RISK MANAGEMENT IN AMMONIA/ UREA PLANTS

26th Oct 2021 Research Gate is an academic social networking site www.researchgate.net RISK MANAGEMENT IN AMMONIA/ UREA PLANTS By Prem Baboo Former Sr. Manager, National Fertilizers Ltd, India AbstractRisk Management is the Identification, Analysis and Economic Control of those Risks which can Threaten the Assets (Property, Human) or the Earning Capacity of an Enterprise” Risk management is the process of identifying, assessing and controlling threats to an organization's capital and earnings. These risks stem from a variety of sources including financial uncertainties, legal liabilities, technology issues, strategic management errors, accidents and natural disasters. The article intended The Fertilizer Plant pose fire, explosion and toxic hazards due to unwanted and accidental release of natural gas as well as process gas containing CO, H2, Methane and toxic gases like Ammonia and Chlorine. The effect zones of the fire and explosion hazard are generally restricted within the plant boundary limits and near the source of generation itself. However, effect of accidental release of Ammonia and other toxic gases may go outside the factory premises. This section deals with the failure modes, listing of failure cases leading to different hazard scenarios, consequence modeling and the risk evaluation. Consequence analysis is basically a quantitative study of the hazard due to various failure scenarios to determine the possible magnitude of damage effects and to determine the distances up to which the damage may be affected using internationally accepted mathematical models. Keyword Ammonia plant, fertilizer production industry, risk management, Risk, Fire, Explosion, Introduction Ammonia is one among the largest volume inorganic chemicals in the Fertilizers and others chemicals process industries. About 80% or more of the ammonia produced is used for fertilizing agricultural crops. From 1980 to 2021, the capacity of single stream ammonia plant has increased drastically in the range from 15003500 TPD. Presently, the largest ammonia plant has the capacity of 3300 TPD But very soon will become as the largest single-stream ammonia plant in the world, which is due onstream in the middle of 2022, has the capacity of 4000 TPD. The large volume of Ammonia storages are also very risky. It is expected that capacity of single stream may even reach 5000 TPD, considering current pace of development. But these large plants also pose increased hazard and risk associated with it. A successful risk management program helps an organization consider the full range of risks it faces. Risk management also examines the relationship between risks and the cascading impact they could have on an organization's strategic goals. Risk management has perhaps never been more important than it is now. The risks modern organizations faces have grown more complex, fueled by the rapid pace of globalization. New This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site risks are constantly emerging, often related to and generated by the now-pervasive use of digital technology. Climate change has been dubbed a "threat multiplier" by risk experts. This article descriptive study which carried out in observation using a cross sectional design. Variables in this study included hazard identification, basic risk analysis, risk control that has been done, existing risk analysis, and risk reduction assessment. The tools used for the data collection were observation sheets, interview guide sheets, and Job Safety Analysis sheets. Data that has been obtained through observation and interviews was processed using Fine semi quantitative technique. Results: The results of hazard identification known to have as many as 6 potential hazards. The assessment results in the basic risk analysis showed that the initial risk level consisted of 3 risks with very high level, 2 risks with a substantial level and 1 risk with priority 3 level. After the risk control effort was applied, the results of the assessment in the existing risk analysis showed that the level of risk has decreased significantly. The main reason for increase in the capacity of a single stream to reduce specific production cost through so-called economy of scale, i.e., if design output is doubled, the capital cost increases by only 50- 60%. There are also some savings on operating costs, particularly in terms of the thermal economy and labour. Though ammonia plant has well proven technology; however, there are problems and failures of process equipments, machineries, instruments and control systems etc., many of these are not reported in the literature. Safety of a plant can be improved, but cannot be guaranteed. explosion toxicity and Mond Indices Computation of Ammonia plants. The Toxicity Index is arrived at from fire and explosion index. The Toxicity Index (TI) is computed using the health factor (Nh) , maximum allowable concentration (MAC) value ranging between <5,5-50,>50 respectively. Similarly for Nh rage from 0-4 ,a corresponding factor , The is assigned. The TI can be calculated using the following formula Hazard Identification Hazard indices computation helps in ranking the most vulnerable unit by assigning the penalties based on the properties of the chemicals used and type of installation.Table-1 shows the fire and 𝑻𝑰 = (𝐓𝐡 + 𝐓𝐬)𝐗 𝟏 + 𝐆𝐏𝐇 + 𝐒𝐏𝐇) 𝟏𝟎𝟎 The Degree of hazard is identified based on FEI and TI range according to the following criteria. Sr. No. 1 2 3 4 5 Table-1 FEI range 0-60 61-96 97-127 128-158 159 & abobe Sr. No. 1 2 3 Table -2 TI range 0-5 5-10 >10 Degree of Hazard Light Moderate Intermediate Heavy Severe Degree of Hazard Light Moderate Severe In Fertilizers Complex the ammonia plant constitutes one of the most hazardous area.It is therefore of vital importance to collect and analyze methodically the data based on accidents. This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. 