SCR (selective catalytic reduction) denitrification system and operating method thereof

Abstract

The invention belongs to the field of operation of flue gas denitrification equipment and pulverized coal boilers and particularly relates to an SCR denitrification system and an operating method thereof. The SCR denitrification system provided herein comprises an ammonia injection grid, a cyclone flue gas mixer and a two-way heat exchange valve; according to the system, the ammonia injection grid and the cyclone mixer are arranged sequentially in a tail flue at the premise of not extending the length of an SCR unit inlet flue, great rotation of gas flow is utilized such that mixing effect of reducing agents NH3 and NOX is greatly improved, the influence of non-uniform flue gas flow speed upon SCR unit denitrification effect, and NH3 escape or low denitrification efficiency problem is avoided; with the mixing effect of NH3 with NOX is enhanced, it is also possible to effectively remove large-diameter dust in flue gas, removal of flyash is achieved, and catalyst abrasion and dusting problems are effectively improved.

Description

technical field [0001] The invention belongs to the field of operation of flue gas denitration devices and pulverized coal boilers, and in particular relates to an SCR denitration system and an operation method thereof. Background technique [0002] Selective Catalytic Reduction (SCR) is the most widely researched and applied denitrification technology at present. Its principle is that NO in flue gas x Under the action of catalyst, with NH 3 As a reducing agent, "selectively" with NH 3 React and generate non-toxic and non-polluting N 2 and H 2 O. At present, in the field of environmental protection technology of pulverized coal boilers, SCR systems are mainly used to remove NO in boiler flue gas. x . [0003] The main factors affecting the denitrification effect of SCR are: denitrification reaction temperature, catalyst activity, flue gas flow field distribution and reducing agent (NH 3 ) and NO X mixed effect. The SCR denitrification devices currently in operation ...

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Problems solved by technology

[0004] Usually, in order to meet the requirements of ultra-clean emission, an additional layer of catalyst is installed, but due to the imbalance of local ammonia nitrogen molar ratio caused by uneven flow field, uneven inlet nitrogen oxide concentration, poor mixing effect, etc., when the local ammonia concentration is too high , all NO x When it has been fully restored, local area NH will appear 3 Largely exceeded the standard, resulting in the occurrence of problems such as dust deposition and corrosion in the air preheater

In view of the above problems, at present, methods such as adjusting the flue deflector or adjusting the ammonia injection grille are used to optimize and adjust the SCR system to improve the SCR outlet NO. X and NH 3 The problem of uneven distribution

However, this method has many shortcomings. For example, in the actual operation process, the flow of flue gas in the flue itself is changeable, and the flue deflector is affected by the length and position of the flue. The effect is limited, especially for the current large-scale boiler units, the cross-sectional size of the flue is very large, and the uniformity of the velocity field and the concentration field cannot be truly achieved; no matter it is a deflector or other conventional mixers, ammonia is sprayed and mixed with flue gas only It can be conventional static mixing, and the mixing range is also mixed in a certain local range. It is impossible to achieve a uniform molar ratio of ammonia nitrogen in the entire flue. When low and high NO X When the emission concentration, there must be local NH 3 The amount of injection is too much, and the escape exceeds the standard; moreover, the method of adjusting the ammonia injection grid is single, only by measuring the NO at the SCR outlet. X It is only suitable for single load and combustion operating conditions, and the ammonia injection grid needs to be adjusted again after the load changes; it cannot be improved Partial waste of catalyst and wear and fouling of catalyst

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