**1. Introduction**

Today, optimizing energy consumption, improving energy efficiency, and reducing GHG emissions are essential for a sustainable operation and lower operating cost of an industrial facility such as Oil, Gas, Refining, and Petrochemical facilities. Every industrial facility depends on more than one form of utilities for its operation. Examples of these utilities include power generation, steam system, instrument and plant air, nitrogen system, hot oil system, etc.

Process streams such as gas and liquid are usually heated or cooled by indirect heat exchange with another fluid: either another process stream or a utility stream such as steam, hot oil, cooling water, or refrigerant. Heating utilities are necessary for proper usage of condensers, distillers, and several other integral types of equipment in the hydrocarbon processing facilities. In hydrocarbon processing plants, steam is the most commonly heat utility used.

Steam is used both as utility and a process fluid (heating agent, diluent to absorb heat of reaction, feedstock, and stripping agent in adsorbers and absorbers). It can be used to drive mechanical drivers such as compressors and pumps, heat exchangers, and ejectors (for producing a vacuum). There are few advantages of using steam as opposed to other methods of process heating. For example, see [1].

In general, the supply-side utility systems for industrial facilities are used to produce the required energy for the facility, and the most common system used is steam system. Other alternatives include hot oil and hot water systems.

Steam system is a better choice for a facility with high power demand and high heating demand required by process and at different level of temperatures. Thus, most of the gas plants, refineries, and petrochemicals that are using steam system often include both boilers and Cogen, as the base-case option. The reason behind using steam system for industrial facilities required both heating and power demand can be summarized as follows:

