Process Design of Turboexpander based nitrogen Liquefier

Abstract

Our country is still dependent on imports for most of its needs in cryogenic refrigerators and liquefiers. These products are proprietary in nature which makes it very
expensive for its cost and maintenance. Also as a strategy of promoting the sale, the company changes their model by limiting the spare parts of the earlier model to enforce on the customers to buy the new product. So it is imperative that our country develops an indigenous
nitrogen liquefier to meet the need of liquid nitrogen. With support from the Department of Atomic Energy, our institute has initiated a program on development and study of a nitrogen liquefier of intermediate capacity in the range of 10-50 litres/hr by using technologies already
developed in our country.
The process is based on a suitable modified Claude cycle which minimizes the number of heat exchangers and also takes care to accommodate the in house developed turbo
expander. The process design is carried out using the standard calculation procedure and is validated by using process simulation software, Aspen Hysys.
Parametric analysis is carried out to access the role of different component efficiencies in predicting overall system efficiency at the design and off design conditions. In this analysis, the available turbo expander efficiency is considered to evaluate the feasible heat exchanger efficiency in order to optimize the plant efficiency. The thermodynamic parameters (temperature, pressure, pinch point temperature) are evaluated to obtain the optimum mass fraction through turbo expander for maximum liquid yield. This investigation not only gives the analysis of nitrogen liquefier, but also it will act as a basic frame work for any liquefier and helium liquefier in particular as a future mission.