CN203927880U - A kind of economizer that improves SCR system underrun denitration ability - Google Patents

Abstract

The utility model discloses an economizer which improves the denitrification capacity of an SCR system in low-load operation. A bypass is arranged on the water supply pipeline connected to the inlet header of the economizer. The bypass is divided into two branches, and one branch leads out It is connected to the middle header of the economizer, and the other is connected to the outlet pipe of the economizer outlet header. In the two branch pipes, a one-way valve, a stop valve and a flow regulating valve are respectively arranged in sequence along the direction of fluid flow. The utility model is adopted to adjust the opening of the two branch valves to adjust the flow rate of the bypass diversion medium, thereby controlling the temperature of the flue gas at the outlet of the economizer by reducing the heat exchange of the economizer system, so that the SCR cannot be reached originally. The low-load working condition of the commissioning condition can meet the temperature requirements of the SCR commissioning, effectively improving the continuous operation time of the SCR denitrification system of the power plant. The denitrification capability of the SCR system is enhanced, helping the power plant to better meet environmental protection indicators in a longer period of time.

Description

A Coal Economizer for Improving the Denitrification Capability of SCR System in Low-load Operation

technical field

The utility model relates to the field of flue gas denitrification of power station boilers, in particular to an economizer for improving the denitrification capability of an SCR system in low-load operation.

Background technique

Selective catalytic reduction (SCR) is mainly used in thermal power plants, motor vehicles, ships and other fields. Its main function is to remove nitrogen oxides produced by boiler or engine combustion. In nitrogen oxides, NO accounts for about 95%, NO ₂ accounts for about 5%, and also contains a small amount of N ₂ O. These gases are discharged into the atmosphere, which will cause acid rain, photochemical smog, and ozone layer depletion. One of the important sources of environmental air pollution. SCR technology is that under the action of a catalyst, the reactant is adsorbed on the catalyst and reacts to generate N ₂ and H ₂ O that are harmless to humans. Due to the presence of the catalyst, the denitrification efficiency can reach a very high level. Selective catalytic reduction method (SCR) has become the most important denitrification technology in the industry.

my country's main energy comes from coal combustion. According to statistics, 67% of my country's nitrogen oxide emissions come from coal combustion, and thermal power plants account for 50% of the national total. It is the top priority to control the total emission of nitrogen oxides in my country. In recent years, in terms of thermal power plants, domestically, it is required to retrofit SCR systems for active units that have not been installed with denitrification equipment. The layout of the SCR process system mainly includes high-temperature and high-dust layout, high-temperature and low-dust layout, and low-temperature and low-dust layout, among which the high-temperature and high-dust layout is the most common, that is, the SCR reactor is arranged between the economizer and the air preheater , this arrangement keeps the temperature of the flue gas entering the SCR denitrification system at 280°C to 420°C, which meets the activity temperature range of most catalysts. In the active temperature range, the SCR system can achieve better results, and the denitrification performance increases with the increase with the increase of flue gas temperature. However, when the flue gas temperature is lower than the lower limit of the catalyst activity temperature range, the catalyst activity is low, so that on the one hand, the denitrification efficiency is low, and on the other hand, the ammonia escape rate is high, and the escaped ammonia will react with the sulfur oxides in the flue gas to form Ammonium sulfate and ammonium bisulfate will cause blockage of catalyst reaction channel and downstream air preheater in severe cases. However, when the flue gas temperature is higher than the upper limit of the active temperature range of the catalyst, the catalyst will be sintered or recrystallized, reducing the service life of the catalyst.

