LESSON LEARNT FROM AICHE PAPER’S

FAC U LT Y : S H S & M K B

LESSON LEARNT FROM AICHE PAPER’S

“Successful Recoveries from Major

WHB Failures Experience”

INTRODUCTION

• The leakage of waste heat boiler located at secondary reformer downstream can cause a serious threat to sustainable plant operation.

• The leakage an cause BFW to enter the HTSC reactor flooding it and causing a thermal shock which can drastically decrease or even end the performance of the catalyst.

• In a worst case scenario catalyst replacement may also be required along with WHB tube rectification

INTRODUCTION

• Terra industries faced two significant WHB failures at different manufacturing sites, both M.W. Kellogg design.

• Both events were similar in severity in that the HTS reactor was completely flooded, one of which had boiler water spraying out of the hot vent (sometimes referred to as high mute vent).

• These events led to a severe catalyst bed temperature decrease of 300 °F (149 °C) in 2 minutes. In addition to the thermal shock, both cases experienced a very long drain time to remove the water from the HTS reactor, thus exposing the catalyst bed to a hot water soak for approximately 12 hours.

• Despite the severity of these events, They made a successful recovery with only repair of the waste heat boiler

EXPERIENCES AT TERRA VERDIGRIS, OKOPERATING CAPACITY 1750 MTPD

SEQUENCE OF EVENTS

• On July 22, the plant was in start up mode.

• The feed gas was established to the primary reformer at 3:15 p.m. and the air was established to the secondary reformer at 4:20 p.m.

• By 5:15 p.m., it was apparent there was a significant leak in one of the 101-C waste heat boilers exchangers. Temperatures indicated it was in the 101-CA.

• The catalyst bed was at approximately 650°F (343.3°C) (when it was flooded with boiler feed water).

• The air was taken out of the secondary reformer at 5:28 pm and the feed gas was out of the primary reformer at 5:40 pm.

EXPERIENCES AT TERRA VERDIGRIS, OK

• The vessel was full of liquid and “bubbling” out of the “high mute” vent. The catalyst bed temperature had dropped to approximately 250°F (121.1°C) (by the time the gas was out of the primary).

• The exchanger is a scabbard/bayonet style and one tube had ruptured. The rupture was approximately 8 inches long

• The concern after the plant was secured was the high temperature shift (HTS) catalyst. The catalyst was Süd-Chemie’s C12-4-02 and it was installed in September 1998. The catalyst was purchased due to a previous 101-C leak putting a large amount of boiler feed water on a previous charge of the same catalyst. Prior experience and the high crush strength of this catalyst were factors in its purchase.

• Süd-Chemie had been contacted during the previous incident and a dry out procedure was suggested. t involved using warm nitrogen and then steam to dry out the catalyst.

EXPERIENCES AT TERRA VERDIGRIS, OK

• The HTS drains were opened & process inlet to the vessel was blinded for removal of the 101-C bundle.

• The top man-way was gapped open to allow nitrogen/steam flow through the vessel. Multiple nitrogen hoses were connected to the bottom outlet pipe and the steam ring in the bottom of the vessel.

• After 40 hours of drying with nitrogen, dry steam was introduced into the steam ring to slowly heat the catalyst, from bottom to top. The steam was used until the catalyst bed was 600°F (315.6°C) on the bottom and 400°F (204.4°C) on the top.

• Blinds were removed, the HTS man-way secured, and the vessel readied for startup. The plant was restarted on July 24 after the dry out and 101-C replacement

• As the table shows, the HTS charge returned to service near start of run conditions and performed well during the entire life of the charge, significantly adding value to Terra’s operations by eliminating a shutdown and the expenses of a catalyst replacement.

EXPERIENCES AT TERRA YAZOO CITY, MSOPERATING CAPACITY 1550 MTPD

SEQUENCE OF EVENTS

• The plant experienced a process upset at 10:34 a.m. on June 14, 2006 due to activation of the Synthesis Gas Compressor trip and throttle valve.

