A heat exchange system for a low-calorific-value gas boiler

Abstract

This utility model discloses a heat exchange system for a low-calorific-value coal gas boiler, including a horizontal flue and a vertical flue. A high-temperature reheater and a low-temperature reheater are arranged in the horizontal flue, while an upper-stage air preheater and a lower-stage air preheater are arranged in the vertical flue. A left-side connecting flue and a right-side connecting flue are located on either side of the middle position between the upper-stage and lower-stage air preheaters, and a bypass flue connects the left-side and right-side connecting flues. A steam-flue gas heat exchanger is installed on the bypass flue, connecting to both ends of the flue gas heat exchange side of the steam-flue gas heat exchanger. Both ends of the steam heat exchange side of the steam-flue gas heat exchanger are connected to a steam bypass, which connects to the outlet of the low-temperature reheater and the inlet of the high-temperature reheater. This system increases the flue gas temperature of the lower-stage air preheater, reduces the possibility of ammonium bisulfate condensation, mitigates the corrosion risk of ammonium bisulfate on the heating surfaces of the lower-stage air preheater, and significantly extends the service life of the equipment. It also reduces the risk of reheater overheating and increases the flexibility of reheat steam temperature regulation.

Description

Technical Field

[0001] This utility model relates to the field of boiler system technology, and in particular to a heat exchange system for a low-calorific-value gas boiler. Background Technology

[0002] Low-calorific-value gas boiler systems are commonly used thermal energy equipment in industrial production. They generate heat energy by burning low-calorific-value gas, providing a heat source for industrial production. They are widely used in steel plant gas power generation and coal chemical plant semi-coke tail gas power generation. To improve the boiler's thermal efficiency, waste heat recovery devices, such as air preheaters and economizers, are typically installed in the boiler's tail flue to recover waste heat from the flue gas, reduce exhaust gas temperature, and improve the boiler's thermal efficiency.

[0003] Because the exhaust gas from the combustion of low-calorific-value coal gas contains sulfur oxides and nitrogen oxides, gas-fired boilers often add excessive amounts of ammonia at low loads to meet nitrogen oxide emission requirements. This escaped ammonia reacts with sulfur oxides and water vapor to form ammonium bisulfate, which exists in gaseous form in the denitrification system. As the flue gas temperature decreases along the flow path, especially at low loads, the cold-end flue gas temperature of the air preheater is below the dew point of ammonium bisulfate. Ammonium bisulfate exists in liquid form, and its strong viscosity causes adhering fly ash to deposit on the flue gas side of the air preheater, clogging the heating surface tubes and, in severe cases, causing corrosion of the heating surfaces.

[0004] The low-temperature reheater and low-temperature superheater are placed in parallel flue gas ducts, and reheat steam temperature is typically regulated using flue gas dampers. Under low-load operating conditions, the steam flow rate in the reheater decreases, and the flue gas damper on the reheater side is only open by 5% during operation, almost completely closed, with no adjustable margin. In the high-temperature reheater, some tube walls experience excessively high metal temperatures, leading to overheating and posing a serious safety hazard. To ensure unit operation safety, emergency water spray desuperheating is used to regulate the reheater temperature. However, the introduction of desuperheating water reduces the unit's economic efficiency. In a certain ultra-high pressure gas turbine unit with reheat, due to high high-pressure cylinder exhaust temperature, mismatched boiler heating surfaces, and excessive reheater heating surfaces, the emergency desuperheating water in the reheater exceeded design values ​​under different unit loads, resulting in low unit economic efficiency. Studies have found that the impact of reheat steam desuperheating water on the turbine heat rate is greater than that of superheater desuperheating water. At the same time, the frequent addition of desuperheating water will cause the temperature of the desuperheater pipes to change repeatedly and be subjected to large thermal shocks, which may lead to thermal fatigue cracks and eventually cause the heated surface tubes to crack and burst, affecting the safe operation of the unit. Utility Model Content

[0005] To improve the economic efficiency of the unit, the reheater of a low-calorific-value gas boiler is usually de-heated by flue gas dampers to regulate the reheat steam temperature. Considering the limitations of the aforementioned flue gas damper regulation, and in order to solve the technical problem of sulfur oxides in the combustion exhaust gas of a low-calorific-value gas boiler reacting with ammonia and water vapor to generate ammonium bisulfate, which leads to blockage and corrosion of the air preheater heating surface, a heat exchange system for a low-calorific-value gas boiler is provided.

