Decyanation method and decyanation system for effectively reducing hydrocyanic acid content

Abstract

The invention relates to the technical field of solid waste treatment, and discloses a decyanation method and a decyanation system for effectively reducing the content of hydrocyanic acid. The decyanation method specifically comprises the following steps: in a decyanation tower, heating a solution through a reboiler, introducing hot nitrogen into a tower kettle to carry out synergistic steam stripping, and strongly analyzing dissolved HCN by utilizing a Henry law principle, so that the content of HCN in a discharged material of the tower kettle is reduced to be less than 1ppm; and meanwhile, the operating pressure at the top of the decyanation tower is controlled in a low-pressure range of 10-25kPa, so that the boiling point of the solution is obviously reduced, and the steam consumption of the reboiler is reduced by about 20%. The system is also integrated with a feed preheating energy recovery unit, a tower top condensate shunting rectification unit and a non-condensable gas safety treatment unit. The method has remarkable and synergistic beneficial effects in the aspects of decyanation efficiency, energy consumption control, safety, environmental protection and economic benefits, and comprehensively overcomes the bottlenecks in the prior art.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, specifically to a decyanation method and system for effectively reducing the content of hydrogen cyanide. Background Technology

[0002] Hydrogen cyanide (HCN), as an important basic chemical raw material, is widely used in synthetic fibers, plastics, pesticides, and pharmaceuticals. During its production, the reaction gases typically contain unreacted ammonia. Industrially, dilute sulfuric acid solution is commonly used for washing and absorption in an ammonia removal tower to generate ammonium sulfate solution. However, this process produces a large amount of ammonium sulfate solution containing hydrogen cyanide. Hydrogen cyanide is a highly toxic and volatile substance with a boiling point (25.7℃) far lower than water. If it cannot be effectively removed from the ammonium sulfate solution, it will overflow and disperse in large quantities during subsequent evaporation, concentration, crystallization, and drying processes, severely polluting the atmosphere and causing hazards. Furthermore, hydrogen cyanide is flammable and explosive, posing a significant safety hazard. Therefore, developing an efficient and economical decyanation process to reduce the hydrogen cyanide content in the ammonium sulfate solution to a safe level is a crucial step in achieving clean production and comprehensive resource utilization of hydrogen cyanide.

[0003] Currently, the most common method for removing hydrogen cyanide is steam stripping based on physical properties. This involves increasing the heat load of the reboiler in the decyanation tower to raise the pressure of the gas phase at the top of the tower, distilling off a large amount of water vapor and HCN gas, and sending it to a higher-pressure ammonia removal tower. The HCN content in the bottom of the decyanation tower can be controlled at approximately 10-30 ppm. However, this traditional decyanation process has the following drawbacks: First, when the hydrogen cyanide content is reduced to 10-30 ppm, simply increasing the temperature to enhance the stripping effect becomes weak. This is mainly because the dissolution of HCN in the liquid phase and its partial pressure in the gas phase tend to be in equilibrium at this level, making it difficult to further disrupt this equilibrium. Second, conventional processes require maintaining a high operating pressure (40-65 kPa) to distill HCN from the top of the tower and overcome the pressure of the subsequent system. This directly leads to an increase in the boiling point of the solution in the bottom of the tower. To maintain the boiling state in the tower, the reboiler must consume a large amount of energy to provide sufficient heat load. This "high energy consumption" results in limited decyanation effect, leading to poor economic operation of the entire system. In addition, the large amount of water vapor and HCN mixture distilled from the top of the tower also increases the load on subsequent condensation or absorption units.

[0004] Therefore, there is an urgent need in this field for an innovative decyanation process that can overcome the bottlenecks of existing technologies. This process not only needs to remove the hydrocyanic acid content in ammonium sulfate solution to a level far below current standards, fundamentally eliminating safety and environmental hazards, but also needs to significantly reduce process energy consumption, especially steam consumption, to achieve a dual improvement in environmental and economic benefits. Summary of the Invention

[0005] The purpose of this invention is to provide an effective method and system for reducing the content of hydrogen cyanide, thereby solving the technical problem.

