Method for sectional removal of reaction waste heat in hydrocyanic acid production process

Abstract

The invention provides a method for sectional removal of reaction waste heat in a hydrocyanic acid production process, and belongs to the technical field of chemical engineering. Ammonia, methane and oxygen are used as reaction raw material mixed gas, a gas-phase reaction is carried out under the catalytic action of platinum rhodium alloy to generate reaction synthesis gas containing hydrocyanic acid, and the reaction synthesis gas enters a subsequent ammonia recovery and hydrocyanic acid refining unit after being cooled by a multi-stage heat exchanger; the multi-stage heat exchanger is formed by connecting at least two heat exchangers in series and comprises a first-stage heat exchanger and a second-stage heat exchanger, the reaction synthesis gas with the temperature of 1000-1200 DEG C is introduced into the hot side of the first-stage heat exchanger, water with the temperature not lower than 100 DEG C is introduced into the cold side of the first-stage heat exchanger, and the cold side of the first-stage heat exchanger generates low-pressure steam not higher than 0.3 MPaG by removing heat; and the cold side of the second-stage heat exchanger generates 2.0-4.0 MPaG high-pressure steam by removing heat. According to the method, decomposition of the reaction synthesis gas containing hydrocyanic acid at high temperature is reduced, and meanwhile, the removed reaction waste heat can be matched with devices needing heat sources of different grades.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrocyanic acid processes, and in particular to a method for removing reaction waste heat in a staged manner in a hydrocyanic acid production process. Background Art

[0002] Hydrocyanic acid, a key chemical raw material, plays a vital role in the manufacture of products such as adiponitrile, methacrylic acid, and sodium cyanide. Adiponitrile is a key intermediate used primarily in the production of materials such as nylon 66, nylon 610, and HDI. In recent years, my country has seen continuous advancements in adiponitrile production technology. In particular, the independently developed technology for synthesizing adiponitrile from butadiene has broken through foreign technological blockades and monopolies. The construction of a million-ton / year nylon new materials industrial base based on this technology will significantly increase demand for hydrocyanic acid. However, current domestic hydrocyanic acid production capacity cannot fully meet this demand. Furthermore, hydrocyanic acid is a highly toxic substance, and its transportation poses significant safety risks, making it unsuitable for large-scale, long-distance transport. Given this situation, further refinement of the production process for hydrocyanic acid and its derivatives is necessary to ensure a secure supply and smooth production.

[0003] The main production processes for hydrocyanic acid are the Ansler process, the acrylonitrile by-product process, and the light oil cracking process. The production capacity of the acrylonitrile by-product process is limited by the production capacity of acrylonitrile. While producing hydrocyanic acid, the acrylonitrile by-product process also produces a large number of other byproducts. If these by-products are not fully utilized or recovered, it will result in a waste of resources. The light oil cracking process has not yet achieved industrialization and standardization. Because the raw materials, intermediate products, and final products used in this production process are mostly flammable, explosive, or highly toxic and hazardous substances, the potential risks in production operations are relatively high. Currently, it is mainly used by domestic small and medium-sized enterprises and is not suitable for large-scale production. Due to the advantages of the Ansler process, such as readily available and stable raw materials, mature and reliable technology, relatively low production costs, high product purity and stable quality, and compliance with environmental protection requirements, the Ansler process is currently the main method used in the industrial production of hydrocyanic acid.

[0004] The Angle method for preparing hydrocyanic acid uses a mixture of ammonia, methane-containing gas and oxygen-containing gas in appropriate proportions to form a reaction raw gas, which is then fed into a reactor and reacts in the gas phase at high temperature over a platinum-rhodium alloy catalyst to produce a reaction synthesis gas containing hydrocyanic acid.

