CN103728994B - A kind of cement plant SCR denitration efficiency monitoring control method - Google Patents

Abstract

A method for monitoring and controlling the SCR denitrification efficiency of a cement plant belongs to the technical field of cement production emission safety. The denitrification efficiency control device of the SCR reactor includes: an inlet detection device and an outlet detection device, which are used to periodically measure the NOx content and ammonia content in the flue gas and send them to the calculation control device. The calculation control device is used to receive the periodic data of the detection device and accurately calculate the denitrification efficiency of the reactor and the amount of ammonia escape, and send control instructions to the ammonia injection control device inside the SCR reactor according to the calculated data results. The ammonia injection control device is used to receive control instructions and periodically send real-time ammonia injection data to the calculation control device. The ammonia injection control device controls the ammonia injection amount by receiving the control instructions. The invention aims at realizing accurate measurement and precise control of denitrification efficiency, ammonia slip rate and ammonia injection amount of an SCR reactor, and reduces ammonia slip amount while maintaining high denitrification efficiency.

Description

A monitoring and control method for SCR denitrification efficiency in a cement plant

technical field

The invention belongs to the technical field of cement production emission safety, and in particular relates to a method for monitoring and controlling the SCR denitrification efficiency of a cement plant.

Background technique

NOx is a common air pollutant, which has great damage to the environment. NOx mainly includes NO and NO ₂ , which can induce urban photochemical smog and stimulate human lungs. At present, my country's cement production ranks first in the world, and the cement industry is the third largest source of NOx emissions in my country. In 2011, the NOx emissions reached 3.843 million tons. Therefore, it is of great significance to monitor and control the denitrification efficiency of SCR reactor in cement plant to control NOx emission.

The "Twelfth Five-Year Plan" of the cement industry has clearly defined the goal of reducing nitrogen oxide emissions by 10%. China's current "Cement Industry Air Pollutant Emission Standard" (GB4915-2004) stipulates that the NOx emission limit is 800mg/Nm ³ . Today, with the development of my country's cement industry, it is positioned as a green industry that is in harmony with the natural environment. Environmental friendliness will also be an important feature for cement development to enter the ecological stage. Therefore, the NOx emission standards of my country's cement industry will become increasingly strict, and the state's control over NOx emissions will also continue to increase.

Currently, NOx emission control technologies in the cement industry mainly include selective non-catalytic reduction (SNCR) technology and selective catalytic reduction (SCR) technology. Selective non-catalytic reduction (SNCR) technology sprays reducing agents (ammonia, urea, etc.) Water, the general NOx reduction rate is between 10% and 50%. The Selective Catalytic Reduction (SCR) technology uses an appropriate catalyst, and under certain conditions, ammonia is used as a reducing agent in the catalytic reaction to convert pollutant NOx into harmless nitrogen and water vapor. The main reaction is as follows:

4NO+4NH ₃ +O ₂ →4N ₂ +6H ₂ O (formula Ⅰ)

2NO ₂ +4NH ₃ +O ₂ →3N ₂ +6H ₂ O (formula Ⅱ)

Under ideal conditions, SCR technology can make the removal rate of NOx reach more than 90%. Although the fixed investment is large, the operating cost is low. It is the best fixed source NOx treatment technology currently available. At present, the evaluation of the operation status of the SCR denitrification system mainly depends on two indicators: denitrification efficiency and ammonia slip. Theoretically speaking, under the best conditions, 1 mol of NOx needs 1 mol of NH ₃ to be completely reduced. Therefore, if the amount of ammonia injection is insufficient, the denitrification efficiency will be easily reduced, but if the amount of ammonia injection is too large, the denitrification efficiency can be guaranteed. But it is easy to increase the escape amount of ammonia gas, causing secondary environmental pollution. When the ammonia-nitrogen molar ratio is less than 1, the denitrification efficiency increases with the increase of the molar ratio, but the amount of ammonia slip also increases slowly. Therefore, real-time monitoring of the SCR system is of great significance to accurately control the amount of ammonia injection to reduce the amount of ammonia escape while maintaining a high denitrification efficiency of the catalyst.

