Flue gas heat exchange system for urea pyrolyzing furnace

Abstract

The utility model relates to the technical field of flue gas heat exchange systems, and discloses a flue gas heat exchange system for a urea pyrolyzing furnace, which comprises a flue gas heat exchanger, the flue gas heat exchanger is arranged in the boiler; a heat exchange tube group which is arranged in a vertical manner is arranged in the flue gas heat exchanger; the flue gas heat exchanger is respectively connected with a hot air pipeline and a cold air pipeline; the cold air pipeline is also connected with a cold primary fan; the hot air pipeline is also connected with the urea pyrolyzing furnace; the cold primary air fan is used for collecting natural air; natural air is fed into the flue gas heat exchanger through the cold air pipeline, is heated by the heat exchange pipe group, and is fed into the urea pyrolyzing furnace through the hot air pipeline. The system provided by the utility model is low in energy consumption, can be effectively integrated with a boiler, is high in operation stability, and is beneficial to improving the economical efficiency and the reliability of a urea pyrolysis process.

Description

A flue gas heat exchange system for a urea pyrolysis furnace Technical Field

[0001] This utility model relates to the technical field of flue gas heat exchange systems, specifically to a flue gas heat exchange system for a urea pyrolysis furnace. Background Technology

[0002] Currently, coal-fired power plants are working to achieve nitrogen oxide (NOx) reduction. x Ultra-low emissions are commonly achieved using selective catalytic reduction (SCR) denitrification technology, the core of which lies in a stable supply of ammonia (NH3) as the reducing agent. Urea-to-ammonia production has become the mainstream technology due to its high safety and convenient storage and transportation. Among these technologies, urea pyrolysis decomposes a 50% urea solution into NH3 and CO2 using a high-temperature heat source (350-650℃). Compared to urea hydrolysis, pyrolysis offers significant advantages such as rapid load response (only 5-30 seconds), no pressure vessel safety hazards, and low risk of byproduct corrosion.

[0003] However, the existing urea pyrolysis furnace heat source system has the following significant drawbacks: the electric heating type pyrolysis furnace requires high-grade electrical energy (electrothermal conversion efficiency <95%), has high power consumption and high operating costs; while the pyrolysis technology using boiler tail flue gas can effectively reduce power consumption, it has problems such as low waste heat utilization efficiency, ash corrosion on the heated surface and poor coupling with the boiler body.

[0004] Therefore, there is an urgent need to develop a highly efficient, integrated, and low-energy-consumption flue gas heat exchange system to improve the economy and reliability of the urea pyrolysis process. Summary of the Invention

[0005] The present invention aims to provide a flue gas heat exchange system for a urea pyrolysis furnace, which has low energy consumption, can be effectively integrated with the boiler, and has strong operational stability, thereby helping to improve the economy and reliability of the urea pyrolysis process.

[0006] The basic solution provided by this utility model is as follows: a flue gas heat exchange system for a urea pyrolysis furnace, including a flue gas heat exchanger; the flue gas heat exchanger is located inside the boiler; the flue gas heat exchanger is provided with heat exchange tubes arranged in a vertical manner; the flue gas heat exchanger is connected to a hot air duct and a cold air duct respectively; the cold air duct is also connected to a primary air cooler; the hot air duct is also connected to the urea pyrolysis furnace; the primary air cooler is used to collect natural air; the natural air is sent to the flue gas heat exchanger through the cold air duct, heated by the heat exchange tubes, and then sent to the urea pyrolysis furnace through the hot air duct.

[0007] Furthermore, the flue gas heat exchanger is equipped with a cold air duct header and a hot air duct header; the cold air duct is connected to the cold air duct header; and the hot air duct is connected to the hot air duct header.

[0008] Furthermore, the cold air duct includes a main duct, and a first branch duct and a second branch duct connected to the main duct; one end of the main duct is connected to a cold primary air fan; the first branch duct is connected to a flue gas heat exchanger, and the second branch duct is connected to a hot air duct.

[0009] Furthermore, the main pipeline, the first branch pipeline, and the second branch pipeline are respectively equipped with a main valve, a first valve, and a second valve.

[0010] Furthermore, a thermometer is installed on the hot air duct.

[0011] Furthermore, the flue gas heater is arranged above the low-temperature superheater in the rear vertical shaft inside the boiler.

[0012] Furthermore, the flue gas heater is suspended inside the boiler.

[0013] Furthermore, the inlet of the cold air duct header and the outlet of the hot air duct header pass through the side wall of the boiler, respectively.

