Pilots and Process Safety

I am talking about Flare Pilots! Do not underestimate the need for keeping your flare systems and pilots, including their ignition systems in good condition. A working flare is a silent sentinel for process safety. For a troubleshooting guide on flare systems see this link.

Lessons from Deepwater Horzon incident investigation by USCG

The US Coast Guard has released its investigation report on the Deepwater Horizon disaster. There are lessons to be learnt for us in the chemical processing industry. The key findings from the report are given below:
"Failure to Use the Diverter Line: When the drilling crew directed the uncontrolled well flow through the Mud Gas Separator (MGS), the high pressure exceeded the system’s capabilities and caused gas to discharge on the Main Deck. Alternatively, the crew could have directed the well flow through a “diverter line” designed to send the flow over the side of the MODU (Mobile Offshore Drilling Unit). Although the diverter line also may have failed under the pressure, had it been used to direct the flow overboard, the majority of the flammable gas cloud may have formed away from the Drill Floor and the MODU, reducing the risk of an onboard explosion.
Hazardous Electrical Equipment: At the time of the explosions, the electrical equipment installed in the “hazardous” areas of the MODU (where flammable gases may be present) may not have been capable of preventing the ignition of flammable gas. Although DEEPWATER HORIZON was built to comply with IMO MODU Code standards under which such electrical equipment is required to have safeguards against possible ignition, an April 2010 audit found that DEEPWATER HORIZON lacked systems to properly track its hazardous electrical equipment, that some such equipment on board was in “bad condition” and “severely corroded,” and that a subcontractor’s equipment that was in “poor condition” had been left in hazardous areas. Because of these deficiencies, there is no assurance that the electrical equipment was safe and could not have caused the explosions.
Gas Detectors: Although gas detectors installed in the ventilation inlets and other critical locations were set to activate alarms on the bridge, they were not set to automatically activate the emergency shutdown (ESD) system for the engines or to stop the flow of outside air into the engine rooms. The bridge crew was not provided training or procedures on when conditions warranted activation of the ESD systems. Thus, when multiple gas alarms were received on the bridge, no one manually activated the ESD system to shut down the main engines. Had it been activated immediately upon the detection of gas, it is possible that the explosions in the engine room area could have been avoided or delayed.
Bypassed Systems: A number of gas detectors were bypassed or inoperable at the time of the explosions. According to the chief electronics technician, it was standard practice to set certain gas detectors in “inhibited” mode, such that gas detection would be reported to the control panel but no alarm would sound, to prevent false alarms from awakening sleeping crew members. Similarly, the crew bypassed an automatic shutdown system designed to cut off electrical power when ventilation system safety features failed, possibly allowing flammable gas to enter an enclosed area and reach an ignition source. The chief electrician had been told that it had “been in bypass for five years” and that “the entire fleet runs them in bypass.”
Design of the Main and Emergency Power Sources: Although the arrangement of main and emergency generators on DEEPWATER HORIZON met IMO MODU Code requirements to have completely independent engine-generator rooms along with independent power distribution and control systems, it did not prevent a total failure of the main electrical power system, when the explosions and fire damaged multiple generators and their related power distribution and control equipment. The design did not adequately take into account that the proximity of the air inlets to each other created a risk that flammable gases could impact all six generators at once.
Crew Blast Protection: DEEPWATER HORIZON did not have barriers sufficient to provide effective blast protection for the crew. Although the barriers separating the Drill Floor from adjacent crew quarters met the standards of the IMO MODU Code, those specifications are only designed to slow the spread of fire, not to resist an explosion. They did not prevent personnel in the crew accommodations area from sustaining injuries.
Command and Control: Because of a “clerical error,” by the Republic of the Marshall Islands, DEEPWATER HORIZON was classified in a manner that permitted it to have a dual-command organizational structure under which the OIM was in charge when the vessel was latched on to the well, but the master was in charge when the MODU was underway between locations or in an emergency situation. When the explosions began, however, there was no immediate transfer of authority from the OIM (Offshore Installation Manager) to the master, and the master asked permission from the OIM to activate the vessel’s EDS. This command confusion at a critical point in the emergency may have impacted the decision to activate the EDS".

