The recent Energy Voice article from the Equinor chairman concerning the Mariner project heralding a ‘significant point of reference’ for growth highlighted the energy efficiency achievements associated with the platform.
I view energy efficiency as a key enabler to net zero and it is a topic I have been involved with for many years.As part of my energy efficiency work, I investigated Norwegian practices and compared them with the UK.
There were many differences, here are three;
1. Power for offshore installations is usually supplied from gas turbines burning fuel from the oil and gas processing plant and converting that to electricity or coupling the gas turbine to a machine such as a gas compressor.
There are two main generic types of gas turbine – aero-derivative and industrial. As the name implies aero-derivatives are aviation engines used in a static environment. Aero-derivative turbines are designed to be energy efficient as that is very import for the aviation industry.
Not so with industrial type gas turbines; they are typically 5-10% less efficient than a comparable aero-derivative.
Industrial machines do have some advantages – they can be cheaper, require less frequent maintenance, they have a wide fuel composition tolerance and they can be procured within a shorter time frame.
My comparison showed that aero-derivative machines prevailed in Norway because of the energy efficiency advantages – not the case in the UK where there are many more offshore industrial gas turbines.
2. Offshore gas flaring is probably the most obvious source of inefficient use of energy with consequent greenhouse gas emissions.
On UK installations gas is always flared due to the design of the oil and gas processing plant.
Though not a large quantity of gas, a continuous flow of gas is routinely sent to flare from some of the process plant.
In addition the flare requires pilot flames to be maintained burning at all times and a purge of hydrocarbon gas is introduced into the pipes to prevent unsafe air ingress that could lead to an explosive mixture.
On many Norwegian installations the flare system is designed differently. Flare gas recovery systems are deployed which results in no flaring during continuous operations.
Flare gas recovery systems improve energy efficiency but they are costly and add additional operational complexity.
3. Returning to gas turbines, all UK offshore gas turbines are open cycle – gas is burned to produce energy and the very hot exhaust gases are vented to the atmosphere. Around 60 -70% of the energy is lost in the exhaust gases.
Some UK fields use this hot gas as a heat source for some of the oil and gas treatment operations hence improving energy efficiency.
There is another option for gas turbines that will significantly improve energy efficiency – combined cycle.