[0006] The technical solution of the present invention is as follows: A method for effectively reducing the content of hydrogen cyanide in a decyanation process is disclosed. The specific method involves: preheating an ammonium sulfate solution containing hydrogen cyanide and feeding it into a decyanation tower, where it is heated to 100-108°C via a reboiler. Simultaneously, hot nitrogen gas is introduced into the bottom of the decyanation tower, the temperature of which is 10-30°C higher than the bottom temperature. The pressure at the top of the decyanation tower is controlled at 10-25 kPa, and the temperature at the top is controlled at 80-105°C. After condensing the vapor phase at the top of the tower, a portion of the condensate is returned to the decyanation tower, while the other portion is collected and sent to a distillation tower. The uncondensed non-condensable gas is sent to a tail gas absorption tower for treatment. The tail gas absorption tower operates under negative pressure under the action of a centrifugal axial flow fan. An ammonium sulfate solution with a hydrogen cyanide content of less than 1 ppm is collected from the bottom of the tower and sent to subsequent ammonium sulfate treatment processes.

[0007] In a further optimization, the hot nitrogen gas is heated by a nitrogen heating unit and then introduced into the bottom of the decyanation tower.

[0008] Further optimization involves preheating the ammonium sulfate solution by exchanging heat with the high-temperature material extracted from the bottom of the decyanation tower.

[0009] Further optimization involves adjusting the reflux ratio of the liquid phase after condensation at the top of the decyanation tower via a control valve.

[0010] To further optimize the process, the uncondensed non-condensable gas is absorbed by the tail gas absorption tower and then enters the alkaline washing tower for further treatment.

[0011] Further optimization resulted in the ammonium sulfate solution from the bottom of the decyanation tower containing less than 1 ppm of hydrocyanic acid.

[0012] A decyanation system for effectively reducing hydrogen cyanide content includes: The decyanation tower is equipped with an inlet for receiving the flowing ammonia solution, a bottom outlet for discharging the treated solution, a top gas outlet for discharging the gaseous products, and a nitrogen inlet for introducing hot nitrogen. A nitrogen heating unit, the outlet of which is connected to the nitrogen inlet of the decyanation tower, is used to supply hot nitrogen into the tower; A reboiler, connected to the bottom of the decyanation tower, is used to heat the solution inside the tower; A condenser, the inlet of which is connected to the top gas phase outlet of the decyanation tower, is used to condense the top gas phase products of the tower; The material handling unit is connected to the outlet of the condenser and is used to process the condensed liquid phase and the uncondensed gas phase.

[0013] Further optimizations include a reflux control system and a tail gas treatment system. The reflux control system includes a reflux pipeline and a collection pipeline. The reflux pipeline is used to return a portion of the condensate to the top of the column, and the collection pipeline is used to collect a portion of the condensate and transport it to the distillation column. The tail gas treatment system includes a tail gas absorption tower and an alkaline scrubbing tower for treating uncondensed non-condensable gases.

[0014] Further optimization includes a feed preheating unit, which comprises a feed preheater and a transfer pump. The first channel of the feed preheater is connected upstream of the feed inlet of the decyanation tower, and its second channel is connected to the bottom outlet of the decyanation tower. It is used to receive the ammonium sulfate solution containing hydrogen cyanide from the ammonia removal tower and to extract the ammonium sulfate solution. The inlet of the transfer pump is connected to the bottom outlet of the decyanation tower, and the outlet is connected to the inlet of the second channel of the feed preheater.

[0015] Further optimization involves using a nitrogen heater as the nitrogen heating unit.

