A urea hydrolysis product gas recycle ammonia supply system

Abstract

The utility model discloses relate to the field of SCR flue gas denitration reducing agent urea hydrolysis ammonia production, be applicable to the ammonia supply pipeline system of urea hydrolysis ammonia production. The ammonia supply system of the utility model discloses by urea hydrolysis reactor, pressure regulating valve, product gas collection pipe, venturi jet device, SCR denitration device, cut -off valve, throttle valve, temperature measuring point, first pressure measuring point, second pressure measuring point, steam heat tracing device and ammonia supply circulation pipeline composition. The utility model discloses avoid the product gas ammonia supply pipeline to form big section flow dead zone, avoid the product gas recondensation and crystallization problem caused by flow dead zone, and the system not only reliable safety, simultaneously provides reliable pressure gradient setting for the circulation flow of ammonia supply pipeline, makes the product gas form effective reliable flow in ammonia supply circulation pipeline.

Description

Technical Field

[0001] This utility model relates to the field of SCR flue gas denitrification reducing agent urea hydrolysis for ammonia production, and is applicable to ammonia supply pipeline systems for urea hydrolysis for ammonia production. Background Technology

[0002] SCR flue gas denitrification typically uses liquid ammonia or urea as reducing agents. To eliminate the significant hazard posed by liquid ammonia storage, most SCR denitrification units have replaced liquid ammonia with urea as the reducing agent. Urea hydrolysis technology is the main process for SCR denitrification and ammonia production. The urea hydrolysis process typically involves feeding a 50% urea solution into a urea hydrolysis reactor, where it forms a mixed gas containing ammonia, carbon dioxide, and water vapor under specific temperature and pressure conditions; this is commonly referred to as product gas. The product gas is then piped to the boiler SCR flue gas denitrification system. After being metered and adjusted by the net metering module, it mixes with hot-diluted air and enters the inlet flue of the SCR denitrification unit to participate in the denitrification reaction.

[0003] In actual transportation, the product gas is prone to condensation and crystallization, clogging the pipelines and affecting the normal operation of the SCR denitrification unit. Therefore, the product gas needs to be heated to above 150°C. Currently, the commonly used product gas supply pipeline layout adopts a main pipe system, with each unit's product gas branch pipe connected to the main pipe. The end of the main pipe is either a blind end or a branch pipe for the SCR denitrification system at the end of the product gas supply. This layout easily creates a large flow dead zone when the SCR denitrification system at the end of the pipeline is shut down, causing product gas re-condensation and crystallization in that section, leading to pipeline blockage and affecting the stable operation of the SCR denitrification system. Chinese patent CN202321873344 proposes a ring-shaped ammonia supply system, in which each urea hydrolysis unit and SCR denitrification unit are installed at both ends of the ring-shaped ammonia supply system. The urea hydrolysis unit, as the product gas supply point, has the highest pressure, while each SCR denitrification unit, as the product gas consumption point, has the lowest pressure. This ring-shaped ammonia supply system does not form an effective pressure gradient, making it difficult for the product gas to circulate within the system. Furthermore, there are too many switching valves on the ring-shaped ammonia supply main pipe, making it difficult to guarantee the heat tracing effect. Summary of the Invention

[0004] This invention overcomes the shortcomings of existing technologies by proposing a simple, reliable, and rationally designed anti-crystallization urea hydrolysis product gas circulation ammonia supply system with a Venturi ejector. This system achieves stable circulation of the product gas in the ammonia supply pipeline, avoids product gas condensation and crystallization problems caused by flow dead zones, and provides system reliability and safety.

[0005] The technical solution adopted in this utility model is: a urea hydrolysis product gas circulation ammonia supply system, characterized in that it includes a urea hydrolysis reactor, a pressure regulating valve, a product gas collection pipe, a Venturi jet injector, an SCR denitrification device, a shut-off valve, a throttle valve, a temperature measuring point, a first pressure measuring point, a second pressure measuring point, a steam heating device, and an ammonia supply circulation pipeline.

[0006] The urea hydrolysis reactor is the core equipment for urea hydrolysis to ammonia production, and typically includes at least two reactors, with one as a backup. Each urea hydrolysis reactor is connected to a product gas collection pipe via a branch pipe for each product gas outlet. Each product gas outlet branch pipe is equipped with a pressure regulating valve to adjust the product gas supply pressure.

[0007] The product gas collection pipe is connected to the ammonia supply circulation pipeline via a Venturi ejector. The inlet of the Venturi ejector is connected to the product gas collection pipe, the outlet of the Venturi ejector is connected to the upstream interface of the ammonia supply circulation pipeline, and the throat of the Venturi ejector is connected to the downstream interface of the ammonia supply circulation pipeline.

[0008] The Venturi jet is made of 316L austenitic stainless steel or 2205 biaxial stainless steel.

