Ingeniero Petroleo

SECTION 14

Refrigeration
Selection of a refrigerant is generally based upon temperature requirements, availability, economics, and previous experience. For instance, in a natural gas processing plant, ethane
and propane may be at hand; whereas in an olefins plant, ethylene and propylene are readily available. Propane or propylene may not be suitable in an ammonia plant because of theRefrigeration systems are common in the natural gas processing industry and processes related to the petroleum refining, petrochemical, and chemical industries. Several
applications for refrigeration include NGL recovery, LPG recovery, hydrocarbon dew point control, reflux condensation for
light hydrocarbon fractionators, and LNG plants.

FIG. 14-1
Nomenclature
GHP
h
h′VD
k
m
n
P
Q
r
ST
W
X
η
σ
ρ
∆h

=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=

gas horsepower defined by Eq 14-7b
enthalpy, Btu/lb
isentropic enthalpy, Btu/lb
specific heat ratio
refrigerant flow, lb/hr
number of stages
pressure, psia
heat duty, Btu/hr
compression ratio
entropy, Btu/(lb • °R)
temperature, °F
work of compression, Btu/hr
weight fraction
isentropic efficiency
surfacetension, dynes/cm
density, lb/ft3
enthalpy change, Btu/lb

Subscripts
L = liquid state
V = vapor state
A, B, C, D = denote unique points of operation on P-H
diagrams
b = bypass
i = isentropic
cd = condenser
ref = refrigeration
s = suction
d = discharge
n = stage number
T = Total
1, 2 = stage number

Expansion valve: a valve for controlling the flow of refrigerant to an evaporatoror chiller.
Flash gas: the gas resulting from the instantaneous evaporation of refrigerant by a pressure reducing device, such as
a control valve.
Frost Plug: small diameter closed nozzle protruding from
the side of an insulated vessel which indicates liquid level
in the vessel by accumulation of frost.
Halocarbons: a family of refrigerants consisting of fluorinated and/or chlorinatedhydrocarbons.
Hot gas bypass: warm discharge gas recycled to chiller for
maintaining system’s operating integrity at minimum load
conditions.
Liquid refrigerant receiver: a vessel in a refrigeration system designed to ensure the availability of adequate liquid
refrigerant for proper functioning of the system and to store
the liquid refrigerant when the system is pumped down.
Refrigerant: the fluidused for heat transfer in a refrigeration system, which absorbs heat at a low temperature and
low pressure and rejects heat at a higher temperature and
a higher pressure.
Ton of refrigeration: amount of heat required to melt 1 ton
of ice in 24 hours, equivalent to 12,000 Btu/hr at 32°F.

Accumulator: a storage vessel for liquid refrigerant; also
known as surge drum.
Bubble point: thetemperature at which the vapor pressure
of the liquid refrigerant equals the absolute external pressure of the liquid-vapor interface.
Capacity, refrigerating system: the cooling effect produced
by the total enthalpy change between the refrigerant entering the evaporator and the refrigerant leaving the evaporator.
Chiller, Evaporator: a heat exchanger in which the liquid
refrigerant is vaporizedby a process stream which is in turn
cooled.
Compression ratio: ratio of outlet to inlet absolute pressures for a compressor.
Condenser: a heat exchanger in which the refrigerant, compressed to a suitable pressure, is condensed by rejection of
heat to a cooling medium.
Cooling medium: any substance whose temperature is such
that it is used, with or without change of state, to lower thetemperature of refrigerant either during condensing or subcooling.
Effect, refrigerating: the rate of heat removal by a refrigerant in a refrigeration system. It is equal to the difference
in specific enthalpies of the refrigerant at two designated
thermodynamic states.

14-1

risk of contamination, while ammonia may very well serve the
purpose. Halocarbons have been used extensively...