers, cream crackers, snack crackers, water biscuits, puff biscuits, maltkist (sugar topped cracker), “TUC” type, “Ritz” type, vegetable crackers.

In general crackers may have some of the following features which influence the baking process:

  • Doughs which are leavened and fermented with ingredients such as yeast, ammonia and sodium bicarbonate
  • Doughs generally have a high water content (15 – 25%)
  • Cracker doughs are laminated, (the dough sheet is made up from multiple thin layers)
  • Cracker doughs spring or lift in the first part of the oven to achieve the open, flaky texture. This requires humidity and high heat input.
  • Some crackers are baked in strips or complete sheets and broken into individual products after baking
  • Some crackers require a colour contrast between dark blisters and a pale background colour
  • Traditional English crackers such as cream crackers and water biscuits are normally baked on light wire-mesh bands
  • Traditional American crackers, such as soda or saltine are baked on heavy mesh oven bands which are pre-heated to transfer heat rapidly by conduction into the dough pieces
  • Crackers are baked to low moisture contents (1.5% – 2.5%), which requires a high energy input

 

DGF oven

 

Baker Pacific Direct Gas Fired Oven for cracker baking 

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Heat Recovery System

The Heat Recovery System (HRS) uses the waste heat from the burner flues. This may be used to heat one or two final zones of the oven. These zones would not require burners, giving a saving in capital and running costs.

All gas burners draw in a large amount of air for combustion. 1.0m3 of gas requires 3.0m3 of oxygen, (approximately 15m3 of air) for complete combustion. This air is exhausted through the extraction system of a direct gas fired oven and through the natural draught burner flue of an indirect oven. The hot air and burnt gas in the burner flues of an Indirect Radiant oven are at a high temperature, typically up to 200oC in the first zones and this hot air can be recovered and used for baking in a Heat Recovery System.

A proportion of the hot gases in the burner flues are diverted to an HRS collection pipe which runs along the top of the oven. Hot gases are collected from each zone with a burner. The hot gases are drawn along the collection pipe by a fan and blown into radiant ducts in the final oven zone.

 

HRS oven 2

 

The HRS zone is constructed with radiant ducts above and below the oven band. The hot gases recovered from the burner flues are fed by the fan to the ducts. The fan is located on top of the oven at the end of the collection pipe.

Oven efficiency with Heat Recovery System

Independent tests were carried out on 3 ovens in the same factory producing identical rotary moulded biscuits with the same baking time. The tests measured the oven efficiency by calculating the energy usage (gas) in kWh (kilowatt hours) to produce one kilo of baked biscuit.

 

Oven efficiency table

 

The Baker Pacific Indirect Radiant oven was 18% more efficient than the DGF/cyclotherm oven and 6% more efficient than the DGF/convection oven. The savings in gas consumption per 8 hour shift (23 tonnes of biscuits) are approximately 212 m3 of gas compared to the DGF/cyclo and 62 m3 compared to the DGF/convection ovens.

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Baked potato snacks

Production process

“Baked not fried” has become an established healthy, low fat choice for consumers in many markets. Potato snacks and crackers are baked with infrared radiation on Direct Gas Fired ovens or hybrid DGF/Indirect Radiant ovens.

DGF-IR oven

Baker Pacific Direct Gas Fired / Indirect Radiant oven

The production process for potato snacks follows that for crackers and wheat based snacks quite closely. With some modification, cracker lines can produce baked potato snacks in addition to potato crackers.

Potato crackers from Khong Guan, Indonesia                           Potato snacks from Walkers, UK

The ingredients for baked potato snacks may be mixed on continuous mixers or on horizontal high speed mixers with suitable modifications or on plough share type mixers with bottom discharge. All the dry ingredients are blended, fat is added and finally water is added. Horizontal high speed mixers require a steam jacket and suitable modifications to the bearings and seals. The dough is heated during mixing to gelatinise the starches.

