CN202791972U - Boiler tail flue gas waste heat utilization system - Google Patents

Abstract

The utility model discloses a boiler tail flue gas waste heat utilization system capable of increasing the efficiency of the boiler by about 3%, comprising an air preheater connected with the flue outlet of the boiler, a dust collector connected with the air preheater, and a dust collector The induced draft fan connected, the smoke cooler connected with the induced draft fan and the desulfurization tower connected with the flue gas outlet of the smoke cooler. The flue gas waste heat utilization system also includes a bypass economizer connected between the flue outlet of the boiler and the outlet of the air preheater; the smoke cooler adopts an indirect heat exchanger; the flue gas waste heat utilization system It also includes two heaters, a primary fan and a secondary fan, the two heaters are connected in parallel on the heat medium pipe of the smoke cooler, and the primary fan and the secondary fan are respectively connected to two heaters. The air inlet of the air device and the air outlet of the two air heaters are connected to the inlet of the air preheater, so that the boiler exhaust gas temperature is 80°C-120°C and the boiler inlet air temperature is 50°C-80°C.

Description

A boiler tail flue gas waste heat utilization system

technical field

The utility model relates to a technology for utilizing waste heat of flue gas at the tail of a boiler in a thermal power plant, in particular to a system for utilizing waste heat of flue gas at the tail of a boiler.

Background technique

At present, the exhaust gas temperature of boilers in thermal power plants at home and abroad is generally 120°-130°C, which is also recommended in textbooks. The reason for this choice is mainly that the boiler flue gas will cause low-temperature corrosion to the metal wall when the temperature is low. In order to prevent the occurrence of low-temperature corrosion, the temperature of the boiler exhaust gas cannot be lower.

The waste heat utilization system of the flue gas at the boiler tail of a representative thermal power plant in Germany, which includes an air preheater, a bypass economizer, an electrical dust collector, an induced draft fan, a smoke cooler, and a wet method connected to the boiler flue outlet in sequence. It consists of a desulfurization tower, a chimney, and a heat medium water preheater connected to the heat medium pipe of the smoke cooler. The exhaust gas temperature of the boiler (exit smoke temperature of the air preheater) is 160°C, and the inlet air temperature of the boiler is 120°C. .

Fig. 1 is a representative thermal power plant with relatively high efficiency boiler exhaust heat utilization system at the tail of the boiler, which includes an air preheater 1 connected to the flue outlet of the boiler 1, an electric dust collector 4, an induced draft fan 5, It consists of a low-temperature economizer 9, a wet desulfurization tower 7, and a chimney 8. The exhaust gas temperature of the boiler (the temperature at the outlet of the air preheater) is 125°C.

The more obvious feature of the above two systems is that the exhaust gas temperature of the boiler is higher than 120 °C.

Analysis of equipment downstream from boiler exhaust:

For the electric dust collector, the flue gas temperature is preferably around 100°C, the dust removal efficiency is high, and there is no risk of flue gas low-temperature corrosion;

For the induced draft fan, the flue gas temperature is around 100°C and the efficiency is high;

For the wet desulfurization tower, the working temperature is around 50°C and the efficiency is the best;

From the perspective of boiler efficiency, under the premise that low-temperature corrosion of flue gas does not occur, the lower the exhaust gas temperature, the higher the efficiency.

To sum up, efficient utilization of boiler flue gas waste heat and further reduction of boiler exhaust gas temperature to about 100°C are beneficial to all aspects.

Generally, the heat brought into the boiler by burning coal is equivalent to the heat brought out by the main steam and reheated steam of the boiler, the heat brought by the low-pressure part of the bypass economizer, the heat brought by the boiler exhaust, the heat loss of unburned carbon, Radiation and convective heat loss and not accounted for heat loss.

The following table is the thermal efficiency calculation data of a certain 10000MW boiler:

It can be seen from the above table that the temperature of the flue gas outlet of the air preheater of a certain 10000MW boiler is 128°C, and the temperature of the air inlet of the boiler air preheater is 25°C, the resulting heat loss of the boiler exhaust is 4.88%, corresponding to The thermal efficiency of the boiler is 94.31%. The minimum metal wall temperature at the cold end of the air preheater in this system is around 76°C.

Contents of the invention

The purpose of this utility model is to provide a boiler tail flue gas waste heat utilization system, which can automatically control the temperature of the boiler exhaust smoke, and greatly reduce the difference between the boiler exhaust smoke temperature and the inlet air temperature, and solve the low-temperature corrosion of the flue gas. Under the premise of improving the efficiency of the boiler from the current 94% to over 96%, the high-efficiency utilization of the low-temperature heat of the flue gas at the tail of the boiler can be realized, and the purpose of energy saving can be achieved.

