Emerson Impact Partner Applied Control’s Julia Imhoff and Miranda Hunter teamed with Renaissance Technologies’ Terry Wilford to discuss a novel way to avoid catalyst damage for a high exothermic reaction. Here is their session’s abstract:
When producing renewable biodiesel, a goal during the process is to produce the correct reaction between oils and catalysts. During production, if the reactor undergoes an upset condition, the catalyst could be destroyed due to a high exothermic reaction. This failure could cost the refiner millions. Precautions need to be in place so that the reactor does not see a massive surge of high reactive fresh oil. This can be achieved with extensive control system logic, but at a very high cost. Therefore, a cost-effective, never-been-done-before solution was utilized by controlling the failure speed of the Fisher control valves configured with appropriate accessories. Regardless of the type of failure, the valves will fail slow enough to prevent disruption and save the downstream equipment.
Miranda opened by describing how the refinery switchover to biodiesel required a large reactor that must manage a problematic reaction. Instead of refining crude oil, it switched to refining soybean oil. The process involves heating the oil, adding hydrogen, running it through catalysts, and then pulling out S, O2, and N2. All of this occurs inside the reactor.
They need to maintain the temperature in the reactor. To do this, they need to bring quench oil into the reactor to keep it from high temperatures. They also need to maintain liquid level by avoiding losing too much liquid level, so gases are not pushed into the liquid circuit.
Not maintaining control can destroy the catalyst and possibly damage the reactor. It’s essential to control how slow the valve fails in conditions such as loss of power, signal, and air. The valves in the application could fail open or fail close.
A DVC6200 digital valve controller can control the fail speed on the air loss but not power and signal.
Miranda and Julia went into their shop to see if they could engineer a way to slow down power and signal loss failures. Using solenoid valves and relay switch, they routed the actuator air output out of a solenoid with a needle valve to slow the release of air from the actuator. This solution accomplished the two cases of loss of power or signal to slow down the fail open or close stem travel.
Here’s a view of the solution for both single-acting and double-acting actuators.
Visit the Fisher valves & instruments section on Emerson.com for more on the components used in this solution.
