Custom Solutions for Carbon-Capture Applications

Custom Solutions for Carbon-Capture Applications

When carbon-capture startup 280 Earth reached out to Bionetics, they were facing a measurement challenge that no off-the-shelf flowmeter could solve. Their process continuously moves a CO₂/air mixture through a two-inch pipeline, but the composition of that mixture changes hour by hour. CO₂ concentrations swing from as low as 56% to as high as 93% by volume, while pressure and temperature fluctuate along with the dynamic conditions of liquefaction and storage. Stable process control required more than just a flowmeter, it required an intelligent flow measurement system that could adapt to changing process conditions.

280 Earth needed something highly specific: a flowmeter that could measure the CO₂ mass flow rate in a line carrying both CO₂ and air. On top of that, the sensor must adjust the measurement in real time to account for the actual conditions inside the pipe. The mixture’s density, viscosity, heat capacity, thermal conductivity, and even velocity vary drastically depending on the concentration, temperature, and pressure. No standard instrument can account for all of these variables, especially when the composition itself keeps changing. The challenge was clear: the meter had to be smart enough to keep up with a living, breathing process.

This kind of problem is exactly where Bionetics thrives.

A Measurement Problem That Required First-Principles Engineering

The customer’s pipeline, a 2” schedule-80 line with a tight insertion depth requirement, was only the starting point. The real complexity came from the media itself. With CO₂ mass flows ranging from 10–80 kg/hr and air flows between 0-40 kg/hr, the resulting mixture occupied a wide thermodynamic envelope. A flowmeter calibrated to a fixed gas type would be wildly inaccurate under such conditions, because thermal flowmeters depend heavily on the fluid’s heat-transfer characteristics. If the mixture changes, the thermal response changes with it.

The solution would require a true hybrid of hardware, physics, and software.

We began with a Rheotherm thermal mass flow probe—robust, reliable, and known for its sensitivity. The Rheotherm is sensitive to the total mass flow in the pipe, but requires knowledge of the gas composition for an accurate reading. To account for the changing process conditions, Bionetics designed a custom measurement algorithm that lives on the customer’s system and constantly adjusts the CO₂ flow reading based on external inputs. The customer measures CO₂ concentration with their own gas analyzer, while pressure and temperature come from additional upstream instrumentation. All of these values feed into a Bionetics-developed program that converts the raw Rheotherm signal into accurate CO₂ mass flow.

To accomplish this, the algorithm computes the real-time thermodynamic properties of both pure CO₂ and pure air, using custom surface-fit functions developed from NIST data. From there, it calculates the effective density, viscosity, thermal conductivity, and heat capacity of the actual CO₂/air mixture present at any moment. These mixture properties feed into an iterative heat-transfer calculation that determines the true fluid velocity corresponding to the thermal signal measured by the probe. Once velocity is known, the algorithm determines CO₂ mass flow by combining velocity with mixture density, the effective pipe area, and the customer’s live concentration data.

This is measurement from first principles—not guesswork, not a one-size-fits-all calibration. It’s a dynamic model of the customer’s real process.

Creating Accuracy Through Custom Calibration

Even the best theoretical model must be validated in the real world, especially when dealing with CO₂ under pressure. CO₂ behaves very differently from air: it is highly pressure-dependent, prone to cooling effects, and sensitive to compressibility changes around the probe tips. For this reason, Bionetics performed a detailed in-house calibration using both pure CO₂ and a 70/30 CO₂/air mixture. These two gases allowed us to bracket the customer’s operating range and ensure accuracy at both ends of their concentration spectrum.

Calibration required careful planning. A standard CO₂ tank can supply multiple test points because it contains 75 pounds of liquefied CO₂. But the 70/30 mixture cannot be liquefied in the tank, meaning that even two tanks in parallel only supply enough gas for a few data points. The Bionetics team collected most of the data on pure CO₂, supplementing it with the limited but critical mixture data needed to verify the behavior of the algorithm.

This range allowed us to validate whether the model correctly compensated for pressure effects. It also forced us to deal with CO₂’s natural tendency to cool rapidly as it expands, which introduces temperature instability and consequently affects the probe’s heat-transfer signal. To minimize the amount of cooling flow disturbances, our engineers installed multiple regulators and heat exchangers as well as flow straighteners in the calibration system to ensure the fluid was at equilibrium conditions when the measurement was taken. Despite these refinements, the data still reflected natural CO₂ variability—something any instrument measuring real CO₂ must contend with.

After cleaning up a handful of points affected by pressure transients and evaporative cooling, we fit the final dataset to a second-order polynomial correction. The resulting calibration delivered a practical accuracy of approximately ±5% of reading across the customer’s required flow range. Given the complexity of the gas behavior and the extreme sensitivity of thermal instruments to temperature and pressure, this level of performance is a strong success for such a challenging application.

The End Product: A Flowmeter That Adapts to Reality

The final instrument provides 280 Earth with something far beyond a standard meter. It is a system that senses, calculates, and adapts to the changing properties of a real CO₂/air mixture in real time. It runs a custom Bionetics software package directly on their equipment, using their live gas-analyzer data. It corrects automatically for pressure and temperature. And it delivers CO₂ mass-flow information they can trust while operating in one of the most demanding process environments in industry.

This project demonstrates what Bionetics does best: transforming complex measurement problems into precise, practical tools. The combination of physical modeling, custom software, and purpose-built calibration allows us to create instruments that simply do not exist anywhere else.

Why Customized Instrumentation Matters

Industries working with mixed gases, high-pressure CO₂, or rapidly changing media often discover that catalog instruments fall short. Real processes do not behave like controlled laboratory conditions, and the farther a system moves from idealized assumptions, the more value a custom-engineered measurement solution provides. Bionetics aims to bridge that gap—building sensors and algorithms that are grounded in physics and tailored to the environment where they will actually operate.

If your application includes unusual fluids, non-standard mixtures, aggressive conditions, or measurement challenges that traditional instruments can’t quite satisfy, our engineering team would be glad to help. When the application demands innovation, Bionetics can deliver it.