Several temperature control schemes for tank-type equipment and their applications

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This post was last edited by yunrun on 2019-7-31 at 19:19. Temperature control in tank equipment simply refers to the process of adjusting the temperature of the material to meet the desired level. This article compares the advantages and disadvantages of several approaches to temperature control in tank equipment, providing a reference for such control measures. There are usually several ways to regulate the temperature of materials in tank-type equipment: ① Directly bringing the heating or cooling medium into contact with the materials ； ②Heat transfer through the tank’s jacket ； ③Use a heat exchanger. During the temperature regulation process, the temperature controller uses the temperature signals provided by the temperature sensors to control the timing and intensity of the flow of heating or cooling medium, thereby regulating the temperature of the material inside the tank to meet the requirements of the process. The choice of temperature control scheme is usually determined by the structure of the tank equipment, process conditions, and investment costs. Changhui Instruments presents several common temperature control solutions for tank-type equipment for your reference. 1. Temperature control system for introducing heating or cooling medium into the tank jacket. The principle behind the design of this system is partitioned heat exchange, characterized by hot and cold fluids being separated by a solid wall, with heat transfer occurring through that solid wall. In this design, steam and refrigerant are directly introduced into the jacket; due to the difference in temperature from the material inside the tank, heat transfer occurs through the tank wall, thereby raising or lowering the temperature of the material. The system controls the temperature of tanked materials by regulating the duration and intensity of steam or refrigerant supply. Temperature control systems that use heating or cooling media fed into the jacket of tanks are widely used for temperature control in solution preparation tanks and material storage tanks, as well as in some reaction tanks. ①Temperature control system without refrigerant recirculation. The temperature control system without refrigerant recirculation is shown in Figure 1; when temperature control of the material is not required, no steam or refrigerant is introduced into the jacket. When the material inside the tank needs to be heated or kept at a high temperature, steam is introduced from the upper interface of the jacket. Upon coming into contact with the cooler wall of the tank, the steam releases heat and condenses into a liquid, which then flows down along the wall surface due to gravity. Meanwhile, heat is transferred through the tank wall to the material inside, thereby raising its temperature or maintaining it at a high level. When temperature control is completed, the supply of steam is stopped, and compressed air is introduced from the upper part of the jacket to purge the remaining steam and condensed water inside it; once purging is complete, the compressed air supply is turned off. When the material inside the tank needs to be cooled or kept at a low temperature, the refrigerant is introduced from the lower interface of the jacket. Upon coming into contact with the wall of the tank, which is at a higher temperature, the refrigerant absorbs heat through heat transfer; as the refrigerant continues to flow in and out, the temperature of the material is reduced. When the cooling process is complete, stop the supply of refrigerant. Then, introduce compressed air from the upper part of the jacket to blow out any remaining refrigerant in the jacket into the waste discharge pipe; once it has been completely blown out, turn off the compressed air. A safety valve must be installed in the jacket piping to prevent safety accidents caused by excessive pressure in the jacket. A temperature sensor needs to be installed inside the tank to monitor the real-time temperature of the material. A steam trap should be installed at the condensate discharge point of the jacket to ensure smooth drainage of the condensate. To ensure the precision of temperature control, it is necessary to use a thermostat to regulate the timing and intensity of the steam or coolant supplied to the jacket, and to make timely feedback adjustments based on the real-time temperature of the material. Temperature control systems without refrigerant recirculation are widely used in the pharmaceutical industry for the temperature control of solution preparation tanks and material storage tanks whose cooling medium is water, as well as some reaction tanks. http://yunrun.com.cn/upload/201907/31/201907310102131689.png Figure 1: Temperature control system without refrigerant recirculation. ② Temperature control system with refrigerant recirculation. When it is necessary to reuse the refrigerant as much as possible in order to save operating costs or reduce pollutants, the refrigerant remaining in the jacket after heat exchange is not discharged directly, but is instead recovered entirely through recirculation pipes. The temperature control system for refrigerant backflow is shown in Figure 2; this design includes refrigerant backflow pipes installed at appropriate locations. The process control for raising and maintaining the temperature of the material is the same as that of the temperature control system with no refrigerant recirculation. When temperature control is completed, the supply of refrigerant is stopped, and compressed air is introduced from the upper part of the jacket to purge it, forcing the remaining refrigerant in the jacket into the return pipeline for recovery. In pharmaceutical production, this design scheme can be employed when cooling media for tank equipment are not water but solutions such as ethylene glycol. http://yunrun.com.cn/upload/201907/31/201907310112086229.png Figure 2: Temperature control system for refrigerant recirculation. 