Small SNCR denitrification equipment-Foshan yiqing environmental protection engineering technology co. LTD

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Flue gas denitrification

Ultra Low Emission

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Small SNCR denitrification equipment

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Small SNCR denitrification equipment

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It is mainly engaged in industrial dust, industrial flue gas comprehensive treatment, technology research, industrial development and engineering contracting, production and sales of environmental protection equipment, a comprehensive large-scale environmental protection engineering company, is a national high-tech enterprises. It is a professional environmental protection contracting second-class enterprise, and the product quality management system of Yiqing Environmental Protection has obtained ISO9000 certification. Products: desulfurization tower, dust collector, dust removal equipment, catalytic combustion, etc.

SNCR or Selective Non-Catalytic Reduction Selective non-catalytic reduction is a method to reduce NOx without using a catalyst in the temperature range of 850 to 1100°C. The most commonly used drugs are ammonia and urea. In general, SNCR denitrification efficiency can reach 25% to 40% for large coal-fired units and up to 80% for small units. Because the method is greatly affected by the size of the boiler structure, it is mostly used as a supplementary treatment means of low-NOx combustion technology. Its low engineering cost, simple arrangement, small footprint, suitable for old plant transformation, new plants can be used in accordance with the boiler design.

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Keywords: sanitation equipment, environmental equipment, environmental services

Keywords: industrial flue gas desulfurization, denitrification, VOCs treatment equipment

Details

Introduction

SNCR, or selective non-catalytic reduction; selective non-catalytic reduction is a method of reducing NOx without using a catalyst in the temperature range of 850 to 1100°C. The most commonly used drugs are ammonia and urea. In general, SNCR denitrification efficiency can reach 25% to 40% for large coal-fired units and up to 80% for small units. Because the method is greatly affected by the size of the boiler structure, it is mostly used as a supplementary treatment means of low-NOx combustion technology. Its low engineering cost, simple arrangement, small footprint, suitable for old plant transformation, new plants can be used in accordance with the boiler design.

The reaction equation is mainly as follows
4NH3+4NO+O2→4N2+6H2O

4NH3+2NO+2O2→3N2+6H2O

8NH3+6NO2→7N2+12H2O

And the main chemical reaction for the reduction of NOx using urea as a reducing agent is

(NH2)2CO→2NH2+CO

NH2+NO→N2+H2O

CO+NO→N2+CO2

The reaction of SNCR NO reduction is very sensitive to temperature conditions, and the choice of the injection point on the furnace chamber, also known as the choice of temperature window, is the key to the efficiency of SNCR NO reduction. The ideal temperature range is generally considered to be 850°C to 1100°C, and varies with the reactor type. When the reaction temperature is lower than the temperature window, due to the limitation of residence time, the chemical reaction is often not carried out sufficiently, resulting in a lower NO reduction rate, while the increase in NH3 not involved in the reaction will also result in the escape of ammonia, which will produce NH4HSO4 and (NH4)2SO4 when encountering SO2, easily causing the air preheater blockage and the risk of corrosion. And when the reaction temperature is higher than the temperature window, the decomposition of ammonia will reduce the reduction rate of NOx , and the oxidation reaction of NH3 starts to play a leading role:

4NH3+5O2→4NO+6H2O

How to choose the right temperature conditions while reducing the leakage of reductant becomes the key to the successful application of SNCR technology.

Features

Used in cases where denitrification efficiency requirements are not high, the characteristics of this method are as follows.

(1) Simple system: It does not need to change the equipment settings of the existing boiler, but only needs to add ammonia or urea storage tank, ammonia or urea injection device and its injection port on the basis of the existing coal-fired boiler, so the system structure is relatively simple;

(2) Small investment in the system: Due to the simplicity of the system and the fact that no expensive catalyst is needed for operation, the investment cost is lower than that of SCR method.

(3) Low resistance: less impact on the normal operation of the boiler;

(4) Smaller system footprint: the smaller ammonia or urea storage tank needed can be placed on top of the boiler steel frame without additional footprint.

(5) Denitrification efficiency is 40 to 50 percentage points lower than SCR method.

Process Flow

SNCR process systems mainly include: (1) reductant storage and preparation systems: including the necessary conveying equipment, tank equipment, etc.; (2) dilution systems: including dilution pumps or fans and other equipment; (3) conveying systems; (4) metering and distribution systems; (5) urea solution injection systems; (6) others: other systems for SNCR denitrification include water, gas, steam, as well as control and fire-fighting systems.