26th Oct 2021 Research Gate is an academic social networking site www.researchgate.net Units M.F FEI Index Mond Index MI Primary 21 130.4 2531 Reformer Secondary 21 128 2579 Reformer Converter 21 128.2 2568 HT Converter 21 135.4 2562 LT Metanator 21 252 2109 Amm 21 166 2553 Converter Seperator 4 22.4 2075 Amm 4 23.8 412 Storage Amm 4 23.8 412 Tanker Table-3 Brief Description of Ammonia Production The raw material of Ammonia production are Natural gas, Steam, Air and Power. In old plant Heavy oil/Naphtha were used which requires partial oxidation with oxygen. In the plant, ammonia is produced from synthesis gas containing hydrogen and nitrogen in the ratio of approximately 3:1. Besides these components, the synthesis gas contains inert gases such as Toxicity of Hazard Degree ---- FEI Heavy TI --- ------ Heavy ----- ---- Heavy ------ ---- Heavy ------- --24.12 severe Severe ---High 21.2 13.3 High light High High 14.2 Light high argon and methane to a limited extent. The source of H2 is demineralized water and the hydrocarbons in the natural gas. The source of N2 is the atmospheric air. The source of CO2 is the hydrocarbons in the natural gas feed. Product ammonia and CO2 is sent to urea plant. The main function of the plant is illustrated in the following sketch (figure-1) This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Fig-1 Brief Description of Process The process steps necessary for production of ammonia from the above-mentioned raw materials are as follows: 1. The hydrocarbon feed is de sulphurized to the ppb level in the desulphurization section. 2. The de sulphurized hydrocarbon feed is reformed with steam and air into raw synthesis gas (process gas). The gas contains mainly hydrogen, nitrogen, carbon monoxide, carbon dioxide and steam. – 3. In the gas purification section, the CO is first converted into CO2. Then the CO2 is removed from the process gas in the CO2 removal section. – 4. The CO and CO2 residues in the gas outlet of the CO2 removal unit are converted into methane by reaction with H2 (Methanation) before the synthesis gas is sent to the ammonia synthesis loop. 5. The purified synthesis gas is compressed and then routed to the ammonia synthesis loop, where it is converted into ammonia. In order to limit the accumulation of argon and methane in the loop, a purge stream is taken. The liquid ammonia product is depressurised during which the dissolved gases, letdown gas and inert gas, are flashed off. This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net Fig-2 The natural gas feedstock coming from source limit contains minor quantities of sulphur compounds which have to be removed in order to avoid poisoning of the reforming catalyst in the primary reformer, and the low temperature shift catalyst in the CO converter, Particularly the low temperature shift. Converter Converter, is sensitive to deactivation by sulphur and sulphur sulphur-bearing compounds. Prior to hydrogenation, the feed gas sulphur absorption catalyst. After desulphurization, the content nt of sulphur is less 26th Oct 2021 Research Gate is an academic social networking site is mixed with Hydrogen rich recycle stream which is coming from syn gas compressor 2nd stage discharge. Then the Feed gas is heated in Heater in the reformer flue gas section. Since the gas contains organicc sulphur compounds, the desulphurization takes place in two stages. The organic sulphur compounds are converted to H2S by the hydrogenation catalyst, and the H2S absorption takes place in the than 0.1 vol. ppm. A sketch of the desulphurization section is given in Figure –3 This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net Fig-3 Hydrogenation The preheated natural gas is fed to the hydrogenator. The vessel contains Hydrogenation Catalyst, which is a cobalt cobaltmolybdenum based catalyst. catalyzes the following reactionsRSH + H2 → RH + H2S R1SSR2 + 3H2 → R1H + R2H + 2H2S R1SR2 + 2H2 → R1H + R2H + H2S (CH)4S + 4H2 → C4H10 + H2S COS + H2 → CO + H2S Where R is hydrocarbon radical. The hydrogenation catalyst must not get into contact 26th Oct 2021 Research Gate is an academic social networking site with hydrocarbons without the presence of hydrogen. The result would be poor conversion of the organic sulphur compounds causing an increased sulphur slip to the reforming section. The temperature also plays lays an important role with regard to catalyst activity; at low temperatures the hydrogenation reactions progress very slowly and conversion is not optimal while at high temperatures undesirable cracking reactions may occur with deactivation of catalyst duee to carbon lay-down lay on the catalyst itself. The optimum temperature range is This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site between 350 and 400°C. In case natural gas containing CO and CO2 is fed to the Hydro generator, the following reactions will take place. CO2 + H2 ⇔ CO + H2O CO2 + H2S ⇔ COS + H2O Therefore, the presence of CO, CO2 and H2O influences the sulphur slippage from downstream the Sulphur absorbers, The catalyst is oxidized at delivery and resumes its activity when sulphided. The Catalyst can be sulphided during initial start-up with natural gas feedstock at not high temperature and not high H2 flow to minimize the possibility of the MoO3 being reduced to MoO2 that means catalyst irreversible deactivation. In the sulphided state the catalyst is pyrophoric and it must be not exposed to air at temperatures above 70°C. The equilibrium composition for the reaction between