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Corrosion aspects in urea plants

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Special stainless steel grades developed Design requirements Fabrication requirements

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CONSEQUENCES OF LOSS OF PASSIVATION AIR

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• Initial Shut-down June 2nd, 2013 for a planned maintenance outage. • The inspection of the R-101 Reactor produced a number of routine findings and small repairs. • All internal surfaces (liner and

weld overlays) are in passive state

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Shiphon Jet Pumps

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While revamping a Stamicarbon Urea plant, in most of the cases, the specific reaction volume is decreased with the revamp. As a result the residence time of the urea solution in the reactor will decre

ase and thus the efficiency of the reactor will go down. However, by changing the internals of the reactor (using a different type of trays) the efficiency in the reactor can be improved. In the past two types of trays were used in Stamicarbon Urea plants: the conventional trays and the high efficiency trays. Now a new type of trays is introduced, which improves the efficiency of the reactor and thus results in savings of the high-pressure steam consumption. These trays are called the Siphon Jet Pumps. The first trays have successfully been installed in SKW Piesteritz. In this paper the Siphon Jet Pumps are introduced and several aspects around these trays are discussed.

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Urea Synthesis gas lines suffering from leakages

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In the 2014 turnaround all original AISI316L-UG high-pressure gas lines were replaced in the urea synthesis section, in accordance with advice from Stamicarbon. The material utilized for the replaced

gas lines was again AISI316L-UG, because there were still some such tubes in stock, dating from the time the plant was constructed.The affected areas showed evidence of stress corrosion cracking (SCC), but reduction in the wall thickness was also observed. This was attributable to condensation corrosion, which is normally observed in the gas lines. It was most severe in the heat-affected zones (HAZ) near the welds. The affected elbows were subjected to metallographic examination in Brazil as well as in Stamicarbon laboratory. This paper presents the investigations carried out on the elbows and piping removed from the urea synthesis gas lines in order to find the root cause of the leakages. 

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THE VALUE OF A RELIABLE LEAK DETECTION MONITORING SYSTEM IN HP SYNTHESIS SECTION

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• A urea plant contains large amount of toxic ammoniaat elevated temperature and pressure. • For instance:the synthesis section of a1000MTD urea plant contains > 35ton of NH3 • Keeping this ammon

ia inside the process equipment is essential from a safety,environmental andeconomica lpoint of view

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Sustainable plant operation without stripper level indication

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Stripper level indication is critical in CO2 Stripping plant as loss of level can cause CO2 Slippage towards the LP Section whilst too high level causes unequal distribution of CO2 resulting in poor s

tripper performance.  The stripper level indication (Radioactive type) LT-1043 got erratic at our plant and we sustained plant operation without this indication by: 1. Keep the plant load constant and avoid any changes in plant load.  2. Observe the stripper outlet temperature as this temperature will change with increase or decrease of the stripper bottom level.  3. Observe the steam consumption of the stripper as the steam flow will change with a change in the liquid level. 4. Observe the N/C Ratio and keep it constant. 5. Observe the downstream section pressure at constant plant load.

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Round table Operations, topic RADAR

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Reliable radar level measurement in Urea synthesis equipment

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As we all know measuring level in high pressure urea synthesis equipment is not an easy job. Extreme process conditions especially with respect to the corrosiveness of the process media and the w

ay the equipment is constructed  eliminates most of the measuring principles available. Radio-active level measurements are common practice in urea synthesis equipment, but there is a tendency in the market to eliminate radio-active level measurements in Urea plants, due to several reasons (maintainability, public aversion against radio-activity, legislation, etc). During the symposium of 2008 the radar level measurement was introduced as an alternative for radio-active level measurements in the Urea synthesis equipment, based on experience of a few radar measurements in operation at that moment. Currently, 4 years ahead, radar technology became Stamicarbon’s standard for level measurement applications in the urea synthesis. This document gives an update on our latest developments, experiences and requirements, which results in a reliable radar level measurement in Urea synthesis equipment.

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New Overpressure Protection System for the Urea Synthesis

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The motivation for the development of the New Overpressure Protection System for the Urea Synthesis results from the following safety-related and process-related facts: Urea plants in Germany be

long to the so-called accident plants. For these plants it is required that the security is improved constantly. The management wants to constantly improve the environmental-protection and upgrading the technological conditions to increase the production and to save energy.

