Reduce Utility Cost And Improve Gross Refinery Margin

In a hydrocarbon plant, utility costs are high. As can be seen from the chart below, a major portion of these costs goes towards energy, i.e. steam and power. It is therefore essential to conserve energy in order to maximize gross refinery margin.

As system pressure rises, water boils at a higher temperature. Once water (liquid state) reaches its boiling point in a closed vessel, steam (gaseous state) forms.

This steam can be supplied at any pressure by regulating pressure inside the closed vessel. When released, it can carry large amounts of heat over a long distance through pipelines.

Importance of generating steam at high pressure :

In refineries, the product needs to be heated at high temperatures. When steam delivers its latent heat to the product to be heated in a closed vessel, the vapour returns to liquid state (saturated condensate).

When this high pressurized saturated condensate, which still contains 100% sensible heat, enters a lower pressure zone, flashing occurs (i.e. low pressure condensate can only contain its corresponding sensible heat, rest heat forms flash steam). The only difference between flash steam and steam is the way the method of formation.

The Conventional Approach

In hydrocarbon plants, flash steam is traditionally condensed with the help of a fin fan cooler or flash condenser.

The fin-fan cooler runs on electricity and is not economical to operate and maintain. The forced draft centrifugal fan provides air to flash steam coils. While absorbing latent heat from the flash steam, all heat is dissipated to the atmosphere. The mass gets recovered but the entire heat component in the flash steam gets wasted.

Flash condensers require centrifugal electric pumps to force cooling water into the heat exchanger. While absorbing the latent heat from flash, the heated water is diverted to the cooling tower, which again in a waste of energy.

The Forbes Marshall Solution

Flash steam is nothing but excess energy in the condensate let out at low pressure. Recovering the flash steam and utlising it in the process, reduces fuel consumption and increases steam system efficiency.

Flash steam, or low pressure steam, contains 50% of the total condensate energy, though only 10% by mass. Traditionally this steam is vented to the atmosphere since there is no application for low pressure steam in the process. By replacing traditional methods with a thermocompressor, the low pressure steam can effectively boosted to a pressure level useful for the process, by using as high pressure motive steam, and reduce energy consumption by 30% or more.

Forbes Marshall thermocompressors maximise flash steam recovery and enhance condensate removal by providing effective ‘blow off’. They are supplied with a complete control loop and can recover up to 100% flash steam.

Advantages of Forbes Marshall Thermocompressor Based System over Fin-Fan Cooler Based System

Use of a thermocompressor based flash recovery system instead of a fin-fan cooler based system ensures reduction in utility costs through minimised wastage of steam and condensate. Energy Intensive Index (EII) of plants can be improved. All these factors together help to increase the Gross Refinery Margin (GRM). The table illustrates the advantages of a thermocompressor system at a glance.

Thermocompressor Based System	Fin-Fan Cooler Based System
Recovers heat content/enthalpy from the high temperature condensate in the form of flash steam to the next usable level	Recovers only mass in the form of water/condensate at subcooled temperature
A thermocompressor based flash recovery system recovers mass as well as heat or in other words, 100% flash steam can be efficiently recovered for use in the process.	A large quantum of heat content is vented to the atmosphere through flash steam. Not only is energy wasted, but this further adds excess heat to the atmosphere, affecting plant atmospheric temperature conditions.
Compact system that can be easily mounted on pipe rack platforms	Flash steam recovery not possible
Minimal piping and fittings required	Large footprint. Needs to be mounted on the highest elevation for best performance. Additional structure and supports compulsory.
Low capital investment	Large piping and fittings required
Nil operating cost	High capital investment, operating cost and less efficient system