Desulfurization and denitrification are the processes of acid-base neutralization. Desulfurization is the removal of SO2(sulfur dioxide) from the flue gas, and de-stocking is mainly the removal of NOx(nitrogen oxides) from the flue gas. These two substances into the atmosphere will form acid rain, acid rain is very harmful to the human body, so the country has been advocating environmental protection. The flue gas fueled by coal contains these substances, especially in thermal power plants, and desulphurization must be built at the same time in thermal power plants, and denitrification countries have not yet begun to enforce it.

The working principle of the desulfurization and denitrification equipment is to reduce the generated NOX to N2, thereby removing NOX from the flue gas. According to the treatment process, it can be divided into wet denitrification and dry denitrification, mainly including: acid absorption method, alkali absorption method, selective catalytic reduction method, non-selective catalytic reduction method, adsorption method, plasma activation method, etc. Some people also use microbes to treat NOX exhaust gases.

The process of desulfurization is to make alkaline desulfurizer (such as limestone, CaO, sodium hydroxide, etc.) into slurry, mixed with boiler flue gas, sulfur dioxide and water to form acid, and then react with alkaline desulfurizer to form CaSO4(calcium). The principle of denitrification and desulfurization is similar, that is, the denitrification agent is changed to ammonia or urea.