The demand for rapid changes in power generation is increasing and thus leading to a requirement for the quick start of boilers. However, one has to be careful to not heat a boiler too rapidly, as it might lead to material failures. This example uses a nonlinear boiler model that captures the key dynamical properties.
Drum Boiler Model
The nonlinear drum boiler model is connected to a feedwater pump, a furnace and a valve at the steam outlet. In order to prevent overflow of water inside the boiler, the feedwater needs to be controlled so that the water level is kept at its set point.
Complete drum boiler model.
Optimize Startup Time
As the startup time is shortened, the thermal stresses operating on the boiler walls increase. The gray-dashed curves are not within the tolerable thermal stress limits. The following plot shows that the startup is quickest at around 3000 seconds.
Use the Wolfram Language to carry out parametric analysis.
The magnitude of the thermal stress should be below 10 for safe operation.
Simulation Using Optimized Startup Time
The boiler starts with an initial volume of water and steam. As the steam outlet valve is opened, steam leaves the boiler and water is fed using the feedwater pump. As heat is added to the boiler, water is converted into steam. After startup, the rate of evaporation of water is equal to the inflow of feedwater. The high-enthalpy steam obtained from the boiler can be subsequently used to drive a turbine and generate electricity.
Fluid Undergoes Phase Change
Water is converted to steam inside the boiler.
The blue curve in the top plot shows the volume of water. The orange curve in the middle plot shows the volume of steam. The red curve in the third plot shows the amount of heat added by the furnace.