[0009] The SCR denitrification unit consists of several units, each connected to the ammonia supply circulation pipeline via an ammonia supply branch of the SCR denitrification unit. Each ammonia supply branch of the SCR denitrification unit is equipped with a shut-off valve, which is installed at the root of the connection point of the ammonia supply circulation pipeline and is placed as close as possible to the ammonia supply circulation pipeline to reduce the length of the supply branch upstream of the shut-off valve.

[0010] The throttling valve is located on the ammonia supply circulation pipeline, downstream of the connection point between the ammonia supply branch of the SCR denitrification unit and the ammonia supply circulation pipeline.

[0011] The ammonia supply circulation pipeline is a ring-shaped circulation pipeline, including an upstream ammonia supply pipeline, a downstream product gas return pipeline, and an ammonia supply branch for the SCR denitrification unit. The product gas collection pipeline, the upstream ammonia supply circulation pipeline, the downstream return circulation pipeline, and the ammonia supply branch for the SCR denitrification unit are connected sequentially.

[0012] The first pressure measuring point is set on the ammonia supply circulation pipeline upstream of the Venturi outlet, and the second pressure measuring point is set on the return circulation pipeline downstream of the Venturi ejector throat inlet.

[0013] Furthermore, a steam tracing device and temperature measuring points are installed on the ammonia supply circulation pipeline, and the steam tracing device is installed in sections according to the ammonia supply circulation pipeline. The temperature measuring points are installed at different locations on the ammonia supply circulation pipeline.

[0014] Compared with existing technologies, this invention has the following advantages and implementation effects: The technical solution of this invention avoids the formation of large flow dead zones in the ammonia supply pipeline, preventing product gas condensation and crystallization problems caused by these dead zones, thus improving system reliability and safety. Simultaneously, it provides a reliable pressure gradient setting for the circulating flow of the ammonia supply pipeline, allowing the product gas to form an effective and reliable flow within the ammonia supply circulation pipeline.

[0015] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the system of this utility model; 1-Urea hydrolysis reactor, 2-Pressure regulating valve, 3-Product gas collection pipe, 4-Venturi jet injector, 5-SCR denitrification device, 6-Shut-off valve, 7-Throttle valve, 8-Temperature measuring point, 9-First pressure measuring point, 10-Second pressure measuring point, 11-Steam tracing device, 12-Ammonia supply circulation pipeline. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and through embodiments. The present invention is not limited to the following embodiments.

[0018] See Figure 1 A urea hydrolysis product gas circulation ammonia supply system is characterized in that it includes a urea hydrolysis reactor (1), a pressure regulating valve (2), a product gas collection pipe (3), a Venturi jet injector (4), an SCR denitrification device (5), a shut-off valve (6), a throttle valve (7), a temperature measuring point (8), a first pressure measuring point (9), a second pressure measuring point (10), a steam heating device (11), and an ammonia supply circulation pipeline (12).

[0019] The urea hydrolysis reactor (1) is the core equipment for urea hydrolysis to ammonia production, and usually includes at least two, with one as a backup. The urea hydrolysis reactor is connected to the product gas collection pipe (3) through each product gas outlet branch pipe. Each product gas outlet branch pipe is equipped with a pressure regulating valve (2) to regulate the product gas supply pressure. The product gas collection pipe (3) is connected to the ammonia supply circulation pipe (12) through a Venturi jet (4). The inlet of the Venturi jet (4) is connected to the product gas collection pipe (3), the outlet of the Venturi jet (4) is connected to the upstream interface of the ammonia supply circulation pipe (12), and the throat of the Venturi jet (4) is connected to the downstream interface of the ammonia supply circulation pipe (12).

[0020] The SCR denitrification unit (5) is connected to the ammonia supply circulation pipeline (12) via the ammonia supply branch of the SCR denitrification unit. A shut-off valve (6) is installed on the ammonia supply branch of the SCR denitrification unit at the root of the connection point of the ammonia supply circulation pipeline (12) and is placed as close as possible to the ammonia supply circulation pipeline to reduce the length of the supply branch upstream of the shut-off valve. A throttle valve (7) is arranged on the ammonia supply circulation pipeline (12) and is located downstream of the connection point between the ammonia supply branch of the SCR denitrification unit and the ammonia supply circulation pipeline (12). The ammonia supply circulation pipeline (12) is a ring circulation pipeline, including the upstream ammonia supply pipeline, the downstream return pipeline of the product gas, and the ammonia supply branch of the SCR denitrification unit. The upstream ammonia supply circulation pipeline, the downstream return circulation pipeline, and the ammonia supply branch of the SCR denitrification unit are connected in sequence. The first pressure measuring point (9) is set on the upstream ammonia supply circulation pipeline at the Venturi outlet, and the second pressure measuring point (10) is set on the downstream return circulation pipeline at the inlet of the Venturi ejector throat.

[0021] A steam tracing device (11) and temperature measuring points (8) are installed on the ammonia supply circulation pipeline. The steam tracing device (11) is set in sections according to the ammonia supply circulation pipeline. The temperature measuring points (8) are installed at different locations on the ammonia supply circulation pipeline.