2. Temperature control system in which the heating or cooling medium is introduced directly into the tank. The principle of this temperature control system is mixed heat exchange; its characteristic is that the hot and cold fluids exchange heat with each other directly within the tank. In this design, steam and refrigerant are introduced into the tank, where they mix directly with the material to facilitate heat transfer, thereby raising or lowering the temperature of the material or maintaining it at a constant level. Compared with the jacket temperature control method, this design results in a significant increase in both the heat transfer coefficient and the heat exchange area, offering advantages such as high heat transfer rates and simpler equipment. The system controls the duration and intensity of the steam or refrigerant supplied, in order to regulate the temperature of the material inside the tank. However, since the heating or cooling medium in this system comes into direct contact with the material, a risk assessment is required to ensure that it has no adverse effect on the material’s properties. The temperature control system, in which a heating or cooling medium is directly introduced into the tank, is shown in Figure 3; when temperature control is not required for the material, no steam or coolant is introduced into the tank. When the material inside the tank needs to be heated or kept at a high temperature, steam is introduced from the steam interface. Upon coming into contact with the material at a lower temperature, the steam releases heat and condenses into a liquid, thereby raising the temperature of the material or keeping it at a high level. Meanwhile, the condensed water remains in the tank and mixes with the material. When heating is complete, stop supplying steam. When the material inside the tank needs to be cooled or kept at a low temperature, the refrigerant is introduced from the refrigerant inlet. Upon coming into contact with the material at a higher temperature, the refrigerant absorbs heat, thereby cooling the material or keeping it at a low temperature; meanwhile, the refrigerant remains inside the tank and mixes with the material. When the cooling is complete, stop supplying the refrigerant. Since both the condensed steam and the refrigerant remain inside the tank after being added, when using this method for temperature control, it is necessary to consider the amount of steam and refrigerant that needs to be added in order to achieve the desired temperature control effect. This system can be used for temperature control of materials for which high control precision is not required and that are not sensitive to temperature, as well as for temperature control in treatment tanks used for deactivating waste. For example, this temperature control system can be used for the inactivation tanks of bacteriologically contaminated waste liquids in the workshop for recombinant protein drug bulk solutions. http://yunrun.com.cn/upload/201907/31/201907310123583701.png Figure 3: Temperature control system in which the heating or cooling medium is introduced directly into the tank. 3. Temperature control system that achieves indirect temperature control via a jacket, using a temperature control circuit. The principle of this temperature control system, which relies on interwall heat exchange, is that it requires a temperature control circuit composed of a jacket, pipes, pumps, heat exchangers, a temperature controller, and temperature sensors. The temperature control circuit is filled with a heat carrier, which circulates continuously driven by a pump. As it passes through the jacket, it exchanges heat with the material inside the tank, thereby raising or lowering its temperature or maintaining it at a specific level. The heat carrier can be water, or it can be heat transfer oil, etc. The system regulates the temperature of the heat carrier through a heat exchanger, and controls the temperature of the material inside the tank via interwall heat exchange in the jacket. The system requires valves for the replacement and replenishment of the heat transfer fluid, as well as an expansion tank or expansion vessel to maintain stable pressure of the heat transfer fluid in the circuit. The temperature control system that uses a temperature control loop for indirect jacketed temperature control is shown in Figure 4; when the material does not require temperature control, the temperature control loop can either remain inactive or operate without performing any temperature control. When the material inside the tank needs to be heated or kept at a high temperature, the heat carrier in the temperature control circuit is heated; this heat carrier then transfers the heat through the jacket and to the material inside the tank, thereby raising its temperature or maintaining it at a high level. When the material inside the tank needs to be cooled or kept at a low temperature, the heat carrier in the temperature control circuit is cooled; this cold fluid then flows through the jacket, removing heat from the material inside the tank via the tank walls, thereby cooling the material or maintaining it at a low temperature. When temperature control is completed, the operation of the pump in the temperature control circuit or the temperature control of the heat carrier is stopped, thereby ending the temperature control of the material. If necessary, a compressed air inlet can also be provided on the circuit to purge the entire circuit or the jacket section. The temperature of the material inside the tank is controlled through a heat carrier in the jacket, and this heat carrier is regulated by a heat exchanger in the temperature control circuit. Since heat transfer occurs twice via the partition walls, the efficiency of heat exchange is not high; however, this system enables high precision in temperature control. Since the temperature control circuit does not come into direct contact with the material, there is no need for components to meet hygienic design requirements, resulting in lower construction costs. A temperature control system that uses a temperature control loop for indirect jacketed temperature control is generally employed in pharmaceutical production processes where high temperature accuracy is required, long-term temperature control is necessary, and the materials should not be subjected to intense stirring. Such systems can be used in devices like pasteurization tanks or S/D inactivation tanks used in the production of blood products. http://yunrun.com.cn/upload/201907/31/201907310135175535.png Figure 4: Temperature control system with indirect temperature control via a jacket through a temperature control circuit. 