Desulfurization of combustion gases

Case study

1° The Context

In order to eliminate the combustion gases emitted by coal-fired plants, incinerators and industrial plants, one of the methods used is the flue-gas desulfurization (FGD). It is a process used to eliminated the sulphur dioxide (SO2). Read more.

2° The Challenge

The gauge to measure the level of the fluid (lime slurry)  involved in the desulfurization process show failures. This gauge is connected to a ball valve having multiple dead zones. The lime slurry infiltrates in these spaces, creates deposits causing measurement errors. To overcome this problem, an operator used a bar to scrape the sides and mechanically rod out the deposits. Common and dangerous operation!

initial valve installation desulfurization process

3° The Solution

The solution developed by Guichon :

  • replace the ball valve by a piston valve in Hastelloy. The piston valve protruding slightly into the tank, eliminates dead space and is self rodding.

LOGO GUICHON

guichon valve solution for desulfurization process
guichon_valve_desulfurization
Advantages :

  1. No dead space
  2. Hastelloy material (no corrosion due to Chloride)
  3. High utilization rate of limestone
  4. High rate of removal of sulfur dioxide =  less pollutant gases
  5. Reliable and simple operation
  6. Sealed system operation / Operator safety

Information about desulfurization process :

Combustion of coal generates NOx, SO2, particulates, and other pollutants that contaminate the environment. Pollution control legislation by governments across the globe has mandated a significant reduction in emissions from these power plants. The most effective way to significantly reduce emissions of SO2, and in some cases mercury, is through the use of flue gas desulfurization (FGD). There are several FGD methods available, examples include various dry scrubbing methods, sea water scrubbing, and wet scrubbing with lime or limestone. The majority of the scrubbers currently being installed use the wet limestone technology. This method is the best suited to scrubbing the high volume of flue gas emitted by large power plants. A schematic of an FGD system is shown in Figure 1.

Figure 1.example flue gas desulfurization
Lime and limestone play a significant role in the removal of polluants from flue gas streams of coal-fired power plants, incinerators and industrial facilities. Flue gas desulfurization (FGD) primarily refers to the removal of sulfur dioxide (SO2). However, lime and limestone are also used in the removal of other pollutants such as hydrogen chloride (HCl), sulfur trioxide (SO3), fine particulates and mercury.

In the wet FGD processes these products are slurried with water and sprayed into a flue gas scrubber vessel. The acidic gases, normally SO2 and HCl, are absorbed into the water where they chemically react with the lime and limestone. The reaction products, primarily calcium sulfite, can then be oxidized to produce calcium sulfate.

The acidic gases combine with lime to form a dry product which is removes from the flue gas stream in particulate control devices such as bag houses or electrostatic precipitators.