HIGH PRESSURE VESSEL LEAKAGE IN UREA PLANTS (A case study) ARTICLE DETAILS ABSTRACT (original) (raw)

IJERT-Urea Plant Equipments Inspection

International Journal of Engineering Research and Technology (IJERT), 2020

https://www.ijert.org/urea-plant-equipments-inspection https://www.ijert.org/research/urea-plant-equipments-inspection-IJERTV9IS030546.pdf There are many equipment's in urea plant which have very important for holding time, partition plate passing, weep holes monitoring, medium pressure absorber, high pressure carbamate condenser, etc.Startup of medium pressure absorber, is one of the most difficult operations of chemical processes in urea plants. In the last few years we have accomplished both theoretical studies and experimental verifications. Perfect sealing of trays by special quality PTFE (Gore-Tax)As a result, significant reduction of startup time period can be achieved by implementing the developed perfect sealing and checking of holding with recommended standard rules. This paper summarizes our recent results from these studies and make standard. Passing rate of partition plate holding check of ferrules. Weep hole monitoring and checking of the leakage through liner in HP vessels. Absorber columns, and trays, can now be designed with a high degree of reliability. Absorber columns have been widely used in the past to separate mixtures of liquids into individual components like ammonia and carbamate mixture. PROCESS DESCRIPTION The urea process is characterized by a urea synthesis loop with a reactor operating at about 140-175 kg/cm2 (g) (for stripping process) with ammonia to carbon dioxide molar ratio at urea reactor inlet of 2.8-3.9. This allows a CO2 conversion into urea of 60-68% in the reactor itself, also perforated trays which prevent back-flow maintained plug flow and favour gas absorption by the liquid. Different type of HET vortex mixture with booster are used now a day to increase the conversion rather than vessel size and pressure. Different types of HET are developed like super cup etc. There are two kinds of chemical reactions at the same time in the urea reactor: 2NH3 + CO2 ↔ NH2-COO-NH4 + 136230 kJ/kmol of carbamate (at 1.03 kg/cm2; 25°C); NH2-COO-NH4 ↔ NH2-CO-NH2 + H2O-17575 kJ/kmol of urea (at 1.03 kg/cm2; 25°C) The First reaction is strongly exothermic and the second one is weakly endothermic and occurs in the liquid phase at low speed. Downstream the urea synthesis the decomposition (and relevant recovery) of unconverted chemical reagents is carried out in three subsequent steps: High Pressure Decomposition in H.P. stripper; Medium Pressure Decomposition in M.P. Decomposer and, finally, Low Pressure Decomposition in L.P. Decomposer. The decomposition reaction is the reverse reaction of the first one above showed, viz.: NH2-COO-NH4 ↔ 2NH3 + CO2 (-Heat) and, as can be inferred from the equation, it is promoted by reducing pressure and adding heat. The urea reactor effluent solution enters the stripper, under slightly lower pressure than the urea reactor, where a fair part of the unconverted carbamate is decomposed, due to the stripping action of either NH3orCO2, so that the overall yield of the H.P. synthesis loop referred to CO2 is as high as 80-85% (on molar basis). Ammonia and carbon dioxide vapours from the stripper top, after mixing with the carbamate recycle solution from M.P. section, are condensed at the same pressure level of the stripper, in the H.P. carbamate condenser; thus producing the LS steam which is used in downstream sections. After separating the inert gases which are passed to M.P. section, the carbamate solution is finally recycled to the reactor bottom by means of a liquid/liquid ejector, which exploits H.P. ammonia feed to reactor as motive fluid. This ejector and the kettle-type carbamate condenser above mentioned, allow a horizontal layout, which is one of the main features of urea process. Downstream of the stripper residual carbamate and ammonia are recovered in two recycle stages operating at about 17.5 kg/cm 2 (g) (M.P. section) and 3.7 kg/cm2 (g) (L.P. section) respectively. Ammonia and carbon dioxide vapours coming from carbamate decomposition are condensed and recycled to H.P. section. The solution leaving the L.P. section arrives to the concentration section where process condensate is removed in order to reach a concentration of about 96-97% which is required to feed granulator. Urea Sections are characterized by the following main process steps: a) Urea synthesis and NH3, CO2 recovery at high pressure; b) Urea purification and NH3, and carbamate recovery at medium and low pressures; c) Urea concentration; d) Waste water treatment. Urea solution production unit is also provided with the following: Auxiliary installation; f) Steam networks; g) Condensate Recovery & Flushing networks.Even if the inspections was made before the first start up, For the inspection of the urea reactor, stripper Carbamate condenser and Carbamate Separator All inspectors were used rubber gasket and a wood cover in order to avoid possible damaging on the gasket seating area of manhole. The weep holes are provided for the following Equipment's: 1. Urea reactor 2. Stripper 3. Carbamate condenser and 4. Carbamate separator IJERTV9IS030546 (This work is licensed under a Creative Commons Attribution 4.0 International License.) www.ijert.org