HS mixer

 

 

 

 

 

 

 

 

 

APV Baker High Speed Mixer

The dough is sheeted and gauged to produce a dough sheet of approximately 0.75mm thickness. Potato doughs are tough and require heavy duty forming equipment. The robustness and accuracy of the gauging equipment is critical as variations in thickness of the snacks will cause variations in colour after baking. Achieving the minimum variation in thickness requires large diameter gauge rolls, 400mm diameter and these may be of solid construction to minimise deflection.

gauge rolls

 

 

 

 

 

 

 

 

Heavy duty gauge rolls from Baker Perkins

 

Ripple snacks are formed on a final gauge roll unit, which has grooved rolls, which intermesh to form the ripple in the dough sheet. By using one plain and one grooved roll, other forms such as hollow flutes can be made. These rolls only form the dough sheet and do not alter the thickness. When making plain products the ripple roll gap is opened to allow the product to pass through without ripples.

Pic 5

 

After gauging, the snacks are cut by a rotary cutter. The scrap dough is lifted and may be milled before returning to the mixer. Cracker doughs which have a strong, extensible dough sheet may be returned to the sheeter.

Triangle snacks

 

Potato snacks are baked on pre-heated Z47 type wire mesh or heavy mesh oven bands, such as Ashworth CB5. The ovens require high radiant heat and may be either a Direct Gas Fired (DGF) oven or hybrid DGF / Indirect Radiant oven. Convection ovens are unsuitable as the convective air will disturb the very light snacks on the band and will cause snacks to be blown off the band. Baking times are of the order of 4 minutes and the output of a 1.0m x 40m oven will typically be around 500kgs / hour.

About - ovens

Baker Pacific Radiant oven baking by infrared radiation

The snacks are conveyed directly to the oil spray and flavour applicator. The flavours may be added to the oil and the slurry pumped through the oil spray. This method has the disadvantage of possible blockages and increased cleaning time, particularly where more than one flavour is applied on the same line. The alternative is to use a flavour applicator after the oil spray machine. The flavour is metered on to the snacks while they are agitated in a rotating drum. After flavouring the snacks are cooled and conveyed to packaging.

Storeveyor

 

 

Storeveyor for potato chips from Gough Engineering

Packaging is usually a vertical Form fill seal pack, but may also be a block bottomed bag or a bag in a box.

Crinklys - Walkers packs

Crinklys potato snacks from Jacobs and Walkers Baked from UK

 

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Oven efficiency

OVEN EFFICIENCY                                                                       

Energy use

We are concerned not only to bake high quality biscuits, but also to achieve the lowest cost per kg of baked product. We need therefore to consider the amount of energy required by the oven. As energy costs increase in almost every country, the efficiency of the oven is of growing importance. In certain countries such as India, fuel is very expensive and represents an important element of the total production cost.

The energy used by the oven is predominantly from gas or oil fuel. Electricity is rarely used for baking now, due to its high cost. In a gas/oil fired oven the fuel represents around 95-96% of the total energy usage and electricity (for powering the drive, fans and other electrical systems) about 4-5%.

The energy input to the oven is used primarily to bake the biscuit, to achieve the structure, reduce the moisture content by evaporation and to colour the biscuit. Each type of biscuit requires a certain amount of energy to achieve a good quality result. In the example we will use, a typical rotary moulded product requires 0.2120 KWh (182 kcal) of energy per kg of baked product.

In addition to the energy required to bake a good product, energy is lost in several ways:

  • By extraction of moist air from each oven zone
  • By heat loss through the insulation and outer covers of the oven
  • By the return circuit of the oven band
  • By heat loss from the heater module or heat exchanger

In order to minimise the heat loss, (wasted energy), we need to pay attention to the extraction system to achieve the final moisture content required, without excessive waste of heat from the burners, insulate the baking chamber adequately and also insulate the return band, particularly where the band temperature is high, for example when baking crackers.

In the following energy calculations, we will just consider the energy from the gas or oil fuel.

 

Example                                                                                          

The following calculations of the energy balance of an oven are taken from an actual installation. Details of the product and the oven are given below, so that different data for other ovens can be substituted to make calculations of energy use accordingly.

