Researchers are using NETL's low-pressure and high-pressure Water Tunnel Facilities to study technical feasibility and environmental effects of CO₂ storage in freshwater and saltwater environments. Understanding the physical, chemical, and thermodynamic characteristics of CO₂ in such environments is necessary in order to develop successful storage or sequestration strategies – a major step toward the national goal of reducing the volume of greenhouse gases released into the atmosphere.

Researchers have been collecting data on the effects of temperature, pressure, salinity, and dissolved CO₂ concentration in cold, liquid environments. NETL's onsite Water Tunnel Facilities also are being used to test new concepts and perform fundamental research. For example, a recent study examined the size, stability, and settling velocities of CO₂ drops coated with calcium carbonate (limestone) powder. The coated CO₂ drops replicate mineral carbonation, which holds promise for long-term, unmonitored CO₂ storage since mineral carbonates are benign, stable, and long-lived in water environments.

The Water Tunnel Facilities also are frequently used in conjunction with NETL's Hydrate Laboratory to investigate how CO₂ /hydrate compounds – carbon dioxide trapped in ice – form and dissolve. Research has shown that such compounds form naturally in deep saltwater environments, as discrete particles or as “shells” on CO₂ drops. Understanding the process that forms a stable, dense, ice-like CO₂ /hydrate is critical to successful introduction of CO₂ into deep-water environments. To achieve long-term sequestration in CO₂ /hydrate compounds, the CO₂ must be injected in high enough concentrations and in a manner that prevents the compound from dissolving. NETL has performed these studies in collaboration with researchers from the University of Pittsburgh , Oak Ridge National Laboratory, and the University of Massachusetts, Lowell .

The High-Pressure Water Tunnel Facility (HWTF) permits an accurate simulation of what occurs when CO₂ is injected into an open-water environment. A fluid particle, such as a CO₂ droplet, is suspended in the HWTF. It can then be observed in a section of the water column, where it is held stationary by a countercurrent flow of water or seawater. Screens or other restraining devices are not used to hold the droplet, since such devices could change the structure of the droplet, and also introduce unnatural heat transfer characteristics relative to the water environment. The HWTF has specialized internal mechanisms that permit the operator to modify and control the water flow for extended periods, providing a unique opportunity to assess what would happen to the stability of the a fluid particle under various flow conditions. System flow can be reversed to stabilize both positively buoyant (floating) and negatively buoyant (sinking) particles.

In addition to the HWTF, other laboratory equipment includes:

• A low-pressure water tunnel and static water tank
• Two environmental chambers with a temperature range of 40–200 °C
• Two variable-volume view cells with pressure ratings up to 135 MPa
• A stirred autoclave with capacities of 50 mL and 100 mL
• Precision syringe pumps
• National Instruments hardware and software
• Analog and digital cameras
• Video recording and analysis equipment
• Professional DVD creation and editing equipment

Ron Lynn, Chief Engineer for the HWTF, performs real-time measurement of objects stabilized in the HWTF.
The HWTF is seen behind a 2.5-cm thick Lexan window.

NETL’s HWTF, with inset image showing a hydrate-covered CO₂ drop
stabilized for observation by a countercurrent flow of seawater.

Eilis Rosenbaum and Yi Zhang perform experiments in the Hydrate Laboratory.
The blue and white structures are the environmental chambers in which various reactors
are contained for both CO₂ sequestration and methane hydrate research.

For more information contact: Robert Warzinski