• This upset resulted in a collateral trip of the 1500- psi Auxiliary Boiler, which ultimately led to the removal of process gas

• However, sufficient process steam was maintained in the reformer and the plant restart was initiated simultaneously with startup of the Auxiliary Boiler. The plant resumed minimum production at 7:30 p.m.

• At 12:45 a.m. on June 15, 2006, a displacement of the process gas, process air, and process steam indicated a leaking WHB (101-CA)

• At 1:15 a.m., a rapid temperature decrease at the HTS Converter inlet was observed along with a drastic increase in BFW demand.



SEQUENCE OF EVENTS

• Water was observed raining out of the high mute vent. Shutdown was initiated and within 30 minutes the temperature at the HTS Converter inlet had decreased to approximately 425°F (218.3°C).

• By 3:00 a.m. when the process steam was removed and nitrogen purge initiated, the entire HTS catalyst bed had decreased to 350°F (176.7°C).

PRECAUTIONS TAKEN

• The was catalyst was replaced 4 months earlier so it was of main concern during this period.

• At the point in which the process gas was removed, the low point bleeds on the WHB (101-C) were opened along with the HTS inlet low point bleed, and HTS outlet bleeds.

• All of the low point locations were draining copious amounts of water. Water was also being emitted from the front-end mute vent.

• A stream of water continued to drain from these bleeds until approximately 7:00 a.m.

• At this time, the nitrogen to the front end for purge purposes was stopped in order to verify that water had ceased draining from the 101-C leak.

PRECAUTIONS TAKEN

• In an attempt to improve chances of salvaging the HTS catalyst, the nitrogen purge was re established through the warm reforming section and allowed to continue through the HTS and out the 103-C and 104-C bleeds.

• Initially this warm purge was near 350°F (176.7°C) as indicated at the HTS inlet. At 12:15 p.m. water stopped draining from the 103-C and 104-C bleeds and nitrogen was redirected to purge through the remaining downstream equipment.

• This warm purge at approximately (1415 cubic meters) continued until 4:00 p.m.

• On June 15 when process gas blinds were installed for the replacement of the 101-C. At the conclusion of this continuous purge the nitrogen temperature had decreased to approximately 200°F (93.3°C).

• Investigation of the removed WHB revealed three leaking tubes adjacent to one major tube rupture.

PRECAUTIONS TAKEN

• As a final measure to improve chances of salvaging the HTS catalyst, a nitrogen pressurization and release/dump sequence was initiated.

• This procedure established a high-pressure limit of 15- psig due to upstream blind limitations. The procedure also allowed a 1-hour hold period at pressure in order to allow time for some nitrogen diffusion into the pores of the catalyst.

• At each pressure dump/release, some moisture was noted at the drains. This process continued for 10 sequences at which time the bleeds began to dry.

• The sequence was then modified to hold pressure 4-6 hours and was

continued throughout the duration of the outage.

• Purging was discontinued at 8:00 a.m. on June 19 in preparation for start up. Start up procedures were followed with slower heat up rates for the HTS to guard against excessive moisture vaporization.

• During outage a spare charge of HTSC catalyst was purchased in case a second outage is needed but catalyst regained full functionality.

CATASTROPHIC FIRE IN AMMONIA PLANTCOMPRESSOR ROOM

INTRODUCTION

• GPN is the leading French producer of Nitrogen fertilizers.

• The site is the largest fertilizer facility in France.

• The Ammonia plant, known as “AM2”, was started in 1978 which a capacity of 1000 MTPD which after revamping was increased to 1170 MTPD .

• In September 2009 a catastrophic fire took place in the compressor deck onsite .resulting in a total loss of 20 million US dollars and a plant shutdown of 11 months.

• The plant took a turnaround in 2008 and next turnaround was planned in 2014.

