December 2017

Special Focus: Plant Design, Engineering and Construction

What you need to know when installing critical power utilities during a plant turnaround

For refineries and petrochemical plants, turnarounds (TARs) are a necessary, and stressful, activity.

Smith, B., Aggreko

For refineries and petrochemical plants, turnarounds (TARs) are a necessary, and stressful, activity. Common TAR operations include implementing capital projects in the plant, inspecting vessels to maintain jurisdictional compliance, reinforcing equipment to reduce the risk of a loss of containment and changing out spent catalyst.

While they are critical to the long-term operational efficiency of the facility, TARs also cost a great deal of money without directly generating any revenue. Therefore, plant management is under immense pressure perform the TAR as efficiently and safely as possible, and to get the plant back online quickly.

TARs often prove challenging during repairs or upgrades to the facility’s electrical power system. Such work might vary from relatively short-duration (i.e., 2 d–7 d) production curtailments for power equipment repairs or inspections, to TAR extensions driven by long-duration, critical-path electrical system work.

Refiners and plant operators continually look for ways to minimize TAR extensions, or to eliminate the need to curb production solely for electrical work. To avoid shutting down a process unit, it becomes necessary to duplicate a unit’s electrical infrastructure on a temporary basis.

Historically, setting up temporary critical power utilities has not been practically possible, as it required finding service providers with application expertise in high-voltage/current scenarios and with the ability to efficiently add generation capacity. Until recently, few vendors could supply this depth and breadth of equipment and services. In addition, most vendors were not equipped to help plant management address a myriad of other issues related to the TAR, including the movement of equipment onsite and the coordination of maintenance activities, ensuring that TAR activities are completed per schedule and, most importantly, protecting the facility’s personnel and contractors.

Early planning is a prerequisite

When developing and delivering critical power utilities for TARs, early planning is crucial to ensure a safe and less stressful TAR. However, in many instances, crucial aspects of planning temporary power generation are not addressed until just a few months prior to the planned TAR start date.

To avoid unexpected surprises that might extend the time frame and cost of a TAR or raise safety risks to personnel, a checklist of best practices should be followed when planning critical power utilities for TARs. The following are some of the main points to consider.

Follow proper safety labeling and personal protective equipment (PPE) protocols

Safety is the primary concern of any plant operation, and TARs are certainly no exception. Electrical hazards such as arc flashes are a very real concern, which makes proper labeling of electrical equipment and panels an absolute necessity.

FIG. 1. A representative ARC flash decal for a generator circuit breaker panel, which clearly lists the required level of flash and shock protections when working on and around the generator.
FIG. 1. A representative ARC flash decal for a generator circuit breaker panel, which clearly lists the required level of flash and shock protections when working on and around the generator.

All electrical equipment should be labeled with up-to-date arc flash decals (FIG. 1). Arc flash calculations should be conducted in conjunction with the project design, and placed on equipment prior to delivery to the job site. Each piece of equipment can be properly designed and labeled with arc flash decals that clearly show the incident energy, arc flash boundary and safe working distance values. This decal allows plant personnel to quickly understand system configurations and PPE requirements, without any confusion.

The importance of proper equipment labeling was evident in a recent temporary generator installation that was performed for a plant on the US Gulf Coast. Prior to the installation, engineers reviewed the existing arc flash labels on the equipment to be powered by the generator.

The arc flash values listed on each piece of equipment were calculated based on house power, but revised arc flash calculations based on the temporary generator showed that the level of incident energy would be raised. Therefore, the original label presented false information to personnel working in and around the equipment, which created an unsafe, and potentially deadly, working environment.

The engineers resolved this issue by placing a temporary label over the original that showed the corrected incident energy and arc flash boundary. With this updated information, plant personnel then dressed to a higher PPE level to lower their risk of injury.

This exercise was instructive to the plant’s engineers. When temporary power was installed previously, they did not consider the likelihood of an increase in incident energy or arc flash boundaries. Going forward, they will routinely update their arc flash calculations when temporary power is installed to ensure that personnel have the correct information and dress with the appropriate level of PPE.

