AbstractSolid fuels as bark and waste-wood are typically burned on grates. To ensure good stability and load following properties for grate boilers both the drying and combustion processes must be well controlled. This presumes good instrumentation for the grate, special measurements and control systems for combustion power and good knowledge of the process behaviour.This paper presents the principles for modelling the grate boiler. Simulation model is developed on the basis of process experiments. The methods and devices for modelling and simulation are also handled. The paper further proposes a control system for the supply and combustion parts of a grate boiler.