[ Pobierz całość w formacie PDF ]
.Thistechnology is compatible with renewable energy systems, but the draw-back is the amount of energy necessary to maintain such a storage sys-tem.Dedicated photovoltaic panels or wind generators would need to beadded to compress the gas.Hydride storage has a lot of promise for com-pact hydrogen storage, and is a good avenue of inquiry for the renewableenergy enthusiast.An explanation of the hydride process and a practicalmethod of working with hydrides is discussed in The Solar HydrogenChronicles, edited by Walt Pyle.Metal organic frameworksCurrently, metal organic frameworks (MOFs) also look very promising for180solar hydrogen systems.These materials do not require high pressures and Gas processing systemhigh temperatures to operate the system, so they do not require the level ofextra energy input that hydride systems need.With only modest pressure atroom temperatures, hydrogen can be adsorbed and retrieved in MOFs.Onegram of a metal organic framework can have a surface area of 3000 squaremeters.It is also a very inexpensive material.Low tech alternativesProbably the most convenient gas storage options for the averagerenewable energy experimenter are low pressure storage in bags; and low,medium or high pressure storage in hollow tanks.Containers for low pressure storage (under about 60 psi) can be bladdertanks, pillow tanks, collapsible pressure vessels or LPG tanks.Most flexibletanks store gases at just a little above atmospheric pressure.Manufacturerssuch as Aero Tec Laboratories offer flexible storage devices.LPG tanks or other tanks made with a good grade of stainless steel aresufficient for medium pressure storage (60 to 125 psi).Stainless steel witha high nickel content and very low carbon content is more resistant tohydriding, otherwise known as embrittlement.(Hydriding is a great char-acteristic for the storage medium in a hydride storage system, but it s nota good characteristic for containment tanks!)181 Gas processing systemEmbrittlement occurs when the metal absorbs hydrogen which cancause the metal to crack.If you make your own tanks, to prevent hydrogenfrom getting into the metal, do not use water while welding.Also, preheatthe metal before welding and allow the weld to cool slowly.Embrittlementproceeds faster at high pressures and higher temperatures.High pressure storage, around 2000 psi and uprequires specially constructed high pressure cylinders.Double drum storageShort term storage can also be accomplished intanks or drums that would not be considered or usedfor long term storage.For instance, I use recycled 55gallon drums for oxygen and hydrogen storage.Thesedrums are very inexpensive and I can quickly weld thetops on, fabricate a relief port and inlet/outlet portquite easily.With some drums I have epoxied the topson.For me it works, as I do not use them for more thanone season.The drums are readily available and theprice is right.Two recycled55 gallon drumsI do have to be concerned about what was stored infor short term182gas storagethe drums beforehand.Contaminating the hydrogen Gas processing systemsupply with prior drum contents can be a problem.The drums must beabsolutely clean from contaminating substances.Although I use this tem-porary storage method for my experiments, I must caution the reader thatstorage in any thing other than your AHJ approved storage devices is notan officially sanctioned practice and is not considered safe.For drum storage, two 55 gallon drums are needed.One drum is securelypositioned above the other.The top drum has a constantly open vent whichreleases any excess gas that cannot be stored in the drums.The bottomLow pressurestorage indouble tanksusingwater pressure183 Gas processing systemdrum has a gas inlet near the top of the drum.It has an outlet on the otherside near the bottom.A transfer tube connects the bottom tank to the toptank.The bottom tank is filled with water and when gas is routed to thetank, it pushes the water through the tube and through to the top tank.Thegas is partially pressurized by the weight of the water in the top tank.It isa simple affair and works quite well.Any type of general gas or barb fittings can be used to make the gasoutlet port and inlet and transfer ports.I usually epoxy these into place.The regulator needs to be positioned at a height above where the gasfeeds in to the bottom drum, so that water does not flow into the regulatorwhen the bottom drum is filled with water.I could expand my storage byconnecting up more pairs of drums.Floating tank storageA water tank storage device can be built, very much like those used tostore methane in some rural areas.This consists of an inverted drum ortank within another tank or drum that is filled with water.As the gas fillsthe inner tank, the inner tank floats upwards in the water, and is kept fromtilting by guide rails or guy wires.A stop keeps the tank from rising total-ly out of the water.For a more permanent setup, round concrete spring184tiles can be put in the ground and a inverted tank inserted for larger area Gas processing systemgas storage.This is an easily builtstructure and relatively inexpensive,the most costly part usually being thefabrication of the inverted tank.Tankscan be made from fiberglass, andother resin cloth type products.Largesize tanks can also be purchased fromsuch places as Aquatic Eco Systems,or other agricultural suppliers.Calculating tank capacityTo calculate the cubic foot capacityof a cylindrical tank, multiply 0.79times the diameter
[ Pobierz całość w formacie PDF ]