© 2019 Department of Petroleum Resources. All rights reserved Department of Petroleum Resources (DPR) PROCEDURE GUIDE

Page 97 of 114
 
96 | P a g e 
 
 
Xn =  the value of Xi for nitrogen; and 
 
W = Wobbe Index of Regasified LNG in MJ/m3(st) calculated in accordance with 
the formula: 
W  =    𝐻𝑣
√𝑑𝑟
   
                       Where: 
 
 
 
dr= relative density of Regasified LNG compared with air 
calculated in accordance with the formula: 
𝑑𝑟  =    
∑( X𝑖 * M𝑖)
28.9625    
 
 
1.18 FUEL GAS MEASUREMENT 
 
1.18.1 Special consideration for fuel gas system 
For single meter run configuration, it shall be possible to route the gas stream through 
a bypass line for inspection and maintenance of the fuel meter run. When the system is 
in this bypass mode, flow calculations shall continue based on average flow rate in a 
user selectable time periods (that is from one minute to one hour) prior to opening to 
by-pass. 
 
Orifice meter should be preferred to gas turbine meter unless the cost of long upstream 
meter run lengths for the orifice meter outweighs the cost of annual flow calibrations 
at operating conditions of the gas turbine meter, and the cost of one spare gas turbine 
meter (in stores). 
 
Also, a gas turbine meter should be preferred if the flow range of the fuel stream 
requires frequent changes of orifice plates during regular operation. 
 
For every small fuel gas stream, in particular non-fuel streams withdrawn from the fuel 
distribution system downstream of the main fuel metering system, the following 
methods should be considered: 
 
• 
For streams smaller than specified by ISO 5167 and AGA 7, one of the 
following methods shall be used: 
 
- Small, full bore, gas turbine meters, designed to manufacturer’s standard 
(minimum 6 mm). 
- Integral orifice meters (smaller than 12 mm). 
 
- Other suitable type of small flow meter with equivalent accuracy. 
 
1.19 FLARE GAS MEASUREMENT 
 
1.19.1 Functional requirements 
1.19.1.1 General 
 
The system shall measure flow rate and accumulate quantities of flare gas, in 
accordance with the following guides. The calculation can either be done in a dedicated 
flow computer or in SAS. If the flare gas releases are due to the operational upset,