Dec-2015

Integrated plant control and monitoring

Turbomachinery controls (TMC) such as antisurge and load-sharing controls, as well as its solution hardware platforms, have been evolving through faster system response, higher availability and standardisation of control applications.

Shun Yoshida
Compressor Controls Corporation

Article Summary

Packaged turbomachinery control solutions that horizontally integrate critical control and safety functions (such as condition monitoring systems, overspeed detection systems and surge detection systems) are considered to be the best practice in terms of maximising the solution performance, reducing project execution risks and achieving quality lifecycle support experience. 

As end users continue to optimise operations through consolidation of resources it is becoming increasingly important to have a highly consistent and well integrated plant control and monitoring environment. However, due to the typical project execution structures involving multiple contractors and suppliers, achieving deep and consistent integration between TMC and primary operator interface, typically provided as a part of distributed control system (DCS), has been a challenge in some projects. In many cases contractors and suppliers each execute highly segmented projects within the scope, often communicating via the exchange of static design documents.

Evolution of turbomachinery control
Turbomachinery trains, often times consisting of various stages of centrifugal compressors with gas/steam turbine or electric motor drivers, are critical components of continuous manufacturing processes. In industrial applications such as refining and petrochemical, availability and efficiency of critical turbomachinery units directly affect the availability and efficiency of the respective process units.

These machines must safely and reliably operate under varying process conditions and within multiple mechanical limits such as surge and choke. Therefore, it is imperative that these machines be equipped with robust TMC solutions that can not only detect and mitigate fast occurring events such as surge but also provide fast, accurate and stable control of process variables.

For instance, if a TMC system that prioritises machine protection over stable process control overreacts to process disturbances, it will not only pose the risk of frequent machine and process disruptions, but it will also drive increased safety margin which may sub optimise the compressor operation below its maximum attainable efficiency and throughput. On the other hand, if a system is designed only to provide stable process variables, control response may be too slow to protect the machine from surging, potentially resulting in compressor mechanical damages that require lengthy shutdowns for repair.

In order to meet the challenge of achieving these seemingly conflicting objectives, TMC systems have evolved with advancement and standardisation of algorithms that combine various control responses, as well as control hardware platform optimised for high speed response and maximised availability. Equally important to having a strong technical base, if not more, are the engineering services offered by a TMC contractor that range from instrument and control valve selection, process piping review, control strategy development, to performing surge test on actual machines. 

Evolution of plant control and monitoring technologies
As the TMC system evolved over time, so did DCS systems backed by rapid advancements in computer and network technologies, particularly in their centralisation of control and monitoring capacities. In order to improve the safety and efficiency of plant operations, which have now become a critical part of social infrastructure, there is much demand by end users to improve their operators’ ability to make quick and accurate decisions in abnormal situations and to support capturing and sharing of operational knowledge. Correspondingly, consolidation of previously dispersed operator HMI screens, the development of remote control and monitoring solutions, and mitigation of associated cyber security risks have become critical in designing plant operation environment.

Operator decision support in abnormal situations
Another revolution in recent times has been the integration of DCS data with higher level business systems such as enterprise resource planning (ERP) and manufacturing execution systems (MES) to dynamically adjust the plant operation in accordance with available resources and market conditions. Thanks to the vertical integration of control systems with production management systems, much of the plant operations under normal process conditions are now automated, enabling end users to run the plant with a smaller number of operators. In abnormal or infrequent operating conditions, including plant start-ups and shutdowns, turn-down and recovery operations from incidents or equipment malfunctions, decisions that experienced operators make remain instrumental to keeping the plant running safely due to the lack of automation under such conditions.

The phenomenon known as the “Great Crew Change” poses a challenge here. According to the American Petroleum Institute (API), nearly half of the current oil and gas workforce is projected to retire in the next 5 to 7 years. This can create a serious gap in the plant workforce including the retirement of skilled operators who have been trained through real-life experience of handling abnormal operating situations. In order to account for this potential skills gap, it important that future operators have access to a decision support system containing optimised alarms, detailed diagnostic information coming from field instruments and equipment, time-synchronised logs of ongoing events, as well as standard operating procedures (SOPs) outlining causalities and recommended actions. Additionally, in order to safeguard the plant control systems from malicious attempts, control system hardware and HMIs are oftentimes placed in a physically segregated environment under strict area control. Therefore, the demand for a tighter system integration between sub-systems such as TMC and DCS for realising remote operator access to the detailed sub-system information should only grow stronger.

Stepping stones for truly integrated experience
In order to provide a true integration between TMC and DCS without inflating the amount of engineering effort and costs associated with it, it seems that a both strategic and technical approach is needed to streamline the project execution work. Leveraging its meticulously standardised and refined control applications and hardware can simplify the DCS integration process from both physical and software perspectives.

Standardisation on physical interface includes network protocol and architecture used to communicate the data between the two systems, which will not only simplify the engineering process for contractors in planning for necessary network infrastructure and ‘cablings, but it would also significantly reduce time to establish communication between TMC and DCS during integration factory acceptance test (IFAT) which will result in additional cost savings.

Standardisation on software or HMI design enables automation contractor(s) to properly estimate the number of I/O points, required network bandwidth and system specifications while addressing consistency in operator interface designs. It also enables early design review of HMI with end user operators, thereby contributing to higher customer satisfaction.

When developing standard designs for TMC application interface, a careful consideration must be taken to ensure that the display modules follow the same HMI standards as the rest of the DCS HMI. This includes faceplate layout, alarm integration and process trends. Integration of rationalised alarms, instrument and equipment diagnostic data and critical loop configuration parameters are all key to creating high performing operator interface.