the zinc oxide and hydrogen sulphide is expressed by the following equation: K(p) T =PH2S/PH2O=2.5 X 10-6 at 3800C. The catalyst is not reacting with oxygen or hydrogen at any practical temperature. Zinc sulphide is not pyrophoric and no special care during unloading is required. Steam operations should not be carried out in 11-R-202 A/B: the zinc oxide would hydrate and it would then be impossible to regenerate the ZnO material in the reactor. After desulfurization and scrubbing, the natural gas is sent to the primary reformer for steam reforming, where superheated steam is fed into the reformer with the methane. The gas mixture passed through reformer tubes which contains Nickel catalyst and externally heated by the combustion of fuel, normally natural gas and purge gas, to approximately 770 0 C in the presence of a nickel catalyst where methane is converted into CO/CO2 and H2. At this temperature, the following endothermic reactions are driven to the right, converting the methane to hydrogen, carbon dioxide and small quantities of carbon monoxide. CnH2n+2 + 2H2O ⇔ Cn-1H2n + CO2 + 3H2 – heat CH4 + 2H2O ⇔ CO2 + 4H2 - heat (39.4 kcal/mol) CO2 + H2 ⇔ CO + H2O - heat (9.84 kcal/mol) This gaseous mixture is known as synthesis gas. Conversion in primary steam reformer is about 70% of the hydrocarbon feed into synthesis gas. The reactions are endothermic, thus the supply of heat to the reformer is required to maintain the desired reaction temperature. The hot flue gases contain lot of energy and recovered upto maximum possible extent before releasing to atmosphere through chimney. This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net Fig-4 Studies on the prediction of remaining life and ageing ng of material for pressurized tubes of industrial furnace operated at elevated temperature. The results of mechanical properties tested at high temperature (800 and 8500 C) had shown that the aged metal’s mechanical properties improved after the solution heat treatment. In other words, the outlet pigtail tubes after being employed to about 80000 h can be further used continuously, operated at high temperature, for another design life (100000 h) by using solution heat treatment processing based on their proposed posed methodology for predicting the remaining life and ageing of material of furnace tubes. There are numerous incidents of reformer tube failure and fire in ammonia plant. The probable causes of fire are direct impingement of flame on the tube due to the partial blockage of burner tips is possible. 26th Oct 2021 Research Gate is an academic social networking site This may cause overheating of the tubes, which ultimately led to one tube rupture. Flame impingement from a nearby leaky tube might result in overheating and the ultimate rupture of the other nearby tubes. Sometimes times situation may lead to explosion in reformer furnace furnac as discussed an incident of fire in an ammonia plant which began with leakage in tube of a natural gas pre heater ignited a small fire. The small fire ultimately developed into tube to burst resulting resulti in large fire and plant shutdown. Reformer tube can also fail by stress corrosion cracking. During welding, the steel in the heat affected zone (HAZ) can get sensitized and this may subsequently lead to stress corrosion cracking. The premature failure off a primary reformer tube in an ammonia plant in which ch number of catalyst tubes found to have failed just below the inlet flange weld within about 2 years in service. This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Stress corrosion cracking (SCC) may get Therefore it is recommended to cool the steel aggravated further due improper welding below 1000 C after every weld pass, use filler procedure. Preventing such failure by following metal electrodes with low carbon content (such the proper welding procedure is very important. as the 321 grades) and stabilising the steel grades with black outer surface indicative of high addition of Nb (up to 1%) will help preventing temperature and the oxide scale was adherent. sensitisation during welding.Reformer tubes There was no indication of any localised damage from a fertilizer plant made of modified HK 40 in the form of pits. steel which failed after 4 years service during Categories of Risk associated with the startup of plant. At that time only 60 burners Fertilizers Complex (out of 576 burners) were firing in the reformer. The manufacture of anhydrous liquid ammonia The gas in the catalyst tubes was mainly involves processing of hydrocarbons under high hydrogen and steam at low pressure of 3 kg/cm2 temperature, high pressure conditions in the only. Seven tubes had ruptured in the bottom presence of various catalysts, chemicals etc. portion in one corner of the radiant chamber. Typical risks are as follows: Their visual observation - the tubes had a rather Ammonia Plants 1 Fire / Explosion Risks  Glands/seal leaks in valves, pumps, compressors handling hydrogen, natural gas, naphtha, synthesis gas etc.  Hose/pipe failure, leakage from flanged joints carrying combustible gases, vapours, liquids 2 High / Low  Burns due to contact with hot surfaces of pipelines, Temperature Exposure equipments, etc. or leaking steam lines, process fluids at high Risks temperature.  Frost bite due to contact with anhydrous liquid ammonia at -33 deg. C  Burns due to contact with pyrophoric catalyst 3 Toxic Chemicals  Asphyxia due to inhalation of simple asphyxiants like CO2 , Exposure Risks N2, H2, CH4, naphtha etc. and chemical asphyxiants like CO, NH3, Nickel carbonyl, V2O5, Hydrazine, NOx, SOx, H2S etc.  Acute toxicity due to inhalation of catalyst dusts containing heavy metals like Ni, Cr, CO, Mo, Fe, Zn, Alumina etc. and silica gel molecular sieves, insulation fibers/dusts. 