2008

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The 53rd Annual AIChE Ammonia Safety Symposium

53rd AIChE Ammonia Safety Symposium

In September 2008, 350 engineers from about 40 countries and 110 companies attended the

American Institute of Chemical Engineers’ (AIChE) 53rd Ammonia Safety Symposium at the Hyatt

Regency in San Antonio, Texas. The conference venue was right on the Riverwalk, which was quite

enjoyable. Many attendees visited the city’s Alamo exhibit and its Botanical Gardens.

Dr Amit Roy, President & CEO, IFDC

The symposium’s keynote speaker was Dr. Amit Roy, the President and CEO of International

Fertilizer Development Centre (IFDC). His topic was “Fertilizer: A Key to Achieving Food

Security and Cutting Poverty.” Dr. Roy stated that the Millennium Development Goal of cutting

hunger and poverty in half by 2015 could be met only with a concerted effort to increase agricultural

productivity. Nutritionally depleted soils are a basic obstacle to higher productivity and, therefore,

fertilizers are essential to the solution. To be fully effective, however, improved soil fertility must be

accompanied by the use of high-yielding varieties of crops and improved farm management

techniques. These techniques include more efficient use of water and nitrogen fertilizer, particularly

urea. Another priority is better value chains that deliver inputs on time and at an affordable price, and

deliver crops to the market in shape to be sold for a profit.

This process is further complicated because agriculture, which has traditionally provided food, feed,

and fiber, is now producing fuel. The rampant demand for fuel, particularly ethanol, in North

America, China, and India has driven the price of grain to all-time highs. Fertilizer prices have also

skyrocketed because the global supply and demand situation is tight and the cost of energy is high.

Manufactured nitrogen fertilizer is essential for improving and sustaining agricultural productivity. It

is the basis for producing almost half of the world’s food. But the difficulty in managing this

nitrogen and reducing its presence in the environment is challenging. Globally, the efficiency of

nitrogen fertilizer use, particularly urea, is less than 50 percent—and less than 30 percent for cereal

production in developing countries. Further development of scientific and technical expertise is

needed to increase efficiency in the production and use of nitrogen fertilizer to ensure the continuing

supply of food and to protect the environment.

Dr. Roy believes that the fundamental mission of the fertilizer industry is to help feed the world. This

is the very reason it sprang into existence. Although each individual company must focus on making

a profit, the initial mission has not changed. And there is nowhere that fertilizer is more necessary

than in Africa. Further, at no time is it more necessary than now for the industry to respond to the

current challenges of alleviating poverty, high-energy cost, and climate change.

Following are excerpts from conference papers that dealt specifically with safety:

Self Supported Flare Stack Vibrations in Ammonia Plant The 70-meter flare stack in QAFCO’s No. 3 ammonia plant was vibrating because of ammonium

carbonate/bi-carbonate formation in the gas flow path. Counter current mixing of CO2-rich flash

gases from the CO2 removal section and ammonia water from the ammonia recovery section

precipitated the salts. The flare system was unblocked by draining most of the deposits and ammonia

water and then heating the stack with process gas.

Surging gas flow through the stack was the main cause of the vibrations. Once the pressure increased

at the bottom to a certain level surging led to the flare shaking and swaying.

The ammonia plant has only one flare stack for both the CO2-rich and the ammonia-rich gases.

QAFCO now permanently diverts CO2 rich flash gases from the CO2 removal system to the primary

reformer fuel header.

Waste Heat Boiler (WHB) Change from Bayonet to Firetube

Pakistan’s Dawood Hercules Chemicals replaced its bayonet WHB with a new firetube unit after

about 20 years. Chemical cleaning of the old BFW/steam system during the revamp was a disaster.

Dawood improved the water chemistry control to avoid corrosion. However, a major cause of tube

failures in the old boiler was an uneven/reverse circulation in one of the risers. A zigzag baffle was

installed but finally Dawood replaced the WHB with a new fire-tube exchanger. The paper presented

operating experiences of WHBs, tube failures, and details of the switch to the new unit in an

ammonia plant, where space was tight.

