Modelling embedded technologies in energy service networks - Modelling Distributed Energy Resources in Energy Service Networks - page 58

Some important characteristics that centrifugal compressors possess are [171]:

Maintenance costs are low due to few moving parts;

●

Water cooling is not necessary for operation;

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A high flow processing capacity with a constant continuous delivery.

●

In a centrifugal compressor work is provided on the gas by an impeller which at
a high velocity is then discharged into a diffuser. Subsequently, the gas velocity is
reduced and its kinetic energy is converted into static pressure which increases the
outlet potential of the fluid. This type of compressor consists of a casing with flow
passages, a rotational shaft fixed to the impeller, bearings and seals to prevent gas
leakage along the shaft.

4.2.2 Compressor modelling equations
Based on its features explained in the previous section, when operational the
compressor is modelled as an additional load in the gas system. Hence, the main equa-
tion employed in natural gas network analysis for a compressor is the horsepower load,
which is a function depending on the amount of gas flowing through the control device
and the pressure difference between the suction and discharge points.
Figure 4.6 shows a simple illustration of a compressor present in node k . Variable
G km specifies the thermal power being provided by flow F km , which is directly pro-
portional to the gross heating value (GHV) of the fluid. Related to terms (3.37) and
(3.53), the thermal power flowing through a low pressure pipe km can be detailed as:

p k 2 − 1 / 2

p m

G km = GHV · (4.17)

K km

The equation that calculates the amount of horsepower the compressor consumes
when active can be described as [174]:

G com
Dk

K com
k

= · G km ( p k 2 − p k 1 ) (4.18)

Term (4.18) determines the load demand for compressor G com

Dk , measured in ther-
mal power and is a function of the inbound and outbound pressures, p k 1 and p k 2
respectively. Similarly, the compressor load is also influenced by the rate flow going
through the device G km and the efficiency factor of the compressor K com
k

.

p k 1 p k 2 p m

com

G jk

G km* G km

G Dk com

Figure 4.6 Representation of gas pipeline with a compressor station [129]