ICSS works on the design, modification, commissioning and optimisation of industrial control strategies. The work is not limited to adjusting PID controller parameters: a loop depends on its measurement, actuator, process dynamics, interactions with other equipment, operating sequences and plant protection limits.
Commissioning experience makes it possible to analyse the control strategy and the plant’s physical response together. Trends, events and tests are compared with PFUPs, P&IDs, electrical diagrams and control-logic diagrams to distinguish incorrect tuning from measurement, sizing, logic, communication or process issues.
Areas of work
Control and regulation work may cover:
- Boilers and HRSGs: one- or three-element drum-level control, feedwater flow, demand distribution between several valves, multi-stage attemperators, and steam pressure and temperature.
- The water–steam cycle: variable-speed feedwater pumps, HP/IP/LP bypass valves, attemperation, condensate, deaerator, auxiliaries and coordination between several pressure levels.
- Steam or gas turbines: speed, load, valve positioning, test sequences, load recovery, coordination with bypass systems, and start or shutdown conditions.
- Pressure, flow, level, temperature, enthalpy, speed, power, combustion, excess-air, oxygen-correction, load-control and AGC loops.
- Sequences, degraded modes, limiters, selectors, tracking functions and transfers between different control modes or actuators.
This list is not exhaustive. The method remains applicable to other plants whenever their physical behaviour, instrumentation and control strategy can be studied. ICSS can therefore apply methods proven in power generation to other industrial processes.
Designing a strategy suited to the process
A control strategy may combine several controllers in cascade or parallel, a split-range, minimum or maximum selectors, tracking functions that prepare a mode change, and bumpless transfers. Parameters may also be adapted to the operating point, for example according to available pressure, load, or the difference between steam and feedwater conditions.
When a loop’s natural response is too late, feed-forward can be added to PID feedback. It uses a load variation, valve position, flow or another process indicator to act before the controlled variable moves significantly away from its setpoint. This anticipatory action must remain coordinated with feedback loops, limiters and existing protections.
ICSS can also modify an existing strategy without replacing it entirely. It is often preferable to retain functions that perform well, isolate the cause of the difficulties, and then add the necessary tracking, limiting, compensation or feed-forward actions.
Controlled implementation
- Establish the initial operation. Reconstruct the different modes, transfer conditions, limitations, tracking functions and interactions with other systems.
- Analyse available data. Examine trends, events and tests to characterise the fault and verify that the measurement and actuator correctly represent the process.
- Prepare the modification and rollback. Define the new functions, adjustable values and activation criteria and, where required by the context, provide a selector for immediate return to the previous operation.
- Commission and adjust. Proceed through progressive tests, monitor effects on other equipment and adapt parameters based on the behaviour actually observed.
Modifications can be made on an operating unit when the architecture, tools and operating conditions permit. They are then prepared with a rollback option, test-stop criteria and monitoring extended to functions that could be affected. The objective is not merely to produce a smoother curve, but to preserve plant availability, safety and operating consistency.
Field experience
Distributing feedwater flow between two valves
At Kwinana, drum-level control used a small valve sized for approximately 30% of the flow and a main valve, controlled by several separate controllers. In one-element mode, the main valve did not open, which could leave insufficient available flow following the loss of a measurement required for three-element control.
The strategy was rebuilt around a common overall demand, followed by distribution logic and bumpless transfer between the two valves. Tracking functions were added for feedwater-pump changes, pressure-limiter action and manual operation. The modification was commissioned on an operating unit with a selector allowing operators to return to the previous concept during testing.
Coordinating multi-stage attemperators
At Niehl III, two attemperation stages had to maintain steam temperature while limiting stress on the steam turbine. The first stage, located upstream of the final superheater, responded too slowly and remained in use longer than necessary. The final stage then had to handle rapid transients on its own, without sufficient feedwater pressure in every situation.
The new concept coordinated both stages, dynamically adapted PID parameters to the pressure difference between steam and feedwater, and added feed-forward actions. The pressure delivered by the variable-speed feedwater pumps became an additional variable when valve opening alone was no longer sufficient.
This coordination was particularly important during the transition to low-load operation. In this mode, gas-turbine load is greatly reduced while the steam turbine remains connected. Steam temperature must decrease progressively to keep turbine stress within its limits, while the boiler undergoes significant transients during load reduction. Insufficient attemperator response could trip the steam turbine.
Boiler logic, bypass systems and transients at Sohar 3
At Sohar 3, ICSS worked on an architecture combining ALSPA P320 and Emerson Ovation. Modifications included an HRSG preheating mode, calculation and display of HP/IP/LP drum-temperature gradients, and transfer of exhaust-gas flow from ALSPA Controgas to Ovation.
The work also included analysing bypass pre-positioning strategies during load rejections and steam-turbine valve tests. A sequence observed during turbine shutdown led to a combined study of condenser-vacuum margin, reheated-steam bypass attemperation response and the thermal load sent to the condenser. This type of analysis avoids attributing an event to a single loop when several physical phenomena and control functions contribute to the transient.
Experience applicable to different processes
The methods used for HRSGs, water–steam cycles, turbines and their auxiliaries also apply to conventional power plants, hydropower, geothermal, concentrated solar power, water treatment, desalination and other industrial installations. Each new application begins with understanding the process and operating objectives, without imposing a solution from another project when its assumptions cannot be transferred.