Dr K. Wendelberger, Siemens, Germany
Experience shows that the typical approach in setting up power plant automation structures – to copy and modify, to apply fixed standards, and to adapt them to the required project and/or customer specifications – can be extremely time consuming.
All I&C functions must be modified individually to each plant design and to the selected variant from a wide range of process technologies. At the same time, they must be consistent and suit each other.
The best way to reduce the effort in creating the required I&C functions, while also improving quality, is a new approach in standardisation. Choosing a suitable solution from a portfolio of proven best-practice multi-variant standards, and adapting it to the project’s specific requirements by picking the right variant, will automatically bring: increased quality, improved documentation and – in the best of cases – reduced project execution time.
Applying this approach, Siemens Energy’s newly developed Advanced Rapid Technology Engineering (ART-E) aims to improve quality as well as to ease the handling of different variants in power plant process design at the earliest possible stage.
Variability in process technologies
Each power plant has its own process configuration, which requires an individual automation structure. At first sight, the variability of plant process technologies presents an obstacle to defining standards for I&C engineering documents. To illustrate this general challenge, the feedwater supply system of a steam power plant will be considered in more detail below.
|Figure 1: Diagram of a steam power plant feedwater supply system|
The major variants of the feedwater supply system (see Figure 1) are:
- 1. The feedwater system can consist of one, two or three feedwater pumps, which can be continuously controllable or fixed-speed (especially in small power plants).
- 2. The feedwater pumps can be motor driven or turbine driven.
- 3. The feedwater pumps can have one single discharge valve or one main and one bypass valve.
- 4. There can be one single recirculation valve or one control valve and an isolation valve. Additionally, the minimum flow can be controlled via a continuously operated valve (closed-loop control) or via an on/off valve (open-loop control).
- 5. The feedwater pumps can have suction valves or not.
- 6. The feedwater flow measurement can include the recirculation mass flow or not. There can be a separate recirculation mass flow measurement or not.
- 7. There can be two feedwater control valves in parallel, or one control valve in parallel with one isolation valve. If there are two control valves in parallel, there can be one low-load and one high-load valve, or two identical valves. The control valves can have separate isolation valves or not.
- 8. The boiler can be of the drum type (requires drum level control) or a once-through boiler (requires evaporator outlet control).
These are only the major variants of a feedwater system – many more alternatives can be defined by considering further details and measurement locations.
Variants of the different systems as listed above can also occur more or less independently of each other, which means the overall feedwater system can have a huge number of different configurations. And each configuration sets different requirements in engineering documents (function diagrams, plant displays and text descriptions).
Such high variability prevents defining a separate standard for each variant of the process. Each system would otherwise have too many standards to maintain and it would be impossible to ensure the most modern control concepts are implemented.
Each process system therefore needs a standard that covers all possible variants of the process technology. The user can then select the variant of the standard that suits the specific project’s process configuration.
This selection would be enabled by an easy-to-maintain software tool with only one standard per process system, dispensing with manual adjustments of the standard to suit the actual process configuration.
Standardisation and efficiency
As shown above, engineering high-level automation functions for power plants offers considerable opportunity for spending lots of time in determining automation structure for each customer’s individual requirements. And each plant’s designated process technology can vary greatly – from the manufacturers to the working points and operating conditions. As a result, either defined automation standards must be adjusted during execution to meet a project’s specific requirements, or alternative standards must be designed to ensure project-specific requirements are met.
Manually adapting a standard to the project specifications is very time consuming and can only be performed accurately by an experienced engineer with a deep understanding of the control concept. On the other hand, pre-defined, proven, standardised elements provide substantial opportunities to save time and reduce potential sources of failure, especially in I&C functions such as:
- the function diagrams for open- and closed-loop control, in which it is defined how measurement signals are used and processed to determine actuator commands for optimal plant performance,
- the plant displays, which deliver information about the current performance of the plant to the operator, and which allow the operator to apply commands manually;
- the text descriptions of the control loops.
High variability of individual plant process technologies means maximum benefits are provided by a modular standardisation concept with each module covering a single system within the complete process. Thus the need of manual adaption is minimised and the user can simply define and select the corresponding variant for their specific project.
