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Reformer outlet system reliability, design and repair

Summary

Reformer furnace outlet collection systems operate under severe service conditions that push the metallurgical limits of the materials used. For that reason, reliable long-term performance depends strongly on the operational control and maintenance practices applied by the owners, as well as the design margins and inherent robustness of the mechanical design. In this article, Daniel Barnett and Joe Price of BD Energy Systems, LLC present the significant operational and maintenance factors that influence reformer outlet system reliability and discuss the adequacy of design margins typically applied, the failures and the repair methods that have been successfully applied when outlet system failures occur, and design features that can be applied to make the outlet system more robust and therefore more reliable.

Abstract

The issue Steam methane reformer furnaces, or SMRs, are used in a number of common synthesis gas production applications. These may support the production of ammonia, methanol, gas-to-liquids, hydrogen, or reducing gas. The operating conditions of each process differ and there is also a range of conditions within each of these production applications depending on the specific technology used in the plant. However, almost all applications result in outlet system conditions that challenge the design limits of the materials of construction. In general, ammonia plant reformer furnaces have lower operating temperatures but significantly higher pressures when compared to methanol and hydrogen applications, while reducing gas applications have lower pressure but even higher temperatures than methanol and hydrogen applications. Table 1 shows the typical range of operating conditions for the reformer furnace outlet system for each of these applications. Note that for the purposes of this comparison we are examining conventional designs, we are not therefore including ammonia plant applications that incorporate the use of enriched air or excess air to the secondary reformer, nor are we including methanol plant applications that incorporate the use of an oxygen-fed secondary reformer. Keywords: steam methane reformer; synthesis gas; ammonia; methanol; hydrogen; pigtail; manifold

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Protecting your assets

Summary

The steam reformer is often regarded as the most complex and expensive part of an ammonia, methanol or hydrogen plant. Monitoring the reformer during both normal and transient conditions, such as during start-ups, is therefore extremely important. By using a holistic approach to steam reformer reliability and maintenance programs, plant reliability can be increased and premature tube failures avoided.

Abstract

Steam reformers are critical assets to many refining and chemical manufacturing plants and facilities, and it is well known that the reformer is one of the most challenging assets to maintain and operate. Common problems in reformer operations include burner firing, flue gas distribution and catalyst damage. While these are only a few of the problems that can occur, all directly affect reformer tube life and lead to premature tube failure, pigtail failure, and damage to the header and convection section. In order to increase reliability and operate with a higher degree of confidence, it is increasingly important to incorporate a holistic approach to steam reformer reliability and maintenance programs. When using such an approach between turnarounds, operators should consider these essential elements: l preventative maintenance; l reformer tube inspections; l advanced engineering services; l reformer tube life assessments; l reformer performance monitoring surveys; l infrared (IR) temperature correction software. Keywords: preventative maintenance; reformer tube inspection; IR temperature correction software; start-up incidents; reforming catalyst; carbon formation; catalyst loading; start-up monitoring

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Ammonia plant designs for reduced steam export

Summary

Most modern ammonia plants are net exporters of energy, typically to a downstream urea plant. A standalone ammonia plant, on the other hand, must be energy neutral, since steam or power export to another user is not always a feasible option. Dedicated design features are needed to achieve this target. In this article KBR and Ammonia Casale discuss their process design concepts for standalone ammonia plants.

Abstract

Modern natural gas based ammonia plants are highly energy efficient. The energy consumption of some newer plants is already approaching the theoretical minimum. The efficiency gained over the years is attributable to various technology improvements, including: l Improved catalysts – they provide higher conversion as well as lower pressure drops. l High efficiency machine trains – compressors and drivers with higher efficiency reduce ISBL steam consumption and increase export steam availability. l Improved furnace efficiency – this minimises the fuel consumption for the primary reformer. l Reduced primary reformer duty and integration with gas turbine exhaust – reduced furnace duty can reduce heat loss to the stack. Using the exhaust of the gas turbine driver as combustion air in the primary reformer furnace can improve energy efficiency further. l Lower reformer feed steam to carbon ratio – reduced consumption of process steam increases export steam besides improving overall heat integration. l Low energy CO2 removal process – CO2 removal processes requiring lower heat for solution regeneration assist in reducing reformer feed steam to carbon ratio and provide spare additional waste heat for efficient integration. l Increased front-end pressure – increased front-end pressure reduces duty on the synthesis gas compressor. For example, by using a mild primary reformer higher pressure can be used in the front-end. l Higher ammonia conversion – higher per pass conversion reduces duty on refrigeration system l High-pressure steam in synthesis loop – recovering waste heat to highest grade HP steam maximises ISBL steam production in the synthesis loop. l Medium pressure condensate stripper – avoids heat and steam loss to vent and improves energy efficiency l Dry synthesis loop – feeding dry make-up syngas directly to ammonia converter improves energy efficiency. Keywords: KRES, natural gas, coal, steam generation, steam superheater; pre-reformer; Megammonia; ATR

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RK-400: Improving alkali-promoted reforming catalysis

Summary

In today's competitive business climate, producers of ammonia, methanol, and hydrogen must continuously seek to implement strategies that optimise plant performance. This includes equipping plants with the latest advances in technology and catalysis. In this article, S.M. King, M. Stenseng and N. Petersen of Haldor Topsøe A/S discuss Topsøe's most recent innovation in alkali-promoted catalysis. The new RK-400 is an alkali-promoted reforming catalyst that is based on a novel method of catalyst preparation and engineered to provide improved protection against carbon formation coupled with high activity, leading to optimal operation with longer catalyst and reformer tube lifetimes.

