An Integrated Method for Sustainable Manufacturing Systems Design

In the past decade, there has been an increasing awareness in development of sustainable manufacturing systems as governments in many countries have been enforcing ever-stricter environmental policies and regulations in industry by promoting energy saving and low emissions manufacturing activities. Lean manufacturing can be helpful for achieving a sustainable manufacturing system as it can reduce production wastes and increase manufacturing efficiency. Nevertheless, this lean approach does not include a consideration in energy consumption and carbon dioxide (CO2) emissions when designing a lean manufacturing system. This paper presents a methodology which can be useful for measuring energy consumption and CO2 emissions for a typical manufacturing system design at an early stage. A case study was carried out for obtaining computational results using the developed methodology based on data collected from a real production line.


Introduction
To develop a sustainable manufacturing system, system designers need not merely to apply traditional methods to improve system efficiency and productivity but also to examine the environmental impact on the developed system.This is because governments in many countries have been enforcing ever-stricter environmental policies and regulations by promoting energy saving and lowemission manufacturing activities in industry.A manufacturing system can be defined as a process or system of transforming raw materials, components or parts into final products that meet customer's needs and specifications [1].The traditional manufacturing system design is involved in determination and analysis of such as material-handling methods, system capacities, production methods, material flow, shop-floor layouts, system flexibilities and operations.Nevertheless, there is an environmental consideration that needs also to be addressed today; this leads to a new challenge for manufacturing system designers to develop an effective approach by incorporating environmental parameters or constraints [2].
The concept of manufacturing sustainability may be defined as the creation of manufactured products by minimizing negative environmental impacts on usage of energy or natural resources.The environmental issues in manufacturing activities focus on energy consumption and CO2 emissions.Koc and Kaplan presented an investigation on energy consumption for a particular ring type yarn manufacturing system [3].Lind et al. developed a production simulation tool that was used for making a trade-off decision based on considerations of ergonomic constraints, levels of automation and environmental impacts [1].Wang et al. proposed the process integration (PI) method that was used for evaluating CO2 emissions for a steel industry [4].Gutowski et al. conducted a thermodynamic analysis by examining the resources used in manufacturing processes [5].Branham et al. used the quantitative thermodynamic analysis for quantifying energy in different categories applied into manufacturing processes or systems [6].
Lean concepts are widely adopted by many manufacturing plants as a popular model for improving system efficiency and productivity without additional investments.Lean manufacturing is a systematic approach to eliminate non-value added wastes in various forms and it enables continuous improvement [7].These wastes are overproduction, waiting for parts to arrive, unnecessary movement of materials, the waste in processing, unnecessary inventory, excess motion and the waste of rework [8].However, traditional lean manufacturing does not consider environmental wastes which also need to be identified as these wastes add no values on manufactured products.This paper presents an integrated method by incorporating parameters of energy consumption and CO2 emissions into a manufacturing system design at an early stage.A case study was used for obtaining computational results based on data collected from a real production line.

Energy consumption and COemissions of a typical manufacturing system
In a manufacturing system, energy is used for operating machines, air conditioning systems, illumination systems and other supportive equipment such as compressors which supply compressed air to some machines [3].
Energy and CO2 emissions are generated by either combusting fossil fuels directly or using electricity which is generated indirectly by using fossil fuels or renewable resources.To describe amounts of energy consumption and CO2 emissions, the following notations are used: Notations: m: number of processes in a manufacturing system ni: number of machines involved in process i, where {1, 2,...., m} i Ei (kWh): energy consumption for a machine involved in process i Ei cond (kWh): energy consumption of an air conditioning system Ei illum (kWh): energy consumption of an illumination system Ei air comp (kWh): energy consumption of a compressed air needed for a machine involved in process i TE (kWh): total energy consumption of a manufacturing system Ni (kw): installed power for a machine involved in process i Ri (kg/h): manufacturing rate for a machine involved in process i i W (hr): operating time for a machine involved in process i µi (%): efficiency for a machine involved in process i Tei (kg/kWh): amount of CO2 emissions per KWh released from a machine, an air conditioning system and an illumination system, which involved in process i Z : CO2 emission factor using different energy sources Te (kg/kWh): total amount of CO2 emissions released from the manufacturing system qi (kg): mass of materials involved in process i

Energy consumption
The energy consumption Ei for a machine involved in process i is given by The operating time i W for a machine involved in process i is calculated by: Mass of materials qi transferred from a machine involved in process i is obtained by: ( 1) The energy consumption of an air conditioning system Ei cond in a manufacturing system is given by: The energy consumption of an illumination system Ei illum is calculated by: The energy consumption of a compressed air needed for a machine involved in process i air comp i E is calculated by: where ] can be determined by: The total energy consumption TE for a manufacturing system is given below: 1 ( ) where {1,2,...., m} i Hence, equation (8) will be as follows:

COemissions
The amount of CO2 emissions ei released from a machine involved in process i is calculated by: The total amount of CO2 emissions Te can be calculated as follows [10].

