A high-efficiency ammonia recovery device

Abstract

The present invention discloses a high-efficiency ammonia recovery device, comprising a storage unit (1), a packing unit (4), a heat exchange unit (3), and a separation and defoaming unit (2) which are sequentially connected and installed on the top of the storage unit (1), a heat exchange tube (34) in the heat exchange unit (3) being vertically arranged so that the ammonia-containing gas in the heat exchange tube (34) is cooled and cooled, and a portion of the gaseous ammonia is condensed and coalesced to form droplets of low-temperature liquid ammonia which fall into a packing layer (45) of the packing unit (4), and a top cavity of the separation and defoaming unit (2) is connected to a cold recovery unit (6) located in the liquid phase space of the storage unit (1) through a connecting tube (5). The ammonia recovery device of the present invention has a compact structure, takes up little space, saves investment, and is safe and reliable. The liquid ammonia separated from the ammonia-containing gas can be mixed with the ammonia-containing gas through the packing, has high mass and heat transfer efficiency, can fully utilize the latent heat and sensible heat of the liquid ammonia and the sensible heat of the low-temperature gas, and has a high comprehensive utilization rate of thermal energy.

Description

Technical Field

[0001] The present invention belongs to the field of chemical industry and ammonia refrigeration technology, and in particular relates to a device for recovering ammonia from ammonia-containing gas that can be used in the synthetic ammonia industry or ammonia refrigeration system. Specifically, it is a high-efficiency ammonia recovery device that integrates storage, heat exchange, separation, heat recovery and other functions. Background Art

[0002] Flash gas, vent air, and purge gas from the synthetic ammonia industry contain high ammonia content, typically 10-60% by volume. In ammonia refrigeration systems in the synthetic ammonia industry and other industrial ammonia refrigeration systems, the ammonia content can reach over 90% by volume. Simply discharging or burning these gases would cause severe environmental pollution and waste energy. With the increasing dual crises of energy and the environment, energy conservation and emission reduction are imperative for factories. Currently, there are two basic technologies for recovering ammonia from flash gas, vent air, purge gas, or purge gas from ammonia refrigeration systems in the synthetic ammonia industry: water scrubbing and absorption, and cooling and separation.

[0003] Flash gas, vent air, and purge gas are sent to the ammonia scrubbing tower and scrubbed with desalted water. The gas at the top of the ammonia scrubbing tower is sent to the off-site treatment area (such as hydrogen recovery, combustion, etc.). The ammonia concentration at the bottom of the ammonia scrubbing tower is generally around 5-15% (mass). The ammonia concentration is relatively low, far below the minimum standard of 20% (mass) in HG / T 5353-2018 "Industrial Ammonia Water". Therefore, the ammonia in the ammonia scrubbing tower needs to be sent to the ammonia distillation system to distill and recover ammonia or add liquid ammonia to prepare high-concentration ammonia water, resulting in high operating costs and not conducive to energy conservation and emission reduction.

[0004] To overcome the shortcomings of the water-washing absorption method, cooling separation is widely used both domestically and internationally to recover ammonia from ammonia-containing gases, especially those with high ammonia concentrations. This method first cools the ammonia-containing gas through heat exchange, then passes it into a separator to separate the condensed liquid ammonia, thereby recovering the majority of the ammonia in the ammonia-containing gas. The cooling separation method consumes only refrigeration (or electricity) and produces a liquid ammonia product as a byproduct, without consuming desalted water or steam.

[0005] CN200510046814.X discloses a method for recovering ammonia from purge gas. The purge gas is first condensed in a heat exchanger and then passed to a gas-liquid separator for gas-liquid separation. The separated liquid ammonia is then returned to the preceding heat exchanger for reduced pressure evaporation and heat exchange, providing a portion of the cooling capacity. The gas exiting the gas-liquid separator can be directly returned to the preceding heat exchanger for heat exchange, or further cooled by an energy converter before being re-entered by the preceding heat exchanger. This method is energy-efficient and environmentally friendly, with high economic benefits and a rapid payback period, addressing the environmental issues associated with purge gas washing and post-processing. However, this method involves a large number of heat exchangers and separators, resulting in significant cooling losses in the equipment and pipelines, making it difficult to achieve effective system heat balance. Furthermore, it fails to account for the temperature pinch point, low pressure differential, and low energy conversion efficiency of the shell-and-tube side of the heat exchanger. Consequently, this method has drawbacks such as a large footprint, high investment, and poor practicality.

[0006] CN200520081206.8 discloses an unpowered ammonia recovery device that utilizes isentropic expansion of an energy converter to reduce the temperature of the purge gas. The expanded, low-temperature, low-pressure purge gas then exchanges heat with the pre-expansion, high-temperature, high-pressure purge gas through a four-stage heat exchanger to recover cooling energy. The latent heat of vaporization of the resulting liquid ammonia is recovered through a three-stage separation process, thereby reducing the purge gas temperature. This device extracts ammonia from the purge gas without consuming energy, significantly increasing its added value. The entire device features automatic control for easy operation, is silent, and does not pollute the environment, making it an ideal environmentally friendly and energy-saving device. The core device, the energy converter (expander), operates at a very high speed, requiring a speed of over 50,000 rpm to achieve high refrigeration efficiency. This makes it unsuitable for applications with small and fluctuating gas volumes. Furthermore, if the gas composition of the purge gas fluctuates significantly, especially if the hydrogen content varies significantly, the efficiency of the energy converter decreases dramatically, resulting in insufficient cooling capacity and deteriorating device operation. Consequently, this method suffers from low reliability and limited operational flexibility. Furthermore, the large number of heat exchangers and separators required leads to high investment and maintenance costs. Summary of the Invention

[0007] The purpose of the present invention is to address the problems existing in the prior art and provide a high-efficiency ammonia recovery device that integrates functions such as storage, heat exchange, separation, and heat recovery. The high-efficiency ammonia recovery device is composed of a storage unit, a filler unit, a heat exchange unit, a separation and defoaming unit, a cold recovery unit and other components. It is simple and convenient to operate and has a high comprehensive utilization rate of thermal energy.

