Maximising operational efficiency
16 January 2012
Maximising throughput, availability and product quality, while minimising operating, maintenance and energy costs, helps to get more out of a process plant. Simon Ellam, of Siemens Industry Automation, outlines some of the areas that can have a big impact on maximising a process plant’s operational efficiency.
Operational efficiency is the ability for an organisation to execute its tactical plans while maintaining a healthy balance between costs and productivity. Companies operating process plants are concerned with economic efficiency of plant operation as a ratio of earnings and costs. All factors that contribute to this equation need to be optimised: throughput, plant availability and product quality. All factors that impact on this equation have to be minimised: operating cost and maintenance costs, energy consumption and raw material consumption, off-spec products, emissions, safety risks and environmental pollution.
There are many areas that can support efficiency objectives and true process optimisation across a process plant. The following are indicative – though not exhaustive - of some key aspects to consider on the road to improved operational efficiencies.
Transparent process operation
The DCS is the ‘window to the process’ - the human-machine interface. Any action in the process plant can be operated and controlled via the DCS. Clearly structured user interfaces offer an excellent overview of the entire production process and provide safe and comfortable process operation. Considering the overall supply chain of a production plant from raw material supply via production to product delivery, the production itself is the central step, and the DCS is the central data source for information on production. The integration of the DCS into the IT processes of supply chain management is the foundation of cost transparency in production, such that the financial effect of specific operation sequences can be accounted or predicted.
Advanced Process Control (APC)
APC methods can be an essential tool to help improve operational efficiency of process plants with respect to productivity and economics, product quality, operability and availability, agility, safety and environmental issues. APC solutions can be realised much more cost effectively due to a DCS embedded implementation with standard function blocks and pre-defined wizards and templates for implementing basic APC principles.
Energy management, as defined in DIN 4602, is the predictive, organised and systematic coordination of the procurement, conversion, distribution and use of energy to cover requirements while taking into account ecological and economic aims. Process plant tools can assist with the standardisation, visualisation and archiving of energy and output averages with time stamps. The plant consumption data is gathered via field bus and the transparency of energy consumptions is a basic prerequisite for plant energy management optimisation strategies. In this way energy management is anchored alongside the operator station and maintenance stations as the third pillar of the process control system.
The transformation of production orders to a detailed schedule of batches on certain plant units at given starting times contains optimisation potential in the sense of efficient plant operation. Several optimisation targets have to be pursued at the same time while considering limited production resources. These can include: compliance with delivery dates and specifications of product quality; maximising capacity throughput; minimising cleaning efforts when different products are run in the same tank reactor and avoiding peak loads in energy consumption. Again, process optimisation tools can help with batch planning and automatic execution of planned batches.
Simulation and training
Simulation is a technology to help replicate processes using a simplified model to copy the reality. Simulation helps to increase efficiency in different phases of the plant life cycle. In the early stages of DCS engineering, simulation is used by engineers to test DCS software with the goal of increasing engineering efficiency and accelerate plant commissioning. In later stages of plant operation and in order to increase operation efficiency the appliance of Operator Guidance Systems (OGS) and Operator Training Systems (OTG) can be applied for operator training purposes using simulation models. It can also be utilised in operation if, for example, the evaluation of a new operation such as accelerating product grade changes or start-up and shutdown procedures need to be closely examined.
If new process plants are realised and simulation methods used from the beginning in all plant life cycles, benefits are clear in areas such as problem free plant start up and fast and efficient commissioning. The early preparation of the operator team using a realistic simulation and the early test of DCS software contribute to such advantages also.
An OTS typically contains the same OS pictures as the real plant, in combination with real or PC-emulated controllers, in order to provide a realistic training environment for operators. Instead of the real process, a dynamic process simulator is linked to the controllers. This allows efficient and realistic operator training and repeatable training scenarios without undue safety risk.
Safety and security
The goal of safety engineering is to avoid accidents and consequential damages after occurrence of errors in order to achieve maximum safety for humans, process and the environment. Operation and construction of process plants with risk potential have to comply with the international standard IEC 615 11 for functional safety of safety instrumented systems. A ‘safety instrumented system’ is a combination of sensor, logic devices (such as the PLC) and actuators that detects abnormal situations and drives the process back to a safe state. To help support safety objectives in the plant, solutions such as a safety integrated approach can provide real peace of mind.
To provide standard and fail safe functions combined into a single controller and fieldbus architecture can offer impressive economic benefits whilst actually increasing the overall safety levels of a manufacturing process. DCS architectures can now accommodate the connection of safety field devices – from E-stops and safety instruments to safety enabled variable speed drives onto a single plant wiring infrastructure, eliminating the need for costly installation of separate hard-wired safety circuits. Combine this with integrated safety engineering tools and operator displays that integrate safety critical operator information into standard plant based mimics this can provide a win for both operational efficiency and for ever increasing safety requirements.
The costs arising in the operational phase of a process plant constitute a significant share of the overall life cycle cost over the typical 15-20 year asset life of a plant control system. The baseline for profitable life cycle costs is high plant availability, achieved by a robust DCS with solid application software based on standards and by preventative plant maintenance. Service costs for engineering support, maintenance and upgrades play an important role as well. Consequently, plant management should be aware that the main requirements for a comprehensive service package include: investment protection through service products; system availability by ensuring serviceability; serviceability using suitable migration concepts and clear obsolescence management linked to the market withdrawal of technical components or software versions.
Obsolescence has typically proved a cyclic problem that has culminated in the large amount of legacy control systems we see on UK plant infrastructure. The conclusions that plant owner/operators quite rightly draw is that a large part of the decision making process to migrate to a modern process control system is it’s ability to be modernised and innovated without reproducing the same legacy issues that have gone before. A modern DCS platform should come with those lifecycle guarantees built in and so process manufacturers no longer need to feel that this is a cross they have to bare.
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