The technical solution to achieve the above purpose is: a boiler tail flue gas waste heat utilization system, including an air preheater connected to the flue outlet of the boiler, a dust collector connected to the air preheater, an induced draft fan connected to the dust collector, A smoke cooler connected to the induced draft fan and a desulfurization tower connected to the flue gas outlet of the smoke cooler, wherein,

The flue gas waste heat utilization system also includes a bypass economizer connected between the flue outlet of the boiler and the outlet of the air preheater;

The smoke cooler adopts an indirect heat exchanger with an intermediate heat medium;

The flue gas waste heat utilization system also includes two heaters, a primary fan and a secondary fan, the two heaters are connected in parallel on the heat medium pipe of the smoke cooler, the primary fan and the secondary fan The fans are respectively connected to the air inlets of two air heaters, and the air outlets of the two air heaters are connected to the inlet of the air preheater, so that the exhaust gas temperature of the boiler is 80 ° C ~ 120 ° C and the temperature of the boiler inlet air is 50°C to 80°C.

In the above boiler tail flue gas waste heat utilization system, the flue gas waste heat utilization system further includes a thermostat connected in series with the two heaters, and the heat pipe of the thermostat is connected to the low-temperature heat source of the steam turbine.

The boiler tail flue gas waste heat utilization system of the utility model uses a smoke cooler to recover the boiler flue gas waste heat, and heats the primary air temperature and the secondary air temperature at the inlet of the air preheater through two parallel air heaters, so that The air inlet temperature of the air preheater reaches 50 ℃ ~ 80 ℃; if the waste heat of the flue gas recovered by the smoke cooler cannot meet the heat required by the two air heaters, the thermostat absorbs the low-temperature heat source of the steam turbine to meet the heat balance . Due to the use of thermostats, it will automatically increase the temperature of the heat medium water in the smoke cooler, thereby automatically increasing the outlet air temperature of the two heaters, and indirectly and automatically controlling the exhaust gas temperature of the boiler (the outlet smoke temperature of the air preheater ) is 80 ℃ ~ 120 constant, which solves the low-temperature corrosion of the flue gas. On this basis, because the difference between the boiler exhaust gas temperature and the inlet air temperature is greatly reduced, the boiler efficiency is effectively improved, and the boiler The efficiency has been increased from about 94% at present to more than 96%, realizing the high-efficiency utilization of the low-temperature heat of the flue gas at the tail of the boiler, greatly reducing the power supply coal consumption of the unit, and having huge social and economic benefits of energy saving and emission reduction.

Description of drawings

Fig. 1 is the structural representation of the waste heat utilization system of flue gas at the tail of the boiler in the prior art;

Fig. 2 is a structural schematic diagram of a boiler tail flue gas waste heat utilization system of the present invention.

Detailed ways

In order to enable those skilled in the art to better understand the technical solution of the present utility model, its specific implementation will be described in detail below in conjunction with the accompanying drawings:

Please refer to Fig. 2, a boiler tail flue gas waste heat utilization system of the present utility model includes an air preheater 2 connected to the flue outlet of the boiler 1, a dust collector 4 connected to the air preheater 2, and a dust collector 4. The induced draft fan 5 connected to the induced draft fan 5, the smoke cooler 6 connected to the induced draft fan 5, the desulfurization tower 7 connected to the flue gas outlet of the smoke cooler 6, the chimney 8 connected to the desulfurization tower 7, and the flue gas outlet connected to the boiler 1 The bypass economizer 3 between the outlet of the air preheater 2 also includes two heaters 61, 62, a primary fan 63, a secondary fan 64 and a thermostat 65, wherein:

The smoke cooler 6 adopts an indirect heat exchanger with an intermediate heat medium, and the intermediate heat medium is water;

The two heaters 61, 62 are connected in parallel on the heat medium pipe of the cooler 6, the primary fan 63 and the secondary fan 64 are respectively connected to the air inlets of the two heaters 61, 62, and the two heaters 61, The air outlet of 62 is connected to the inlet of air preheater 2;

A thermostat 65 and two heaters 61, 62 are connected in series on the heat medium pipe of the smoke cooler 6, and the heat pipe of the thermostat 65 is connected to the low-temperature heat source 10 of the steam turbine.

