POWER SYSTEMS

ECB 3153AN ASSIGNMENT

OFFSHORE POWER SYSTEMS

By Ali Yahya Surajuddin Mohamed,15667

Introduction

The electric power supply on an oil production platform is regarded as an auxiliary system, designed to supply the platform with the necessary electric power throughout its lifetime with sufficient reliability and availability[1]. The power systems have usually been split into the following two categories:

Main Power System. Emergency Power System.

The former being designed to supply all the electric power required for the daily operation of the platform while the latter is to comply with most national requirements regarding power supply in emergency situations.

Understanding the selection criteria for offshorepower generation is critical so as to meet the minimum factors necessary that range from power demand, costs comparisons to space requirements and fuel availability and suitability to the respective power system. This short paper shall take on three of the main options used to generate electricity that feeds offshore oil platforms.

1.Solar Power System.

Solar power is the technology of obtaining usableenergy from the light of the Sun. It has been used as a traditional technology for centuries and is coming into widespread use where other power supplies are absent, such as in remote locations and in space. What deems it preferable to other power systems is its reduced overall maintenance in most cases there are no movable parts. Although it does have a relatively high initial installation cost, a long life expectancyof at least 25 years, minimal noise and air pollution as well as its suitability for unmannedfacilities tend to negate the mentioned disadvantages. Therefore more focus will be shed on the effectiveness and how efficient the systemis to generate useable electricity for offshore rigs.

A Solar power system itself may be divided into several types according to design specifications,for instance Photovoltaic(PV) technology requiresa very large landscape otherwise knows as a footprint, as it only outputs about 5 to 6 watts per square meter under typical weather conditionsthat is direct sun exposure.[2]

For that reason, a more prominent technology in the form of Concentrated Solar Power (CSP) plantsis introduced to generate electric power by usingmirrors to concentrate/focus the sun's energy andconvert it into high-temperature heat. That heat is then channeled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity.

Land-based parabolic trough system, a type of CSP plants.(Credit: Argonne National Laboratory)

According to Rod MacGregor, the CEO of an American power company that

manufactures Solar Steam generators, he claims that steam derived from solar technology can generate up to 80% of the total annual enhanced oil recovery project needs [3], lowering the amount of natural gas required by the same percentage eventually lowering emissions rate as well as financial costs but is it as efficient?.

2.Gas Turbine Generator

The use of gas turbines for generating electricity dates back to 1939. Today, they are one of the most widely-used power generating technologies.

Gas turbines are a type of internal combustion (IC) engine in which burning of an air-fuel mixture produces hot gases that spin a turbine toproduce power. It is the production of hot gas during fuel combustion, not the fuel itself that the gives gas turbines the name. They utilize a variety of fuels, including natural gas, fuel oils, and synthetic fuels.

In a simple cycle gas turbine; the exhaust gases

leaving the turbine in the open cycle are not re-circulated. This lead to the innovation of a combined cycle gas turbine where exhaust gases instead of being released as waste are captured and channeled to a steam turbine to be used as a heating agent.

Diagram of Combined Cycle Gas-Steam Turbine(Electrical and Energy Systems, Universiti Teknologi Petronas)

Utilizing such design, Gas turbines can be particularly efficient (up to at least 60%) when waste heat from the turbine is recovered by a heat recovery steam generator to power a conventional steam turbine in a synchronized configuration. They can also be run in a cogeneration that is where the exhaust is used for space or water heating, then cooling the inlet air to increase the power output.

Currently, in broad manners, Gas Turbine-based powers systems are more efficient compared to

Solar power systems although both have relativelyhigh costs, yet the latter is preferred when the emissions issue is brought, consequently Wind power systems tend to be the best in-between solution among the two previously mentioned.

3.Wind Power

Onshore wind energy sticks out as being extremelyimportant because it’s one of the most cost-effective and mature of all the renewable technologies.

A wind turbine is a device that converts kinetic energy from the wind into electrical power. This energy is created when the atmosphere is heated unevenly by the sun. A wind turbine extracts energy from moving air by slowing the wind down, and transferring this energy into a spinning shaft, which usually turns a generator to produceelectricity.

Diagram of Wind Turbine(Electrical and Energy Systems, Universiti Teknologi Petronas)

The amount of power that could be captured from awind turbine is said to be in the range of 35% to45% of the turbine capacity with maximum efficiency of nearly 60% known as the Betz Limit [5].

The power in the wind that is available for harvest depends on both the wind speed and the area swept by the turbine’s blades, two importantfactors which are widely present offshore thus easing and lowering the costs of power transmission directly to the oil rig. However Offshore wind energy is not the best investment right now because of its very high costs, immature technologies and development constraints. According to the Telegraph[4], Offshore wind farms are 90 per cent more expensive than fossil fuel generators and 50 per cent more expensive than nuclear power.This high expense is a result of the technical

difficulties of offshore turbine construction whereby extra construction and materials are needed to set up turbines in the sea and investment in new offshore technologies that may not work may also attributed to this cost.

ConclusionWind turbines, Solar systems or the conventional Gas turbines? The answer, of course, is that it is not as simple as stating which technology is better – all three have their benefits as well asdrawbacks and which technology is best depends very much on the application and the location of the fed system. In addition the combination or synchronization any two or all three systems together to perform as a single unit is another option related to offshore power generation .

References:

[1] Myhre J. C,. Electrical Power Supply to Offshore Oil Installations By High Voltage Direct Current Transmission. Norwegian University of Science and Technology. 2001, pp. 20 – 27.

[2] Ausubel J. H,. Renewable and nuclear Heresies. Int. J. of Nuclear Governance, Economy and Ecology, 2007 Vol.1, No.3, pp.229 – 243.

[3] Chang E. Y,. The Solar Powered Oil Rig. Breaking Energy, July 14th, 2011. Retrieved August 4th 2014from http://breakingenergy.com/2011/07/14/the-solar-powered-oil-rig/

[4] Alleyne R,. Britain's Offshore Wind power. The Telegraph, Sept 27th, 2010. Retrieved August 5th 2014 from http://www.telegraph.co.uk/earth/energy/windpower/8028328/Britains-offshore-windpower-costs-twice-as-much-as-coal-and-gas-generated-electricity.html

[5] Ragheb M,. Wind Energy Conversion Theory, Betz Equation. 2014.