4 Corrosive /  Severe burns, damage to eyes, skin and body tissues due to Radioactive Chemicals contact with anhydrous ammonia Exposure Risk Table-4 The risks of process hazards resulting in major / policies of the particular organization. There events (fires, explosions and toxic releases) are, are a number of models which illustrate the idea in principle, minimized by good design and the of “Layers of Protection”. The basic unmitigated application of process safety principles. Older risk posed by a process hazard is reduced by a plant was not subjected to the same level of number of “barriers” which either prevent the scrutiny that new plant is today. The adoption of hazard from being materialized or / and mitigate process safety principles is influenced by the the effect of the hazard once the event has country legislation, the linkages of the happened. A simple popular descriptive model, organization to global companies and the vision This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site is shown below Figure No= 5 to illustrate the concept. Fig-5 Fig-6 This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site The barriers are also known as safeguards, controls, safety measures or “Layers of Protection”. Each barrier has a finite probability of failure so multiple barriers are required to reduce the risk of the event taking place to an acceptable level. The barriers need to be fully independent of each other or else they may be subject to a form of common mode failure. The barriers arriers need to be maintained so that their reliability does not decline. The barriers may be of three major types. They may be hardware (e.g. pressure relief valve), systems (e.g. operating procedure), and people (e.g. training). The ranking of vulnerable are shown in the figure- 6,7 The value of strength of explosion is a function of the amount of chemical released, the characteristics of chemicals and the source of fire. The higher the amount of chemicals released, the wider the area that has the potential potentia to be flammable as well as the greater the probability of chemical vapors released close to the source of fire resulting in an explosion. This type of chemical is also very important to consider. Some types of chemicals are not flammable yet some are very ver volatile and flammable. Based on Table 4,, it is known that DFEI value for secondary reformer was 289.74. This value indicates that the impact caused by the fire/explosion secondary reformer is classified as severe. Table 4 This value did not include trauma ma treatment for employees, the ability to rise the company and other non-technical non factors., Fig-7 This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net Fig-8 Urea Plants Risk analysis All the Ammonia plants product uses in Urea plant e.g. Ammonia, Carbon Dioxides , Hydrogen mixed in carbon Dioxides makes explosive mixture with Oxygen which is gives for passivation of stainless steel vessel 26th Oct 2021 Research Gate is an academic social networking site & equipments. The Inters are vents in MP section in Ammonia stripping plants so the MP section is very risky similarly tin CO2 stripping the HP scrubber is very risky for explosion. Numbers of explosion are recoded worldwide.  Ammonia leaks from glands/ pump seals or flanged joints piping resulting in formation explosive mixtures in air.  Accumulation of H2 may take place in HP Section in case CO2 purity from Ammonia Plant is not within allowable limits. Ignition of this accumulated H2 can occur due to dissipation of static charge. High / Low  Burns due to contact with hot surfaces of pipelines, equipments, etc. or leaking Temperature steam lines, process fluids at high temperature. Exposure Risk  Frost bite due to contact with anhydrous liquid ammonia at -33 deg. C Burns due to contact. Toxic  Asphyxia due to inhalation of simple Exposure risk asphyxiants like CO2, N2, Chemicals chemical asphyxiant and ammonia. Solution of Urea, Ammonium carbamate Exposure and ammonium carbonate containing high NH3 content. Risks  Irritation due to inhalation of urea dust. Corrosive / Severe burns, damage to eyes, skin and body tissues due to contact with anhydrous Radioactive ammonia, conc. Urea and Ammonium carbamate solutions Chemicals Exposure Risks Table-5 Fire Explosion Risks / This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Fig-9 Major incident occurred in NFL Panipat detail analysis An incident of ammonia release occurred on 26th August 1992 in National Fertilizers Ltd. Panipat (Haryana) India. On the morning of August 26 some pressure drop was observed in the discharge end of the ammonia pump provided before the urea reactor. When search was made it was observed that the safety valve provided at the discharge end of the pump was passing. On the instruction of the shift in charge the stand-by pump was started and the pump C was isolated. The pump was depressurized and flushed. While the safety valve was being replaced by the maintenance operator with his helper under the foreman maintenance, the operator of the urea plant and the shift in charge of the urea plant, the isolation valve had failed and the liquefied ammonia start releasing at the pressure of 26 kg/cm2. The routine job of replacing the defective safety valve of the ammonia feed pump at 15 years old urea plant and began to replacing the valve when the unthinkable happened. Vaporizing within the seconds to form suffocating clouds of the deadly gas. This hit and choked to death eleven people and injured the ten even as their colleagues sprung into the action diffuse the gas with water spray. The ammonia had released into the atmosphere