Reprinted from March 2016HYDROCARBON ENGINEERING

T he removal of spent catalyst and reloading of fresh catalyst in refinery vessels is a critical process that affects the operating efficiency of the refinery, the time and cost of the

turnaround, and, most important of all, the safety of refinery and contractor personnel. In fluidised catalytic cracker units (FCCUs), the main issue is typically efficient removal and transport of hot residual catalyst so that the unit, which generates revenues of up to US$1.5 million/d, can be brought back online as quickly as possible. In fixed bed reactors, on the other hand, which usually do not have built-in catalyst removal systems, the greatest unloading issue is getting the job done quickly, while at the same time ensuring the safety

of personnel during confined space entry. In contrast, catalyst loading often boils down to increasing the density of the load in order to optimise run life while at the same time avoiding any reduction in particle size that increases pressure drop. In recent years, new technology has emerged that approaches critical catalyst handling challenges from a better perspective. This article will provide an overview of these technologies and explain how they can be deployed to increase a refinery’s operating performance.

FCCU catalyst unloadingThe traditional method of removing residual catalyst in FCCU turnarounds starts with blowing the material into

21st century catalysts

Steve Bryant, and Bill Murff, Clean Harbors Inc., USA, explore how catalyst handling advances can increase refinery throughput and improve safety.

Reprinted from March 2016 HYDROCARBON ENGINEERING

the storage silo. The material is normally blown over at a temperature of 800 - 1200˚F, which is too hot for loading into roll-off bins or most transportation vessels. The material in the storage silo typically cools very slowly because there is minimal surface area, in relation to the volume, for heat to be released. Furthermore, even after the bulk of the material is blown out of the reactor, a considerable amount of material typically remains in low points and other areas that are inaccessible to the conveying system. The normal approach is to open a manway on the vessel and allow the catalyst to cool to the point where the crew can drop steel hoses in and vacuum the remainder of the catalyst. The biggest drawback of the traditional method is that a considerable amount of time is required for the catalyst in the storage silo and remaining in the reactor to cool to the point that it can be safely placed into rolloff bins. In one major refinery, completely unloading the catalyst from an FCCU that generates US$1 million/d in revenues, took nine days.

The new approach utilises an air to water heat exchanger that is connected to draw points located on the bottom of the regenerator and specific points on the reactor. The residual catalyst in the reactor runs through the heat exchanger and is cooled before it reaches the vacuum box. By the time the material reaches the vacuum box it is already cooled to the point where it can be stored in the vacuum box and replaced with additional residual material without delay. This approach eliminates the need to open the vessel prior to removing the residual catalyst thus eliminating or reducing the exposure and risk to personnel. A key capability of this technology is that it overcomes the challenges of dealing with pieces of refractory that have broken loose and have the potential to be swept up by the vacuum system and produce an obstruction. The individual catalyst containers can be readily sampled for analysis. Refinery personnel analyse the samples and make a judgement as to which containers are filled with good catalyst

(that can be conveyed back into the unit) and which are to be disposed of. When this process was used at the FCCU mentioned above, it took only three days to completely unload the residual catalyst, enabling the refinery to get the unit back online six days earlier than in the past, and generate an additional US$6 million in revenues.

Fixed bed reactor catalyst unloadingUnloading catalyst from fixed bed reactors presents different challenges because these reactors do not have a built-in conveying system to remove the catalyst. Currently, when the catalyst is spent, a person is sent into the reactor with a vacuum hose to remove the catalyst. The time spent to remove catalyst from the vessel depends on the size of the vessel and condition of the material. Personnel working in fixed bed reactors require elaborate personal protective equipment (PPE) and support systems. For example, one custom designed modular/trailer life support system for controlled entry into confined spaces incorporates two primary sources of breathing air, one independent secondary source of breathing air, a five minute egress bottle and an emergency egress line (EEL) for each entrant in the confined space. A standby watchman is stationed at the point of entry with a self-contained breathing apparatus (SCBA) system that is independent from the primary life support system. All entry operations are monitored and controlled by a console operator who maintains constant audio and video communications with the reactor entry technician and vessel manway attending personnel.

These systems are vital to ensuring the safety of confined space entry, yet they obviously add to the cost and time involved in the project. Another factor to consider is that workers can only stay in the vessel for relative short durations, typically no more than four hours, even under the best possible conditions. It typically takes approximately one hour of downtime to remove one person from the reactor and replace them. Furthermore, it is not uncommon for hazardous chemicals, such as lead or arsenic, to be present in the reactor. In this case, employees may have to carry out pre and post blood work.