4. Temperature control system with direct temperature control inside the tank through a temperature control circuit. The principle of this temperature control system, which enables direct temperature control inside the tank via a temperature control circuit, is based on partitioned heat exchange. It consists of a circulation system made up of a temperature control circuit and tank-type equipment, with the temperature control circuit comprising pipes, pumps, heat exchangers, instruments, etc. The material is stored in tank-like equipment, where it circulates continuously within a temperature-controlled circuit via pumps. As it passes through the heat exchanger, it is heated or cooled, after which it returns to the tank to mix with other materials. Temperature sensors located in the tank provide feedback, which is used to adjust the timing and intensity of the steam or coolant flow into the heat exchanger, thereby enabling control over the temperature of the material. The temperature control system that enables direct temperature control inside the tank through a temperature control circuit is shown in Figure 5; when no temperature control is required for the material, the temperature control circuit can either not operate at all or operate without performing temperature control. When temperature control is required for the material inside the tank, the pump in the circuit is turned on to circulate the material within the tank equipment and the temperature control circuit. As the material passes through the heat exchanger, it is heated or cooled, after which it returns to the storage tank to mix with other materials before entering the circuit again. Through this continuous circulation, the temperature of the material is adjusted or maintained at an appropriate level. In this design, the temperature of the material inside the tank is heated or cooled directly through a heat exchanger; only one stage of heat transfer across a partition is required, which results in high heat transfer efficiency. Moreover, this system also enables high precision in temperature control. In this design, the materials need to circulate within a temperature-controlled circuit; therefore, all components of the system that come into contact with these materials must meet the relevant GMP requirements, so as not to have any adverse effect on the quality of the drugs. This results in increased costs for construction and maintenance. A temperature control system that enables direct temperature control inside the tank through a temperature control loop is suitable for material systems that can be stored centrally, require simultaneous supply to multiple usage points, have high temperature requirements, and can tolerate intense agitation – such as temperature control in pharmaceutical water distribution systems and low-temperature ethanol systems used in blood product production. http://yunrun.com.cn/upload/201907/31/201907310152492161.png Figure 5: Application analysis of the temperature control system that enables direct temperature control inside the tank through a temperature control circuit. Different production processes have varying requirements regarding temperature control of the materials, and designers must select appropriate design solutions based on these different conditions. The design schemes mentioned above are the basic ones. In practical applications, in addition to using a particular design scheme alone, it is also possible to simplify a certain scheme or combine variations of several schemes together. The following introduces several typical application scenarios: ① Solution storage tank – For conventional solution storage tanks, cooling functionality is usually sufficient, as long as the temperature remains below a specified level. In such cases, the temperature control system that involves heating or cooling media can be simplified; only the cooling function needs to be retained. See Figure 6 for details. http://yunrun.com.cn/upload/201907/31/201907310157545181.png Figure 6: Temperature control design for solution storage tanks that require only cooling functionality. ② Biological waste inactivation tank: The biological waste inactivation tank can be designed by combining the features of a temperature control system in which heating or cooling media are introduced directly into the tank, with those of a temperature control system in which such media are introduced directly into the jacket. In this design, steam is introduced into the tank for direct heating, while a coolant is used in the jacket for indirect cooling. This approach not only increases the rate at which waste is inactivated but also raises the amount of waste that can be processed per batch; see Figure 7 for details. http://yunrun.com.cn/upload/201907/31/201907310201461155.png Figure 7: Temperatures in biowaste inactivation tanks under direct heating and indirect cooling conditions. ③ Tank equipment with more complex processes: For some tank devices with more complex processes, such as fermentation tanks, a temperature control system that involves the direct use of heating or cooling media supplied to the jacket, along with a temperature control system that regulates the jacket temperature through a temperature control circuit, can be employed – as shown in Figure 8. In the temperature control circuit, inlets for steam and refrigerant are added; a temperature control system that uses heating or cooling media directly supplied to the jacket is employed during the sterilization of the culture medium, thereby improving heat exchange efficiency and reducing processing time. During fermentation, a temperature control system that uses a jacket for indirect temperature regulation through a temperature control circuit is employed to ensure stable and precise cultivation temperatures, allowing production to proceed strictly in accordance with the established process. http://yunrun.com.cn/upload/201907/31/201907310209083062.png Figure 8: Temperature control design for fermenters, enabling rapid sterilization of the culture medium and precise temperature regulation during the fermentation process. In addition to the conditions listed above, there are many other scenarios regarding temperature control in tank-type equipment. In the engineering design of temperature control systems for tank-type equipment, it is necessary to take into account both construction costs and regulatory requirements, while also ensuring that the production process can be met, in order to develop temperature control systems that satisfy all relevant requirements. The design concepts and operation methods of several temperature control systems described in the text have been effectively applied in actual production processes, and these control schemes can serve as a reference for designing temperature control systems. Author: Yan Liujun Source: Technology Library yunrun.com.cn/tech/