Earth-Cooling Air Tunnels for Thermal Power Plants: Initial Design by CFD Modelling

Abstract

Climate change and the increase of the consumption of energy resources are expected to further strain anticipated water stress scenarios. The operation of existing thermal plants depends greatly on their cooling capacity, for which large amounts of water are withdrawn and consumed. Dry-cooling systems, on the other hand, do not require water, but they are less efficient and more expensive relative to conventional water-based systems, because of their dependency on the ambient temperature. This paper introduces the new idea of replacing water-based cooling systems in thermal power plants with earth-cooling air tunnels. Based on the concept of existing earth-air heat exchangers, the system takes advantage of the low and relatively constant underground temperature for cooling ambient air before it is introduced in the air condenser of the plant. In this work, we present an initial design of such an open-loop system for a 20 MW concentrated solar power plant. A sensitivity study of both geometric and flow parameters is realized using computational fluid dynamics simulations. Under the requirements of the study, we find that a system using a design of pipes with 0.5 m diameter and about 300 m length can be considered a technically viable zero-water alternative to water-cooling technologies.

Economic Analysis of a Zero-Water Solar Power Plant for Energy Security

“…The Earth-CAT system analyzed here has been designed for a 20-MW solar power plant with thermal storage [16]. Figure 1 Compared to a wet-cooling system, the air mass flow required is much larger due to the higher heat capacity and density of water.…”

“…The Earth-CAT system analyzed here has been designed for a 20-MW solar power plant with thermal storage [16]. Figure 1 shows the flow conditions assumed for the cooling air (…”

“…The air pressure at the inlet of the Earth-CAT system is approximately 1.1 bar to compensate for the losses in the pipes and the air condenser. This is a conservative value since the pressure losses are considered to be approximately 226 Pa in both the condenser and the cooling system [16].…”

“…Potable water and water for food production, residential use, power generation and other water-requiring processes will become scarce [13][14][15]. This kind of effect on power generation has already been seen during the last decades, when episodes of water scarcity occurred in countries such as France, the United States of America, India, and Australia [16]. This problem can be addressed by replacing water-based cooling systems with dry cooling systems that almost completely eliminate the use of water in thermal power plants.…”

“…The performance of open-loop and horizontal Earth-CATs has been technically evaluated in Ref. [16] for a 20-MW solar power plant located in the Iberian Peninsula. In that study, the viability of the system was analyzed through computational fluid dynamics (CFD), and sensitivity studies of the geometric characteristics of the pipe (diameter, length, distance between pipes, thickness, and material) and the flow conditions of the air (velocity and inlet temperature) were realized.…”