[0005] The main reaction formula is as follows:

[0006] 2CH4+2NH3+3O2→2HCN+6H2O

[0007] The side reaction formula is as follows:

[0008] 2CH4+O2→2CO+4H2

[0009] 4NH3+3O2→2N2+6H2O

[0010] CH4+2O2→CO2+2H2O

[0011] In the Angle method for preparing hydrocyanic acid, hydrocyanic acid inevitably undergoes decomposition and polymerization reactions. The main reason for the decomposition reaction of hydrocyanic acid is that the Angle method requires the reaction to proceed at high temperatures. Under high temperature conditions, the chemical bonds within the hydrocyanic acid molecules are easily broken, resulting in decomposition. The polymerization reaction of hydrocyanic acid mainly occurs when the interaction between hydrocyanic acid molecules is enhanced in the presence of water condensation, resulting in polymerization reactions. The decomposition and polymerization reactions of hydrocyanic acid not only greatly reduce the yield of hydrocyanic acid, but the polymers produced by the polymerization reactions can clog equipment and gas pipelines, affecting the normal operation of production. In the prior art, to prevent the decomposition and polymerization reactions of hydrocyanic acid, the hydrocyanic acid reaction synthesis gas must be rapidly cooled after leaving the high-temperature reaction zone before entering the subsequent ammonia recovery and hydrocyanic acid refining units. High-temperature reaction synthesis gas containing hydrocyanic acid can be rapidly cooled by direct contact with a cooling medium, or the waste heat can be removed by a heat exchanger. Among them, the method of rapid cooling by direct contact with a cooling medium has relatively special requirements for the equipment structure and is less commonly used. The steam pressure generated by removing the waste heat by a heat exchanger is relatively high, resulting in a relatively small heat transfer temperature difference between the hot and cold sides. In order to reduce the temperature to the target, the required heat exchange tube length is relatively long, and the residence time required to pass through the high-temperature zone is relatively long, which leads to relatively more decomposition of hydrocyanic acid in the reaction synthesis gas containing hydrocyanic acid (generally referring to the loss rate of hydrocyanic acid calculated as ammonia). Summary of the Invention

[0012] To address the shortcomings of the prior art, the present invention discloses a method for staged removal of reaction waste heat in a hydrocyanic acid production process. This method optimizes and improves the cooling of hydrocyanic acid-containing reaction syngas, reducing the decomposition of the hydrocyanic acid-containing reaction syngas at high temperatures. Furthermore, the removed reaction waste heat can be used to adapt to different heat source requirements.

[0013] To achieve the above technical objectives, the present invention provides a method for removing reaction waste heat in a staged manner in a hydrocyanic acid production process. Ammonia, methane, and oxygen are used as a reaction raw material mixed gas, and a gas phase reaction is carried out under the catalysis of a platinum-rhodium alloy to generate a reaction synthesis gas containing hydrocyanic acid. The reaction synthesis gas is cooled by a multi-stage heat exchanger and then enters a subsequent ammonia recovery and hydrocyanic acid refining unit.

[0014] The multi-stage heat exchanger is composed of at least two heat exchangers connected in series, including a first-stage heat exchanger and a second-stage heat exchanger. The reaction synthesis gas with a temperature of 1000-1200°C is introduced into the hot side of the first-stage heat exchanger, and water with a temperature of not less than 100°C is introduced into the cold side of the first-stage heat exchanger. The cold side of the first-stage heat exchanger generates low-pressure steam not higher than 0.3 MPaG by removing heat; the cold side of the second-stage heat exchanger generates high-pressure steam of 2.0-4.0 MPaG by removing heat.

[0015] The traditional multi-stage heat exchanger heat transfer scheme generally has the process of reducing the specifications of the steam produced from high to low as the reaction synthesis gas is cooled from high temperature to low temperature. However, the research and development team of the present invention unexpectedly discovered through a large number of experiments and experience summaries that the reaction synthesis gas containing hydrocyanic acid needs to be quickly cooled in the high temperature zone to reduce the decomposition of hydrocyanic acid, and it is precisely impossible to produce steam of too high a grade. Therefore, in order to achieve the rapid cooling effect of the reaction synthesis gas containing hydrocyanic acid, the present invention adopts the method of heat transfer and cooling with low-pressure steam in the high temperature zone, which can obtain a larger heat transfer temperature difference, reduce the effective heat exchange area, and thus improve the heat exchange efficiency. At the same time, the method of heat transfer and cooling with low-pressure steam can reduce the actual heat exchange area of the heat exchanger. If a shell-and-tube heat exchanger is used, the required shell and tube length of the heat exchanger can be shortened, thereby reducing the residence time of the reaction synthesis gas containing hydrocyanic acid in the high temperature zone.

