Advanced Controls and Coupled 1-D, 3-D CFD Simulation for Optimum Plant Performance and Safety

Industrial plant explosions or fires either due to negligence, accident, or incompetence can have a devastating impact on human life, surroundings, and the economy. One such disaster is the Great Molasses Flood AKA the Boston Molasses disaster in 1919 where a 2.3-million-gallon molasses-filled storage tank exploded releasing molasses onto the streets at a speed of 35mph, killing 21 and injuring 150. During the summers, even today, the residents living close to the explosion claim the streets to smell molasses. This is the extent to which an industrial explosion can impact the environment. Today, advanced control and calibration units, process simulation technologies, and 1-D and 3-D CFD simulation tools can help design and control a component or an entire processing unit for optimum plant performance, plummeting any chances of a disaster. On contrary, there are also times when we feel insecure about these emerging technologies, which someday or already are too complex for our civilization to have control over!

Control and Calibration Units

Industrial plants with modern infrastructure and high production load require advanced control and calibration units not just to enhance the performance of the plant but also to ensure safety and to align with the emission protocols imposed by regulatory bodies. An automated calibration solution that can guide the not-so-skilled workforce in a metrologically efficient manner through calibration management software can cut costs, improve calibration efficiency, and will be compliant with industry standards. It is noted that the use of a high accuracy calibrator in a nuclear power plant can increase electricity production by up to 2 percent.

The various advanced control systems beyond the single loop method, that are widely used to operate or automate industrial processes include:

Cascade Control: Also known as the primary and secondary control type which consists of a primary loop that provides the setpoint and the secondary loop works as per the setpoint, reducing variations in the primary control variable. An example of a cascade control system is a jacketed reactor where the reactor temperature controller acts as the initiator by giving a setpoint to the jacket temperature controller. Here, it is the responsibility of the jacket to maintain the inside temperature of the reactor.

Feedforward Control: This type of control system is predictive. Here, the controller predicts the disturbance and clears it before entering the system. The prediction of the controlled variable is done from the process modeling information and in case that information is not available, it can be generated using an open-loop step. For cases where disturbance measurement is difficult, a combination of both feedback and feedforward control systems is used. 

Ratio Control: This type of control system is widely used in chemical processes. Suppose we have feed streams A, B, and C fed into a continuous reactor. The feed streams B and C are taken as the ratio of feed stream A, i.e., the flow measurements to A are computed as the set point for B and C.

Multivariable Control System: This type of control system uses algorithms or models to generate multiple outputs to the controllers, based on multiple inputs, thereby ensuring efficient control of the process. These control systems are more intelligent and effective when compared to distributed control systems (as they are dependent on operator skills).            

1-D and 3-D CFD Simulation

CFD simulation tools are now widely used for component and system-level analysis and optimization for optimum plant performance and safety. CFD simulations can be 1-dimensional or 3-dimensional and the deciding factor is the problem to be resolved. A 1-dimensional CFD simulation provides insights into how flow rates and pressure changes in one unit can affect the other parts of the system or network. While 3-D CFD simulations are used for the detailed study of flow interactions and heat transfer within a component of the complex system. It is essential to understand the tradeoff between 1-D and 3-D simulation tools, to ensure the right tool is used for the design implication.

By using CFD simulation, a battery pack can be virtually integrated into a drivetrain, providing predictions of the operating modes under different drive conditions. 1-D CFD simulation of the entire battery pack will help analyze if any component-level simulation is required, i.e., component-level 3-D CFD simulation will be performed only if there are any variations or abnormalities in the flow pattern or the temperature distribution at a system level. In the case of chemical plants or power generation units, consisting of multiple pumps, valves, separators, distillation columns, and mixers, performing a 3-D CFD simulation for the entire system can be a tedious task, and hence a 1D CFD simulation for the entire system would be apt and will provide insights on whether a detailed component level simulation needs to be carried out or not.

Coupling 1-D and 3-D CFD simulation can enhance the performance of a system and there are two coupling methodologies – manual or automatic and one-way or two-way coupling. A manual or automatic one-way coupling between 1-D and 3D CFD involves the transfer of all information that is gained through 3-D simulation into the 1-D system-level simulation, i.e., the transfer of information is unidirectional. This becomes two-way when the information from 1-D system-level simulation is sent to 3-D CFD analysis or vice-versa.

With new emerging processes and technologies in industrial power plants, evaluating the plant's performance before its implementation is substantial to avoid any fires or explosions due to a faulty unit /subsystem or undesirable flow conditions. CFD simulation, 1-D or 3-D, can help predict the possible design flaws before execution; and advanced control and calibration units can automate various processes to ensure optimum plant performance and utmost safety. We strive to live in a world that is safe and comfortable for our humanity and these technologies ought to drive us on that route.

To learn more about how meshing and CFD can be used for mixing reactants in a Y-Pipe, click the button below -