[0008] The purpose of the present invention is to be solved by the following technical solutions:

[0009] A high-efficiency ammonia recovery device is characterized in that: the device includes a storage unit, a packing unit is installed on the top of the storage unit, a heat exchange unit is installed on the top of the packing unit, and a separation and defoaming unit is installed on the top of the heat exchange unit. The heat exchange tubes in the heat exchange unit are vertically arranged so that the ammonia-containing gas in the heat exchange tubes is cooled and part of the gaseous ammonia is condensed and coalesced to form droplets of low-temperature liquid ammonia that fall into the packing layer of the packing unit, and the top cavity of the separation and defoaming unit is connected with the cold recovery unit located in the liquid phase space of the storage unit through a connecting tube; when in use, the ammonia-containing gas discharged from the synthetic ammonia industry or the ammonia refrigeration system is input from the ammonia-containing gas input port on the storage unit, and the ammonia-containing gas enters the packing unit upward and undergoes countercurrent contact with the low-temperature liquid ammonia cooled and separated by the heat exchange unit in the packing layer of the packing unit. Temperature, making full use of the latent heat and sensible heat of the low-temperature liquid ammonia, and then the ammonia-containing gas flows upward through the heat exchange tube of the heat exchange unit to exchange heat with the refrigerant medium (usually liquid ammonia) in the heat exchange unit for cooling, and the low-temperature liquid ammonia condensed from the cooled ammonia-containing gas flows downward through the inner wall of the heat exchange tube to the packing unit, and the low-temperature gas leaving the heat exchange unit passes through the separation and defoaming unit to separate the low-temperature liquid ammonia entrained in the low-temperature gas and flows into the heat exchange tube, and the separated low-temperature gas enters the cold recovery unit through the connecting pipe, and the cold recovery unit recovers the cold of the low-temperature gas and sends it to the boundary area for treatment through the gas output port; the device makes full use of the latent heat and sensible heat of the ammonia-containing gas and the separated liquid ammonia, has good fluid mass transfer and heat transfer effect, and integrates storage, heat exchange, separation, heat recovery and other functions into one, with a compact structure and high comprehensive utilization rate of thermal energy.

[0010] The gas flow rate in the heat exchange tube of the heat exchange unit is not higher than 0.3 m / s. If the gas flow rate is too high, the low-temperature liquid ammonia condensed in the heat exchange tube cannot form a liquid film and flow downward, resulting in poor heat exchange effect and the inability to perform preliminary separation of the condensed liquid phase.

[0011] The length of the heat exchange tube in the heat exchange unit is not less than 300 mm; and the heat exchange tube can separate droplets with a diameter of not less than 100 μm, preferably a heat exchange tube that can separate droplets with a diameter of not less than 150 μm.

[0012] The heat exchange tube arrangement density in the heat exchange unit is 330 tubes / m 2 ~2385 pieces / m 2 ; The preferred solution is: the heat exchange tube arrangement density is 1127 / m 2 ~2385 pieces / m 2 .

[0013] A cylinder flange is provided on the top of the cylinder of the storage unit, which is fixedly connected to the packing lower flange of the packing unit so that the inner cavity of the cylinder can communicate with the packing unit, the packing upper flange of the packing unit is fixedly connected to the heat exchange lower flange of the heat exchange unit so that the packing unit can communicate with the heat exchange unit, the heat exchange upper flange of the heat exchange unit is fixedly connected to the separation lower flange of the separation and defoaming unit so that the heat exchange unit can communicate with the separation and defoaming unit, and the inlet end of the connecting pipe is connected to the cavity at the top of the separation and defoaming unit.

[0014] The storage unit is a horizontal or vertical structure. A liquid ammonia feed pipe is provided on the top of the cylinder of the storage unit, a manhole is provided on the cylinder and a support is provided at the bottom of the cylinder.

[0015] The liquid ammonia feed pipe is inserted into the inner cavity of the cylinder to a distance of 200 to 300 mm from the bottom of the cylinder; a liquid ammonia inlet is provided at the top of the liquid ammonia feed pipe, and air holes are distributed on the liquid ammonia feed pipe located at the upper part of the inner cavity of the cylinder, and the flashed gas in the liquid ammonia entering through the liquid ammonia inlet flows into the gas phase space of the storage unit through the air holes.

[0016] A protruding connecting cylinder is provided on the top of the cylinder of the storage unit, and a cylinder flange for fixing and connecting the filling unit is provided on the top of the protruding connecting cylinder.

[0017] The packing unit includes a packing lower flange, a packing cylinder, a packing upper flange, a packing layer, and a packing support. The packing lower flange and the packing upper flange for connection are respectively located at the bottom and top of the packing cylinder, and a packing support for supporting the packing layer is provided at the lower part of the inner cavity of the packing cylinder. The ammonia-containing gas is in full countercurrent contact with the liquid ammonia separated from the heat exchange unit in the packing layer, so that the temperature of the ammonia-containing gas is reduced and the latent heat and sensible heat of the separated liquid ammonia are fully utilized.

[0018] The filler in the packing layer is a random metal filler or a structured metal filler; the random metal filler includes metal Raschig rings, metal Pall rings, metal ring saddles, and metal step rings, wherein the common nominal sizes of the random metal filler are Dg16, Dg25, Dg38, Dg50, etc., preferably Dg25, and the theoretical plate number is 1 to 10, preferably 3 to 5; the structured metal filler includes metal wire mesh and perforated metal plate, the common specifications of metal wire mesh are 250, 500, 700, etc., the common specifications of perforated metal plate are 125, 250, 350, 500, 700, etc., preferably 500 type structured packing.

[0019] The heat exchange unit includes a heat exchange lower flange, a heat exchange cylinder, a heat exchange upper flange, a heat exchange tube, a heat exchange upper tube sheet, and a heat exchange lower tube sheet. The heat exchange lower flange and the heat exchange upper flange for connection are respectively located at the bottom and the top of the heat exchange cylinder. The heat exchange upper tube sheet and the heat exchange lower tube sheet for encapsulating the heat exchange tube are arranged above and below the inner cavity of the heat exchange cylinder. The refrigerant inlet and the refrigerant outlet are respectively provided on the heat exchange cylinder at the lower part and the upper part of the area formed by the heat exchange upper tube sheet and the heat exchange lower tube sheet. The ammonia-containing gas from the packing unit flows upward in the heat exchange tube, exchanges heat with the refrigerant medium outside the heat exchange tube for cooling. The liquid ammonia separated by cooling and condensation flows downward along the inner wall of the heat exchange tube to the packing unit, realizing efficient falling film heat exchange function in the heat exchange tube.

