Energy management in flour plants

“Energy prices don’t seem to be reduced in the near future. Therefore, energy management system and recovery of energy, where applicable, must be applied to decrease the energy consumption and the increase in the margins.”

fatih balcı


Assist. Prof. Dr.
Fatih BALCI

Gaziantep University, Department of Energy Systems Engineering

Energy use is an important issue in the flour plants. Over the past decade, the significant increase in energy costs has contributed to reducing plant profit margins. Since profit margins are generally relatively low in wheat processing plants, efficient management of energy consumption has become a necessity instead of preference. Energy management has not been considered as a vital issue so far compared with others such as production planning, marketing and the quality of product which thought a higher priority in the plant. The amount of energy used in the flour mill is an important economical consideration. Nearly 75 % of total energy consumption of a flour plant is spend by milling process. Increasing the usage will increase the cost of product directly as well as the reduction in the total margins of the plant. Energy prices don’t seem to be reduced in the near future. Therefore, energy management system and recovery of energy, where applicable, must be applied to decrease the energy consumption and the increase in the margins. On the other side, current/prospective environmental legislations and concerns over the environment to increase industrial energy efficiency. Manufacturers prefer to use the most cost-effective techniques to increase energy efficiency in their plants.

ENERGY REQUIREMENT-CONSUMPTION IN FLOUR PLANTS
The milling of wheat into flour is the most energy required process in flour plants. So it is important to control the energy consumption of flour mill. Milling is the process by which the endosperm is extracted from the grain by passing it through series of rollers rotating at different speeds. The break system primarily comprised of roller mills that run in opposite directions at different speeds. Its purpose is to separate the endosperm from the rest of the kernel (Olaoye et al., 2014). The most energy intensive operation was identified as the milling unit with energy intensity followed by the packaging unit. Therefore, milling should be targeted to decrease the energy consumption to make the system energy efficient. Inefficient or excessive usage of energy during milling leads to economic loss and increase in costs of flour. A better efficient utilization of fuel, electricity, thermal energy and labor are the major components of manufacturing cost in flour plants.

The processes that degrade the quality of energy resources can only be identified through a detailed analysis of the whole system (Ezeike, 1981). Wheat processing involves operations such as cleaning, tempering/conditioning, holding bin, and milling. These operations require high and regular energy supply to function, thus an efficient energy system is needed. Inefficient industrial energy use could lead to huge economic losses as excessive energy consumption adds to the costs of goods produced especially in energy intensive industries.

In principle the milling process is established in three stages that are break, purification and reduction systems. The break is used to open the wheat kernel and continue to scrape endosperm from bran, step by step, by sequential passages. The purification system is to separate the outer branny material from inner white endosperm. The aim of this purification system is to purify the milling material that almost no flour is produced. The reduction system is to deliberately mill the center particles of the wheat grain into flour (Mustapa Kamal et al., 2006).

Unit energy consumption of mill is depend on hardness, test weight and ash content in grain. Unit energy consumption increases with the increase of hardness and test weight, and decreases with grain ash content. Kernel hardness, feed rate, roll gap, roll speed, roll differential and tempering procedure affect amount of energy used significantly during milling. Grinding is one of the most energy-intensive processes (McCabe et al., 2004). About 60-75% of energy in industrial processing is spent on grinding (Danciu et al., 2009). The energy of grinding cereals has also attracted the attention of scientists. The amount of energy consumed during the grinding process depends on the type of mill applied, the mill settings and on the physical and chemical properties of grain and the degree of grinding. The energy consumption of the grinding process increases with grain moisture content. Energy consumption of grain grinding also depends on kernel hardness. Hard wheat requires more energy for grinding than soft wheat (Warechowska, 2014).

MONITORING AND MEASUREMENT SYSTEM FOR ENERGY CONSUMPTION
Energy management is becoming a key skill in the manufacturing operations of many companies. Existing solutions for measurement, analysis and control of energy do not address all the requirements of energy management at the organization, factory or process level because they do not adequately develop in the workforce an awareness of the energy used in their business. To achieve the desired efficiency improvements, energy use should be measured in more detail and in real-time, to derive an awareness of the energy use patterns of every part of the manufacturing system (Vikhorev, 2013). For many manufacturers, energy must be monitored more closely and controlled in real-time. A flow diagram, including the major operations with every significant process equipment that directly or indirectly has an effect on the energy should be prepared. It will also include temperatures, flows and compositions of the various process streams that are reconciled using a consistent energy and material balance. Vikhorev (2013) proposed a framework that integrates standards for energy data exchange, on-line energy data analysis, performance measurement and display of energy usage. This solution allows achieving the desired efficiency improvements with the real-time measurement of the energy use to derive an awareness of the energy use patterns of every part of the production process. Also this paper proposed a framework for energy monitoring and management that allows decision support systems and enterprise services to take into consideration the energy used by each individual productive asset and related energy using processes, to facilitate both global and local energy optimization.