[0016] Conventional heat exchangers often fail to incorporate a segmented design to remove excess heat, often encompassing the entire cooling range from high to low temperatures for the hydrocyanic acid-containing reaction synthesis gas. The present invention, however, utilizes a multi-stage heat exchanger to separate the entire cooling range into different temperature zones, offering multiple benefits.

[0017] First, the segmented design enables the generation of heat sources of varying specifications or grades. During the cooling process of the hydrocyanic acid-containing reaction syngas, heat from different temperature zones has different energy qualities. By employing a multi-stage heat exchanger, these heat of varying energy qualities can be removed separately and converted into heat sources of varying specifications or grades. These heat sources can be used to meet various thermal energy needs within the facility or plant, such as heating, steam generation, and hot water supply, thereby achieving cascaded energy utilization and efficient conversion.

[0018] Secondly, the segmented design also helps reduce overall energy consumption and costs. By enabling more precise control of heat removal and the generation of heat sources of varying specifications, the segmented design makes the entire heat exchange process more efficient and energy-efficient. Furthermore, the segmented heat exchanger can be customized to meet specific needs, reducing unnecessary energy loss and waste, thereby lowering overall energy consumption and costs.

[0019] Finally, the segmented design improves the heat exchanger's flexibility and adaptability. Because heat exchangers for different temperature zones can be designed and operated independently, they can be flexibly adjusted and optimized based on actual production needs. This flexibility enables the segmented heat exchanger to better adapt to complex and changing production environments, improving overall production efficiency and stability.

[0020] The cold side of the primary heat exchanger of the present invention generates low-pressure steam no higher than 0.3 MPaG by removing heat, which not only improves cooling efficiency but also allows for direct connection to a suitable pipeline network for subsequent use, effectively promoting energy reuse. Simultaneously, the cold side of the secondary heat exchanger generates high-pressure steam of 2.0 to 4.0 MPaG by removing heat. Using high-pressure steam for heat removal and cooling not only achieves effective cooling but also generates a high-quality heat source. This high-pressure steam can be supplied to large power equipment in devices or factories as a turbine-driven energy source, or directly connected to a matching pipeline network system for use. This not only optimizes energy conversion efficiency but also enhances the comprehensive utilization value of energy.

[0021] Furthermore, the hot side outlet temperature of the first-stage heat exchanger is 580-630°C, and the hot side outlet temperature of the second-stage heat exchanger is 210-300°C. Since the reaction synthesis gas containing hydrocyanic acid will undergo a decomposition reaction at high temperature, mainly hydrocyanic acid will react with water at high temperature to produce carbon monoxide and ammonia. The reaction formula is as follows:

[0022] HCN+H2O→CO+NH3

[0023] Based on previous research and production experience, the research and development team of this invention has determined that the equilibrium constant of this reaction is 180 at around 630°C, and the reaction can proceed to the right. Therefore, the reaction synthesis gas containing hydrocyanic acid needs to be quickly cooled to below 630°C to reduce its residence time in the high-temperature zone to avoid the decomposition of hydrocyanic acid. Therefore, the hot side outlet temperature of the first-stage heat exchanger of this invention is 580-630°C to prevent the decomposition of hydrocyanic acid.

[0024] Furthermore, the multi-stage heat exchanger also includes a third-stage heat exchanger. The cold side of the third-stage heat exchanger removes heat to produce low-pressure steam no higher than 0.3 MPaG or hot water at 120-130°C. By using the low-pressure steam generated by the third-stage heat exchanger for heat removal and cooling, a lower-grade heat source can be obtained. The generated low-pressure steam can be directly incorporated into a suitable pipeline network for use.

[0025] Furthermore, the hot side outlet temperature of the three-stage heat exchanger is 120-200°C.

[0026] Furthermore, the multi-stage heat exchanger further includes a four-stage heat exchanger, and the hot side outlet temperature of the four-stage heat exchanger is not less than 110°C.

[0027] To prevent hydrocyanic acid polymerization, the research and development team of this invention paid special attention to ensuring that the temperature of the hydrocyanic acid-containing reaction syngas at the hot side of the heat exchanger at the outlet does not fall below the dew point of the hydrocyanic acid gas to prevent polymerization. This outlet temperature was carefully determined through simulation calculations and combined with actual operating data to ensure that the dew point of the hydrocyanic acid gas does not exceed 80°C. Therefore, a syngas temperature of 110°C at the outlet of the four-stage heat exchanger is a typical, safe, and effective parameter.

