Safety design of the boil-off gas burning system is required for safety transferring and safety burning of the boil-off gas led from the cargo tank to the main boiler as a fuel.
Here the essential design conditions and problems on the safety design are enumerated and among these problems the characteristics of boil-off gas/oil combined firing are picked up to investigate.
The firing test was carried out in a test furnace by natural gas using two kinds of actual dual fired burners, one of ring type gas nozzle and the other of multi-lance type gas nozzle.
The dual firing characteristics are got from the above test and the minimum considerations for safety design of the dual firing system from a firing characteristics point of view are obtained on the following items:
(1) Safe combustion ratio of fuel oil and fuel gas including consideration for minimum quantity of either fuel oil or fuel gas.
(2) Excess air supply ratio at each stage of normal operating, load changing and starting of dual firing.
(3) Consideration for keeping stable combustion and for protecting furnace from rapid rising of the internal pressure of the furnace during a rapid load change.
(4) Consideration for keeping safe combustion even if a great deal of inert gas is mixed with fuel gas.
(5) LPG/N
2 mixture gas having equivalent firing characteristics and flame stability to methane gas, which can be substituted for methane gas in the shop test of dual firing.
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