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ASSIST FOR CHEMICALS
by H. Zetzsche,
In 1965 Esso Chemie G.m.b.H. of Hamburg negotiated a long-term contract for the supply of propylene from its plant in
Cologne to a large chemical firm on the Wesel-DatteIn Canal in the Ruhr, After checking the cost of using a commercial
shipper to transport the gas, Esso Tankschiff Reederei G.m.b.H. investigated the possibility of using one of its own inland
waterway vessels.
Economic and technical considerations made the 800-ton asphalt barge Esso Erlangen an ideal candidate for conversion
to a gas tanker. Over the past few years, asphalt plants had been established at all refineries of Esso A.G. in Germany.
As production had risen, imports from Belgium had declined and so had the need for special asphalt vessels traveling
from Antwerp up the Rhine. At the same time, the Esso Erlangen was fitted with two suspended insulated tanks which
could be replaced with pressurized gas tanks while utilizing the same foundations. This avoided having to remove the
bulkheads and install additional stiffenings, which would have made the project not worth the effort.
The conversion began by lengthening the 220-foot-long ship by 49 feet (67 and 15 m) and removing and selling the
asphalt equipment.
She was then sent to Cologne to Pintsch Bamag A.G., a firm specializing in the manufacture of pressure tanks. Here
were installed four gas tanks, two of approximately 8,570 cu. ft. (243 m3) and two of 8,720 cu. ft. (247 m3). The 434
tons of propylene (density 0.521) they can carry are enough to meet the terms of the contract on each delivery.
Designed for an operating pressure of 293 psig (20 atii) and a test pressure of 410 psig (28 atii), these cylindrical pres-
sure tanks are equipped with an arched dome containing hose valves and fittings. They were welded electrically, and
the circumferential and longitudinal welds were subjected to an X-ray test. For uniform loading and discharging, they
are connected by pipeline.
In replacing the Esso Erlangen's asphalt tanks with pressurized gas tanks, Esso Tankschiff was
able to make use of the original foundations. Here, one of the four new propylene tanks is lowered
into position on the 269-foot-long ship.
A spray phase permits liquid propylene to be sprayed into the gas compartments. This prevents an increase in pres-
sure or at least keeps the pressure within reasonable limits, because gas present in the vessel is cooled and liquefied
by the liquid gas entering the tanks through the spray line.
While the tanks were being installed, loading equipment was made ready. Meeting the latest operating and safety re-
gulations, this equipment is fitted with metal loading arm swivel joints. Liquid propylene is pumped from the refinery
into the tanks of the Esso Erlangen at a pressure of approximately 176 psig (12 atii). With a 6-inch (150 mm) hose,
she can be loaded in about five hours.
At the customer's discharge terminal, pure gas is pumped at 50 to 60° C. (122 to 140° F.) from shore into the vessel's
tanks at a pressure higher than the pressure in the tanks. The resulting pressure on the surface of the liquid in the
tank forces it through an immersion tube, and it is led off to the shore tanks. This method obviated the installation of
a separate pump unit on board, which would have reduced the ship's capacity and raised the cost of converting it.
The discharge time is about four hours.
The safety facilities on the Esso Erlangen have earned the praise of authorities. Each tank has two locked safety
valves (one is a standby valve) to relieve any excess pressure. Other hydraulically operated safety valves shut off
the loading pipe immediately in case of danger. A gas-detecting system warns the crew both acoustically and opti-
cally when the smallest quantities of gas are present. A gasalarm unit in the wheel-house checks the gas concen-
tration in the forward and aft holds, in the crew room and in the engine room.
The newly converted LPG tank barge loads at the gas terminal of Esso Chemie in Cologne. Loading
equipment was fitted with metal loading-arm swivel Joints. Instruments on the tank domes indicate
contents and pressure, which can be relieved immediately through safety valves.
A number of operating precautions are observed. Other ships are not allowed in the loading and unloading areas,
and the Esso Erlangen's broad yellow band serves as a warning forbidding other vessels to come alongside. She
is given the right of way in the locks on the Wesel-Dattein Canal.
The Esso Erlangen has been transporting propylene regularly from Cologne via Friedrichsfeld on the Rhine through
the Wesel-Dattehi Canal to the customer's terminal in Marl since July 1967 without difficulty and to the complete
satisfaction of the customer. She is good evidence of the importance of close cooperation between Esso marine
and chemical affiliates - cooperation which in Germany is to be intensified in the future.
The author is in charge of the Inland Waterway Department of Esso Tankschiff Reederei G.m.b.H.