Boil-off gas compressor for LNG fueled ship

1. A boil-off gas compressor for LNG-fueled vessels using LNG as fuel for propulsion engines of the LNG-fueled vessels, the boil-off gas compressor comprising:

a compressor housing;

an impeller housed in the compressor housing and configured to rotate to compress combustible boil-off gas;

a motor housing;

a motor housed in the motor housing and configured to drive the impeller;

a partition wall disposed between the compressor housing and the motor housing;

a rotational shaft connecting the motor and the impeller and configured to transmit rotation driving force of the motor to the impeller;

a first bearing configured to support the rotational shaft; and

a second bearing configured to support the rotational shaft,

wherein the first bearing and the second bearing are disposed in the motor housing, and the motor is interposed between the first bearing and the second bearing,

wherein the first bearing is spaced from the partition wall and disposed in the motor housing between the partition wall and the motor, the first bearing being configured to lift the rotational shaft such that a bearing gap is formed between the first bearing and the rotational shaft,

wherein the compressor housing and the motor housing are integrally formed and partitioned by the partition wall,

wherein there is a leakage gap between the partition wall and the rotational shaft,

wherein the compressor housing is in fluid communication with the motor housing through the leakage gap between the rotational shaft and partition wall configured to allow the combustible boil-off gas to leak from the compressor housing to the motor housing through the leakage gap such that the combustible boil-off gas received in the motor housing causes a pressure inside the motor housing to be higher than atmospheric pressure and inhibit external oxygen that would have caused explosion from flowing into the motor housing.

2. The boil-off gas compressor according to claim 1 , wherein the motor is driven by a high speed frequency inverter and the impeller is directly connected to the motor without a separate set-up gear.

3. The boil-off gas compressor according to claim 1 , wherein each of the first bearing and the second bearing is a self-lubricating type bearing not using lubricant oil.

4. The boil-off gas compressor according to claim 1 , further comprising a secondary compressor housing and a secondary impeller housed in the secondary compressor housing, wherein the impeller and the compressor housing are disposed at one of both sides of the motor housing, and the secondary impeller and the secondary compressor housing are disposed at the other of both sides of the motor housing.

5. The boil-off gas compressor according to claim 4 , wherein the compressor housing and the secondary compressor housing are connected to each other such that the boil-off gas compressed while passing through the impeller is cooled by an intermediate cooler and then supplied to the secondary impeller such that the boil-off gas is additionally compressed by the secondary impeller.

6. The boil-off gas compressor according to claim 1 , wherein the partition wall between the motor housing and the compressor housing comprises an insulating member.

7. The boil-off gas compressor according to claim 6 , further comprising a heater configured to avoid decreasing of the motor's temperature.

8. The boil-off gas compressor according to claim 1 , further comprising:

a pressure sensor configured to detect the pressure of the interior of the motor housing.

9. The boil-off gas compressor according to claim 1 , wherein the motor housing comprises a supply hole through which an inert gas is supplied from an exterior to the motor housing and a vent hole through which an interior gas is discharged.

10. The boil-off gas compressor according to claim 1 , wherein the interior of the motor housing is filled with the combustible boil-off gas.