SEQUENCE OF EVENTS

• On Wednesday, September 28, 2011, the ammonia plant start-up was in progress after 10 days of cold shut-down for maintenance work.

• The synthesis gas compressor was started at 5:30 p.m., Liquid ammonia product export to the storage spheres started at 4:30 a.m., the morning of September 29.

• At 6:00 a.m., the morning shift operator and the shift supervisor did their routine synthesis gas compressor check. Nothing abnormal was observed.

• At 8:30 a.m., the production rate was stable at 865 MTPD and the team was preparing the start-up of the purge gas treatment unit.

• The plant was in steady state operation, and all process parameters of the ammonia synthesis section were normal.

SEQUENCE OF EVENTS

• At 8:33 a.m., three fire detectors located in the compressor room alarmed simultaneously.

• On the video monitor in the control room, the flames could be clearly seen, thus confirming the fire alarm.

• At 8:34 a.m., the synthesis section emergency shut-down was activated manually from the control room. At the same time, the site fire brigade left the fire station.

• At 8:43 a.m., as the fire was developing, the operators realized that there was a risk of extension of the fire.

• The plant was tripped completely and the natural gas cut-off valve was isolated. The control room operators started to depressurize the process gas through the vents.

SEQUENCE OF EVENTS

• Around 8:45 a.m., the emergency management team was set up in the administration building.

• On site, the firemen identified a very noisy, high pressure gas leak, located on the discharge side of the compressor, along the wall of the building.

• The firefighting strategy consisted of establishing water curtains to protect the machine and the piping inside the building in order to limit the extent of the fire.

• At 8:57 a.m., the roof of the building, partly consisting of transparent polycarbonate plates, began to burn producing a heavy, black smoke.

• At 9:00 a.m., the west wall of the compressor room, made of concrete blocks, collapsed, and the gas fire, which up to now was contained inside the building, escaped outside, threatening the main pipe rack.

SEQUENCE OF EVENTS

• All the plant personnel, with the exception of the firefighting team, were evacuated and sheltered inside the blast-proof control room building.

• At 9:06 a.m., the civil fire brigade arrived on site and up to 70 firemen were prepared to support and replace the site firemen

• At 9:17 a.m., the site firemen established fire hoses outside the building to protect the main pipe rack.

• At 9:24 a.m., the synthesis loop residual pressure was less than (150 psig). At this point (300 psig) nitrogen hose was connected to the loop in order to inject inert gas.

• At 9:55 a.m. (1 hour and 22 minutes after the incident start) the fire was totally extinguished

DAMAGE DONE

• DAMAGE TO BUILDING • Wall in front of compressor collapsed from bottom• The steel structure of the building was damaged and effected• Roof plates on top of compressor deck were partially burnt• The outside wall covering in Eternit was destroyed and broken

into small pieces, which were sprayed all over. This contained asbestos so it had to be cleaned causing 3 weeks delay in repairs

• Damage to the Syngas Compressor• The instrument and lubrication lines were damaged by the fire

and the debris.• The control cabinet was totally burnt.• The floor grating was distorted.

DAMAGE DONE

• DAMAGE TO PIPING AND VALVES

• The main compressor discharge line was apparently intact, only the small bore piping was damaged. Two small process lines were broken (see Figure 2).

• The piping in the main pipe rack was impacted by the fire but had not failed (except for small steam tracing and instrument air lines).

• DAMAGE TO THE INSTRUMENTATION

• Inside the deck the instrumentation was badly damaged including actuators of control valves

• The instrumentation in piping rack was also partially effected

ORIGIN OF THE FIRE

• The origin of the fire was quickly identified. It was a (2900 psig) high pressure synthesis gas leak on the 1 inch by-pass line of the synthesis compressor discharge valve, as shown in Figure.

• This line was completely bent, as can be seen in Figures and ruptured just downstream of a manual block valve (154UH102). The 1 inch manual valve itself was severely damaged as well.

