Solartron Mobrey 7828, Technical Manual

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7828 Density Transmitter Technical Manual
Calculated parameters
78285000_AA
B-3
B.2.2 API DENSITY REFERRAL
This calculation uses an iterative process to determine the density at the base
temperature by applying temperature and pressure corrections using the API-ASTM-IP
petroleum measurement tables.
The information required for the API density is:-
•
Reference pressure and reference temperature
•
Line pressure - this is not measured by 7828, and must be entered as part of the
configuration.
•
Product type: Refined product, crude product or user defined.
Density/Temperature Relationship
Correction factors in the revised API-ASTM-IP petroleum measurement tables are based
on the following correlation equations:
ρ
t /
ρ
15
= exp ( -
α
15
∆
t ( 1 + 0.8
α
15
∆
t ) )
where:
ρ
t = Density at line temperature t
°
C
ρ
15
= Density at base temperature 15
°
C.
∆
t = (t - 15)
°
C
α
15
= Tangent thermal expansion coefficient per deg C at base
temperature of 15
°
C.
The tangent coefficient differs for each of the major groups of hydrocarbons. It is
obtained from the following relationship:
α
ρ
ρ
15
0 1 15
15
2
=
+
K K
where K
0
and K
1
are known as the API factors.
Hydrocarbon Group Selection
The hydrocarbon group can be selected as:
•
General refined products
•
General crude products
•
User defined.
K
0
and K
1
are programmed into the 7828 for the first two groups.