A urea hydrolysis gas capture and energy-saving reheating device

Abstract

The present invention discloses a urea hydrolysis gas capture and energy-saving reheating device, comprising: a gas capture unit arranged in the upper gas phase space of a urea hydrolyzer and extending out of the urea hydrolyzer to be connected to an ammonia supply pipeline or a reheating unit; the reheating unit comprises a shell and a steam coil arranged in the shell, the shell is arranged in the ammonia supply pipeline or connected to the gas capture unit through a product gas inlet and connected to the ammonia supply pipeline through a product gas outlet, the steam inlet of the steam coil is connected to a steam source and the steam outlet is connected to the steam inlet of the urea hydrolyzer; a temperature reduction and pressure reduction unit is arranged on the pipeline between the steam outlet of the steam coil and the steam inlet of the urea hydrolyzer. The present invention can quickly collect the product gas in the urea hydrolyzer and make full use of the heat of the superheated steam to reheat the product gas and increase the temperature of the product gas, so as to avoid problems such as blockage and corrosion of the pipeline system caused by too low temperature of the product gas during transportation, thereby improving reliability and economy.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technology, and more specifically to a urea hydrolysis gas capture and energy-saving reheating device. Background Art

[0002] Urea hydrolysis technology for ammonia production has the characteristics of low energy consumption, simple process system and easy implementation, and has been widely used in flue gas denitrification projects in power plants. The principle of urea hydrolysis is to use a heat source to heat a urea solution of a certain mass concentration to above 140°C. Under this temperature condition, urea undergoes a hydrolysis reaction to generate gaseous NH3 and CO2, providing a reducing agent (NH3) for the flue gas denitrification system. The urea hydrolysis reaction generally occurs in a closed shell and tube pressure vessel (urea hydrolysis reactor). The urea solution flows on the shell side, and the heating steam flows on the tube side, and heat is transferred through the tube wall. The product gas generated by the urea hydrolysis reaction is transported to the denitrification system through a pipeline. The heating steam source generally uses medium and low pressure auxiliary steam that is easily obtained in the power plant. In order to make full use of the latent heat energy of the steam and improve the heat transfer efficiency, the auxiliary steam usually needs to be cooled and reduced to saturated steam before entering the hydrolysis reactor.

[0003] Conventional urea hydrolysis ammonia production systems in power plants usually draw in auxiliary steam at 0.8-1.2MPa and 300℃, which is then cooled and decompressed to 0.7-0.8MPa and 170-180℃ saturated steam and then introduced into the hydrolysis reactor to heat the urea solution to 140-160℃, reaching the optimal temperature range required for urea hydrolysis. Under certain temperature and pressure conditions, urea undergoes hydrolysis to generate ammonia-containing product gas at 0.4-0.6MPa and 140-160℃. The product gas gathers in the gas phase space above the hydrolyzer and is transported to the SCR denitration ammonia injection system through the interface at the top of the hydrolyzer and the plant pipeline. The auxiliary steam is generally cooled and decompressed by a simpler and more economical booster pump for water spraying and cooling.

[0004] The main problems with this conventional technology are: on the one hand, the auxiliary steam at ~300℃ is cooled to saturated steam at 170-180℃ by water spraying and then reused, which wastes a lot of thermal energy; on the other hand, the urea hydrolysis product gas at 140-160℃ is transported to the SCR denitrification area through the plant pipeline, resulting in a decrease in temperature due to heat loss. When the temperature is too low (below 140℃), water vapor condensation and NH3 and CO2 repolymerization to produce corrosive polymers are likely to occur in the pipeline, causing serious blockage and corrosion to the pipeline system, affecting the normal ammonia supply of the system and the normal operation of the SCR denitrification device. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention proposes a urea hydrolysis gas capture and energy-saving reheating device which can fully utilize the heat of superheated steam to further increase the temperature of the urea hydrolysis product gas so as to reduce the risk of blockage and corrosion of the ammonia supply pipeline system, save energy consumption, and improve the reliability of system operation.