[0014] The working principle and advantages of this utility model are as follows:

[0015] This invention relates to a flue gas heat exchange system for a urea pyrolysis furnace. It features low energy consumption, effective integration with the boiler, and strong operational stability, thus contributing to improved economy and reliability of the urea pyrolysis process. The key points are:

[0016] First, the cold air duct of this solution uses natural air as input. Compared with the existing heat exchange system that uses primary hot air as input, the primary hot air often carries a lot of dust, which causes great wear and tear on the duct and may clog the duct, resulting in low overall energy utilization. In this solution, the natural air is clean air that does not carry dust (or only carries trace amounts of dust), which can effectively reduce system wear and is more conducive to the decomposition of high-temperature urea.

[0017] Secondly, this solution uses a flue gas heat exchanger as the main heat exchange mechanism, eliminating the risk of tripping or power outages and achieving low energy consumption. Furthermore, this solution effectively integrates the flue gas heat exchanger with the boiler—placing the heat exchanger inside the boiler and above the low-temperature superheater in the rear shaft. Utilizing the vertical space of the rear shaft to arrange the heat exchanger effectively reduces the floor space occupied by the heat exchange system and avoids layout conflicts with the boiler room. Secondly, the flue gas temperature at the outlet of the low-temperature superheater in the rear shaft is typically 350-400℃, while the hot air temperature required for urea pyrolysis needs to be stable at 450±10℃. Placing the flue gas heater above the low-temperature superheater allows for temperature gradient matching with the boiler, directly exchanging heat with the upstream high-temperature flue gas (approximately 450-500℃). This avoids the temperature decay caused by heat absorption by the low-temperature superheater, ensuring that the hot air temperature at the inlet of the subsequent pyrolysis furnace meets the requirements. The flue gas heat exchanger as a whole can be deeply coupled with the boiler's thermal system, maximizing waste heat utilization.

[0018] Third, in this design, the flue gas heat exchanger is suspended, and the heat exchange tubes within it are arranged vertically. Specifically, the suspension structure prevents thermal coupling interference between the flue gas heat exchanger and the underlying heating surface (such as the economizer), maintaining the flue gas flow direction consistent with the temperature gradient and contributing to improved overall heat exchange efficiency. Secondly, the suspension allows for free vertical expansion, which, combined with the vertically arranged heat exchange tubes, avoids thermal stress concentration caused by temperature rise, reducing the risk of tube deformation (compared to horizontally arranged tubes, which are prone to deformation and collapse in the middle), thereby extending the tubes' service life and improving the operational stability of the heat exchange system. Furthermore, this high-level arrangement places the flue gas heater in a higher flow velocity zone, and the flue gas flow helps reduce dust accumulation; the suspension method allows for the complete replacement of the flue gas heat exchanger, facilitating maintenance.

[0019] Fourth, the heat exchange system of this scheme has high flexibility. Through three-stage adjustment of the main valve (main pipeline), the first valve (first branch pipeline), and the second valve (second branch pipeline), flexible distribution of cold air flow can be achieved. When the hot air temperature at the outlet of the flue gas heat exchanger (i.e., in the hot air duct) is too high (e.g., >500℃), a certain proportion of cold air can be mixed in through the second branch pipeline to quickly reduce the temperature to a safe range, preventing the pyrolysis furnace from overheating and reducing the heat absorption load on the heat exchanger. Furthermore, in practical applications, according to actual process requirements, by adjusting the opening of the second valve to mix in different proportions of cold air, the hot and cold air after heat exchange can be mixed to the pyrolysis process temperature required by the pyrolysis furnace under the corresponding load, facilitating control. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the overall structure of an embodiment of the flue gas heat exchange system for a urea pyrolysis furnace according to the present invention.

[0021] The markings in the accompanying drawings of the instruction manual include: boiler 1, flue gas heat exchanger 2, hot air pipe 3, main pipe 4, first branch pipe 41, second branch pipe 42, main valve 5, first valve 51, second valve 52, thermometer 6, urea pyrolysis furnace 7. Detailed Implementation

[0022] The following detailed explanation illustrates the specific implementation methods:

[0023] The embodiment is basically as shown in Figure 1: a flue gas heat exchange system for a urea pyrolysis furnace 7, including a flue gas heat exchanger 2.

[0024] The flue gas heat exchanger 2 is located inside the boiler 1; in this embodiment, the flue gas heater is arranged above the low-temperature superheater in the rear vertical shaft inside the boiler 1 and is arranged in a suspended manner.

[0025] The flue gas heat exchanger 2 is equipped with heat exchange tube groups arranged vertically (in this embodiment, the heat exchange tube groups consist of multiple heat exchange tube rows arranged in a strip array along the vertical direction); the flue gas heat exchanger 2 is connected to the hot air duct 3 and the cold air duct respectively; the cold air duct is also connected to the primary air fan; the hot air duct 3 is also connected to the urea pyrolysis furnace 7. Specifically, the flue gas heat exchanger 2 is equipped with a cold air duct header and a hot air duct header 3; the inlet of the cold air duct header and the outlet of the hot air duct header 3 pass through the side wall of the boiler 1 respectively. The cold air duct is connected to the cold air duct header; the hot air duct 3 is connected to the hot air duct header 3.