[0020] The top end of the heat exchange tube is flat and does not exceed the upper edge of the upper heat exchange tube plate to avoid liquid accumulation; the bottom end of the heat exchange tube is a 30-60° bevel and protrudes downward from the bottom surface of the lower heat exchange tube plate, so that multiple point-shaped droplets with the same number as the heat exchange tubes evenly enter the packing layer of the packing unit, thereby improving the liquid phase distribution effect in the packing layer.

[0021] The separation and defoaming unit includes a separation lower flange, a head located on the top of the separation and defoaming shell, and a defoaming assembly located in the separation and defoaming shell. The separation lower flange is used to fixedly connect the separation and defoaming unit and the heat exchange unit; the defoaming assembly can separate the inner cavity of the separation and defoaming shell and the cavity of the head, so that the low-temperature gas leaving the heat exchange unit needs to pass through the defoaming assembly to separate the low-temperature liquid ammonia entrained in the low-temperature gas before entering the cavity of the head; the cavity of the head is connected to the inlet end of the connecting pipe to transport the low-temperature gas.

[0022] Generally speaking, the cryogenic gas entrained with cryogenic liquid ammonia from the heat exchange unit is first subjected to gravity separation and then passes through a defoamer assembly to remove the entrained mist.

[0023] The defoaming assembly adopts a metal wire mesh structured packing capable of separating liquid droplets with a diameter of not less than 5 μm and mist in low-temperature gas, preferably a 500 type metal wire mesh structured packing.

[0024] The connecting pipe passes vertically downward through the defoaming assembly in the separation and defoaming unit, the heat exchange sleeve of the heat exchange unit, and the packing sleeve of the packing unit, and then communicates with the inlet pipe of the cold recovery unit located in the inner cavity of the storage unit.

[0025] The connecting pipe is a grooved pipe. An upper elastic ring, a middle elastic ring, and a lower elastic ring are arranged on the outer wall of the connecting pipe located at the defoaming assembly, the heat exchange sleeve, and the packing sleeve from top to bottom. The upper elastic ring, the middle elastic ring, and the lower elastic ring are respectively fixed in the grooves of the grooved pipe to prevent movement; at the same time, the elastic ring has a sealing effect to prevent different fluids from mixing, resulting in a fluid short circuit and poor operation of the equipment.

[0026] In addition, the outer diameter of the upper elastic ring is greater than or equal to the outer diameter of the middle elastic ring and greater than or equal to the outer diameter of the lower elastic ring, so as to facilitate the installation and disassembly of the connecting pipe.

[0027] The inlet end of the communicating pipe is arranged on the top of the separation and defoaming unit to communicate with the top cavity of the separation and defoaming unit, and the outlet end of the communicating pipe is connected with the inlet pipe of the cold recovery unit extending out of the storage unit.

[0028] The cold recovery unit is composed of a single-tube heat exchange tube or a heat exchange tube bundle. The cold recovery unit is arranged at the lower part of the liquid phase space of the storage unit. The low-temperature gas input from the connecting pipe and passing through the cold recovery unit exchanges heat with the liquid ammonia in the storage unit, recovers the cold through the cold recovery unit, and then leaves the high-efficiency ammonia recovery device.

[0029] The heat exchange unit provided by the present invention utilizes a vertical heat exchange tube structure. The ammonia-containing purge gas within the heat exchange tube exchanges heat with the liquid ammonia medium outside the heat exchange tube, cooling the purge gas. In the heat exchanger's tube side, the temperature of the inner wall of the heat exchange tube is the lowest. Therefore, the ammonia-containing purge gas within the heat exchange tube condenses and coalesces into droplets on the inner wall of the heat exchange tube. These droplets then flow downward along the inner wall of the heat exchange tube by gravity. (This requires a low velocity of the rising ammonia-containing purge gas, generally no higher than 0.3 m / s, to prevent the droplets from forming a downward gravity flow.) This results in efficient vertical liquid film heat exchange.

[0030] For a heat exchange unit to form a liquid film, liquid ammonia must condense. Therefore, if the heat exchange tubes are not long enough, only a trace amount of liquid ammonia will condense, but a stable liquid film cannot be formed. The heat exchange effect is poor, worse than falling film heat exchange, and this needs to be considered during the design process. During the design of the heat exchange unit in this application, after heat exchange design calculations and the effect of steady-state fluid flow, the heat exchange tube length is generally not less than 300 mm and is at least 0.3 times the diameter of the heat exchange unit.

[0031] Since the ammonia-containing purge gas in the heat exchange tube condenses and coalesces into droplets on the inner wall of the heat exchange tube, it is different from the conventional gravity separator (gravity separator is suitable for separating droplets with a diameter greater than 200μm). The separation method in the heat exchange tube adopted in this application is that part of the ammonia in the ammonia-containing purge gas first contacts the inner wall of the heat exchange tube, condenses, coalesces, and forms droplets. Therefore, the diameter of the separated droplets is better than that of the traditional conventional gravity separator, and can achieve the separation of droplets of 100μm, but preferably can separate droplets with a diameter of not less than 150μm.

[0032] The uniform distribution of fluid in the packing layer not only ensures the wetting of the packing surface, but also ensures the uniform distribution of gas. Therefore, the initial uniform distribution of the top of the packing unit is an important condition for ensuring that the packing unit achieves the expected separation effect. Therefore, this important condition is achieved by using uniformly distributed heat exchange tubes that can drip droplets of low-temperature liquid ammonia. Due to the combined structure of the heat exchange unit located directly above the packing unit, each heat exchange tube of the heat exchange unit is equivalent to a spray point of the packing unit. For the arrangement based on the center distance parameters of the heat exchange tubes in GB / T 151-2014, the theoretical number of heat exchange tubes can reach 2385 / m 2 (φ16*1.5, tube center distance 22mm), 1847 pieces / m 2 (φ19*1.5, tube center distance 25mm), 1127 pieces / m 2 (φ25*2, tube center distance 32mm), 721 pieces / m 2 (φ32*2, tube center distance 40mm), 500 pieces / m 2 (φ38*2.5, tube center distance 48mm), etc. The general small packed tower spray point density is not less than 330 / m 2 ; Under the same spray density, the more spray points there are, the better the operating effect of the packing unit.

