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SCR denitration technology in cement plant

Date:2019-06-16 17:44     writer:cement editor     Views:

SCR denitrification technology popularized selective catalytic reduction (SCR) is to spray ammonia or other suitable reducing agent into the flue gas upstream of the catalyst, and use the catalyst to convert NOx in the flue gas into nitrogen and water, so as to achieve the denitrification method of reducing NOx.It is known that this technology has been widely used in thermal power industry. At present, 90% production lines in thermal power industry in China adopt SCR technology for denitrification, and this technology has also been successfully applied in glass kiln and other furnaces.However, so far, SCR technology has not been widely used in the cement industry.

In fact, SCR is one of the most widely used denitrification technologies in industry, which is famous for its high efficiency in NOx removal.Ideally, the NOx removal rate can reach more than 80%, and ammonia injected into the flue gas almost completely reacts with NOx, which is the best fixed source NOx treatment technology at present.In the case of the implementation of NOx emission value of 100mg/Nm3 in the power industry, emission requirements can still be well achieved.

However, why is such a high efficiency denitrification technology rarely used in the cement industry?The reason is that the application of SCR technology in cement industry is restricted by the complicated working environment, high investment, high maintenance cost and high resistance.

However, why is such a high efficiency denitrification technology rarely used in the cement industry?Temperature limitation: it is understood that the most commonly used catalyst today is porous Ti2O5 (carrier) to make honeycomb modularization, the carrier surface has catalytic active components V2O5 and WO3, reaction temperature in 280℃ ~ 400℃ is better.However, in the new dry cement production line, the advanced temperature of the preheater outlet has been reduced to below 300℃, and the actual denitrification effect of SCR installation is affected to some extent.At the same time, in order to implement the national energy saving and consumption reduction policy, China's production line above 2500t/d is generally installed with waste heat boiler, its exhaust temperature reaches 150℃ below, for such smoke, is no longer suitable for installing SCR system.The reason is that the application of SCR technology in cement industry is restricted by the complicated working environment, high investment, high maintenance cost and high resistance.

Dust limitation: the dust content in the end of cement furnace is up to 80 ~ 100mg/Nm3, which is easy to cause blockage of catalyst pores, aggravation of catalyst wear, increase of pressure drop of the system, and pose a serious threat to normal operation of induced draft fan, thus affecting long-term stable operation of cement furnace production line.

Alkaline environment restriction: sodium, potassium and other water-soluble alkali metal compounds in the flue gas of cement furnace are easy to react with V2O5 in the catalyst, thus poisoning the catalyst and reducing the activity of the catalyst.

Limit of exhaust resistance: due to the installation of SCR, exhaust resistance will increase by 500 ~ 1000pa, which will increase the burning power consumption by 0.75 ~ 1.5kwh /t for tons of clinker.

Cost limitation: the adoption of SCR technology for denitrification requires additional devices, occupying space, large investment and high operating costs.According to the data, the total investment of 5000t/d production line using SCR to reduce NOx is about 40 million yuan.Affected by the above factors, SCR is rarely used in cement enterprises. However, with the continuous strict environmental protection standards and continuous improvement of technology, SCR can actually be used as an alternative direction.

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