(9a) Exploring Key Differences between Steam Turbines and Electric Motors As Main Compressor Driver in Critical Compressor Service

Ethylene, with a global demand of 165 million metric tons, is one of the fundamental products produced by modern petrochemical industry. Different types of feedstocks such as naphtha (from refineries), ethane (from natural gas) etc. are used as raw material worldwide to produce ethylene. Most companies use the steam cracking process to convert the aforementioned feedstocks into ethylene. Since the steam cracking process ensures the availability of excess steam, steam turbines are traditionally preferred as the main driver for compressors.

But recently, various studies for using electric motors instead of steam turbines as the main driver for an ethylene plant have been conducted because of their carbon-friendly outlook and ease of maintenance. However, questions such as availability of low-cost electricity, load shedding etc. need to be answered before concluding the superiority of any main driver.

This study explores the key differences present between two types of drivers (namely, Steam Turbines and Electric Motors) on the basis of Utility Requirement, Cost (both Capital expenditure and Operational Expenditure), Carbon Footprint and Maintenance requirements. As a result, it is shown that motor drivers are beneficial and leave less carbon footprint if there is no steam requirement for other equipment of the plant. On the other hand, the opposite is true if steam is required for other equipment of ethylene plant.

Additionally, recent technology developments are helping OEMs to decrease the utility requirement in case of steam turbine drivers. So, this study also talks about the elimination of two such utilities, i.e. Control Oil for control valves (which are used to actuate the inlet steam of turbines) and LP steam for ejectors (which are used to suck air out of condensers in order to maintain the exhaust pressure of turbines). While the former is replaced by air actuated control valves, the latter gives way to electric deaerators. This change has not only decreased the utility requirement of steam turbine drivers, but also helped in reducing the space required by steam turbine auxiliaries and made the operation of steam turbines drivers safer.