Conventional energy management methods at the factory floor are limited because the energy performance of individual processes cannot be understood without continuous measurement of energy consumption and an infrastructure to map process energy data onto relevant business performance measures. This lack of insight limits the scope for timely decisions to reduce energy use. Effective industrial energy management is often very context specific, since it depends on many local factors such as product design, process choice, national fuel mix, etc. This means that it can be difficult to replicate energy saving solutions derived from one industry in a different industrial sector and/or location (Vikhorev, 2013).

Each process, motor, pump, roll, machine etc. must be monitored according to their flow rate and energy consumption daily base. Also, the data should be interpreted into a meaningful directive to the operators. The fluctuations of energy usage, on the other hand, must be monitored by the data. Any dysfunction must be handled in limited time to maintain the process again the routine working. The main method is same for all flour plants, however, in the light of energy consumption, manufacturing processes varies from one plant to another. Thus energy management for a plant must be unique for the successful implementation.

EFFECTS OF ENGINES ON ENERGY CONSUMPTION AND CHOOSING THE RIGHT ENGINE
Electric energy is a crucial factor in global industrial production. It can be saved the unnecessary energy consumption by having a definite control of flour mill maintenance plan, minimizing process time and cutting down the maintenance expenses. Having a complete control of energy usage of each process is the main step of energy saving.

Electrical motors account for approximately three quarters of electricity use in the milling industry. Energy efficient motors offer reduced energy use during operation. A high efficiency motor is more expensive than a standard efficiency motor. However, in high energy cost locations the increased installation expense can be offset with energy savings. Careful attention to efficiency ratings can result in hundreds of dollars of savings per year for a 20­horsepower motor operating continuously. In many applications, variable speed drives can result in more savings than high efficiency motors, depending on the process (Gwirtz, 2008). In addition, significant amounts of energy are required to power the large motors for grinding. Motors are used in the milling and grinding processes in a flour milling plant. The following section applies to these systems or any other systems that use motors. Using a systems approach that looks at the entire motor system to optimize supply and demand of energy services often yields the most savings. For example, in pumping, a systems approach analyzes both the supply and demand sides and how they interact, shifting the focus of the analysis from individual components to total system performance.

Motors and pumps that are sized inappropriately result in unnecessary energy losses. Where peak loads can be reduced, motor size can also be reduced. Correcting for motor oversizing saves 1.2% of their electricity consumption, and even larger percentages for smaller motors (Xenergy, 1998).

High efficiency motors reduce energy losses through improved design, better materials and tighter tolerances and improved manufacturing techniques. Poor motor cooling can increase motor temperature and winding resistance, shortening motor life, in addition to increasing energy consumption. In addition to energy savings, this can help avoid corrosion and degradation of the system.

PLANT DESIGN & PROCESS POSITIONING AND ENERGY CONSUMPTION
Mill cost is the most important factor when designing a flour mill. Thus, lowering the mill’s cost factor automatically improves the mill’s profit ratio. One of the most important mill cost factors is energy consumption. Electrical energy costs in milling are usually the third largest item of plant operating expense, next to raw material and labor. Energy use varies from mill to mill; however, the big power consumer of energy in the milling process is grinding. Main equipment’s that involved in grinding process are roller mill, sifter and purifier. Thus, reducing the number of use of these equipment items subsequently reduce the electrical energy cost. Measuring the electric or energy power consumption should be related to the production rate or wheat ground. Thus the better flour mill is the one that can produce constant production with less energy. Methods to reduce energy uses may range from the recycle concept at break system in flour milling process, mainly at second break (Mustapa Kamal, 2006).

The grinding texture and energy efficiency requires continuous improvements to respond to maintenance needs and process optimization in order to reduce energy consumptions. To achieve these goals, the industrial plant needs a monitoring network with a real-time tool able to record and elaborate all the main variables related to energy flows.

In order to optimize the energy supply and if possible to avoid high-rate power peaks, the energy consumed must be recorded and visualized at a centralized point in the plant.

AUTOMATION AND COMPUTERIZED CONTROL SYSTEMS
In flour plants, the energy consumption is very high. Each process consumes generally more energy than it needs. The optimum energy supply must be calculated. Sometimes higher energy level will be needed depending on the type of raw material and the flow rate. The main energy save is the total of minor energy from each motor, pump etc.. A conceptual software-based approach for energy data analysis, which provides automated energy monitoring and decision support across every production levels and allows automated control and analysis of energy consumption in manufacturing systems. This kind of software must be used to monitoring energy use of each process in daily base and then must convert the daily data into a meaningful decision. The changes in the flow rate must be controlled and the energy consumption fluctuations must be reported. By this way, probable failures might be forecast and system continues to run without interruption.

Commercially available energy management systems (EMS) can collect energy data using one or more parameters and they can be used to identify opportunities for daily energy. They can be used with a range of sensor technologies to monitor energy carried by electricity and gas as well as other energy carriers. They can analyze these data to separate energy use resulting from production schedules from that which is driven by the weather. They can be used to target process, plant or site efficiency improvements and to display information at a range of levels from shop floor to stakeholder’s level. However, these systems suffer from lack of standardization and real-time automatic correlation of energy data across multiple production levels. Existing EMS have been shown to reduce energy use by 5% (Carbon Trust, 2008).

It is far too easy to regard the energy consumption as a fixed overhead, and yet substantial savings are possible often with little or no capital investment. Automation of most processes will usually bring about more efficient operation as the plant can be operated continuously at the correct process variable. Operator involvement is essential, however, as the automation must provide the right degree of flexibility, otherwise the systems tend to be overridden and the full saving potential not achieved (Carbon Trust, 2004).

Real-time optimization in the food industry is a key tool for the direct minimization of water and energy use. The large diversity of food products requires the existence of an optimization system capable of adapting to operating changes and specification variations. The interactions among separate water networks and the effects of heat integration can be rigorously taken into account within a real-time optimization framework. The achievement of energy efficiency of up to 65 % for the process industry through real-time optimization is claimed by Rajan (2006). Due to increasing energy costs and concerns regarding climate change, there is an urgent need to improve energy efficiency.

Measurement and control systems are integral parts of manufacturing systems. New energy management concepts form a basis for decisions on energy efficiency improvement measures.

To develop new energy management concepts, attention has to be given to sensors and control devices, the KPIs, and the techno-human interfaces. Energy efficiency should also be represented in the information and communication technology (ICT) systems for production. Due to new options for enhanced collaboration, further energy savings can be realized in supply chains (Bunse, et al. 2011).

HEAT RECOVERY METHODS, SYSTEMS & HEAT EXCHANGERS
Another way to improve the energy and resource efficiency of manufacturing processes is the recovery of waste streams and heat losses. Energy conservation is vital for the sustainable development of the food industry. Reduced energy consumption through conservation can benefit not only energy consumers by reducing their energy costs but also the society in general by reducing the use of energy resources and the emission of many air pollutants such CO (Wang, 2014). Energy efficiency improvement and waste heat recovery in the food industry have been a focus to increase the sustainability of food processing in the past decades. Most of the energy conservation technologies can readily be transferred from other manufacturing sectors to the food processing sector. Heat exchangers also play a key role in waste heat recovery. Several energy conservation technologies including heat transfer enhancement, fouling removal, optimization of heat exchanger design, and optimization of heat exchanger network have been used to improve the energy efficiency of heat exchangers (Wang, 2008).

Compact and enhanced heat exchangers are now widely used in industry and their performances for clean conditions are well known for a large variety of operating conditions. Enhanced heat transfer surfaces and compact heat exchangers are now widely used in the food and process industry; and their performances under clean conditions are well known. However long-term thermal and hydraulic performances under fouling conditions and the cleanability of enhanced heat transfer surfaces are still factors limiting their use and their acceptance in industry. Enhanced heat transfer surfaces, provide higher heat transfer coefficients than conventional plain tubes, and will be more sensitive to fouling. Furthermore, the fouling margin implies an extra-surface, which generally costs more compound to plain stainless steel or copper tubes. In consequence, some specific recommendations need to be given for both fouling resistances values and operating conditions (Thonon, et al., 2013).

For most manufacturing processes the fixed power level, which corresponds to a non-loaded machine tool in stand-by mode, has a significant contribution to the total power consumption. Therefore, a proper selection of the right equipment (and related maximum capacity) could reduce the energy consumption (Duflou, et al., 2012).

As a summary, effective energy management in production is a need towards increased energy efficiency in flour production plants. In order to reduce energy consumption and costs it is essential to use energy management during especially in milling process. A new model for the grain milling process may be developed in collaboration of academia and industry partners. Thus developed systems might be used in other manufacturing companies and might help to increase the awareness for energy efficiency across industry.

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