[0033] The present invention has the following advantages over the prior art:

[0034] The high-efficiency ammonia recovery device of the present invention uses a single device to realize the functions of liquid ammonia storage, heat exchange of ammonia-containing gas, separation of liquid ammonia, and efficient recovery and utilization of cold. The device has a reasonable and compact structure, small footprint, low investment, safety and reliability, simple operation, and high operational flexibility. It utilizes the principle of efficient mass transfer and heat transfer of fluids to achieve efficient utilization of the sensible heat of the ammonia-containing gas and the latent heat and sensible heat of the separated liquid ammonia, and has a high cascade utilization rate of thermal energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Attachment Figure 1 Schematic diagram of the structure of a high-efficiency ammonia recovery device with a built-in connecting pipe according to the present invention;

[0036] Attachment Figure 2 Schematic diagram of the structure of a high-efficiency ammonia recovery device with an external connecting pipe according to the present invention;

[0037] Attachment Figure 3 It is a structural schematic diagram of the separation and defoaming unit of the present invention;

[0038] Attachment Figure 4 Schematic diagram of the structure of the heat exchange unit of the present invention;

[0039] Attachment Figure 5 Schematic diagram of the structure of the packing unit of the present invention;

[0040] Attachment Figure 6 It is a structural schematic diagram of the connecting pipe of the present invention;

[0041] Attachment Figure 7 It is a structural schematic diagram of a conventional ammonia recovery device in the prior art.

[0042] Among them: 1 - storage unit; 11 - cylinder; 12 - liquid ammonia feed pipe; 13 - support; 14 - manhole; N1 - liquid ammonia inlet; N3 - ammonia-containing gas inlet; N4 - gas outlet; 2 - separation and defoaming unit; 21 - separation lower flange; 22 - separation head; 23 - defoaming assembly; 3 - heat exchange unit; 31 - heat exchange lower flange; 32 - heat exchange cylinder; 33 - heat exchange upper flange; 34 - heat exchange tube; 341 - top end; 34 - bottom end; 35 - heat exchange upper tube plate; 36 - heat exchange lower Tube sheet; 37—heat exchange sleeve; N5—refrigerant inlet; N6—refrigerant outlet; 4—packing unit; 41—packing lower flange; 42—packing cylinder; 43—packing upper flange; 44—packing sleeve; 45—packing layer; 46—packing support; 5—connecting pipe; 51—grooved pipe; 52—upper elastic ring; 53—middle elastic ring; 54—lower elastic ring; 6—cold recovery unit; V001—ammonia collection tank; V002—separator; E001—ammonia cooler; E002—exhaust gas heater. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0044] like Figure 1-6As shown: a high-efficiency ammonia recovery device, the device includes a storage unit 1, a packing unit 4 is connected and installed on the top of the storage unit 1, a heat exchange unit 3 is connected and installed on the top of the packing unit 4, and a separation and defoaming unit 2 is connected and installed on the top of the heat exchange unit 3. The heat exchange tube 34 in the heat exchange unit 3 is vertically arranged so that the ammonia-containing gas in the heat exchange tube 34 is cooled and the droplets of low-temperature liquid ammonia are condensed and coalesced to fall into the packing layer 45 of the packing unit 4, and the top cavity of the separation and defoaming unit 2 is connected to the cold recovery unit 6 located in the liquid phase space of the storage unit 1 through the connecting pipe 5; when in use, the ammonia-containing gas discharged from the synthetic ammonia industry or the ammonia refrigeration system is input from the ammonia-containing gas input port N3 on the storage unit 1, and the ammonia-containing gas is The low-temperature liquid ammonia that is cooled and separated by the heat exchange unit 3 enters the packing unit 4 upward and is cooled by countercurrent contact in the packing layer 45 of the packing unit 4, which fully utilizes the latent heat and sensible heat of the low-temperature liquid ammonia. Then the ammonia-containing gas flows upward through the heat exchange tube 34 of the heat exchange unit 3 to exchange heat with the refrigerant medium in the heat exchange unit 3 for cooling. The low-temperature liquid ammonia condensed from the cooled ammonia-containing gas flows downward to the packing unit 4 through the inner wall of the heat exchange tube 34. The low-temperature gas leaving the heat exchange unit 3 passes through the separation and defoaming unit 2 to separate the low-temperature liquid ammonia entrained in the low-temperature gas and flows into the heat exchange tube 34. The separated low-temperature gas enters the cold recovery unit 6 through the connecting pipe 5. The cold recovery unit 6 recovers the cold energy of the low-temperature gas and sends it to the boundary area for treatment through the gas output port N4.

[0045] like Figure 1-2 As shown, the storage unit 1 is a horizontal or vertical structure, and a protruding connecting cylinder is provided on the top of the cylinder 11 of the storage unit 1, and a cylinder flange for fixedly connecting the packing unit 4 is provided on the top of the cylinder 11 of the storage unit 1; a liquid ammonia feed pipe 12 is provided on the top of the cylinder 11 of the storage unit 1, and the liquid ammonia feed pipe 12 is inserted into the inner cavity of the cylinder 11 to a distance of 200 to 300 mm from the bottom of the cylinder 11, and a liquid ammonia inlet N1 is provided on the top of the liquid ammonia feed pipe 12, and air holes are distributed on the liquid ammonia feed pipe 12 located at the upper part of the inner cavity of the cylinder 11, and the flashed gas in the liquid ammonia entering through the liquid ammonia inlet N1 flows into the gas phase space of the storage unit 1 through the air holes; in addition, a manhole 14 is provided on the cylinder 11 and a support 13 is provided at the bottom of the cylinder 11. The cold recovery unit 6, which is composed of a single heat exchange tube or a heat exchange tube bundle, is arranged in the lower part of the liquid phase space of the storage unit 1. The low-temperature gas input from the connecting pipe 5 and passing through the cold recovery unit 6 exchanges heat with the liquid ammonia in the storage unit, recovers the cold through the cold recovery unit 6, and leaves the high-efficiency ammonia recovery device through the gas output port N4.

