Advanced Process Control Systems on DCS
What we actually control
Advanced process control is a specific set of loops, not a philosophy. On power plant and refinery utilities we have implemented and commissioned:
Coordinated plant load control. Boiler and turbine controlled as one unit against a load target rather than separately against local setpoints.
Primary and secondary frequency control. Response to grid frequency deviation, and to dispatch, with the response measured at acceptance rather than assumed.
Solid fuel allocation by calorific value. Distribution of fuel across feeders according to heat value, with automatic calculation of the calorific value of petroleum coke from the combustion result.
Steam temperature control. Cascade regulators working against a superheater model, rather than a single loop chasing an outlet measurement.
Combustion air and oxygen. Primary and secondary air control, with an oxygen cascade controller referenced to boiler mode and fuel.
Emissions. SO2 and NOx regulation through furnace temperature and lime dosing, held against the permit limit rather than against a comfortable margin.
Automatic boiler start-up from a hot state. As a DCS sequence, with the same ramp and the same drum stress every time.
Island mode and load rejection. Governor transfer, load shedding by priority, and frequency control in the islanded network.
Delivered as named optimisers
On four boilers of one plant we implemented, as a set — documented on our 260 t/h CFB boiler advanced controller project:
- Performance monitoring system
- Combustion optimiser
- Steam temperature and pressure optimiser
- Fuel optimiser
- SOx and NOx emission optimiser
They run together against a real-time optimisation target rather than as independent loops, with plant coordinated control above them setting the load.
Continuous performance work
After commissioning, control loop performance is monitored, loops are retuned, and alternative control strategies are implemented where the existing one limits the unit. Deviations that indicate a developing problem are reported with the corrective measure, not only the alarm.
Advanced Boiler Load Controllers
Advanced load controllers for a 260 t/h CFB boiler on Emerson Ovation — combustion, fuel allocation and emissions held against the permit limit. See the CFB boiler advanced controllers project.