A double-tower ammonia distillation system

Abstract

The utility model provides a double-tower ammonia evaporation system, which belongs to the technical field of ammonia evaporation, and includes a first ammonia water heat exchanger, a thiocyanate tower, a second ammonia water heat exchanger, a first liquid alkali mixer and a fixed ammonia tower; the first ammonia water heat exchanger is respectively connected to the inlet at the middle and upper section of the thiocyanate tower and the outlet at the bottom of the thiocyanate tower; the first ammonia water heat exchanger is connected to the second ammonia water heat exchanger through a first pipeline; the second ammonia water heat exchanger is respectively connected to the inlet at the middle and upper section of the fixed ammonia tower and the outlet at the bottom of the fixed ammonia tower; the first liquid alkali mixer is also connected before the second ammonia water heat exchanger and the fixed ammonia tower; the second ammonia water heat exchanger is connected to the bottom of the first liquid alkali mixer, and the top of the first liquid alkali mixer is connected to the inlet at the middle and upper section of the fixed ammonia tower; the upper section of the fixed ammonia tower is connected to the lower section of the thiocyanate tower. The utility model can effectively remove sulfide and cyanide by using two towers in series, and improve the removal rate. The removal rate of sulfide and total cyanide can be increased by 50% to 80%.

Description

Technical Field

[0001] The utility model belongs to the technical field of ammonia distillation and relates to a double-tower ammonia distillation system. Background Art

[0002] Ammonia distillation tower is a desorption tower that releases ammonia dissolved in circulating water. It is an operating device that volatilizes and releases ammonia dissolved in circulating water through heat transfer of heat carrier. Its working principle is: using general heat carrier water vapor as heating agent, so that the equilibrium vapor pressure of ammonia on the circulating water surface is greater than the partial pressure of ammonia in the heat carrier, and the vapor and liquid two phases are in countercurrent contact to transfer mass and heat, so that ammonia is gradually released from the circulating water. At the top of the tower, we get a mixture of ammonia vapor and water vapor, and at the bottom of the tower, we get relatively pure circulating water. The purpose of adding alkali source is to convert fixed ammonium salt into volatile ammonium salt.

[0003] Ammonia distillation towers are widely used in industrial production, especially in the chemical, pharmaceutical, and food industries. In the chemical industry, ammonia distillation towers can be used in processes such as ammonia purification and drying to ensure the purity and quality of the product. In the pharmaceutical industry, ammonia distillation towers can be used to prepare drugs and medical materials to ensure the safety and effectiveness of the products. In the food industry, ammonia distillation towers can be used in processes such as food evaporation and concentration to improve the taste and quality of food. In addition, ammonia distillation towers can also be used in processes such as wastewater treatment and waste gas treatment in the environmental protection industry to reduce pollution to the environment.

[0004] However, the existing ammonia evaporation tower is directly used for wastewater treatment, especially for coking wastewater treatment. Since the coking wastewater contains sulfide, cyanide and other substances, when the remaining ammonia water enters the ammonia evaporation tower, liquid alkali is added to decompose and fix ammonia. While the liquid alkali reacts with ammonia, it also reacts with sulfide and cyanide to generate salts that enter the ammonia evaporation wastewater, causing the problem of increased sulfide and cyanide in the ammonia evaporation wastewater.

[0005] In addition, in order to prevent equipment failure and inability to treat wastewater, many units now install two ammonia distillation towers, one for use and one for backup, resulting in a waste of resources. Utility Model Content

[0006] In view of the above problems, the utility model provides a double-tower ammonia distillation system.

[0007] In order to achieve the above purpose, the technical solution adopted by the utility model is:

[0008] A double-tower ammonia distillation system, comprising a first ammonia water heat exchanger, a thiocyanate tower, a second ammonia water heat exchanger, a first liquid alkali mixer and a fixed ammonia tower;

[0009] The first ammonia water heat exchanger is respectively connected with an inlet at the middle and upper section of the thiocyanate tower and an outlet at the bottom of the thiocyanate tower;

[0010] The first ammonia water heat exchanger is connected to the second ammonia water heat exchanger through a first pipeline;

[0011] The second ammonia water heat exchanger is respectively connected with an inlet at the middle and upper section of the fixed ammonia tower and an outlet at the bottom of the fixed ammonia tower;

[0012] The first liquid alkali mixer is also connected before the second ammonia water heat exchanger and the fixed ammonia tower; the second ammonia water heat exchanger is connected to the bottom of the first liquid alkali mixer, and the top of the first liquid alkali mixer is connected to the inlet at the upper middle section of the fixed ammonia tower;

[0013] The upper section of the fixed ammonia tower is connected to the lower section of the thiocyanate tower.