[0028] Furthermore, the cold side of the four-stage heat exchanger produces low-pressure steam or hot water of not less than 110°C by removing heat.

[0029] By using a four-stage heat exchanger to generate low-pressure steam or hot water for heat transfer and cooling, a low-grade heat source can be obtained. This low-pressure steam or hot water can be directly connected to an appropriate pipe network system for use. In addition, these low-grade heat sources can be used to produce a cold source of suitable temperature through mature waste heat recovery facilities to meet other cooling needs within the device. For example, low-pressure steam or hot water can be used to produce cold water at 5 to 15°C through a lithium bromide ice machine. This cold water can then be used for cooling in the subsequent ammonia recovery and hydrocyanic acid refining processes. This design not only achieves efficient heat recovery and reuse, but also significantly improves the energy efficiency of the entire system.

[0030] In a further example of the present invention, the weight percentages of the reaction raw material mixed gas are: 5-35% ammonia, 5-30% methane and 15-45% oxygen.

[0031] In a further example of the present invention, the feed rate of the reaction raw material mixed gas is 600-150000 kg / h, the feed temperature is 10-40° C., and the feed pressure is 0.01-0.1 MPaG.

[0032] In a further embodiment of the present invention, the multi-stage heat exchanger is a shell-and-tube heat exchanger. The heat exchanger removes excess heat and can generate steam at varying pressure levels. The wide application of shell-and-tube heat exchangers and their ability to generate steam that is well matched to the heat load requirements of the device make them highly suitable for the application scenarios of the present invention due to their compact structure and high heat transfer efficiency.

[0033] In a further embodiment of the present invention, the tube length of the shell-and-tube heat exchanger is 1.5 to 3 meters. Using low-pressure steam for heat transfer and cooling can achieve a greater heat transfer temperature difference, thereby reducing the required heat exchanger tube length. This not only reduces equipment manufacturing costs but also improves heat recovery efficiency.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention provides a method for removing residual reaction heat in a staged manner in the hydrocyanic acid production process. The method removes heat from the reaction synthesis gas containing hydrocyanic acid through a primary heat exchanger to generate low-pressure steam, thereby reducing the residence time in the high-temperature zone to reduce the decomposition of hydrocyanic acid, thereby improving the yield of the device product.

[0036] 2. The method for removing the reaction waste heat in a staged manner in the hydrocyanic acid production process of the present invention generates steam or hot water of different pressure levels through a multi-stage heat exchanger, matching the needs of the device or factory for different grades of heat sources, thereby reducing the overall energy consumption of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 A schematic diagram showing a method for removing residual heat of reaction in a stepwise manner in a process for synthesizing hydrocyanic acid according to the present invention is shown.

[0039] The above drawings include the following reference numerals:

[0040] A. Reactor, B. Primary heat exchanger, C. Secondary heat exchanger, D. Third-stage heat exchanger, E. Fourth-stage heat exchanger, F. Waste heat recovery facility, 100. Reaction raw material mixed gas, 101. Reaction synthesis gas containing hydrocyanic acid. DETAILED DESCRIPTION

[0041] To facilitate understanding of the present invention, the present invention will be described in more detail below, with preferred embodiments of the present invention provided. However, it should be understood that these embodiments are provided for illustrative purposes only and are not intended to limit the present invention in any manner, i.e., they are not intended to limit the scope of protection of the present invention.

[0042] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention pertains. The experimental methods described in the following examples are conventional methods unless otherwise specified.

[0043] The methane gas described herein is generally provided by natural gas, which may contain small amounts of C2+ hydrocarbon components (such as ethane, ethylene, propane, propylene, butane, butylene, and isobutane), which can be refined as needed. Air is generally used as the oxygen, but oxygen-enriched air or pure oxygen can also be used. The hydrocyanic acid-containing reaction synthesis gas primarily comprises hydrocyanic acid, unreacted ammonia and methane, water, nitrogen, hydrogen, carbon monoxide, and carbon dioxide.

