D. Baglee, A. Melvin and M.J. Knowles
Institute for Automotive and Manufacturing Advanced Practice (AMAP) University of Sunderland
Corresponding Author: D. Baglee Email: david.baglee@sunderland.ac.uk Email: michael.knowles@sunderland.ac.uk
Abstract
The food and drink processing industry is the fourth highest industrial energy user in the UK, largely due to its extensive use of refrigeration systems, meaning energy is one of the major costs in this industry. This paper is based on a project whose objective was to identify, develop and stimulate the development and application of more energy efficient refrigeration technologies and business practices for use throughout the food chain.
The focus of this paper was the investigations carried out into the operations and supply network configuration and design in order to identify areas where energy savings can be made through the reduction of refrigeration usage whilst not compromising food safety and quality.
The investigation identified that maintenance is a key activity for refrigeration systems since poorly maintained systems are known to exhibit increased running costs and reduced reliability.
Key words: Food and Drink Industry, Refrigeration, Supply Chain
1 Introduction
The food and drink processing industry is the fourth highest industrial energy user in the UK (Carbon Trust 2012), it is also one of the largest users of refrigeration technology with many businesses within the sector finding that refrigeration costs make up a significant proportion of their energy bill. This paper is based on a project titled ‘Fostering the developments of technologies and practices to reduce the energy inputs into the refrigeration of food’ funded by the Department for Environment, Food and Rural Affairs (DEFRA). The overall objective of the project was to identify, develop and stimulate the development and application of more energy efficient refrigeration technologies and business practices for use throughout the food chain.
Refrigeration systems are major users of energy in the food and drink industry and as such they are a major source of cost to companies working in this sector. The literature contains many examples of the development of new and refined technologies (c.f. Tani et al 2012) or new refrigerant formulations (c.f. Bayrakci 2011, Rasti et al 2012). What is missing from the
literature, however, is any discussion of how the efficiency of refrigeration can be improved by optimising its operation and use. A great deal of attention has been placed on improving the operational efficiency of manufacturing operations by reconfiguring maintenance practice, process flow, supply chain, operational procedures and factory layout. The hypothesis which will be examined here is that such techniques can be applied to industrial refrigeration to improve the efficiency and reduce the cost of operation.
The aim of this work was to analyse food manufacturing supply chains to identify areas where energy savings can be made through the reduction of refrigeration usage as a result of operations/supply network improvements whilst not compromising food safety and quality.
The focus of this paper was the investigations carried out into the operations and supply network configuration and design and the effect they have on the use of refrigeration and to identify any operations which were not seen as important by the case study companies yet after detailed analysis has shown as a major contributor to system failure and high energy usage.
Maintenance is a key activity for refrigeration systems since poorly maintained systems are known to exhibit increased running costs and reduced reliability. By optimising the use of refrigeration systems it is envisaged that the requirements for maintenance, and indeed the impact of suboptimal maintenance can be improved.
The paper will discuss the impact of maintenance on energy use in industrial refrigeration before describing the development of instruments and tools used for data collection. Four supply chains are presented as particular case studied and key areas of wastage in the food supply chains studied will be identified, and their contribution to unnecessary refrigeration usage and the implications for system maintenance are then be assessed.
2 Impact of Maintenance on Energy Use in Industrial Refrigeration
It is widely accepted that the demand for refrigeration will rise in the future, as will the corresponding energy requirements (Sivak 2009, Hermes et al 2009). While the topic of energy efficiency in refrigeration has been well documented, very little work has been done on the role of maintenance. Due to the lack of available data it has been necessary to investigate the link between maintenance activity and energy efficiency in the literature. Litt et al (1993) concluded that maintenance provides no significant improvement in energy consumption but several significant flaws existed in their study. The refrigerators tested had an average age of 16 years and many had received no maintenance during their life. The tasks carried out were not significant, consisting mainly of cleaning and gasket replacement.