[0046] like Figure 1-3As shown, the separation and defoaming unit 2 includes a separation lower flange 21, a head 22 located at the top of the separation and defoaming housing, and a defoaming assembly 23 located within the separation and defoaming housing. The separation lower flange 21, connected to the heat exchange upper flange 33, is used to securely connect the separation and defoaming unit 2 and the heat exchange unit 3. The defoaming assembly 23 uses a wire mesh structured packing, preferably a 500-type wire mesh structured packing, capable of separating droplets and mist in the low-temperature gas with a diameter of no less than 5 μm. The defoaming assembly 23 separates the inner cavity of the separation and defoaming housing from the cavity of the head 22, ensuring that the low-temperature gas leaving the heat exchange unit 3 passes through the defoaming assembly 23 to separate the low-temperature liquid ammonia entrained in the low-temperature gas before entering the cavity of the head 22. The cavity of the head 22 is connected to the inlet end of the connecting pipe 5 to transport the low-temperature gas. In addition, a channel for the connecting pipe 5 is retained in the defoaming assembly 23.

[0047] like Figure 1-2 As shown in Figure 4, the heat exchange unit 3 includes a heat exchange lower flange 31, a heat exchange cylinder 32, a heat exchange upper flange 33, a heat exchange tube 34, a heat exchange upper tube sheet 35, and a heat exchange lower tube sheet 36. The heat exchange lower flange 31 for connecting the packing upper flange 43 and the heat exchange upper flange 33 for connecting the separation lower flange 21 are respectively located at the bottom and top of the heat exchange cylinder 32. The heat exchange upper tube sheet 35 and the heat exchange lower tube sheet 36 for encapsulating the heat exchange tube 34 are arranged above and below the inner cavity of the heat exchange cylinder 32. The heat exchange lower tube sheet 35 and the heat exchange lower tube sheet 36 are arranged above and below the inner cavity of the heat exchange cylinder 32. The heat cylinder 32 is provided with a refrigerant inlet N5 and a refrigerant outlet N6. Furthermore, to improve efficiency, the top end 341 of the heat exchange tube 34 is flat and does not extend beyond the upper edge of the heat exchange upper tube sheet 35 to prevent liquid accumulation. The bottom end 342 of the heat exchange tube 34 is beveled and protrudes downward from the bottom surface of the heat exchange lower tube sheet 36. This allows a number of liquid droplets, equal in number to the number of heat exchange tubes 34, to evenly enter the packing layer 45 of the packing unit 4, improving the liquid distribution within the packing layer 45. Furthermore, a heat exchange sleeve 37 is provided within the heat exchange unit 3 for the passage of the connecting pipe 5. Ammonia-containing gas from the packing unit 4 flows upward within the heat exchange tube 34, exchanging heat with the refrigerant medium outside the heat exchange tube 34 to reduce its temperature. The cooled, condensed, and separated liquid ammonia flows downward along the inner wall of the heat exchange tube 34 to the packing unit 4, achieving efficient falling-film heat exchange within the heat exchange tube 34.

[0048] It should be emphasized that the gas flow rate in the heat exchange tube 34 of the heat exchange unit 3 is not higher than 0.3 m / s and the length of the heat exchange tube 34 is not less than 300 mm, so that droplets can be generated and fall. The heat exchange tube 34 can separate droplets with a diameter of not less than 100 μm, and preferably a heat exchange tube that can separate droplets with a diameter of not less than 150 μm.

[0049] like Figure 1-2As shown in Figure 5, the packing unit 4 includes a packing lower flange 41, a packing cylinder 42, a packing upper flange 43, a packing layer 45, and a packing support 46. The packing lower flange 41 for connecting the cylinder flange and the packing upper flange 43 for connecting the heat exchange lower flange 31 are respectively located at the bottom and top of the packing cylinder 42. A packing support 46 for supporting the packing layer 45 is provided at the lower part of the inner cavity of the packing cylinder 42. In addition, a packing sleeve 44 is reserved in the packing layer 45 for the connecting pipe 5 to pass through. The packing in the packing layer 45 adopts random metal packing or structured metal packing, wherein the random metal packing includes metal Raschig rings, metal Pall rings, metal ring saddles, and metal step rings, and the structured metal packing includes metal wire mesh and perforated metal plate. The ammonia-containing gas is in full countercurrent contact with the liquid ammonia separated from the heat exchange unit 3 in the packing layer 45, thereby reducing the temperature of the ammonia-containing gas and making full use of the latent heat and sensible heat of the separated liquid ammonia.

[0050] In order to select appropriate packing in the high-efficiency ammonia recovery device provided by the present invention, experiments were conducted using HG / T 21556.2-1995 stainless steel ball ring packings of different specifications while achieving the same mass and heat transfer effects in the packing unit 4. The experimental results are shown in Table 1.

[0051] Table 1 HG / T 21556.2—1995 Experimental data of stainless steel ball ring packing

[0052] Stainless steel ball ring packing nominal diameter <![CDATA[Packing bulk density kg / m 3 > Packing layer height m Packing layer pressure drop Pa DN16 396 1.75 204 DN25 393 2.00 186 DN38 318 2.40 148

[0053] As shown in Table 1, the smaller the nominal diameter of the stainless steel ball ring packing, the higher the packing density, and therefore the lower the required height of the packing layer 45. However, the smaller the nominal diameter of the stainless steel ball ring packing, the higher the pressure drop of the packing layer 45. Therefore, from the overall perspective, DN25, i.e., HG / T 21556.2-1995-PRSS-25 S30408 ​​stainless steel ball ring packing, is the best choice.

[0054] like Figure 1-2As shown in Figure 6, there are two cases of the connecting pipe 5; one is that the connecting pipe 5 is built-in, in which case the connecting pipe 5 is a grooved pipe 51, and the connecting pipe 5 passes vertically downward in sequence through the defoaming assembly 23 in the separation and defoaming unit 2, the heat exchange sleeve 37 of the heat exchange unit 3, and the packing sleeve 44 of the packing unit 4, and then is connected with the inlet pipe of the cold recovery unit 6 located in the inner cavity of the storage unit 1, and an upper elastic ring 52, a middle elastic ring 53, and a lower elastic ring 54 are provided on the outer wall of the connecting pipe 5 located at the defoaming assembly 23, the heat exchange sleeve 37, and the packing sleeve 44 from top to bottom, and the outer diameter of the upper elastic ring 52 is ≥ the outer diameter of the middle elastic ring 53 ≥ the outer diameter of the lower elastic ring 54; the other connecting pipe 5 is external, in which case the inlet end of the connecting pipe 5 is arranged at the top of the separation and defoaming unit 2 to connect with the top cavity of the separation and defoaming unit 2, and the outlet end of the connecting pipe 5 is connected with the inlet pipe of the cold recovery unit 6 extending out of the storage unit 1. Example

[0055] like Figure 1 、 Figure 3-6 The high-efficiency ammonia recovery device provided by the present invention is shown.