Abstract

Steam reforming of hydrocarbons has been an established industrial process since the 1930s. It is the main process step in the production of synthesis gas (hydrogen, carbon monoxide, and carbon dioxide), which is needed for the production of ammonia and methanol. The process is also used to provide the hydrogen used for hydrotreating and hydroprocessing in refineries. The main reaction in the steam reformer is the highly endothermic reaction of superheated steam with hydrocarbons in the presence of a catalyst: CnH2n+2 + nH2O nCO + (2n+1)H2 The carbon monoxide then undergoes the water-gas shift reaction to produce additional hydrogen: CO + H2O CO2 + H2 Keywords: reforming catalyst; carbon formation; alkali promoter

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Plant Manager+

Summary

No. 19: High pressure pumps – which is better reciprocating or centrifugal?

Abstract

Mr Majid Mohammadian of OCI Nitrogen in the Netherlands starts up the following discussion: Please share your experiences, ideas and selection criteria for high-pressure pump types in urea plants. Is it a matter of cost, efficiency, capacity, etc.? Keywords: reciprocating pump; centrifugal pump; shear rates; flow rates; viscosity

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Waste heat boiler incidents

Summary

Waste heat boilers can be the Achilles heel of an ammonia plant, with stress cracking and/or corrosion going undetected until a plant outage occurs. Nitrogen+Syngas reviews three case studies from recent AIChE meetings which illustrate the problem.

Abstract

In an ammonia plant, the reforming of natural gas or gasified solid matter to synthesis gas is achieved at high temperatures, and the reaction heat is then recovered as high pressure steam in one or several waste heat boilers. Heat is conducted through steel pipes through which the hot process gas passes to a water side where high pressure steam is generated for use in the reformers or for export elsewhere in an integrated process plant. Because of the high temperatures and pressures involved, waste heat boilers (WHBs) are subject to thermal and mechanical stresses and corrosion. The hidden nature of these stresses and corrosion mean that waste heat boilers can be prone to unexpected failures, which typically result in unplanned shutdowns for repair and/or emergency maintenance work. This work and the lost production are obviously costly for the plant operator. Keywords: GNFC, IFFCO, AIChE, WHB

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Is the party over for Trinidad?

Summary

Trinidad became a preferred destination for methanol and ammonia producers in the 1990s as US gas prices rose. However, gas curtailments in Trinidad are now coinciding with the shale gas boom in the US, and threatening the industry that has been built there.

Abstract

Trinidad had been a long-time oil producer, from fields on the west side of the island, with production dating as far back as 1867, and the island was a major global oil producer throughout the 20th century, with output peaking in 1978 at 84 million barrels. However, oil production stagnated thereafter, and has ranged between 130,000 – 170,000 bbl/d over the past decade. During the 1980s and 90s, the discovery of large offshore gas fields to the north and east of the island led to a change in strategic direction, as Trinidad’s gas-based industries overtook the declining oil industry. Trinidad’s gas boom happened at a time when gas prices were rising in other parts of the world, particularly the continental United States, and Trinidad rapidly developed a large cluster of gas-based ammonia and methanol production, serving as an adjunct to the US market. Trinidad also developed liquefied natural gas exports, and used the gas for other energy intensive industries such as aluminium, iron and steel. As Trinidad’s fortunes rose, so that of the US nitrogen and methanol industries declined. Keywords: LNG, methanol, ammonia, urea, Methanex, MHTL, GTL

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The global outlook for nitrogen

Summary

Agricultural demand for nitrogen appears to be slowing somewhat, although technical demand is keeping overall demand growth at its familiar 2% per annum level. But capacity overbuild continues in the nitrogen industry, especially in China.

Abstract

The nitrogen industry has had several years of high prices, due to a run of high commodity prices driven by demand in China and tight grain markets which have supported high fertilizer prices. Even after the global economic crash in 2007, markets like China and India have kept the fertilizer side of the business buoyant. However, the high prices now seem to have had their inevitable effect in producing extra capacity around the world which has led to markets falling back. The outlook for demand The world economy finally seems to be recovering from the Eurozone crisis. World GDP growth fell from 4% to 3.2% in 2012 and will grow by 3.3% this year, but is projected to return to 4% growth in 2014. This is mainly due to recovery in the developed half of the world economy, which will rise from 1.2% growth this year to 2.2% next year, with the US in particular seeing above average growth, and while Europe has had two years of zero or negative growth, should average 1.3% in 2014 according to IMF projections. Developing world growth fell from 6.4% in 2011 to 5.1% in 2012, but should return to 5.7% growth by 2014. There are still concerns over China’s potential for a ‘hard landing’, however, with a growing property bubble in the country and many lenders overextended. Keywords: technical, biofuels, India, supply, demand, shale

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