The full report is available in this link.

Ammonia and thermal expansion

For my friends in the ammonia industry, let me remind you ammonia can also kill you in another way apart from exposure to it. 25 years ago, I witnessed a large leak due to thermal expansion of liquid ammonia which was not understood by the technical services team of the plant who had carried out an in house modification. The liquid ammonia which was blocked in, expanded due to thermal expansion and a pressure gauge in the line gave away, rocketing the gauge and causing a large leak. The flying projectile could have killed people.Airgas has published a technical bulletin about ammonia, which all personnel in ammonia facilities should read. Read it in this link.

Process Safety and Reaction calorimetry

In many batch processes, I keep observing companies hesitant to spend money to obtain reaction data prior to scale up to plant scale. The old adage "we have never done it before and nothing has happened" is often the answer. One incident that happens due to lack of understanding of reaction chemistry is enough to wipe out ALL your gains.An article written in 1991 points out the need for complete data prior to scale up to plant scale. One of the case studies mentioned is quoted below:
"A specific example of this type of approach was given by Homare Shinohara, of Eisai Chemical Co, who described the design of a manufacturing plant for pharmaceutical intermediates based on amino-thiaziazol carboxylic acid, generally known as F-15. Thiaziazol compounds are often used as a side chain at the 7-position of cephalosporin antibiotics. Thiaziazol carboxylic acid chloride (F-15Cl), for example, is being used at Eisai for the synthesis of two new antibiotics currently under development, E-1040 and E-1077. E-1040 is an injection drug, which is said to have the strongest bactericidal activity against Pseudomonas among the cephalosporins currently available, although less efficacious against Staphylococci. It is currently proceeding to Phase III testing. A development of E-1040, E-1077 is described as a fourth-generation cephalosporin having a wide spectrum of antibiotic activity from Gram-positives including Staphylococci to Gram-negatives including Pseudomonas. This compound is currently in e-phase II testing in Japan.
For the production of these compounds F-15 must be chlorinated. However, this intensely exothermic reaction can also produce two kinds of by-products: anti-F-15 acid chloride and phosphoric-amide-F-15 acid chloride. The resultant concentrations of these by-products is directly dependent upon the temperature of the reaction mass.
As a preliminary, the decomposition temperatures of the starting materials and final desired product were determined to confirm their safety. Shinohara's research team then used a Mettler Contalab to firstly determine the conditions required to suppress byproduct synthesis and then measure the heat of reaction to assist in the final plant design. To confirm the results the heats of reaction were also calculated using a Mettler RC 1.
It was determined that the reaction temperature should be maintained below -10ºC and that reaction heats generated depended upon the method of addition of phosphorus pentachloride - continuous, one or two portions. Although at 400 kJ/kg the reaction heats produced with continuous and one portion addition were 50kJ/kg higher than that for a two portion addition, possibly due to the absorption of heat by simultaneous crystallisation, it was decided to base the plant design on a 500-litre, glass-lined reactor with continuous addition of phosphorous pentachloride over a 30-minute period.
On calculation of the heat removal capacity of the jacket on the reactor using brine at -30¡C it was found to be insufficient to maintain the temperature below -10¡C. Further calculations determined the phosphorus pentachloride addition period would need to be extended to 3.3 hours, despite pilot-scale production of 5kg batches being satisfactorily achieved with additions over 30 minutes".
Read the full article with other examples in this link.

VFD's and process safety

VFD (Variable frequency drives) are used for conserving energy. The process safety issues when using VFD's must be considered when using them. To cut costs, some users try to install a single VFD for both the running and standby motors of a pump. This poses issues in safely locking out energy supply when one pump is given for maintenance. Read a good article on VFD's in this link.