Unloading reactors with robotic systemsBoth the safety and cost involved in unloading catalyst from fixed bed reactors can be improved by replacing the person with a robotic system. This approach also frequently improves productivity since robots operate continuously with the hose buried in the catalyst, vacuuming at optimal capacity. Robots do not require suiting up or take breaks, and do not have limits on time spent working in the reactor. As a result, robots typically provide a 15% time saving compared to manual unloading. One approach, which has already been proven in several projects, uses a hydraulically propelled robot with a vacuum hose that is lowered into the reactor by an overhead structure or crane. The

Figure 1. Vacuum truck with air to water heat exchanger extracting spent catalyst from an FCCU.

Reprinted from March 2016HYDROCARBON ENGINEERING

robot consists of a body with arms on either side that extend outwards to contact the sides of the reactor to stabilise the robot. An articulated member with two joints extends downward from the body with a vacuum hose on its end that looks somewhat like the trunk of an elephant. A camera system near the end of the hose provides feedback to assist an operator located outside the reactor in guiding the robot.

A new robotic system provides an even less expensive alternative for small to medium size fixed bed reactors because it does not require an overhead structure. It consists of a self supporting articulated truck-mounted vacuum system with a vertical reach of up to 126 ft and a horizontal reach up to 114 ft. The 15 ft 3 in. of telescopic action allows the operator to accurately position the boom with a dongle, over 830˚ of total boom articulation including 278˚ at the Z-tip section provides an infinite range of boom configurations. This approach is designed for use in reactors that are small enough that the boom is able to reach all areas from which catalyst needs to be removed. This new robotic system also occupies a smaller footprint than other robots, which can be a considerable advantage in the typical congested refinery layout. A robot mounted from an overhead structure requires both a crane and vacuum truck; however, the new robot does not require a crane while the catalyst is being removed. After the catalyst is fully unloaded, the vacuum truck can be sent to another job while a crane moves into the spot vacated by the vacuum truck in order to load the fresh catalyst. This approach does a markedly better job of conserving valuable space during turnarounds.

Sock loadingCatalyst loading is another critical operation because of its impact on the ability of the unit to operate at optimal levels. Optimised catalyst loading typically results in lower catalyst attrition, lower radial spreads, longer cycle lengths and improved use of reactor capacity. One approach to catalyst loading, called sock loading, involves placing the catalyst into a hopper on the top of the reactor manway and discharging it through a canvas or rubber sock. One end of the sock is attached to the loading hopper discharging pipe while the other end travels to within three feet of the catalyst support grate or grid. The loading technician crimps the sock to restrict the free fall of material as he or she spreads the catalyst evenly in a random pattern. As the bed level rises, the sock is cut to keep the free fall of catalyst to the required distance, while discarded sections are removed from the reactor. This minimises breakage of the catalyst particles, which can increase the pressure drop across the catalyst bed during operating conditions, creating a costly decrease in the end of run (EOR) time for the reactor.

Dense loadingA second approach to catalyst loading, called dense loading, is accomplished by using a mechanical device

to introduce catalyst cylinders into the reactor so that each cylinder can fall freely to the catalyst surface. With this approach, individual cylinders assume a horizontal rest position prior to being impinged by adjacent cylinders. In the vast majority of applications, dense loading provides a uniform distribution of catalyst throughout the entire diameter of the reactor and better total bed density as the catalyst is being loaded. In typical applications, loading density can be increased by as much as 20%, depending on the specific characteristics of the catalyst. Dense loading can also improve reactor operations such as, improving liquid or gas flow, reducing the potential for catalytic bed settling and increasing catalyst run cycles.

State of the art dense loading takes advantage of a loader consisting of a vertical tube with a rotating head on the bottom. The technology is computer controlled with four adjustable variables for superior control. Whips or brushes are not used, resulting in significantly reduced attrition during the loading process. The result is that the catalyst density is optimised while the particle size of the catalyst is maintained, which avoids increasing the pressure drop in the unit. This is important because most units in the field are pressure drop limited. This technology also has the ability to dense load closer to the trays than the other major dense loaders. The loader is designed so it can fit any reactor configuration.

ConclusionCatalyst handling plays a critical role in the success or failure of every refinery. The leading catalyst handling service providers are continually searching for ways to improve the safety of this process, reduce the time required for loading and unloading, and maximise the operating efficiency and throughput of refineries. The recent technological advances described in this article enable the delivery of turnkey catalyst handling services that can make it possible to execute complex catalyst changes from start to finish with the highest possible levels of safety, reduced turnaround duration and high levels of value.

Figure 2. Dense loading technology provides high catalyst density while reducing particle attrition.