CN203927879U - A kind of economizer that improves SCR operational percentage under running on the lower load - Google Patents

Abstract

The utility model discloses an economizer which improves the operation rate of the SCR under low-load working conditions. A bypass is arranged on the water supply pipe at the inlet of the economizer, and the bypass pipeline is connected with the middle header of the economizer. A check valve, a throttle valve and a flow regulating valve are sequentially installed on the bypass along the direction of medium flow. The utility model utilizes the adjustment of the opening of the bypass valve under low-load conditions to reduce the medium flow between the inlet header and the intermediate header of the economizer in the boiler, thereby reducing the heat release on the flue gas side of the economizer and saving energy. The rise of the flue gas temperature at the outlet of the coal burner has effectively improved the operation rate of the power plant's SCR under low-load conditions. Better achieve environmental protection indicators in a long-term range.

Description

A Coal Economizer for Improving the Commissioning Rate of SCR in Low Load Condition

technical field

The utility model relates to the field of flue gas denitrification of power plant boilers, in particular to an economizer which improves the operation rate of SCR under low-load working conditions.

Background technique

Selective catalytic reduction (SCR) is currently the most mature denitrification technology in industry. This technology 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, causing acid rain, photochemical smog, and ozone layer depletion. 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, the emission standards of air pollutants have become increasingly stringent. In terms of thermal power plants, domestically, it is required to retrofit SCR systems for active units without 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 slip rate is high, and the escaped NH ₃ will react with the SO ₃ in the flue gas to form Ammonium sulfate (NH ₄ ) ₂ SO ₄ and ammonium bisulfate NH ₄ HSO ₄ , in severe cases, will cause blockage of the catalyst reaction channel and the downstream air preheater. 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 the flue gas temperature of the SCR system on the SCR 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 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 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.

Contents of the invention

Purpose of the utility model: In order to overcome the deficiencies in the prior art, the utility model provides an economizer which improves the operation rate of SCR under low-load conditions.

Technical solution: In order to solve the above technical problems, the utility model provides an economizer that improves the operation rate of SCR under low load conditions, including a shell, an economizer outlet header set in the shell, and a economizer The heat exchange device connected to the outlet header of the coal generator, the inlet header of the economizer connected to the heat exchange device, and the SCR reactor connected to the bottom of the shell; the heat exchange device includes a group connected to the outlet header of the economizer The economizer suspension pipe, the economizer intermediate header connected to each economizer suspension pipe, and a set of economizer serpentine pipes connected to the economizer intermediate header, the economizer snake shaped pipe is connected to the inlet header of the economizer; a branch pipe is provided between the inlet Through valves, shut-off valves and flow regulating valves.

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, an economizer ash hopper is provided at the bottom of the housing.

Further, the two ends of the branch pipe are respectively provided with a three-way pipe connector, and the connection method between the branch pipe and the intermediate header is welding.

Further, the regulating valve is an electrically controlled regulating valve.

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

The utility model utilizes the adjustment of the opening of the bypass valve under low-load conditions to reduce the medium flow between the inlet header and the intermediate header of the economizer in the boiler, thereby reducing the heat release on the flue gas side of the economizer and saving energy. The temperature of the flue gas at the outlet of the coal burner rises. Since there is no heat exchange equipment between the outlet of the economizer and the inlet of the SCR reactor, the temperature of the flue gas entering the SCR system also increases, making some low The load conditions meet the temperature requirements for SCR operation, which effectively improves the operation rate of SCR in power plants under low load conditions. In addition, the increase in the temperature of the SCR system leads to an increase in the activity of the SCR catalyst, and the SCR system obtains a higher denitrification capacity, thereby helping the power plant to better meet environmental protection indicators in a longer period of time.

Description of drawings

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

Fig. 2 is a schematic diagram of branch pipe connection of the present invention.

