Double-effect evaporation and heat pump coupled steam stripping deamination system and process

Abstract

The invention discloses a double-effect evaporation and heat pump coupled steam stripping deamination system and process. The system comprises a feed preheater, a deamination steam stripping tower, a compression heat pump, a flash tank and an evaporator, a cold side inlet of the feeding preheater is used for feeding, and a cold side outlet of the feeding preheater is communicated with a liquid phase feeding hole of the deamination stripping tower; a steam inlet of the deamination stripping tower is communicated with an outlet of the compression heat pump, a liquid phase outlet of the deamination stripping tower is communicated with an inlet of the flash tank, and a steam outlet of the deamination stripping tower is communicated with a hot side inlet of the evaporator; a gas phase outlet of the flash tank is communicated with an inlet of the compression heat pump, and a liquid phase outlet of the flash tank is communicated with a cold side inlet of the evaporator; a cold side outlet of the evaporator is communicated with a backflow port of the flash tank, and a hot side outlet of the evaporator is communicated with a hot side inlet of the feeding preheater. The method can reduce the consumption of cooling circulating water and steam in the stripping deamination process, and is economical and energy-saving.

Description

Technical Field

[0001] The invention relates to chemical separation technology, in particular to separation and energy-saving technology for a deammoniation system. Background Art

[0002] At present, the total amount of ammonia nitrogen in my country's annual wastewater discharge exceeds 450,000 tons. Among them, high-concentration ammonia nitrogen wastewater (concentration>500mg / L) discharged by high-energy-consuming and high-emission industries such as metallurgy, medicine, and chemical industry accounts for more than 80% of the total discharge. Especially in the lithium battery industry, the production of ternary precursors will produce a large amount of high-concentration ammonia nitrogen wastewater, and the ratio between the two is about 1:20, that is, each ton of ternary precursor will produce about 20 tons of high-concentration ammonia nitrogen wastewater, and the concentration is usually above 4000mg / L. In addition, with the rapid development of the new energy vehicle industry in recent years, the demand for lithium-ion batteries will also increase rapidly, and high-concentration ammonia nitrogen wastewater treatment technology with high efficiency and low energy consumption is in urgent need of breakthroughs.

[0003] Under current technical conditions, the processes that can treat high-concentration ammonia nitrogen wastewater mainly include steam stripping separation, membrane separation, chemical precipitation and biochemical methods. Among these methods, steam stripping separation is the main method for industrial application. The other methods have problems such as poor effect, high cost and easy secondary pollution, and are difficult to industrialize. The traditional steam stripping deammonification process can achieve a high ammonia nitrogen removal rate, and can also prepare high-concentration ammonia water at the top of the tower for recycling, which also avoids the problem of secondary pollution. However, the traditional steam stripping deammonification process requires a large amount of purchased steam, and about 120kg of steam is required for each ton of ammonia nitrogen wastewater. Figure 1 The schematic diagram of the conventional steam stripping deamination process is shown in FIG. Figure 1 As shown, in the traditional steam stripping deammonification process, ammonia nitrogen wastewater enters from the top of the deammonification stripping tower T01, and external steam is introduced into the tower bottom to provide heat. During the rising process in the tower, the steam takes out the ammonia nitrogen and part of the water vapor in the ammonia nitrogen wastewater from the top of the tower. A top condenser E01 is provided at the top of the deammonification stripping tower T01, and a tower bottom cooler E02 is provided at the tower bottom of the deammonification stripping tower T01. For occasions where the ammonia water concentration at the top of the tower is required to be low, reflux can be omitted. The ammonia-containing steam coming out of the top of the tower is condensed to obtain an ammonia water product, and the tower bottom discharges the deammonified water. This process consumes a lot of steam, and the water temperature is high when the wastewater enters the subsequent system, making it difficult to use heat. The steam consumption per ton of ammonia nitrogen wastewater is about 120kg. In addition, a large amount of circulating water is required to cool (condense) the deammonified water in the tower bottom of the ammonia steam at the top of the tower to the storage device. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a double-effect evaporation and heat pump coupled steam stripping deamination system and process, which can reduce the consumption of cooling circulating water and steam in the steam stripping deamination process and achieve economic and energy-saving effects.