Product                                                              

Rotary moulded biscuit

Dimensions:                58 x 37mm

Weight:                       5.1 gms

Baking time:                3.8 mins

                

Oven

Baking chamber:         1.25 x 100m

Zones:                          8 (7 burners)

Oven band:                  8.25 kgs/m2

Extraction fans:           34 m3/min (maximum)

Oven output:               3,200 kgs/hr

 

Data from independent test results

Total energy used by the oven:          0.4043 KWh/kg of baked biscuits

Of this, the energy required to bake the product to the required quality:  

                                                                  0.2120 KWh/kg of baked biscuits

Waste energy:                                      0.1923 KWh/kg of baked biscuits


Product

The total energy requirement to bake the product is 0.2120 KWh/kg of baked biscuit

This gives a total energy usage (gas) to bake the biscuit of:

3200 x 0.2120 = 678.4 KWh per hour

This is the energy utilised to bake the biscuit, form the structure, remove the moisture and colour the biscuit.

Latent heat of evaporation

An important element in energy use is providing the latent heat of evaporation. In order to evaporate the moisture in the dough (14 % by dough weight) to a final moisture content of 3.0% latent heat is required. The latent heat energy required to evaporate the water from the product is 539 cal/gm of water.

Moisture to be removed to reach final moisture content of 3.0%: 0.135 kg per kg of biscuits

Moisture to be removed: 0.135 x 3200kgs = 432 kgs per hour

Latent heat required to evaporate 432 kgs of water:

432,000 gm x 539 cal = 232848 kcal = 270.75 KWh per hour


Heat loss from extraction system from baking chambers            

Volume of air extracted from each zone

34m3/min x 60mins x 8 zones = 16320 m3/hour (maximum)

Estimated average extraction damper setting: 40%

Actual volume of air extracted from baking chamber = 6528m3/hour

The air extracted has been heated from ambient temperature over the oven (55oC) to an average baking temperature (200oC). This requires an energy input as follows:

Weight of the air extracted = 6528 x 0.746 kg = 4870 kgs

The energy required to raise the temperature of this air in the oven from 55oC to 200oC (145oC) is:

145 x 1.009 KJ/kg x 4870 kg = 712505 KJ = 198 KWh perhour

Energy required to raise the temperature of the water vapour from 100oC to 200oC

1.996 x 432 x 100 = 86227 kJ = 23.97 KWh perhour

Heat loss from extraction system per hour = 222 KWH

Specific heat of water vapour: 1.996 kJ/kgK

Density of water vapour at 100oC = 0.958

1 KJ = 0.000278 KWH


Heat loss from return band

Oven band drum centres:  111m

Band width 1.25m

Band weight: 8.20kgs/m2

Specific heat of carbon steel: 0.12kcal/kgo

Band temperature at delivery end: 140oC

Return band temperature at feed end: 105oC

(estimated temperatures)

Weight of band (on return circuit): 111 x 1.25 x 8.20 = 1137.75

Temperature loss: 140 – 105 = 35oC

Heat loss: 0.12 x 1137.75 x 35 = 4778.55 kcal (5.56 KWh) per revolution of the band

Bake time: 3.8 mins

Heat loss per hour: 5.56 KWh x 60/3.8 = 87.8 KWh


Heat loss from the insulation and outer covers of the oven:                              

 Oven baking chamber:                                  1.25m x 100m

Width over covers:                                          2.3m

Height of covers                                               1.23m

Average bake temperature:                        200oC

Average temp in heater modules:             350oC

Ave. outer side cover temperature:          55oC

Ave. outer top cover temperature:           55oC

Rockwool insulation thickness (s):            200mm sides and 250mm top

Rockwool thermal conductivity (k):          0.066 W/m.oC  

 

Heat loss from sides and top of the oven through the insulation

Heat loss = k A dT / s

Total area of oven sides: 100m x 2m x 2 = 400m2

This includes 7 heater modules and baking chamber sides

Area of heater modules on burner side: 13m2 x 7 = 91m2

Area of heater modules on non burner side: 2m2 x 7 = 14m2

Total area of heater modules = 105m2

Total area of oven sides (less heater modules) = 295m2

Heat loss from sides of baking chamber sections:

0.066 x 295m2 x (200 – 55oC) / 0.2 = 14116   W

 

Heat loss from heater modules:

0.066 x 105m2 x (350 – 55oC)/ 0.2 = 10222 W

 

Heat loss from top of oven:

0.066 x 100m x 2.3m x (200 – 55oC) / 0.25 = 8804 W

 

Total heat loss through the insulation of oven sides and top:   33.1 KW


Heat loss from radiation from oven delivery end:

Area of oven delivery end covers       6m2

Area of oven end hood:                      14m2

Total area                                           34m2

 Heat loss = ∑ σ   (Th4  – Tc4) A

∑ = emissivity

σ = 5.6703 10-8 (W m2 k 4) (Stefan Boltzmann constant)

T = absolute temp. (Kelvin)

A = Area m2

0.5 x 5.6703 x 10-8  x (298 x 108  ) x 34m2 = 28725 W

 Heat loss from radiation at the delivery end: 28.7 KW


Heat loss from burner flues

Total energy used: 0.4043 kWh x 3200kgs = 1294 KWh/hour

7 burners: average energy used per hour per burner = 1294/7 = 185 kWh

Gas consumption: 185/9.8 kWh/m3 = 18.9 m3 / hour per burner (average)

Gas/air volume required per burner: 18.9m3 gas + 301m3 air = 319.9m3

 Estimated average temperature of flue gases: 200oC

Gas / air weight at 200oC per burner = 319.9 x 0.746 kg/m3 = 239 kgs/hour/burner

Estimated energy in flue gases: 239kgs x 200 x 1.026 KJ = 49043 KJ

= 13.6 kWh /hour/burner

Estimated water vapour content of flue gases:  119.5 kgs /burner/hour

Energy required to raise the temperature of the water vapour from 100oC to 200oC

1.996 x 119.5 x 100 = 23852 KJ = 6.6 kWh /hour/burner

 

 Total heat energy in flue gases: 7 x (13.6 + 6.6) kWh = 141.4 kWh per hour

Of this 50% can be used in the Heat Recovery System

Specific heat of water vapour: 1.996 kJ/kgK

Specific heat of air: 1.026 kJ/kgK

Density of water vapour at 100oC = 0.958

Density of air at 2000C = 0.746 kg/m3

1 KJ = 0.000278 KWH

Combustion process: CH4 + 3O2 = Heat + 2H20 + CO2 + O2 (see Appendix 3)

Note 1: For complete combustion 10% excess air is required (this amount can vary considerably depending on the burner and heat exchanger design)

Note 2: air contains 20.9% oxygen


From calculations above, the energy consumption of the oven per hour:

For product:                                        678.4 kWh       50.6 %

Heat loss from extraction                   222.0               16.6 %

Heat loss from burner flues2              141.4                 10.5 %

Heat loss from return band:               87.8                   6.5 %

Est. heat loss of air from oven end:    75.0                   5.6 %

Est. loss from thro’ metal, fans etc.   75.0                   5.6 %

Heat loss through insulation:              33.1                   2.5 %

Heat loss from radiation:                    28.7                   2.1  %

Total                                                   1341.4 kWh    100.0%

Note 1: estimated accuracy in the assumptions and base data is +/- 5%

 Note 2: the heat loss can be considerably larger than given depending on the design of the heat exchanger and flue. Please see Appendix 3, “Combustion Analysis”.


 

     

  • The overall oven efficiency is 50%
  • Of the heat loss through the burner flues, up to 50% can be recovered and used for baking in a Heat Recovery System
  • In this Baker Pacific oven installation (picture below), the Heat Recovery System reduced the energy requirement by 15% (as calculated by an independent test) 

                 

            Indirect Radiant Oven with Heat Recovery System


Comparison of Oven Efficiencies

 Comparison of oven efficiency for different oven types

Product Oven type Oven size KWH/kg of biscuits
Snack cracker DGF/conv 1.2m x 90m 0.477
Rotary moulded DGF/conv 1.5m x 100m 0.441
Rotary moulded DGF/conv 1.2m x 60m 0.430
Rotary moulded DGF/cyclo 1.2m x 60m 0.492
Rotary moulded IR (cyclo) + HRS 1.2m x 100m 0.404
Rotary moulded IR (cyclo) 1.2m x 100m 0.475

 


 

 References

Armstrong Group, “Specific Heat – Specific Gravity”, www.armstrong-intl.com

J.S. Alakali and others: “Specific Heat Capacity of Palm Oil”; Dept. of Biosource Engineering, McGill Univ. Canada, Dept of Food Science, Unive of Agriculture, Makurdi, Nigeria

Y.S. Kim and others: “ Physical, Chemical and Thermal Characterisation of Wheat Flour Products”; Dept. of Bio. and Agriculture Eng. Kansas State Univ., USA

Sugar Engineers, “Specific Heat Capacity”, www.sugartech.co.za

Testo Inc:  “Combustion Analysis”: www.testo.com

“kW and kWh explained”                   www.energylens.com

“Thermal Conductivity”                      www.quats.com

“Thermal properties for water”         www.engineeringtoolbax.com

“Thermal properties for air”              www.engineeringtoolbax.com

“Food and Foodstuff”                         www.engineeringtoolbox.com


Heat transfer for baking

Three modes of heat transfer are used in baking biscuits: radiation, conduction and convection.

Heat transfer - ovens   

1. Direct Gas Fired / Indirect Radiant oven        2. Conduction from steel band          3. Convection oven 

 Radiation

All objects above a temperature of absolute zero radiate energy to their surroundings. This energy or radiation is emitted as electromagnetic waves which travel at the speed of light. The waves may travel through a vacuum or other medium. When they impact an object, they are partially absorbed and partially reflected. Good emitters are also good absorbers of thermal radiation.

Infra-red radiation is in the wavelength band of 0.7-300 microns (above visible light). Higher temperatures produce shorter wave lengths. Typical wavelengths in a radiant oven are around 4.6 – 6.4 microns, which provides good heat penetration of the dough pieces. Infrared radiation for baking is emitted principally by the DGF burner flames and by the radiant tubes in an Indirect Radiant oven.

Radiant tubes and burners

Radiant tubes in an Indirect Oven                                        High rate direct gas fired burners

The most important mode of heat transfer for baking is infrared radiation, which has the following advantages:

  • Penetrative heat transfer: Infrared radiation penetrates biscuit doughs by approximately 4mm, (depending on wavelength and moisture content). It is the only heat transfer mode to truly bake the product from the centre. This is the key advantage of baking by infrared radiation
  • Biscuit structure: because radiation penetrates the dough pieces, it is essential to achieving good structure with optimum volume and texture and is always the main mode of heat transfer in the first part of the baking process
  • Even moisture content: radiant baking ensures a low moisture gradient from centre to the outer surface of the biscuit. It is the best heat transfer mode to  avoid “checking” (cracks appearing in the biscuit after baking)
  • Efficiency: heating of the surrounding air in the baking chamber is not necessary, which lowers energy consumption
  • Colouring: radiation enables highlighted colour contrasts for crackers and rotary moulded products, whereas convection gives an overall, bland, even colour
  • Versatile: infrared baking is suitable for all types of biscuit

Conduction

Conduction transfers heat from the oven band directly to the base of the dough pieces. The heat transfer is dependent on the temperature and heat mass of the oven band and the surface area of the band in contact with the dough piece. With steel bands and heavy mesh bands this approximates to full contact and is very effective.

Ovens with band pre-heat can quickly transfer heat into the base of the dough pieces and achieve rapid development of the biscuit structure and texture; this is particularly valuable for cracker baking.

Convection

Convection baking uses hot air jets which impinge directly on the top of the dough pieces and the underside of the oven band. This system effectively dries and colours the surface of the dough pieces. However it produces a hard, dry skin on the dough pieces and will prevent good expansion and “lift” of the product if used at the start of the baking process. Also it is a cause of a moisture gradient between the surface (very dry) and the centre of the biscuit (more moist). This may result in “checking”, (cracking of biscuits after baking), unless the moisture gradient is reduced after baking.

Convection v Radiation v Conduction

 

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Key components – burners

 

Our key components file lists over 50 key components for biscuit oven construction. These components have all been used and proven and are recommended by Baker Pacific. The file for each component provides a picture, specifications and manufacturer’s details.

  1. Bearings
  2. Burners
  3. Clamping elements, chains, sprockets…….
  4. Control handles
  5. Electrical equipment
  6. Electric cable and trunking
  7. Electric sensor and monitoring equipment
  8. Fans and Blowers
  9. Gas equipment
  10. Insulation and seals
  11. Oven bands
  12. Pneumatic equipment
  13. Painting and coatings
  14. Pressure Switches
  15. PLC equipment
  16. Motors and gearboxes
  17. Motors – DC
  18. Radiant tubes
  19. Refractory
  20. Thermocouples
  21. Temperature controllers
  22. UPS

The complete Key Components file is available for USD 85.00 and may be ordered at our Contacts page.