Detailed ways

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

As shown in Figures 1 and 2, an economizer that improves the SCR commissioning rate under low-load conditions includes a shell 20, an economizer outlet header 2 set in the shell 20, and a coal economizer The heat exchange device connected to the outlet header 2 of the economizer, the inlet header 10 of the economizer connected to the heat exchange device, and the SCR reactor connected to the bottom of the shell 20; Economizer suspension pipe 3 connected to box 2, economizer intermediate header 4 connected to each economizer suspension pipe 3, a group of economizer serpentine pipes connected to economizer intermediate header 4 6. The serpentine pipe 6 of the economizer is connected to the inlet header 10 of the economizer; a branch pipe 5 is provided between the inlet header 10 of the economizer and the intermediate header 4 of the economizer. The pipeline 5 is respectively provided with a one-way valve 9, a shut-off valve 8 and a flow regulating valve 7 sequentially along the direction of fluid flow. Reserved layer 14, catalyst first layer 15 and catalyst sub-layer 16, an economizer ash hopper 12 is provided at the bottom of the housing 20, and a first three-way pipe connector 18 is provided at both ends of the branch pipe 5 . The second three-way pipe connector 19, the flow regulating valve 7 is an electric control regulating valve.

The operating conditions of the SCR denitrification system are determined according to the active temperature range of the SCR catalyst, which is generally designed to be 300°C to 400°C. Under low-load operating conditions, the flue gas 1 at the inlet of the economizer enters the economizer, the temperature of the flue gas 11 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 , so the temperature of the flue gas 13 at the inlet of the SCR reactor is approximately equal to the temperature at the outlet of the economizer, which is lower than the lower limit of the operating temperature range of the SCR system. At this time, the bypass stop valve 8 is opened, and the opening of the regulating valve 7 is gradually increased to control The medium flow rate of the bypass, due to the shunt effect of the bypass, the flow rate 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, so that the economizer The temperature of the flue gas 11 at the outlet of the coal burner and the flue gas 13 at the inlet of the SCR rises by more than 300°C, reaching the operating temperature range of the SCR system, which effectively improves the operating rate of the SCR system and the effective use time of the catalyst.

A kind of strategy of improving the operation rate of SCR in the low-load working condition of the utility model is as follows in actual work:

Boiler economizer heat exchange device 17 is mainly composed of economizer suspension pipe 3 and economizer serpentine pipe 5, the serpentine pipe is connected between the inlet header 10 and the middle header 6, and the suspension pipe is connected in the middle Between the header box and the outlet header 2, the heat exchange area of the serpentine tube is larger than that of the suspension tube, which plays a major role in heat exchange. Under the low-load operating condition of the boiler, the temperature of the flue gas 11 at the outlet of the economizer is lower than 300°C. At this time, the bypass stop valve 8 is opened, and the valve opening of the regulating valve 7 is gradually increased to control the medium flow of the bypass. Due to the shunting effect of the road, the flow rate of the medium participating in the heat exchange in the serpentine tube 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 heat exchange area of the serpentine tube will be reduced, thereby making the economizer The outlet flue gas temperature rises by more than 300°C. The design and operation temperature range of the SCR system is 300°C to 400°C. Three catalyst layers are designed in the reactor. Layer 16, since there is no heat exchange equipment between the economizer outlet and the SCR reactor inlet, the temperature of the flue gas 13 entering the catalyst 15 of the first layer of the SCR is approximately equal to the temperature at the economizer outlet, 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. In addition, the heat capacity of the medium side is higher than that of the flue gas side. When the same amount of heat exchange 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. under running on the lower load, improve an economizer for SCR operational percentage, it is characterized in that: the SCR reactor that comprises housing, is located at the economizer exit header in housing, the heat-exchanger rig being connected with economizer exit header, the economizer inlet header being connected with heat-exchanger rig and is connected with housing bottom; Described heat-exchanger rig comprises one group of Coal Saver Hanged Pipe connected with economizer exit header, the economizer intermediate header being connected with each Coal Saver Hanged Pipe, the one group of economizer coiled pipe being connected with economizer intermediate header, and described economizer coiled pipe is connected with economizer inlet header; Between described economizer inlet header and economizer intermediate header, be provided with a bypass duct, described bypass duct is provided with successively respectively one-way valve, stop valve and flow control valve on fluid flow direction.

2. the economizer that improves SCR operational percentage under running on the lower load according to claim 1, is characterized in that: described SCR reactor comprises reactor shell, is located at the reserved layer of catalyst, the catalyst first floor and the catalyst sublevel in reactor shell successively.

3. the economizer that improves SCR operational percentage under running on the lower load according to claim 1, is characterized in that: described housing bottom is provided with an economizer hopper.

4. the economizer that improves SCR operational percentage under running on the lower load according to claim 1, is characterized in that: the two ends of described bypass duct are respectively equipped with a three-way pipe connector.

5. the economizer that improves SCR operational percentage under running on the lower load according to claim 1, is characterized in that: described control valve is electronic control and regulation valve.