[0056] The liquid ammonia separated by the ammonia separator of the ammonia synthesis unit of a 2000t / d large-scale water-coal slurry synthetic ammonia plant is decompressed in two stages. The purge gas from the first stage flash evaporation is combined with the fresh gas for compression and sent to the ammonia synthesis loop for reaction. The ammonia-containing purge gas from the second stage flash evaporation (2.5MPaG, -5.3℃, 191Nm 3 / h, ammonia volume content 14.6%) and ammonia-containing purge gas from the ammonia refrigeration system (1.6MPaG, 40℃, 0Nm 3 / h ("hot ammonia" working condition), 1189Nm 3 / h ("cold ammonia" working condition), ammonia volume content 90.2%) merges into the ammonia-containing gas inlet N3 of the high-efficiency ammonia recovery unit, and then enters the DN450*1500 packing unit 4 (HG / T21556.2-1995-PRSS-25 The cooled ammonia gas flows upward through the heat exchange tubes 34 of the heat exchange unit 3 (to ensure that each stainless steel ball ring packing on the top surface can be wetted, a heat exchange tube 34 with a diameter of 19*1.5 and a center-to-center distance of 25 mm is preferably selected to match the heat exchange unit 3 and the packing unit 4), exchanges heat with the liquid ammonia outside the heat exchange tubes 34 (0.0 MPaG, -32.8°C, 15 kg / h ("hot ammonia" operating condition), 700 kg / h ("cold ammonia" operating condition)), and the temperature is reduced to -30.0°C. The liquid ammonia outside the heat exchange tubes 34 absorbs heat and evaporates, and the generated gaseous ammonia returns to the ammonia refrigeration system. During the heat exchange process of the heat exchange unit 3, some liquid ammonia in the ammonia-containing gas in the heat exchange tube 34 condenses and flows evenly downward along the inner wall of the heat exchange tube 34, realizing the falling film heat exchange function of the heat exchanger and improving the heat exchange effect of the heat exchanger. The condensed liquid ammonia in the heat exchange tube 34 of the heat exchange unit 3 passes through the groove at the bottom end 342 of each heat exchange tube 34 and evenly enters the packing layer of the packing unit 4 in the form of multiple droplets with the same number of heat exchange tubes (the spray density reaches 1847 points / m 2 ), thereby improving the liquid phase distribution effect of the filler. The low-temperature gas passing through the heat exchange unit 3 enters the heat exchange tube (specification φ45*2.5, total length 7500mm) of the cold recovery unit 6 through the separation and defoaming unit 2 and the connecting pipe 5. The heat exchange tube exchanges heat with the 40℃ liquid ammonia from the ammonia refrigeration system input from the liquid ammonia inlet N1. After the temperature rises to 30℃, it is sent to the boundary area (1.5MPaG, 30℃, 176Nm 3 / h ("hot ammonia" working condition), 301Nm 3 / h ("cold ammonia" working condition), ammonia volume content 7.3%), and recovered 11.5kg / h ("hot ammonia" working condition) and 819kg / h ("cold ammonia" working condition) of liquid ammonia.

[0057] "Hot ammonia" working condition (normal working condition): The liquid ammonia separated from the ammonia separator of the ammonia synthesis unit is decompressed in two stages. The liquid ammonia after the second-stage flash evaporation is heated to 20-30℃ through heat exchange and sent to the urea unit or hot ammonia users.

[0058] "Cold ammonia" working condition: When the urea unit or hot ammonia user reduces load or stops, the liquid ammonia separated by the ammonia separator of the ammonia synthesis unit is decompressed in two stages. The excess liquid ammonia after the second-stage flash evaporation is finally sent to the atmospheric pressure ammonia storage tank after the third-stage flash evaporation with the temperature reduced to -38 ~ -33.4℃.

[0059] Table 2 Data of an embodiment of a high-efficiency ammonia recovery device

[0060]

[0061] Comparative Example

[0062] like Figure 7 A conventional ammonia recovery device in the prior art is shown.

[0063] The liquid ammonia separated by the ammonia separator of the ammonia synthesis unit of a 2000t / d large-scale water-coal slurry synthetic ammonia plant is decompressed in two stages. The purge gas from the first stage flash evaporation is combined with the fresh gas for compression and sent to the ammonia synthesis loop for reaction. The ammonia-containing purge gas from the second stage flash evaporation (2.5MPaG, -5.3℃, 191Nm 3 / h, ammonia volume content 14.6%) and ammonia-containing purge gas from the ammonia refrigeration system (1.6MPaG, 40℃, 0Nm 3 / h ("hot ammonia" working condition), 1189Nm 3 / h ("cold ammonia" working condition), ammonia volume content 90.2%) merges into the ammonia-containing gas inlet N3 of the ammonia cooler E001, and then enters the tube side of the ammonia cooler E001 to exchange heat with the liquid ammonia in the shell side (0.0MPaG, -32.8℃, 17kg / h ("hot ammonia" working condition), 950kg / h ("cold ammonia" working condition)) and the temperature drops to -30.0℃. The shell side liquid ammonia absorbs heat and evaporates, and the generated gaseous ammonia returns to the ammonia refrigeration system. The gas after heat exchange passes through the separator V002 for gas-liquid separation. The separated gas recovers the cold capacity through the tail gas heater E002 and is sent to the boundary area (1.45MPaG, 30℃, 176Nm 3 / h ("hot ammonia" working condition), 302Nm 3 / h ("cold ammonia" working condition), ammonia volume content 7.5%, the separated liquid ammonia (11.4kg / h ("hot ammonia" working condition), 818kg / h ("cold ammonia" working condition)) is returned to the ammonia collection tank V001 for storage.

[0064] "Hot ammonia" working condition (normal working condition): The liquid ammonia separated from the ammonia separator of the ammonia synthesis unit is decompressed in two stages. The liquid ammonia after the second-stage flash evaporation is heated to 20-30℃ through heat exchange and sent to the urea unit or hot ammonia users.