ANALYSIS

• The immediate cause of the incident appears to be a hydrogen-rich gas leakage on a 1 inch ASME class 2700 lb., welded bonnet, forged steel valve (Figure)located on the by-pass line of the synthesis gas compressor main discharge valve.

• This manual valve is operated during each plant start-up in order to pressurize the synthesis loop.

• The investigation concluded the only possible failure mechanism was as follows:

1. Grooved rivet (#35) was missing.2. Nearly complete unscrewing of the yoke bushing (#11) during operation of the valve.3. Rupture of the last thread as a consequence of the internal pressure rise during the normal start-up process.4. Vibration of the stem (#4) and loss of tightness of the packing.5. Gas leakage and ignition.

RECONSTRUCTION

• The reconstruction work started on November 28, 2011, and employed up to 250 people. It was completed on May 10, 2012.

• One third of the compressor room building, from the floor to the roof, was dismantled and rebuilt, including replacement of the steel frame.

• A complete overhaul of the synthesis gas and the refrigeration compressors, including auxiliaries, was performed.

• All electrical, instrumentation cables, and cable trays from the control room building to the compressor room were replaced. In total 40 km (25 miles) of cable was installed.

• The damaged piping and valves were replaced or repaired depending on the results of the inspections. A total of 150 m (500 feet) of piping (up to 40 mm, or 1.6 in thick) was replaced.

MEASURE FOR FUTURE PREVENTION

AUDIT OF MANUAL VALVES :

• A complete visual inspection of all manual valves on flammable gas lines was also performed. This inspection was conducted together with a valve specialist, a pressure vessel inspector, and a plant operator. A total of 1290 manual valves have been inspected as part of this program. The items reviewed in this program include the following:

mechanical integrity, external corrosion, condition of packing, and operability.


LEAK DETECTION SYSTEM:• To identify flammable gas leakage as soon as possible the

following measures have been adopted.• After each major plant shutdown, a pressure test is performed with

(300 psig) nitrogen on the front end, and (1500 psig) nitrogen on the synthesis loop. All valves on flammable gas lines are tested for leakage using a bubble-test.

• Leak testing with portable gas detectors – after each plant start-up, each manual valve which has been operated during the start-up each valve is tested for leakage

• Leak detection with fixed gas sensors in the compressor room - the existing 3 gas sensors have been complimented by 6 additional gas sensors, with automatic synthesis compressor shut-down (2 out of 3 voting).

• High pressure flanges leak detection – each high pressure flange on the synthesis gas compressor and on the synthesis loop has been fitted with a leak detection system consisting of a closed box, with a vinyl hose connected to a bubbling bottle. Operators can immediately identify a leak during their rounds. A total of 509 flanges have been equipped with such a system (See Figure ).

• A task force was also formed whose purposeWas to ensure the mechanical integrity of all Plant equipment, Give recommendations and Close them on time, after extensive work the Plant resumed operation in September 7, 2012

Example of leak detection system onhigh pressure flanges (each individual vinylhose is connected to a flange, and identifiedwith a metal tag. The tag number is referenced on the plant drawings).


FIRE IN AN AMMONIA SYNTHESIS STARTUPHEATER

• Yara Tertre Belgium operates an integrated nitrate fertilizer site including one MW Kellogg ammonia plant built in 1968.

• The plant underwent a revamp in 2008 with the addition of an aMDEA based CO2 removal system

• On September 6th 2008, during the restart of the plant, a fire took place in the start up heater.

• A rupture of a coil outlet caused the fire. Huge flames surrounded the SUH and affected the surrounding equipment.

• The fire caused wiring and insulation to be burned but fortunately no one was injured

INTRODUCTION

• The startup heater is usually used during startup to heat up the gas to achieve a temperature required for the exothermic reaction of ammonia formation

• The SUH (fig 2) is a standard vertical gas fired heater with double helicoidal coils. The coils design is composed of 2 ¼ Cr 1Mo tubes, 101,6 mm outside diameter with 10,3 mm minimum wall thickness based on API RP530 .

