Planeteers Takes EIC Accelerator Money to Limestone Carbon Storage

Limestone dissolved in carbonated water turns into calcium bicarbonate, the same compound found in mineral water, and in nature that reaction takes thousands of years. Planeteers, a Hamburg company formed in December 2022, says its reactor does it in minutes: CO2 from a chimney is dissolved in water, mixed with a limestone slurry, and the resulting bicarbonate is released into rivers and the sea, where the CORDIS project objective says it stays stored for 10,000 to 100,000 years.

The EIC Accelerator selected the project, REACT Carbon, at its 6 May 2026 cut-off for blended finance. CORDIS records a grant agreement signed on 2 October 2026 with an EU contribution of €2,499,998.99, running from 1 November 2026 to 31 October 2028. The project is days old. What can already be checked is the company's first site, and there the record is specific: a validated project on a carbon registry that has not yet issued a single credit.

Limestone, carbonic acid and a diffuser

The process is described in most detail in a 2024 article in the cement and lime journal ZKG, written by managing director Frank Rattey and project manager Elizaveta Chernysheva. CO2 from a biogenic or fossil point source dissolves in water as carbonic acid, which reacts with a limestone slurry to form bicarbonate. The mixture is equilibrated in a diffuser system before it is released into a water body. Sensors in the reactor log conductivity, pH and CO2, and alkalinity is measured before release. The authors list industrial by-products such as filter cake, off-spec lime and kiln dust as feedstock, and they project the method to be about 2.5 times more cost-efficient in the long run than thermal processes. That is a projection, with no published cost per tonne behind it in the article.

The ZKG authors contrast the method with amine scrubbing, which needs significant heat to regenerate its chemicals, and Carmeuse's investment profile notes that conventional CO2 transport and storage buildouts can take close to a decade. Planeteers stores the carbon in solution instead, which ties each reactor to a water body that can take the discharge. The CORDIS objective names the scrubber, the alkalinity reactor and the diffuser as the three stages the EIC project funds.

The company has described a second route as well. When Frontier bought 255 tonnes from Planeteers in September 2024, it described a pressure-swing process that turns limestone into hydrated carbonate minerals, which are mixed into the outflow of a water treatment plant to take up CO2 from the air. The company website now lists this as a separate patented technology producing ikaite. The EIC project concerns the point-source reactor, not this mineral route.

The first site: validated, not yet credited

Planeteers' first production unit, Helix, sits at the AZV Südholstein sewage works in Hetlingen. On the Isometric registry, the project captures CO2 from a power plant that burns methane from fermented sewage sludge, converts it into dissolved bicarbonate and carbonate with alkaline material, and releases it into the ocean. Isometric approved the project on 12 December 2025 after validation by Normec Verifavia, with a crediting period from 1 January 2026 to 31 December 2030. The registry lists initial credit issuance as in progress and gives 2027 as the date of the expected first certificates.

Two details on the registry differ from the company's own account. The Helix project page says it follows Isometric's protocol for enhanced weathering in closed engineered systems; the registry lists Biogenic Carbon Capture and Storage v1.2 as the protocol. The registry also states storage of more than 1,000 years, where CORDIS and the ZKG article give 10,000 to 100,000 years. The registry states its figure as a minimum, and it is the only one of the two tied to a certification.

The second site, Ostrea at Kiel's wastewater treatment plant on the Baltic, is funded under Schleswig-Holstein's 2021 to 2027 business programme, part-financed by the European Regional Development Fund. Its project page says commissioning is under way with production expected shortly. The capacity is not stated.

What REACT Carbon promises

The CORDIS objective is a market plan more than a technical one. It names the compliance carbon market as the target, meaning the obligations of emitters under the EU Emissions Trading System, and says the project lays the foundation for entering it. The first customers it names are the cement and limestone industries, which it says emit around 160 million tonnes of CO2. Assuming carbon capture and storage prices rising to €146 a tonne, the company estimates its EU market value at no less than €2.0 billion. Those are the applicant's figures, not the EIC's. CORDIS records no total project cost and, with the project days old, no reports.

The company website calls Voluta its "EIC project", aimed at hard-to-abate industry for 2027, with location and details to be announced. The link to industry fits its investors: Carmeuse, a lime and limestone producer, made Planeteers the first investment of its venture arm, announced on 9 January 2026.

1. Scrubber, alkalinity reactor and diffuser at industrial scaleToo earlyProject started 1 November 2026; Voluta has no published site.
2. Measurement, reporting and verificationValidatedHelix passed third-party validation in December 2025; no verification report or credit yet.
3. Entry to the compliance carbon marketNot shownNo cement or lime plant customer has been announced.
4. Voluntary removal salesSold255 tonnes to Frontier's buyers in 2024; delivery status not public.

The money

Startup City Hamburg reported on 31 July 2024 that Planeteers had closed a seed round in the "significant single-digit million" range, with BonVenture, Smart Energy Innovationsfonds of Energie 360° and ClimaNow joining existing investors. BonVenture's own note gives the same investors and range. Carmeuse's portfolio page dates its seed investment to December 2025, sixteen months after the round was announced; no source discloses an amount. The register summary on North Data also lists a state aid grant of €387,666 in September 2025.

The EIC award was blended finance. CORDIS records the grant; whether the EIC Fund has taken or committed equity is not public, and the EIC Fund's portfolio page did not display a company list when checked on 4 November 2026.

The register summary shows no balance sheet, revenue or staff figure, and no insolvency entry. It records Frank Rattey and Florian S. Birner as managing directors, and a publication of 20 January 2026 lists co-founder Florian Brinkmann as no longer a managing director. The company has given no reason in any source found.

Why it matters to Europe

The EU has built a certification framework for carbon removals with EU-wide methodologies, so that removals can be counted against emissions that cannot be avoided. REACT Carbon's case, in its CORDIS objective, is that emitters under the EU Emissions Trading System need cost-effective ways to comply, starting with the cement and limestone industries. The ZKG authors add that the feedstock can be the lime industry's own by-products, such as filter cake, off-spec lime and kiln dust. CORDIS tags the project 100% to climate action and clean air.

Planeteers was not asked for comment for this article. The reporting is based on publicly available sources, listed below.