[0016] The beneficial effects of this technical solution are: 1. The present invention introduces hot nitrogen gas into the bottom of the decyanation tower. This is not only a simple superposition of physical processes, but also a fundamental innovation based on Henry's Law. As an inert carrier gas, the hot nitrogen gas continuously reduces the partial pressure of HCN in the gas phase during its ascent in the tower, thereby drastically disrupting the dissolution equilibrium of HCN in the liquid phase. This greatly promotes the mass transfer rate and resolution of HCN from the liquid phase to the gas phase. This synergistic effect of steam stripping and carrier gas stripping enables the HCN content in the ammonium sulfate solution at the bottom of the tower to be removed to below 1 ppm, or even to a level that is undetectable by instruments. This means that there is almost no HCN volatilization during the subsequent evaporation and concentration process of the ammonium sulfate unit, which completely eliminates the risk and hazard of explosion caused by HCN enrichment, while ensuring the product quality of the by-product ammonium sulfate. 2. The pressure at the top of the decyanation tower is reduced from the conventional 40-65 kPa to 10-25 kPa. The reduction in system pressure directly leads to a decrease in the boiling point of the mixture. Under low pressure, the energy required for vaporization of the material in the tower is significantly reduced. This reduces the steam consumption of the reboiler, which maintains the boiling state in the tower, by about 20%. Low-pressure operation also allows the gas phase at the top of the tower to enter the condensation system smoothly without overcoming excessive resistance, reducing the potential demand for compression work. More importantly, the combination of low-pressure operation and the introduction of hot nitrogen produces an unexpected synergistic energy-saving effect: the introduction of nitrogen maintains and optimizes the fluid dynamics state in the tower, ensuring good mass transfer efficiency under low pressure and avoiding problems such as decreased tray efficiency or flooding that may occur due to pressure reduction. At the same time, the system also recovers the waste heat of the high-temperature material in the tower bottom through the feed preheater, further reducing the total energy consumption. These three factors together constitute a highly efficient energy-saving system. 3. For the separated HCN, this invention achieves a closed loop of efficient recovery and harmless treatment of HCN through a multi-stage treatment process of low-pressure condensation, partial reflux, partial distillation, and alkaline washing of non-condensable gas. After condensation at the top of the column, part of the liquid phase is collected and sent to the distillation column to obtain high-purity HCN product, which improves the economic efficiency of the process. The trace amounts of uncondensed HCN are thoroughly purified by the tail gas absorption tower and alkaline washing tower to ensure that the emission gas fully meets the standards and eliminates pollution to the atmosphere.

[0017] In summary, this invention achieves significant and synergistic benefits in terms of cyanide removal efficiency, energy consumption control, safety and environmental protection, and economic benefits by cleverly combining and synergistically enhancing the two core technologies of hot nitrogen and low-pressure operation, and integrating them with the internal thermal coupling design of the system. This comprehensively overcomes the bottlenecks of existing technologies. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the decyanation system of the present invention; In the diagram: 1-Decyanation tower, 2-Reboiler, 3-Nitrogen heater, 4-Condenser, 5-Feed preheater, 6-Transfer pump. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0022] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0023] A specific embodiment of a decyanation method and system for effectively reducing hydrogen cyanide content according to the present invention.

[0024] Example 1

[0025] A decyanation system for effectively reducing hydrogen cyanide content includes a decyanation tower, a nitrogen heating unit, a reboiler, a condenser, a material handling unit, a reflux control system, a tail gas treatment system, and a feed preheating unit.

[0026] The decyanation tower 1 is equipped with an inlet for receiving the ammonia solution, a bottom outlet for discharging the treated solution, a top gas outlet for discharging the gaseous product, and a nitrogen inlet for introducing hot nitrogen. The nitrogen heating unit is a nitrogen heater 3, whose outlet is connected to the nitrogen inlet of the decyanation tower 1. It supplies hot nitrogen to the tower, preventing cold gas from impacting the bottom temperature, ensuring process stability, and maintaining the hot nitrogen temperature at 10-30°C higher than the bottom temperature, further promoting the vaporization of light components. Simultaneously, because the pressure at the top of the tower increases due to the nitrogen inlet, and because it is not necessary to send the distilled material to the upstream system (pressure 40-65 kPa), the pressure at the top of the tower is kept relatively low (10-25 kPa), reducing the steam consumption of the reboiler 2 by approximately 20%. The material-side inlet of reboiler 2 is connected to the lower part of the column bottom, and the outlet is connected to the upper part of the column bottom or the vapor phase space, forming a closed loop for heating the solution inside the column. The inlet of condenser 4 is connected to the top vapor phase outlet of the decyanation column 1, condensing and cooling the high-temperature vapor phase mixture (mainly containing water vapor, HCN vapor, and nitrogen) coming out of the top of the decyanation column 1, so that most of the water vapor and HCN are condensed into liquid for reflux and collection. By controlling the condensation rate, the top temperature of the column can be precisely controlled within the range of 80~105℃. The material processing unit is connected to the outlet of condenser 4 to process the condensed liquid phase and the uncondensed gas phase.