Considering the impact of temperature on the SCR denitrification system and downstream equipment, the operating temperature of the SCR system is generally designed at 300°C to 400°C, and within this temperature range, the catalyst can be guaranteed to operate at a relatively high activity. Since the power generation load of the power station is controlled by the dispatching command of the power grid, during the peak period of power consumption, the boiler of the power station is kept running under BMCR or high load conditions, and the inlet temperature of the denitrification device can be guaranteed to be within the operating temperature range of the SCR, and the denitrification system can operate normally. However, power plant boilers cannot operate at high load for a long time. During the off-peak period of electricity consumption, the power grid’s demand for power generation load of the power plant is low, and the power plant boiler operates under low load. At this time, the reaction temperature of the flue gas in the SCR system is low. The activity of the denitrification decreases with the decrease of temperature, so the denitrification efficiency is also low. In addition, when the flue gas temperature at the inlet of the denitrification device does not reach the lower limit of the operating temperature of the denitrification system, the denitrification system will stop operating, and the emission of nitrogen oxides will increase, making it difficult for the power station to meet the environmental protection indicators stipulated by the state. On the other hand, although the catalyst stops working, it is still being scoured by flue gas, and the wear of the catalyst by the fly ash does not decrease, resulting in a reduction in the service life of the catalyst. Therefore, under the low-load operating conditions of power plant boilers, ensuring the efficiency of the SCR denitrification system and improving the commissioning time of the SCR denitrification system are technical problems that need to be solved in the domestic denitrification field.

Utility model content

Purpose of the invention: In order to overcome the deficiencies in the prior art, the utility model provides an economizer that improves the denitrification capability of the SCR system in low-load operation.

Technical solution: In order to solve the above technical problems, the utility model provides an economizer that improves the denitrification capacity of the SCR system under low load operation, including the furnace flue shell, the economizer outlet header installed in the furnace flue shell, A set of economizer suspension pipes connected to the economizer outlet header, an economizer intermediate header connected to each economizer suspension pipe, a set of economizers connected to the economizer intermediate header The serpentine pipe, the economizer inlet header connected to the economizer serpentine pipe, and the SCR reactor connected to the bottom of the furnace flue shell; the economizer inlet header and the economizer outlet header are set There is a first branch pipe, and the first branch pipe is respectively provided with a first one-way valve, a first stop valve and a first flow regulating valve in sequence along the fluid flow direction, and each economizer is connected in the middle A second branch pipe is provided between the first branch pipe or the inlet header of the economizer, and the second branch pipe is respectively provided with a second one-way valve, a second shut-off valve and second flow regulating valve.

Further, the SCR reactor includes a reactor shell, a catalyst reserve layer, a catalyst first layer and a catalyst second layer sequentially arranged in the reactor shell.

Further, one end of the second branch pipe is connected to the first branch pipe through a three-way pipe connector, and the other end of the second branch pipe is connected to several economizer intermediate headers by welding.

Further, an economizer ash hopper is provided at the bottom of the furnace flue shell.

Further, two ends of the first branch pipe are respectively provided with a three-way pipe connector.

Beneficial effect: compared with the prior art, the utility model has the following advantages:

The utility model adopts the method of adjusting the opening degree of the two branch valves to adjust the flow rate of the bypass shunt medium, so as to control the flue gas temperature at the outlet of the economizer by reducing the heat exchange of the economizer system, so that the SCR cannot be reached originally. The low-load working condition of the commissioning condition can meet the temperature requirements of the SCR commissioning, effectively improving the continuous operation time of the SCR denitrification system of the economizer in the power plant. The increase in gas temperature leads to an increase in the activity of the SCR catalyst, and the denitrification capability of the SCR system is enhanced, helping the power plant to better meet environmental protection indicators in a longer period of time.

Description of drawings

Fig. 1 is a structural representation of the utility model.

Fig. 2 is a schematic diagram of the connecting device of the first branch pipe and the second branch pipe of the present invention.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is described further.

