Biscuit ovens Industrial Services Process Version 1.0 Last update: July 2015 Table of Content GLOSSARY ............................................................................................................................................................ 2 AWARENESS ......................................................................................................................................................... 3 Some facts ........................................................................................................................................................... 3 Performance indicators to follow-up in DOR, WOR, MOR ................................................................................... 8 OPERATIONAL OPPORTUNITIES ........................................................................................................................... 9 O1 - Optimization of the temperature in the oven .............................................................................................. 9 O2 - Optimize the positioning of extraction dampers ....................................................................................... 11 O3 - Adjustment of burners ............................................................................................................................... 14 O4 - Baking conditions during unplanned/planned stoppages ......................................................................... 15 DESIGN IMPROVEMENT OPPORTUNITIES ........................................................................................................... 17 D1 - “Close the loop” sensor .............................................................................................................................. 17 D2 – Water recovery from ovens ....................................................................................................................... 18 D3 – Improving radiation oven heat exchange with fans .................................................................................. 19 TECHNOLOGICAL CHANGE OPPORTUNITIES ....................................................................................................... 20 No technological change opportunity has been shared so far. ......................................................................... 20 YOUR FEEDBACK ................................................................................................................................................ 20 Biscuit ovens Glossary BEX Baking Excellence is the name of a Cat 2 R&D lead project – Process Development. Inspection hatches Inspection doors. QMS Quality Management System - QMS model for biscuits : MI 33.727. Baking curve For baked goods to develop in the expected way, achieving the expected temperature colour, the product temperature in the oven needs to follow a temperature profile curve, unique to each product, which we call the “baking curve” for that product. 1 Example of Baking Curve Extraction profile Inside the oven, the product moisture evolves following a curve, unique to each product, which we call the “extraction profile” for that product Up/down heat Refers to the temperature distribution between the top and bottom of the balance oven. PID A proportional-integral-derivative controller (PID controller) is a control loop feedback mechanism, widely used in industrial control systems. A PID controller calculates an error value as the difference between a measured process variable and a desired set point. 2 Biscuit ovens Awareness Introduction Baking is one of the Key Unit Operations in biscuit manufacturing and responsible for product texture development. Ovens for biscuits vary depending on type of fuel, number of zones, and heat transfer among others characteristics. Also, for a given product the possible settings of operational parameters such as temperature and moisture extraction rate may be a source of variation. Together, these factors make baking the most complex unit operation within biscuit manufacture. Within Nestle factories ovens can vary considerably. They have different age, manufacturer and configuration and normally the operation of an oven vs. another is not standardized. Also, over the years many ovens have been transformed in order to deliver necessary capacity increases. This means that critical settings have been defined by operators through trial and error and only by using external temperature controls as a guide. Maipu factory-Chile is a pilot to evaluate the potential in terms of improvements and energy savings since 2012. It was confirmed that an oven with basic conditions and optimized process parameters can save energy related to fuel consumption. Some facts Introduction Specific energy consumption can vary widely among different plants, and depends on the types of product manufactured and the condition of the equipment. Energy efficiency improvement is an important way to reduce these costs and to increase predictable earnings, especially in times of high energy price volatility. There are a variety of opportunities available at individual plants to reduce energy consumption in a cost-effective manner. Prerequisite: have basics in place Before optimizing the oven operation, it is mandatory to put the oven back to basic conditions. To know whether your oven can be considered in “basic conditions”, a pre assessment needs to be performed using BEX check list. 3 