[0027] The reflux control system includes a reflux pipeline and a collection pipeline. The reflux pipeline is used to return a portion of the condensate to the top of the tower, maintaining a stable gas-liquid balance and temperature distribution within the decyanation tower 1. The collection pipeline is used to collect a portion of the condensate rich in HCN and transport it through a pipeline to a distillation tower for further purification, realizing the resource recovery of HCN and improving the economic efficiency and environmental friendliness of the process. The tail gas treatment system includes a tail gas absorption tower and an alkaline scrubbing tower, which perform final treatment on the uncondensed nitrogen and HCN gases. The tail gas absorption tower and alkaline scrubbing tower ensure that the emitted gases meet safety standards, preventing environmental pollution and safety accidents.

[0028] The feed preheating unit includes a feed preheater 5 and a transfer pump 6. The first channel of the feed preheater 5 is connected upstream of the feed inlet of the decyanation tower 1, and its second channel is connected to the outlet of the bottom of the decyanation tower 1. It receives the ammonium sulfate solution containing hydrogen cyanide from the ammonia removal tower and extracts the ammonium sulfate solution. The preheater 5 is connected to the ammonia removal tower via a pipeline. Its principle is to utilize the residual heat of the high-temperature material extracted from the bottom of the decyanation tower 1 to preheat the ambient temperature (or low temperature) ammonium sulfate solution entering the decyanation tower 1. This thermal coupling design significantly reduces the steam consumption of the subsequent reboiler 2 and is one of the key aspects of system energy saving. The inlet of the transfer pump 6 is connected to the outlet of the bottom of the decyanation tower 1, and its outlet is connected to the inlet of the second channel of the feed preheater 5, providing power for the fluid transport of the entire system. This serves two purposes: first, to transport the treated bottom liquid to the downstream process; and second, to drive the high-temperature material to circulate back to the feed preheater 5, achieving energy recovery.

[0029] A decyanation method for effectively reducing hydrocyanic acid content, comprising the following steps: Step 1, Ammonia Removal Treatment: Collect the ammonium sulfate solution containing 0.2%~0.6% hydrogen cyanide after ammonia removal in the ammonia removal tower; Step 2, Solution Preheating: The ammonium sulfate solution from Step 1 is preheated to 90°C by the feed preheater 5 and the high-temperature material collected by the transfer pump 6. Step 3: Entering the decyanation tower 1: The preheated ammonium sulfate solution from step 2 enters the decyanation tower 1;

[0030] Step 4, Heating for Cyanide Removal: Two steps are performed inside cyanide removal tower 1: (1) The solution in the tower is heated by reboiler 2 to keep its temperature at 100~108℃; (2) Hot nitrogen gas heated by nitrogen heater 3 is introduced into the bottom of the decyanation tower 1; The synergistic effect of hot nitrogen and reboiler 2 heating forces the hydrocyanic acid in the ammonium sulfate solution to be desorbed into the gas phase, making the hydrocyanic acid content in the bottom product of the tower less than 1 ppm.

[0031] Step 5: Diversion and Treatment of Top Condensate: The gaseous phase at the top of the decyanation tower 1 enters condenser 4 for condensation. The condensed liquid product is divided into two parts: (1) A portion of it is used as reflux liquid and is returned to the top of the decyanation tower 1 through the control valve TV102 to control the temperature at the top of the tower at 104°C and maintain a stable gas-liquid balance in the tower. (2) A portion of the product, which is rich in HCN, is collected through the control valve LV102 and sent to the distillation column for distillation and purification to recover HCN; Step 6, Non-condensable gas treatment: The non-condensable gas is sent to the tail gas absorption tower for absorption through the control valve HV101, and then enters the inlet of the alkaline scrubbing tower fan through the pipeline to ensure that the emission meets the standards. The gas phase outlet of the tail gas absorption tower is a centrifugal axial flow fan, that is, the tail gas absorption tower is slightly negative pressure, which can form a large pressure gradient, avoid nitrogen accumulation in the condenser and other areas, and make the steam rise and liquid flow more smoothly. Step 7, Output of the bottom solution: Part of the ammonium sulfate solution from step 6 collected from the bottom of the decyanation tower 1 is sent to the downstream ammonium sulfate process for evaporation, crystallization and drying; the other part is returned to step 2 as a heat source for preheating the feed, completing the closed-loop utilization of energy. The hydrogen cyanide content of the ammonium sulfate solution is less than 1 ppm.

[0032] This invention significantly enhances the cyanide removal depth by introducing hot nitrogen gas, while keeping the column top pressure at a low level (10~25 kPa). This lowers the boiling point of HCN, reduces reboiler steam consumption by approximately 20%, and allows the column top gas phase to enter the condensation system without overcoming excessive resistance. The heat from the column bottom material is recovered via the feed preheater 5, significantly reducing the overall system energy consumption. Through multi-stage treatment involving condensation reflux, distillation, and tail gas absorption, stable process operation is ensured, along with efficient HCN recovery and harmless tail gas treatment, forming a closed-loop, safe, and environmentally friendly complete process chain.

[0033] Comparative Example 1

[0034] Cyanide removal was carried out using steam stripping, and the process parameters for this method are shown in Table 1.

[0035] Comparative Example 2

[0036] The cyanide removal was carried out by distillation in a distillation column, and the process parameters of this method are shown in Table 1.

[0037] Example 2

[0038] The HCN recovery rate of Example 1, Comparative Example 1 and Comparative Example 2 were tested respectively, and the test results are shown in Table 1.

[0039] Serial Number Decyanation methods <![CDATA[Feed rate (m 3 / h)]]> Ammonium sulfate concentration (wt%) Feed HCN concentration (wt%) Feed temperature (°C) Control the temperature of the column bottom (°C) Control the temperature at the top of the tower (°C). Tower top control pressure (kPa) Cyanide content in exported products (ppm) HCN recovery rate (%) Comparative Example 1 Steam stripping 1 20 0.2-0.6 60 110-115 105-110 60 40-80 80-90 Comparative Example 2 Distillation column 1.2 20 0.2-0.6 60 110-115 105-110 50-70 30-50 90-95 Example 1 The method of the present invention 12 20 0.2-0.6 70-80 95-110 90-100 5-35 0-10 98-99.9

[0040] Both comparative documents 1 and 2 use traditional processes, and the HCN content in their bottom product is 40-80ppm and 30-50ppm, respectively, which is much higher than that of the present invention, which significantly reduces the content to 0-10ppm by introducing hot nitrogen gas. This meets the product requirements and eliminates the safety and environmental hazards in subsequent processes from the root.

[0041] Regarding HCN recovery rate, the HCN recovery rates of Comparative Example 1 and Comparative Example 2 were 80-90% and 90-95%, respectively, while the recovery rate of the present invention was 98-99.9%. It can be seen that a considerable portion of the valuable HCN raw materials in the former could not be recovered, resulting in resource waste and environmental pressure.

[0042] In terms of process, Comparative Example 1 and Comparative Example 2 both operate under high tower top pressure (50-70KPa), resulting in high energy consumption. This invention controls the operation at 5-35KPa, and combined with the enhanced transfer effect of hot nitrogen, it achieves deeper cyanide removal and higher recovery rate, while also achieving an energy-saving effect of reducing reboiler steam consumption by 20%, demonstrating the comprehensive advantages of this invention in terms of efficiency and energy consumption.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A dehydrocyanation process effective to reduce the hydrocyanic acid content, characterized in that, The specific method is: The ammonium sulfide solution containing hydrocyanic acid is preheated and sent to the dehydrocyanation tower (1), heated to 100-108°C by a reboiler (2), and hot nitrogen gas is introduced into the tower bottom of the dehydrocyanation tower (1), the temperature of the hot nitrogen gas is 10-30°C higher than the tower bottom temperature, the tower top pressure of the dehydrocyanation tower (1) is maintained at 10-25 KPa, the tower top temperature is 80-105°C, the gaseous phase at the tower top is condensed, part of the condensed liquid is refluxed to the dehydrocyanation tower (1), and the other part is taken out and sent to a rectification tower, the uncondensed non-condensable gas is sent to a tail gas absorption tower for treatment, the tail gas absorption tower is operated under negative pressure by a centrifugal axial fan, ammonium sulfide solution with a hydrocyanic acid content less than 1 ppm is taken out from the tower bottom and sent to a subsequent ammonium sulfide treatment process.