from the open port of the safety valve in the form of the spray. Some person was completely drenched with the liquefied ammonia. The atmosphere was suddenly filled with dense cloud of ammonia involving the persons within it. The rescue and relief operation were soon started but by the time the victims taken to the factory hospital 11 persons had died and 10 others sustained serious injuries. On the day of accident also the valve had been hammered to ensure total stoppage of the flow. The maintenance team had brought another safety valve. The task involved removing of the existing valve and fitting another valve at its place in order to bring the defective valve to the workshop for repairing and testing. The condition found after the incident that the existing had been removed isolation valve had failed and started releasing the ammonia gas through the open port of the safety valve. Immediately after that the area got covered with foggy fumes. The information of the event reached to all quickly and rescuers with selfcontained breathing apparatus entered the cloud for searching the trapped persons. Emergency siren was raised, though no one This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site acted as per the responsibility distribution in the onsite emergency plan. As soon as the information of the ammonia leakage spread in the plant, the about 25 breathing sets were brought from safety department to the site of incident. About 21 breathing sets were used by the persons involved in the rescue operation. The fire services of the plant were involved in spraying of water in the leakage zone. Keeping the wind direction in view the areas towards wind ward direction were being evaluated in the plant. The urea plant was shut down by use of emergency push button which closes the activities with shortest possible period. The nearest fire call point was broken to inform the fire department about the event. The first fire tender reached within 3-4 minutes after starting the event. After that the order fire tender also joined. There was need to stop the alternate ammonia pump. The switch was in the area where the cloud was dense. Nobody could approach the valve. Then electric department was asked to switch off the power from the main supply to the plant. The person who were rescued reach the factory hospital within 8-10 minutes. After the event has controlled the cause of the valve failure was checked, it was found that the valve collar of the globe valve had broken allowing the spindle of the valve in upward direction. The person engaged in the rescue and control operations were also affected by the ammonia exposure. They were first taken to the company hospital. But next day such people were admitted in the hospital. Cause of valve Failure The subsequent accident investigations indicated that the cause of the incident was lifting of valve spindle due to rupture of the collar of the valve. The careful investigation of the broken pieces of the valve indicated that about half of the collar had developed damage some time back as it has turned black, whereas the remaining part of the broken surface was shining white. This indicated that the crack had taken place some time back due to repeated hammering of the lever. Lessons learnt from the event the causes of the frequent failure of safety valves should be identified and necessary actions should be taken. The safety valve and the isolation valve before the safety valves should be marked with the identified numbers. The isolation valve before the safety valves should be locked open. The safety work permit should be signed by the safety officer duly countersigned by the issuing authority. The permit signing authority should ensure that the precaution indicated in the permit. The isolation of the machine having toxic or flammable substances should be dissolved in water by suitable process and should be lagoon to release slowly in the atmosphere the designer instructions regarding type of valve to be used should be strictly followed. In case the deviations from the original designed are required the manufacturer of the machines should be consulted. Every proposal for change the process should be critically analyzed by HAZOP study. Globe valve should be tested for any crack in the collar by dye penetration test or other equivalent technique. Condition of the thread should also be checked to not allow any slip. The emergency plan should be made a practical instrument for mitigate the effect of the events. The escape route from pump platform should be increased to promote the escape of the person in case of such events. Provision of waste spray in ammonia compressor area should be considered. All the SCBAs should be equipped with low pressure alarms and working in continuous positive pressure mode. The SCBA working only on demand mode should be marked and levels that these will not use when there is risk of live or health Quick modification done in other units of NFL After the Panipat incident, the motorized valve provided in other units of NFL so that in case of incident this ammonia can be protected to vented out as fig No. 9 This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net Fig --10 Incident on dated 18/09/2018 failure of one plunger packing of ammonia reciprocating pump In NFL Vijaipur unit, one reciprocating plunger packing failed on date 18/09/2018. A huge amount dense ammonia cloud observed. The ammonia pump has five plungers and discharge pressure is about 250 bar. The plant was running on full load at about 11.30 hrs. Ammonia leakage was started due failure of 5th number plunger. Immediately one stopped the plant and closed the booster pump motorized suction valve from control room to immediately control the 26th Oct 2021 Research Gate is an academic social networking site situation; this lesson one has learnt from the Panipat incident. This motorized valve was provided after Panipat incident. The manual valve cannot be operated in field because huge dense ammonia was there. In high pressure pump house area a water curtains also provided with control valve which can be operated from control room. An ammonia sensor also provided in each pump house and at 50 ppm of ammonia the alarm appears on central control room. Immediately water curtains control valve open to control ammonia. This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Fig- 11 This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. 