[0006] The present invention provides a urea hydrolysis gas capture and energy-saving reheating device, comprising: a gas capture unit, which is arranged in the upper gas phase space of a urea hydrolyzer and extends out of the urea hydrolyzer to be connected to an ammonia supply pipeline or a reheating unit; a reheating unit, which comprises a shell and a steam coil arranged in the shell, wherein the shell is arranged in the ammonia supply pipeline or is connected to the gas capture unit through a product gas inlet and is connected to the ammonia supply pipeline through a product gas outlet, the steam inlet of the steam coil is connected to a steam source and the steam outlet is connected to the steam inlet of the urea hydrolyzer; and a temperature and pressure reduction unit, which is arranged on a pipeline between the steam outlet of the steam coil and the steam inlet of the urea hydrolyzer.

[0007] According to an embodiment of the urea hydrolysis gas capture and energy-saving reheating device of the present invention, the gas capture unit is a T-shaped pipe assembly and includes a longer collecting pipe arranged along the axial direction of the urea hydrolyzer and a shorter exhaust pipe arranged along the radial direction of the urea hydrolyzer.

[0008] According to an embodiment of the urea hydrolysis gas capture and energy-saving reheating device of the present invention, a plurality of groups of gas collecting holes are arranged at intervals on the lower surface of the collecting pipe, each group of gas collecting holes is evenly arranged along the radial direction of the collecting pipe, and both ends of the collecting pipe are blocked by end covers; the exhaust pipe extends out of the urea hydrolyzer shell and is connected to the ammonia supply pipeline or the reheating unit.

[0009] According to one embodiment of the urea hydrolysis gas capture and energy-saving reheating device of the present invention, a flow equalizing plate is provided at the product gas inlet of the shell in the reheating unit. The flow equalizing plate is a perforated plate with a plurality of small holes evenly opened and is arranged on the entire cross-section of the shell of the reheating unit.

[0010] According to one embodiment of the urea hydrolysis gas capture and energy-saving reheat device of the present invention, when the shell of the reheat unit is connected to the gas capture unit through the product gas inlet and is connected to the ammonia supply pipeline through the product gas outlet, the shell of the reheat unit and the shell of the urea hydrolyzer are connected by flange connection or by welding, the center line of the shell of the reheat unit is opposite to the center line of the exhaust pipe and the diameter of the shell of the reheat unit is larger than the diameter of the exhaust pipe.

[0011] According to one embodiment of the urea hydrolysis gas capture and energy-saving reheating device of the present invention, when the shell of the reheating unit is arranged in the ammonia supply pipeline, both ends of the shell of the reheating unit are connected to the ammonia supply pipeline through cone sections or head openings.

[0012] According to an embodiment of the urea hydrolysis gas capture and energy-saving reheating device of the present invention, the steam coil is a serpentine coil, a spiral coil, a U-shaped coil or a tube-in-tube coil, and the ammonia supply pipeline is connected to the SCR denitrification system.

[0013] According to an embodiment of the urea hydrolysis gas capture and energy-saving reheating device of the present invention, the steam source is 0.8-1.2MPa, ~300°C auxiliary heating steam of the power plant, and the steam after passing through the reheating unit and the temperature and pressure reduction unit is 0.7-0.8MPa, 170-180°C saturated steam.

[0014] According to an embodiment of the urea hydrolysis gas capture and energy-saving reheating device of the present invention, the product gas temperature output by the gas capture unit is 140-160°C, and the product gas temperature after passing through the reheating unit is 180-200°C.

[0015] Compared with the prior art, the urea hydrolysis product gas capture and energy-saving reheating device of the present invention can quickly collect the product gas in the urea hydrolyzer and fully utilize the heat of the superheated steam to reheat the product gas, so as to further increase the temperature of the product gas, avoid the problem of pipeline system blockage and corrosion caused by the product gas being too low in temperature during the process of being transported to the SCR denitrification area, and at the same time reduce the steam heat loss and the water consumption of the steam cooling and pressure reduction device, thereby improving the reliability and economy of the system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic structural diagram of a urea hydrolysis product gas capture and energy-saving reheating device according to an exemplary embodiment of the present invention is shown.