ENGRO 40 YEARS' EXPERIENCE OF TOTAL RECYCLE UREA PLANT ASIM RASHEED QURESHI & ABDUR REHMAN CHOUDHARY

This paper shares the learning's of Engro 40 years' experience, revamping of urea plant to improve efficiency & capacity, many catastrophic incidents & operational emergencies of total recycle urea plant. Engro's urea-1 plant voyage started from 515MTD urea plant with local ammonia venting without vent stack systems to the EPA and OSHA practiced 780MTD capacity plant with two vent stack systems which is the part of this paper. Under the energy improvement drive engro approached casale trays for their latest design and high efficiency trays for the urea reactor. Rapid and complete depressurization of ammonia reservoir (13met) in the atmosphere without vent stack systems is one the major catastrophic incident in the history of engro which lead to in level-2 emergency. as a result of such incidents engro had gone through a wide-ranging project named large ammonia release (LARA) to handle such incidents in future by making the plant inherently safe. Plant major hardware modifications to make it inherently safe are also part of this paper. Urea plant reactor bulged due to weep-hole leakage which causes plant shut down for 40 days, major learning of this incidents are also part of the paper. Bursting of pressure safety devices during startup & shut down was frequent at urea plant in last 30year's. Reactor pressure during aqua ammonia circulation was reduced to max 1500psig from 3000psig and high pressure loop pressure was also maintained at lower side to avoid pressure safety device (PSD) rupturing and hammering. This paper also covers change in urea plant startup & shut down sop which gives rise to 90% decrease in PSD rupture. A pressure safety device is the last line of defense in case of pressurization of any vessel. This paper also covers many incidents of rupturing of PSD of high pressure decomposer; gas condenser; low pressure decomposer and high pressure absorber cooler, due to abnormal urea plant operations. High pressure decomposer sight glass leakage and

Trouble Shooting during Heavy Leakage from Urea Plant HP Loop

In high Pressure Urea reactor, sudden pressure drop by any reason can cause bulging of liner. In any reason (heavy leakage in HP section of urea plant, PSV popped etc.) the HP loop pressure goes to zero, then how to drain out urea /carbamate solutionfrom HP loop without pressure to take shut down.At gravity, it is very difficult to drain out urea solution from 1½ " line and also huge amount of effluent generation. the urea reactor is a typical gas liquid urea and ammonium carbamate reactor involving not only back mixing phenomenon but also significant aspect of heat and mass transfer between high corrosive vapors and liquid phase.Urea Reactorcontaining about 34-35 % Urea,33-34 % ammonia,14% CO2 and rest is water.In M/S. saipem process all the safety has been taken in account e.g.to protect the reactor in case a sudden pressure increases an automatic system has been providedwith interlocks to stop the fluid inlet feed. The temperature profile is progressively rising inside the reactor due to density variation. In this article, all procedure described at zero kg/cm 2 pressure Feed in in Urea reactor as well as draining of urea solution to take shut down and how to manage effluent generation at draining of HP loop. The experienced gained when our 31 stream HP loop PSV-2(HP loop Carbamate separator PSV) sudden popped with heavy leakage from upstream flange of PSV-2 on dated 11/10/2018 at 11.50 hrs. and pressure of HP loop went to zero kg/cm 2 .At that time the plant was running on full and constant load.