Biscuit ovens Energy users In a biscuit oven, the main energy users are: in a ovens Fuel (ex: gas) used in burners or electricity used in heaters Electricity to power the fans that circulate the air inside the oven and additional electrical devices, like drivers, lights. Steam (DSI) injected into the product for some products Compressed air for oven belt alignment (negligible) Conveyor cleaning is done by friction, using brushes. No water is used for cleaning. Gas and electric ovens have equivalent power, around 2,5MW per year, for an 89 m long oven with 5 zones. However, usually electricity price is much higher than gas, which makes electric ovens far more expensive to run. Oven description types Typical biscuit ovens will have up to 6 heated zones. Product is fed by a & panner onto the oven band which runs the full length of the oven in a single pass. In the first zone(s) heat is transferred to the product then evaporation of water takes place. Despite high temperatures, the product remains at the wet bulb temperature at this stage. The middle heated zone(s) set the structure of the product as the outer surfaces moisture is reduced, and the product is developing (growing) The next heated zone(s) add the color via toasting reactions, as well as finalizing the product moisture. In the final zones the temperatures are reduced to prevent over toasting of the outer surface of the product. Temperatures are controlled using modulating burners or heaters. Air flows for recirculation and exhaust are controlled with a combination of duct dampers and/or variable speed fans. Ovens can be classified according to the major type of heat exchange. There are 3 different types of oven: convection, direct and cyclothermic. 1. In direct ovens, the source of heat (like burners or resistances) is inside the chamber. Most of the heat exchange is done by radiation. (Fig. 1). Fig. 1 – One zone of a direct gas fired oven Continued on next page 4 Biscuit ovens Some facts, Continued Oven description & types (continued) 2. In convection ovens, the source of heat is outside the oven (normally in the top part) and most of the heat exchange is done by circulating air (convection). o if the products of combustion go into the chamber, it is a direct convection oven (Fig. 2). Fig. 2 – One zone of a direct gas fired convection oven o If the products of combustion are not in contact with products it is an indirect convection oven (Fig. 3). Fig. 3 – One zone of an indirect gas fired convection oven 3. Cyclothermic ovens work with heat transfer by radiation and are especially suited for the production of soft dough biscuits, cakes, bread and pastry. Fig. 4 – One zone of a cyclothermic oven Continued on next page 5 Biscuit ovens Some facts, Continued Impact of maintenance, basic conditions and training Compared to other products, like chocolate bars that do not require gas for their production, biscuits have a huge impact in terms of energy consumption. For example, one of Nestle biscuit factories which produce around 30.000ton/year consumes around 166.000 m3 of natural gas per month. (For comparison, a domestic oven consumes 14 m3 of natural gas per month.) A proper maintenance on ovens, optimized process adjustments and people play an important role to reduce gas consumption and resulting emissions to the environment. An optimization work concluded that if proper maintenance, basic conditions, and training for oven operators are established, the energy consumption could decrease by around 15%. Critical parameters In biscuit manufacturing, the baking curve temperature profile, extraction profile and up/down heat balance are critical parameters. If the settings are not optimized, it will generate losses. For example: when one zone has a lower temperature than required, another zone will have to overcome the deficiency in temperature; operating with extraction dampers open more than necessary generates heat losses through the chimney. During production if adjustments in heat balance are made in an inappropriate way the imbalance generates energy losses. In general, all these factors are linked and each of them must be well adjusted and integrated to avoid energy losses. Maintenance of temperature control devices Temperature sensors have to be calibrated and controlled by a well-adjusted PID to guarantee a minimum oscillation of the temperature curve. If not, the temperature is not reliable and burners may work on/off irrespective of the real requirement, which may result in an over energy consumption. Therefore, it is important to ensure proposer operation of the following : Temperature sensors Temperature controllers For that, put in place preventive maintenance, including : For temperature sensors: control electrical status and calibration. For temperature controllers: it is necessary to control signal to guarantee a proper PID adjustment (+/-1ºC variation during operation). For burners: it is recommendable to check the burners work accordingly to the temperature controller output every 6 months. Also, a proper flame characteristic is important to avoid energy losses (refer to solution O3 Adjustment of burners). Continued on next page 6 Biscuit ovens Some facts, Continued Maintenance of Burners The air used during combustion may contain contaminated particles that deposit in the internal pieces inside the burner. This situation can cause a combustion with lack of air and the following consequences: Environmental contamination Lower performance than expected for the burner Reduced temperature in the oven chamber Encrusting of particles in combustion chamber and on the heat exchanger, preventing a proper heat exchange There are two types of maintenance (all points described here should be in AMM): Preventive maintenance – It is suggested to perform it every 6 months. However, if during predictive maintenance the instruments are detecting out of norm parameters, the preventive maintenance should be done earlier. - Clean the burners and check if they don´t have any damage or missing parts. Predictive maintenance : - Using instruments to measure the function parameters as gas pressure, combustion air pressure, [CO] in the combustion gases and security electrical current. - Check visually the state of the flame and then perform the correspondent activity (replacement, adjustment) - Check the mix air/gas with proper equipment and adjust if necessary. Maintenance Each zone of convection ovens has a combustion chamber to generate heat of combustion within the zone. chamber Any crack or damage in the combustion chamber will imply loss of energy that can be equivalent to 20% or more. Additionally, dust on the burner system can also reduce the efficiency of the heat transfer. It is necessary to perform periodic checks in the amount of oxygen used by the burner to identify any losses. The following inspections must be performed: Visual inspections – Once a year it is necessary to disassemble the inspection hatches to check: – – If there are particles inside the combustion chamber and on the heat exchanger If there is any crack inside the walls of the combustion chamber and heat exchanger. If there is dust, it should be cleaned. If there are cracks, it is recommended to replace the combustion chamber. Continued on next page 7 Biscuit ovens Some facts, Continued Maintenance of combustion chamber (continued) Predictive maintenance – Normally combustion gases exhausted through the chimney have a percentage of oxygen between 4 to 5%. A higher value could indicate the presence of cracks or failure in the isolation of inspections hatches. The combustion gases should be inspected every 3 months An MI for oven maintenance is under development at R&D Santiago and will cover these points. The MI is planned to be published by July 2016. Maintenance The function of extraction dampers is to modulate the amount of humidity inside of Extraction each zone following the limits established in QMS. Dampers Adequate damper maintenance is necessary. Otherwise, the dampers could be difficult to operate manually by the operator and the flow of air going out of the chamber could be blocked by products of combustion and other deposits. An adjustment of the extraction speed needs to be in place to guarantee no condensation will happen inside the zone. Condensation can generate improper moisture content inside the oven to cook biscuits and energy losses (more heat used to compensate the additional moisture). It is necessary to do: Preventive maintenance – checking mechanical and electrical functionality of opening and closing movements and checking whether the speed of extraction is adequate each 6 months both for manual and automatic systems. Predictive maintenance – it is recommendable to check the dampers work accordingly the output controller by using electrical instruments. Sealing of combustion chamber Any crack or damage in the combustion chamber or heat exchanger eventually implies a large energy loss, equivalent to 20% or more. Performance indicators to follow-up in DOR, WOR, MOR Performance indicators at process level It´s important to track energy consumption on this process and here is a recommendation of performance indicators to be used: Gas consumption in the oven per ton of product GJ/tproduct Electricity consumption in the oven per ton of product kWh/tproduct Energy and For a complete overview of : water metering how to meter energy and water in a factory, at factory level and how to drive performance with performance indicators, please refer to the GI-254.05 ”Energy and Water metering”. 8 Biscuit ovens Operational opportunities Introduction Operational opportunities address the operational losses as defined in the “Loss categories” section of GI-254.06 Energy and water rating of key processes: Not Occupied losses Planned Stoppages losses Unplanned stoppages losses Speed Loss losses (energy & water losses due to the fact that the process is not working accordingly to nominal performance) Waste and rework losses O1 - Optimization of the temperature in the oven Industrial Services Do It Yourself Solutions for energy and water savings Opportunity identification Process Operational Design improvement Technological change Lack of maintenance, calibration and non-optimized baking profiles can generate more usage of energy (even 30% more), emissions and quality problems. The baking profile could be non-optimized for 2 reasons: The baking profile as input into the HMI is not optimized The baking profile as input into the HMI is optimized but the actual baking curve is different When the baking profile is not optimized, energy is wasted through application of heat at the wrong time and too much extraction at the wrong stage of baking. There is an opportunity to avoid a waste of energy by ensuring the correct temperature control (adjusted PID) and temperature baking curve. How to it/improve fix Follow the steps: 1. Baking profile : comparing actual vs QMS a. Verify whether the baking profile and temperatures set up in the HMI are the ones established on the QMS model for biscuits (MI 33.727). b. Use the Scorpion data logger to measure the actual oven temperatures and baking curve. Check if there are any deviations from what was defined in 1a. If your factory does not have the data logger, contact R&D Santiago to support the activity. 