Seeking advice on dry recovery of liquid ammonia technology

Microwave vacuum drying offers fast, energy-efficient drying with high quality, and is widely used in industries such as food processing; it is a very promising drying method. The microwave vacuum dryer combines microwave drying and vacuum drying technologies, taking full advantage of their respective strengths. It enables the materials to be dried rapidly at lower temperatures, resulting in dried products with excellent quality. In a vacuum environment, heat transfer of water or solvent molecules is relatively easy, **which reduces drying time and increases production efficiency**. Therefore, vacuum drying is a low-temperature and rapid drying technique, which holds significant practical value, especially in the drying of heat-sensitive materials as well as flammable and explosive hazardous substances. Compared to traditional drying methods, microwave vacuum drying offers significant advantages in terms of drying speed and product quality. Under conditions of a vacuum degree of 0.080 MPa, a microwave power of 1400 W, and a material layer thickness of 20 mm, the complete drying time for 923 g of material with a moisture content of 10% using microwave drying was 1090 seconds, which is significantly less than the 7–8 hours required for conventional drying. Vacuum level has little impact on the drying time of materials ； The optimal drying time is achieved when the thickness of the material is 15–20 mm. To dry 120 g of powdered material with a thickness of 15 mm, the drying time is 1,020 seconds. Microwave irradiation has no significant effect on the properties of powdered materials such as their mechanical sensitivity; therefore, it is entirely feasible to use microwave vacuum drying for powdered materials.

Microwaves are a type of electromagnetic wave whose energy is much greater than that of ordinary radio waves; they are generated by converting electrical energy into high-frequency microwaves using magnetrons. Metals cannot absorb or conduct microwaves; when microwaves hit metals, they are reflected. Microwaves can pass through insulating materials such as glass, ceramics, and plastics without losing energy. However, substances composed of \"polar molecules\" can absorb microwaves and convert them into thermal energy within the material. Water is composed of \"polar molecules,\" so when microwaves pass through water-containing foods, the water molecules in those foods vibrate at high frequencies, generating a large amount of heat as a result, which causes the temperature to rise. Due to the strong penetration power of microwaves, heating of objects occurs in a way that affects the entire interior, rather than being a traditional heating from the outside in; as a result, the heating speed is fast. Ammonia is also a polar molecule, and heating it with microwaves can accelerate its evaporation rate.