[0044] Example 1:

[0045] This embodiment uses a primary heat exchanger, a secondary heat exchanger, a tertiary heat exchanger, and a quaternary heat exchanger to remove the residual heat of the reaction synthesis gas generated by the Angle method for synthesizing hydrocyanic acid in a staged manner. The specific method is as follows:

[0046] The composition of the reaction raw material mixed gas is:

[0047] substance methane ammonia oxygen Composition wt% 25％ 30％ 45％

[0048] The total flow rate of the reaction raw material mixed gas was 900 kg / h, the feed temperature was 40° C., and the feed pressure was 0.1 MPaG.

[0049] A reaction raw material mixture 100 of 30% ammonia, 25% methane and 45% oxygen is sent to a reactor A containing a platinum-rhodium alloy catalyst, where a gas-phase reaction is carried out at high temperature to generate a reaction synthesis gas 101 containing hydrocyanic acid. The reaction synthesis gas 101 is sequentially sent to a first-stage heat exchanger B, a second-stage heat exchanger C, a third-stage heat exchanger D, and a fourth-stage heat exchanger E for cooling before entering the subsequent ammonia recovery and hydrocyanic acid refining units.

[0050] The inlet temperature of the reaction synthesis gas containing hydrocyanic acid on the hot side of the first-stage heat exchanger B is 1150°C. After passing through the first-stage heat exchanger B, the temperature is reduced to 630°C, after passing through the second-stage heat exchanger C, the temperature is reduced to 300°C, after passing through the third-stage heat exchanger D, the temperature is reduced to 200°C, and after passing through the fourth-stage heat exchanger E, the temperature is reduced to 110°C.

[0051] The cold side of the first-stage heat exchanger B generates 0.3MPaG low-pressure steam by removing heat, the cold side of the second-stage heat exchanger C generates 4.0MPaG high-pressure steam by removing heat, the cold side of the third-stage heat exchanger D generates 0.3MPaG low-pressure steam by removing heat, and the cold side of the fourth-stage heat exchanger E generates 110℃ hot water by removing heat.

[0052] The primary heat exchanger B uses low-pressure steam to transfer heat and cool down, and the average heat transfer temperature difference is 720℃. The required tube diameter of the primary heat exchanger B is 25mm, and the effective heat exchange area is 6.3m 2 , actual heat exchange area 7.2m 2 The required tube length is 1.2m, and the generated low-pressure steam of 0.15MPaG can be directly incorporated into a suitable pipe network for use.

[0053] The secondary heat exchanger C generates high-pressure steam for heat removal and cooling. The generated 4.0 MPaG high-pressure steam is directly incorporated into a suitable pipe network and further used to drive the turbine of large power equipment in the device or factory.

[0054] The three-stage heat exchanger D generates low-pressure steam to remove heat and cool down the device. The generated 0.3MPaG low-pressure steam can be directly incorporated into a suitable pipe network for use.

[0055] The fourth-stage heat exchanger E uses hot water to remove heat and cool the system. The resulting 110°C hot water is passed through a lithium bromide ice machine to extract 7°C cold water, which is then used for heat exchanger cooling in the subsequent ammonia recovery and hydrocyanic acid refining processes. The outlet temperature of the hydrocyanic acid-containing reaction synthesis gas on the hot side of the fourth-stage heat exchanger is kept below the dew point of the hydrocyanic acid gas under operating conditions to prevent polymerization. The dew point of the hydrocyanic acid gas under these operating conditions is no higher than 80°C.

[0056] Example 2:

[0057] This embodiment uses a primary heat exchanger, a secondary heat exchanger, and a tertiary heat exchanger to remove the residual heat of the reaction synthesis gas generated by the Angle method for synthesizing hydrocyanic acid in a staged manner. The specific method is as follows:

[0058] The composition of the reaction raw material mixed gas is:

[0059] substance methane ammonia oxygen Composition wt% 8.5％ 9.2％ 16.5％

[0060] The total flow rate of the reaction raw material mixed gas is 140,000 kg / h, the feed temperature is 10° C., and the feed pressure is 0.05 MPaG.

[0061] A reaction raw material mixture gas 100 of 8.5% ammonia, 9.2% methane and 16.5% oxygen and 65.8% nitrogen is sent to a reactor A containing a platinum-rhodium alloy catalyst, where a gas-phase reaction is carried out at a high temperature to generate a reaction synthesis gas 101 containing hydrocyanic acid. The reaction synthesis gas 101 is sequentially sent to a primary heat exchanger B, a secondary heat exchanger C, and a tertiary heat exchanger D for cooling before entering a subsequent ammonia recovery and hydrocyanic acid refining unit.