2. With QMS & Scorpion information, assess with support from R&D Mastership specialist how to get back to QMS parameters (time/temperature/moisture/humidity). See Maipu example below. Continued on next page 9 Biscuit ovens O1 - Optimization of the temperature in the oven, Continued How to estimate the energy/water savings? The energy savings consist in fuel savings: the right set up of the baking curve will avoid excessive temperature where not necessary and ensure the correct opening of the dampers, A biscuit oven model is under development by PTC Orbe, which will help understand the savings associated with this opportunity. Expected in Q4 2015. Project example On the following example, Maipu factory improved the baking curve by establishing basic conditions. The results can be evaluated on the final product (better hardness and moisture), see pictures below. Before improvement, the temperature curve is higher than required, resulting in over energy consumption. The moisture is trapped inside the biscuit because of formation of a crust on the outside due to excessive heat in the first zone After Improvement the temperature curve is a smooth progression with less total energy usage. The moisture is now extracted evenly through the baking process and is not trapped inside the biscuit Contact person Product Mastership Pillar, R&D Santiago At time of writing: Sandra Vaz 10 Biscuit ovens O2 - Optimize the positioning of extraction dampers Industrial Services Do It Yourself Solutions for energy and water savings Opportunity identification Process Operational Design improvement Technological change The main process requirement of the oven exhaust is moisture removal. Extraction dampers are located in the top part of each zone to guarantee an adequate moisture release from the product. Fig. 4 – Manual extraction damper A lot of heated excess air is exhausted through the dampers. By optimizing the extraction profile (damper opening), there is an opportunity to reduce the exhaust flow to reduce energy consumption while still meeting requirements. A possible sign of incorrect positioning or excessive opening of the damper is an extraction air temperature deviation (for example 20 or 30°C above set point). How to it/improve fix The project consists in defining the best opening of the extraction dampers considering product characteristics. Their positioning can be adjusted manually or automatically based on the electrical input. Two points should be considered in terms of extraction dampers and energy savings: 1- Define extraction damper opening to optimize moisture inside the chambers while minimizing heat losses. This optimization is especially critical in the last zones, where no more moisture extraction should take place. It is better to start this process at the exit zone of the oven and work towards the inlet. In some cases there may be limitations on entry zones as increased dew points will result in higher levels of condensate heat transfer and resultant condensation on the product surface that can cause product issues. Continued on next page 11 Biscuit ovens O2 - Optimize the positioning of extraction dampers, Continued How to fix it/improve (continued) The graph below shows an example of extraction profile: Average damper opening: Using the Scorpion data logger, it is possible to identify whether the moisture level in the oven is correct for each extraction zone. *Note: it is important to define the extraction profiles during the product development phase, and to make sure they are applied during operation. Example of incorrect moisture extraction profile Example of correct moisture extraction profile After identifying potential improvements on the graph, adjustments related to the extraction opening can be executed by production; otherwise, the technical department should be contacted to check engineering design of the zone. Continued on next page 12 Biscuit ovens O2 - Optimize the positioning of extraction dampers, Continued How estimate energy savings? Project example to The fuel savings are related to the reduced amount of extracted heat, thanks the to a proper extraction profile. As soon as the modelling tool developed by PTC Orbe and R&D Santiago is in place, it will be possible to have a good estimate of the savings. The modelling tool will integrate all components of the baking process including, time, conduction, convection, radiation, humidity, air extraction, air recirculation and biscuit moisture content to be able to predict energy savings through process modifications. The tool is expected to be launched by Q4 2015. R&D Santiago is working on project DCCB-103213 – BEX, which scope includes defining the best extraction profile to bake biscuits and evaluating impact in terms of energy savings. Trials were run on Line L8 at Maipú factory, including redefining baking and extraction profiles, as well as initiatives related to QMS and maintenance. The result was an important improvement of line efficiency and savings of around 142k CHF (approx. 