[0065] "Cold ammonia" working condition: When the urea unit or hot ammonia user reduces load or stops, the liquid ammonia separated by the ammonia separator of the ammonia synthesis unit is decompressed in two stages. The excess liquid ammonia after the second-stage flash evaporation is finally sent to the atmospheric pressure ammonia storage tank after the third-stage flash evaporation with the temperature reduced to -38 ~ -33.4℃.

[0066] Table 3 Comparative example data of conventional ammonia recovery device in the prior art

[0067]

[0068] The reference points of the data reflected in the embodiment and the comparative example are: the temperature of the ammonia-containing gas after cooling by the heat exchange unit 3 (or the ammonia cooler E001) is -30°C and the amount of separated liquid ammonia is not much different. By comparing the data in Table 2 of the embodiment and Table 3 of the comparative example, it can be concluded that, compared with the conventional ammonia recovery device in the prior art, the high-efficiency ammonia recovery device provided by the present invention has the following advantages in recovering ammonia:

[0069] (1) One high-efficiency ammonia recovery unit replaces four units of conventional ammonia recovery units, occupies a small area, does not require a complex piping system or a liquid level control system for the separator, saves investment, and reduces the cooling loss to the environment.

[0070] (2) The use of fillers to achieve sufficient gas-liquid mass and heat transfer makes full use of the cooling capacity of the separated liquid ammonia, reducing the amount of refrigerated ammonia required by the heat exchange unit 3 (or ammonia cooler E001) (the difference is 13% under the "hot ammonia" working condition and 36% under the "cold ammonia" working condition), thereby reducing the power consumption of the ammonia refrigeration system;

[0071] (3) Heat exchange unit 3 adopts a high-efficiency vertical liquid film heat exchanger to replace the traditional kettle type (BKU) heat exchanger, which has a high heat transfer coefficient (the heat transfer coefficient can be increased by 28%), good heat exchange effect, and low investment;

[0072] (4) Each heat exchange tube 34 of the heat exchange unit 3 becomes a liquid phase spray point of the packing unit 4. The spray point density is high, which improves the mass transfer and heat transfer effect of the packing unit 4;

[0073] (5) The connecting pipe 5 adopts an elastic ring to achieve the isolation of low pressure difference gas, with a compact structure and easy installation.

[0074] The above embodiments are only for illustrating the technical ideas of the present invention and cannot be used to limit the scope of protection of the present invention. Any changes made on the basis of the technical solutions in accordance with the technical ideas proposed by the present invention fall within the scope of protection of the present invention; any technologies not involved in the present invention can be implemented by existing technologies.

Claims

1. A high-efficiency ammonia recovery device, characterized by: The device comprises a storage unit (1), a packing unit (4) is connected and installed on the top of the storage unit (1), a heat exchange unit (3) is connected and installed on the top of the packing unit (4), and a separation and defoaming unit (2) is connected and installed on the top of the heat exchange unit (3). The heat exchange tube (34) in the heat exchange unit (3) is vertically arranged so that the ammonia-containing gas in the heat exchange tube (34) is cooled and cooled, and part of the gaseous ammonia is condensed and coalesced to form droplets of low-temperature liquid ammonia that fall into the packing layer (45) of the packing unit (4), and the top cavity of the separation and defoaming unit (2) is connected to the cold recovery unit (6) located in the liquid phase space of the storage unit (1) through the connecting tube (5); when in use, the ammonia-containing gas discharged from the synthetic ammonia industry or the ammonia refrigeration system is input from the ammonia-containing gas input port (N3) on the storage unit (1) The ammonia-containing gas flows upward into the packing unit (4) and is cooled and separated by the heat exchange unit (3). The low-temperature liquid ammonia is subjected to countercurrent contact cooling in the packing layer (45) of the packing unit (4). Then, the ammonia-containing gas flows upward through the heat exchange tube (34) of the heat exchange unit (3) to exchange heat with the refrigerant medium in the heat exchange unit (3) for cooling. The low-temperature liquid ammonia condensed from the ammonia-containing gas after cooling flows downward to the packing unit (4) through the inner wall of the heat exchange tube (34). The low-temperature gas leaving the heat exchange unit (3) passes through the separation and defoaming unit (2) to separate the low-temperature liquid ammonia entrained in the low-temperature gas and flows into the heat exchange tube (34). The separated low-temperature gas enters the cold recovery unit (6) through the connecting pipe (5). The cold recovery unit (6) recovers the cold energy of the low-temperature gas and sends it to the boundary area for treatment through the gas output port (N4).

2. The high-efficiency ammonia recovery device according to claim 1, characterized in that: The gas flow rate in the heat exchange tube (34) of the heat exchange unit (3) is not higher than 0.3 m / s.

3. The high-efficiency ammonia recovery device according to claim 1, characterized in that: The length of the heat exchange tube (34) in the heat exchange unit (3) is not less than 300 mm; and the heat exchange tube (34) is capable of separating droplets with a diameter of not less than 100 μm.

4. The high-efficiency ammonia recovery device according to claim 1, characterized in that: The heat exchange tubes (34) in the heat exchange unit (3) are arranged at a density of 330 tubes / m 2 ~2385 pieces / m 2 .

5. The high-efficiency ammonia recovery device according to claim 1, characterized in that: A cylinder flange is provided on the top of the cylinder (11) of the storage unit (1), and the cylinder flange is fixedly connected to the packing lower flange (41) of the packing unit (4) so ​​that the inner cavity of the cylinder (11) can communicate with the packing unit (4); the packing upper flange (43) of the packing unit (4) is fixedly connected to the heat exchange lower flange (31) of the heat exchange unit (3) so that the packing unit (4) can communicate with the heat exchange unit (3); the heat exchange upper flange (33) of the heat exchange unit (3) is fixedly connected to the separation lower flange (21) of the separation and defoaming unit (2) so that the heat exchange unit (3) can communicate with the separation and defoaming unit (2); and the inlet end of the connecting pipe (5) is connected to the cavity at the top of the separation and defoaming unit (2).