A case study
Figure 1 illustrates a process flow chart or precedence diagram for producing plastic and woven sacks at a company.The study was carried out for analysing the energy consumption and CO2 emissions for a manufacturing system consisting of machines for carrying out process tasks, an air conditioning system, an illumination system and a compressor system.Air conditioning is necessitated to maintain reasonable temperatures required for operators, effective machining operations and quality of products.The production line comprises 10 different processes tasks, each process task involves a number of machines and each machine has energy, mass inputs and different specifications.Table 2 shows the symbols representing the manufacturing processes used by the factory.3 shows collected data from the company.These include the mass of materials involved in process i per month, number of machines involved in process i, waste ratio, manufacturing rate and installed power.

Comparative results
Table 4 shows computational results in energy consumption and CO2 emissions of machines involved in a process task and Figure 2 illustrates these results.Energy consumption of the machines involved in a process task of a manufacturing system depends on the installed power Ni and the operating time i W .As shown in Figure 2, the machines for completing process task G have the largest energy consumption and the machines for completing process task K have the least energy consumption.This is because the machines involved in process task G have the highest installed power Ni (200 kw) and the highest operating time i W (646 h), while the machines involved in process task K have the lowest installed power Ni (zero kw) as this process is a manual task.CO2 emissions released from the machines involved in a process task of a manufacturing system depends on the ICMIT 2016 0 energy consumption used by the machines, the emission factor and the energy source.Table 4 alos shows the amount of CO2 emissions which are subject to the CO2 emission factor Z using different energy sources and Figure 3 illustrates these results.As shown in Figure 3, the machines in completing process task G have the highest amount of CO2 emissions Tei (91244910178 kg/kWh using oil as indirect energy to generate electricity, 66167449497 kg/kWh using oil as direct thermal energy and 6616751966 kg/kWh using solar as indirect energy to generate electricity), respectively.This is because the machines involved in process task G have the highest amount of energy consumption.By contrast, the machines involved in process task K generate zero CO2 emissions as this process is a manual task.The amount of CO2 emissions that released from this task is released from the air conditioning and illumination system only which is 4431 kg/kWh.The results in Table 4 also show that using the solar source of energy has the lowest total of CO2 emissions Te of 15679203081 kg/kWh, followed by oil as a direct energy source to generate thermal energy of 1.6×10 11 kg/kWh and oil as indirect energy source to generate electricity of 2.2×10 11 kg/kWh, because solar energy has the least emission factor Z (0.05 kg/kWh) followed by oil as direct energy source (0.5 kg/kWh) and oil as indirect energy source (0.6895 kg/kWh).The amount of total CO2 emissions Te using oil as indirect energy source is higher than using oil as direct energy source because electricity is already generated through oil and the emission factor Z for using oil as indirect energy source is higher than the emission factor for using oil as direct energy source.

Conclusions and discussions
When designing a manufacturing system, engineers used to focus on key performance indicators in terms of system productivity and capacity; environmental considerations are often overlooked.This paper presents an integrated method which addresses environmental sustainability relating to manufacturing activities.The developed method was aimed at helping decision-makers to design a manufacturing system incorporating a number of environmental parameters in terms of energy consumption and CO2 emissions.The computational results were validated based on data collected from a real case in industrial case.In addition, the developed method allows a joint analysis of the system performance using environmental constraints.

iw
(kg): mass of materials transferred from a machine involved in process i Gi(kg): mass production per month ¥i (%): total waste ratio for a machine involved in process i Ęi (kWh): energy consumption of air conditioning per month Ěi (kWh): energy consumption of illumination per month ζ air comp i (kWh/m 3 ): energy consumption per cubic meter of a compressor i X (m 3 /h): compressed air used for a machine involved in process i per hour comp air i U (m 3 /h): capacity of compressed air in cubic meter per hour of a compressor comp air i N (kWh): installed power for a compressor ei (kg/kWh): amount of CO2 emissions per kWh released from a machine involved in process i

Figure 1 .
Figure 1.The process flow of plastic and woven sacks.

Table 1 .
Amount of CO2 emission factor per kWh using deferent energy sources.

Table 2 .
Manufacturing processes tasks for producing plastic and woven sacks.

Table 3 .
Data collected from a plastic and woven sacks company.

Table 4 .
Calculated results for energy consumption and CO2 emissions Figure 2. Energy consumption calculated results.Figure 3. The amount of CO2 emissions using oil as direct energy source and indirect energy source and solar as indirect energy source to generate electricity.