26th Oct 2021 Research Gate is an academic social networking site www.researchgate.net Fig-12 Hazard Identification There are various modes in which flammable and toxic chemicals can leak into atmosphere causing adverse affects. It may be small leaks from gaskets of the flanged joints, or guillotine Sr. No. 1 2 3 Failure Mode Probable Cause Flange / Gasket failure Incorrect installation failure of a pipeline of even catastrophic failure of the storage tank. Some typical modes of failures and their possible ible causes are discussed below , Table No-6 Remarks gasket Incorrect Attention to be paid during selection and installation of gaskets. Weld failure It is normally due to poor quality Welding to be done by certified of welds welders with right quality of welding rods. Inspection and radiography must also be done. Pipe corrosion erosion Sometimes fabrication or Pipes material of construction or failure due to stress installation leaves stress in the should be selected correctly. pipes. Erosion or corrosion also is Design should take care of sometimes the cause. erosion effects. And installation of pipes should not leave any stress This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 4 5 6 7 8 9 10 26th Oct 2021 Research Gate is an academic social networking site Over pressurization of Over pressurization can occur due pipeline to failure of SRV or incorrect operation. Deficient installation of Pipes design and installation is pipes sometimes not as per appropriate standard. Leaks from valve Leaks from glands, bonnets or failures valves spindle is sometimes the cause. Instruments failure Multifarious instruments are used for control of process parameters. Any such instrument failure can cause mishap. Failures of protective Protective system like SRV, system bursting discs, vent header, drain lines etc. are provided to take care of abnormal conditions. Operational effort Plant operational parameters should not be exceeded beyond the permissible limits. Other failures There are external other reasons causing the failures. Necessary procedures should be there to prevent. It must be ensured that installation is as per correct standards completely. Right selection of valves and their maintenance should be ensured. Reliability of instruments working must be ensured through proper selection and maintenance. Reliability of protective system must be ensured highest through inspection and proper maintenance. Operating procedures must be complete and strictly followed. Design and operating philosophy must consider all possible reasons. Table-6 Selected failure cases and likely consequences) facilities of onshore oil/gas production facilities outlines the failure cases those selected for at Fertilizer Complex Equipment Failure case Associated hazards Sr. No. Ammonia Plant NG at B/L 1 NG Compressor Discharge 2 HTS Effluent 3 Converter effluent 4 HP ammonia scrubber vapour 5 6 Process condensate 7 HP Ammonia scrubber liquid 8 HP Ammonia scrubber liquid 9 Urea Plants Ammonia at B/L 1 HP Ammonia pum 2 3 Reactor 4 HP Carbamate pump 5 6 Table-7 Instrument tapping failure Instrument tapping failure. Large hole in bottom Catastrophic Failure Instrument tapping failure, Instrument tapping failure Large hole in bottom, Large hole in bottom. Large hole in bottom, Flammable Flammable Flammable/ Toxic Flammable/ Toxi Flammable/ Toxic Toxic Toxic Flammable/ Toxic Flammable/ Toxic Instrument tapping failure 10 mm failure Instrument tapping failure, Large hole in bottom, Pump seal failure Flammable/ Toxic Flammable/ Toxic Flammable/ Toxic Flammable/ Toxic Flammable/ Toxic This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Role of Oxygen and stainless steel higher temperature and pressure and where aggressive condition of urea Carbamate mixture exists, stainless steel of higher chromium and nickel contents are found to be more effective against corrosion. At this condition, the influence of Nickel is also apparent. However, the corrosion rate of 2RE-69 stainless steel is about 5 times as low as that of SS-316L which indicates that the favorable influence of Chromium is much larger than the unfavorable influence of Nickel. Since the liquid phase in urea synthesis behaves as an electrolyte, the corrosion is of an electrochemical nature. Stainless steel in a corrosive medium owes its corrosion resistance to the presence of a protective oxide layer on the metal. As long as this layer is intact, the metal corrodes at a very low rate. Passive corrosion rates of austenitic urea grade stainless steels are generally between <0.01and (max.) 0.10 mm/a. Upon removal of the oxide layer, activation and consequently, corrosion set in unless the medium contains sufficient oxygen or oxidation agent to build a new layer. Active corrosion rates can reach values of 50 mm/a. Stainless steel exposed to Carbamate containing solutions involved in urea synthesis can be kept in a passivation (non corroding) state by a given quantity of oxygen. If the oxygen content