Contents of the invention

A cement plant SCR reactor denitrification efficiency monitoring and control system is characterized in that: it is a control device including ammonia injection, inlet detection device, outlet detection device, calculation and control device, which can monitor the denitrification efficiency of SCR reactor, ammonia A system for accurate measurement and real-time control of escape rate and ammonia injection volume. The ammonia injection control device adjusts the ammonia injection amount by receiving the control data from the calculation control device. And the ammonia injection amount data is periodically fed back to the calculation control device through the line. The inlet detection device periodically detects the temperature and NOx content of the flue gas entering the SCR reactor, and inputs it into the calculation control device through the line. The outlet detection device conducts periodic NOx content detection and ammonia (NH ₃ ) content detection on the flue gas discharged from the SCR reactor. The calculation and control device can receive the data transmitted by the inlet detection device, the outlet detection device and the ammonia injection control device, calculate the denitrification efficiency and the ammonia escape rate, and display them on an external screen. The display device can also display the inlet temperature and outlet ammonia escape data. . When the denitrification efficiency is too small or the amount of ammonia escape is too large, the calculated denitrification efficiency or ammonia escape rate value will flash and display with an alarm prompt. The computing control device sends control data to the ammonia injection control device. In order to achieve the purpose of controlling the denitrification efficiency and ammonia slip.

In the denitrification efficiency detection and control system of the present invention, the inlet detection device includes: a flue gas temperature detection device and a NOx content detection device.

In the denitration efficiency detection and control system of the present invention, the outlet detection device includes: a NOx content detection device and an ammonia content detection device.

In the denitrification efficiency detection and control system of the present invention, the ammonia injection control device includes: an ammonia injector, a distribution pipeline, a distribution supply pump, a special ammonia water storage tank, a spare ammonia water storage tank, and a system for receiving and transmitting data and controlling ammonia injection. amount of microcomputers.

In the denitrification efficiency detection and control system of the present invention, the calculation and control device includes: a calculation device, an external display device, an alarm device and a control device.

A method for controlling the denitrification efficiency monitoring and control system of the SCR reactor in a cement plant. The steps are as follows: periodically detect the temperature value (T) of the inlet detection device, and judge whether the temperature value is within the set range (T≥150 ℃).

If the temperature value exceeds the range of catalyst use (T<150°C), an alarm signal will be sent to the calculation and control device, and the calculation and control device will display the temperature data in flickering display with an alarm prompt, indicating that the temperature range is exceeded. It is recommended to adjust the production parameters to make the flue gas temperature Stable within the set range.

If the temperature measured by the inlet detection device is within the use range of the low-temperature catalyst, the NOx content M ¹ _NOx value is periodically transmitted to the calculation control device.

The NOx content M ² _NOx value at the outlet and the ammonia content M ² _NH3 value periodically measured by the outlet detection device are input into the calculation control device.

In accordance with the relevant national standards for measuring NOx, all measured values were converted into NO ₂ meters, and the units of M ¹ _NOx and M ² _NOx were mg/Nm ³ . The unit of ammonia content M ¹ _NH3 and M ² _NH3 is mg/Nm ³ .

The ammonia injection control device inputs the periodically measured ammonia injection amount M ¹ _NH3 into the calculation control device.

The calculation and control device calculates the denitrification rate (△NOx) and ammonia slip rate (NH _{3 slip} ) through periodic input data, and displays them. The display device can also display the data of inlet temperature and outlet ammonia slip. The computing control device sends a control command to the ammonia injection control device, and adjusts the ammonia injection control device to control the ammonia injection amount.

When the denitrification rate is less than or equal to 60%, the calculation control device will alarm and flash to display the denitrification rate data.

When the outlet ammonia content M ² _NH3 ≥ 20mgNH ₃ /Nm ³ , the calculation control device will give an alarm and display the data of the amount of ammonia escaped in a flickering manner.

When the ammonia escape rate NH _{3 escape} ≥ 5%, the calculation control device will alarm, and flashing display ammonia escape rate data.

When the calculation control device sends out an alarm, the control device sends a control command to the ammonia injection control device. Adjust the amount of ammonia injection to control the denitrification rate or the amount of ammonia escape.

