Energy analysis of manufacturing processes on the moon.

Abstract

A methodology for the energy analysis of high temperature lunar manufacturing processes is presented. The Moon's environment creates unique thermodynamic and heat rejection problems due to the absence of an atmosphere and large ambient temperature swing as it goes from lunar day to lunar night; it is a perfect vacuum at the surface. The methodology combines availability analysis, the Pinch technology and a mathematical heat rejection model to minimize energy requirement and the lift-off mass from earth. The availability analysis is used to identify process irreversibilities and to determine the quality of energy from various exit streams. The Pinch technology is used to identify hot and cold streams for potential process heat integration. The heat rejection model is used to optimize the radiator area with temperature as the driving factor. The methodology presented allows one to identify all power consumption, production and rejection in the process, and then determine the feasibility of heat and work integration without a significant mass penalty. It provides a means to design a power system to minimize waste energy. This would result in reduction of the power requirement, cost of power and the power system's mass. The hydrogen reduction of ilmenite process for oxygen production on the Moon is used as a case study to demonstrate the energy analysis methodology. The study was limited to the reduction and electrolysis processes. The availability analysis estimated that the two processes required 56 kW to meet sensible heat and heat of reaction demands but produced 53 kW of process irreversibilities. This 53 kW of unavailability included 9.4 kW of energy potential in the product solid stream and product oxygen stream. The Pinch technology found that the product solid stream and product oxygen stream may be split to help meet the heating demands of the feed ilmenite stream. This would reduce the 56 kW of power demand by 24%. If oxygen were to be brought from 1273 K to 300 K, its entire heat content may be recovered and heat rejection is eliminated. The heat exchanger area requirement is estimated to be more than ten times the radiator area if the radiator were operated at 1273 K.