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Blockage of leak detection system

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A leak detection system is installed at the High Pressure equipment items of a Urea Plant in order to detect any leakage in these HP Equipment. Normally vacuum is maintained in this system, blockage i

n the system is checked by opening atmospheric valves and breaking the vacuum on a defined frequency of one month. We could not check the blockage on this defined frequency, we performed a blockage test after a period of 10 months; blockage was found in valves V-16 & V-17 in the leak detection system of the HP Stripper. After further investigation it revealed that the blockage in the leak detection system was inside the stripper top dome. We tried to de-block the system with instrument air having a pressure of 7 bar and with low pressure steam but this failed. Then on the running plant we tried to de-block using an argon cylinder having a pressure of 100 bar and de-blocked the lines at 30 bar. The root cause of the blockage was corrosion inside the leak detection tube due to moisture ingress through the atmospheric valves. The equipment condition was found healthy on inspection during a turnaround.

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Leak Detection Safeguarding Stamicarbon's High Pressure Urea Vessels

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Urea solutions are not very corrosive, but ammonium carbamate, an intermediate in urea synthesis is highly corrosive. To protect the carbon steel high pressure synthesis equipment from corrosion, stai

nless steel loose liners are commonly applied. With a loose liner a hazardous situation may arise if a leak occurs and carbamate containing fluids enters the space between liner and carbon steel. For this reason Stamicarbon designed a system which continuously monitors for leaks to allow safe operation of said equipment.

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Advance Monitor Leak Detection Monitoring System

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Stamicarbon’s ADVANCE MONITOR™ Leak Detection Monitoring System for both new and existing High Pressure equipment. Existing Leak Detection Monitoring System can be inspected to ensure proper operation

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Stamicarbon Stripper Performance in Non-Stamicarbon Plants

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This paper describes the successful experience of a Stamicarbon designed Safurex® HP Stripper in a world scale Snamprogetti urea plant commissioned in early 2001. The Stamicarbon designed Safurex® HP

Stripper replaced a bi-metallic designed Snamprogetti stripper in 2003 which suffered extreme corrosion issues within a short period after startup in the bottom channel section of the vessel that caused persistent operational outages and huge financial losses. The problems encountered with the original HP bi-metallic stripper and results of the decision to replace the bi-metallic tube stripper with a HP Safurex® stripper are addressed. The subject Safurex® stripper was in service for 850 operational days from March 2003 up until November 2006, after which the subject stripper was returned to Canada and installed in another Snamprogetti urea plant in 2007. The subject stripper has been in operation in Canada since 3Q 2007 and has had no issues in its new location as of this writing.

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Stamicarbon Critical Proprietary Equipment

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Quality & Safurex • Proprietary Equipment • PEQ procurement

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Report of the steps description

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A specialty SAFUREX™ for HP stripper tubes

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This paper presents a historical overview of the corrosion behavior of the Safurex® HEx tubes in HP strippers and gives an account of the development of the new specialty grade. 

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Urea storage and handling, let's keep caking in the kitchen

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Reviewing the history of urea technology and Urea technology development, we may conclude that from the beginning of commercial Urea Technology development and Urea Production until now much attention

has been given to developing and optimizing the synthesis- and recycling-section in the urea plant, that in the last decade increased attention has been given to developments and optimizations regarding Urea shaping technology (granulation and prilling), whereas over the entire Urea history, also much attention has been given to storage and handling, indicating the importance of product quality, storage and handling. The most important problems occurring in Storage and Handling are directly or indirectly related to (results of) caking, like lump-formation and dusting. Therefore the mechanism of caking of Urea has been made the subject of a paper because we realize that large efforts and considerable amounts of money can be involved with the consequences of caking. In this paper the mechanism of caking via water sorption and desorption is discussed. Especially the caking, spreading through a heap of Urea, observed even in Urea of good quality will be highlighted. This is often caused by moisture migration. The mechanisms of caking are then explained by discussing some examples from practice.

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Granulation The Stacx Project

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The Agrium Fort Saskatchewan Urea plant has been operating with a Stamicarbon CO2 stripping synthesis section and an NSM (now HFT) fluidized bed granulation section since the original start-up in 1983

. The Urea Synthesis section had a nameplate capacity of 908 tonnes per day, while the urea granulation section consists of two trains (North and South), each with a nameplate capacity of 544 tonnes per day. These two trains are independent of each other. Over the last 20 years, the Fort urea plant has been operated at rates up to 1250 tonnes per day while producing good quality granular product. Well over 6 million tonnes of urea have been produced. It was decided to convert the Fort Saskatchewan granulation trains to Stamicarbon technology. The conversion project was completed in three months1 and the granulation plant was restarted on September 30, 2003. This paper presents a summary of the project, the changes completed, the operating results, potential savings in operating costs, and the product characteristics associated with the conversion.

