Design Plant-wide Control to Waste Heat Recovery Generation on Cement Industry Based HYSYS

Waste heat recovery generation (WHRG) is a power plant system that utilizes the flue gas to generate an electrical power in cement industry. This plant has various unit operations, such as economizer, evaporator, superheater, steam drum, and turbine. To design WHRG plant, steam drum needs to be controlled in the first place, for the reason that this unit operation will affect steam quality utilized to drive the turbine. There are three finest control elements which can be applied on steam drum; they are level control, pressure control, and mass flow rate control. The control structure on steam drum has deficiency on overcoming the load change value. To handle this problem, WHRG plant needs the other control structure. Plantwide control (PWC) is one of control method to handle the default load changes value. There are two kinds of design methods part based on PWC, the first part is top-down and the second part is bottom-up. Top-down part is a method used to optimize a particular process by determining the advantageous function, while bottom-up part is a method used to maintain the stability rate of the system. Since this study was aimed to control WHRG plant by considering the stability rate, bottom-up part was utilized. The stages used in designing the research based on bottom-up part are determining the operational objectives and limitations, analyzing the degree of freedom in the form of degree of freedom value used to calculate the total of manipulated variable (MV), determining variable process needs controlling, determining the manipulator of production rate, determining the structure of regulatory control layer, determining the adjustment of controller based on Relative Gain Array (RGA) method, and administering open loop test derived from the resulted system's responses. Based on PWC method, there are three kinds of control structures; they are boiler follow (BFC), turbines follow (TFC), and coordinate controller (CC). The output response resulted by this simulation show that CC is the most precise control structure to handle the load changes on WHRG plant. It can analyze with low value of IAE, settling time, and maximum overshoot of the control result. The IAE value of CC is 857.3439, BFC = 1182.895, while TFC = 887.1246. CC control structure produces IAE better than BFC and TFC. Hence, the precise control structure for WHRG plant is CC.