[0062] The inlet temperature of the reaction synthesis gas containing hydrocyanic acid on the hot side of the first-stage heat exchanger B is 1150℃. After passing through the first-stage heat exchanger B, the temperature is reduced to 580℃, after passing through the second-stage heat exchanger C, the temperature is reduced to 210℃, and after passing through the third-stage heat exchanger D, the temperature is reduced to 120℃.

[0063] The cold side of the first-stage heat exchanger B generates 0.15MPaG low-pressure steam by removing heat, the cold side of the second-stage heat exchanger C generates 2.1MPaG high-pressure steam by removing heat, and the cold side of the third-stage heat exchanger D generates 120℃ hot water by removing heat.

[0064] The primary heat exchanger B uses low-pressure steam to transfer heat and cool down, and the average heat transfer temperature difference is 705℃. The required primary heat exchanger B has a tube diameter of 25mm and an effective heat exchange area of 315m 2 , actual heat exchange area 443m 2 The required tube length is 2.2m, and the generated low-pressure steam of 0.15MPaG can be directly incorporated into a suitable pipe network for use.

[0065] The secondary heat exchanger C generates high-pressure steam for heat removal and cooling. The generated 2.1 MPaG high-pressure steam is directly incorporated into a suitable pipe network and further used to drive the turbine of large power equipment in the device or factory.

[0066] The tertiary heat exchanger D generates low-pressure steam for heat removal and cooling. The resulting 120°C hot water is passed through a lithium bromide ice machine to extract 12°C cold water, which is then used for heat exchanger cooling in the subsequent ammonia recovery and hydrocyanic acid refining processes. The outlet temperature of the hydrocyanic acid-containing reaction synthesis gas on the hot side of the tertiary heat exchanger is kept below the dew point of the hydrocyanic acid gas under operating conditions to prevent polymerization. The dew point of the hydrocyanic acid gas under these operating conditions is no higher than 80°C.

[0067] Comparative Example 1

[0068] Based on the method for removing the residual heat of reaction in the hydrocyanic acid synthesis process in Example 1, the cold side of the primary heat exchanger B in this embodiment is cooled by removing the generated 4.0 MPaG high-pressure steam to remove heat. The specific method is as follows:

[0069] The composition of the reaction raw material mixed gas is:

[0070] substance methane ammonia oxygen Composition wt% 25％ 30％ 45％

[0071] The total flow rate of the reaction raw material mixed gas was 900 kg / h, the feed temperature was 40° C., and the feed pressure was 0.1 MPaG.

[0072] A reaction raw material mixture 100 of 30% ammonia, 25% methane and 45% oxygen is sent to a reactor A containing a platinum-rhodium alloy catalyst, where a gas-phase reaction is carried out at a high temperature to generate a reaction synthesis gas 101 containing hydrocyanic acid. The reaction synthesis gas 101 is sent to a primary heat exchanger B for cooling and then enters a subsequent ammonia recovery and hydrocyanic acid refining unit.

[0073] The inlet temperature of the reaction synthesis gas containing hydrocyanic acid on the hot side of the first-stage heat exchanger B is 1150°C, and the temperature is reduced to 200°C after passing through the first-stage heat exchanger B.

[0074] The primary heat exchanger B uses 4.0MPaG high-pressure steam to transfer heat and cool down the temperature, and the average heat transfer temperature difference is 600℃. The required primary heat exchanger B has a tube diameter of 25mm and an effective heat transfer area of 7.6m 2 , actual heat exchange area 9.6m 2 , tube length 1.6m.

[0075] Comparing Example 1 with Comparative Example 1, in Example 1, the cold side of the primary heat exchanger B is cooled by removing 0.3 MPaG low-pressure steam to transfer heat, and the average heat transfer temperature difference obtained is 720°C. The required tube diameter of the primary heat exchanger B is 25 mm, and the effective heat exchange area is 6.3 m2 , actual heat exchange area 7.2m 2 , the required tube length is 1.2m; in comparison, in Comparative Example 1, the cold side of the first-stage heat exchanger B is cooled by removing the 4.0MPaG high-pressure steam to transfer heat and cool down, and the average heat transfer temperature difference obtained is 600℃. The required first-stage heat exchanger B has a tube diameter of 25mm and an effective heat exchange area of 7.6m 2 , actual heat exchange area 9.6m 2 , tube length 1.6m.

