Windtech: Wind-power generation with CO2 harvesting

GERMANY: A German consultancy promises to make wind power even greener. Eize de Vries talks to company founder Jörg Spitzner about Blancair, its innovative wind-turbine concept unveiled to an invited audience at WindEnergy Hamburg.

New concept… Designed for improved net systems efficiency
New concept… Designed for improved net systems efficiency

Established in 2007 as specialists in lightweight structures for the aerospace industry, Spitzner Engineers has also worked on advanced solutions for wind-energy applications.

Its Blancair project aims to enable a decisive step forward in the transition from nuclear and fossil-fuel energy generation sources towards renewables.

"The main renewables like wind and solar are far more climate friendly than fossil fuels, especially coal and lignite, but they still have a small indirect carbon footprint," says company founder Jörg Spitzner.

(See Reducing the carbon footprint)

"Blancair is the first industrial-scale renewable-energy generating system that helps curb climate change by boosting turbine performance and yield and, in parallel, removes CO2 from ambient air efficiently," he claims.

Many of the Hamburg-based consultancy’s staff share a background in aerospace engineering.

The company’s philosophy is to always consider possible synergies on new developments.

The first conceptual ideas for Blancair were conceived around 18 months ago, with an initial focus on CO2 harvesting, but other benefits emerged during the development process.

The main operating principle is that when a turbine is running, a mass of air inside each blade is pulled through openings in the blade-tip section by centrifugal force and thus continuously replenished.

This induces an airflow in blade-tip direction and an air-pressure difference inside the rotor hub.

Second element

The second main element to the Blancair concept is a CO2-separation filter module mounted atop the rear of the nacelle.

This unit in turn is connected to the rotor hub and blade internals via a piping system through the nacelle and the generator.

"The pressure difference in the piping system creates a natural airflow that sucks ambient air through the CO2-separation module, where the CO2 is removed, transferred to ground level and stored.

"The ‘remaining’ air, without CO2, is then led through a dehumidifier, where it is also desalted," explains Spitzner.

In the next step, the cleaned and dried air flows through the piping system and the direct-drive generator (the preferred prototype option) into the hub and blade internals before being released into the external environment.

All steps take place in a fully passive system, so as not to require electric pumps or cooling fans.

Generator-temperature management normally represents a system loss because the heat energy in the coolant (air or liquid) is simply dissipated in the external environment via a rooftop cooler.

With Blancair, by contrast, most of this thermal energy is reused as input for the CO2-separation filter and dehumidifier units, both of which require 70-100oC operating temperatures for optimal functioning.

A smaller proportion of the thermal energy stays in the dried, dehumidified, desalted airflow pulled through the nacelle and blade internals opening, and this offers some unexpected additional benefits.

These include better protecting critical nacelle internals, including mechanical, electrical and power-electronic components, against corrosion and premature failure caused by high air humidity and water condensation.

Research project  

A second benefit was discovered more recently. "A masters student from the Technical University of Hamburg (TUHH) did his thesis in our firm during 2017," says Spitzner.

"His research topic was composite materials and structures, and possible contributing factors and failure mechanisms degrading rotor blade-performance and lifetime.

"The research, conducted under the supervision of professor Bodo Fiedler, who heads the university’s institute of polymer and composites, resulted in outcomes that were impressive but extremely worrying."

The student’s main findings were that high air humidity inside blades causes water vapour to condensate and settle at exposed surfaces of the internal blade structure.

This has a negative impact on the blade’s structural stiffness characteristics and erodes the long-term fatigue-loading resistance and capabilities of the glass-fibre-reinforced composite materials.

This unwelcome phenomenon is a particular problem for offshore wind, says Spitzner, with no conventional solution currently available.

"Our Blancair concept, whereby dried and pre-heated air flows through the blade’s inner structure, effectively counteracts such composite-material degradation," he says, adding that the student is now engaged in a PhD project, building on his thesis research.

Reducing wake effects

Airflow acceleration losses are compensated for by Blancair’s blade-tip design with aerodynamically optimised air outflow.

"This optimised shape reduces tip vortices and associated aerodynamic losses, and has shown a positive aerodynamic performance effect comparable to tip winglets.

"Most important to us is that it has a positive net impact on the system’s total efficiency," says Spitzner.

He concedes, however, that it is hard to attach concrete figures to this total efficiency gain because implementation is at an early stage, and there are many variables to consider, including turbine rating, rotor size and speed, and operating conditions.

Another early-stage research topic is whether optimised Blancair blade-tip outflow could reduce wake disturbances between turbines in a wind-farm arrangement.

"This is a highly relevant theme for us and the wind industry, and we had our kick-off expert meeting in October," says Spitzner.

"It is also a highly complex topic with many different technological, physical and environmental variables to consider.

With Blancair technology now developed and protected by a patent granted this year, our primary objective is building a prototype.

This will be a new Blancair-dedicated concept, except for the blade structural design, to best meet our specific requirements."

Prototype step

Spitzner’s drivetrain preference for the prototype is direct drive, because this configuration allows the easiest and most cost-effective integration with Blancair technology and the internal piping.

For the stored CO2, Spitzner sees multiple opportunities and possible applications, especially for boosting plant growth inside greenhouses, the food industry, and as a "raw material" for producing synthetic fuels.

The focus here is on power-to-gas, whereby either methane is produced in a chemical process, or synthetic "e-diesel" created with a Fischer-Tropsch reactor.

"The entire conversion process requires our CO2 separation unit, an electrolysis unit for producing hydrogen, and a compact containerised Fischer-Tropsch reactor.

All three elements can fit together in the tower base, and we have already engaged in talks with several interested parties about these and other multi-purpose options," says Spitzner.

His background in aerospace tells him there is little prospect for electric aircraft because of the high mass and relatively low energy density of the batteries, but he is more optimistic about the potential for synthetic liquid fuels for aircraft and container shipping.

"Blancair is one of the possible solutions to boost the transition from fossil-fuel energy to renewables and, in parallel, introduce technology that removes carbon from the atmosphere," says Spitzner.

"With worldwide energy demand and CO2 emissions still rising, there is little time to be lost. We are determined to bring Blancair to the market quickly, expand globally, and to seek strong cooperation partners to take up the challenge together."

Reducing the carbon footprint

Renewables-based power systems are not CO2-neutral as often mistakenly suggested.

Their low-carbon footprint is composed of lifecycle energy inputs during materials extraction and processing, transport, manufacture, installation, use phase and final decommissioning for recycling or disposal.

Multiple sources indicate that the carbon footprint for wind is in the range of 4g of CO2/kWh, compared with about 6g of CO2/kWh for solar PV, but this depends on several conceptual, environmental, physical and other variables.

Calculations performed by Spitzner indicate that one state-of-the-art 4MW Blancair-designed onshore turbine could, on average, "neutralise" the emission of 100 tonnes of CO2 annually.

This is roughly equivalent to the annual CO2 absorption of 80,000m2 of forest area, and equates to the CO2 emissions of driving around 800,000km by car.

Additional solutions for wind

Spitzner Engineers earlier developed a large rotor blade in close cooperation with the university of applied sciences in Bremerhaven, which is now deployed by a leading OEM.

The company has also produced a software-based simulation tool for predicting remaining turbine lifetime, and a modular load-optimised segmented rotor blade that enables a much higher degree of production automation compared with traditional construction methods.

Another example of its work in wind-industry applications is a research project dedicated to improving rotor-blade aerodynamic performance by adding a new root-area aerofoil, a tip winglet and passive boundary layer control.

Hamburg-based Spitzners Engineers received a German renewable energy award for the successfully sold final product in 2013.

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