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2.2.1 SCR De-nitration theory and process SCR
The flue gas de-nitration catalyst also named as SCR flue gas de-nitration catalyst, industrial terminology referred to SCR catalyst. SCR is the abbreviation of selective catalytic reduction, SCR reaction theory: due to the effect of SCR catalyst, because of selectivity, NOx and NH3 can be generated to pollution-free N2 and H2O. So SCR catalyst is also known as de-nitration catalyst, it is the main core of de-nitration process of coal-fired enterprises and boiler flue gas, can be widely used in electric power, steel, chemical and other industries for de-nitration, also can be used for nitrate, nitric acid manufacturers, high-temperature waste incinerators and the other systems.
The SCR De-nitration theorem is used of appropriate SCR catalyst under certain temperature (200-400 °C), ammonia and the others as reducing agent, utilizing the selectivity of the reducer, preferentially reacting with the nitrogen oxides, restoring it into nitrogen and water. High efficiency of the selective catalytic reduction, it is currently able to find the best treatment technology which can be widely applied to the stationary sources of NOx. Among them, the main NH3 reduced to NOx reaction as below:
SCR method is of reliable and efficient technology to denitrate which is simple, high de-nitration efficiency, low liquid ammonia consumption, stable de-nitration performance, now in the world are widely promoting to use the technology for NOx in flue gas of power plants and other enterprises to meet emission standards.
Bellowing diagram showing the simple low-temperature SCR De-nitration process: (flue gas is feed from the top of the reactor, discharged from the bottom).
2.2.2 SCR De-nitration process characteristics SCR
Reduction temperature of SCR de-nitration is relatively low which can be processed at temperature 200 °C ~ 400 °C, de-nitration reaction is fast and relative stable with low energy consumption characteristics. SCR de-nitration efficiency can reach to 95%, ammonia leak rate less than 2×10-6, NOx concentrations in tail gas below 100ppm, normal operating temperature about 400 °C, the reaction requires catalyst and reducer coordinate, injection point is set to single plane suitable for a variety of units.
The SCR catalyst is required to achieve the following several requests: a.high NOx removal rate, low ammonia slip rate, low purified exhaust NOx concentration; b.In low temperature and wide temperature range, with high catalytic activity, that’s operating temperature window width. c. has the ability of good anti-chemical stability, thermal stability, mechanical stability; d.relatively low running costs.
2.2.3 Applications
SCR De-NOx catalyst is of high-tech products, mainly used for efficient de-nitration of nitrate exhaust of the thermal power plant flue gas, waste incineration industry, nitric acid plants, nitrate plant, steel plant, fertilizer plant and other industries. Technical theory is: the catalyst in a certain temperature (300 - 400 ° C), ammonia and others as reducing agent, advantage of the selectivity of the reducer, priority react with nitrogen oxides of industrial emissions, catalytic reduce NOx to pollution-free nitrogen and water, its function is catalytic accelerate reaction, achieve the purpose of removal NOx.
2.2.4 The quality standard of SCR De-nitration Catalyst SCR
No. | Test Items | Technical Specification |
Carrier specifications:150X150X50 Wall thickness= 3.7±0.1 | ||
1 | Space velocity | ≥1×104h-1 |
2 | Temperature windowOptimal operation temperature | 150°C-420°C 400°C |
3 | NOx conversion rateService life | ≥90% ≥2 years |
4 | Bulk density | 0.72±0.05g/mL |
5 | Crushing strength | ≥14 MPa (Front) ≥4 MPa (Side) |
6 | Coating loading | >8.0% |
7 | Metal oxide loading | >9.0% |
8 | Expulsion rate | < 2% |
9 | Appearance | Pure black |
10 | Package | Moisture-proof and Sealed |