Reply 1# lc88ms: When I applied for the position, adding a microwave generator inside the unit on the 131st floor would speed up the drying process, with very noticeable effects; it could **reduce the drying time without affecting the quality of the products. A microwave generator can be a transistor; for high power levels, it is a vacuum tube. Microwave energy is generated by the microwave generator, which consists of two components: the microwave tube and its power supply. The function of the microwave tube power supply (referred to simply as the power supply or microwave source) is to convert the commonly used alternating current electricity into direct current electricity, thereby creating the conditions necessary for the operation of the microwave tube. The microwave tube is the core of a microwave generator; it converts direct current electricity into microwave energy, providing stable continuous-wave microwave power for applications in the processing of grains, oils, and foods, agricultural products, pharmaceuticals, rubber vulcanization, ceramics, sintering, chemical product manufacturing, and high-tech fields. Advantages: continuously adjustable power, stable performance, and comprehensive safety protection measures. It can operate continuously for long periods, features high energy conversion efficiency, and is easy to operate. The microwave generator is the key component of drying equipment, consisting of an electromagnetic control tube and a microwave power supply. The microwave path generated by the magnetron tube is transmitted losslessly through the waveguide assembly into the microwave dryer ； A microwave dryer is a space in which the material to be dried and microwaves interact with each other; here, microwave energy is converted into internal energy of the material, causing the moisture within it to evaporate and thus drying the material ； The function of the dehumidifying cooling assembly is to remove the moisture vapor generated by evaporation from objects and to cool the materials through ventilation ； In the microwave equipment that imposes continuous penalties on materials, there is also a material transportation system as part of the setup. The conveying rate and speed control of this system must meet the process requirements of the materials to be dried; they are continuously sent to the fine-wave dryer and subsequent drying stages, and the dried materials are then transported on to the next processing step. Traditional systems are mostly composed of speed-regulating electromechanisms and speed reducers. The material conveyor belts are made of media materials that absorb low-power microwaves, such as polytetrafluoroethylene glass fiber belts and polyethylene belts ； A control system is used to regulate various operating parameters of equipment. It ensures that the output power, transfer speed, and dehumidification and cooling systems of the equipment can be controlled and adjusted in a timely, convenient, and flexible manner in accordance with the requirements of the optimal process specifications. The moderation system can be installed on the microwave generator or separated from the main unit. Microwave vacuum drying offers fast, energy-efficient drying with high quality, and is widely used in industries such as food processing; it is a very promising drying method. The microwave vacuum dryer combines microwave drying and vacuum drying technologies, taking full advantage of their respective strengths. It enables the materials to be dried rapidly at lower temperatures, resulting in dried products with excellent quality. In a vacuum environment, heat transfer of water or solvent molecules is relatively easy, **which reduces drying time and increases production efficiency**. Therefore, vacuum drying is a low-temperature and rapid drying technique, which holds significant practical value, especially in the drying of heat-sensitive materials as well as flammable and explosive hazardous substances. Compared to traditional drying methods, microwave vacuum drying offers significant advantages in terms of drying speed and product quality. Under conditions of a vacuum degree of 0.080 MPa, a microwave power of 1400 W, and a material layer thickness of 20 mm, the complete drying time for 923 g of material with a moisture content of 10% using microwave drying was 1090 seconds, which is significantly less than the 7–8 hours required for conventional drying. Vacuum level has little impact on the drying time of materials ； The optimal drying time is achieved when the thickness of the material is 15–20 mm. To dry 120 g of powdered material with a thickness of 15 mm, the drying time is 1,020 seconds. Microwave irradiation has no significant effect on the properties of powdered materials such as their mechanical sensitivity; therefore, it is entirely feasible to use microwave vacuum drying for powdered materials.

Principle of microwave drying: Microwaves refer to electromagnetic waves with frequencies ranging from 300 megahertz to 300 gigahertz. Dielectric materials are composed of polar molecules (water molecules) and non-polar molecules; under the influence of an electromagnetic field, these polar molecules shift from their original random distribution to aligning themselves in accordance with the polarity of the electric field. Under the influence of high-frequency electromagnetic fields, these orientations change in response to the variations in the alternating electromagnetic field. This process leads to the movement of molecules and to frictional effects (under an electromagnetic field of 2054 megahertz, water molecules can make 2.45 billion displacements per second), thereby generating heat. At this point, the field energy of the alternating electromagnetic field is converted into thermal kinetic energy within the medium, causing the temperature of the medium to rise continuously. Microwave heating uses the object being heated itself as a heat source, which is known as a bulk heating method. It does not require a process of heat conduction, allowing for uniform heating to be achieved in a short time. This feature enables materials with poor heat conductivity to be heated and dried in a short time, improving energy efficiency, and it also allows the heating furnace to be smaller in size compared to conventional heating furnaces. At the same time, when the material is under the action of the microwave electromagnetic field, its overall temperature rises. At this time, the surface temperature drops due to the evaporation of water from the surface of the material ； This results in a temperature gradient that is higher on the inside and lower on the outside, with the direction of this gradient being exactly the same as the direction of water evaporation. So the efficiency is extremely high. Microwave drying differs from traditional drying methods in that the direction of heat conduction is the same as the direction of water diffusion. Compared with traditional drying methods, it offers advantages such as a high drying rate, energy savings, high production efficiency, uniform drying, clean production, easy automation control, and improved product quality; as a result, it is receiving increasing attention in various fields of drying. Abroad, it is now widely used in the food industry, materials chemistry, pharmaceutical industry, mining industry, ceramic industry, laboratory analysis, and the processing of wet natural rubber, among other fields. Therefore, to address the issue of slow drying speed in your original design, it is theoretically possible to add a microwave generator inside the existing device in order to accelerate the drying process. However, our country started relatively late in terms of research on the application of microwave drying technology. Although considerable achievements have been made, most of them remain at the experimental stage or at a small-scale production level. Research on composite microwave drying technology needs to be expanded, and there is still insufficient research on the theories of instantaneous mass and heat transfer in microwave drying. The development of equipment and instruments compatible with microwave drying technology also requires further improvement. There are still many issues to be resolved regarding its scaling, continuity, and automation – these are all things you need to consider when putting it into practice. In short, thorough consideration is needed to develop a detailed feasibility plan.

