Abu Dhabi Gas Liquefaction Company Ltd Job Training Mechanical Technician Course Module 9 Compressors

 
Boil-off gas (BOG) compressors in the STOREX area take vapour from the top of 
the LNG tanks. This vapour (gas) is removed to help maintain the correct operating 
pressure inside the tanks during filling and emptying operations. Before the BOG 
compressors were installed the boil-off gas was all sent to flare. The BOG 
compressors help to save money by using this gas. They also reduce pollution by 
reducing the amount of gas going to flare. 
(a) V-type Reciprocating Compressor—Front View 
(b) V-type Reciprocating Compressor—Rear View 
Figure 4.16: Emergency Air Compressor (Tag# 35-K-2)
Electric motor 
Belt drive 
Cylinder 
Figure 4.17: Air Compressor for Diesel Start-up (Tag# 33-K 301B) 

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Personnel & Training Division
Job Training—Mechanical Technician 
Compressors/Rev. 0.0 
Page 27 of 90
There are two BOG compressors, known as the ‘Old’ BOG (Tag# 27-K-103) and the 
‘New’ BOG (Tag# 48-K-301). Both are driven by electric motors. 
Gas from the New BOG compressors is used as fuel gas in Train III boilers and gas 
from the Old BOG goes to fuel heaters in Trains I and II regeneration equipment. 
The Old BOG compressor is: 
• in-line vertical
• three-stage 
• four-cylinder (four casings) 
• double-acting 
There is one crankshaft housed in a single crank case. This crankshaft operates all 
four pistons. The four cylinders are housed in four separate casings and are connected 
so that:
• two stage-1 cylinders are connected in parallel 
• stage-2 and stage-3 cylinders are connected in series with the stage-1 cylinders 
This arrangement is shown in Figure 4.18. 
Figure 4.18: Cylinder Configuration of Old BOG Compressor 
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