[0022] Figure 1 In the system, the urea hydrolysis reactor (1) uses a urea solution with a mass concentration of 50% as raw material and reacts at 140~160℃ and 0.4~0.6MPa. The ammonia-containing product gas produced by the hydrolysis reaction is adjusted to 0.4~0.45MPa by the pressure regulating valve (2) and then enters the product gas collection pipe (3). The product gas in the product gas collection pipe (3) is injected into the upstream ammonia supply pipeline of the ammonia supply circulation pipeline (12) through the Venturi ejector (4). The ammonia supply pressure is stabilized at 0.35~0.4MPa, and the throat of the Venturi ejector (4) is reduced to form a negative pressure chamber, which draws in the downstream return product gas of the ammonia supply circulation pipeline (12). A first pressure measuring point (9) is set on the upstream ammonia supply pipeline of the ammonia supply circulation pipeline (12) to adjust the outlet pressure regulating valve (2) of the urea hydrolysis reactor and control the pressure stability of the upstream ammonia supply pipeline.

[0023] The SCR denitrification unit (5) is connected to the ammonia supply circulation pipeline (12) through the ammonia supply branch of the SCR denitrification unit. The ammonia supply branch of the SCR denitrification unit is equipped with a shut-off valve (6), which is installed at the root of the connection of the ammonia supply circulation pipeline (12) and is as close as possible to the ammonia supply circulation pipeline to reduce the length of the supply branch upstream of the shut-off valve. When a single SCR denitrification unit (5) is shut down, the shut-off valve (6) of the ammonia supply branch is shut off, which does not affect the overall circulation of the ammonia supply circulation pipeline (12).

[0024] A throttling valve (7) is installed on the downstream product gas return pipeline of the ammonia supply circulation pipeline (12) to significantly reduce the pressure of the downstream product gas return pipeline to below 0.3 MPa, which facilitates the formation of an effective pressure gradient and enables the ammonia supply circulation pipeline to operate continuously. At the same time, the pressure reduction in the downstream product gas return pipeline can effectively increase the superheat of the product gas, further preventing the product gas from condensing and crystallizing. A steam tracing device (11) indirectly traces the ammonia supply circulation pipeline (12) to ensure that the product gas temperature is not lower than 150°C.

[0025] As described above, the ammonia supply circulation pipeline (12) forms a certain pressure gradient through the Venturi jet (4) and the throttle valve (7), which can realize the continuous circulation of product gas in the ammonia supply circulation pipeline (12). When a single urea hydrolysis reactor (1) or a single SCR denitrification device (5) is shut down, the formation of a dead zone at the end of the product gas supply ammonia main pipe is avoided, effectively reducing the risk of product gas condensing and crystallizing in the ammonia supply main pipe.

[0026] It should be noted that the Venturi jet (4) that generates a pressure gradient on the ammonia circulation pipeline (12) can be implemented by a gas compressor or a volumetric pump, but this involves additional energy consumption and increases the complexity of the system. This utility model does not describe it separately, but this method does not deviate from the system of this utility model and is still within the protection scope of this utility model.

Claims

1. A urea hydrolysis product gas circulation ammonia supply system, characterized in that: It includes a urea hydrolysis reactor, a pressure regulating valve, a product gas collection pipe, a Venturi jet injector, an SCR denitrification unit, a shut-off valve, a throttling valve, temperature measuring points, a first pressure measuring point, a second pressure measuring point, a steam tracing device, and an ammonia supply circulation pipeline. The urea hydrolysis reactor is provided in at least two units, including one as a backup. Each urea hydrolysis reactor is connected to the product gas collection pipe via a branch pipe from its product gas outlet. A pressure regulating valve is installed on each product gas outlet branch pipe. The product gas collection pipe is connected to the inlet of the Venturi jet injector. The outlet of the Venturi jet injector is connected to the upstream interface of the ammonia supply circulation pipeline, and the throat of the Venturi jet injector is connected to the downstream interface of the ammonia supply circulation pipeline. The ammonia supply circulation pipeline is a ring-shaped circulation pipeline. Several SCR denitrification units are connected to the ammonia supply circulation pipeline via branch pipes. The shut-off valve is installed on the ammonia supply branch pipe of the SCR denitrification unit, at the root of the connection point of the ammonia supply circulation pipeline, and as close as possible to the ammonia supply circulation pipeline. The throttling valve is installed on the ammonia supply circulation pipeline and located on the SCR branch pipe. Downstream of the connection point between the ammonia supply branch and the ammonia circulation pipeline of the denitrification unit, the first pressure measuring point is located on the ammonia circulation pipeline upstream of the Venturi jet outlet, and the second pressure measuring point is located on the downstream return circulation pipeline at the inlet of the Venturi jet throat. Steam tracing devices are arranged in sections on the ammonia circulation pipeline, and the temperature measuring points are installed at different locations on the ammonia circulation pipeline.

2. The urea hydrolysis product gas circulation ammonia supply system according to claim 1, characterized in that: The Venturi jet (4) is made of 316L austenitic stainless steel or 2205 biaxial stainless steel.

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