[0076] Therefore, the primary heat exchanger B of Example 1, which generates 0.3 MPaG low-pressure steam for heat transfer and cooling, can effectively increase the average heat transfer temperature difference by 20% compared to the primary heat exchanger B of Comparative Example 1, which generates 4.0 MPaG high-pressure steam for heat transfer and cooling. This reduces the effective heat exchange area of the primary heat exchanger B by 20%, that is, improves the heat exchange efficiency of the primary heat exchanger B by 20%. The actual heat exchange area of the primary heat exchanger B is reduced by 33%, and the required tube length for the same tube diameter is reduced by 33%, effectively reducing the residence time of the hydrocyanic acid-containing reaction synthesis gas 101 in the high-temperature zone by 33%. Furthermore, the decomposition of hydrocyanic acid in the hydrocyanic acid-containing reaction synthesis gas 101 in the high-temperature zone is reduced by more than 5% (hydrocyanic acid loss rate calculated as ammonia).

[0077] Comparative Example 2

[0078] Based on the method for removing the reaction waste heat in stages in the hydrocyanic acid synthesis process of Example 2, the cold side of the primary heat exchanger B in this embodiment is cooled by removing the generated 2.1 MPaG high-pressure steam to remove heat. The specific method is as follows:

[0079] The composition of the reaction raw material mixed gas is:

[0080] substance methane ammonia oxygen Composition wt% 8.5％ 9.2％ 16.5％

[0081] The total flow rate of the reaction raw material mixed gas is 140,000 kg / h, the feed temperature is 10° C., and the feed pressure is 0.05 MPaG.

[0082] A reaction raw material mixture 100 of 8.5% ammonia, 9.2% methane and 16.5% oxygen and 65.8% nitrogen is sent to a reactor A containing a platinum-rhodium alloy catalyst, where a gas-phase reaction is carried out at a high temperature to generate a reaction synthesis gas 101 containing hydrocyanic acid. The reaction synthesis gas 101 is sent to a primary heat exchanger B for cooling and then enters a subsequent ammonia recovery and hydrocyanic acid refining unit.

[0083] The first stage heat exchanger B uses 2.1MPaG high pressure steam to transfer heat and cool down the machine, and the average heat transfer temperature difference is 610℃. The required first stage heat exchanger B has a tube diameter of 25mm and an effective heat transfer area of 362m 2, actual heat exchange area 584m 2 , tube length 2.9m.

[0084] Comparing Example 2 with Comparative Example 2, in Example 1, the primary heat exchanger B generates 0.15 MPaG low-pressure steam to remove heat and cool down, and the average heat transfer temperature difference obtained is 705°C. The required primary heat exchanger B has a tube diameter of 25 mm and an effective heat exchange area of 315 m 2 , actual heat exchange area 443m 2 , the required tube length is 2.2m; in comparison, the primary heat exchanger B in comparative example 2 adopts 2.1MPaG high-pressure steam to remove heat and cool down, and the average heat transfer temperature difference obtained is 610℃. The required primary heat exchanger B has a tube diameter of 25mm and an effective heat exchange area of 362m 2 , actual heat exchange area 584m 2 , tube length 2.9m.

[0085] Therefore, in Example 2, the primary heat exchanger B generates 0.15 MPaG low-pressure steam by removing heat for cooling. Compared with Comparative Example 2, in which the primary heat exchanger B generates 2.1 MPaG high-pressure steam by removing heat for cooling, the average heat transfer temperature difference can be effectively increased by 16%, thereby reducing the effective heat exchange area of the heat exchanger by 16%, that is, improving the heat exchange efficiency of the heat exchanger by 16%. Furthermore, the actual heat exchange area of the primary heat exchanger B is reduced by 32%, and the required tube length for the same tube diameter is reduced by 32%, effectively reducing the residence time of the reaction synthesis gas 101 containing hydrocyanic acid in the high-temperature zone by 32%. Furthermore, the decomposition of hydrocyanic acid in the reaction synthesis gas 101 containing hydrocyanic acid in the high-temperature zone is reduced by more than 4.5% (hydrocyanic acid loss rate calculated as ammonia).

