Manufacturing urea for fertilizer is a severe process, requiring extreme heat and pressure, specialized, heavy-duty equipment—and constant attention to process safety.
Koch Ag and Energy Solutions, a wholly owned subsidiary of Koch Industries Inc., operates five production facilities in North America, as well as a terminal and distribution system for fertilizer and natural gas. The company’s plant in Fort Dodge, Iowa, was built in the 1960s and makes urea-ammonium nitrate and ammonia, and uses many of Emerson’s Fisher control valves, Fieldvue valve controllers and ValveLink PLUG-IN for the company’s PRM, or Plant Resource Manager, software.
In the course of urea manufacture, hot carbon dioxide and ammonia are combined at 4,000 psig, and a recent process hazards analysis (PHA) identified several new safety requirements, according to Nick Hunter, reliability engineer, Koch Ag and Energy, who presented "Koch Ag and Energy Solutions gains added safety protection with Fisher" at the 2019 Emerson Global Users Exchange in Nashville, Tennessee.
"We found some operating requirements that had to be added," said Hunter. These included:
"We also had tight footprint constraints to fit existing process piping, and two parallel valve assemblies weighing 4,000 pounds each."
"There are additional opportunities for Fisher Z500s at this site and across Koch, but the best part was collaborating with Emerson and Impact Partner Stover Controls: they really helped us achieve a safer plant." Nick Hunter of Koch Ag and Energy discussed how a new high pressure, high performance valve solution addressed the company’s increased safety standards.
To meet the Fort Dodge plant's safety requirements, Koch Ag and Emerson developed a solution that consisted of a Fisher Z500 severe service ball valve with bi-directional shutoff, chrome carbide ball and seat coating, and a Bettis G5024-SR4 actuator for high-torque output and fast-stroke speed. The assembly was factory acceptance tested at the Emerson Innovation Center flow lab.
"To serve in severe on/off applications, the Z500 has a floating, metal-seated ball, which enables it to withstand extremely high pressures," explained Jeff Van Arb, product engineer, Emerson. "The Z500 can achieve bubble shut-off to 25,000-psi."
Meanwhile, large and heavy enough to be shipped on its own semi-trailer truck, the Bettis G5024-SR4 is a G-series, Scotch-yoke actuator with quarter-turn valve actuation, compact/modular design, pneumatic or hydraulic actuation, spring-return or double-acting, symmetric or canted yoke, multiple manual override options, and torque ratings up to 6-million inch-pounds.
The new valve and actuator were installed in August 2018. The Z500 valve and Bettis G5024-SR4 immediately enabled Koch Ag to achieve the safety integrity level (SIL) targets it was seeking, and the new valve and actuator also passed their leak test after one year of service. Because the Fort Dodge plant shuts down every 90 days to change out the platinum gauze used in its nitric acid process, the new valve and actuator can do a full-stroke valve test at that time, which means partial-stroke testing isn't needed.
Notes from the test stated, "The valve was put in the tester, and the actuator mounting foot was removed, so the valve could be opened and closed manually. A seat leak test was performed, and a video was made. No seat leakage. Packing and gaskets were also checked for leakage, and none was found. Actuator mounting foot was reattached as found. Inlet and outlet were cleaned, and pictures were taken."
Hunter added, "There are additional opportunities for Z500s at this site and across Koch, but the best part was collaborating with Emerson and Impact Partner Stover Controls because they really helped us achieve a safer plant."