Intermittency of renewable electricity generation poses a challenge to thermal power plants. While power plants in the public sector see a decrease in operating hours, the utilization of industrial power plants is mostly unaffected because process steam has to be provided. This study investigates to what extent the load of a combined heat and power (CHP) plant can be reduced while maintaining a reliable process steam supply. A dynamic process model of an industrial combined CHP plant is developed and validated with operational data. The model contains a gas turbine (GT), a single pressure heat recovery system generator (HRSG) with supplementary firing and an extraction condensing steam turbine. Technical limitations of the gas turbine, the supplementary firing, and the steam turbine constrain the load range of the plant. In consideration of these constraints, different operation strategies are performed at variable loads using dynamic simulation. A simulation study shows feasible load changes in 5 min for provision of secondary control reserve (SCR). The load change capability of the combined cycle plant under consideration is mainly restricted by the water–steam cycle. It is shown that both the low pressure control valve (LPCV) of the extraction steam turbine and the high pressure bypass control valve are suitable to ensure the process steam supply during the load change. The controllability of the steam turbine load and the process stability are sufficient as long as the supplementary is not reaching the limits of the operating range.