[0014] Furthermore, the double-tower ammonia distillation system also includes an ammonia distillation wastewater cooler, which is connected to the second ammonia water heat exchanger through a second pipeline.

[0015] Furthermore, the first ammonia water heat exchanger is also connected to a pipeline flowing into the remaining ammonia water after oil removal.

[0016] Furthermore, a third pipeline is connected between the pipeline for flowing into the residual ammonia water after oil removal and the first pipeline;

[0017] A fourth pipeline is also connected between the first pipeline and the second pipeline;

[0018] The pipeline for the residual ammonia water after oil removal, the first pipeline, the second pipeline, the third pipeline and the fourth pipeline are all provided with control valves.

[0019] Furthermore, a second liquid alkali mixer is connected between the first ammonia water heat exchanger and the thiocyanate tower;

[0020] The first ammonia water heat exchanger is communicated with the bottom of the second liquid alkali mixer, and the top of the second liquid alkali mixer is communicated with the inlet at the middle and upper section of the thiocyanate tower.

[0021] Furthermore, a control valve is provided on the pipeline connecting the first ammonia water heat exchanger and the second liquid alkali mixer;

[0022] The bottom of the second liquid alkali mixer is also connected with a pipeline for flowing into liquid alkali, and a control valve is arranged on the pipeline for flowing into alkali liquid that is connected with the second liquid alkali mixer.

[0023] Furthermore, a first reducer is provided on the top of the fixed ammonia tower, the first reducer is connected to the precooling tower or the sulfur-ammonia saturator through an ammonia vapor pipeline, and a control valve is provided on the ammonia vapor pipeline connecting the first reducer and the precooling tower or the sulfur-ammonia saturator;

[0024] The first divider is also connected to the circulating water supply pipe and the circulating water return pipe respectively;

[0025] A second reducer is provided on the top of the thiocyanate tower, the second reducer is connected to the precooling tower or the sulfur-ammonia saturator through an ammonia vapor pipeline, and a control valve is provided on the ammonia vapor pipeline connecting the second reducer and the precooling tower or the sulfur-ammonia saturator;

[0026] The second divider is also connected to the circulating water supply pipe and the circulating water return pipe respectively;

[0027] Control valves are provided on both the circulating water supply pipe and the circulating water return pipe.

[0028] Furthermore, the bottom of the thiocyanate tower and the bottom of the fixed ammonia tower are also connected to external steam pipelines respectively, and the external steam pipelines are provided with steam regulating valves and control valves.

[0029] Furthermore, a control valve is provided on the pipeline connecting the second ammonia water heat exchanger and the first liquid alkali mixer;

[0030] The bottom of the first liquid alkali mixer is also connected with a pipeline for flowing into liquid alkali, and a control valve is arranged on the pipeline for flowing into alkali liquid that is connected with the first liquid alkali mixer.

[0031] Furthermore, a control valve is provided on the pipeline connecting the first ammonia water heat exchanger and the outlet at the bottom of the thiocyanate tower;

[0032] A control valve is provided on the pipeline connecting the second ammonia water heat exchanger and the outlet of the bottom of the fixed ammonia tower;

[0033] The ammonia vapor wastewater cooler is also connected to a pipeline for passing wastewater into the biochemical pool; a control valve is provided on the pipeline for passing wastewater into the biochemical pool;

[0034] The ammonia wastewater cooler is connected to the circulating water inlet pipe and the circulating water return pipe respectively, and the circulating water inlet pipe and the circulating water return pipe are both provided with control valves;

[0035] A control valve is provided on the pipeline connecting the upper section of the fixed ammonia tower and the lower section of the thiocyanate tower.

[0036] The beneficial effects of a double-tower ammonia distillation system of the utility model are:

[0037] The utility model uses two towers in series, one tower (thiocyanate tower) first evaporates sulfide and cyanide, and then mixes with liquid alkali to decompose fixed ammonia and enters another tower (fixed ammonia tower) for distillation, so that sulfide and cyanide can be effectively removed and the removal rate is improved. According to simulation tests, the removal rate of sulfide and total cyanide can be increased by 50% to 80%;

[0038] At the same time, the ammonia vapor coming out from the side of the top of the fixed ammonia tower enters the thiocyanate tower as a heat source, which also increases the number of tower plates in the ammonia distillation section, thereby reducing the amount of external steam used. The amount of external steam used is reduced from the original 160~180kg / ton of residual ammonia water to 80~100kg / ton of residual ammonia water.

[0039] The ammonia vapor coming out of the upper side of the fixed ammonia tower enters the thiocyanate tower as a heat source, which increases the number of trays in the ammonia distillation section and reduces the steam consumption;

[0040] When the double-tower ammonia distillation system is used, liquid alkali is not added to the thiocyanate tower. After the sulfide and cyanide are removed in the thiocyanate tower, liquid alkali is added to decompose and fix ammonia, thus avoiding the reaction between sulfide and cyanide and liquid alkali; sulfide and cyanide are better removed, thereby improving the removal rate of sulfide and cyanide, which is beneficial to the subsequent biochemical system;

[0041] At the same time, the thiocyanate tower and the fixed ammonia tower are used in series, which increases the number of trays in the retention section, has a high removal rate for indicators such as ammonia nitrogen, and can save steam consumption;

[0042] Moreover, when a problem occurs in one of the towers, it can be switched to single-tower operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of a double-tower ammonia distillation system according to an embodiment of the utility model;

[0044] In the figure: 1, fixed ammonia tower; 11, first fractionator; 12, first liquid alkali mixer; 2, thiocyanate tower; 21, second fractionator; 22, second liquid alkali mixer; 3, first ammonia water heat exchanger; 31, first pipeline; 32, third pipeline; 4, second ammonia water heat exchanger; 41, second pipeline; 42, fourth pipeline; 5, ammonia wastewater cooler; 6, control valve; 61, first control valve; 62, second control valve; 63, third control valve; 64, fourth control valve; 65, fifth control valve; 66, sixth control valve; 67, seventh control valve; 68, eighth control valve; 69, ninth control valve; 610, tenth control valve; 611, the eleventh control valve; 612, the twelfth control valve; 613, the thirteenth control valve; 614, the fourteenth control valve; 615, the fifteenth control valve; 616, the sixteenth control valve; 617, the seventeenth control valve; 618, the eighteenth control valve; 619, the nineteenth control valve; 620, the twentieth control valve; 621, the twenty-first control valve; 622, the twenty-second control valve; 623, the twenty-third control valve; 624, the twenty-fourth control valve; 625, the twenty-fifth control valve; 626, the twenty-sixth control valve; 627, the twenty-seventh control valve; 628, the twenty-eighth control valve; 629, the steam regulating valve. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the utility model are described clearly and completely below. In the following description, many specific details are set forth to facilitate a full understanding of the utility model, but the utility model can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the utility model, so the utility model is not limited by the specific embodiments disclosed below.

[0046] Embodiment A double tower ammonia distillation system

[0047] See also Figure 1 The utility model provides a double-tower ammonia distillation system, including a first ammonia water heat exchanger 3, a second liquid alkali mixer 22, a thiocyanate tower 2, a second ammonia water heat exchanger 4, a first liquid alkali mixer 12, a fixed ammonia tower 1, an ammonia wastewater cooler 5 and a control valve 6; wherein the control valve 6 includes a first control valve 61 to a twenty-eighth control valve 628 and a steam regulating valve 629.

[0048] The pipe inlet of the first ammonia water heat exchanger 3 is connected to the pipeline flowing into the residual ammonia water after oil removal; the pipeline flowing into the residual ammonia water after oil removal is provided with a first control valve 61;

[0049] The first ammonia water heat exchanger 3 is respectively connected with the inlet at the middle and upper section of the thiocyanate tower 2 and the outlet at the bottom of the thiocyanate tower 2; wherein the tube side outlet of the first ammonia water heat exchanger 3 is connected with the inlet at the middle and upper section of the thiocyanate tower 2 (i.e., the inlet slightly above the middle of the thiocyanate tower 2), and the shell side inlet of the first ammonia water heat exchanger 3 is connected with the outlet at the bottom of the thiocyanate tower 2 through a pipeline; a third control valve 63 is provided on the pipeline connecting the shell side inlet of the first ammonia water heat exchanger 3 and the outlet at the bottom of the thiocyanate tower 2;

[0050] A second liquid alkali mixer 22 is also connected between the first ammonia water heat exchanger 3 and the thiocyanate tower 2; that is, the tube outlet of the first ammonia water heat exchanger 3 is connected to the bottom of the second liquid alkali mixer 22 through a pipeline, and the top of the second liquid alkali mixer 22 is connected to the inlet at the middle and upper section of the thiocyanate tower 2 through a pipeline; a second control valve 62 is provided on the pipeline connecting the first ammonia water heat exchanger 3 and the second liquid alkali mixer 22; the bottom of the second liquid alkali mixer 22 is also connected to a pipeline for flowing in liquid alkali, and a twelfth control valve 612 is also provided on the pipeline for flowing in alkali liquid connected to the second liquid alkali mixer 22;

[0051] A second reducer 21 is provided on the top of the thiocyanate tower 2. The second reducer 21 is connected to a precooling tower or a sulfur-ammonia saturator through an ammonia vapor pipeline. An eighteenth control valve 618 is provided on the ammonia vapor pipeline connecting the second reducer 21 with the precooling tower or the sulfur-ammonia saturator; the precooling tower or the sulfur-ammonia saturator is used for precooling or saturating the evaporated gas phase ammonia vapor and acid gas mixture before desulfurization.

[0052] The second decompressor 21 is also connected to the circulating water supply pipe and the circulating water return pipe respectively, wherein the circulating water supply pipe connected to the second decompressor 21 is provided with a twentieth control valve 620 and a twenty-first control valve 621, and the circulating water return pipe connected to the second decompressor 21 is provided with a twenty-second control valve 622;

[0053] The shell side outlet of the first ammonia water heat exchanger 3 is connected to the tube side inlet of the second ammonia water heat exchanger 4 through the first pipeline 31, and the first pipeline 31 connecting the shell side outlet of the first ammonia water heat exchanger 3 and the tube side inlet of the second ammonia water heat exchanger 4 is provided with a fourth control valve 64 and a fifth control valve 65;

[0054] The second ammonia water heat exchanger 4 is respectively connected with the inlet at the middle and upper section of the fixed ammonia tower 1 and the outlet at the bottom of the fixed ammonia tower 1; wherein the tube-side outlet of the second ammonia water heat exchanger 4 is connected with the inlet at the middle and upper section of the fixed ammonia tower 1 (i.e., the inlet slightly above the middle of the fixed ammonia tower 1), and the shell-side inlet of the second ammonia water heat exchanger 4 is connected with the outlet at the bottom of the fixed ammonia tower 1 through a pipeline; a seventh control valve 67 is provided on the pipeline connecting the shell-side inlet of the second ammonia water heat exchanger 4 with the outlet at the bottom of the fixed ammonia tower 1;

[0055] The first liquid alkali mixer 12 is also connected before the second ammonia water heat exchanger 4 and the fixed ammonia tower 1; that is, the tube outlet of the second ammonia water heat exchanger 4 is connected to the bottom of the first liquid alkali mixer 12 through a pipeline, and the top of the first liquid alkali mixer 12 is connected to the inlet at the upper middle section of the fixed ammonia tower 1 through a pipeline; a sixth control valve 66 is provided on the pipeline connecting the second ammonia water heat exchanger 4 and the first liquid alkali mixer 12; the bottom of the first liquid alkali mixer 12 is also connected to a pipeline for flowing in liquid alkali, and the pipeline for flowing in alkali liquid connected to the first liquid alkali mixer 12 is also provided with a thirteenth control valve 613 and an eleventh control valve 611;

[0056] A first reducer 11 is provided on the top of the fixed ammonia tower 1. The first reducer 11 is connected to a precooling tower or a sulfur-ammonia saturator through an ammonia vapor pipeline. A nineteenth control valve 619 is provided on the ammonia vapor pipeline connecting the first reducer 11 with the precooling tower or the sulfur-ammonia saturator. The precooling tower or the sulfur-ammonia saturator is used for precooling the evaporated gas phase ammonia vapor and acid gas mixed gas before desulfurization or adjusting the saturation.

[0057] The first decompressor 11 is also connected to the circulating water supply pipe and the circulating water return pipe respectively, wherein the circulating water supply pipe connected to the first decompressor 11 is provided with a twenty-fourth control valve 624, and the circulating water return pipe connected to the first decompressor 11 is provided with a twenty-third control valve 623;

[0058] The shell side outlet of the second ammonia water heat exchanger 4 is connected to the tube side inlet of the ammonia waste water cooler 5 through the second pipeline 41, and the second pipeline 41 connecting the shell side outlet of the second ammonia water heat exchanger 4 and the tube side inlet of the ammonia waste water cooler 5 is provided with an eighth control valve 68 and a ninth control valve 69; the tube side outlet of the ammonia waste water cooler 5 is connected to the pipeline for passing the waste water into the biochemical pool; the pipeline for passing the waste water into the biochemical pool is provided with a tenth control valve 610; the shell side inlet of the ammonia waste water cooler 5 is connected to the circulating water inlet pipeline, and the circulating water inlet pipeline is provided with a twenty-sixth control valve 626; the shell side outlet of the ammonia waste water cooler 5 is connected to the circulating water return pipeline; the circulating water return pipeline is provided with a twenty-fifth control valve 625;

[0059] The bottom of the thiocyanate tower 2 and the bottom of the fixed ammonia tower 1 are also connected to external steam pipelines respectively, wherein the external steam pipeline connected to the lower section of the fixed ammonia tower 1 is provided with a steam regulating valve 629 and a fourteenth control valve 614, and the external steam pipeline connected to the lower section of the thiocyanate tower 2 is provided with a steam regulating valve 629 and a fifteenth control valve 615;

[0060] The upper section of the fixed ammonia tower 1 is also connected to the lower section of the thiocyanate tower 2 through a pipeline. The pipeline connecting the upper section of the fixed ammonia tower 1 and the lower section of the thiocyanate tower 2 is provided with a sixteenth control valve 616 and a seventeenth control valve 617 .

[0061] Furthermore, a third pipeline 32 is connected between the pipeline for the residual ammonia water after oil removal and the first pipeline 31. The connection point between the third pipeline 32 and the pipeline for the residual ammonia water after oil removal is located at the front end of the first control valve 61 (the front end is the end far away from the first ammonia water heat exchanger 3 and connected to the first control valve 61). The connection point between the third pipeline 32 and the first pipeline 31 is located between the fourth control valve 64 and the fifth control valve 65. A twenty-seventh control valve 627 is also provided on the third pipeline 32.

[0062] A fourth pipeline 42 is also connected between the first pipeline 31 and the second pipeline 41. The connecting point of the fourth pipeline 42 and the first pipeline 31 is located between the fourth control valve 64 and the fifth control valve 65, and the connecting point of the fourth pipeline 42 and the first pipeline 31 is located at the front end of the connecting point of the third pipeline 32 and the first pipeline 31, that is, the connecting point of the fourth pipeline 42 and the first pipeline 31 is close to the second ammonia water heat exchanger 4, and the connecting point of the third pipeline 32 and the first pipeline 31 is close to the first ammonia water heat exchanger 3; the connecting point of the fourth pipeline 42 and the second pipeline 41 is located between the eighth control valve 68 and the ninth control valve 69; a twenty-eighth control valve 628 is also provided on the fourth pipeline 42.

[0063] The process flow of a double-tower ammonia distillation system of the utility model is as follows:

[0064] Open the first control valve 61, the second control valve 62, and the third control valve 63, and close the twelfth control valve 612 and the twenty-seventh control valve 627. The remaining ammonia water after oil removal enters the first ammonia water heat exchanger 3, exchanges heat with the waste water flowing out of the bottom of the thiocyanate tower 2 (the liquid phase in the thiocyanate tower 2), and then enters the upper and middle section of the thiocyanate tower 2 through the second liquid alkali mixer 22 to carry out thiocyanate removal reaction. At this time, no liquid alkali is added to the second liquid alkali mixer 22.

[0065] Open the fourth control valve 64, the fifth control valve 65, the sixth control valve 66, the thirteenth control valve 613 and the eleventh control valve 611, and close the twenty-eighth control valve 628. The waste water flowing out of the bottom of the thiocyanate tower 2 enters the first ammonia water heat exchanger 3, exchanges heat with the remaining ammonia water, enters the second ammonia water heat exchanger 4 and exchanges heat with the evaporated ammonia waste water flowing out of the bottom of the fixed ammonia tower 1 (the liquid phase in the fixed ammonia tower 1), and then enters the first liquid alkali mixer 12 to mix with the inflowing liquid alkali. The resulting mixed liquid enters the upper middle section of the fixed ammonia tower 1 for ammonia solidification reaction.

[0066] Open the seventh control valve 67, the eighth control valve 68, the ninth control valve 69, the tenth control valve 610, the twenty-fifth control valve 625 and the twenty-sixth control valve 626, and the ammonia wastewater flowing out of the bottom of the fixed ammonia tower 1 enters the second ammonia water heat exchanger 4, exchanges heat with the wastewater flowing out of the first heat exchanger, and then enters the ammonia wastewater cooler 5, and after being cooled by circulating water, enters the biochemical system for biochemical reaction.

[0067] Open the fourteenth control valve 614, and adjust the steam regulating valve 629 to control the external steam flow rate, so that 0.35~0.5MPa external steam enters the bottom of the fixed ammonia tower 1, and makes reverse vapor-liquid contact with the mixed liquid entering from the middle and upper sections and descending layer by layer in the fixed ammonia tower 1, and performs a heat and mass transfer process. In this process, the fixed ammonia in the mixed liquid is decomposed into free ammonia, which is distilled out to form gradually rising ammonia vapor.

[0068] Open the sixteenth control valve 616 and the seventeenth control valve 617, and close the fifteenth control valve 615, the nineteenth control valve 619, the twenty-third control valve 623 and the twenty-fourth control valve 624, so that the first reducer 11 is in a closed state, and the gradually rising ammonia vapor (gas phase) enters the bottom of the thiocyanate tower 2 through the pipeline, serving as a heat source for the thiocyanate tower 2.

[0069] Open the eighteenth control valve 618, the twentieth control valve 620, the twenty-first control valve 621 and the twenty-second control valve 622, and the ammonia gas enters the thiocyanate tower 2, and makes vapor-liquid reverse contact with the remaining ammonia water entering from the middle and upper section and descending layer by layer in the thiocyanate tower 2. Sulfide, cyanide, carbonate and other substances in the remaining ammonia water are distilled out in the thiocyanate tower 2 and are cooled together with the ammonia gas (i.e., the gaseous ammonia gas and acid gas mixture) by the second reducer 21, and then enter the pre-cooling tower or the sulfur-ammonia saturator for pre-cooling or adjustment of saturation, so as to facilitate the later desulfurization or desulfurization of ammonia.

[0070] The reaction in two towers in series in a double-tower ammonia distillation system of the utility model includes:

[0071] The reactions in the thiocyanate tower 2 include:

[0072] NH4OH→NH3↑+H2O thermal decomposition reaction;

[0073] (NH4)2S→2NH3↑+H2S↑ pyrolysis reaction;

[0074] NH4CN→NH3↑+HCN↑ pyrolysis reaction;

[0075] (NH4)2CO3→2NH3↑+CO2↑+H2O thermal decomposition reaction;

[0076] NH4HCO3→NH3↑+CO2↑+H2O thermal decomposition reaction;

[0077] The reactions in the fixed ammonia tower 1 include:

[0078] NH4Cl+ NaOH→NaCl↓+NH4OH Fixed ammonium salt decomposition;

[0079] (NH4)2SO4+2NaOH→Na2SO4↓+2NH4OH Fixed ammonium salt decomposition;

[0080] NH4OH→NH3↑+H2O decomposes fixed ammonium salt;

[0081] The utility model uses two towers in series, one tower (thiocyanate tower 2) first evaporates sulfide and cyanide, and then mixes with liquid alkali to decompose fixed ammonia and enters another tower (fixed ammonia tower 1) for distillation, so that sulfide and cyanide can be effectively removed and the removal rate is improved. According to simulation tests, the removal rate of sulfide and total cyanide can be increased by 50% to 80%.

[0082] At the same time, the ammonia vapor coming out of the upper side of the fixed ammonia tower 1 enters the thiocyanate tower 2 as a heat source, which also increases the number of tower trays in the ammonia distillation section, and can reduce the amount of external steam. The amount of external steam is reduced from the original 160~180kg / ton of residual ammonia water to 80~100kg / ton of residual ammonia water.

[0083] When assembling the double-tower ammonia distillation system, the diameter of the fixed ammonia tower 1, the diameter of the thiocyanate tower 2, the diameter of each pipeline, etc. are all designed according to the amount of residual ammonia water.

[0084] When a problem occurs in the fixed ammonia tower 1 in the double-tower ammonia distillation system, only the thiocyanate tower 2 is used for treatment. The process flow at this time is as follows:

[0085] Open the first control valve 61, the second control valve 62, the third control valve 63 and the twelfth control valve 612, and close the twenty-seventh control valve 627, the eleventh control valve 611 and the thirteenth control valve 613. The remaining ammonia water after oil removal enters the first ammonia water heat exchanger 3, exchanges heat with the waste water flowing out of the bottom of the thiocyanate tower 2 (the liquid phase in the thiocyanate tower 2), and then enters the second liquid alkali mixer 22 to mix with the inflowing liquid alkali. The resulting mixed liquid enters the upper middle section of the thiocyanate tower 2 for reaction.

[0086] The fourth control valve 64, the twenty-eighth control valve 628, the ninth control valve 69, the tenth control valve 610, the twenty-fifth control valve 625 and the twenty-sixth control valve 626 are opened, and the fifth control valve 65 and the eighth control valve 68 are closed. The ammonia wastewater flowing out of the bottom of the thiocyanate tower 2 enters the first ammonia water heat exchanger 3, exchanges heat with the remaining ammonia water, and then enters the ammonia wastewater cooler 5. After being cooled by circulating water, it enters the biochemical system for biochemical reaction.

[0087] The fifteenth control valve 615 is opened, the fourteenth control valve 614, the sixteenth control valve 616 and the seventeenth control valve 617 are closed, and the steam regulating valve 629 is adjusted to control the external steam flow rate, so that the external steam of 0.35-0.5 MPa enters the bottom of the thiocyanate tower 2, and performs vapor-liquid reverse contact with the remaining ammonia water entering from the middle and upper section of the thiocyanate tower 2 and descending layer by layer in the thiocyanate tower 2, thereby performing ammonia evaporation reaction.