[0005] According to one aspect of an embodiment of the present invention, a steam stripping deammoniation process coupled with double-effect evaporation and heat pump is provided, comprising the following steps:

[0006] The water vapor pressurized by the compression heat pump enters the deamination stripping tower from the tower bottom, and contacts the ammonia nitrogen wastewater entering the deamination stripping tower from the tower top after being preheated by the feed preheater in reverse direction, and performs stripping;

[0007] The deammonified water extracted from the deammonification stripping tower kettle enters the flash tank for flash evaporation, and the water vapor obtained by flash evaporation enters the compression heat pump for pressurization;

[0008] The ammonia-containing steam extracted from the top of the deammoniation stripping tower enters the evaporator and acts as a heat source to exchange heat with the deammonified water entering the evaporator from the flash tank. The ammonia-containing steam releases heat to become an ammonia-water gas-liquid mixture that enters the feed preheater and acts as a heat source to preheat the ammonia nitrogen wastewater before being extracted as an ammonia-water product. The deammonified water absorbs heat and evaporates before returning to the flash tank.

[0009] According to another aspect of an embodiment of the present invention, a double-effect evaporation and heat pump coupled steam stripping deamination system is provided, comprising a feed preheater, a deamination stripping tower, a compression heat pump, a flash tank and an evaporator; the cold side inlet of the feed preheater is used for feeding, and the cold side outlet of the feed preheater is connected to the liquid phase feed port of the deamination stripping tower; the steam inlet of the deamination stripping tower is connected to the outlet of the compression heat pump, the liquid phase outlet of the deamination stripping tower is connected to the inlet of the flash tank, and the steam outlet of the deamination stripping tower is connected to the hot side inlet of the evaporator; the gas phase outlet of the flash tank is connected to the inlet of the compression heat pump, and the liquid phase outlet of the flash tank is connected to the cold side inlet of the evaporator; the cold side outlet of the evaporator is connected to the reflux port of the flash tank, and the hot side outlet of the evaporator is connected to the hot side inlet of the feed preheater.

[0010] The present invention has at least the following advantages and features:

[0011] 1. The deamination stripping tower of the embodiment of the present invention is used in combination with a flash tank and an evaporator. The double-effect evaporation greatly increases the steam production. By coupling the heat pump to increase the steam quality as a stripping agent, zero consumption of steam and circulating water is achieved, which significantly reduces the operating cost.

[0012] 2. Compared with the prior art, the steam stripping and deammoniation process of double-effect evaporation coupled with a heat pump adopted in the embodiment of the present invention has mild conditions, simple operation, and the assisting device operates safely and stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic flow chart of a conventional steam stripping deamination process is shown.

[0014] Figure 2 A schematic flow chart of a steam stripping and deammoniation process of double-effect evaporation coupled with a heat pump according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0015] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] Please refer to Figure 2 A double-effect evaporation and heat pump coupled steam stripping and deamination system according to an embodiment of the present invention comprises a feed preheater E1, a deamination stripping tower T1, a compression heat pump C1, a flash tank V1 and an evaporator E2.

[0017] The cold side inlet of the feed preheater E1 is used for feeding, and the cold side outlet of the feed preheater E1 is connected to the liquid phase feed inlet of the deamination stripping tower T1.

[0018] The steam inlet of the deamination stripping tower T1 is connected to the outlet of the compression heat pump C1, the liquid phase outlet of the deamination stripping tower T1 is connected to the inlet of the flash tank V1, and the steam outlet of the deamination stripping tower T1 is connected to the hot side inlet of the evaporator E2. The steam outlet and liquid phase outlet of the deamination stripping tower T1 are respectively arranged at the top and bottom of the tower.

[0019] The gas phase outlet of the flash tank V1 is connected to the inlet of the compression heat pump C1, and the liquid phase outlet of the flash tank V1 is connected to the cold side inlet of the evaporator E2. The gas phase outlet and the liquid phase outlet of the flash tank V1 are respectively arranged at the top and the bottom of the flash tank. In some specific embodiments, the liquid phase outlet of the flash tank V1 is divided into two paths, one of which is connected to the cold side inlet of the evaporator E2, and the other is used to output the deammonified water.