How to Improve Safety and Reliability of the High Pressure Synthesis Section of Urea Plants

Nitrogen and Syn gas, 2021

This paper elaborates the most critical safety hazards: Ruptures and toxic ammonia leaks. The paper also provides the Top 10 prevention and mitigation measures. To minimize / avoid that incidents do repeat, we recommend to make use of the Center for Chemical Process Safety: Risk Based Process Safety Management approach. Pay proper attention to avoid ruptures, to handle leaks and to apply the right and state-of-the-art leak detection systems.

Damage of atmospheric Tank in Urea Plant & Trouble shooting

This paper intended to damaged of ammonical waste atmospheric Tank in Urea Plant due to Vacuum was created inside the vessel.A case study, What was the reason behind this accident and modification done for future.Brief description of Pressure Vessel and its Classification.

Leakbeforebreak analysis of Type 304 stainless steel piping

The nuclear materials production reactors at the Savannah River Plant (SRP) were designed and built in the 1950's and have operated successfully since that time. Unlike commercial power reactors, the production reactors are moderated and cooled by heavy water and are operated at moderately low temperatures and internal pressures. In addition, the entire primary coolant pressure boundary is constructed of Type 304 stainless steel or its cast equivalent, CF-8, except for seals, gaskets and other serviceable parts. Due to the low applied stresses coupled with high toughness, the primary coolant piping is highly tolerant of defects. In the operational history of the plant, several instances of minor leakage from stress corrosion cracks have occurred in the piping, thus exemplifying a Leak-Before-Break (LBB) capacity of the system. Fundamentally, LBB capability provides the assurance that a postulated through-wall crack could be detected by the resulting leakage before the onset of c...

Study the Effect of Urea as Inhibitor for Corrosion in Mild Steel in 2204-Tank

The effect of urea as a corrosion inhibitor on mild steel in the present of water taken from the 2204-tank located in Al-Shaiba Crude Oil Refinery in Basrah was investigated by using potentiodynamic measurement. It is found that the inhibition efficiency (IE) and coverage ratio of urea at 1.5 g/L increase by increasing the concentration of urea until reach 99.46% and 0.994, respectively. The corrosion rate is reduced with increasing the concentration of inhibitor until 1.5g/L; however, after that the corrosion rate increases. Urea inhibitor acts as a cathodic inhibitor.

Determining Useful Life of Reactor Pressure Vessels

The length of useful life of the reactor vessel is much more questionable than the estimate of a probable breakdown. It particularly arises as a need and an obligation after regular technical inspections. The problem of determining the remaining life of the vessel is especially arises when there are errors or cracks on the vessel walls. Research on high quality vessels leads to the conclusion that hydraulic tests are harmful, which was confirmed by a large number of cracks that appeared after these hydraulic tests. This fact gives a basis for evaluation of these tests and their adjustment depending on the length of exploitation. The analysis of causes for a change in material properties from manufacturing all the way to the removal from exploitation was performed on over fifty vessels in oil processing. Special attention was given to a reactor vessel that operates under heavy operating conditions and with a complex catalytic chemical process using hydrogen. Changes in material characteristics were monitored from the production of the reactor vessel until its shutdown and removal from service. The causes for crack occurrence and expansion in vessel walls and heads were analyzed. The occurrence of new cracks and expansion of old cracks was particularly considered during hydraulic tests.

THE EXPLOSION HAZARD IN UREA PROCESS

www.reasercGate.net, 2021

In Urea plant passivation air is used in reactor, stripper and downstream of the all equipments. The reactor liner material used Titanium, Zirconium, SS 316L (urea grade), 2RE-69 and duplex material .except Titanium and Zirconium all stainless steel required more passivation air. In CO 2 some quantity of Hydrogen is present about 0.14% to 0.2%. The passivation oxygen and Hydrogen makes explosive mixture. To avoid a fire or explosion in a process vessel is to introduce inert (noncombustible) gases in such a way that there is never a mixture with a combustible concentration in exit of MP vent. Mixtures of fuel, oxygen, and inert gases are not combustible over the entire range of composition. In CO 2 stripping process the HP scrubber is the risky vessel and this vessel consisting blanketing sphere, Heat exchanger part and a scrubbing part. With help of triangular diagram that shows the shape of the combustible/noncombustible regions for a typical gaseous mixture of fuel, oxygen, and inert at specified temperature and pressure. Present article how to avoid that combustible rang and how to tackle that gases in CO 2 & ammonia stripping process.