47kCHF/month). Table 1 shows the evolution of efficiency, before, during trial and currently: Efficiency 77,0% 82,0% Losses 6,7% 3,5% 85,0% Contact person 2,0% Table 1 Product Mastership Pillar, R&D Santiago At time of writing: Sandra Vaz 13 Before trial During trial Currenty Biscuit ovens O3 - Adjustment of burners Industrial Services Do It Yourself Solutions for energy and water savings Opportunity identification Process All burners have a best way to operate taking into account the gas and air (oxygen) mix. If the mix is not adequate or if the burners are not working properly the energy consumption increases. Fig. 5 – Good flame (blue) How to it/improve Operational Design improvement Technological change Fig. 6 – Flame that needs adjustments fix Ensure that the flame from the burners is stiff and blue, by balancing the gas/air mixture to the gas mixer. The technical department should be involved in this procedure, and a qualified technician should do this work. No yellow flame should be observed. How to estimate the energy/water savings? The energy savings consist in savings on the fuel: by ensuring a proper functioning of the burners and the gas/air adjustment. This can be measured (gas consumption/kilogram biscuit) before and after the improvement. An MI for oven maintenance is under construction in R&D Santiago and will have all information to have this point under control. Project example No specific factory example: this is part of standard operating conditions. If your factory has implemented such a project, please share it with the contact below and the Energy team at CO-Engineering. Contact person Product Mastership Pillar, R&D Santiago At time of writing: Sandra Vaz 14 Biscuit ovens O4 - Baking conditions during unplanned/planned stoppages Industrial Services Do It Yourself Solutions for energy and water savings Opportunity identification How to it/improve Process Operational Design improvement Technological change Biscuit lines normally run during at least 6 days a week 24 hours during normal production. Like all lines technical or operational stoppages can happen during production in 2 ways: Planned: for example during lunch time or a packaging or product changeover Unplanned: non-expected stoppages due to un planned upstream or downstream stoppage. During these situations ovens remain working with the temperature defined in QMS and all the energy used at this moment is wasted. As no product is inside the oven there is an opportunity to reduce the temperature during stoppages and reduce energy consumption. fix Establish a procedure to reduce temperature and fan speed settings when no product is going through the oven. Determine the lowest reliably achievable temperature: Most oven burners will have sufficient turndown to achieve temperatures between 80 – 100°C. A trial should be undertaken to establish the lowest reliably achievable temperature, to avoid flame instability and burner lock out. Determine the time taken to recover to operating temperature: Similarly the time taken to recover to operating temperature should be checked with a trial, this time can have variation from oven to oven. Determine lowest fan settings achievable: Limiting factors will be safe operation of motors due to cooling, and minimum safe airflows, check with supplier if necessary. Create an SOP for procedure during line stoppage: A stoppage known to be in excess of the time determined above will warrant reduced temperatures or shutting down the oven. A procedure should be implemented in agreement with operations which gives consideration to any other production impacts. These adjustments are based on the temperature inertia and may vary between convection and radiation ovens. Each factory should evaluate the best solution (timings and temperatures). How to The energy savings consist in savings on the fuel: estimate the In case of stand-by mode: reduced temperature results in reduced fuel energy/water required. Close extractions reduces the hot air exhausted, and therefore savings? the fuel needed to heat it. Saving calculation is explained in O1 Optimization of the temperature in the oven and O2 - Optimize the positioning of extraction dampers In case of switching off the burners: the savings is the amount of fuel that would have been used in case burners hadn’t been switched off. This can be measured (fuel consumption during this time). Continued on next page 15 Biscuit ovens O4 - Baking conditions during unplanned/planned stoppages, Continued Project example This project will be implemented as part of BEX project DCCB-102323 in line 8 Maipu factory and then replicated to other lines and factories. It is planned to be finished by Q3 2013. Sharing of the results is planned for the Oven Workshop Q4 2015 – Marília Factory. Example from an oven in line L8 –Maipu factory: The energy consumption for a 6 min baking time for a defined baking temperature profile is 410.000 kcal/hr. During a line stoppage: If no actions was taken and the oven worked with the normal temperature curve, the energy consumption is the same (410.000kcal/hr) If the temperature was reduced 50°C in each zone, the oven energy consumption is reduced to 196.000 kcal/h, meaning around 37% energy savings. Contact person Product Mastership Pillar, R&D Santiago At time of writing: Sandra Vaz 16 Biscuit ovens Design improvement opportunities Introduction The design improvement