Adding a microwave generator would speed up the drying rate; I think it is feasible.

““A requirement to dry the recovered liquid ammonia” shouldn’t be part of the experimental setup. As it involves large-scale industrial production, although I have never used such equipment, I believe the idea of installing a microwave generator inside the device to speed up the drying process is not feasible. The reasons are as follows: First, the cost is too high. I just checked the microwave oven at home; it has a power of 1300W, and it cost over 600 yuan when it was purchased. The principle behind this thing is the same as what the original poster said. Some time ago, the research institute planned to conduct an industrial experiment in one of our factory’s processes to examine the impact of accelerating the concentration rate on the quality of the intermediate products. Requirements: Steam consumption of 8–10 t/h, at 0.8 Mpa. Due to insufficient pressure limitations of the boiler, the temperature of the saturated steam was too low (only 0.6 Mpa). We contacted some of the better microwave equipment manufacturers in China in order to have the material heated before it is fed in, but we were told that there are no ready-made devices with such high power; they would have to be custom-made, and the investment required would be over one million yuan (I think it’s not feasible to carry out such a project). II. The manufacturing and maintenance of high-power microwave generators are relatively difficult. The frequency of microwaves is 240 megahertz or higher; the principle of drying relies on the vibration and friction of molecules and atoms within the material, occurring hundreds of millions of times per second, which generates heat and thus leads to heating. It is an electromagnetic wave with an extremely high frequency. Ignoring the issue of negative pressure, most companies in the industry roughly calculate based on a microwave output power of 1 Kw to dry 1 kg of water within 1 hour. A 1KW microwave can roughly dry 0.7-0.9kg of water in 1 hour. The poster might as well roughly estimate what power level the microwave generator needs to have in order to be practically useful. After checking some information, it turns out that the larger microwave dryers used in China’s food industry and tile manufacturing sector have a capacity of 35 Kw. Microwave generators of over 100 KW have not been reported. PS: High-frequency induction welding (several hundred kilohertz) uses alternating current generated by the principle of oscillation. In high-power applications, vacuum tubes are also commonly used; MOSFETs, IGBTs, SCRs, etc., are not very suitable. The difficulty of manufacturing high-power microwave generators is evident (the most likely applications are probably for military communications, jamming devices, etc.). Thirdly, the environmental conditions required are difficult to meet; those who have used induction cookers know that the items to be heated must be placed in non-conductive containers. Otherwise, a “short circuit” can occur, which may easily damage the magnetron. The instructions also state that one should stay at a distance of more than 1 meter from the microwave oven while it is in use. PS: Those who are exposed to high-frequency induction heating should know that insomnia and only having daughters are by no means exaggerations. “Adding a microwave generator inside the device is difficult to meet the requirements of the operating environment, and it inevitably increases costs. So I think microwave heating makes sense in principle here, but it is difficult to meet the requirements of practical use. Give it a try: grab a handful of material and use the microwave oven on the scrap disposal station to see how much heating effect can be achieved. The original poster might as well talk about your manufacturing processes and the “design flaws,” so we can all work together to find solutions.

What was said upstairs is great! There is a huge difference between large-scale industrial applications and small laboratory setups!