Denitration rate: △NOx=(M ¹ _NOx —M ² _NOx )/M ¹ _NOx

Ammonia escape rate: NH _{3 escape} = M ² _NH3 /M ¹ _NH3

The main purpose of the present invention is to monitor the denitrification efficiency and ammonia slip rate of the SCR reactor in a cement plant in real time, adjust the denitrification efficiency and ammonia slip rate by controlling the amount of ammonia injection, and minimize ammonia slip while maintaining a high denitrification efficiency. The control process is simple and fast, and the design is reasonable, which can effectively reduce pollutant emissions and provide strong support for promoting the greening process of the cement industry.

Description of drawings

Figure 1 shows the SCR denitrification efficiency monitoring and control system in a cement plant

Figure 2 is a flow diagram of the method for controlling the denitrification efficiency monitoring and control system of the SCR reactor in the cement plant

detailed description

The control system and control method for the detection of SCR denitrification efficiency in cement plants will be further described below according to Fig. 1 and Fig. 2 of the accompanying drawings and the embodiments.

The design scale of the cement production line in the embodiment is 2500t clinker/day, and the actual output is 2500t clinker/day. The SCR reactor is installed after the waste heat boiler and before the bag filter for coal mill drying. The temperature of the inlet flue is about 200°C, the total air volume is about 175,000m ³ /h, and the NOx content in the flue gas is about 600mg/Nm ³ .

The catalyst in the SCR reactor can use medium and low temperature catalysts, such as MnOx-CeO ₂ -TiO ₂ type catalysts, which can achieve a catalytic efficiency of more than 90% at around 200 ° C, and the suitable ammonia nitrogen ratio is 0.9:1.

SCR reactor denitrification efficiency monitoring and control system in cement plant, including ammonia injection control device, inlet detection device, outlet detection device, calculation control device.

The flue gas enters the inlet flue and flows through the inlet detection device. The entrance detection device includes: flue gas temperature detection device and NOx content detection device. Measured by the flue gas temperature detection device, the temperature meets the set range (T≥150°C). The NOx content detection device measures the NOx content in the flue gas periodically (the set period is 5 minutes), and periodically sends the content value to the calculation control device.

The flue gas flows through the ammonia injection control unit. The ammonia injection control device includes: ammonia injector, distribution pipeline, distribution supply pump, special ammonia water storage tank, spare ammonia water storage tank and a microcomputer for receiving and transmitting data and controlling the amount of ammonia injection. The ammonia injection device injects a certain amount of ammonia gas into the flue gas (receives the ammonia injection amount control command issued by the calculation control device), and periodically transmits the actual ammonia gas injection data to the calculation control device.

After the flue gas mixed with ammonia passes through the ammonia injection control device, it flows through the channel equipped with deflectors, flows into the SCR reactor, and undergoes a selective catalytic reduction reaction with the denitration catalyst in the reactor to convert NOx into harmless N ₂ and H ₂ O, the main reaction formula is as follows:

4NO+4NH ₃ +O ₂ →4N ₂ +6H ₂ O (formula Ⅰ)

2NO ₂ +4NH ₃ +O ₂ →3N ₂ +6H ₂ O (formula Ⅱ)

The flue gas passing through the SCR reactor flows through the outlet detection device. The outlet detection device includes: NOx content detection device and ammonia content detection device. At this time, the flue gas contains NOx gas and ammonia gas remaining after participating in the selective catalytic reduction reaction. The NOx content detection device and the ammonia content detection device periodically detect the remaining content respectively, and send the detection data to the calculation control device.

The flue gas passes through the outlet of the SCR reactor and is discharged to the subsequent bag filter.

The relevant data are transmitted to the computing control unit. The calculation control device includes: a calculation device, an external display device, an alarm device and a control device. The calculation device calculates the denitrification rate (△NOx) and ammonia slip rate (NH _{3 slip} ), and displays them through an external display device, which can also display the data of inlet temperature and outlet ammonia slip. The operation control device sends a control command to the ammonia injection control device, and adjusts the ammonia injection control device to regulate the amount of ammonia injection.

