Hybrid Turbo-Compressor: A Technology Solution to Enable and Fully Exploit the Electricity and Gas Sector Coupling
Authors: Baldanzini Fabio , Rubino Dante Tommaso , Baldini Marco , Rodà Bruno , Tarenzi Marco 
Published: September 2023

Abstract
One of the main challenges that the operators have to cope with in the transition towards a “decarbonized” energy is the management of the inherent variability and intermittency of renewable energy sources. One straightforward remedy is to resize the electric grid for maximum potential capacity and/or implement a suitable energy storage system to balance the upstream energy supply variability. In this framework recent agreements and closer integrations between electric and gas grid operators at the European level (e.g. ENTSO-E and ENTSO-G) as well as country level are aimed at fostering the so called electricity and gas “sector coupling”, which from this point of view is the most effective way to fully unlock the potential renewable energy. Apart from Power-To -Gas plants, in this paper we will discuss another technology that may leverage and also enable the “sector-coupling” approach at the level of local compressor station for gas transmission and storage, namely the so-called hybrid gas turbines.
With mechanical gas turbine hybridization, an electric motor-generator and a clutch are added to the turbo-compressor shaft line, traditionally a gas turbine coupled with a compressor. As the electric machine can operate both as generator and motor, the hybrid train enhance the customer plant flexibility by allowing the production of electric energy or reducing the emissions by operating the compressor in full electric mode. In such way, one of the main hybrid gas turbine added values is given by the potential integration with renewable energy sources, where available and/or accumulated on the plant.
Starting from large LNG fleet experience, where electric motors are used as gas turbine helper, different and innovative train configurations have been developed to meet different customer requirements. Leveraging on this heritage, specific hybrid-GT multi-purpose trains have been designed to address the above-mentioned points and more in general the energy transition challenge.
In particular, the first configuration is characterized by the gas turbine and electric machine at the shaft-line ends and the centrifugal compressor is pass-through, connected to the electric motor/generator through an optional clutch. Given the reduced footprint, it is a best for brownfield application just adding a motor generator. The second configuration is characterized by the electric motor in pass-through position, connected through a clutch on both sides to the gas-turbine and compressor. As a result, it is a best fit for pure power generation.
It is then outlined how the role of a Hybrid Control Management System coupled with a Digital Optimizer is crucial in controlling the hybrid train operating modes and detecting an optimized operating condition in terms of fuel consumption, electrical power intake/outtake, emission requirements and gas turbine life optimization. The paper provides an overview of pros & cons of each hybrid train architectures and their technical challenges, with the technical viewpoint of the European leading transmission system operator, with a strong commitment on decarbonization. A case study will be presented demonstrating also the capability of hybrid technology configurations in terms of emission reduction supporting transmission operators when facing more demanding emission regulation.