Cooling of Waste Flue Gasses

This application provides a method of capturing thermal energy from furnace offgas prior to gas cleaning.

The process and equipment included for the harvesting of thermal energy from furnace offgas aim to replace radiant trombone coolers, forced draft coolers or spray coolers that are commonly used for cooling hot furnace offgas before it is cleaned in bag filters. These traditional coolers are bypassed and or replaced with heat exchangers.

The heat exchangers use a thermal collector fluid to absorb the thermal energy while the hot process gas is cooled down at the same time. The hot thermal fluid is then utilized in an Organic Rankine Cycle (ORC) where heat from the thermal fluid is transferred to the motive fluid of the ORC which in turn drives the turbine that generates the electricity.

Waste heat can also be harvested from existing gas ducting already operational in the plant.

The temperature of the thermal fluid in the output stream can be in a range of 65°C to 300°C, not normally achievable with low pressure water cooling circuits.

Advantages of the system include:

  • Electricity production from a thermal heat source which is otherwise wasted heat.
  • Small footprint compared to trombone coolers.
  • Outlet temperatures above Sulphur dew point to prevent corrosion but well controlled.
  • Inlet temperatures up to 500°C while structural integrity is maintained.
  • Exceptional temperature control within 5°C of the flue gas.
  • Lower temperatures to the bag filter, reduces the need for dilution air for cooling.
  • Lower temperature reduces the actual volume in the filter and the filtering velocity.
  • Low filter velocities improve filtering and filter medium life.