Our second key component file includes oven burners for Direct Gas Fired ovens and burners for Indirect Fired ovens.

SECTION 2: BURNERS

 

Eratec

MFB burners (metal-fibre burners)

Eratec 1

 

Eratec high rate infra-red ribbon burners for Direct Gas Fired Ovens

  • Direct heat transfer by radiation (without contact and air movement)
  • High radiant power density 100 – 1000KW/m2
  • Precise control and power modulation
  • Energy consumption savings compared to conventional Direct Gas Fired Burners (up to 20% saving depending on the oven and number of burners)
  • Low pollution (up to 80% less CO and NOX)
  • Safe for people and equipment (no burn back)
  • Low maintenance

 www.era-tec.fr


Flynn Burners

 Flynn 1

 

Flynn Direct Gas Fired Burner installation

 

 

 

Flynn distributor

www.flynnburner.com


 Maxon burners

Maxon

Maxon dual fuel installation

Natural Gas Low Temp Burners

OVENPAK® 400 Series

MAXON’s OVENPAK® 400 Series is the world’s most flexible and reliable industrial burner. The OVENPAK® burns most any fuel gas and requires only low pressure fuel. This natural gas burner provides clean combustion with low NOx levels while providing unmatched turndown.

OVENPAK® Gas Burners provide outstanding performance in ovens and dryers, paint finishing lines, paper and textile machines, food baking ovens, coffee roasters, grain dryers, and fume incinerators.

www.maxoncorp.com

 


Mont Selas

 

Enviro Mont™ Burner

Mont Selas in conjunction with RMR Thermal Solutions have developed an Expanded Nitmesh Tube Firing Burner (patent pending) for use in tunnel baking ovens to replace the old industry standard ribbon burner, to achieve typical gas savings up to 25% *.

  • UP TO 25% GAS SAVINGS*
  • HIGH TURN DOWN
  • EASILY RETROFITTED
  • LOW MAINTENANCE
  • EXCELLENT FLAME STABILITY

Nitmesh is a woven metal fibre and is welded over the slot in the burner tube, it is well proven technology and has excellent flame retention properties and reduces the risk of flash back.

The Expanded Nitmesh burner can be supplied in 1¼”, 1½” and 2” sizes as direct replacements for existing ribbon burners with nominal ratings from 4kW to 44kW.

Burners are designed to work on natural gas or LPG on air blast, high pressure and atmospheric pre-mix systems and will operate with an air turn down ration of up to 8:1 (dependent on flame sensing safeguard limitations).

The improved efficiency of Nitmesh comes from the extra radiant heat provided by the hot surface of the Nitmesh material which can become incandescent, as opposed to the gas flame on a ribbon burner which provides only a limited amount of radiant heat due to its low emissivity. Most of the heat from a ribbon burner is provided by natural convection heating the oven roof area above the burner which then re-radiates the heat back to the product on the conveyor. For bottom burners the base of the conveyor will be heated by natural convection plus the additional radiant heat provided by the incandescent surface of the Nitmesh.

Burners supplied in varying lengths and sizes to suit your individual requirements.

We can also offer a comprehensive site installation service, and oven profiling, following installation to further improve on the operational efficiency of the oven and reduction of your carbon emissions. For further information and site visit to determine requirements please contact our Chadderton office.

*Subject to operational conditions.

Mont Selas

www.montselas.co.uk

 

 

Weishaupt

Weishaupt

Weishaupt natural gas burner installation on an Indirect Radiant oven

 

  • Exemplary efficiency: The digital combustion management system ensures that only exactly the amount of energy is consumed that is needed at the time.
  • Excellent emission levels: Weishaupt Low NOx technology (standard for gas burners, optional for oil burners) is exemplary in reducing emissions with special mixing assemblies for intensive flue gas recirculation
  • Sophisticated technology: All W range burners work fully automatically. Powerful microprocessors continuously control and monitor the combustion process for maximum efficiency.
  • Silent operation: The transversely mounted fan draws air through a sound attenuated inlet.
  • Versatility: The W range offers oil and gas burners in five ratings from 12 kW to 570 kW.
  • Long life: More than 50 years of experience and development work have gone into Weishaupt burner technology. Only the best materials are used in manufacture

www.weishaupt.co.uk


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