[0017] Figure 2 A schematic side view of the structure of a collecting pipe of a gas capture unit in a urea hydrolysis product gas capture and energy-saving reheating device according to an exemplary embodiment of the present invention is shown.

[0018] Figure 3 A schematic structural diagram of a flow equalizing plate of a reheating unit in a urea hydrolysis product gas capture and energy-saving reheating device according to an exemplary embodiment of the present invention is shown.

[0019] Description of reference numerals:

[0020] 1-gas capture unit, 11-collecting pipe, 12-end cover, 13-exhaust pipe, 2-reheat unit, 21-shell, 22-flow equalizing plate, 23-steam coil, 24-steam inlet, 25-steam outlet, 26-product gas outlet, 3-temperature reduction and pressure reduction unit. DETAILED DESCRIPTION

[0021] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0022] Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0023] Hereinafter, the urea hydrolysis product gas capture and energy-saving reheating device of the present invention will be described in detail.

[0024] Figure 1 A schematic structural diagram of a urea hydrolysis product gas capture and energy-saving reheating device according to an exemplary embodiment of the present invention is shown.

[0025] like Figure 1 As shown, according to an exemplary embodiment of the present invention, the urea hydrolysis product gas capture and energy-saving reheating device includes a gas capture unit 1, a reheating unit 2 and a temperature reduction and pressure reduction unit 3. The gas capture unit 1 is arranged in the urea hydrolyzer to quickly collect the product gas, the reheating unit 2 uses the heat of the superheated steam to heat the product gas and further increase the temperature of the product gas, and the temperature reduction and pressure reduction unit 3 is used to further reduce the temperature and pressure of the steam after sufficient heat exchange to obtain saturated steam that meets the requirements, which is further used to heat the urea solution.

[0026] According to an exemplary embodiment of the present invention, the gas capture unit 1 of the present invention is arranged in the upper gas phase space of the urea hydrolyzer and extends out of the urea hydrolyzer to be connected to the ammonia supply pipeline or the reheat unit 2 .

[0027] Preferably, the gas capture unit 1 is a T-shaped pipe assembly and comprises a longer collecting pipe 11 arranged along the axial direction of the urea hydrolyzer and a shorter exhaust pipe 13 arranged along the radial direction of the urea hydrolyzer.

[0028] Figure 2 The side view of the collecting pipe of the gas capture unit in the urea hydrolysis product gas capture and energy-saving reheating device according to an exemplary embodiment of the present invention is shown. Figure 2 As shown, a plurality of groups of gas collecting holes are arranged at intervals on the lower surface of the collecting pipe 11, and each group of gas collecting holes is evenly arranged along the radial direction of the collecting pipe 11. Both ends of the collecting pipe are blocked by end caps 12, which can quickly collect and discharge the product gas of urea hydrolysis. The exhaust pipe 13 extends out of the urea hydrolyzer shell and is connected to the ammonia supply pipeline or the reheat unit 2.

[0029] As a result, the product gas generated during the ammonia production process of the urea hydrolyzer continuously escapes from the liquid phase to the gas phase space above the urea hydrolyzer, is quickly captured by the gas collecting holes on the collecting pipe 11 in the gas capture unit 1, and is discharged to the reheat unit 2 through the exhaust pipe 13.

[0030] Compared with the conventional design in which the urea hydrolysis product gas is directly discharged to the plant transmission pipeline through an outlet on the top of the urea hydrolyzer, the structural design of the present invention can quickly and evenly collect and discharge the hydrolysis product gas accumulated on the top of the urea hydrolyzer, thereby minimizing the adverse effects of product gas accumulation on the urea hydrolysis reaction and improving the urea hydrolysis efficiency.

[0031] The reheat unit 2 of the present invention directly introduces auxiliary steam to reheat the urea hydrolysis product gas, and specifically includes a shell 21 and a steam coil 23 arranged in the shell 21. The shell 21 is arranged in the ammonia supply pipeline or connected to the gas capture unit 1 through the product gas inlet and connected to the ammonia supply pipeline through the product gas outlet 26. That is, the reheat unit 2 can be directly connected to the urea hydrolyzer, or it can be installed separately on the ammonia supply pipeline away from the urea hydrolyzer body. When installed on the top of the urea hydrolyzer, it is preferably installed vertically, and when installed on the ammonia supply pipeline at the product gas outlet, it is preferably installed horizontally. The steam inlet 24 of the steam coil 23 is connected to the steam source and the steam outlet 25 is connected to the steam inlet of the urea hydrolyzer, so that the product gas entering the shell 21 of the reheat unit 2 can fully exchange heat with the superheated steam flowing in the steam coil 23 to increase the temperature.