[0006] The present invention adopts the following technical solution:

[0007] A heat exchange system for a low-calorific-value gas boiler includes a horizontal flue and a vertical flue at the boiler tail. A high-temperature reheater and a low-temperature reheater are arranged in the horizontal flue. An economizer, an upper-stage air preheater, and a lower-stage air preheater are arranged in the vertical flue at the boiler tail. A left-side connecting flue and a right-side connecting flue are respectively located on either side of the upper-stage and lower-stage air preheaters within the vertical flue at the boiler tail. A bypass flue connects the left-side and right-side connecting flues. A steam-flue gas heat exchanger is installed on the bypass flue, connecting both ends of the flue gas heat exchanger's heat exchange side. Both ends of the steam heat exchanger's heat exchange side are connected to a steam bypass, which connects to the outlet of the low-temperature reheater and the inlet of the high-temperature reheater.

[0008] Preferably, an electric isolation door and an electric regulating door are installed on the left connecting flue and the right connecting flue, respectively.

[0009] Preferably, the upper-stage air preheater and the lower-stage air preheater are both tubular structures, in which flue gas flows inside the tube and air flows outside the tube.

[0010] Preferably, the steam-flue gas heat exchanger is a tubular or shell-and-tube structure, with steam flowing inside the tubes and flue gas flowing outside the tubes or on the shell side.

[0011] Preferably, an electric shut-off valve is installed on the steam bypass at both ends of the steam heat exchange side of the steam flue gas heat exchanger.

[0012] Preferably, a connecting pipeline between the high-temperature reheater and the low-temperature reheater is installed between the high-temperature reheater and the low-temperature reheater, and an electric regulating valve is installed on the connecting pipeline between the low-temperature reheater and the high-temperature reheater.

[0013] Preferably, the steam heat exchange side of the steam flue gas heat exchanger is equipped with a temperature sensor and a pressure sensor.

[0014] The beneficial effects of this utility model are as follows: By adopting a steam-heated flue gas system, this utility model increases the flue gas temperature of the lower-stage air preheater, reduces the possibility of ammonium bisulfate condensation, mitigates the risk of corrosion of the heating surface of the lower-stage air preheater by ammonium bisulfate, and significantly extends the service life of the equipment; at the same time, by exchanging heat between some of the low-temperature reheater steam and flue gas, the risk of reheater overheating is reduced, and the flexibility of reheat steam temperature regulation is increased. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of this utility model;

[0016] In the diagram: 1. Upper-stage air preheater; 2. Lower-stage air preheater; 3. Left-side connecting flue; 4. Right-side connecting flue; 5. Left-side electric isolation valve for flue; 6. Left-side electric regulating valve for flue; 7. Right-side electric isolation valve for flue; 8. Right-side electric regulating valve for flue; 9. Bypass flue; 10. Steam-flue gas heat exchanger; 11. Steam bypass; 12. Connecting pipeline between low-temperature reheater and high-temperature reheater; 13. Low-temperature reheater; 14. High-temperature reheater; 15. Electric regulating valve; 16. Bypass steam inlet electric shut-off valve; 17. Bypass steam outlet electric shut-off valve. Detailed Implementation

[0017] The technical solution of this utility model will be further described in detail below through specific embodiments and with reference to the accompanying drawings:

[0018] Example: Figure 1 As shown, a heat exchange system for a low-calorific-value coal gas boiler includes a horizontal flue and a vertical flue at the boiler tail. A high-temperature reheater 14 and a low-temperature reheater 13 are arranged in the horizontal flue. An economizer, an upper-stage air preheater 1, and a lower-stage air preheater 2 are arranged in the vertical flue at the boiler tail. A left connecting flue 3 and a right connecting flue 4 are respectively arranged on the left and right sides of the vertical flue at the middle position between the upper-stage air preheater and the lower-stage air preheater. The left connecting flue is connected to the inlet of a flue gas bypass 9, and the right connecting flue is connected to the outlet of a flue gas bypass. A steam-flue gas heat exchanger 10 is arranged on the bypass flue, and the bypass flue connects to both ends of the flue gas heat exchange side of the steam-flue gas heat exchanger. Both ends of the steam heat exchange side of the steam-flue gas heat exchanger are connected to a steam bypass 11, which connects to the outlet of the low-temperature reheater and the inlet of the high-temperature reheater.