It can be seen from the above examples that the SCR denitrification efficiency monitoring and control system can achieve the purpose of effectively monitoring and controlling the denitrification efficiency and ammonia escape.

The control method of the SCR denitrification efficiency detection and control system of the cement plant will be further described below according to Fig. 2 of the accompanying drawings and the embodiments.

The flue gas enters the inlet flue and flows through the inlet detection device.

The temperature detection device at the entrance periodically detects the temperature (T) of the incoming flue gas, and judges whether the temperature value is within the set range.

The measured temperature value = 120°C < 150°C, which is beyond the use range of the catalyst.

Send an alarm signal to the calculation control device, the calculation control device will flash and display the temperature data with an alarm prompt, indicating that the temperature range is exceeded, and it is recommended to adjust the production parameters.

After adjusting the production parameters, the temperature measured by the inlet detection device = 190°C, which is within the range of catalyst use.

The NOx content detection device periodically transmits the NOx content M ¹ _NOx value to the calculation control device.

The ammonia injection control device sprays ammonia into the flue. The periodically measured ammonia injection amount M ¹ _NH3 is input into the calculation control device.

The outlet detection device inputs the periodically measured NOx content M ² _NOx value and ammonia content M ² _NH3 value at the outlet into the calculation control device.

All measurements _were converted to NO2 meters. M ¹ _NOx value at the inlet = 600mg/Nm ³ .

The unit of M ¹ _NOx and M ² _NOx is mg/Nm ³

The unit of ammonia content M ¹ _NH3 and M ² _NH3 is mg/Nm ³ .

The calculation and control device calculates the denitrification rate △NOx and the ammonia slip rate NH _{3 escape} through periodic input data, and displays them. The display device can also display the data of the inlet temperature and the outlet ammonia slip. The calculation control device sends a control command to the ammonia injection control device to adjust the ammonia nitrogen ratio of ammonia injection to 0.9. The ammonia injection control device regulates the amount of ammonia injection, and the amount of ammonia injection is 208mg/Nm ³ .

After a period of time, the denitrification system shows 89%, the ammonia escape amount is 10mg/Nm ³ , and the escape rate shows 4.8%.

Among them: denitrification rate: △NOx=(M ¹ _NOx –M ² _NOx )/M ¹ _NOx

Among them: Ammonia escape rate: NH3 _escape = M ² _NH3 /M ¹ _NH3

When the denitrification rate is less than or equal to 60%, the calculation control device will alarm and flash to display the denitrification rate data. At this time, send control instructions to the ammonia injection control device to gradually increase the amount of ammonia injection, and the amount of ammonia injection reaches about 235mg/ ^Nm3 (increase the ammonia nitrogen ratio, increasing to 1), so as to achieve the purpose of improving the denitrification efficiency.

After a period of time, it can be seen through the display device that the denitrification rate gradually rises and returns to 89%, which is in the higher range of denitrification efficiency. At the same time, the amount of ammonia escape begins to increase, which is displayed as 15mg NH ₃ /Nm ³ . At this time, a control instruction is sent to the ammonia injection control device to stabilize the current ammonia injection amount. In order to achieve a high denitrification efficiency while controlling the amount of ammonia escape.

When the outlet ammonia content M ² _NH3 ≥ 20mgNH ₃ /Nm ³ , the calculation and control device will alarm and display the data of the outlet ammonia content (M ² _NH3 ) in flicker. At this time, send a control command to the ammonia injection control device to gradually reduce the amount of ammonia injection (reduce the ammonia-nitrogen ratio), so as to reduce the increase in ammonia escape.

After a period of time, it can be seen through the display device that the amount of ammonia escape gradually decreases to M ² _NH3 =17mg NH ₃ /Nm ³ , returning to a lower range, and the denitrification efficiency at this time is displayed as 91%. At this time, a control command is sent to the ammonia injection control device to stabilize the current ammonia injection amount and maintain a high denitrification efficiency.

When the ammonia slip rate NH _{3 slip} ≥ 5%, the calculation control device will alarm, and flashing display ammonia slip rate NH ₃ slip data. At this time, if the outlet ammonia content M ² _NH3 < 20mgNH ₃ /Nm ³ , it can be judged to choose to turn off the alarm, and continue to maintain the current ammonia injection volume and denitrification efficiency. Or send a control instruction to the ammonia injection control system to reduce the amount of ammonia injection.