Furthermore some of the refrigerators where in an extremely poor overall condition, for example the doors of some models were being held together by the seals suggesting poor structural condition. These faults were not rectified as part of the maintenance performed. Full lifecycle assessment (LCA) is crucial in determining the true benefit of a course of action such as widespread replacement (Techato et al 2009).
A study in the USA by Miller and Pratt (1998) carried out as part of the Energy Star program analysed the energy savings obtained by replacing old refrigeration equipment in New York and found a strong correlation between the age of refrigerators and their baseline energy
usage. The authors concluded that ‘degradation’ plays a major part in energy consumption and can be regarded as a separate factor to labelled energy rating and age.
From these studies it is possible to conclude that the condition of refrigeration equipment has a substantial effect on energy consumption. In determining the effects of maintenance on the efficiency of refrigeration equipment it is necessary to study both maintenance policies/procedures and energy consumption. Initial investigations involving a variety of refrigeration users have highlighted various shortcomings in maintenance policy. Most maintenance is reactive, occurring only in response to a failure in the refrigeration plant. Any planned maintenance which does occur is generally related to service agreements or compliance requirements. Furthermore it was found that very little monitoring and recording of either maintenance activity or energy consumption is undertaken. This lack of monitoring means the relationship between running costs, maintenance and usage patterns is generally neglected.
The work carried out by the University of Sunderland has shown that a large number of companies do not collect and analyse maintenance data and therefore are unable to develop a new maintenance strategy based historical trends. In addition, companies rarely collected data regarding the cause and effect of a failure and what corrective action had been implemented.
The research has also shown that cost to maintain (including energy consumption) and utilisation costs (running cold rooms on maximum with less that 20% full) were rarely recorded. In addition, the majority of companies studied did not employ condition monitoring techniques to detect, at an early stage, the onset of poor performance and eventually equipment failure. Further studies have shown that the food and drink industry, which are not part of large and dedicated supply chains, and therefore are not subject to the financial pressure often found within supply chain to ensure production and delivery times, often suffer from the lack of maintenance strategy developments and technical advancements to ensure just in time methods.
Research and case studies in other areas of engineering have demonstrated the energy efficiency benefits of maintenance. The Carbon Trust performed a case study at RAF Kinloss (Select Committee on Defence, 2007) where they used monitoring techniques and auditing to identify areas where the most substantial savings were possible. In a similar study for Westbury Dairies, a computer monitoring system was installed which it is estimated could lead to policies which could save the diary £400,000 of its £2 million energy bills (Carbon Trust 2007).
3 Supply Chain Case Studies
In order to assess the use of refrigeration in food and drink supply chains, four different supply chains were studied to identify areas of waste and in particular, implications for maintenance.
3.1 Dairy
The dairy industry involves a wide range of processes being carried out at a range of different temperatures to ensure that a) the product is safe to consume and b) is maintained in a safe condition. The production of yoghurt is presented as a case study in this area.
Two dairies producing yoghurt were studied. Raw milk is collected from farms in and around the areas of the sites. On arrival, the raw milk is tested for temperature, taste, added water, acidity and antibiotics. Once the load passes these receiving tests it is pumped into large storage silos. All raw milk within these silos is processed within 72 hours of receipt at the plants.
Upon receipt raw milk is standardized this involves reducing the fat content and increasing the total solids, the fat content is then reduced by using centrifugation to separate the fat from the milk. The solid content of the milk can then be increased further by evaporating off some of the water or by adding milk powder. After the solid composition has been modified to the required consistency the milk is pasteurized. This involves heating the milk to 50°c for 15 seconds to destroy the microorganisms in the milk that may interfere with the controlled fermentation. The pasteurised milk is then homogenised at 180°c to break up the fat globules in the milk. This process produces a smoother and creamier end product.
The processed milk is transferred to an incubation tank where the temperature is reduced to 41°c. Here two different methods are used to reduce the temperature. First is a cooling jacket which takes approximately 8 hours to cool the yoghurt to the required temperature and the second is central agitation which takes approximately 4 hours. Once the yoghurt has been cooled to the acquired temperature of 41°c culture is added accordingly. This whole process takes around 8-10 hours depending on the yoghurt type.
