The goal is to enhance flexibility in the siting of natural gas storage for distributed generation and peaking facilities.
Mississippi State University (MSU) - Swalm School of Chemical Engineering Diagnostic Instrumentation and Analysis Laboratory
Mississippi State, Mississippi 39762
This project is designing, constructing, and demonstrating (on a proof-of-concept (POC) scale) a gas hydrate formation and dissociation process suitable for safe, aboveground storage of natural gas. A scaled-up test of a promising laboratory process that operates at moderate pressures and temperatures in a quiescent system using a surfactant solution is being conducted.
The current distributed electric generation model in the United States is primarily designed to provide emergency and stand-by power to minimize the impact of electric outages. This service is dominated by diesel generating equipment because of the need for on-site fuel storage. Successful scale-up of this inherently safe gas-hydrate laboratory process for on-site storage of natural gas could facilitate penetration of distributed electric generation or smooth peaking requirements of industrial processes. On-site natural gas storage would guard against electric utility outages and supplement low pressure or availability of gas from the servicing pipeline during periods of peak demand.
When cooled in the presence of water, natural gas molecules become stabilized within a compact crystalline structure (gas hydrate) that can serve as an efficient method for storing gas. Theoretically, 181 standard cubic feet (scf) of natural gas can be stored in one cubic foot of gas hydrate. This project is designed to test the concept of using gas hydrates to safely store natural gas aboveground near end-users.
A test bay (consisting of roof, concrete pad, and control room) to accommodate the hydrate tests was constructed. Upon completion of the process facility structure, the hydrate formation tank, deionized water supply, chiller, burner/boiler, and surge tanks were all put in place. Piping, insulation, wiring, and other installations to integrate the system were also completed at this time. Hebeler Corporation constructed the formation tank and it was delivered to the test site in MSU's Research Park in July 2003. The 3-foot diameter, 6-foot long tank was constructed according to ASME Boiler and Pressure Vessel Code specifications and was pressure and leak checked before delivery.
The system operates by using a glycol-water solution to cool the system. The solution is circulated from a 12-ton capacity chiller through heat exchanger/adsorber plates inside the hydrate formation tank and then in series through the exterior jacket of the tank. Disposal of gas from dissociated hydrates at the end of each run is burned in a steam boiler, simulating the eventual end use of the gas in an industrial application.
Start-up testing of the gas hydrate storage system was conducted in March 2004. Equipment and instrumentation checkouts were successful. There were no leaks in the hydrate formation tank when the vessel was hydrostatically tested to 850 psig, the 12-ton refrigeration system performed satisfactory in the checkout and the desired 28°F circulating glycol-water solution was achieved. The chiller cooled the 210 gallons of water in the formation tank from ambient temperature to the desired 35°F operating temperature within 3 to 3.5 hours.
Natural gas (90 percent methane, 6 percent ethane, and 4 percent propane) was injected into the headspace of the vessel above a 33.8°F to 37.1°F water – SDS solution. Gas was injected in five batches until a pressure of about 550 psig was attained. Hydrates formed immediately and pressure declined to about 470 psig. The procedure was repeated with four more batch injections of natural gas. The gas stored in the hydrates during the test represented about 15 percent of the full 5 Mscf storage capacity of the system. Pressures, temperatures (taken via probes at five locations), gas flow rates, and water levels in the hydrate formation tank were monitored and recorded every five minutes. The hydrates decomposed when pressure in the tank was reduced below the equilibrium pressure.
Testing of the gas hydrate storage system at full system capacity and at constant formation pressure is completed. The final report [PDF-3.15MB] is now available.