The arrangement of control panels poses safety risks, as well. For example, placing potential high-risk 480-volt (V) contactors near 120-V control circuits that require troubleshooting may result in the generation, or unplanned release, of large amounts of energy that could threaten the entire facility. To limit safety risks, a company is in the process of retrofitting its larger equipment to lower incident and arc flash energy levels through engineering controls that include isolation and barriers of higher voltage sources. In addition, the company is rearranging control panels to include greater functionality and make them easier to read and use, further lowering the risk of unplanned energy releases.

Determine electrical needs

Larger refineries and petrochemical plants may assemble dedicated teams whose sole purpose is to design and manage the TAR, including properly identifying the operating voltage, power and other electrical parameters required prior to selecting the amount and type of equipment needed.

Most refineries and plants are much smaller in terms of capacity, equipment and the number of personnel. As a result, members of the TAR team are distracted from their day-to-day activities and do not have time to work on other projects aimed at enhancing and maintaining permanent equipment and assets. The more that companies can outsource TAR activities to a trusted vendor, the more time the plant’s electrical staff can spend on projects where they can uniquely provide value.

Pre-scoping of the job should commence approximately 1 yr before the TAR is scheduled to begin. Typically, this begins with the vendor conducting a thorough walkthrough of the facility with the plant’s engineers. The walkthrough is designed to give the vendor a detailed understanding of which equipment the plant needs to keep running during the TAR, how much load will be required and the best fueling options based on availability and need. With this information, the vendor can then design and spec out the most efficient temporary power system for that specific TAR.

During a walkthrough prior to a large-scale TAR in a 195-Mbpd refinery in the mid-continental US, personnel discovered that the refiner wanted to limit nitrogen oxide (NOx) emissions coming from diesel generators. The refiner needed assurances that the selected power source was highly reliable for the high-load needs of heat stress relief applications, as well. The company proposed switching to natural gas as a fuel source, which would essentially eliminate the refiner’s emissions concerns, while significantly lowering its fuel costs. The refiner agreed, and a natural gas generator was installed. The natural gas generators used in this TAR reduced NOx emissions by more than 80%, and saved $250,000 in diesel fuel costs. It also avoided the logistical challenges associated with frequent diesel fuel deliveries to the facility. The generators resulted in 50%–65% fewer service intervals compared to diesel generators.

In another TAR project, a refiner on the US West Coast required a significant amount of short-term power for the removal and replacement of its fluid catalytic cracker (FCC) reactor. Historically, generators have been placed quite close to where the power is used during a TAR. Space was at a premium in this TAR, which made locating the power near the work more challenging.

The generators would have to be periodically refueled, implying that additional personnel and trucks would be onsite at a time when the facility aimed to minimize personnel and equipment for safety reasons. In addition, a generator’s combustion process naturally produces emissions that must be monitored. It is not uncommon for slight changes in ambient conditions to activate the workers’ carbon monoxide (CO) alarm, forcing them to curtail work even if they are not in danger.

After the walkthrough was conducted, it was decided to locate the generators in a vacant tank pad area some distance from the FCCU. The generators would be close enough to run cables, but far enough away that workers would not need to worry about CO emissions from the generators. Centrally locating generators allows for higher kilowatt (kW) capacity with fewer units. Therefore, generators can run higher on their efficiency curve, which saves fuel. These designs inherently incorporate redundancy, which is not as easy or cost-effective when generators are scattered. Finally, this design option reduces the number of personnel required in the plant to refuel the generators, which provides safety benefits during the TAR.

The company installed 17 MW of power at the centralized location. Generator voltage was increased to 4,160 V. Transformers near the equipment then stepped the voltage down to 480 V for use in the plant. This arrangement saved the customer more than $1.4 MM in combined generator rental and fuel costs. In addition, it made worker-related CO emissions a non-issue. In fact, total emissions were 18% lower than anticipated.

Pinpointing locations and selecting connections

Approximately 6 mos–9 mos prior to project startup and with the facility’s short-term power needs understood, the next step is to determine the optimal placement of generators and routing of cables in the facility. Depending on the size and scope of the TAR, localized power at the site may be ideal. Larger TARs may call for a distributed, mini-grid style power configuration. Simultaneously, the best cabling and connection options must be selected to link the backup generator to the plant’s power supply.

