Page 44: of Maritime Reporter Magazine (September 1973)

MA Awards Contract To Garrett

To Study Brayton Cycle Power

The U.S. Department of Commerce Maritime

Administration has awarded The Garrett Corpo- ration a $310,000 cost-shared contract, which is the initial study in a program to develop ad- vanced closed Brayton Cycle turbine power for a liquefied natural gas ship refrigeration system.

The Quincy Shipbuilding Division of General

Dynamics, which is building three of the cryo- genic tankers, will act as a subcontractor to

Garrett on the project. The Garrett study will be conducted by both AiResearch Manufacturing

Company of Arizona and AiResearch Manufac- turing Company, Los Angeles.

During the study phase, a 9,000-shp closed- cycle engine will be designed for auxiliary power applications. This engine, which would be the largest of its kind yet developed, would provide power for a liquefied natural gas refrigerator system for LNG tankers.

The refrigeration system, also being designed under the contract, is of an advanced design which will insure zero boil-off of the LNG cargo.

This functional application for advanced engine technology promises increased efficiency for LNG shipping systems by eliminating boil-off of the cargo.

A secondary objective is to look beyond the 9,000-shp power plant and define a technologi- cally advanced, economical, closed gas turbine main propulsion plant. Such advanced propulsion systems could be incorporated into future large cargoships in the 1980-90 time period.

If the study proves successful, a second phase will follow during which a 9,000-shp liquid natural gas refrigeration system will be built and de- livered by the end of 1976. General Dynamics is presently building a tanker capable of carrying 125,000 cubic meters of liquid natural gas. It is anticipated that the closed-cycle LNG Refrigera- tion System will be installed on this tanker, al- though the system has been sized for a second generation LNG tanker having a capacity of 165,000-200,000 cubic meters. The experience gained with the 9,000-shp auxiliary power unit for the refrigeration system is expected to pro- vide a technological building block for develop- ment of the closed-cycle power plant as main propulsion.

The closed gas turbine engine is a sealed system in which the working fluid, clean dry gas, is con- tinuously recirculated through the engine. High pressures of 200 to 500 psi are used to minimize the physical size and weight of the system.

The use of clean dry gas as the working fluid assures corrosion-free operation with low mainte- nance and long life. The engine is extremely efficient, with specific fuel consumption compar- able to a diesel. It can operate on a variety of fuels, produces very little noise, and is vibration free. Very low exhaust pollution results from the external combustion approach.

A closed Brayton Cycle power plant differs from an open-cycle, an example of which is a jet engine, in that gases are continually recircu- lated in a closed loop. In the proposed closed- cycle power plant, the gas is compressed in con- ventional gas turbine fashion by a rotating compressor. After the gas exits the compressor, it is heated by passing through a recuperator and then a radiant heater, which takes the place of combustion in an open-cycle gas turbine.

The heated gas then passes through a turbine and into the recuperator, where heat is rejected into the compressor discharge air. After passing through the recuperator, the gas goes through a cooler which lowers the temperature to near ambient levels. The gas then re-enters the com- pressor to complete the loop.

The relatively low weight and small size of the 9,000-shp unit permit it to be containerized and quickly installed on the ship deck structure.

The LNG Refrigeration System is a fully- sealed reverse closed Brayton Cycle system in which mechanical energy is put into the system and thermal energy is extracted. This is a re- verse of the process of the standard Brayton

Cycle. In the LNG Refrigeration System, me- chanical energy is put in through a compressor, and thermal energy is extracted by multiple heat transfer units and a turbo-expander. The system uses gaseous nitrogen as its working fluid and employs heat transfer equipment of conventional design.

The heart of the LNG Refrigeration System is a patented AiResearch turbo-expander unit utilizing gas bearings. Use of gas bearings elimi- nates conventional oil lubrications systems, there- by reducing maintenance, increasing operational life, and preventing contamination of the process fluids. Gas bearings also eliminate the need for dynamic bearing seals.

The LNG Refrigeration System, like the closed gas turbine power plant, will be containerized and mounted on the deck structure.

As part of the contract work, the method of integrating the LNG Refrigeration package into the ship with minimal impact will be studied.

Other goals of the study are to evaluate optimum cycle efficiencies and operational techniques, op- eration and life cycle costs, maintenance and time between overhaul expectancies, and overall eco- nomics. The system will be designed in accord- ance with the American Bureau of Shipping and

U.S. Coast Guard regulations.

General Dynamics will provide design guidance from the shipbuilder standpoint and will assure that appropriate maritime codes are met. Gen- eral Dynamics' role also is to study the economics of ship operations.

The Garrett Corporation is located at 9851

Sepulveda Boulevard, Los Angeles, Calif. 90009.

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