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NETWORK / 23 / DECEMBER 2017 / JANUARY 2018 energy in the system and higher overall heat transfer e ciency. Thermosyphons are increasingly being used in cutting-edge energy management applications, ranging from temperature control of satellites and avionics to the world's most e cient solar collectors. Practical advantages include simplicity of design, long asset life and low maintenance requirements. As shown in the cross section diagram (le• ) of the Immersion Tube Thermosyphon Heater, there are no moving parts within the system as steam and water travel under the in• uence of natural convection and gravity. Signi- cantly, application of thermos- yphons for heat transfer o€ ers new potential for adaptive responses from rapid changes in energy demands in preheat applications. The - gures in - gure 3 highlight a comparison of temperature control achieved by a 930kW Immersion Tube Thermosyphon Heater and a 1.2 MW water bath heater operating on a same site, with similar changes in gas • ows one year earlier. The thermosyphon heater was able to adapt easily to changes in process gas • ow while maintaining a constant station exit tem- perature, while the water bath experienced signi- cant under and overshoots from the 3˚C set-point. Losses related to over-heating of gas latent heat absorbed during phase change, large quantities of heat can be transferred e ciently at a constant temperature, which is a useful attribute for optimising gas preheat- ing applications. Under vacuum, water can change to steam at temperatures below 50˚C. By comparison, a process using hot water at 50˚C is limited to transferring between 84 and 200 kilojoules per kilogram. This subtle di€ erence of relying on phase change rather than a di€ erence in tempera- ture to transfer heat enables heat transfer rates 10-25 times higher than that of water, with less • uid in the system. The two-phase Loop thermosyphon used in the new preheater design o€ ers signi- - cant advantages in optimising heat transfer, including rapid response, a lower store of were quanti- ed by comparing fuel consump- tions of each technology relative to that of an ideal preheater (de- ned by the ability to maintain a steady 1°C outstation tempera- ture). As the main function of the heater is to maintain a gas temperature above freezing, any fuel used to warm process gas beyond 1˚C o€ ers no additional bene- ts. The table above compares annualised results of fuel use and emissions associated with over-heating losses for the two preheat technologies. The UK's gas networks are an essential component in the development of a smart, low carbon energy system that is responsive and dynamic. As renewable sources of power generation are increasingly integrated within UK power networks, traditional gas infrastruc- ture will face new stresses to simultaneously satisfy peak daily gas and peak hourly power demands. The increase in gas-power system interdependencies will intensify variations in hourly gas demand, posing new operational stresses on assets such as pre-heat. The introduction of two-phase thermos- yphons o€ ers one example of an innovative solution to a complex problem, and represents an exciting opportunity for a new generation of fast responding pre-heat technologies that provide increased network • exibility while maintaining high standards of e ciency. Overheating losses (% of fuel consumed) Additional CO2 (mT/year) Additional Fuel (£/year) ITTH 930 kW 1.3 2,900 430 WBH 1.2 MW 25 96,200 14,400 Figure 1 Figure 2 Figure 3