[0086] In summary, the method for removing reaction waste heat in a staged manner in a hydrocyanic acid production process of the present invention removes heat from the reaction synthesis gas containing hydrocyanic acid through a primary heat exchanger to generate low-pressure steam, thereby reducing the residence time in the high-temperature zone to reduce the decomposition of hydrocyanic acid, thereby improving the yield of the device product; steam or hot water of different pressure levels is generated through a multi-stage heat exchanger to match the needs of the device or factory for different grades of heat sources, thereby reducing the overall energy consumption of the device; and heat is removed through the heat exchanger to control a suitable outlet temperature of the reaction synthesis gas containing hydrocyanic acid, so as to avoid polymerization of hydrocyanic acid and scaling of subsequent equipment, thereby improving the operating stability of the device.

[0087] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these shall fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A method for removing residual heat of reaction in a hydrocyanic acid production process in a staged manner, characterized in that: Ammonia, methane and oxygen are used as the reaction raw material mixture, and a gas phase reaction is carried out under the catalysis of platinum-rhodium alloy to generate a reaction synthesis gas containing hydrocyanic acid. The reaction synthesis gas is cooled by a multi-stage heat exchanger and then enters the subsequent ammonia recovery and hydrocyanic acid refining unit; The multi-stage heat exchanger is composed of at least two heat exchangers connected in series, including a first-stage heat exchanger and a second-stage heat exchanger. The reaction synthesis gas with a temperature of 1000-1200°C is introduced into the hot side of the first-stage heat exchanger, and water with a temperature of not less than 100°C is introduced into the cold side of the first-stage heat exchanger. The cold side of the first-stage heat exchanger generates low-pressure steam not higher than 0.3 MPaG by removing heat; the cold side of the second-stage heat exchanger generates high-pressure steam of 2.0-4.0 MPaG by removing heat.

2. The method for removing the residual heat of reaction in a stepwise manner in a hydrocyanic acid production process according to claim 1, characterized in that: The hot side outlet temperature of the first-stage heat exchanger is 580-630°C, and the hot side outlet temperature of the second-stage heat exchanger is 210-300°C.

3. The method for removing reaction waste heat in a staged manner in a hydrocyanic acid production process according to claim 1, characterized in that: The multi-stage heat exchanger further comprises a three-stage heat exchanger, and the cold side of the three-stage heat exchanger generates low-pressure steam not higher than 0.3 MPaG or hot water at 120-130° C. by removing heat.

4. The method for removing residual heat of reaction in a hydrocyanic acid production process according to claim 3, characterized in that: The hot side outlet temperature of the three-stage heat exchanger is 120-200°C.

5. The method for removing residual heat of reaction in a hydrocyanic acid production process according to claim 1, characterized in that: The multi-stage heat exchanger further comprises a four-stage heat exchanger, and the cold side of the four-stage heat exchanger generates low-pressure steam not higher than 0.2 MPaG or hot water at 110-130° C. by removing heat.

6. The method for removing residual heat of reaction in a hydrocyanic acid production process according to claim 5, characterized in that: The hot side outlet temperature of the four-stage heat exchanger is not less than 110°C.

7. The method for removing residual heat of reaction in a staged manner in a hydrocyanic acid production process according to claim 1, characterized in that: The weight percentages of the reaction raw material mixed gas are: 5-35% ammonia, 5-30% methane and 15-45% oxygen.

8. The method for removing reaction waste heat in a staged manner in a hydrocyanic acid production process according to claim 7, characterized in that: The feed rate of the reaction raw material mixed gas is 600-150000 kg / h, the feed temperature is 10-40° C., and the feed pressure is 0.01-0.1 MPaG.

9. The method for removing reaction waste heat in a staged manner in a hydrocyanic acid production process according to any one of claim 8, characterized in that: The multi-stage heat exchanger is a shell and tube heat exchanger.

10. The method for removing reaction waste heat in a staged manner in a hydrocyanic acid production process according to claim 9, characterized in that: The tube length of the shell and tube heat exchanger is 1.5 to 3 meters.

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