Industrial Process Safety a Critical Consideration When Scaling Up Production: T2 Laboratories

Success in business often starts out with a well-intended idea. In the case of T2 Laboratories, a growing market for the gasoline additive methylcyclopentadienyl manganese tricarbonyl (MCMT), inspired the company owners to leverage their chemical industry experience to generate profits.   

Although neither of the T2 owners had previously worked with reactive chemical processes, a customer of theirs asked them to produce MCMT. After thinking about it, they felt it was the smart and prudent move to start small and then build up.

Between 2000 and 2001, T2’s owners ran 110 test batches of MCMT in a one-liter reactor. They suffered growing pains during those test batches, but overall the tests encouraged them to press on with development. After successful testing, T2 decided to ramp up and designed and constructed a full-scale MCMT production plant. T2 hired consulting engineers to assist in the process design, control system engineering, and project management. Due to limited funding, T2 purchased and refurbished used equipment, including the 2,450-gallon high-pressure batch reactor used for the three-step MCMT reactions.

Safety regarded a secondary consideration

Although much thought was given to building the production facility and defining the process, not much time was spent designing in safety and a safety-related action plan.  T2 created a three-step process that occurred sequentially within a single process reactor. The National Annealing Box Company of Washington, PA, originally constructed the reactor in 1962 for an internal pressure of 1,200 psig. T2 purchased the reactor in 2001 and contracted a firm specializing in pressure vessels to refurbish, modify, and test the reactor. The modifications included replacing and adding of piping nozzles and reducing the maximum allowable working pressure from 1,200 psig to 600 psig.

In addition, a 4-inch diameter vent pipe with two 90-degree pipe bends was connected to the 4-inch in diameter rupture disk. The disk acted as an overpressure protection device for the reactor. The rupture disk tolerance was set at 400 psig. A pressure control valve installed in a 1-inch diameter vent pipe, which branched off the 4-inch diameter vent pipe below the rupture disk.

The MCMT process required heating and cooling. A heating system circulated hot oil through 3- inch piping installed around the inside of the reactor. A cooling jacket covered the lower three quarters of the reactor. A pipe from the city water system connected to the bottom of the jacket through a control valve and a common supply/drain connection. Water injected into the jacket and, as it boiled, steam vented to atmosphere through an open pipe connected to the top of the jacket.

Testing did not account for emergencies

The T2 owners performed laboratory testing in a 1-liter glass reactor to establish the MCMT process chemistry and determine maximum product yield. They never observed extreme exothermic behavior during testing and test temperatures never exceeded 380°F. By not investigating the reaction’s behavior at higher temperatures, the owners did not observe the potential for an exothermic runaway. Testing is just that: determining the temperature extremes that the operation is capable of handling.

In addition, cooling requirements in the one-liter laboratory reactor did not accurately indicate the amount of cooling needed in the full-scale T2 reactor. Although the laboratory reactor required occasional heating and did not require cooling, additional cooling was determined to be necessary after the occurrence of multiple process glitches during early production batches.

While laboratory testing is important, a reliance on laboratory testing can lead to dangerous underestimation of full-scale batch temperatures. Conducting a process hazard analysis (PHA) in the development phase helps establish operating limits and identify operating strategies to prevent runaway reactions. PHAs for batch reactor systems should evaluate potential process deviations and equipment malfunctions, including agitator failure, loss of cooling, contamination, and mischarging feed stocks, all of which are common causes of runaway reactions. 

The benefits of third-party evaluation ignored

Along the way, a T2 design consultant identified the need to perform a hazard and operability study (HAZOP) during scale-up. A comprehensive HAZOP likely would have identified the need for testing to determine the thermodynamic and kinetic nature of the reaction, as well as the limitations of the cooling and pressure relief systems. It appears T2 never performed the HAZOP. 

T2 sized the reactor relief devices based on anticipated normal operations, without considering potential emergency conditions. The rupture disk was sized based on the maximum expected hydrogen gas generation during normal operation. No thought was given to the potential of a runaway reaction.

As T2’s production increased, so too, did its production capabilities. The initial batch size of production increased by 33 percent in 2005. No new analysis was performed surrounding this recipe change, which may have introduced significant new risks. A greater volume of reactants increased the energy the reaction could produce, and likely altered cooling and pressure relief requirements.

Safety issues often come to light when multiple problems surface over time without appropriate deployment of effective countermeasures.  Consistent safety planning, especially during periods of business expansion, help to safeguard business safety and profitability in the long run. 

The learn more about steps to take for ensuring better plant and control systems process safety click here.