The working principle of the boiler tail flue gas waste heat utilization system of the utility model is: the flue gas in the boiler 1 passes through the flue through the air preheater 2 and the bypass economizer 3 to make the temperature of the exhaust gas of the boiler (air preheater The temperature of the smoke device at the outlet) cools down to 80 ℃ ~ 120 ℃ and then enters the dust collector 4, and the flue gas after dust removal by the dust collector 4 is boosted by the induced draft fan 5 and then enters the smoke cooler 6 for cooling, so that the flue gas is cooled to 85 ℃ The left and right enter the desulfurization tower 7 for desulfurization, and then evacuate through the chimney 8; the heat released by the smoke cooler 6 in the process of cooling the flue gas is carried by the heat medium water to the two heaters 61 and 62 respectively and heated by the primary fan 63 The primary air of the boiler and the secondary fan 64 heat the secondary air of the boiler, raise the temperature of the primary air and the secondary air to 50° C. to 80° C., and then enter the air preheater 2 . When the ambient temperature decreases or the load of the steam turbine unit decreases, the heat released by the smoke cooler 6 is not enough to increase the temperature of the primary air and secondary air to control the exhaust gas temperature of the boiler at 80°C-120°C, and the low-temperature heat source of the steam turbine is required to enter The thermostat 65 is used to increase the heat medium water temperature of the cold smoke device 6, thereby automatically improving the outlet air temperature of the two heaters 61, 62, and indirectly and automatically controlling the boiler exhaust gas temperature to be constant.

When the system of the utility model raises the air inlet temperature of the air preheater 2 to about 60°C, combined with the bypass economizer 3, the boiler exhaust gas temperature is 100°C, so that the cooling of the metal wall of the air preheater 2 The minimum temperature at the end is about 80°C, which is about 75°C higher than the minimum temperature at the cold end of the metal wall of the general air preheater of the existing domestic and foreign boilers. Therefore, the problem of low-temperature corrosion of flue gas on the heating surface of the boiler tail is firstly solved.

Among the boiler heat loss, the exhaust heat loss is the largest item, accounting for almost 5%. The heat loss of the exhaust gas depends on the difference between the boiler exhaust gas temperature and the inlet air temperature. The utility model system greatly reduces the difference between the boiler exhaust gas temperature and the inlet air temperature, so it effectively improves the boiler efficiency, realizes the efficient utilization of the low-temperature heat of the flue gas at the boiler tail, and realizes the high efficiency of the low-temperature heat of the flue gas at the boiler tail. Utilization has greatly reduced the power supply coal consumption of the unit, and has huge social and economic benefits of energy saving and emission reduction.

Of course, both the bypass economizer 3 and the thermostat 65 are related to the thermal system of the steam turbine. Among them, the bypass economizer 3 will reduce the extraction steam of the steam turbine extraction steam recovery system, and the thermostat 65 will increase the extraction steam of the steam turbine low-pressure extraction steam recovery system. Both of these two aspects will cause changes in the heat consumption of the steam turbine, but this The change relative to the improvement of boiler efficiency has much less impact on the coal consumption of power supply of the unit, so the overall coal consumption of power supply of the unit will be reduced by more than 6g/kWh.

Those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the utility model, rather than as a limitation to the utility model, as long as within the spirit of the utility model, the above-mentioned The changes and modifications of the embodiments will all fall within the scope of the claims of the present utility model.

Claims (2)

1. boiler tail flue gas bootstrap system, comprise the air preheater that is connected with the flue outlet of boiler, the deduster that is connected with air preheater, the air-introduced machine that is connected with deduster, the cold smoke device that is connected with air-introduced machine and the desulfurizing tower that is connected with the exhanst gas outlet of cold smoke device, it is characterized in that

Described smoke waste heat utilization system also comprises the bypass economizer between the outlet of the flue outlet that is connected to boiler and air preheater;

Described cold smoke device adopts the indirect-heating heat exchanger that middle heating agent is arranged;

Described smoke waste heat utilization system also comprises two steam air heaters, a primary air fan and an overfire air fan, these two steam air heaters are connected in parallel on the heat medium pipe of described cold smoke device, described primary air fan and overfire air fan are connected to the air inlet of two steam air heaters separately, the air outlet of described two steam air heaters connects the import of described air preheater, and making exhaust gas temperature is 80 ℃～120 ℃ and to make boiler inlet temperature be 50 ℃～80 ℃.

2. boiler tail flue gas bootstrap system according to claim 1 is characterized in that, described smoke waste heat utilization system also comprises a hot permanent device of connecting with described two steam air heaters, and the heat pipe of the permanent device of this heat connects the low-temperature heat source of steam turbine.

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