At medium-deep and deep depths of Earth crust lays vast and so far mostly untapped reserves of geothermal energy. This energy source has the potential of meeting humanity’s needs for thousands of years. However, its large-scale deployment has been hindered by a lack of effective and dependable exploitation technologies. Gravity heat pipes have recently garnered significant attention due to their exceptional heat transfer capability and their ability to harness geothermal heat without water-mining. Nevertheless, the challenge of extending gravity heat pipes to depths sufficient for deep geothermal energy exploitation still persists. In this study, we introduce an innovative ladder-structure inner pipe design to overcome this shortcoming. This design incorporates a series of stepped ladders and small condensate guiding pipes, allowing for the development of super-long gravity heat pipes (SLGHPs). Combined with an optimal working fluid, this novel structure enables kilometers-long gravity heat pipes. As a direct outcome of this innovation a 4,149-meter SLGHP using ammonia as the working fluid was constructed and installed in a geothermal well. The SLGHP geothermal system demonstrated the ability of a continuous heat output exceeding 1 MW, with a heat flux across the radial section of the SLGHP reaching 4x10⁷ W/m². Furthermore, an ammonia vapor-driven power generator was developed and integrated with the SLGHP system. During a 72-hour test, this generator successfully produced electricity at a steady rate of approximately 7 kW. The breakthrough design of SLGHPs holds the potential of unlocking Earth’s deep geothermal energy reserves, providing a sustainable and reliable energy source for generations to come.

中文翻译：

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开发千米长重力热管用于地热能开发

地壳的中深层和深层蕴藏着巨大的、迄今为止大部分尚未开发的地热能储备。这种能源有潜力满足人类数千年的需求。然而，由于缺乏有效、可靠的开发技术，其大规模部署受到阻碍。重力热管由于其卓越的传热能力以及无需开采水即可利用地热的能力，最近引起了广泛关注。然而，将重力热管延伸到足以开发深层地热能的深度的挑战仍然存在。在本研究中，我们引入了一种创新的阶梯结构内管设计来克服这一缺点。该设计结合了一系列阶梯和小型冷凝水引导管，允许开发超长重力热管（SLGHP）。结合最佳的工作流体，这种新颖的结构可实现数公里长的重力热管。作为这项创新的直接成果，在地热井中建造并安装了使用氨作为工作流体的 4,149 米长的 SLGHP。 SLGHP地热系统展示了超过1MW的连续热量输出的能力，SLGHP径向截面的热通量达到4x10 ⁷ W/m ²。此外，还开发了氨蒸汽驱动发电机并将其与 SLGHP 系统集成。在 72 小时的测试中，该发电机成功地以约 7 kW 的稳定速率发电。 SLGHP 的突破性设计具有释放地球深层地热能源储备的潜力，为子孙后代提供可持续且可靠的能源。