SEQUENCE OF EVENTS

• Ammonia plant start up was in progress and start up heater was in service

• Process gas pressure was 100 bar and temperature at startup heater outlet was 420o C where as flue gas temperature was 825 o C

• At about 1845 hrs on the day of incident small flames were observed on the coil outlet of SUH. This observation led to the immediate S/D of the plant with the following conditions

Stoppage of the fuel gas flow to the SUHIsolation of the synloop from the syngas compressor with

automatic safety ball valvesDepressurizing of the synloop was started

• The flames increased as the SUH could not be isolated from the synthesis reactor and finally the inlet process manual valve to the SUH was closed.

SEQUENCE OF EVENTS

• Suddenly, a loud noise was heard, and big flames could be observed in the bottom of the SUH, in the area where the coils exit the SUH and from the top of the chimney.

• Internal and external fire brigades were called and took appropriate actions to protect the surrounding equipment's, such as the ammonia converter and the related inlet piping.

SEQUENCE OF EVENTS

• When entering the SUH after the incident, it was clear that one of the coils exiting the heater had ruptured as shown in fig 6 and 7. The shell area in the conical part of the heater where the coils exit was bent aside, and a strong thinning of the shell was observed.

WHAT HAPPENED ?

• The fracture of the coil was caused by high temperature due to radiation from the refractory and the lack of cooling as the flow through the coil was closed (fig 10,11)

• As the leak in the coil was discovered during start-up of the plant, the flow of syngas through the coils was interrupted as the valve was closed. The lack of internal cooling immediately led to overheating of the impaired area of the coil from the hot refractory resulting in the rupture.

• As the coil was already leaking and the leak was increasing, it is difficult to predict the development of the fire in case the flow through the coils had not been interrupted.

WHAT HAPPENED ?

• Due to local dramatic thinning of wall caused by external corrosion the coil suffered creep damage in the area where the damage took place.

• The thin walled areas suffered much high mechanical stresses and creep damage in startups

PREVENTIVE ACTIONS

• Inspection of the other synthesis process piping which have process conditions around 100°C (210 °F) should be investigated. When done in Yara Tertre, some other externally corroded piping was found and repaired.

• Due to the long exposure at high temperatures, the coils may have been subject to swelling that could lead to cracks in the future.

• The possibility of hydrogen attack was also suspected. According Nelson curves (API941), the operating conditions of hydrogen partial pressure and temperature are within the recommend limits but it is not the case for the design conditions

• Protection against humidity and a permanent small flow through the coils in order to maintain a constant temperature around 120°C (250 °F) should be considered for the future

NICKEL CARBONYL , HOW TO AVOID IT , DETECT IT & TREAT ITS EFFECTS

• In an Ammonia plant the reformer and methanator catalyst contain Ni which if exposed to CO under specific conditions (normally in startups & shutdowns) can form Ni(CO)4 which is highly hazardous,

• Ni(CO)4 is Highly toxic FlammableDifficult to detect

• In this presentation we will discuss Properties & hazards of Ni(CO)4

Favorable conditions for its formationGuidelines to prevent its formationMethods to detect & expose it if formed

HISTORY & USES

• Used largely for the production of Ni.

• Nickel carbonyl was discovered in 1889 by Ludwig Mond and co-workers

• It is a highly volatile liquid, boiling point 43°C (109°F), and is formed from nickel and carbon monoxide.

Ni + 4CO ------- Ni(CO)4

• At atmospheric pressure, the forward reaction takes place at low temperatures, less than about 100oC. (212oF).

• The reverse reaction takes place above about 180oC. (356oF).

• Used in producing nickel ,as pellets in stainless steel, and also in electroplating

CHEMISTRY

• Ni(CO)4 is produced when reduced nickel is exposed to CO containing atmosphere under specific temperature & pressure conditions.