Synloop Superheater Issues

Between May 2002 and August 2004, PT Kaltim Pasifik Amoniak (KPA) in Indonesia had

significant problems with a steam superheater in its ammonia synthesis loop. The first problem was a

through-wall leak at the weld of the item’s dished bottom head. A crack approximately one third of

the way around the circumference was discovered in May 2002. This crack was in the vessel’s

closing weld. Repairs were made and the seam was monitored closely for the next two years.

Repeat indications of problems at the weld seam were found and other repairs were necessary and

eventually the entire exchanger was replaced.

In September 2003, pressure tests detected leakages at 60 tube-to-tube sheet weld joints. These welds

were repaired. Unfortunately, water leaked into the process side during start up and was blown into a

hot downstream S-50 converter, destroying its internals and necessitating complete replacement of

the internals and catalyst. However, further leakage at tube-to-tubesheet welds occurred and the

exchanger was completely replaced with a new one in 2005.

Cracking by nitrogen, hydrogen, or alkaline stress corrosion contributed to the shell-to-head weld

joint failure. High residual stress from local post weld heat treatment (PWHT) was the main factor.

Insufficient PWHT probably resulted from the design of the vessel bottom, where large inlet, outlet,

and manway nozzles were too close to the weld. The author recommended excluding a closing weld

from vessel bottom so that no localized PWHT would be needed.

Failures in Ammonia Plant Vertical Waste Heat Boilers The authors investigated corrosion problems in ammonia plant waste heat boilers that exhibited

deposits on the water/steam side. The paper gave a brief description of the operating conditions for

different designs including synloop waste heat boilers.

According to the authors, all the boilers that had experienced failures had received full PWHT in the

treatment furnace without their tube bundles being protected from oxide formation. They recommend

that all new boilers should be PWHTed under nitrogen atmosphere to avoid any oxide formation.

The potential sources of deposits, the analysis of potential causes and the remedies to avoid

premature failure were discussed. Oxide scale generated during PWHT, remedies, and actual

inspection results, were also discussed.

The authors suggested that all plants be equipped with an automatically operated intermittent

blowdown system to eliminate any doubt whether the intermittent blow down is operated as per

operating instructions or not. The use of oxygen scavengers should be limited because some oxygen

is useful to maintain the magnetite layer.

Nickel Carbonyl - How to Avoid it, Detect it and Treat its Effects Ammonia plant reformers and methanators contain nickel catalysts that are exposed to carbon

monoxide. Nickel carbonyl is extremely toxic and forms readily when carbon monoxide comes in

contact with nickel under certain conditions. Nickel carbonyl is a chemical hazard that can be easily

overlooked as part of the plant process controls for Safety & Health assessment as it is not part of the

main process. Several incidents involving serious injury were reviewed and the best practice for

avoiding nickel carbonyl formation was described. Methanation is the process step most susceptible

to carbonyl formation but the potential hazard exists in the front end of all syngas plants.

Transfer Line Failure In 2007, the primary reformer outlet transfer header failed in KRIBHCO’s No. 1 ammonia plant in

Hazira, Surat, India. Old, cracked, refractory and a damaged liner, which exposed the refractory to

hot gases probably led to the failure. The liner was replaced with a new stainless steel liner.

Facility Siting in Ammonia Plants

Facility siting has evolved considerably with advances in consequence-prediction tools for

explosions, fires, and toxic material releases. Ammonia plants are exposed to all three hazards and

advances in risk analysis have made it practical to use quantitative risk-based techniques to evaluate

risk and prioritize mitigation strategies. The siting of portable buildings according to API RP-753

and the likely changes to API RP-752 for permanent buildings were discussed along with a summary

of typical risk-mitigation options.

Jet and pool fire exposures (for siting purposes) for occupied buildings are limited to buildings

located relatively close to fire sources, but explosion and toxic hazards can potentially affect all

occupied buildings in an ammonia plant. A full range of release-case magnitudes and locations as

well as numerous meteorological conditions can be included in an evaluation.

Roundtable Workshop on the Thursday The topics covered included:

• Protection of a transfer line from hot spots

• Catastrophic failure of a refractory lined carbon steel primary reformer outlet header

• High temperature embrittlement, effects and proposed solutions

• Danger of sudden pressure increase in an ammonia storage tank

• Electrical safety in high voltage panels

• Mixed feed coil rupture due to creep

The 2009 meeting will be in Calgary, Alberta, Canada.