序章

化石エネルギーとは、石油、天然ガス、石炭を指します。石炭が豊富で石油とガスが少ないという中国の資源特性により、中国の化石エネルギーは石炭に大きく偏っています。石炭の広範な使用は、特に燃焼中に多くの環境影響を引き起こし、粒子状物質、二酸化炭素、二酸化硫黄、窒素酸化物などの多くの大気汚染物質を放出し、環境汚染を引き起こします。

中でも窒素酸化物（NOx）は主要な大気汚染物質であり、酸性雨、光化学スモッグ、都市部の霧、オゾン層破壊、その他多くの環境問題を引き起こす可能性があります。人体内のヘモグロビンと容易に結合し、血液中の酸素の輸送を阻害し、中枢神経系の麻痺を引き起こし、人間の心血管機能や肺機能を危険にさらします。

工業生産で広く使用されている NOx 制御技術には、低窒素燃焼技術、選択的無触媒還元技術 (SNCR)、選択的触媒還元技術 (SCR) などがあります。

2. CO-SCR技術の紹介

CO-SCR technology reduces NOx to N2 by using carbon monoxide (CO) as a reducing agent. CO is a reducing gas that is widely present in sintering and coking flue gas and vehicle exhaust. It is also a colorless and odorless toxic gas, which can cause poisoning when the CO concentration in the air exceeds 0.1%. Using CO instead of NH3 for selective catalytic reduction of NOx can not only reduce pollution control costs but also eliminate NO and CO in the flue gas, achieving waste treatment through waste.

2.1 CO-SCR technology principle

The reaction process of CO reducing NO can be divided into four steps: adsorption of reactant molecules (CO and NO first undergo gas-phase diffusion and contact with the catalyst surface, and are adsorbed by the unsaturated metal active sites on the catalyst surface, forming NO(a) and CO(a) species, while CO and NO gradually diffuse into the pore structure of the catalyst as the reaction continues); dissociation of adsorbed molecules (when the reaction reaches a certain temperature, active NO(a) is decomposed into N(a) and O(a) species); recombination of surface active substances and desorption of product molecules (CO(a) is oxidized by the active O(a) species to generate CO2, while the active N(a) species combines to generate N2, and the final products CO2 and N2 generated by the reaction are discharged from the flue). Meanwhile, the combination of other active species can produce by-products such as N2O and O2, and the specific steps are as follows:

Adsorption of reactant molecules:

CO(g) → CO(a)

NO(g) → NO(a)

Dissociation of adsorbed molecules:

NO(a) → N(a) + O(a)

Recombination of surface active substances and desorption of product molecules:

CO(a) + O(a) → CO(g)

N(a) + N(a) → N2(g)

N(a) + NO(a) → N₁O(a)

N:O(a) → NO(g)

N.O(a) → N₂(g) + O(a)

2.2 CO-SCR catalyst

The catalyst is the key material in the entire catalytic reaction system. Currently, in the CO-SCR denitration technology that uses CO as a reducing agent to remove NOx, commonly used catalysts include noble metal catalysts, single transition metal catalysts, and composite transition metal catalysts. Noble metal catalysts generally refer to platinum, palladium, rhodium, iridium, silver, etc. Noble metals are often present in a nanometer state as catalysts, or they can be supported on carriers or exist on molecular sieves by ion exchange. The oxides of non-noble metals such as copper, cobalt, iron, chromium, and manganese have good activity for removing nitrogen oxides. Single metal catalysts often have the disadvantages of a narrow reaction temperature window, poor reaction activity under oxygen-rich conditions, and poor resistance to SO2 poisoning. Composite metal catalysts doping appropriate additives can improve these problems to some extent. Compared with single transition metal oxide catalysts, bicomponent or multicomponent composite transition metal oxide catalysts often have higher dispersion of active components and better activity and stability of the catalysts.

2.3 CO-SCR technology characteristics

The CO-SCR technology uses the harmful gas CO in flue gas to reduce nitrogen oxides and achieve flue gas denitrification. Its advantages mainly include:

(1) CO, as a reducing gas, has strong reducibility at 100-400℃ and is a good NOx reducing agent;

(2) the reducing agent comes from the flue gas itself, and the denitrification cost is greatly reduced;

(3) it also reduces the emissions of CO and NOx, achieving the goal of "treating waste with waste";

(4) there is no ammonia escape, and no secondary pollution is caused.