|A sketch of a smaller airship. Credit: Jesse Blenn|
A small Bolivian company, Reparando SA, is exploring the delivery of natural gas (NG) delivery to remote areas by using an airship, rather than a pipeline. Reparando is a heavy equipment repair and road construction company that moved into selling and installing bifuel natural gas conversion systems for heavy-duty diesels (running the engines on 70% NG).
The company worked with Jesse Blenn, a US airship expert, on a preliminary design for a 150-meter airship capable of carrying about 35,000 Nm3 of natural gas . The basic design is extensible up to a length of around 300m, which would result in a ship capable of carrying about 300,000 m3.
At 35,000 m3, the volume is approximately equivalent to the compressed gas carried by three natural gas tank trucks. But in some areas of Bolivia where the roads are bad, it could take a truck up to one week to go 500 miles.
The ship as designed uses twelve internal inflatable gasbas: six for helium (the ship requires about 40% helium volume to lift the empty structure) and six for natural gas. The upper six bags hold the helium, the lower six the natural gas.
This, Blenn points out, is very similar to the design of the system used by the Zeppelin Graf Zepplin I (LZ 127) in which the lower bags carried fuel gas which weighed nearly the same as air, and deflated as the fuel was used. The LZ 127 racked up nearly 1 million kilometers in flight.
With the natural gas on board, the ship has additional lift to carry diesel fuel, although the goal is to convert the airship engines to run primarily on natural gas. The diesel serves as ballast and backup. When running on natural gas, the four engines would consume about 3% of the natural gas payload in a round trip of 1,000 kilometers at a speed of 100 km/h.
Discharge of the natural gas occurs through the mooring tower. The airship carries a normal operating pressure of about 35 mm water column, which will push the natural gas out within about 20 minutes through the twin NG valves.
The twin nose engines supply the pressure and the 35,000 cubic meters of replacement internal air volume). (Four other natural gas engines provide propulsion.)
The mooring tower will include a proprietary automatic valve connection (purged with CO2), and a seal and bearing system which conduct the gas down to a duct where an auxiliary fan maintains the flow to storage. The reverse process handles the filling, but the inflation pressure is supplied from the tower base, not the engines.
Blenn estimates that the airship could be built for around $US3 million (in South America). Airships, according to Blenn, have an operational life of about 10 years to first replacement of the outer fabric, and several decades for hard structures if refurbished.