6. The high-efficiency ammonia recovery device according to any one of claims 1 to 5, characterized in that: The storage unit (1) is a horizontal or vertical structure. A liquid ammonia feed pipe (12) is provided on the top of the cylinder (11) of the storage unit (1), a manhole (14) is provided on the cylinder (11), and a support (13) is provided at the bottom of the cylinder (11).

7. The high-efficiency ammonia recovery device according to claim 6, characterized in that: The liquid ammonia feed pipe (12) is inserted into the inner cavity of the cylinder (11) to a distance of 200 to 300 mm from the bottom of the cylinder (11); a liquid ammonia inlet (N1) is provided at the top of the liquid ammonia feed pipe (12), and air holes are distributed on the liquid ammonia feed pipe (12) located at the upper part of the inner cavity of the cylinder (11).

8. The high-efficiency ammonia recovery device according to claim 5, characterized in that: A protruding connection cylinder is provided on the top of the cylinder (11) of the storage unit (1), and a cylinder flange for fixedly connecting the filler unit (4) is provided on the top of the protruding connection cylinder.

9. The high-efficiency ammonia recovery device according to any one of claims 1 to 5, characterized in that: The packing unit (4) comprises a packing lower flange (41), a packing cylinder (42), a packing upper flange (43), a packing layer (45), and a packing support member (46). The packing lower flange (41) and the packing upper flange (43) for connection are respectively located at the bottom and the top of the packing cylinder (42). A packing support member (46) for supporting the packing layer (45) is provided at the lower part of the inner cavity of the packing cylinder (42). The ammonia-containing gas is in full countercurrent contact with the liquid ammonia separated from the heat exchange unit (3) in the packing layer (45), thereby reducing the temperature of the ammonia-containing gas and fully utilizing the latent heat and sensible heat of the separated liquid ammonia.

10. The high-efficiency ammonia recovery device according to claim 9, characterized in that: The filler in the packing layer (45) is a random metal filler or a structured metal filler; the random metal filler includes a metal Raschig ring, a metal ball ring, a metal ring saddle, and a metal step ring; the structured metal filler includes a metal wire mesh and a perforated metal plate.

11. The high-efficiency ammonia recovery device according to any one of claims 1 to 5, characterized in that: The heat exchange unit (3) comprises a heat exchange lower flange (31), a heat exchange cylinder (32), a heat exchange upper flange (33), a heat exchange tube (34), a heat exchange upper tube sheet (35), and a heat exchange lower tube sheet (36). The heat exchange lower flange (31) and the heat exchange upper flange (33) for connection are respectively located at the bottom and the top of the heat exchange cylinder (32). The heat exchange upper tube sheet (35) and the heat exchange lower tube sheet (36) for encapsulating the heat exchange tube (34) are arranged above and below the inner cavity of the heat exchange cylinder (32). A refrigerant inlet (N5) and a refrigerant outlet (N6) are respectively provided on the heat exchange cylinder (32) at the lower and upper parts of the area formed by the tube sheet (35) and the lower heat exchange tube sheet (36); the ammonia-containing gas from the packing unit (4) flows upward in the heat exchange tube (34), exchanges heat with the refrigerant medium outside the heat exchange tube (34) for cooling, and the liquid ammonia separated by cooling and condensation flows downward along the inner wall of the heat exchange tube (34) to the packing unit (4), realizing the falling film heat exchange function in the heat exchange tube (34).

12. The high-efficiency ammonia recovery device according to claim 11, characterized in that: The top end (341) of the heat exchange tube (34) is flat and does not exceed the upper edge of the heat exchange upper tube plate (35); the bottom end (342) of the heat exchange tube (34) is beveled and protrudes downward from the bottom surface of the heat exchange lower tube plate (36), so that a plurality of point-shaped liquid droplets, the same number as the heat exchange tube (34), uniformly enter the packing layer (45) of the packing unit (4).

13. The high-efficiency ammonia recovery device according to any one of claims 1 to 5, characterized in that: The separation and defoaming unit (2) comprises a separation lower flange (21), a head (22) located at the top of the separation and defoaming shell, and a defoaming assembly (23) located in the separation and defoaming shell. The separation lower flange (21) is used to fixedly connect the separation and defoaming unit (2) and the heat exchange unit (3); the defoaming assembly (23) can separate the inner cavity of the separation and defoaming shell and the cavity of the head (22), so that the low-temperature gas leaving the heat exchange unit (3) needs to pass through the defoaming assembly (23) to separate the low-temperature liquid ammonia entrained in the low-temperature gas before entering the cavity of the head (22); the cavity of the head (22) is connected to the inlet end of the connecting pipe (5) to transport the low-temperature gas.

14. The high-efficiency ammonia recovery device according to claim 13, characterized in that: The defoaming assembly (23) uses a metal wire mesh structured filler capable of separating droplets with a diameter of not less than 5 μm and mist in the low-temperature gas.

15. The high-efficiency ammonia recovery device according to any one of claims 1 to 5, characterized in that: The connecting pipe (5) passes vertically downward through the defoaming assembly (23) in the separation and defoaming unit (2), the heat exchange sleeve (37) of the heat exchange unit (3), and the packing sleeve (44) of the packing unit (4), and then communicates with the inlet pipe of the cold recovery unit (6) located in the inner cavity of the storage unit (1).

16. The high-efficiency ammonia recovery device according to claim 15, characterized in that: The connecting pipe (5) is a grooved pipe (51), and an upper elastic ring (52), a middle elastic ring (53), and a lower elastic ring (54) are sequentially provided on the outer wall of the connecting pipe (5) located at the defoaming assembly (23), the heat exchange sleeve (37), and the filler sleeve (44) from top to bottom, and the outer diameter of the upper elastic ring (52) is greater than or equal to the outer diameter of the middle elastic ring (53) and greater than or equal to the outer diameter of the lower elastic ring (54).

17. The high-efficiency ammonia recovery device according to any one of claims 1 to 5, characterized in that: The inlet end of the connecting pipe (5) is arranged at the top of the separation and defoaming unit (2) to communicate with the top cavity of the separation and defoaming unit (2), and the outlet end of the connecting pipe (5) is connected to the inlet pipe of the cold recovery unit (6) extending outside the storage unit (1).

18. The high-efficiency ammonia recovery device according to any one of claims 1 to 5, characterized in that: The cooling recovery unit (6) is composed of a single heat exchange tube or a heat exchange tube bundle.

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