Dew Point Heating

The temperature at which air becomes saturated with moisture is known as the dew point. This saturated state means the air is holding the maximum amount of moisture possible at its current temperature. Cooling the air beyond the dew point creates condensation or precipitation in which the moisture separates from the air, such as rain, for example—or dew forming on a surface (which is where the dew point gets its name).

In everyday applications, dew points are generally used as one part of the equation to determine relative humidity when forecasting the weather. In the industrial sector, however, dew points serve a much more important purpose.

What is Dew Point Heating?

When you heat air, the dew point adjusts to correlate with the new temperature—meaning that the amount of moisture the air can maintain at that temperature also changes. Dew points aren’t just for open air, however. Dew point also refers to the amount of moisture contained in any gas. With proper dew point analysis, gases can be heated to avoid damage from hydrate contaminants.

This process is known as dew point heating—one of several fuel gas heat conditioning processes. Others include performance heating and regeneration gas heating. Dew point heating is often used in fuel gas heating for gas turbines and power generation.

Where Does Fuel Gas Come From?

Fuel gases are pushed through a sophisticated network of pipelines from the location at which they originate to other locations where they are needed. The gas must be highly pressurized in order to move efficiently through the pipes.

This means that the high pressure of incoming fuel must be reduced before it can be used at its destination. When the pressure is reduced, the temperature is likewise reduced in a process known as isenthalpic cooling, or the Joule-Thomson effect.

Fuel gas often contains moisture and contaminants, so there is need for a conditioning system capable of delivering clean gas to turbines as fuel. Instrumentation for such a system may include a heater, pressure regulators, and coalescing filters.

When the temperature of the gas falls during depressurization, water and heavier hydrocarbons condense into liquid. Electric process heaters superheat the gas, ensuring that potentially damaging liquid contaminants aren’t pushed into the turbine nozzles. Heaters also ensure that the gas is heated to the correct temperature for use by the turbines.

Increased Demands on Turbines and Bath Heaters

With rising power demands, engineering firms are taking longer to complete project cycles. Thus, there is a need to coordinate fuel gas heater installation in your plant with these firms well in advance to avoid any delays.

As these power generation demands continue to increase, the challenges of dew point heating are as follows:

  • Lower efficiencies of bath heaters due to poor shell side heat transfer.
  • Already large bath heaters are becoming even larger as power demand increases.
  • Flow rates might vary, based on the number of turbines or auxiliary systems firing off the fuel gas.

Dew point heating is a crucial component of fuel gas heating for gas turbines and power generation. Dew point heating ensures that water or fuel gas condensates do not enter the turbine, which can cause damage to equipment through the creation of extra exhaust during combustion. Moreover, it ensures that the gas is heated to the most efficient temperature before allowing it into the turbines to generate power.