[0088] Open the eighteenth control valve 618, the twentieth control valve 620, the twenty-first control valve 621, and the twenty-second control valve 622, and close the nineteenth control valve 619, the twenty-third control valve 623, and the twenty-fourth control valve 624. The gas phase evaporated from the thiocyanate tower 2 is cooled by the second reducer 21 and then enters the precooling tower or the sulfur-ammonia saturator for precooling or adjusting the saturation, so as to facilitate the later desulfurization or desulfurization of ammonia.

[0089] When a problem occurs in the thiocyanate tower 2 in the double-tower ammonia distillation system, only the fixed ammonia tower 1 is used for treatment. The process flow at this time is as follows:

[0090] Open the twenty-seventh control valve 627, the fifth control valve 65, the sixth control valve 66, the seventh control valve 67, the eleventh control valve 611 and the thirteenth control valve 613, and close the first control valve 61, the second control valve 62, the third control valve 63, the fourth control valve 64 and the twelfth control valve 612. The remaining ammonia water after oil removal enters the second ammonia water heat exchanger 4, exchanges heat with the waste water flowing out of the bottom of the fixed ammonia tower 1 (the liquid phase in the fixed ammonia tower 1), and then enters the first liquid alkali mixer 12 to mix with the inflowing liquid alkali. The resulting mixed liquid enters the upper middle section of the fixed ammonia tower 1 for reaction.

[0091] The eighth control valve 68, the ninth control valve 69, the tenth control valve 610, the twenty-fifth control valve 625 and the twenty-sixth control valve 626 are opened, and the twenty-eighth control valve 628 is closed. The ammonia wastewater flowing out of the bottom of the fixed ammonia tower 1 enters the second ammonia water heat exchanger 4, exchanges heat with the remaining ammonia water, and then enters the ammonia wastewater cooler 5. After being cooled by circulating water, it enters the biochemical system for biochemical reaction.

[0092] Open the fourteenth control valve 614, close the fifteenth control valve 615, the sixteenth control valve 616 and the seventeenth control valve 617, and adjust the steam regulating valve 629 to control the external steam flow rate, so that the external steam of 0.35~0.5MPa enters the bottom of the fixed ammonia tower 1, and performs vapor-liquid reverse contact with the remaining ammonia water entering from the middle and upper sections and descending layer by layer in the fixed ammonia tower 1, thereby performing ammonia evaporation reaction.

[0093] Open the nineteenth control valve 619, the twenty-third control valve 623 and the twenty-fourth control valve 624, and close the eighteenth control valve 618, the twentieth control valve 620, the twenty-first control valve 621 and the twenty-second control valve 622. The gas phase evaporated from the fixed ammonia tower 1 is cooled by the first reducer 11 and then enters the precooling tower or the sulfur-ammonia saturator for precooling or adjusting the saturation, so as to facilitate the later desulfurization or desulfurization of ammonia.

[0094] When only thiocyanate tower 2 is used for single-tower treatment or only fixed ammonia tower 1 is used for single-tower treatment, the reactions in the tower include:

[0095] NH4OH→NH3↑+H2O;

[0096] (NH4)2S→2NH3↑+H2S↑;

[0097] NH4CN→NH3↑+HCN↑;

[0098] (NH4)2CO3→2NH3↑+CO2↑+H2O;

[0099] NH4HCO3→NH3↑+CO2↑+H2O;

[0100] NH4Cl+ NaOH→NaCl↓+NH4OH;

[0101] (NH4)2SO4+2NaOH→Na2SO4↓+2NH4OH;

[0102] (NH4)2S+NaOH→Na2S↓+NH4OH;

[0103] NH4CN+NaOH→NaCN↓+NH4OH;

[0104] It can be seen from the reactions in each tower during the use of the above-mentioned double-tower ammonia distillation system that when a single tower is used for treatment, while the remaining ammonia water is added with liquid alkali to decompose the fixed ammonia, the liquid alkali also reacts with ammonium sulfide and ammonium cyanide to generate sodium sulfide and sodium cyanide, which are retained in the wastewater, causing an increase in sulfide and cyanide. Therefore, when the thiocyanate tower 2 and the fixed ammonia tower 1 are connected in series, the sulfide and cyanide are first removed in the thiocyanate tower 2, and then the liquid alkali is added to decompose the fixed ammonia, thereby avoiding the reaction of sulfide and cyanide with the liquid alkali.

