The EGPT (Expanding Gas Power Transformation) concept has progressed from early investigations in 2008 to the situation today where commencement of pilot plant installations is imminent. Patents relating to the technology have been awarded and are in force in the great majority of countries with significant natural gas consumption. The possibility of generating power from natural gas pressure letdown has been noted in numerous communications dating back at least to the 1970's. A brief overview of the methods put forward to exploit this resource is presented. Despite the number of proposals which have been put forward with the objective of harnessing this resource, the vast bulk of letdown stations still use the traditional recipe based on the J-T regulator valve with boiler preheat of the incoming gas stream. The factors which have impeded the development of pressure letdown energy are examined from both technical and commercial perspectives. The main obstacle from a technical standpoint is identified as the need for much increased gas heating when the gas is expanded at high efficiency for power production. From a commercial standpoint there are two principal impediments: the capital cost and the operating cost of a power producing pressure letdown station when compared to the standard configuration. A third source of technical and commercial difficulty has been the complexity of some of the arrangements proposed and the need for extraneous equipment and consumables at the pressure letdown site. Like most of the other methods proposed to exploit gas expansion energy, EGPT makes use of an expander-generator. Unlike any of the other methods proposed, the EGPT approach makes use of ambient thermal energy upgraded by a new type of heat pump using a transcritical cycle to produce the necessary gas warming at high efficiency. Independent investigations of the concept carried out in three different countries by different teams have reported similar and highly positive findings. The studies indicate that the EGPT system has potential for cost effective applications ranging from small low-pressure letdown stations producing tens of kilowatts up to large high-pressure stations producing up to tens of megawatts. All applications of EGPT technology generate carbon-free power, avoid wasteful consumption of gas and provide substantial reductions in CO_2 emissions. In some particular cases additional synergies provide even more benefits. The particular merits of applications at gas fired power stations where EGPT can provide inlet air cooling and at island letdown stations where EGPT installations could provide power for hydrogen production are examined. The paper concludes with an overview of progress toward pilot plant installations to demonstrate the technical and commercial performance of an exciting new clean energy technology.
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