[0032] Figure 3 The structure schematic diagram of the flow equalizer plate of the reheating unit in the urea hydrolysis product gas capture and energy-saving reheating device according to an exemplary embodiment of the present invention is shown. Figure 3 As shown, preferably, a flow equalizing plate 22 is provided at the product gas inlet of the shell 21 in the reheat unit 1. The flow equalizing plate 22 is a perforated plate with a plurality of small holes evenly opened thereon and is arranged on the entire cross-section of the shell 21 of the reheat unit.

[0033] When the product gas enters the reheat unit 2, it is blocked by the equalizer plate 22, and the flow rate is rapidly reduced and diffused, and evenly enters the shell 21 of the reheat unit through the dense small holes on the equalizer plate 22. After being rectified by the equalizer plate, the urea hydrolysis product gas is evenly heated by the high-temperature steam in the coil to increase the temperature. When the product gas actually flows through the steam coil 23 in the shell 21, it is heated by the high-temperature steam in the steam coil and the temperature is further increased. Then, it is discharged to the ammonia supply pipeline through the product gas outlet 26 and then sent to the SCR denitration system.

[0034] The diameter and height of the reheat unit 2 are determined by calculation according to the required heat exchange amount. The steam coil 23 can be in various forms such as serpentine coil, spiral coil, U-shaped coil or tube-in-tube coil, and the heat exchange area is based on meeting the design temperature requirements of the product gas.

[0035] When the shell 21 of the reheat unit 2 is connected to the gas capture unit 1 through the product gas inlet and connected to the ammonia supply pipeline through the product gas outlet 26, the shell 21 of the reheat unit 2 is connected to the shell of the urea hydrolyzer through a flange connection or welding, the center line of the shell 21 of the reheat unit 2 is directly opposite to the center line of the exhaust pipe 13 and the diameter of the shell 21 of the reheat unit 2 is greater than the diameter of the exhaust pipe 13. When the shell 21 of the reheat unit 2 is set in the ammonia supply pipeline, both ends of the shell 21 of the reheat unit 2 are connected to the ammonia supply pipeline through a cone section or a head opening. Among them, the ammonia supply pipeline is connected to the SCR denitration system to transport the product gas to the flue gas denitration.

[0036] Compared with the conventional design in which the urea hydrolysis product gas is directly discharged to the plant area transportation pipeline through an outlet on the top of the hydrolyzer, the structure of the present invention makes full use of the heat of the superheated steam to further increase the temperature of the product gas, which can avoid steam condensation and polymer generation during the transportation of the product gas, reduce the risk of pipeline system blockage and corrosion, and improve the stability and reliability of the system's ammonia supply.

[0037] The present invention also includes a temperature reduction and pressure reduction unit 3, which is arranged on the pipeline between the steam outlet 25 of the steam coil 23 and the steam inlet of the urea hydrolyzer. The high-temperature steam in the steam coil 23 is directly connected to the auxiliary heating steam (0.8-1.2MPa, ~300°C) of the power plant, enters the steam coil 23 through the steam inlet 24 of the steam coil 23, and is fully heat-exchanged with the product gas outside the pipe before being discharged from the steam outlet 25. At this time, the discharged steam still has a certain degree of superheat, and needs to be further reduced in pressure and temperature to saturated steam by the temperature reduction and pressure reduction unit 3 before entering the urea hydrolyzer to heat the urea solution.

[0038] The steam source used in the present invention is 0.8-1.2MPa, ~300°C power plant auxiliary heating steam, and the steam after passing through the reheat unit 2 and the temperature reduction and pressure reduction unit 3 is 0.7-0.8MPa, 170-180°C saturated steam. The product gas temperature output by the gas capture unit 1 of the present invention is 140-160°C, and the product gas temperature after passing through the reheat unit 2 is 180-200°C.

