Drum Boiler Level Control via Dynamic Gain Shaping

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Solution Overview

Problem

Drum level control in power plant boilers is challenging due to complex dynamics of two-phase flows, wave presence, unknown heat and pressure disturbances, and load demands, leading to frequent trips and equipment damage, especially during transient operations.

Innovation Solution

A level control system that includes sensors to measure liquid level, gas flow rate, pressure, temperature, and feed-liquid flow rate, with a signal processing unit generating filtered output signals, a flow demand control unit determining feed-liquid flow demand, and a shaping unit adjusting gas flow rate based on pressure and temperature, to maintain water level within predetermined limits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional feed water control valve actuation is used to control water level, then water level control is attempted, but inverse response is exhibited especially during transient operations causing instability

Engineering Contradiction:

Improvewater level control reliabilityVSAvoidwater level stability during transient operations

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent applies dynamic control by adjusting controller gains based on operating conditions. The controller transitions between different control modes (manual override, automatic control, anti-surge mode) depending on transient vs steady-state conditions, thereby adapting the control strategy to maintain stability during transient operations while ensuring reliability during normal operation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements feedback control by continuously monitoring water level, steam flow rate, and feed water flow rate, then using this information to adjust the feed water control valve. The controller uses feedback from level sensors and flow meters to automatically correct deviations and maintain stable water level within the drum.

Inventive Principle:

Principle #23Feedback

2Speed

If controller response is increased to address inverse characteristics, then water level control responsiveness is improved, but system instability and trips increase especially at lower pressures

Engineering Contradiction:

Improvecontroller response speedVSAvoidsystem stability under pressure variations

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes controller parameters dynamically based on pressure conditions. At lower pressures, the controller uses different gain values and control strategies compared to higher pressures. The anti-surge mode activates when pressure drops below a threshold, fundamentally changing the control behavior to prevent instability while maintaining responsiveness.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If steam flow rate measurement is used for control, then feed water flow demand can be determined, but incorrect measurements due to sensor faults or malfunctions may cause false control actions leading to trips

Engineering Contradiction:

Improvesteam flow rate measurement accuracyVSAvoidcontrol system reliability under sensor faults

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent prepares for sensor failures by implementing redundant measurement systems and fault detection mechanisms. The controller can switch to alternative control modes or use estimated values when sensor measurements become unreliable, thereby cushioning against the impact of sensor faults and preventing false trips.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

4Productivity

If aggressive feed water flow response is applied to correct water level deviations, then water level control effectiveness is improved, but inverse response and oscillations are exacerbated during transient conditions

Engineering Contradiction:

Improvewater level correction speedVSAvoidwater level stability during transient operations

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent applies preliminary anti-action by detecting transient conditions before they cause instability. The controller identifies when the system is in a transient state (e.g., during load changes or pressure variations) and preemptively reduces control aggressiveness or switches to anti-surge mode, thereby preventing oscillations and inverse response before they occur.

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS7931041B2System and method for controlling liquid level in a vessel

Publication Date: 2011.04.26 GE INFRASTRUCTURE TECH LLC

AI summary

A system includes sensors configured to measure vessel parameters. A signal processing unit receives sensor output signals and generates a first, second, third, fourth, and fifth filtered output signals representative of liquid level, gas flow rate, feed-liquid flow rate, vessel pressure, and vessel temperature, respectively. A flow demand control unit receives the first filtered output signal and generates an output signal representative of feed-liquid flow demand. A shaping unit receives the second, fourth, and fifth filtered output signals and generates an output signal representative of shaped gas flow rate. A liquid level control unit controls the liquid level within predetermined limits by controlling one or more components based on the output signals from the flow demand control unit, the shaping unit, and the third filtered output signal.