Oct-2013

Refinery power failures: causes, costs and solutions: part 2

Technologies are discussed to help refiners formulate strategies in managing risks and crisis due to emergency shutdowns, thereby minimising financial loss.

WILLIAM H GRAF, WILLIAM F VUKOVICH and THOMAS W YEUNG
Hydrocarbon Publishing Company

Article Summary

Part 1 of this series (PTQ, Q3 2013) discussed how electrical disruptions and power failures at refineries regularly cause enormous damage in terms of lost production, excessive repair costs, and can lead to environmental and safety concerns, raising the questions of how these outages can be prevented and how an affected refinery can be brought back online as quickly as possible. In this article, vital prevention techniques, protective devices, quick restart equipment, and supply security methods will be discussed.

Electricity is the lifeblood of the refinery operation. Optimal design and excellent construction mean nothing if the plant cannot receive a consistent and reliable power supply. Plant shutdowns, whether planned or unplanned, will decrease production and reduce profits, as shown by US refiner HollyFrontier, which reported a loss of $98 million for Q1 2013 because of planned and unplanned shutdowns.1

Not only is power reliability essential for profits, it is also important for national fuel supply security and environmental concerns. On 8 July 2013, Eni’s Taranto refinery in Italy suffered a leak of untreated fluid following a power outage. Italy’s industry ministry declared that the refinery must invest in a power feed system to prevent further blackouts, or else the refinery would lose its permits.2 The necessity of flaring following electrical failure is common, as on 30 May 2013 when a simple Mylar balloon caused a short circuit in a substation at ExxonMobil’s Torrance, California, refinery in the US resulting in the evacuation of workers and elevated flaring. 

Refineries require a lot of power to operate. The overall mitigation strategy primarily consists of two parts: risk management and crisis management (see Figure 1). In handling risk management, a refinery must install the most reliable equipment available in the market that can withstand disruptions caused by weather, power surges, blackouts, and any other outside elements. Since no equipment is perfect, reliability engineers and operators still need to prepare for worst-case scenarios as well as the most frequently occurring possibilities. This is where they utilise prevention techniques to detect and fix problems before they lead to a power failure, and select protective equipment accordingly. When a problem does arise, the second part of the strategy — crisis management — comes into play. This involves the recovery technologies that allow for safe shutdown and continued operation, and the restart methods that will not lead to the same problem that caused the previous failure.

Prevention and protection
One of the most important preventative measures a refinery can take is to have an efficient maintenance programme. Studies show thatthe failure rate of electrical equipment is three times higher for components that are not part of a scheduled preventative maintenance programme as compared to those that are.³ Accordingly, maintenance is often a high priority for refiners; at a National Petrochemical & Refiners Association’s (NPRA) conference in the US, a Gulf Coast refinery representative said that his company spends about 20% of the maintenance budget on proactive activities. It focuses on rotating equipment and predictive and preventative maintenance programmes such as oil analysis, vibration analysis, thermal imaging, and craft training programmes. An East Coast refinery representative added that his company spends about 15% to 20% on proactive maintenance and in the long term will have it up to 65% to 70% of the budget.⁴

Protective measures will keep refining equipment from being damaged or failing when exposed to hazards such as arc flashes or short circuits. This requires the proper selection of distributive equipment including transformers, switchgears, motor control centres, motors and cables that can handle extreme conditions, and are able to withstand dangerous events. This also necessitates the proper selection and use of equipment such as protective relays, circuit breakers and grounding devices in order to protect distributive equipment from dangerous conditions. Good protective technology can also protect operators and other personnel from injury. The following sections discuss the causes of and remedies to major equipment failures in a refinery, with specific refinery applications to show the latest technologies adopted.

Transformers
Transformers are an essential part of power distribution. They increase or decrease voltage for downstream distribution and operation. A properly operating transformer keeps the electrical system and load at optimal utilisation voltage levels.

Almost every malfunction is a result of the failure of the device’s insulation system. The insulation is what keeps the transformer in electrical balance and, when the insulation ceases to function, the entire transformer is susceptible to immediate failure. Faults, heat and mechanical damage will lead to insulation failure, but the electrical engineer can avoid these issues by selecting a unit capable of withstanding expected operating and fault conditions.

A study done by Hartford Steam Boiler during a 20-year period showed that 13% of all transformer failures in the US were caused by inadequate maintenance. It is important for maintenance personnel to check the insulator fluid. These tests will indicate the health of the transformer. Regular testing such as an insulation resistance test, dielectric absorption test, power factor test, dissolved gas in oil test, acidity test, colour test, and insulating liquid test will allow reliability engineers to track a transformer’s degradation and determine if replacement or repair is necessary.³
The right transformer will provide the correct level of power for refinery units. In May 2013, it was announced that Siemens will be providing 220kV/110kV power transformers and 35kV/10kV distribution transformers as part of the electrical system for China National Petroleum Corporation’s planned Guangdong Petro-chemical Refinery.⁵

Switchgears
Switchgear is a combination of electrical enclosures, buses, protective relays, circuit breakers, fuses, controls and indicating devices that are used to distribute power to and protect other electric equipment. Receiving power from generators or transmission cables, they will distribute their power to other switchgear (or switchboards) and motor control centres.