[0020] The cold side outlet of the evaporator E2 is communicated with the reflux port of the flash tank V1, and the hot side outlet of the evaporator E2 is communicated with the hot side inlet of the feed preheater E1.

[0021] In this embodiment, the compression heat pump C1 adopts a screw compressor. The inlet of the screw compressor is provided with a nozzle for spraying water into the inlet. The deamination stripping tower T1 is a packed tower or a plate tower.

[0022] Furthermore, if the steam discharged from the compression heat pump C1 is insufficient for the stripping treatment, steam may be added to the deamination stripping tower T1.

[0023] A double-effect evaporation and heat pump coupled steam stripping and deamination process according to an embodiment of the present invention comprises the following steps:

[0024] The water vapor pressurized by the compression heat pump C1 enters the deamination stripping tower T1 from the tower bottom, and contacts the ammonia nitrogen wastewater entering the deamination stripping tower T1 from the tower top after being preheated by the feed preheater E1 in reverse direction, and performs stripping;

[0025] The deammonified water extracted from the bottom of the deammonification stripping tower T1 enters the flash tank V1 for flash evaporation, and the water vapor obtained by flash evaporation enters the compression heat pump C1 for pressurization;

[0026] The ammonia-containing steam extracted from the top of the deammoniation stripping tower T1 enters the evaporator E2, and is used as a heat source to exchange heat with the deammonified water entering the evaporator E2 from the flash tank V1. The ammonia-containing steam releases heat to become an ammonia-water gas-liquid mixture that enters the feed preheater E1, and is used as a heat source to preheat the ammonia nitrogen wastewater and then extracted as an ammonia water product. The deammonified water absorbs heat and evaporates and then returns to the flash tank V1.

[0027] In this embodiment, the deaminated water after endothermic evaporation in the evaporator E2 becomes a gas-liquid mixture and returns to the flash tank V1. The operating pressure of the deammoniation stripping tower is 80 kPaA to 400 kPaA.

[0028] Specifically, in a stripping deammonification process coupled with double-effect evaporation and heat pump according to an embodiment of the present invention, ammonia nitrogen wastewater enters from the top of the deammonification stripping tower T1 after being preheated by the feed preheater E1. The heat source of the feed preheater E1 comes from the cooling waste heat of the ammonia-containing steam at the top of the deammonification stripping tower T1 after double-effect evaporation. The water vapor pressurized by the screw compressor C1 is used as a stripping agent to replace the purchased steam and is introduced from the bottom of the deammonification stripping tower T1. The heat in the rising steam in the bottom of the tower is used to reversely contact the ammonia nitrogen wastewater from the top of the tower for mass transfer and heat transfer, and ammonia-containing steam is evaporated from the ammonia nitrogen wastewater. Ammonia-containing steam that meets the design requirements is extracted from the top of the deammonification stripping tower T1, and high-temperature deammonified water that meets the design requirements is extracted from the bottom of the tower. Due to its high temperature and the fact that the main component of the deammonified water is water, it enters the low-pressure flash tank V1 for flash evaporation to obtain a large amount of water vapor. In addition, the ammonia-containing steam at the top of the deamination stripping tower T1 has a high temperature and a large latent heat. Due to the large temperature difference between the ammonia-containing steam and the deammonified water in the flash tank V1, the ammonia-containing steam can be used as the heat source of the external circulation evaporator E2 of the flash tank V1 to evaporate more water vapor. The water vapor from the flash tank V1 enters the screw compressor C1 and is directly compressed to the bottom of the deamination stripping tower T1, serving as a stripping agent to provide heat for the deamination stripping tower T1. At the same time, in order to control the exhaust temperature at the outlet of the screw compressor C1, water is sprayed at the inlet of the screw compressor C1 to control the exhaust of the compressor to be saturated or slightly superheated steam.

[0029] The following takes the steam stripping deamination process of ammonia nitrogen wastewater as an example to further explain the technical solution of the present invention, and illustrates the superiority of the steam stripping deamination process of double-effect evaporation and heat pump coupling in the embodiment of the present invention by comparing the energy consumption and operating costs with those of the traditional deamination process.

[0030] Application Example 1

[0031] To process 120m 3 The calculation and simulation results of the steam stripping deammoniation process flow of double-effect evaporation and heat pump coupling of / h ammonia nitrogen wastewater are described as an example. The feed conditions and separation requirements are shown in Table 1:

[0032] Table 1 Ammonia nitrogen wastewater feed conditions and separation requirements

[0033]

[0034] Process Description:

[0035] (1) Deamination is carried out in the deamination stripping tower T1. The operating pressure of the tower is 90 kPaA, and an operating pressure drop of 10 kPa is considered for the entire tower.

[0036] (2) Ammonia nitrogen wastewater at 60℃ is heated to 120m 3 / h flow rate into the tower, using the waste heat after double-effect evaporation of ammonia-containing steam at the top of the deamination stripping tower T1, the ammonia nitrogen wastewater is preheated to 63.5℃ in the feed preheater E1 and then enters from the top of the deamination stripping tower T1.

[0037] (3) The water vapor at 110°C is pressurized to 145 kPaA by screw compressor C1 and introduced into the bottom of the deammoniation stripping tower T1 as a stripping agent instead of purchased steam. The heat in the rising steam in the bottom of the tower is used to conduct counter-contact mass and heat transfer with the ammonia nitrogen wastewater from the top of the tower, thereby distilling ammonia-containing vapor from the ammonia nitrogen wastewater.

[0038] (4) The ammonia-containing steam that meets the design requirements, i.e., 9% ammonia, is extracted from the top of the deamination stripping tower T1, and the high-temperature deamination water that meets the design requirements, i.e., the ammonia nitrogen content is less than 15 ppm, is extracted from the bottom of the tower.

[0039] (5) The water temperature after deamination in the tower bottom is 100°C, which is relatively high, and the main component is water. It enters the low-pressure flash tank V1 for flash evaporation. The operating pressure of the flash tank V1 is 30kPaA, corresponding to a saturation temperature of 70°C, and a large amount of water vapor is obtained. In addition, the flash tank V1 is equipped with an external evaporator E2. The 9% ammonia-containing steam discharged from the top of the deamination stripping tower T1 has a temperature of 95°C, a relatively high temperature, a high water vapor content, a large amount of phase change latent heat, and a temperature difference of 25°C with the evaporator E2 of the flash tank V1. It can be used as a heat source for the evaporator E2, and rich steam is produced in the flash tank V1.

[0040] (6) The total steam produced by flash evaporation in the flash tank V1 and evaporation in the evaporator E2 is 10.074 t / h, which is compressed from 30 kPaA to 145 kPaA by the screw compressor C1. Water is sprayed at the inlet of the screw compressor C1 to control the outlet temperature to 110°C, which can produce rich steam with an outlet gas volume of 11.35 t / h. It directly enters the deamination stripping tower T1 kettle as a stripping agent, using the small amount of sensible heat and large amount of latent heat of the steam to provide heat for the deamination stripping tower T1, which can greatly reduce the consumption of purchased steam. In this process, due to the integration of double-effect evaporation and heat pump coupling technology, the waste heat is fully utilized, which can completely avoid the consumption of purchased steam and circulating water, and only a small amount of electrical energy is required to maintain the normal operation of the system.

[0041] The energy consumption levels and operating costs of the traditional deamination process and the steam stripping deamination process coupled with double-effect evaporation and heat pump are calculated and compared when the separation task meets the same separation requirements. The utility specifications and consumption are shown in Table 2.

[0042] Table 2 Specifications and consumption of public works

[0043]

[0044] Note: Steam unit price: 200 yuan / t, circulating water: 0.2 yuan / h, electricity: 0.7 yuan / kWh, annual operating time 8000h.

[0045] Comparison results: When the above two deamination processes meet the same separation requirements, the operating cost of the steam stripping deamination process coupled with double-effect evaporation and heat pump is much lower than that of the traditional deamination process, and the steam and circulating water consumption are both zero, and only a small amount of electricity is required to maintain the normal operation of the system. In terms of economy, the annual operating cost of the steam stripping deamination process coupled with double-effect evaporation and heat pump is about 6.78 million, which is 66.8% lower than the 20.41 million of the traditional deamination process. The economy is very considerable and saves the operating cost of the device to the greatest extent. This technology has the advantages of feasibility, energy saving, economy, and environmental protection. It is in line with the overall development direction of my country's resource utilization, energy conservation and emission reduction, and environmental protection, and has broad prospects for industrialization.