Microwaves are a type of electromagnetic wave that can generate high-frequency electromagnetic fields. Dielectric materials are composed of polar and non-polar molecules. Under the influence of an electromagnetic field, the polar molecules shift from their original random distribution to an arrangement aligned with the polarity of the electric field. In the presence of a high-frequency electromagnetic field, the movement of these molecules and their mutual friction generate energy, which causes the temperature of the dielectric material to rise continuously. Because the frequency of the electromagnetic field is extremely high, the vibration frequency of polar molecules is also very high, resulting in a large amount of heat being generated. When microwave heating is applied in the food industry, under the action of high-frequency electromagnetic fields, polar molecules (water molecules) in the food absorb microwave energy and generate heat, thereby rapidly heating and drying the food. Water and other wet media have corresponding saturation temperatures under certain partial pressures of the medium. The greater the degree of vacuum, the lower the saturation temperature of the water contained in the wet material or of the wet media itself; in other words, the boiling point is lower, making it easier for the water to vaporize and escape, thereby drying the material. Vacuum drying takes advantage of this thermophysical property by using a vacuum pump to remove low-pressure water vapor and other non-condensable gases with low concentrations in the gas phase, under vacuum conditions. During vacuum drying, the dehydration of the material relies on heat conduction to transfer external heat to the material being dried. However, in a low-pressure environment, heat transfer by convection is slow, which hinders the full utilization of the advantages of vacuum drying. Microwave drying utilizes the principle of dielectric heating; high-frequency electromagnetic oscillations are used to induce molecular movement, thereby heating the material. This heating method differs from traditional convection, conduction, and radiation heating, as microwaves directly heat the object, eliminating the constraint posed by heat transfer. Microwave vacuum drying combines the techniques of microwave drying and vacuum drying, taking full advantage of each other’s strengths. Under a certain level of vacuum, the rate of water diffusion increases, allowing the materials to be dried at low temperatures while preserving their nutritional components effectively. Microwaves can provide a heat source for vacuum drying, overcoming the drawback of slow conventional heat conduction in a vacuum environment; as a result, **the drying time is reduced and production efficiency is increased. Therefore, in principle, it is entirely possible for a microwave vacuum dryer to separate magnesium chloride from liquid ammonia, and the separation speed is also fast. But what the original poster needs to consider is whether this device can meet the demands of large-scale industrial production, such as its capacity and level of automation in relation to large-scale industrial applications. Therefore, the original poster suggests that careful consideration should be given to develop a feasible plan.

Microwave heating of objects is a form of overall heating that penetrates deep into the interior, rather than the traditional heating from the outside in, which results in a faster heating rate. Microwave technology is not yet very mature, and it is not widely used in industrial production; at least I have not come across any reports on that. Moreover, the investment required for microwave heating is high, and it should also have some impact on the health of the operators. Microwave heating is widely used in the laboratory stage; it is also feasible for small-scale production. I have used microwaves for nitrification in the laboratory before – it takes about 20 minutes to carry out soil nitrification using this method. Traditional soil nitrification requires the use of nitric acid and sulfuric acid in two separate steps, and it takes more than an hour to complete; thus, microwave heating saves electricity in this case. I previously submitted a suggestion to my workplace, recommending that instead of using aqua regia to dissolve platinum in the process of producing carbon monoxide as an oxidizing agent – a method that is time-consuming, labor-intensive, energy-heavy, and carries a high risk level – a microwave device should be introduced, as it would allow platinum to be dissolved using nitric acid alone. Unfortunately, this suggestion was not accepted, even though the experiment was successful. For ammonia recovered liquid that appears to be dry, infrared heating can be used; it requires much less investment compared to microwave heating, and the results are quite good. This method was effectively used in reaction vessels during the production of T501, with low energy consumption as well.

The question posed by the original poster isn’t clear; I assume it relates to the drying and dehydration of magnesium chloride after treating ammonia water with it. Compared with traditional drying techniques, microwave drying has many advantages. However, it is undeniable that microwave drying requires significant investment, and at present this technology is mainly used for drying pharmaceuticals. Since your issue is a design flaw, make targeted modifications.