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May-2017

More efficient catalyst loading (TIA)

A change in dense catalyst loading technology enabled a major chemicals company to achieve a 10% increase in production capacity in a fixed bed reactor.

Ian Baxter
Cat Tech International
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Article Summary
Dense loading is a technology for improving catalyst performance in fixed bed catalytic process units. It is commonly used throughout the petroleum, petrochemical and chemical industries and involves distributing the catalyst in such a way as to uniformly increase its packed density. Decades of research provide overwhelming evidence that good dense loading can improve the performance of the reactor through reducing void fraction within the fixed catalyst bed. This can lead to improved liquid and gas distribution, higher throughput rates and improved bed stability. In comparison, sock loading, which involves catalyst being distributed from a length of sock attached to a feed hopper, has a tendency to create void spaces more likely to result in flow maldistribution and bed settling during run. Reduced throughput and increasing pressure drop across the reactor are a direct consequence.

History of JE dense loading technology
Cat Tech has over 40 years’ experience as a specialist catalyst handling and tower services company and offers a high performance dense loading technology called the JE. This patented technology has now been used to successfully load over 79 million kg of material in over 25 countries. Its history began in the early 1990s in Japan with the development of a loading technology for maximising catalyst performance. The first commercial application was completed in 1996 and since then the JE has undergone a programme of continual development and optimisation. The JE is a non-abrasive mechanical loading device whereby catalyst spills from an oscillating, single axis, smooth surfaced, spheroid disc. A unique design feature of the JE is minimisation of shear stress on the catalyst particles during loading (see Figure 1). This allows for a true increase in density and uniformity as opposed to an undesirable increase in density when catalyst particles are broken and loaded as a result of the dense loading system itself. In summary, the JE delivers high surface levelness control, high uniform density and low catalyst breakage, all vital to optimising reactor operations.

Case study: AkzoNobel
AkzoNobel is a Dutch multinational company and is a major producer of specialty chemicals. Its headquarters is located in Amsterdam and the company employees approximately 45 000 people in over 80 countries. The business was looking to procure a high performance dense loading service that had a focus on repeatability, reproducibility and best practices in quality, health, safety and environment. Cat Tech started talking to AkzoNobel about its JE dense loading technology as a method to increase reactor capacity.  In early 2015 they elected to use the JE in a pilot trial application and following its successful validation it was again used in two further trials during 2015/2016.

A purification process that uses hydrogen and a solid heterogeneous hydrogenation catalyst in a fixed bed reactor was chosen for the trial. Historically the catalyst has been loaded using a conventional ‘dense’ loading method in order to minimise flow maldistribution and improve the catalyst performance. However, the loading was identified as one of the key process variables and as such AkzoNobel were looking for improved control in this area. Cat Tech mobilised JE dense loading equipment and specialist operator to their production plant. A total catalyst inventory of approximately 6 tons was loaded into a 1m diameter reactor column using the JE technology. The reactor was started up and its performance closely monitored and compared with historic performance data. As seen in Table 1 a noticeable 10% increase in production capacity was achieved following application of the JE. This can be attributed to more 
catalyst and its efficient use through improved liquid gas distribution.

Figure 2 shows the comparative pressure drop over the reactor with time. The initial pressure drop after loading with the JE was around 0.9 bar which was somewhat higher than typical historic levels of around 0.4 bar. This is in line with expectations and attributed to more catalyst and a higher loaded density being achieved. It should be noted, however, that although the initial pressure drop was higher it remained almost constant at 0.9 bar throughout the operating cycle. This is a result of a high uniform loaded density coupled with low catalyst breakage that can otherwise result in the production of dust and fines. In contrast, an initial reactor pressure drop of around 0.4 bar increasing to over 1.7 bar with time was seen following application of the old conventional dense loading method. Catalyst bed settling and the production of dust and fines during loading can all contribute to increasing reactor pressure drop during run. Increasing pressure drop can eventually lead to a reduction in reactor throughput rates as unit operating parameters are adjusted to ensure equipment delta P guidelines are not breached.

As this example demonstrates, not all dense loading is the same. The results detailed here are typical of how the JE in comparison to other conventional dense loading technologies can improve catalyst utilisation and increase production throughput. It is clear that the wrong choice of dense loading technology and service provider can be a critical factor in catalyst management costs and reactor performance. The JE is a proven cost effective technology for increasing reactor capacity performance and is now the method of choice for AkzoNobel under a longer term framework agreement.

This short case study originally appeared in PTQ's Technology In Action Feature - Q2 2017 Issue.

For more information: ibaxter@cat-tech.com

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