drops below this limit, corrosion starts after some time depending upon process conditions and the quality of the passive layer. Hence, If the CO2 after the elimination of the air used for preventing corrosion is as following The optimum passivation is required if more than optimum the chances of explosive mixture and also ammonia losses, i.e. danger for environment also. Flammable gas mixtures and the consequences there of on urea plant safety have been important issues in the entire history of the urea process industry. High chromium stainless steel owe their high resistance to corrosion under oxidizing condition due to the formation of a surface-oxide film which is very adherent and highly impervious; thus the metal is protected from attack or we say it is passive. However, if the oxidizing conditions are lost, the metal is rapidly attacked. The protective film once formed is not damaged in normal course. The presence of sulphur compounds damages this protective film. It is essential that the protective film is not damaged during operation and as such continuous feeding of air has been incorporated in our process. It was found from experiments that SS 316L stainless steel requires 5 ppm of 02 for passivation and 2RE-69 stainless steel requires 3 ppm. Although this value is low and in actual practice as high as 6000 ppm of 02 is being maintained. Material of higher chromium content requires less oxygen to remain passive than low chromium steels. This fact also points to the suitability of using stainless steel with a chromium content of 24.5% in HP stripper. Chromium slows down and nickel accelerates the corrosion of materials in the active state .This is best illustrated by corrosion rates of a number of materials in relation to their Ni contents. At This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. 26th Oct 2021 Research Gate is an academic social networking site www.researchgate.net Sr. No. Components 1 2 3 4 Carbon Dioxide Hydrogen Air Inerts Gases Percentage (Volume) 94.7 1.2 3.8 0.3 Table-8 If we neglect others combustible , the Hydrogen/Total combustible ratio must equal as unity 𝟏= 𝐇𝐲𝐝𝐫𝐨𝐠𝐞𝐧 𝐓𝐨𝐭𝐚𝐥 𝐂𝐨𝐦𝐛𝐮𝐬𝐭𝐢𝐛𝐥𝐞 𝐄𝐱𝐩𝐥𝐨𝐬𝐢𝐨𝐧 𝐌𝐢𝐱𝐭𝐮𝐫𝐞 The Composition of the vent gases assuming that all ammonia added and CO2 has been eliminated , analysis is as following. Sr. No. Components Percentage (Volume) 2 Hydrogen 22.6 3 Air 71,7 4 Others 5.7 Table-9 Gas mixture inside the triangle is formed by the base line and the lines labeled. The mixture indicated by the star is laying inside the above mentioned explosive area and thus explosive as shown in the figure13 This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. 26th Oct 2021 Research Gate is an academic social networking site www.researchgate.net Fig-13 In CO2 Stripping Gas analysis tabulated in Table No-10, and this is found in Explosive range. Analysis of HP Scrubber Gases Categories Inflamables Inertes Oxygen Total Components [%(v/v)] Total % INDIVIDUAL NH3 37.50 76.84 H2 11.30 23.16 CH4 0.00 C2H6 0.00 0.00 C3H8 0.00 0.00 N2 Ar 6.06 0.00 100.00 CO2 12.50 O2 32.64 32.64 O2+Ar 0.00 100.00 100.00 48.80 0.00 18.56 Table -10 This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Brief Description of High P Pressure Scrubber The HP scrubber consisting following three parts. As shown in the 1 6 & 17. 1. Blanketing sphere, which receive the gases coming from reactor. 2. A Heat exchanger part, which is equipped with central down comer through which degasified flow down. A gas distributer with vortex is installed in bottom. 3. A scrubbing part, in which the remaining gases are scrubbed with carbonate nate solution which is coming from LP section and where the NH3 and CO2 are almost tottaly condensed. The synthesis loop is provided with a central drain line connecting all the HP vessel to the outlet of the HP heat Exchanger then to the central drain line. The central drain line and other parts of the HP synthesis section are connected to the HP flush water source, so as to enable them to be flushed. Fig-14 This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site In case Sr. No. 1 2 3 4 5 according to the following compositions 𝐇𝐲𝐝𝐫𝐨𝐠𝐞𝐧 𝟎. 𝟐𝟑 = 𝐇𝐲𝐝𝐫𝐨𝐠𝐞𝐧 + 𝐀𝐦𝐦𝐨𝐧𝐢𝐚 that there are some NH3 and CO2 Components Percentage (Volume) Hydrogen 11.3 Air 35.9 Other 2.8 Ammonia 37.5 Carbon 12.5 Dioxide Table-11 The above mixture gas mixture will be if it is situated inside the triangle formed by the 0.23 explosion limits and the base line. In the operating point marked total combustibles 48.8%, air 35.9%, this point is outside the explosion area as shown in the figure-15 Then The Hydrogen/Total combustibles are Analysis of HP Scrubber Gases Inflammables Inertes Oxygen Total Table-12 Components NH3 H2 CH4 C2H6 [%(v/v)] 18 31 0 0 C3H8 N2 Ar CO2 O2 O2+Ar 0 28 0 14 9 0 100 Total 49 42 % INDIVIDUAL 36.73 63.27 0 0 0 100 9 100 This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Fig-15 Calculation for Explosively The hydrogen present in Carbon Dioxide, hence the composition of vent gases calculated by carbon Dioxide given to Stripper. Carbon Dioxide to HP stripper=37500 Nm3/hr Composition of Carbon Dioxide Non Combustible Gases=112 Nm3/hr Total (Hydrogen +Air + Noncombustible)=1875Nm3/Hr CO2 =95% Hydrogen=1.1% Air=3.6% Noncombustible material=0.3% Vented Gas D/S HP Scrubber=3000 Nm3/Hr Vented Hydrogen=412 Nm3/hr Vented Air=1350 Nm3/hr Ammonia & Carbon Dioxide in Vent Gas=3000-1875=1125 Nm3/hr Then the Vent gas from HP Scrubber This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site 1. Hydrogen=(412*100/3000=13.75% 2. Air=(1350*100/3000)=45% 3. Non Combustible=112.5*100/3000=3.75 % 4. Carbon Dioxide Dioxide37500*0.05=187.5Nm3/hr=281*100/ 3000=9.37% 5. Ammonia=1125187.5=937.5Nm3/Hr=937.5*100/300 0=28.13% 6. Combustible Gases ases are Hydrogen and Ammonia, so the= 7. 