Achieving 50% weight reduction of offshore steam bottoming cycles

Marit J Mazzetti,Brede A.L Hagen,Geir Skaugen,Karl Lindqvist,Steinar Lundberg,Oddrun A Kristensen

doi:10.1016/j.energy.2021.120634

Marit J Mazzetti, Brede A.L Hagen + Show 4 more

Open Access

https://doi.org/10.1016/j.energy.2021.120634

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Abstract

Adding a bottoming cycle to the gas turbines powering offshore oil and gas production plants allows additional power to be produced from recovered excess heat. Hence, the power demand of the platform can be met by burning less natural gas, and the CO2 emissions reduced by up to 25%. However, the weight of the current bottoming cycles must come down to enable widespread implementation. This work presents a thorough weight minimization of a steam bottoming cycle utilizing gas turbine exhaust heat. Unconventional, but feasible designs of heat exchangers, ductwork and structural components are considered along with materials switching. Overall weight reductions of 38% and 52% were achieved for a 16 MW and a 12 MW offshore bottoming cycle respectively when compared to a 16 MW reference system. Key factors in achieving the weight reduction were the use of small steam generator tubes with an inner diameter of only 10 mm, improved condenser design and the use of aluminium structural framework replacing steel. By more than halving the weight of the bottoming cycle, it's implementation potential on offshore platforms has been greatly improved and can move the oil and gas industry towards significantly reduced CO2 emissions.

Highlights

Offshore oil- and gas production is a very energy-intensive process: Typical installations offshore have power demands in the 60e80 MW range
The power required is usually supplied by LM2500 gas turbines in simple cycle configuration with efficiencies of only 38% [1]
The remaining energy is expelled as waste heat in the exhaust leading to unnecessarily high CO2 emissions

Summary

Introduction

Offshore oil- and gas production is a very energy-intensive process: Typical installations offshore have power demands in the 60e80 MW range. The remaining energy is expelled as waste heat in the exhaust leading to unnecessarily high CO2 emissions. There is a large potential for efficiency improvements through implementing a bottoming cycle that produces power from the hot exhaust gases, Fig. 1. Three of about 90 platforms on the Norwegian continental shelf have bottoming cycles installed for more efficient power production, primarily due to lack of available weight allowance on oil and gas platforms. In Norway the oil- and gas production emits 13.4 Mega tonnes/year of CO2, accounting for about a quarter of total emissions in 2018 [5]. Widescale implementation of steam bottoming cycles could reduce CO2emissions from offshore platforms by 15e25% [2e4]

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