2. The method of claim 1, wherein the method is effective to reduce the amount of hydrocyanic acid. The hot nitrogen gas is heated by a nitrogen gas heating unit and introduced into the tower bottom of the dehydrocyanation tower (1).

3. The method of claim 1, wherein the method is effective to reduce the amount of hydrocyanic acid. The preheating of the ammonium sulfide solution is achieved by heat exchange with high-temperature materials taken out from the tower bottom of the dehydrocyanation tower (1).

4. The method of claim 1, wherein the de-cyanation is effective to reduce the amount of hydrocyanic acid. The reflux ratio of the liquid phase after condensation at the tower top of the dehydrocyanation tower (1) is adjusted by a control valve.

5. The method of claim 1, wherein the de-cyanation is effective to reduce the amount of hydrocyanic acid. The uncondensed non-condensable gas is absorbed by the tail gas absorption tower and then enters an alkali washing tower for further treatment.

6. The method of claim 1, wherein the de-cyanation process is effective to reduce the amount of hydrocyanic acid. The hydrocyanic acid content in the ammonium sulfide solution taken out from the tower bottom of the dehydrocyanation tower (1) is less than 1 ppm.

7. A de-cyanation system effective to reduce the hydrocyanic acid content, characterized in that, It comprises: a dehydrocyanation tower (1) provided with a feed inlet for receiving the ammonia-containing solution, a tower bottom discharge outlet for discharging the treated solution, a tower top gaseous phase outlet for discharging the gaseous phase product, and a nitrogen gas inlet for introducing hot nitrogen gas; a nitrogen gas heating unit, the outlet of which is connected to the nitrogen gas inlet of the dehydrocyanation tower (1), for providing hot nitrogen gas into the tower; a reboiler (2) connected to the tower bottom of the dehydrocyanation tower (1), for heating the solution in the tower; a condenser (4) with its inlet connected to the tower top gaseous phase outlet of the dehydrocyanation tower (1), for condensing the gaseous phase product at the tower top; a material treatment unit connected to the outlet of the condenser (4), for treating the condensed liquid phase and the uncondensed gaseous phase.

8. The dehydrocyanation system for effectively reducing the hydrocyanic acid content according to claim 7, characterized in that it further comprises a reflux control system and a tail gas treatment system, the reflux control system comprises a reflux pipeline and a take-out pipeline, the reflux pipeline is used for refluxing part of the condensed liquid to the tower top, and the take-out pipeline is used for taking out part of the condensed liquid and conveying it to a rectification tower; the tail gas treatment system comprises a tail gas absorption tower and an alkali washing tower, for treating the uncondensed non-condensable gas.

9. The de-cyanation system of claim 7, wherein the de-cyanation system is configured to reduce the amount of hydrogen cyanide. it further comprises a feed preheating unit, the feed preheating unit comprises a feed preheater (5) and a material transfer pump (6), the first passage of the feed preheater (5) is connected upstream of the feed inlet of the dehydrocyanation tower (1), the second passage thereof is communicated with the tower bottom discharge outlet of the dehydrocyanation tower (1), for receiving the ammonium sulfide solution containing hydrocyanic acid from the deamination tower and taking out the ammonium sulfide solution; the inlet of the material transfer pump (6) is connected to the tower bottom discharge outlet of the dehydrocyanation tower (1), and the outlet is connected to the inlet of the second passage of the feed preheater (5).

10. The de-cyanation system of claim 7, wherein the de-cyanation system is configured to reduce the amount of hydrogen cyanide. The nitrogen gas heating unit is a nitrogen gas heater (3).

Images