Utilidades industriais/Gases industriais/Gás de combustão.md ..
@@ 163,7 163,11 @@
The heat exchanger used for this purpose is called an economizer, since it economizes energy. They can be used in different processes, but the goal is usually to recover energy or preheat a fluid. In this section we are focusing on economizers for boilers. The first successful economizer was invented by Edward Green in 1845, aiming efficiency increase⁵. Usually in economizers the cold water passes through tubes surrounded by hot gas, as can be seen in Figure 1⁶. The heated water is then fed to the boiler. Economizers are usually specifically designed for the target installation, so that its size is in accordance with the process characteristics and the performance is optimized.
-

+
+

+
+
*Figura 1-* Design of an economizer used for preheating the water fed to the boiler⁶
+
There are two main types of economizers for boilers, depending on the amount of heat transferred. In dry economizers (DE) the fuel gas temperature is only reduced, without phase transition. Since the flue gas remains as a gas at the exit of the economizer, this equipment is usually made of carbon steel⁷.
@@ 186,11 190,9 @@
An interesting approach is to implement a SNOX process, developed by Haldor Topsoe. It includes technologies to remove SO₂, NOₓ and particulates from the flue gas in an integrated process. The steps are as follows: removal of dust, SCR of NO₂ with NH₃, catalytic oxidation of SO₂ to SO₃, and cooling of the gas, so that sulfuric acid condenses and can be easily removed as a concentrated liquid, which can even be commercialized. This process is, therefore, recommended when the flue gas is rich in sulfur. The diagram in Figure 2 explains in detail the SNOX process.¹²
-
### SNOX Process Diagram
-
-
<img src="snox_process_diagram.png" alt="SNOX Process Diagram" style="width:100%;">
+

-
**Figure 2. SNOX process diagram.¹²**
+
*Figura 2-* SNOX process diagram.¹²
There are also other pollutants that should be removed from flue gas, such as mercury and CO₂, but the technologies are not as established as the previously mentioned. In general, flue gas treatment is widely researched nowadays, and recent studies have been made trying to improve and develop new strategies, with an effort to remove more than one pollutant in a single equipment.¹³