FIG. 2. A layout of the facility using maps will help personnel understand the proposed locations of equipment.
FIG. 2. A layout of the facility using maps will help personnel understand the proposed locations of equipment.

The vendor should develop detailed equipment-layout and cable-routing drawings to assist in these efforts. This could include developing layout drawings made through Google Earth or CAD software programs to provide plant engineers with a thorough understanding of the proposed locations of equipment in the facility (FIG. 2). Cable and electrical layouts are also produced to detail the location of cable routes and how each cable will be connected to the equipment.

These diagrams, which effectively show the entire facility drawn to scale, are reviewed in TAR planning meetings. All personnel can weigh in on the equipment layout and cabling proposals, and highlight potential problems early in the process. For example, someone might find that the proposed cabling route will run right through a temporary break room or interfere with the operations of a welding crew. This kind of early feedback allows for changes in the cabling route, or the location of a temporary building, well before any work has begun. Ultimately, this feedback reduces installation time and labor costs by avoiding a complicated and time-consuming change to cabling routes or generator layouts once work crews are in the plant.

Create one-line diagrams

Approximately 3 mos–6 mos prior to the start of the TAR, detailed one-line diagrams should be created for the plant’s electrical power needs. These diagrams are designed to identify the type, size and location of all generators, circuits, panels and cables.

Prior to using one-line diagrams, generators, distribution equipment and other tools for the TAR would arrive at the site without labels. Plant personnel would have to figure out where these different pieces of equipment were supposed to go on the site, and how they fit together.

Coordinating layout drawings with the one-line diagrams ensures that equipment goes to the right locations and that life-critical systems stay active in case of faults. These drawings can also reduce labor hours, as anyone reviewing the drawing will know exactly where to send equipment when it arrives at the facility. Using layout drawings and one-line diagrams to highlight the locations of equipment can save up to 20% in labor costs, as well as the time associated with moving equipment and making connections during TAR operations.

Plan service and refueling access

Whether installing one or multiple generators for the TAR, service access is a crucial consideration. All generators will require periodic maintenance and service, and must be refueled on a scheduled basis.

Not only should each generator be easily accessible to personnel throughout the duration of the TAR, but additional power options must also be planned in the event that a generator is taken offline for service. This might mean installing two generators rather than only one, which allows one generator to pick up the load when the other is being serviced, thus keeping the facility running. The right solution may call for installing a bank of three to four generators at one location, and utilizing the facility’s existing distribution system to transmit power where it is needed. One generator can be serviced at a time, while the others continue supplying power.

Each generator’s fueling needs and options should be organized in advance, as well. Unfortunately, some plants overlook this aspect of critical response planning, and face power shortages at a particular site, or across the whole plant, while waiting for a refueling truck to arrive.

The vendor should be able to recommend and implement refueling strategies to avoid power disruptions. These strategies can include using a generator’s onboard remote monitoring service and associated smart phone app to receive low fuel alerts.

Securing the site and identifying key contacts

As with any high-voltage electrical equipment, temporary generators and cables in a plant can pose risks of injury and should only be accessible by trained personnel. To increase safety, the site should be secured by installing fencing around power generation equipment, anchoring cables in place and securing access rights to qualified and trained workers. This process should be done well in advance of the startup of the generators, rather than as an afterthought.

Plant management must prepare a list of key contacts to reach in case of an emergency with the power generation equipment, as well. These contacts include the plant personnel who will be responsible for managing onsite electrical equipment, along with representatives from any contractors or vendors that work with the plant to support its electrical needs.

Takeaway

For a safe and successful TAR, electrical power requirements must be planned as early as possible, and not treated as a secondary consideration. Vendors now have the capability and practical experience to duplicate a facility’s electrical infrastructure to keep units running during a shutdown. HP

The Author

From the Archive

Comments

Comments

{{ error }}
{{ comment.comment.Name }} • {{ comment.timeAgo }}
{{ comment.comment.Text }}