There are many reasons to improve energy efficiency but the bottom line is cost effectiveness. Increased input cost like power, labour, raw material, infrastructure, etc has compelled the plastic processing industry to increase efficiency. Local and global competition is an addition to the same. In other words, improving productivity is most important than ever before.
To sustain and to make profit, control on costs is the biggest challenge. Production costs can be reduced or controlled by incorporating systems which may require little or no investment. Optimising the process and performance is the answer to face the challenge.
By increasing the energy efficiency, short-term and long-term benefits can be achieved and the bottom line can be strengthened. Efficient use of energy will play an important role in managing the present and forthcoming challenges. Better cooling is one of the ways.
Better cooling, improved efficiency
As cooling time is the biggest factor in plastic moulding cycle and one of the deciding factors for the quality requirements, better control upon the same will improve the productivity to a great extent.
It is essential to have a reliable and consistent cooling system in plastic processing. Most of the time water cooling is a forgotten area and the energy consumed there by, as the equipment is far off from the production area. Hence it is often a neglected area and no attention is paid to it unless there is a problem or there is a break down. Another problem is the cooling lines are often extended as and when the number of machines are increased or the capacities are expanded without considering the available cooling capacity.
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Analysis of cooling performance at regular intervals is always advisable to maintain and/or improve the cooling efficiency. Plastic moulding plant consumes 11% to 16% of the total energy consumed. Little care can reduce the energy consumption substantially. More attention is required if the system is consuming lesser energy than it should have, to find out whether the system is under-cooled.
Opt for right cooling methods
Chilled cooling water temperature can be achieved by water chillers and are used for critical moulds. Chilled water cooling requires better control since the chillers consumes energy and any change in temperature may hamper productivity. Lower temperatures of chilled water leads to mould sweating and will call for mould sweat protector.
Providing cooling to a plastic moulding shop is an expensive affair and proper management of the same can save without compromising on productivity. For an average plant the savings can be up to 25% by inexpensive measurers. The major cost to establish the system is the labour and the time involved.
To identify the water temperature requirement of the normal cooling water and chilled cooling water is the first step towards water cooling optimisation.
It is advisable to insulate/protect the cooling network from external heat and should not be circulated from inoperative machines.
Trying to lower the cooling/chilled water temperature than required will consume more energy and in turn cost money. Increasing water temperatures can improve reliability and dramatically reduce costs, especially with chiller systems.
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After reduction in the cooling water quality and quantity requirement, it is also necessary to increase the energy efficiency by reducing the distribution cost. Most of the plants have still not identified this grey area. It is now necessary to optimise the supply of cooling water. The water circulation pumps for cooling and chilling systems are generally centrifugal pumps and these are often incorrectly sized for the demand. This is either due to expansion/contraction of the system, poor initial specification, or changes to the system that has not been logged correctly. Changes in the system often mean that pipe work has been modified without considering the resulting alteration in the load and efficiency of the pumps at the increased or decreased pressures. The pipe work and pumps must be sized for the current demands.
Optimisation is must
The piping layout is plotted for piping network and then simulated virtually on computers with the help of software for the desired flow (turbulent) of water through every node. During simulation it is also ensured that back pressure due to excess flow from the heat exchanger do not restrict the water passing through the mould. The pump/s, pipe diameter and cooling tower are selected accordingly and the design is optimised. Design can be optimised for new plants and for modification of existing plant.
The author is a consultant specialising in plastics moulding, project planning and implementation, and water cooling optimisation. Email: firstname.lastname@example.org