[0105] Although the embodiments of the present invention have been shown and described, it is understandable to those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principle and spirit of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A double-tower ammonia distillation system, characterized in that: The double-tower ammonia distillation system comprises a first ammonia water heat exchanger, a thiocyanate tower, a second ammonia water heat exchanger, a first liquid alkali mixer and a fixed ammonia tower; The first ammonia water heat exchanger is respectively connected with an inlet at the middle and upper section of the thiocyanate tower and an outlet at the bottom of the thiocyanate tower; The first ammonia water heat exchanger is connected to the second ammonia water heat exchanger through a first pipeline; The second ammonia water heat exchanger is respectively connected with an inlet at the middle and upper section of the fixed ammonia tower and an outlet at the bottom of the fixed ammonia tower; The first liquid alkali mixer is also connected before the second ammonia water heat exchanger and the fixed ammonia tower; the second ammonia water heat exchanger is connected to the bottom of the first liquid alkali mixer, and the top of the first liquid alkali mixer is connected to the inlet at the upper middle section of the fixed ammonia tower; The upper section of the fixed ammonia tower is connected to the lower section of the thiocyanate tower.

2. The double-tower ammonia distillation system according to claim 1, characterized in that: The double-tower ammonia distillation system further comprises an ammonia distillation wastewater cooler, which is connected to the second ammonia water heat exchanger through a second pipeline.

3. The double-tower ammonia distillation system according to claim 2, characterized in that: The first ammonia water heat exchanger is also connected to a pipeline into which the remaining ammonia water after oil removal flows.

4. The double-tower ammonia distillation system according to claim 3, characterized in that: A third pipeline is connected between the pipeline for the residual ammonia water after oil removal and the first pipeline; A fourth pipeline is also connected between the first pipeline and the second pipeline; The pipeline for the residual ammonia water after oil removal, the first pipeline, the second pipeline, the third pipeline and the fourth pipeline are all provided with control valves.

5. The double-tower ammonia distillation system according to any one of claims 1 to 4, characterized in that: A second liquid alkali mixer is also connected between the first ammonia water heat exchanger and the thiocyanate tower; The first ammonia water heat exchanger is communicated with the bottom of the second liquid alkali mixer, and the top of the second liquid alkali mixer is communicated with the inlet at the middle and upper section of the thiocyanate tower.

6. The double-tower ammonia distillation system according to claim 5, characterized in that: A control valve is provided on the pipeline connecting the first ammonia water heat exchanger and the second liquid alkali mixer; The bottom of the second liquid alkali mixer is also connected with a pipeline for flowing into liquid alkali, and a control valve is arranged on the pipeline for flowing into alkali liquid that is connected with the second liquid alkali mixer.

7. The double-tower ammonia distillation system according to any one of claims 1 to 4 and 6, characterized in that: A first reducer is provided on the top of the fixed ammonia tower, the first reducer is connected to the precooling tower or the sulfur-ammonia saturator through an ammonia vapor pipeline, and a control valve is provided on the ammonia vapor pipeline connecting the first reducer and the precooling tower or the sulfur-ammonia saturator; The first divider is also connected to the circulating water supply pipe and the circulating water return pipe respectively; A second reducer is provided on the top of the thiocyanate tower, the second reducer is connected to the precooling tower or the sulfur-ammonia saturator through an ammonia vapor pipeline, and a control valve is provided on the ammonia vapor pipeline connecting the second reducer and the precooling tower or the sulfur-ammonia saturator; The second divider is also connected to the circulating water supply pipe and the circulating water return pipe respectively; Control valves are provided on both the circulating water supply pipe and the circulating water return pipe.

8. The double-tower ammonia distillation system according to any one of claims 1 to 4 and 6, characterized in that: The bottom of the thiocyanate tower and the bottom of the fixed ammonia tower are also connected to external steam pipelines respectively, and the external steam pipelines are provided with steam regulating valves and control valves.

9. The double-tower ammonia distillation system according to any one of claims 1 to 4 and 6, characterized in that: A control valve is provided on the pipeline connecting the second ammonia water heat exchanger and the first liquid alkali mixer; The bottom of the first liquid alkali mixer is also connected with a pipeline for flowing into liquid alkali, and a control valve is arranged on the pipeline for flowing into alkali liquid that is connected with the first liquid alkali mixer.

10. The double-tower ammonia distillation system according to any one of claims 2 to 4, characterized in that: A control valve is provided on the pipeline connecting the first ammonia water heat exchanger and the outlet at the bottom of the thiocyanate tower; A control valve is provided on the pipeline connecting the second ammonia water heat exchanger and the outlet of the bottom of the fixed ammonia tower; The ammonia vapor wastewater cooler is also connected to a pipeline for passing wastewater into the biochemical pool; a control valve is provided on the pipeline for passing wastewater into the biochemical pool; The ammonia wastewater cooler is connected to the circulating water inlet pipe and the circulating water return pipe respectively, and the circulating water inlet pipe and the circulating water return pipe are both provided with control valves; A control valve is provided on the pipeline connecting the upper section of the fixed ammonia tower and the lower section of the thiocyanate tower.

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