opportunities address design losses by implementing design modification on the existing set-up. It does not require the full replacement of the current process. D1 - “Close the loop” sensor Industrial Services Do It Yourself Solutions for energy and water savings Opportunity identification Process Operational Design improvement Technological change Biscuit weight and moisture content is traditionally measured by the operator offline. This leads to possible average moisture and weight not being on target (higher or lower moisture / weight than target). In case the moisture level is lower than target, this means the biscuit was over dried, resulting in an over energy consumption. In case of extreme deviation, this may create rework (or waste). Eventually, this results in energy loss (the energy that was used to process the semi-finished product). R&D Santiago is looking to use a technology developed by PTC York (Using for wafers (“Close the loop”, see DIY on Wafer baking ovens), to control the heat on the oven based on the moisture of the biscuit, which is measured continuously, ensuring consistent moisture. This will reduce the rework (or waste) and therefore the energy related to it. In addition, in case the moisture level was lower than target, bringing it back to the target will lead to a reduction in energy consumption. (In the opposite case, it will increase the energy consumption). How to fix it/improve Contact R&D Santiago for more information. How to estimate the energy/water savings? The savings consist in: Avoiding energy consumption linked with rework / waste Savings on the fuel for the oven: In case this project leads to increase the moisture content, less heat is required from the oven to bake the biscuit, leading to reduction in fuel consumption on the oven Project example This initiative is part of the Project DCCB-103231 done at R&D Santiago. Contact person Product Mastership Pillar, R&D Santiago At time of writing: Sandra Vaz 17 Biscuit ovens D2 – Water recovery from ovens Industrial Services Do It Yourself Solutions for energy and water savings Opportunity identification Process Operational Design improvement Technological change Currently, on rotary moulder lines, the biscuit dough water content varies from 7 to 30%. For example, a rotary moulder biscuit line producing 2000 kg/h of dry biscuits (2% moisture) from initial dough with 10% moisture will generate 160kg/h evaporation. Considering 6days/week of production during 11months/year, the amount of water generated in the form of vapour is 253ton/year just for one line. Other lines with laminated products produce 3 times more. Today all the water released goes to the atmosphere. There is an opportunity to recover this water. It could then be used for general use in the factory or even reused for dough preparation. Improvements related to the water content in the dough are being studied by Project FLEX analytics – R&D Santiago, to evaluate the opportunity to reduce water addition during the dough preparation. How to fix it/improve To recover the water it´s necessary to design a system in the extractors (in the middle of the oven) to condensate the water and recover it. This is still an opportunity to be developed: until now, no suppliers have a solution ready. This opportunity will be explored by R&D Santiago under the BEX platform, generation 5. Project example Still no project connected to this opportunity. R&D Santiago is evaluating the way to move forwards. Contact person Product Mastership Pillar, R&D Santiago At time of writing: Sandra Vaz 18 Biscuit ovens D3 – Improving radiation oven heat exchange with fans Industrial Services Do It Yourself Solutions for energy and water savings Process Operational Design improvement Technological change Opportunity identification In direct ovens, most of the heat exchange is done with radiation. This heat exchange can be improved by installing turbulence fans. All the factories with this kind of ovens should evaluate this opportunity. How to fix it/improve For new ovens: For all ovens which have radiation zones, turbulence must be a requirement when purchasing the new oven. For existing ovens: The work of retrofitting an existing oven with turbulence fans should be undertaken together with R&D Santiago. Indeed a detailed assessment needs to be done to determine the number of fans and right positioning. Fans should be installed inside each radiation zone. (CAPEX requirement) How to estimate the energy/water savings? The overall heat transfer inside the zone can be improved at 25% when turbulence is present, as the internal convection air circulation increases. Project example No specific factory example: this is part of standard operating conditions. If your factory has implemented such a project, please share it with the contact below and the Energy team at CO-Engineering. Contact person Product Mastership Pillar, R&D Santiago At time of writing: Sandra Vaz 19 Biscuit ovens Technological change opportunities Introduction The technological change opportunities address design losses by proposing a different technology than the one currently installed. It requires the replacement of the current process with another technology. No technological change opportunity has been shared so far. Your feedback Send us your feedback This document is part of a continuously improvement process. We count on you for sharing any new ideas or projects. Please contact us. 20
