Produce from process industries like dairy, textile industries, pharma, breweries, paper industry, etc. finds application in our day-to-day life. Most of these industries have heating requirements in one or more processes. Steam is widely used as heat-carrying medium owing to its excellent properties such as high heat transfer coefficient in saturation domain, ease of availability, cost effectiveness, inert, and high thermal capacity. Further, steam has saturation temperatures, near to process temperature requirement at relatively low pressures. In process plants, steam is generally produced at higher pressures than required to improve plant efficiency, to improve handling, to reduce investment cost , and to satisfy different temperature requirements. Due to relatively lower boiler temperature compared to power plant boilers, most of the fuel’s exergy gets destroyed in boiler house. The pressure reduction from boiler to process pressure using pressure reducing valves (PRV), further reduces the exergy captured by process steam from boiler by throttling. Use of expanders in place of PRV is better from thermodynamic, economic, and environmental perspective. Preliminary analysis reveals the economic cost of unit power generation by expanders is independent of its isentropic efficiency. However, it is beneficial to use expanders with high isentropic efficiency for increased over all power output. To arrive at net economic significance of use of expanders, it is significant to analyze its dependence on types of fuel used and the price of electricity.

Various expander options are getting introduced into process industries to reduce the extent of exergy destroyed in throttling process. Due to fluctuating thermal load, the steam requirement in the process is variable by nature. The available technologies have limitations when operated at variable steam flow applications because of its low isentropic efficiency in part loading and design limitations. Poor part load performance can significantly affect the overall power generation hence, there is a technical gap in available technology and intended application. In present work, an expander was designed to address the part loading scenario in process industry. The design was done to meet the requirement of isentropic efficiency in the entire turn down limiting the variation within 10% from peak efficiency. Two most important geometric parameters for design, cut-off, and compression ratio had conflicting findings about their effect on isentropic efficiency in literature. Further, the definition of ideal cycle and prediction of theoretical isentropic efficiency have diverging findings. In this work, an attempt has been made to define the ideal cycle and theoretical prediction of isentropic efficiencies at design point and part loading. The effect of cut-off and compression ratio is studied in detail and experimentally validated. The findings of the study were incorporated in expander design for variable loading application by introducing a mechanism capable of dynamically adjusting the admission, timing, and duration of exhaust. The performance study of the expander with and without dynamic control was performed using the process load variation from textile industry. Experimental results revealed that the expander with dynamic control could deliver isentropic efficiency in the range of 80 – 90 % for the entire turn down, whereas non-volumetric control expanders will deliver only from 30 - 90 %. This study reflects a significant economic and environmental advantage for expanders with dynamic control over non- dynamic controlled machines.