ATHENS- Hellenic Petroleum, Greece's biggest oil refiner, plans capital expenditure of between 3.5 billion 4 billion euros ($9.03 billion) by 2025, about of half of which will be on clean energy projects, its top executive said on Thursday.

Hellenic operates three oil refineries in Greece but has been boosting its renewable energy portfolio under Greece's plan to increase its share of green energy as part of a binding European Union target for a 55% cut in CO2 emissions by 2030.

"We have a plan at the order of 3.5 to 4 billion euros," Chief Executive Andreas Shiamishis said of the group's spending plans at an online briefing presenting the group's strategy for 2020-2025.

Shiamishis said half of that would go into traditional activities and the other half in projects that will help the group's transition to cleaner energy.

Hellenic is also looking to change its corporate structure to improve governance and financing and reduce its carbon footprint.

"Our aim is to reach a 50% improvement (of our carbon footprint) by 2030," Shiamishis said. "To achieve that, we need to transform our business strategy." ($1 = 0.8304 euros)

(Reporting by Angeliki Koutantou Editing by David Goodman) ((angeliki.koutantou@thomsonreuters.com; +30 2102214608; Reuters Messaging: angeliki.koutantou.reuters.com@reuters.net))