To define and implement standards that fit the different configurations of the plant processes, Siemens Energy developed a module-based standardisation system, the ART-E software solution. Each ART-E module refers to a system such as the feedwater system. The module includes: function diagrams for open-loop control, function diagrams for closed-loop control, plant displays and a text description of the automation concept. The ART-E software modules are designed to cover all required features as specified above:
Consistency and matching of the standard documents within and between the modules
All function diagrams are based on a common list of measurement and drives, and the interfaces between the function diagrams are well defined. Signal connections between the function diagrams are closed. The open-loop control concept suits the closed-loop control concept. All function diagrams suit the standards for the plant displays. For instance, the indicators on the screens use the signals as defined in the function diagrams and the plant displays are mapped to the function diagrams.
Availability of each module in different variants
For example, the feedwater module is available for: two or three feedwater pumps, turbine-driven or motor-driven pumps, once-through or drum boilers. ART-E allows the selection of each combination of variants. For instance, the feedwater module can be selected for a supercritical once-through boiler, with one motor-driven and two turbine-driven feedwater pumps, with a start-up continuous control valve and a shut-off valve in parallel. ART-E places no restrictions on the combination of such variants. More than 100 million different project-specific combinations can be selected for the feedwater system.
In this context, it has to be considered that the selection of a certain variant of one module can also influence another module. For example, the feedwater control system and the control of the boiler circulation system cannot be designed independently of each other. ART-E also assures the consistency of the engineering documents across modules.
Choice of the optimal automation concept for the specific plant
For the various plant configurations the required modules in their required variants can be chosen. ART-E ensures that the automation structures that are selected provide an optimal performance of the power plant with the given configuration of the process.
Consistency and matching of the selected documents
ART-E also ensures that the selected engineering documents have the same consistency as discussed above for the documents in the module itself. The function diagrams, plant displays and description suit each other, and the interfaces are well defined, whether the documents stem from the same module or from different modules.
No additional system resources for the running I&C system
After the ART-E selection, the required function diagrams, plant displays and text descriptions are available to suit the specific requirements of the power plant in an optimal way. These engineering documents are normal elements of the I&C system. There is physically no difference between an engineering document selected by ART-E and an engineering document created another way (e.g. manual engineering or copy from another project plus manual adaptation). ART-E does not require any additional resources of the running I&C system.
Modifiability of resulting engineering documents
After the ART-E selection, ‘normal’ function diagrams, plant displays and text descriptions are available. It is still possible to modify these documents manually. This might be necessary in the case of special configurations not covered by the standard, such as systems equipped with fewer measurement devices.
However, since the ART-E standard covers the basic structure of the system, such modifications would only be of subordinate significance and would not affect the basic control structure. Minor modifications are allowed and are not in contradiction to the benefits of ART-E. Figure 2 highlights ART-E’s basic structure.
|Figure 2: Basic architecture of the newly developed ART-E software solution|
The Siemens ART-E standards were originally created by selecting the best-in-practice concepts from the large number of power plants that have been automated worldwide. Most importantly they are continuously improved by an expert team, based on the analysis of performance of the various concepts in the actual power plants, as well as through simulation studies. Finally, they have proven successful in many power plants.
Siemens ART-E comprises a consistent system of modules that allows the selection of variants of a certain standard that suit the configuration of the specific plant. Therefore the engineering documents will accurately suit the considered process technologies and manual adaptations are kept to a minimum. By this means the Siemens Energy modular standardisation approach delivers several benefits:
- Optimal plant performance due to best-in-practice automation concepts.
- Optimised engineering due to reduced effort for creating the various I&C documents.
- Reduced commissioning time due to the high quality of the engineering documents and repeated use of the proven and well-known concepts.
- Easy-to-use because of a consistent control philosophy, standardised layout of function diagrams, uniform concepts for alarming and messaging across the whole plant.
As proven in many power plants worldwide, optimal plant performance based on optimal automation concepts directly raises the profitability of the plant. By means of advanced control concepts the efficiency, flexibility and stability of power plant units can be improved. And as the ART-E software modules consist of best-in-practice solutions, the Siemens standardisation approach not only has a (direct) positive impact on the project handling and the quality of the results, but also has a (indirect) positive effect on the profitability of the plant.
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