Drive technology – the key to lower operating costs Focus on efficiency - cpp - chemical plants & processes

Drive technology – the key to lower operating costs

Focus on efficiency

Drive technology plays a key role, as it represents approximately two-thirds of all power consumed in industry. Embedded in an overall management concept for operational energy, significant cost saving potential can be tapped using efficient drive technology. Product developments, such as a seamless series of high-efficiency motors – also for hazardous areas – and higher power ratings for energy-saving frequency converters, offer additional opportunities to cut costs.

The author: Stefan Rausch Technical Editor, Siemens Large Drives Business Unit

Successful energy management increases the productivity of the energy used in a plant or system within the framework of a continuous improvement process. The Siemens energy management concept is sub-divided into three basic phases. In the “Identify” phase, suitable hardware and software packages acquire, visu-alise and analyse the energy flows in a plant or system. As a result, these become transparent, permitting the process to be optimally configured from an energy perspective and potential cost savings identified. In the second phase, “Evaluate”, powerful software tools calculate the precise energy saving potential and the economics of possible measures. The third phase, referred to as “Realise”, involves implementing specific measures that actually save energy.
Drive technology as an important lever
When it comes to energy saving measures, drive technology is frequently the most important lever. As mentioned previously, this is due to its dominant role in industrial power consumption. This particularly applies to the process sector with its huge number of drives for pumps, fans, compressors, extruders, mixers, kneaders and conveyor belts. A first glance at the operating costs of an individual motor clearly shows the significance of energy consumption in drive technology. Approximately 95% of a motor’s lifecycle costs occur in operation – where power generally represents the largest cost factor by far. The basis for energy efficient drive systems is the efficiency of the motors themselves, especially if they have long operating times, as is the case in many processes. In the meantime, legislation has taken up the issue of motor efficiency. As a result of climate protection, more and more countries around the world are stipulating minimum efficiencies. For instance, from June 16 this year only motors with the high IE2 efficiency class can be marketed in the European Economic Area. IE2 motors have an efficiency up to 7 % higher than their conventional counterparts.
High-efficiency motors
Siemens supplies a seamless range of high-efficiency motors covering the complete valid scope of the standard from 0.75 to 375 kW – not only for standard motors but also for explosion-proof models, to which the new legislation does not even apply. However, this range combined with that of Siemens’ Loher subsidiary means that motors with all types of protection – Ex n, Ex e, Ex p or Ex d – are available with IE2 efficiency. The high-efficiency Ex motors are also certified according to the generally applicable international rules and regulations relating to explosion protection. These include the new international IECEx scheme, which in the medium term will serve as a global platform for the mutual recognition and acceptance of tests and certificates for explosion-proof electrical equipment. The IECEx scheme has already been specified in Australia and New Zealand as well as in many important industrial nations – almost the whole of Europe, China and Russia as well as the US and Canada have signed the appropriate certification agreement.
Beyond the existing series of IECEx and other certified explosion-proof motors, such motors can also be manufactured on request in the even higher IE3 efficiency class. Loher and Siemens are presently developing a seamless series of explosion-proof motors with IE3 efficiency.
The development of non-explosion-proof standard motors has progressed even further, and IE3 (Premium Efficiency) will be mandatory for these types following a transitional phase from 2015 to 2017. Products that meet this standard are already available today. One example is the rugged series of 1LE1 grey cast iron motors in IE2, IE3 and Nema Premium versions for North America, which covers the complete global market for high-efficiency motors.
Up to 70 % cost saving potential
The process industry, in particular, holds additional, decisive potential for saving energy, where the predominant drive applications include pumps, fans and compressors for moving gases and liquids: variable-speed operation of fluid-flow machines, where the power drawn increases proportionally to the speed to the power of three. The partial-load losses are enormous if this kind of machine is driven by a fixed-speed motor and the flow rate is mecha-nically controlled. This is because the motor always runs at full speed, although for flow rates less than the maximum only a fraction of the power is frequently necessary, and due to the above-mentioned “power of three” rule. On the other hand, frequency converters are designed to adapt the speed exactly to actual operational requirements and thus to the power that is drawn. Put another way, the motor only draws the power that is required at a particular operating point – no more and no less.
In many applications, the maximum flow rate is only rarely needed. Depending on the individual pumping profile, variable-speed operation can slash power usage by as much as 70 % for pumps and compressors.
It goes without saying that values such as these are only achieved if the flow rate varies as a result of the underlying process. In spite of this, energy can also be saved in drive tasks where the flow rate remains constant. Soft starters belonging to the Sirius family, for example, avoid current peaks and when compared to motors that are directly connected to the mains supply, they reduce the peak load when starting by up to 60 %.
Frequency converter as the solution
However, for applications with frequent part load operation, a frequency converter is always the best solution to achieve maximum energy efficiency. The seamless, integrated Sinamics family covers all drive applications in the process industry, from small dosing pumps to the central compressors of a gas liquefaction plant and from 0.12 kW all the way up to 120 MW. In order to fully utilise the cost saving potential that can be achieved through variable-speed operation, the power range of frequency converters specifically tailored to applications such as pumps, fans and compressors has been extended. The range of the special G120P converter for pump, fan and compressor applications now includes 90 kW and the Sinamics G150 cabinet unit is available for power ratings up to 2700 kW. In the case of the Dynavert T inverter, explicitly developed by Loher for chemical and petrochemical applications, the range has been increased from 3900 to 6600 kW. Features specific to the chemical industry, such as Namur terminal strips and functions as well as protective separation according to PELV, are also incorporated in this extended power range. Furthermore, the drive units can be fully integrated into higher-level process control systems like Simatic PCS7 using special driver blocks and faceplates.
Close interaction results in cost savings
Drive systems in the process industry are fully integrated into the higher-level automation environment. Communication is established through appropriate interfaces and bus systems, e.g. Profibus, or in the process industry increasingly Profinet. Energy data is also transferred via these interfaces. In a plant-wide solu-tion, the drive technology interacts perfectly with all other products and systems that are decisive for energy management. These include the Sentron Pac multi-function devices for acquiring energy values, software such as b-data and Simatic Powerrate for PCS7, Sirius switchgear and protection devices for intelligent load management and a standardised data interface to selectively shut down loads that are not presently required in the process. The motor, frequency converter and mecha-nical interfaces – such as gear units or couplings – are optimally harmonised and coordinated with one another in the drive system, which in turn further increases the overall system efficiency. This comprehensive interaction of all plant systems and components is a precondition of optimal energy and cost efficiency in line with the state-of-the-art. An integrated solution, in which all essential components and systems are purchased from a single source, not only has a short-term impact but gradually enhances the productivity of the energy used over the complete lifecycle of the plant.
Hall 9, Booth A72

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