Uploaded by B B

Chapter 18 Questions

18.1 How much HHV energy (in Btu or PJ) is contained in the cargo aboard a 145,000 m 3 LNG carrier?
Assume the LNG has a relative density of 0.45, a molar mass of 18, and a heating value
of 1000 Btu/scf (39.4 MJ/Nm3).
18.2 What is the value of the cargo in Exercise 18.1 if the fuel is priced at $5.00 per MMBtu
18.3 What is the equivalent volume of gas (in scf [Nm3]) of the cargo in Exercise 18.1?
18.4 An LNG receiving terminal sends gas to the pipeline at 1000 psig (70 barg). The LNG is
essentially pure methane and is stored in a tank at 2 psig. What is the pump energy (hp, kW)
required to send out 400 MMscfd (10.7 × 10 6 Nm3/day) of gas to the pipeline at 40°F (4.4°C)?
Assume a pressure drop through the vaporizer of 20 psi (1.4 bar) and a pump efficiency of 70%
(see Chapter 2 for pumps).
18.5 The LNG terminal in Exercise 18.4 uses seawater to heat LNG from storage temperature for
send out. For a gas send-out rate of 400 MMscfd (10.7 × 10 6 Nm3/day) and using fresh water
a. What water flow rate (lbm/h, kg/h) is required to heat the LNG, assuming an inlet water
temperature of 50°F (10°C) and an outlet water temperature of 40°F (4°C)?
b. What is the hp (kW) required to lift the water 50 ft (15 m) above sea level to the vaporizer
assuming a pump efficiency of 80%?
18.6 The LNG terminal operator in Exercises 18.4 and 18.5 decides to explore vaporizing LNG at
low pressure, then compressing for send out. The LNG is first pumped to 30 psig (2.1 barg),
then passed through the vaporizer exiting as a gas at −200°F (−129°C) and 25 psig. The gas
then goes to a compressor for compression to the pipeline pressure of 1000 psig. How does the
pump and compressor energy compare with that required using seawater heating (Exercises
18.4 and 18.5)? Assume the pump and compressor are both 70% efficient.
18.7 The LNG terminal in Exercise 18.5 has a standby gas-fired submerged combustion vaporizer.
What portion of the vaporized LNG must be consumed as fuel to heat LNG to 40°F (4.4°C) and
1000 psig (70 barg) if seawater is not used? Assume the vaporizer is 100% efficient (HHV basis).