As shown in Fig. 1 and Fig. 2, an economizer for improving the denitrification capacity of the SCR system at low load operation includes a furnace flue shell 30, an economizer outlet header 2 arranged in the furnace flue shell 30, and a economizer A set of economizer suspension pipes 5 connected to the outlet header 2 of the coal generator, an economizer intermediate header 6 connected to each economizer suspension pipe 5, a set of economizer intermediate headers 6 connected The economizer serpentine pipe 7, the economizer inlet header 14 connected to the economizer serpentine pipe 7, and the SCR reactor connected to the bottom of the furnace flue shell 30; the economizer inlet header 14 is connected to the economizer A first branch pipe 3 is provided between the outlet headers 2 of the coal appliance, and the first branch pipe 3 is respectively provided with a first one-way valve 9, a first stop valve 8 and a first A flow regulating valve 4, a second branch pipe 10 is provided between each economizer intermediate header 6 and the first branch pipe 3 or the economizer inlet header 14, and the second branch pipe 10 along the direction of fluid flow, respectively provided with a second one-way valve 13, a second shut-off valve 12 and a second flow regulating valve 11; the bottom of the furnace flue shell 30 is provided with an economizer ash hopper 16; The SCR reactor comprises a reactor shell 31, a catalyst reserve layer 18, a catalyst first layer 19, and a catalyst second layer 20 which are sequentially arranged in the reactor shell 31; one end of the second branch pipe 3 passes through a tee The pipe 24 is connected with the first branch pipe 3, and the other end of the second branch pipe 3 is connected with several economizer intermediate headers 6 by welding; the two ends of the first branch pipe are respectively provided with a first A three-way pipe connector 22 and a second three-way pipe connector 23 .

The operating conditions of the SCR denitrification system in the economizer of the power station are determined according to the active temperature range of the SCR catalyst, and are generally designed at 300°C to 400°C. Under low-load operating conditions, the gas enters from the inlet flue gas 1 of the economizer, the temperature of the flue gas 15 at the outlet of the boiler economizer is lower than 300 °C, and there is no heat exchange equipment between the economizer outlet and the SCR reactor inlet, Therefore, the flue gas 17 temperature at the inlet of the SCR reactor is approximately equal to the outlet temperature of the economizer, which is lower than the lower limit of the operating temperature range of the SCR system. If the temperature of the flue gas 17 at the SCR inlet is slightly lower than the lower limit of the SCR system operating temperature, open the second stop valve 12 and gradually increase the valve opening of the second regulating valve 11 to control the flow of the diverted medium in the second branch pipe section 10 ; If the temperature of the flue gas 17 at the SCR inlet is lower than the lower limit of the SCR system operating temperature, open the first stop valve 8, and gradually increase the valve opening of the first regulating valve 4 to control the diversion medium of the first branch pipe section 3 Due to the shunt effect of the bypass, the flow of the medium participating in the heat exchange will decrease, resulting in a decrease in the heat exchange between the medium and the flue gas, so the heat release of the flue gas in the heating surface area of the economizer is reduced, making the outlet of the economizer The temperature of flue gas 15 and SCR inlet flue gas 17 rises by more than 300°C, reaching the operating temperature range of the SCR system, effectively improving the operating rate of the SCR system and the effective use time of the catalyst.

The optimization method and control strategy of a kind of SCR low-load operation of the present utility model are as follows during actual work:

The heat exchange surface of the boiler economizer system is mainly composed of the economizer suspension pipe 5 and the economizer serpentine pipe 7. The economizer serpentine pipe 7 is connected between the inlet header 14 and the intermediate header 7, saving coal The suspension pipe 5 of the economizer is connected between the middle header 7 and the outlet header 2, and the heat exchange area of the serpentine pipe 7 of the economizer is larger than that of the suspension pipe 5 of the economizer, which plays a major role in heat exchange. Under the low-load operating condition of the boiler, if the temperature of the flue gas 15 at the outlet of the economizer is lower than the lower limit of the SCR operation temperature, and the difference between the two is small, open the bypass second cut-off valve 12 at this time, and gradually increase the second Adjust the valve opening of the valve 11 to control the flow of the medium in the bypass. Due to the shunting effect of the bypass, the flow of the medium participating in the heat exchange in the economizer serpentine tube 7 will decrease, resulting in a decrease in the heat exchange between the medium and the flue gas. Therefore, the heat release of the flue gas in the heat exchange area of the economizer serpentine tube 7 is reduced, so that the temperature of the flue gas 15 at the outlet of the economizer rises by more than 300°C. If the temperature of the flue gas 15 at the outlet of the economizer is quite different from the lower limit of the SCR operation temperature, the first cut-off valve 8 of the bypass can be opened at this time, and the valve opening of the first regulating valve 4 can be gradually increased to control the medium flow of the bypass. Since the bypass medium does not enter the economizer system at all to participate in heat exchange at this time, it has a greater impact on increasing the outlet temperature of the economizer. By reasonably controlling the opening of the regulating valves of the first branch pipe and the second branch pipe , the temperature of the flue gas 15 at the outlet of the economizer can be flexibly controlled. The design and operation temperature range of the SCR system is 300°C to 400°C. Three layers of catalysts are designed in the reactor. The first layer is the reserved layer 18. In the second layer 20, since there is no heat exchange equipment between the economizer outlet and the SCR reactor inlet, the temperature of the flue gas 17 entering the catalyst 19 of the first layer of the SCR is approximately equal to the temperature at the economizer outlet, reaching the operating temperature of the SCR system interval, effectively improving the operating rate of the SCR system and the effective use time of the catalyst. In addition, the heat capacity of the medium side is higher than that of the flue gas side. When the same amount of heat transfer is reduced, the increase in the outlet temperature of the flue gas side is greater than the decrease in the outlet temperature of the medium side. The economical operation of the boiler has less impact, which ensures the operability of the utility model in engineering.

The above is only a preferred embodiment of the utility model, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the utility model, some improvements and modifications can also be made. Retouching should also be regarded as the scope of protection of the present utility model.

Claims (5)

1. An economizer that improves the denitrification capacity of the SCR system at low load, characterized in that it includes a furnace flue casing (30), and an economizer outlet header (2) arranged in the furnace flue casing (30) , a group of economizer suspension pipes (5) connected to the economizer outlet header (2), an economizer intermediate header (6) connected to each economizer suspension pipe (5), and A set of economizer serpentine pipes (7) connected to the middle header (6) of the economizer, an economizer inlet header (14) connected to the economizer serpentine pipes (7), and the shell of the furnace flue (30) SCR reactor connected at the bottom; a first branch pipe (3) is provided between the economizer inlet header (14) and the economizer outlet header (2), and the first branch The pipe (3) is respectively provided with a first one-way valve (9), a first stop valve (8) and a first flow regulating valve (4) in sequence along the fluid flow direction, and the middle header of each economizer (6) A second branch pipe (10) is provided between the first branch pipe (3) or the inlet header of the economizer (14), and the second branch pipe (10) flows along the fluid In the direction, a second one-way valve (13), a second stop valve (12) and a second flow regulating valve (11) are respectively arranged in sequence. 2. The economizer for improving the denitrification capacity of the SCR system under low load operation according to claim 1, characterized in that: the SCR reactor includes a reactor shell (31), which is sequentially arranged in the reactor shell (31) The inner catalyst reserve layer (18), the first catalyst layer (19) and the second catalyst layer (20). 3. The economizer for improving the denitration capacity of the SCR system under low load operation according to claim 1, characterized in that: one end of the second branch pipe (10) is connected to the first branch pipe ( 3) connected, the other end of the second branch pipe (10) is connected to several economizer intermediate headers (6) by welding. 4. The economizer for improving the denitrification capacity of the SCR system under low-load operation according to claim 1, characterized in that: an economizer ash hopper (16) is provided at the bottom of the furnace flue shell (30). 5. The economizer for improving the denitration capacity of the SCR system under low load operation according to claim 1, characterized in that: the two ends of the first branch pipe (3) are respectively provided with a three-way pipe connector.