[0026] The cold air duct includes a main duct 4, and a first branch duct 41 and a second branch duct 42 connected to the main duct 4. One end of the main duct 4 is connected to a primary air cooler. The first branch duct 41 is connected to a flue gas heat exchanger 2, and the second branch duct 42 is connected to a hot air duct 3. A main valve 5, a first valve 51, and a second valve 52 are respectively installed on the main duct 4, the first branch duct 41, and the second branch duct 42. A thermometer 6 is installed on the hot air duct 3. The thermometer 6 is used to measure the air temperature in the hot air duct 3.

[0027] The cold primary air fan is used to collect natural air; the natural air is sent to the flue gas heat exchanger 2 through the cold air duct, and after being heated by the heat exchange tube group, it is sent to the urea pyrolysis furnace 7 through the hot air duct 3.

[0028] In practical applications, the main valve 5 and the first valve 51 are opened, and the second valve 52 is closed. Clean air is then fed into the cold air header of the flue gas heat exchanger 2 via a primary air blower. The clean air is then heated through the heat exchange tube assembly. The heated high-temperature air is then sent to the urea pyrolysis furnace 7 through the hot air duct 3, where the urea solution undergoes pyrolysis and gasification. Furthermore, during this process, the temperature of the high-temperature air in the duct can be monitored using a thermometer 6 on the hot air duct 3. If the temperature exceeds the reaction temperature required for urea pyrolysis, the main valve 5 and the second valve 52 can be opened to introduce some natural air from the outside to neutralize the high-temperature air and ensure that the temperature reaches the required reaction temperature range for urea pyrolysis.

[0029] This embodiment provides a flue gas heat exchange system for a urea pyrolysis furnace 7, which has low energy consumption, can be effectively integrated with the boiler 1, and has strong operational stability, thus helping to improve the economy and reliability of the urea pyrolysis process.

[0030] The above descriptions are merely embodiments of this utility model. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are knowledgeable of all existing technologies in that field, and possess the ability to apply conventional experimental methods prior to that date. Therefore, those skilled in the art can, based on the guidance provided in this application, improve and implement this solution in conjunction with their own capabilities. Typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of this utility model. These modifications and improvements should also be considered within the scope of protection of this utility model, and will not affect the effectiveness of the implementation of this utility model or the practicality of the patent.

Claims

1. A flue gas heat exchange system for a urea pyrolysis furnace, characterized in that, The system includes a flue gas heat exchanger; the flue gas heat exchanger is located inside the boiler; the flue gas heat exchanger is equipped with heat exchange tubes arranged in a vertical manner; the flue gas heat exchanger is connected to a hot air duct and a cold air duct; the cold air duct is also connected to a primary air cooler; the hot air duct is also connected to a urea pyrolysis furnace; the primary air cooler is used to collect natural air; the natural air is sent to the flue gas heat exchanger through the cold air duct, heated by the heat exchange tubes, and then sent to the urea pyrolysis furnace through the hot air duct.

2. A flue gas heat exchange system for a urea pyrolysis furnace according to claim 1, characterized in that, The flue gas heat exchanger is equipped with a cold air duct header and a hot air duct header; the cold air duct is connected to the cold air duct header; the hot air duct is connected to the hot air duct header.

3. A flue gas heat exchange system for a urea pyrolysis furnace according to claim 1, characterized in that, The cold air duct includes a main duct, and a first branch duct and a second branch duct connected to the main duct; one end of the main duct is connected to a primary air cooler; the first branch duct is connected to a flue gas heat exchanger, and the second branch duct is connected to a hot air duct.

4. A flue gas heat exchange system for a urea pyrolysis furnace according to claim 3, characterized in that, The main pipeline, the first branch pipeline, and the second branch pipeline are respectively equipped with a main valve, a first valve, and a second valve.

5. A flue gas heat exchange system for a urea pyrolysis furnace according to claim 1, characterized in that, A thermometer is installed on the hot air duct.

6. A flue gas heat exchange system for a urea pyrolysis furnace according to claim 1, characterized in that, The flue gas heat exchanger is located above the low-temperature superheater in the rear vertical shaft inside the boiler.

7. A flue gas heat exchange system for a urea pyrolysis furnace according to claim 6, characterized in that, The flue gas heat exchanger is suspended inside the boiler.

8. A flue gas heat exchange system for a urea pyrolysis furnace according to claim 2, characterized in that, The inlet of the cold air duct header and the outlet of the hot air duct header pass through the side wall of the boiler, respectively.

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