The mixture is then transferred to smaller holding tanks and fruit and flavourings are added as required. The holding tanks are connected to the filling machines and the mixture is pumped into pots, sealed and date stamped. At this stage the yoghurt is still around 20¬30°c however in order for the product to be despatched the required temperature is <5°c. This proves problematic since the yoghurts are packed into cardboard trays and placed onto a pallet with restricted access for air movement. Chiller boxes are used to reduce the temperature however;
they are not energy efficient and require large amounts of energy and time to cool the yoghurt.
The sites also use rapid blast systems which hold around 10 pallets, these are set between -3°c to -6°c. However, the pallets of yoghurts still take 2 hours to meet the required temperature of
<5°c.
Table 1 shows a summary of the approximate temperatures of the yoghurt mixture throughout processing.
Table 1. Summary of yoghurt temperatures
Initial After Processing After incubation Filling Dispatch
6°c 180°c 41°c 20-30°c <5°c
The above process is particularly demanding in its use of electricity. This is due to the thermal requirements of its many processes such as pasteurization, homogenization and rapid chilling. The main problems in the dairy industry are:
Achieving and maintaining low temperatures for despatch Storage
All of the sites visited find it difficult to achieve the required temperature for despatch in a short period of time. Many dairy sites have little space for further developments however; the layout of the processing lines could be improved dramatically with little investment. The process was repeated within 3 hours, allowing for cleaning and a visual inspection of seals and pipes as Health and safety regulations dictated. Maintenance tasks were carried out if time permitted, or, in several instances, the equipment would be allowed to run-to-fail in the hope the process was complete.
3.2 Meat
The meat companies studied all manufactured pork products, as products such as bacon or sausages require large amounts of electricity for a 12-15 process production line. The factories varied greatly in size and can slaughter from 1000 to 1700 pigs a day each.
Livestock is received at various times throughout the day and they are normally unloaded within 30 minutes or arrival. The slaughtering process takes approximately 45 minutes however the chilling of the meat, de boning, cutting/slicing and packing takes much longer.
Following slaughtering, carcasses are placed into a steam tunnel/scald tank which has a temperature of around 80°c to soften the skin. They are transferred into a de-hair unit, a singer for 5-10 sec at a temperature of around 700°c and they are then scraped and polished to remove any final hairs. This process required large amounts of energy which is often lost in the atmosphere after use, the equipment was often old, suffered from damaged caused by excessive heat and maintained only after a problem had occurred.
After the de-hair process the carcasses are weighed, stamped to acknowledge they have passed inspection and placed into the deep chill where they are stored between 0-5°c for up to 16 hours overnight depending on the sites specifications. This length of time is needed so that the meat is at an ideal temperature to be able to be cut and de boned, any warmer and the meat would be too tough. The process is again, energy intensive, often the meat is stored in large chillers capable of storing 100+ units however, the chillers usually have between 10 and 30 units stored at any one time. The fan blowers work constantly to ensure the optimum temperature is maintained.
Processed meats, for example, are cooked at a temperature of 80°c and are then placed into the blast chiller at 5°c for 16 hours. They are sliced, packed and date stamped and moved to the cold storage area for approximately 2-3 days at a temperature of <5° until they are ready for despatch. Depending on the site, deliveries are made either directly to the customer or to a logistics company who receive customer’s orders and pick goods accordingly.
One of the sites studied has a major problem with refrigeration due to the amount of machinery used in each of the individual processes. They try to keep rooms chilled to 5°c or below however in reality the temperature is approximately 9-10°c. Also due to the design of the site some chilled rooms are used as a thoroughfare therefore doors are left open. The lack of thermal sensors is widespread, thus when a door is left open or a fan blowing cold air is inoperative, it could be several hours before the fault is detected. Meat or dairy products are often discarded (waste), maintenance is carried out to repair the problem but rarely is data collected and analysed to identify the cause of the fault and plan future maintenance. In
addition, the large blast chiller rooms are often located outside the main building and therefore open to the effects of extreme external temperatures on fan motors, coolant pipes and water pumps. None of the external chillers were fitted with condition monitoring systems to detect early signs of degradation.
