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In the gas producing plant (onshore or ofshore), the gas metering

system is the nal stage o the production step beore it send to the end user

o the gas product. It plays a very important role as a custody transer meter.

Every measurement is required as practical as possible to have a very

accurate measurement or a very minimum error. This issue (measurement

accuracy or error) is very important since it ill determine the quantity o the

gas product that ill be paid by the customer. !arger the error means less

money that ill be paid by the customer in correlation ith the amount that

they received. "ince it plays very important role and almost appear in every

gas producing plant, it ill be good or us to #no the basic principle

regarding this gas metering system. "o hat is the basic principle to

measure the gas that ill be e$ported%

&irst o all, there ill alays be a contract beteen the plant business

units ith the customer. This contract stated the quantity and quality o thegas that they ill buy. The quantity o the gas ill be measured by an

ultrasonic 'o meter. The used o the ultrasonic 'o meter is the most used

'o measurement device right no, but or alternative e can also use an

orice ith diferential pressure transmitter as a measurement device.

sually, it requires a $ *++ 'o meter stream ith active and standby

stream.. This ultrasonic 'o meter installation - conguration shall conorm

to / 0 standard - codes.

"ince the 'o o a gas is very afected by pressure and temperature,

the pressure and temperature transmitter ill also install in the donstreamo the ultrasonic 'o meter to compensate the 'o reading. ll ro

measurement data ill ed to 'o computer to determine the actual gas 'o

in relation ith pressure and temperature variation.

The quality o the gas is related to composition and characteristic o

the gas. The composition o the gas ill be measured by gas chromatograph

and presented in orm o composition. &or e$ample or particular

measurement, 123 (methane) composition is 04, 1 (ethane) composition

is +.+5, etc. This composition data ill be ed to the 'o computer to

calculate the /ross 2eating 6alue (/26). The use o this gas chromatographand also the calculation o /26 shall conorm to /78*9 and /78:*

standard - codes.

The characteristic o the gas ill be measured by a moisture and de

point analy;er. The need o measuring moisture is related ith the ater

content in the gas. The ater vapor in the natural gas mi$ture doesn

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Thus the e$cess o the ater content in the gas ill reduce the value o the

gas. That?$ emission,

and can caused several damage. The de point analy;er ill inorm the end

user so that they can establish a pre8heat stage beore they use the gas to

prevent the condensation orming. The installation and consideration osampling system o this analy;er (de point and moisture) shall reer to 7I

@7 555.

ll the data regarding the measured quantity and quality o the gas

being e$ported can be monitored in the 2uman Aachine Interace (2AI)

called metering station computer. This computer is the interace beteen all

instrument equipment and the operator. The operator can chec# the history,

print the report, diagnose the 'ometer etc. It also the interace beteen

the gas metering system ith other control system available at the plant

such as 71" (7rocess 1ontrol "ystem), E"B (Emergency "hutdon) systemetc.

s a conclusion, e can conclude that the gas metering system

assembly consists o the olloing sub8s#idC

*. Aetering s#id, consist o ultrasonic 'o meter, pressure transmitter,

temperature transmitter, pressure gauge, temperature gauge etc.

. naly;er shelter, consist o gas chromatograph, de point analy;er,

and moisture analy;er.

D. /as metering panel, consist o 'o computer and station computer

(usually gas metering panel are located inside the control room).7lease ta#e note that the mentioned sub8s#id is only or simpliy our

understanding. &or detail arrangement, e should reer to any particular

proect requirement. Fut in typical, the system ill be more or less similar to

the arrangement above. "ee belo picture to get more clear understanding.