[0039] Compared with the conventional method of directly introducing auxiliary steam to spray water to reduce temperature and pressure before sending it into the urea hydrolyzer to heat the urea solution, the technology of the present invention fully utilizes the heat of the auxiliary steam to increase the temperature of the hydrolysis product gas before reducing temperature and pressure, thereby reducing steam heat loss and saving energy consumption. At the same time, since the steam temperature entering the temperature reduction and pressure reduction device is reduced, the water consumption of the water spray pump is also reduced accordingly, saving water resources.

[0040] The present invention will be further described below in conjunction with the embodiments.

[0041] Example:

[0042] After a 40-60%wt. urea solution (40-50°C) is heated to 140-160°C by saturated steam in a urea hydrolyzer, urea and water undergo a hydrolysis reaction to generate a mixed gas (hydrolysis product gas) of 140-160°C of NH3, CO2 and water vapor. The product gas continuously escapes from the solution to the gas phase region at the top of the urea hydrolyzer, is quickly and evenly captured by the gas collecting holes of the collecting pipe 11 on the gas capture unit 1, and is discharged from the exhaust pipe 13 to the reheat unit 2 at the top of the urea hydrolyzer.

[0043] When the product gas enters the reheat unit 2, it is blocked by the equalizer plate 22, and the flow rate is rapidly reduced and diffused through the dense small holes on the equalizer plate 22 to evenly enter the shell 21 of the reheat unit 2. When the product gas flows through the reheat unit 2, it is heated by the steam coil 23 arranged in the shell 21. After the temperature rises to 180-200°C, it is discharged from the product gas outlet 26 to the ammonia supply pipeline in the plant area, and finally transported to the SCR denitrification system. The high-temperature steam in the steam coil 23 in the reheat unit 2 is directly connected to the auxiliary steam of 0.8-1.2MPa and ~300°C of the power plant, enters the steam coil 23 from the steam inlet 24, and is discharged from the steam outlet 25 after heat exchange and cooling. After the temperature and pressure reduction unit 3 further reduces the pressure and temperature to become saturated steam, it enters the urea hydrolyzer to heat the urea solution.

[0044] The uniformly distributed gas collection holes on the gas capture unit 1 can quickly and uniformly collect the product gas accumulated in the gas phase region of the urea hydrolyzer, reduce the internal pressure fluctuation caused by concentrated exhaust, facilitate the continuous escape of product gas from the solution, promote the urea hydrolysis reaction, and improve the urea hydrolysis efficiency.

[0045] The diameter of the shell 21 of the reheat unit 2 is larger than the diameter of the exhaust pipe 13. The flow equalizing plate 22 installed therein has the effect of slowing down and equalizing the flow of the product gas discharged from the exhaust pipe 13, so that the product gas is evenly heated by the steam in the steam coil 3 when passing through the reheat unit 2 at a lower flow rate, thereby achieving an ideal reheating effect.

[0046] The steam coil 3 can adopt various structural forms, such as serpentine coil, spiral coil, U-shaped coil and tube-in-tube steam pipe, etc. The height and diameter of the coil are reasonably determined according to the heat exchange area calculated by heat transfer, and then the diameter of the shell 21 in the reheat unit is determined. The diameter of the shell 21 is generally 2 to 4 times the diameter of the exhaust pipe 21, and the height is preferably 1 to 2 meters.

[0047] The reheat unit 2 makes full use of the heat of the auxiliary superheated steam to further increase the product gas temperature, which can avoid steam condensation and polymer corrosion and blockage problems during product gas transportation, while saving steam heat energy loss and reducing water consumption of the desuperheating water pump.