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INCREASING YOUR CO2 FEED STOCK

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The urea plant needs both ammonia and CO2 as feedstock for producing Urea. • Both ammonia and CO2 are supplied by the ammonia plant. • Mass ratio CO2 /ammonia of ammonia plants •Ammonia plants base

d upon natural gas produce a ratio of 1.3 to 1.5 carbon dioxide to ammonia of which about 18% is in the form of flue-gas. •Ammonia plants based upon coal gasification produce a ratio of 2.7 to 2.8 ton per ton of ammonia

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How green is the Stamicarbon Urea process

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The Stamicarbon urea process, like other processes, unfortunately emits gaseous (ammonia) emissions due to the fact that the urea reaction is an equilibrium reaction. In principle, emission problems c

an be solved in two different ways, either with an in–line and/or with an end-of-pipe solution. The combination of the equilibrium reaction and the presence of inerts make an in-line solution not feasible. Therefore end-of-pipe solutions to eliminate ammonia emissions in both urea melt and finishing plants are still needed to obtain a green and environmentally sustainable process. This paper covers the different available end-of-pipe solutions such as absorbers (including emergency absorber), acidic scrubbers and flares. These options have a wide range of operating windows for further optimization and achieving optimum environmental performance. Flaring reduces the ammonia emission by converting the ammonia into carbon dioxide and nitrogen oxides (NOx). Therefore, the environmental impact evaluation - after implementation of the new end-of-pipe solution - needs to be reviewed, especially when applying continuous emission flare because the environmental impact of these new type emissions are not more tolerable than ammonia emission. Stamicarbon believes that a green urea process combines optimum process conditions with a good choice of end-of-pipe solutions. The available alternatives for end-of-pipe solutions target an optimum “Triple P” balance, i.e. the balancing between financial-economical achievements (profit), environmental impact (planet) and public acceptance (people).

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Greenhouse gas emission reduction and the technologies availabile for it

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Urea is without doubt the most important nitrogen mineral fertilizer currently in use worldwide. Even though the contribution of N mineral fertilizer production to the global anthropogenic greenhouse

gas (GHG) emissions is estimated to be less than 1%, great efforts have been made to understand what the main sources are and in what proportion, so that appropriate mitigation measures can be taken. As for any other chemical, GHG emissions attributable to urea are associated with its life cycle, from the extraction of raw materials to its application and disposal. Since ammonia and carbon dioxide are the raw materials for producing urea, the impact of an ammonia plant is an important consideration when assessing the carbon footprint of urea. This paper focuses on carbon dioxide and nitrous oxide emissions related to ammonia and urea production, and discusses available measures to reduce direct and indirect emissions. Some urea applications such as urea deep placement (UDP) and diesel exhaust fluid (DEF) are also briefly discussed, to illustrate the potential of urea applications to reduce GHG emissions.

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From flaring to environmental friendly ammonia firing and that even done in an economical way

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This paper focuses specifically on the environmental consideration to use an off-gas treatment system for the elimination of ammonia emissions in the urea melt plant. It explains how ammonia venting t

o the atmosphere can environmentally wise be benchmarked against the alternatives of incineration, heating and combustion technologies. The paper explains Stamicarbon’s objections regarding the use of flare systems as environmental mitigation strategy in the urea melt plant and clarifies the most environmental and economical sensible solution available in Stamicarbon’s technology portfolio: the thermal treatment and catalytic DeNOX. An example case of a world scale urea plant is used for quantification and the outcome of the paper reveals Stamicarbon’s bridge that connects today to tomorrow.

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Emission legislation relating to urea production

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The objective of emission abatement is to ensure that the concentration of the pertinent pollutant in the ambient air does not exceed levels specified in national ambient air quality standards or, in

their absence, the current WHO Air Quality Guidelines or comparable guidelines set by other internationally recognized bodies. So there are no globally-applicable emission limits; they differ region by region according to standards set by the local authorities. For the licensor this means that every new project, whether grassroots or revamp, needs a tailor-made approach in close co-operation with the engineering contractor, owner of the facility and local authorities. 

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EMISSION ABATEMENT SOLUTIONS WITH UREA PRODUCTION

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• Introduction • Emission legislation • Emission sources with urea production • GHG emission reduction with urea production • Ammonia emission reduction in the urea melt section • Dust and ammoni

a emission reduction in the urea finishing section • Key take-aways  

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