Synthetic Ammonia Process Technology Exchange Area [Daily Question 2009-03-11]

In ammonia synthesis production, a heat pipe refers to the connection method from the secondary outlet of the reaction gases in the synthesis tower to the waste heat boiler; the pipeline that connects the secondary outlet to the waste heat boiler is known as a heat pipe； The second outlet to the waste heat boiler can also be connected directly using flanges, eliminating the need for pipe connections and thus reducing the significant investment costs associated with such pipes. However, the waste heat boiler must be placed below the synthesis tower, and spring supports must be used at both ends of its base to counteract the effects of thermal expansion. This poses certain difficulties in equipment maintenance, as well as affecting the installation of the equipment and its stable operation over long periods of time. It is necessary to consider all these factors carefully in order to select a suitable connection method for the second outlet pipes. I recommend using a pipe connection method.

A heat pipe utilizes the principles of heat conduction and the rapid heat transfer properties of a cooling medium to swiftly transfer the heat from an object that generates heat to a location outside that object; its heat conduction capacity exceeds that of any known metal. Heat pipe technology has the following application types in the ammonia synthesis industry. 1. Recover low-temperature waste heat to preheat the combustion air, or generate low-pressure steam as a raw material for production ； 2. Recover high-temperature waste heat to generate medium-pressure steam as a supplement to the feed steam, or produce high-pressure steam as a power source for production ； 3. Control the chemical reaction temperature in the fixed-bed catalytic reactor to bring it as close as possible to the optimal reaction temperature curve, thereby increasing the CO conversion rate in the CO conversion reactor as well as the ammonia synthesis rate in the ammonia synthesis tower.

A heat pipe utilizes the principles of heat conduction and the rapid heat transfer properties of a cooling medium to swiftly transfer the heat from an object that generates heat to a location outside that object; its heat conduction capacity exceeds that of any known metal. Heat pipe technology can recover high-temperature waste heat to generate medium-pressure steam, which can be used as a supplement to the feed steam, or to produce high-pressure steam as a power source for production.

A heat pipe utilizes the principles of heat conduction and the rapid heat transfer properties of a cooling medium to swiftly transfer the heat from an object that generates heat to a location outside that object; its heat conduction capacity exceeds that of any known metal. Heat pipe technology has the following application types in the ammonia synthesis industry. 1. Recover low-temperature waste heat to preheat the combustion air, or generate low-pressure steam as a raw material for production ； 2. Recover high-temperature waste heat to generate medium-pressure steam as a supplement to the feed steam, or produce high-pressure steam as a power source for production ； 3. Control the chemical reaction temperature in the fixed-bed catalytic reactor to bring it as close as possible to the optimal reaction temperature curve, thereby increasing the CO conversion rate in the CO conversion reactor as well as the ammonia synthesis rate in the ammonia synthesis tower.

A heat pipe is an efficient heat transfer element, whose thermal conductivity is several hundred to several thousand times higher than that of metals. Heat pipes also possess advantages such as good temperature equalization, adjustable heat flux density, and reversible heat transfer direction. Using it to construct a heat pipe heat exchanger not only retains the inherent advantages of heat pipes such as high heat transfer capacity, small temperature difference, light weight and small size, as well as rapid thermal response, but also features easy installation, simple maintenance, long service life, low pressure loss, and easy separation of the inlet and outlet air channels with no leakage between them. 　　A heat pipe is made by using aluminum (rolled) finned tubes with grooves fabricated on their inner walls; these tubes are sealed at both ends, cleaned, evacuated to a high vacuum, and then filled with an optimal liquid working medium. Depending on the composition and ratio of this liquid working medium, heat pipe exchangers can be classified into KLS low-temperature heat pipe exchangers, GRSC-A medium-temperature heat pipe exchangers, and GRSC-B high-temperature heat pipe exchangers. When one end of a heat pipe is heated, the working fluid inside the pipe vaporizes, absorbing heat of vaporization from the heat source. The vapor then flows to the other end, where it condenses and releases its latent heat into the heat dissipation area. The condensate flows back due to capillary force and gravity, where it is heated and vaporized again; this back-and-forth cycle transfers a large amount of heat from the heating area to the cooling area. Heat transfer within a heat pipe occurs through the phase change of the working fluid. The heat pipes in our company are mainly used to recover the latent heat of the upward and downward flowing coal gas.

Regarding heat pipe exchangers, discussions have taken place on the exchange area of such exchangers; the relevant link is http://bbs.hcbbs.com/viewthread.php?tid=391188&highlight=. In my opinion, heat pipes are often used in air preheaters