[0048] In summary, the beneficial effects of the present invention mainly include the following aspects:

[0049] 1) The gas capture unit arranged in the upper gas phase zone of the urea hydrolyzer can quickly and evenly collect and discharge the hydrolysis product gas accumulated in the upper part of the hydrolyzer, reduce the internal pressure fluctuation caused by exhaust gas, promote the escape of hydrolysis gas from the liquid, and improve the urea hydrolysis efficiency;

[0050] 2) The urea hydrolysis product gas collected by the gas capture unit is heated by the introduced auxiliary steam to further increase its temperature. During the transportation to the SCR denitration area, the temperature of the product gas can be ensured to be always maintained above the dew point temperature, which can effectively prevent the condensation of water vapor in the product gas and the generation of ammonia and carbon dioxide polymers, avoid clogging and corrosion of the pipeline system, and improve the reliability of system operation;

[0051] 3) The auxiliary steam before temperature reduction and pressure reduction is used to further heat the urea hydrolysis product gas to increase the temperature, which reduces the heat loss caused by steam during the temperature reduction and pressure reduction process and saves energy. Compared with the technology of increasing the temperature of the hydrolysis product gas by electric heating, this technology has a significant energy-saving effect.

[0052] 4) After the auxiliary steam has transferred heat with the urea product gas, the temperature is lowered and the pressure is reduced to saturated steam, which can make full use of energy, reduce the water consumption of the water spray pump and save water resources.

[0053] 5) The present invention has a simple structure, low cost and is easy to implement and apply in actual engineering projects.

[0054] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A urea hydrolysis gas capture and energy-saving reheating device, characterized in that: include: A gas capture unit is arranged in the upper gas phase space of the urea hydrolyzer and extends out of the urea hydrolyzer to be connected to an ammonia supply pipeline or a reheat unit; A reheat unit, comprising a shell and a steam coil arranged in the shell, wherein the shell is arranged in the ammonia supply pipeline or connected to the gas capture unit through a product gas inlet and connected to the ammonia supply pipeline through a product gas outlet, the steam inlet of the steam coil is connected to a steam source and the steam outlet is connected to a steam inlet of a urea hydrolyzer; A temperature and pressure reduction unit is arranged on the pipeline between the steam outlet of the steam coil and the steam inlet of the urea hydrolyzer; The gas capture unit is a T-shaped pipe assembly and includes a longer collecting pipe arranged along the axial direction of the urea hydrolyzer and a shorter exhaust pipe arranged along the radial direction of the urea hydrolyzer; A plurality of groups of gas collecting holes are arranged at intervals on the lower surface of the collecting pipe, and each group of gas collecting holes is evenly arranged along the radial direction of the collecting pipe, and both ends of the collecting pipe are blocked by end covers; the exhaust pipe extends out of the urea hydrolyzer shell and is connected to the ammonia supply pipeline or the reheat unit; A flow equalizing plate is provided at the product gas inlet of the shell of the reheat unit, wherein the flow equalizing plate is a perforated plate with a plurality of small holes evenly opened thereon and is arranged on the entire cross section of the shell of the reheat unit; When the shell of the reheat unit is connected to the gas capture unit through the product gas inlet and connected to the ammonia supply pipeline through the product gas outlet, the shell of the reheat unit is connected to the shell of the urea hydrolyzer through a flange connection or welding, the center line of the shell of the reheat unit is opposite to the center line of the exhaust pipe and the diameter of the shell of the reheat unit is greater than the diameter of the exhaust pipe; When the shell of the reheat unit is arranged in the ammonia supply pipeline, both ends of the shell of the reheat unit are connected to the ammonia supply pipeline through the cone section or the head opening.

2. The urea hydrolysis gas capture and energy-saving reheating device according to claim 1, characterized in that: The steam coil is a serpentine coil, a spiral coil, a U-shaped coil or a tube-in-tube coil, and the ammonia supply pipeline is connected to the SCR denitration system.

3. The urea hydrolysis gas capture and energy-saving reheating device according to claim 1, characterized in that: The steam source is 0.8~1.2MPa, ~300℃ auxiliary heating steam of the power plant. The steam after passing through the reheat unit and the temperature reduction and pressure reduction unit is 0.7~0.8MPa, 170~180℃ saturated steam.

4. The urea hydrolysis gas capture and energy-saving reheating device according to claim 1, characterized in that: The temperature of the product gas output by the gas capture unit is 140-160°C, and the temperature of the product gas after passing through the reheating unit is 180-200°C.

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