[0046] In view of the high cost and energy consumption of the existing stripping deamination process, the double-effect evaporation and heat pump coupled stripping deamination system and process for high-concentration ammonia nitrogen wastewater treatment in the embodiment of the present invention fully utilizes the waste heat of the stripping deamination system, integrates the technology of double-effect evaporation and heat pump coupling, achieves the dual purpose of condensation at the top of the deamination stripping tower and reboiling at the bottom of the tower, reduces the consumption of cooling circulating water and steam, and achieves the effect of energy saving and consumption reduction. In addition, the embodiment of the present invention can also obtain a high-concentration ammonia water product and deammoniated water with an ammonia nitrogen content of less than 15ppm.

[0047] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A steam stripping deamination process coupled with double-effect evaporation and heat pump, characterized in that: The following steps are involved: The water vapor pressurized by the compression heat pump enters the deamination stripping tower from the tower bottom, and contacts the ammonia nitrogen wastewater entering the deamination stripping tower from the tower top after being preheated by the feed preheater in reverse direction, and performs stripping; The deaminated water extracted from the kettle of the deammoniation stripping tower enters the flash tank for flash evaporation, and the water vapor obtained by flash evaporation enters the compression heat pump for pressurization; The ammonia-containing steam extracted from the top of the deamination stripping tower enters the evaporator, and is used as a heat source to exchange heat with the deammonified water entering the evaporator from the flash tank. The ammonia-containing steam releases heat to become an ammonia-water gas-liquid mixture that enters the feed preheater, and is used as a heat source to preheat the ammonia nitrogen wastewater before being extracted as an ammonia-water product. The deammonified water absorbs heat and evaporates before returning to the flash tank.

2. The double-effect evaporation and heat pump coupled steam stripping and deamination process according to claim 1, characterized in that: The compression heat pump adopts a screw compressor.

3. The double-effect evaporation and heat pump coupled steam stripping and deamination process as claimed in claim 2, characterized in that: Water is sprayed at the inlet of the screw compressor to control the exhaust gas of the screw compressor to be saturated or slightly superheated steam.

4. The double-effect evaporation and heat pump coupled steam stripping and deamination process according to claim 1, characterized in that: The deamination stripping tower is a packed tower or a plate tower.

5. The double-effect evaporation and heat pump coupled steam stripping and deamination process according to claim 1, characterized in that: The operating pressure of the deamination stripping tower is 80 kPaA to 400 kPaA.

6. A steam stripping and deamination system coupled with double-effect evaporation and heat pump, characterized in that: Includes feed preheater, deamination stripper, compression heat pump, flash tank and evaporator; The cold side inlet of the feed preheater is used for feeding, and the cold side outlet of the feed preheater is connected to the liquid phase feed port of the deamination stripping tower; The steam inlet of the deamination stripping tower is connected to the outlet of the compression heat pump, the liquid phase outlet of the deamination stripping tower is connected to the inlet of the flash tank, and the steam outlet of the deamination stripping tower is connected to the hot side inlet of the evaporator; The gas phase outlet of the flash tank is communicated with the inlet of the compression heat pump, and the liquid phase outlet of the flash tank is communicated with the cold side inlet of the evaporator; The cold side outlet of the evaporator is communicated with the reflux port of the flash tank, and the hot side outlet of the evaporator is communicated with the hot side inlet of the feed preheater.

7. The double-effect evaporation and heat pump coupled steam stripping and deamination system according to claim 6, characterized in that: The compression heat pump adopts a screw compressor.

8. The double-effect evaporation and heat pump coupled steam stripping and deamination system according to claim 7, characterized in that: The inlet of the screw compressor is provided with a nozzle for spraying water into the inlet.

9. The double-effect evaporation and heat pump coupled steam stripping and deamination system according to claim 6, characterized in that: The deamination stripping tower is a packed tower or a plate tower.

10. The double-effect evaporation and heat pump coupled steam stripping and deamination system according to claim 6, characterized in that: The liquid phase outlet of the flash tank is divided into two paths, one of which is connected to the cold side inlet of the evaporator, and the other is used to output the deammoniation water.

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