13.75/41.875 = Hydrogen/ Hydrogen (Hydrogen + Ammonia) Ammonia 32.8% So according to the above figure the point 32.85 is an Explosive mixture Fig-16 This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Fig-17 This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Calculation for Ammonia Stripping Process Where mixtures of two or more flammable gases are encountered, the limits of flammability of the mixture can often be reliably predicted by using the following formulas suggested by Le Chatelier: Where: P1 . . . Pn = volume fractions of components 1, 2, 3, . . . , n of the mixture LFL1… LFLn = lower flammable limits of components 1, 2, 3, .. n of the mixture UFL1…. UFLn = upper flammable limits of components 1, 2, 3, .. n of the mixture EXPLOSIVE LIMITS Explosion Limits in Air Lower Upper Gases Explosion Limits in O2 Lower Upper Minimum O2 Content Minimum Flammable CH4 5 15 5.5 60 12.25 6 H2 CO 4 12.5 74 74 4.5 15.5 94 94 5 6 4.3 13.75 NH3 15.5 27 13.5 79 - - Table-13 The oxygen concentration in the Carbon dioxide "range from 0.1 to 0.8% of oxygen. Let ns examine the two above mentioned concentrations as examples. Normal compositions of carbon dioxide feed gas at the battery limits of the urea plant are: C02- 99.0 % (mole) H2- 0.6 % (mole) N2- 0.4 % (mole) including Argon etc. Example 1_ This mixture is within the explosion limits as can be seen from figure-18 All of the carbon dioxide gas mixtures with oxygen concentrations between 0.1 and 0.8 If we need 0.1 % of oxygen in this gas mixture and we feed this as air the final composition of the non condensable components becomes; Hydrogen 0.6 moles Nitrogen 0.4 moles Air 0.1 moles +0.4moles N2 Total 1.5 moles Table-14 O2 40% moles 53% moles 7.0 % moles 100% moles % mole will be within the explosive limits-. limits We may thus conclude that each high efficiency urea process This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Fig-18 will end up with a hazardous gas mixture, unless provisions are being made to remove the hydrogen from carbon dioxide de and if the ammonia contains hydrogen, to remove this hydrogen as well.There are many plants, running during normal operation or upset conditions, emitting gas mixtures within the explosion limits» k great many plants however have never experienced explo explosion. In those plants all of the conditions required for an explosion (an explosive gas mixture and an ignition source simultaneously) did not occur so far. The potential danger is there however as practice has shown. In a few plants Stamicarbon has experienced experi explosions in the 18 ata purification step of conventional urea plants as well as in the 140 ata purification step in CO2 stripping urea plants in HP scrubber section. Gas sample analysis Gas Flow -524.5 NM3/Hr, CH4-6.78%, 6.78%, Hydrogen 7.45, 18.45, Inerts (N2+O2)-67.32, 67.32, Ammonia This is an open access article; Research Gate is a European commercial social networking si site te for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site Fig-19 Conclusion The fundamental method for prevention of vapor explosion is how to reduce the possibility of leakage. Vapor explosion is an instantaneous process of energy release. Once the vapor explosion takes place, the catastrophic accident becomes inevitable due to the high speed of phase transformation. A leakage detection system should be developed due to impurities in steam-damaged steels. The fundamental method for prevention of vapor explosion is how to reduce the possibility of leakage. Vapor explosion is an instantaneous process of energy release. Once the vapor explosion takes place, the catastrophic accident becomes inevitable due to the high speed of phase transformation. A leakage detection system should be developed due to impurities in steam-damaged steels. The barrier of having an effective start-up procedure was totally ineffective as this not apply to the specific conditions applicable on the day. Failure of people undermined the entire risk management process. Whilst people represent a source of failure they also are the last barrier to detect problems and save the day. Safety Model of a This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers. View publication stats www.researchgate.net 26th Oct 2021 Research Gate is an academic social networking site hazard protected by a series of protective barriers is not understood by the Fertilizers and support personnel. Engineering control that should be conducted include: periodic maintenance of the gas detector and provide cleaning tools to clean the oil spills. In addition, administrative control also need to be conducted, such as: posting information about the national Fire protection association (NFPA) rating of Chemicals which will eventually help minimize the risk. References 1. Book “Fertilizers Technology pure knowledge” by Prem Baboo published in Notion Press-2021. 2. Section of material in fertilizers Industries by Prem Baboo, published in Global scitific journal, Vol-9 issue -1, January-2021. 3. Operational Experience of Dehydrogen Reactor at GFGL by Ashok Agrawal, published in Indian Journal of Fertilizers,Vol-2, Dec2006. 4. Probabilistic risk assessment of Fertilizers Plants by R.S olaniya,H.N. Mathurkar,A.W. deshpandey published in Indian Journal of chemical Technology, Vol-3, March 1996. 5. Guidelines for integrated risk assessment and management in large industrial areas Jan-98. Legends PHA (Process Hazard Analysis), HP-High Pressure, LS-Low pressure steam, MP- medium pressure, LP-Low pressure. This is an open access article; Research Gate is a European commercial social networking site for scientists and researchers.