Facilities and Tools:

The ORNL Seafloor Process Simulator

Figure 1. Front and side views of SPS pressure vessel

The SPS is a 72 liter, temperature-controlled high-pressure vessel capable of simulating deep seafloor pressures and temperatures where hydrates are stable (Figure 1).  Details regarding the SPS can be found in Phelps et al. (2001).  The vessel pressure was measured using a series of piezoelectric transducers (Precise Sensors, model 9112) with a working range of 0-20 MPa (0-2900 psi).  The vessel is stored at seafloor temperatures (2°C to 10°C) in an explosion-proof coldroom.  The large thermal mass of the vessel allows it to maintain a constant temperature, even as the coldroom temperature oscillates. Temperatures within the vessel are measured using Hastelloy-sheathed type K thermocouples (ARI Industries, Inc., Addison, IL ) that are calibrated to an accuracy of + 0.2°C. Thermocouples may be placed in the gas phase, water phase, and at the gas/water interface where hydrates collected upon formation.  Hydrate formation is visualized through several 2-inch sapphire windows on the side of the vessel. Higher magnification images (≥100 micrometer resolution) can be taken using a bore scope system and a high-pressure shroud that can be inserted into the vessel. Temperature, pressure, and gas flow data are collected in time sequence using a data acquisition system consisting of National Instruments Fieldpoint modules connected to a personal computer that logs data at 2 to 30 second time intervals using LabView software.

Hydraulic Torque Wrench and Crane

The large mass of the SPS requires the use of industrial equipment to reconfigure the vessel to accommodate a variety of experiments.  The total weight of the vessel is 3000 lbs and the lid weighs nearly 700 lbs.  In order to fasten and remove the lid sixteen 1.5” bolts are tightened to over 2000 foot pounds.  The tightening/loosening of the bolts is accomplished by using a hydraulic torque wrench (Hydratight).  When the lid is fastened and the SPS is pressurized to 3000 psi each bolt is subjected to over 23,000 pounds of tension.  In order to remove or replace the lid a crane with a maximum lifting capacity of 4000 lbs is used.  By using the crane and the torque wrench the lid can be removed and replaced in less than 2 hours, thereby providing for an efficient turn around time between experiments. 

Parr Vessel

The Parr vessel is a 450 mL stainless steel vessel equipped with two quartz windows, an impellor, and ports for pressure, temperature, and pH measurements.  This vessel is operational at pressures up to 2950 psi and chilled ethylene glycol is circulated through an insulating jacket to control temperature.  The Parr vessel is often used for preliminary experiments before the larger SPS is used.  Using the vessel in this way allows for efficient refinement of experimental methods and a smoother transition for experiments in the SPS. The small size of the Parr vessel also allows for transportation to nearby facilities for further characterization of the hydrate formed inside.  Raman spectroscopy has been used in previous experiments for characterization of CO2 hydrates.

Sapphire Cell

An 8 mL cell made from a single sapphire crystal was designed for hydrate characterization using high flux isotope reactor (HFIR) neutron powder diffractometer and future instruments at the Spallation Neutron Source (SNS).  The sapphire cell is rated to a pressure of 5000 psi and operational at temperatures ranging from 10-300K.  Internal instrumentation is limited to one port and is typically reserved for temperature.  Due to the sapphire construction of the cell visual observation is not restricted to windows as is the case with the SPS and Parr vessel.  In addition to the sapphire cells compatibility with sophisticated instruments it is also has potential application for characterizing sediments containing hydrate. 

Fiber Optic Distributed Sensing System (DSS)

Fiber optic distributed sensing system (DSS) capable of collecting time-resolved temperature (+/- 0.1 degree resolution) and/or strain measurements over a 3-D grid at cm-scale resolution (include link to Luna website: http://www.lunainnovations.com/products/dss.htm) Bragg filters are placed at 1 cm intervals along a fiber optic cable allowing for high resolution temperature and strain data to be collected within large volumes of sediments.  This will allow us to monitor hydrate formation/dissociation within the sediment by measuring slight increases/decreases in temperature that result from the exothermic/endothermic nature of the reaction. In addition, we will monitor fluid flow paths, and temperature gradients within the 72 liter vessel.

Raman Spectroscopy

Raman spectroscopy can be used to positively identify the formation of hydrate inside the Parr vessel or sapphire cell.  Using the spectroscopy method it is possible to determine the hydration number of the hydrate analyzed.  Raman spectra analysis of a mass of hydrate composite consisting of liquid CO2, CO2 hydrate, and water can be used to determine the percentage of each component in the composite.  

Low Temperature X-Ray Diffraction

A Scintag XDS 2000 diffractometer with a vertical theta/theta goniometer and the following specifications is available for hydrate characterization:

*He closed-cycle refrigeration attachment (10-300K)

*Phase identification and lattice parameters as a function of temperature, which can be used for dissociation and thermal expansion studies

*Loading in flowing He glove bag

*Position Sensitive Detector (PSD) - in-situ, time resolved studies

Neutron Diffraction

Neutron diffraction facilities with the following specifications are available:

*Low temperature data collection

-        -Thermal expansion

-        -Thermal stability

*High pressure data

-        -Bulk modulus

-       - Pressure stability

*Vibrational modes

*Guest-host interaction studies

Neutron Scattering at the Spallation Neutron Source (SNS) 

The Spallation Neutron Source:

*Online in 2006

*Most intense pulsed neutron beam in the world at ORNL

*Partnership of 6 DOE labs- $1.4 billion

*Compliments existing facilities at HFIR

The SNS is ideal for:

*Neutron scattering and diffraction of deuterated samples

*Ideal for H-rich materials like hydrate

*Allows isolation of guest molecules or ice structure

*Guest molecule dynamics

*Hydration number