This paper presents a fractional order controller of the class ID α-1 for robust control of the steam pressure in the steam drum of a bagasse boiler. The proposed controller improves the effectiveness on the control, and likewise the energy efficiency of this plant. The dynamics of this process drastically changes with the variation of the specific heat of combustion (I) and the use of a fractional order control looks therefore suitable. A mathematical nominal model of the steam pressure variation in the steam drum of a bagasse boiler was obtained and validated. Experimental studies provided an estimation of the range of variation of the parameters' model when the specific heat of combustion varies in the operating range [Imin, Imax]. The proposed fractional order controller has been compared to the standard PI and PID controllers. All of them have been designed by means of the same frequency specifications and their nominal time responses are similar when input reference changes and in presence of disturbances. The PID controller and the fractional order one have been also designed in order to maximize their robustness when the gain of the steam pressure in the steam drum of bagasse boiler changes in the range [Kmin, Kmax]. Simulated results show that the fractional order controller is more robust than the PI and the PID controllers when the gain of the plant changes but preserving the robustness when time delay varies. © 2014 CEA. Publicado por Elsevier España, S.L. Todos los derechos reservados.