　Heat pipe technology is a heat transfer element known as a “heat pipe,” invented in 1963 by G.M. Grover at the Los Alamos National Laboratory in the United States. It makes full use of the principles of heat conduction as well as the rapid heat transfer properties of refrigerant fluids, enabling it to swiftly transfer the heat from hot objects to locations outside those objects. Its heat conduction capacity exceeds that of any known metal. Heat pipe technology was previously widely used in industries such as aerospace and military manufacturing. Since its introduction into the radiator industry, it has led to a change in the way traditional radiators are designed, breaking away from the conventional approach of relying on fans with high airflow rates to achieve better cooling effects. By utilizing heat pipe technology, radiators can achieve satisfactory cooling results even when equipped with fans that operate at low speeds and produce low airflow rates. This solves the noise problem associated with air-cooled cooling systems, opening up new possibilities for the radiator industry. 　(1) Classified by the operating temperature inside the heat pipe, heat pipes can be divided into low-temperature heat pipes (–273 to 0°C), normal-temperature heat pipes (0–250°C), medium-temperature heat pipes (250–450°C), and high-temperature heat pipes (450–1000°C). 　　[2) Based on the dynamics of the working fluid flow, heat pipes can be classified into cored heat pipes, two-phase closed thermosiphon tubes (also known as gravity heat pipes), gravity-assisted heat pipes, rotating heat pipes, electrohydrodynamic heat pipes, magnetohydrodynamic heat pipes, osmotic heat pipes, and so on. 　　(3) Classified by the combination of the tube shell and the working fluid (this is a *common classification method), they can be divided into copper-water heat pipes and carbon steel ones. Hydrotube, copper-steel composite hydrotube, aluminum-propylene hydrotube, carbon steel-Rong hydrotube, stainless steel-sodium hydrotube, and so on. 　　(4) Classified by structural form, they can be divided into ordinary heat pipes, separated heat pipes, hair pump circuit heat pipes, micro heat pipes, flat heat pipes, radial heat pipes, etc. 　　(5) Classified by their functions, heat pipes can be divided into heat transfer heat pipes, thermal diodes, thermal switches, heat pipes for thermal control, simulation heat pipes, cooling heat pipes, and so on. 　The synthetic ammonia industry is a fundamental chemical industry that holds a very important position within the chemical sector. Ammonia synthesis, from gas generation to ammonia formation, involves heat-intensive processes. Reasonable utilization and control of the heat released during the synthesis of ammonia not only helps to save energy consumption in production and reduce costs, but also improves the CO conversion rate and the ammonia synthesis rate. The former relates to the utilization of waste heat, while the latter involves thermal control of chemical reactions. Given the specific conditions of China’s industrial development, its ammonia synthesis industry can be classified into small-scale, medium-scale, and large-scale ammonia production based on production scale. The raw materials used in production include coal, oil, and natural gas. Due to different raw material routes, the production processes and the equipment used also vary. Based on the characteristics of equipment in different process routes, heat pipe technology is employed in the ammonia synthesis industry in the following application types. 　 　①Recycle low-temperature waste heat to preheat the combustion air, or generate low-pressure steam as a raw material for production ； 　　②The recovered high-temperature waste heat is used to generate medium-pressure steam as a supplement to the feed steam, or to produce high-pressure steam as a power source for production ； 　　③Control the chemical reaction temperature in the fixed-bed catalytic reactor to bring it as close as possible to the optimal reaction temperature curve, thereby increasing the CO conversion rate in the CO conversion reactor as well as the ammonia synthesis rate in the ammonia synthesis tower. 　　For these three application types, the methods of application and the design approaches vary depending on the production scale and the raw material processing routes; adopting different structural designs tailored to specific practical conditions can yield good results.

A heat pipe is an efficient heat transfer element, whose thermal conductivity is several hundred to several thousand times higher than that of metals. Heat pipes also possess advantages such as good temperature equalization, adjustable heat flux density, and reversible heat transfer direction. Using it to construct a heat pipe heat exchanger not only retains the inherent advantages of heat pipes such as high heat transfer capacity, small temperature difference, light weight and small size, as well as rapid thermal response, but also features easy installation, simple maintenance, long service life, low pressure loss, and easy separation of the inlet and outlet air channels with no leakage between them. 　　A heat pipe is made by using aluminum (rolled) finned tubes with grooves fabricated on their inner walls; these tubes are sealed at both ends, cleaned, evacuated to a high vacuum, and then filled with an optimal liquid working medium. Depending on the composition and ratio of this liquid working medium, heat pipe exchangers can be classified into KLS low-temperature heat pipe exchangers, GRSC-A medium-temperature heat pipe exchangers, and GRSC-B high-temperature heat pipe exchangers. When one end of a heat pipe is heated, the working fluid inside the pipe vaporizes, absorbing heat of vaporization from the heat source. The vapor then flows to the other end, where it condenses and releases its latent heat into the heat dissipation area. The condensate flows back due to capillary force and gravity, where it is heated and vaporized again; this back-and-forth cycle transfers a large amount of heat from the heating area to the cooling area. Heat transfer within a heat pipe occurs through the phase change of the working fluid. The heat pipes in our company are mainly used to recover the latent heat of the upward and downward flowing coal gas.

China’s synthetic ammonia industry can be classified by production scale into small-scale, medium-scale, and large-scale synthetic ammonia production. The raw materials used in production include coal, oil, and natural gas. Due to different raw material routes, the production processes and the equipment used also vary. Based on the characteristics of equipment in different process routes, heat pipe technology is employed in the ammonia synthesis industry in the following application types. ①Recycle low-temperature waste heat to preheat the combustion air, or generate low-pressure steam as a raw material for production ； ②The recovered high-temperature waste heat is used to generate medium-pressure steam as a supplement to the feed steam, or to produce high-pressure steam as a power source for production ； ③Control the chemical reaction temperature in the fixed-bed catalytic reactor to bring it as close as possible to the optimal reaction temperature curve, thereby increasing the CO conversion rate in the CO conversion reactor as well as the ammonia synthesis rate in the ammonia synthesis tower. For these three application types, the methods of application and the design approaches vary depending on the production scale and the raw material processing routes; adopting different structural designs tailored to specific practical conditions can yield good results.