Chemical Technology August 2015

DESIGN AND MATERIALS OF CONSTRUCTION

Figure 3: Typical Ambient Air Vaporiser

Figure 4: Improved Defrosting on Ambient Air Vaporiser

Figure 5: Glycol-water Intermediate Fluid Vaporiser integration with different heat sources

Figure 6: IFV LNG Vaporisers in Rankine Cycle

tion. In most instances, when natural gas is supplied to a power plant, the gas pressure is lower than the LNG sendout pressure. Typically, LNG sendout pressure is at 100 barg or higher, and is required to be letdown to 30 barg at the power plant inlet. The potential work from the letdown operation can be recovered using a natural gas expander for power generation. Sufficient power can be produced to operate the LNG regasification facility. Power generation using LNG as the cold heat sink is attractive since power can be generated without the use of fuel gas or emissions. References • Mak, J, Patel, D “LNG Vaporiser Selection Based on Site Conditions”, paper presented at the LNG 17 Conference, Houston, Texas, USA (May 30-31, 2013). • Mokhatab, S, Mak, J, Wood, D, Valalppil, J, “Handbook of Liquefied Natural Gas”, Elsevier Publishing, October 2013. z

issue in cold climate operation. Figure 6 shows one of the configurations using propane as an intermediate fluid in LNG vaporisers. The configura- tion uses two heat exchangers operating in series. The first exchanger uses the heat of condensation of propane to vaporise the LNG at the cryogenic temperature range, and the second heat exchanger uses the sensible heat of sea- water at the higher temperature range. Since direct contact with seawater occurs at higher temperatures, freezing of seawater is avoided. The second exchanger is also used to vaporise the intermediate fluid propane that is recirculated to the first exchanger. In addition to LNG heating, this configuration can also be used to generate power. In this configuration, high pressure propane or butane expanders can be expanded in a gas expander operating in a closed loop Rankine cycle. The vaporised LNG can also be used to generate power using a natural gas expander in an open cycle configura-

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Chemical Technology • August 2015