Ammonia solution conveying system and demineralized water solution conveying system

In SNCR denitrification, the ammonia solution in the storage tank is pumped out in the static mixer with the dilution water from the desalination water tank, and then transported to the furnace front distribution module, into the lance, under the action of compressed air, atomized into liquid droplets sprayed into the furnace temperature suitable area, mixed with the flue gas, and the NOx in the oxidation reduction reaction to produce nitrogen and water. The ammonia solution transfer pump and dilution water transfer pump adopt multi-stage centrifugal pump.

Metering distribution module

The metering and distribution device includes: electric regulating valve, electromagnetic flow meter, pressure sensor, rotameter, pressure gauge, manual ball valve and junction box, etc. The metering and distribution device is used to control the flow of ammonia solution in the injection zone of each boiler and to regulate the injection pressure of compressed air in the injection zone. The metering and distribution device of each boiler is controlled independently by zoning, and each subsystem can operate or shut down independently. The metering and distribution system is located close to the injection system, and each boiler uses an independent flow and pressure control system to provide the high level of control required for complex applications. The injection system is controlled by analyzing the real-time conditions of the boiler (e.g., flue gas volume, NOx and O2 concentrations, etc.) and adjusting the flow rate of the ammonia solution to the spray gun (by adjusting the opening of the electric regulating valve in the water circuit) or by adjusting the pressure of the compressed air, so that the injection system can meet the requirements of the real-time conditions of the boiler and inject the ammonia solution.

Furnace front injection system

The spray gun is composed of nozzle, spray gun rod, protection sleeve and connection parts.

Influencing Factors

Temperature
Temperature has the greatest influence on the reduction reaction of SNCR. When the temperature is higher than 1100°C, the NOx removal rate decreases due to the thermal decomposition of ammonia; when the temperature is lower than below 800°C, the reaction rate of NH3 decreases, the reduction reaction does not proceed adequately, and the NOx removal rate decreases, while the amount of ammonia escaping may also be increasing. As the temperature distribution in the furnace is affected by various factors such as load and coal type, the temperature window changes with the boiler load. According to the boiler characteristics and operating experience, the best temperature window usually appears at the screen superheater and reheater near the folded flame angle and at the area where the final superheater and reheater of the horizontal flue are located.

Reducing agent
Reduction agent at optimum temperature residence time

The longer the residence time of the reducing agent in the optimum temperature window, the better the NOx removal, and the best NOx removal rate can be achieved with a residence time of more than 1s for NH3. Urea and ammonia require a residence time of 0.3s to 0.4s to achieve effective NOx removal.

Reducing agent type

The reducing agents used in the SNCR process and the preparation methods are the same as for the SCR process, mainly NH3 and urea. In order to obtain the desired NOx removal efficiency, the amount of reducing agent (chemical equivalent) is larger than that of the SCR process. Most of the excess reductant decomposes to nitrogen and CO2, however, there are traces of ammonia and CO that remain in the tail gas and cause ammonia leakage problems. In the case of urea as reductant, the chance of N2O generation is greater than that of ammonia because urea can be decomposed into HNCO, which can be further decomposed into NCO, which can react with NO to form dinitrogen oxide:

NCO+NO→N2O+CO

In order to improve the reduction efficiency of SNCR for NOx and reduce the leakage of ammonia, the following key process parameters must be considered in the design stage: fuel type, boiler load, furnace structure, heating surface arrangement, excess air volume, NO concentration, furnace temperature distribution, furnace airflow distribution and CO concentration, etc.

The main products of Yiqing Environmental Protection include various industrial dust treatment equipment, industrial flue gas desulfurization, denitrification, VOCs treatment equipment and flue gas desulfurization, dust removal, denitrification integrated ultra-low emission equipment, Yiqing Environmental Protection since its inception, based on the industry, social development needs, dedicated to the comprehensive treatment of flue gas, dust and flue gas energy saving and other technical fields of research, technology innovation and upgrading to achieve new breakthroughs. The company has the most cutting-edge integrated flue gas treatment solutions, with strong innovation, development and manufacturing capabilities in the cutting-edge field of environmental protection equipment, with a number of patents for integrated flue gas treatment system, and built a leading flue gas simulation generation and treatment system, the acquisition of advanced monitoring equipment, through accurate generation, accurate monitoring accurately obtain the key nodes and links of the flue gas treatment system The working parameters of each key node and link of the flue gas treatment system have been accurately generated and monitored, and the cause-and-effect relationship between the working parameters of the flue gas treatment link has been mastered, and some unique experience has been gained. The scientific research project "New type of kiln flue gas purification system" undertaken by Yiqing Environmental Protection has been awarded the science and technology projects by Guangdong Province and Foshan Municipal Government.

劲旅环境

Introduction

Features

Process Flow

Influencing Factors