When the ammonia escape rate NH _{3 escape} ≥ 5%, and the outlet ammonia content M ² _NH3 ≥ 20mgNH ₃ /Nm ³ . Send control instructions to the ammonia injection control device to gradually reduce the amount of ammonia injection to achieve the purpose of reducing the increase in ammonia escape.

As can be seen from the above examples, the SCR denitrification efficiency detection and control system of the cement plant can monitor the denitrification efficiency of the SCR reactor and the amount of ammonia escape at the outlet in real time, and control the amount of ammonia injection through the calculation control device and the ammonia injection control device, so that To achieve the purpose of controlling the denitrification efficiency and ammonia slip. Through this invention, the cement plant can maintain a high denitrification efficiency while taking into account the control of ammonia escape, so as to achieve a dynamic balance between the two. The design of the detection and control system is reasonable, and the operation is simple and fast.

Claims (1)

1. a cement plant SCR denitration efficiency monitoring control method, it is characterised in that: applying following system, this system includes that spraying ammonia controls device, entrance detection device, outlet detection device, calculation control device, display device and alarm sounds device；

Spray ammonia controls device and connects calculation control device；Entrance detection device and outlet detection device are placed on the entrance and exit in SCR reactor,

Described spray ammonia controls the device control data by reception calculation control device, is adjusted ammonia spraying amount；And periodically actual ammonia spraying amount data are passed through circuit reverse pumping to calculation control device；

Entrance detection device, described entrance detection device carries out periodic temperature detection and NOx content detection, and inputs calculation control device by circuit the flue gas entering SCR reactor；

Outlet detection device, described outlet detection device carries out periodic NOx content detection and ammonia content detection to the flue gas discharging SCR reactor；

Described calculation control device receives entrance and detects device, and outlet detects device and the data of spray ammonia control device transmission, carries out denitration efficiency calculating and the escaping of ammonia rate is calculated and shown by display device；

Step is as follows:

The temperature value of entrance detection device is periodically detected, it is judged that whether temperature value is in catalyst range；

If temperature value exceeds catalyst range, then sending alarm signal to calculation control device, calculation control device is by temperature data flickering display and with alarm, and temp. indicator scope exceeds, suggestion adjusts manufacturing parameter, makes flue-gas temperature stable in range；

If the temperature that entrance detection device records is in catalyst range, then periodically by NOx content M¹ _NOxValue is transmitted to calculation control device；

The exit NOx content M that outlet detection device is periodically recorded² _NOxValue and ammonia content M² _NH3Value is input in calculation control device；

NOx measured value is completely converted into NO₂Meter, M¹ _NOxAnd M² _NOxUnit be mg/Nm³；Ammonia content M¹ _NH3And M² _NH3Unit be mg/Nm³；

Spray ammonia controls the actual ammonia spraying amount M that device will periodically record¹ _NH3It is input in calculation control device；

Calculation control device calculates denitration rate △ NOx and the escaping of ammonia rate NH by the data periodically inputted_{3 Escape}, and display it, calculation control device controls device to spray ammonia and sends control instruction, adjusts spray ammonia and controls device regulation and control ammonia spraying amount；When denitration rate≤60%, calculation control device will be reported to the police, and flickering display denitration rate △ NOx data；As outlet ammonia content M² _NH3≥20mgNH₃/Nm³Time, calculation control device will be reported to the police, and flickering display outlet ammonia content M² _NH3Data；When the escaping of ammonia rate NH_{3 Escape}When >=5%, calculation control device will be reported to the police, and flickering display the escaping of ammonia rate NH_{3 Escape}Data；

When calculation control device sends alarm, by calculation control device, spray ammonia is controlled device and send control instruction；Adjust ammonia spraying amount, regulation and control denitration rate or the escaping of ammonia rate；

Denitration rate: △ NOx=(M¹ _NOx–M² _NOx)/M¹ _NOx

The escaping of ammonia rate: NH_{3 Escape}=M² _NH3/M¹ _NH3。