[0019] The left connecting flue is equipped with a left connecting flue electric isolation door 5 and a left connecting flue electric regulating door 6, and the right connecting flue is equipped with a right connecting flue electric isolation door 7 and a right connecting flue electric regulating door 8.

[0020] The upper and lower air preheaters are both tubular structures, with flue gas flowing inside the tubes and air flowing outside. The steam-flue gas heat exchanger is a tubular or shell-and-tube structure, with steam flowing inside the tubes and flue gas flowing outside the tubes or on the shell side.

[0021] The steam bypass inlet electric shut-off valve 16 is installed at both ends of the steam heat exchange side of the steam flue gas heat exchanger, and the steam bypass outlet electric shut-off valve 17 is installed at the steam bypass outlet.

[0022] A connecting pipe 12 between the high-temperature reheater and the low-temperature reheater is installed, and an electric regulating valve 15 is installed on the connecting pipe between the low-temperature reheater and the high-temperature reheater.

[0023] Temperature and pressure sensors are installed on the steam heat exchange side of the steam flue gas heat exchanger.

[0024] In use, this invention adjusts the electric regulating valve to draw some of the low-temperature reheater steam from the reheater outlet. After passing through a steam-flue gas heat exchanger, the steam is introduced into the high-temperature reheater inlet pipeline, reducing the risk of reheater overheating and increasing the flexibility of reheat steam temperature regulation. Simultaneously, flue gas from the left connecting flue, via the bypass flue, exchanges heat with steam through the steam-flue gas heat exchanger before being introduced into the right connecting flue into the lower-stage air preheater. This increases the flue gas temperature of the lower-stage air preheater, reduces the possibility of ammonium bisulfate condensation, mitigates the corrosion risk of ammonium bisulfate on the heating surfaces of the lower-stage air preheater, and significantly extends the equipment's service life.

[0025] The embodiments described above are merely preferred solutions of this utility model and are not intended to limit this utility model in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A heat exchange system for a low-calorific-value gas boiler, comprising a horizontal flue and a vertical flue at the boiler tail, wherein a high-temperature reheater and a low-temperature reheater are arranged in the horizontal flue, and an economizer, an upper-stage air preheater, and a lower-stage air preheater are arranged in the vertical flue at the boiler tail, characterized in that... The vertical flue at the tail end of the boiler is provided with a left connecting flue and a right connecting flue on the left and right sides respectively, located between the upper and lower air preheaters. A bypass flue is connected between the left and right connecting flues. A steam-flue gas heat exchanger is installed on the bypass flue. The bypass flue connects to both ends of the flue gas heat exchange side of the steam-flue gas heat exchanger. Both ends of the steam heat exchange side of the steam-flue gas heat exchanger are connected to the steam bypass. The steam bypass connects to the outlet of the low-temperature reheater and the inlet of the high-temperature reheater.

2. The low-calorific-value gas boiler heat exchange system according to claim 1, characterized in that, The left-side connecting flue and the right-side connecting flue are respectively equipped with an electric isolation door and an electric adjustment door.

3. The low-calorific-value gas boiler heat exchange system according to claim 1, characterized in that, The upper-stage air preheater and the lower-stage air preheater are both tubular structures, in which flue gas flows inside the tube and air flows outside the tube.

4. The low-calorific-value gas boiler heat exchange system according to claim 1, characterized in that, The steam-flue gas heat exchanger is a tubular or shell-and-tube structure, with steam flowing inside the tubes and flue gas flowing outside the tubes or on the shell side.

5. The low-calorific-value gas boiler heat exchange system according to claim 1, characterized in that, Electric shut-off valves are installed on the steam bypasses at both ends of the steam heat exchange side of the steam flue gas heat exchanger.

6. The low-calorific-value gas boiler heat exchange system according to claim 1, characterized in that, A connecting pipeline between the high-temperature reheater and the low-temperature reheater is installed, and an electric regulating valve is installed on the connecting pipeline between the low-temperature reheater and the high-temperature reheater.

7. The low-calorific-value gas boiler heat exchange system according to claim 1, characterized in that, The steam heat exchanger is equipped with a temperature sensor and a pressure sensor on the steam heat exchange side.

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