Table 2 shows a summary of the approximate temperatures of pork throughout the processes within the factory.
Table 2. Summary of meat temperatures
Initial After cleaning Chill Cutting.& de boning Dispatch
37°c 67-80°c -4 to 5°c 5-10°c <5°c
The main energy usage in the pork factories visited are chilling of carcasses and maintaining temperatures throughout the factory. Temperatures throughout the factories varied greatly due to the design and layout. In some sites, although rooms are chilled to 5°c the actual temperature is much higher due to machinery used in the production processes and rooms being used as a thoroughfare. Transportation is also another main energy user with goods being transported to and from logistics and between sister sites locally, nationally and internationally.
3.3 Fresh Produce
The fresh produce company studied produces salad produce for supermarkets, caterers, food chains and retailers. They use mostly home grown UK leaf from May to October however come October the majority of supplies and more exotic leaves are imported from Spain, France and Italy except from the more common fresh produce which can still be grown locally. Deliveries from Spain take around 3-7 days therefore the site hold a 3-day buffer stock incase problems arise with suppliers. This may impact storage, the need for chilled and or frozen rooms (often at other parts of the plant) and maintenance to ensure rooms are availble and ‘running’ to support storage at a moments notice.
Various temperatures are in operation throughout the factory and these range from <5 °c to ambient. The intake and chilled area is kept below 5°c whereas the preparation area is kept from 5°c to ambient temperature to allow workers to be able to work comfortably.
Once the salad cut surface is exposed to air, the cut surfaces will brown or pink by enzyme action therefore it is important that the factory temperature, wash processes and packaging methods are designed to reduce the effect of the enzyme action. This process is unertaken in a ‘sealed’ room in which hygeine is important, It is necdssry to reduce the risk of cross contamination from wash and clean fluids and to ensure the oils, grease and equipment is maintained and cleaned on a regular basis. In this process maintenance has been recognised as important to ensure pipes, pumps and motors are clean, to reduce contamination, and the equipment is running at the required speed to ensure food is packaged within the specifiied time limit.
Temperatures are monitored every 20 minutes and the site tries to maintain these at <5°c however the temperatures vary throughout the day. The peaks in temperature can be correlated to when the system goes into defrost and the other variations in temperature are when the sites receive and despatch goods.
Table 3 shows a summary of the approximate temperatures of fresh produce throughout the processes within the factory.
Table 3. Summary of fresh produce temperatures
Initial Preparation Pack Dispatch
<5°c <8°c <5°c <3°c
Maintaining low temperatures throughout the factory is a major problem for fresh produce manufacturers since the temperatures can have a great affect on the produce. This site monitors temperatures and tries to maintain them however they are built on an existing factory layout and therefore they have to try and utilize the space they have as best as they can.
3.4 Convenience Food
The small factory which was studied is relatively new and on the visiting date, it had only been situated in a new premise for 5 months. The products produced are a variety of pies, peas and mash. The company receives meat and vegetable deliveries daily and dairy twice a week.
The companies chilling areas are situated at the back of the factory next to the delivery and despatch areas. Here there is a raw materials freezer, raw materials fridge, finished goods freezer and works in progress fridge. This area leads into the preparation room where all ingredients which do not need refrigerating are stored, for example tinned produce, herbs etc.
The companies chilling areas are situated at the back of the factory next to the delivery and despatch areas. Here there is a raw materials freezer, raw materials fridge, finished goods freezer and works in progress fridge. This area leads into the preparation room where all ingredients which do not need refrigerating are stored, for example tinned produce, herbs etc.