• Favourable conditions are low temperature & high pressure.

• Figures 1 to 3 show the equilibrium curves for Ni(CO)4 at a range of pressures, CO concentrations and temperatures.

• The equilibrium amount of nickel carbonyl is temperature dependent. For example if part of a catalyst bed is twenty degrees cooler than the point of measurement, you could make ten times as much nickel carbonyl.

PROPERTIES

• Its high vapour density relative to air means that the vapour can gather in low spots.

• Its vapour pressure suggests that it can be condensed causing accumulation in cold dead spots or legs.

• The fact that liquid nickel carbonyl is denser than water and sparingly soluble in water means that it is possible to trap a liquid spill under water.

POTENTIAL WAYS NICKEL CARBONYL MAYBE FORMED IN YOUR PLANT

• For the formation of nickel carbonyl in an ammonia plant three key conditions must exist - available reduced nickel - carbon monoxide

- physical conditions.• The main sources of available

nickel are the hydrodesulphurization, pre-reforming, primary reforming, secondary reforming and methanation catalysts.

• The main catalysts types that incorporate nickel in order of typical nickel metal content are shown in table

Catalysts Typical NickelContent% w/w

Pre-reforming 50

Methanation 30

Primary Reforming

20

Secondary reforming

10

Hydro-desulphurisatio

n(Ni/Mo type)

5

• Although there are other sources of Ni in an ammonia plant e.g. Ni present in metal piping but catalysts are the most important source

• The catalysts are designed with the increased surface area of Nickel for maximum reaction there by exposing it to form Ni(CO)4.

• The sources of nickel carbonyl formation are greater in methanol plants as compared to ammonia plant however that does not mean that it can not be formed in ammonia plants .

• Controlling of the physical conditions is the key to avoiding the formation of nickel carbonyl in a syngas plant.

POTENTIAL WAYS NICKEL CARBONYL MAYBE FORMED IN YOUR PLANT

CASE HISTORY 1 – AMMONIA PLANT

• An unplanned S/D due to leakage of secondary reformer waste heat boiler led to this incident.

• The following actions were taken: -• ammonia loop shutdown• Methanator isolated and put under a positive nitrogen pressure• low temperature shift by-passed• process gas sent to flare system.

• However the partial shutdown lasted longer than anticipated and the methanator cooled down to 25°C.

• It became necessary to fit a slip plate to complete some other essential maintenance work.

• As a result many workers were exposed and hospitalized

WHAT LED TO THIS ?

• High concentration of CO containing gas slipped into the methanator due to passing of the inlet isolation

• Initially the temperature of the methanator, above 200°C (390°F), meant favouring the decomposition of nickel carbonyl.

• When flow of nitrogen was stopped to insert the slip plate more gas flowed from behind due to less restriction and more toxic gas was formed as the workers had no breathing apparatus they were exposed to toxic gas • Analysis of samples taken from in the methanator showed

nickel carbonyl in excess of 5000 ppm.

methantor

Ni(CO)4


• An ammonia plant decided to replace their methantor , they plotted their operational data with the data obtained from Johnson Mathey as shown in this graph

• The plant conditions (plotted in red) are initially in the area of the graph where formation of nickel carbonyl is not favourable before crossing over into the favourable region during the shutdown.

• It is suggested that during S/D the Methanator be purged with nitrogen while it is still above 200ºC (390ºF).

• It is suggested that during start-up the methanator should be heated at low pressures until the temperature is above 200ºC (390ºF).


• On an ammonia plant they were about to discharge the methanator catalyst for replacement on purging with nitrogen they measure several hundred ppb of Ni(CO)4

• In an attempt to decrease the concentration further purging was done but the concentration actually increased.

• The likelihood is that during the time purging was carried out the equilibrium effect was driving up the concentration

• Safety equipment must be used as it is Very toxic and can cause dizziness, nausea and even cancer leading to death .

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LESSON LEARNT FROM AICHE PAPER’S