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Oct-2015

Improving the reliability of catalyst changeout

Reducing reactor turnaround time using the CATnap catalyst passivation technology.

Josef Felser and George Karl, Bayernoil Refinery GmbH
Ian Baxter and Gary Welch, Cat Tech International Ltdnitrogen
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Article Summary
Bayernoil is an oil refining complex situated near Ingolstadt Germany, an asset of four major shareholders: BP, Varo Energy, ROG and Eni. It consists of two sites located at Vohburg and Neustadt with a combined crude processing capacity of approximately 10 million t/y. Producing a range of products which includes mogas, diesel, jet fuel, LPG and heating fuels, it predominantly supplies the home Bavarian market. The Neustadt site includes a mild hydrocracker (MHC) and a diesel hydrotreater (CHD) unit. The CHD is a 67 000 b/d treater, contains around 321 000 kg of fresh basis catalyst and consists of two reactors in series flow processing a combination of light gas oils. Hydrotreaters are responsible for removing sulphur from gasoline and diesel to produce cleaner fuels and, as in the case of the CHD, are often on the ‘critical path’ of a larger refinery turnaround. Historically, the unit has experienced unloading problems during its catalyst changeout including high concentrations of flammable vapours or lower explosive limit (LEL) and agglomerated catalyst.

The LEL is the lowest concentration of a vapour in air capable of producing a flash fire in the presence of an ignition source. Controlling vapour concentrations to well below the explosive limit, typically

History of CATnap

The CATnap technology has been used successfully to treat over 200 million kg of catalyst to date, with 32 applications in 2014 alone. It has been widely embraced in the Far East and is becoming established in the western world. Its development history started in the mid-1980s in Japan where Kashima Engineering Company (KEC) and Softard Industries developed the technology for passivating self-heating catalysts so that they could be safely removed under air. This has the obvious advantage of eliminating what is commonly referred to as the most dangerous operation in refineries today – inert entry operations. The technology was applied primarily to resid desulphurisation units because of the challenges they afforded with multi-bed reactors and agglomerated catalyst. The chemical treatment process involves the application of a proprietary mixture of high molecular weight aromatic compounds to a reactor system while under oil recirculation during the cooling and shutdown process. These compounds have the ability to coat all surfaces with which they come into contact. This includes reactor internals but most importantly the catalyst itself. This organic film retards oxygen penetration to the reactive metal sulphide surfaces and severely retards the dangerous and exothermic oxidative reactions. This is somewhat different to the conventional shutdown procedure which involves a hot hydrogen strip. The process oil is usually flushed from the unit and replaced with a lighter oil known as the carrier oil which is a very important part of designing the CATnap treatment. Once the unit is flushed and the process oil replaced, it is put on oil recirculation followed by application of the chemical.

KEC and Softard optimised this technology through application to their native refinery and have now expanded throughout the Far East. Cat Tech International Ltd licensed the technology for application in Europe and the Middle East.

Advantages
Although the opportunity to eliminate inert entry was central to developing the technology there are many other significant advantages of CATnap. For Bayernoil, mitigating LEL was a prime objective and validation point for using the technology. The advantages can be categorised in the following sections.

Safety: opportunity to eliminate inert entry
The self-heating or pyrophoric nature of the catalyst and dust is suppressed or eliminated by the CATnap treatment. This allows the safe handling of catalyst in air.

Figure 1 illustrates the passivating effect of CATnap treated catalyst. This thermogram shows the heat released by catalysts as they are heated. The red line represents an untreated catalyst whereas the blue line is the same catalyst treated by the CATnap process. As can be seen, when the untreated sample reaches about 120°C, an exotherm is observed. This is the reaction of the metal sulphides reacting with air. As the temperature is further increased, a second exotherm occurs around 250°C. This is carbon and coke on the catalyst burning. The treated sample does not demonstrate a significant exotherm until 300°C. This demonstrates the dramatic stabilisation provided by the treatment. If catalyst is removed under air, it is noted that many reactors are made of austenitic stainless which may become sensitised and prone to the phenomena of polythionic acid stress corrosion cracking (PSCC). Formation of polythionic acid requires three things to be present: sulphide corrosion products, oxygen and moisture. In the case of unloading in air, NACE international standards1 provide guidelines for protection of the surfaces of austenitic stainless steel through the exclusion of water using dehumidified air.

Dust free operation
Dust from catalyst handling operations typically contains iron and catalyst metal sulphides which are both toxic and pyrophoric in nature. These types of dust are a risk to people and the environment and present a challenge to both organisations and employers. In particular compounds of Nickel are under increasing European regulatory pressure. Exposure of Nickel compounds are associated with increased cancer risk and demonstrating safe and sustainable use by workers is a key requirement under the REACH regulations2. With CATnap, dust and fines adhere to the treated catalyst surfaces resulting in a dust free handling operation. Employers have specific duties under a raft of environmental, occupational and other safety regulations. The technology can therefore be applied as an effective risk control measure in contributing to a safe system of work.

Time savings: reactor shutdown time reduced
Elimination of the hot hydrogen strip and the ability to cool under liquid oil circulation with its superior heat transfer capabilities can typically reduce conventional shutdown time by some 12 to 36 hours. This can have a positive impact on the time value of the unit, particularly if it is on the critical path of a turnaround.
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