The invention relates to a method and equipment for treatment of black liquor at a pulp mill in order to recover chemicals and energy contained therein. So, when the video display is emitting light users of the apparatus can see the images provided by the display device through a two-way mirror material. Therefore, a greater number of irrigation stations can be connected to the controller when the larger module is substituted for the two smaller modules. The duty cycle of the switching devices is controlled to give the desired wind turbine performance.