Several Different Heating Methods for Jacketed Stirring Equipment

The "jacket" of the stainless steel jacketed agitator tank is a closed chamber formed by the outer wall of the tank and the outer shell. The core logic of heating is that the heat medium circulates within the jacket and transfers heat to the internal materials through heat conduction on the tank wall, ultimately achieving the temperature rise or constant temperature of the materials. According to the different types of heat media, the mainstream heating methods are divided into four types: steam heating, electric heating, heat transfer oil heating, and hot water heating. The principles, structures, and applicable scenarios of each method are significantly different. The following is a detailed analysis:

I. Steam Heating: The preferred choice for high efficiency and low cost in medium and low temperatures 1. Core principle: Saturated steam is used as the heat medium, and the heating is achieved by taking advantage of the characteristic that steam "condenses and releases latent heat". After saturated steam is conveyed from the external boiler to the jacket, the tank wall in contact with the lower temperature will rapidly condense into liquid water. During this process, a large amount of latent heat is released (the heat released by the condensation of 1kg of saturated steam is approximately 2200kJ, which is more than five times the heat released by the heating of the same mass of hot water), and the heat is transferred to the material through the tank wall. The condensed water (condensate water) is discharged from the jacket through the steam trap to prevent water accumulation from occupying the jacket space and reducing heat exchange efficiency. 2. Core components - Steam supply system: External steam boiler (providing saturated steam at 0.1-1.0MPa, pressure determines steam temperature, normal pressure steam temperature ≈100℃, 0.6MPa steam temperature ≈158℃), steam pipeline (insulation is required to reduce heat loss); - Jacket accessory components: Pressure reducing valve (stabilizes the steam pressure entering the jacket to prevent sudden temperature changes caused by pressure fluctuations), steam trap (core component, only discharges condensate water but not steam to prevent steam waste), pressure gauge (real-time monitoring of jacket steam pressure to avoid overpressure), safety valve (automatically releases pressure when pressure exceeds the standard to ensure equipment safety). - Temperature control system: A PT100 platinum resistance sensor is inserted into the tank to detect the material temperature in real time. The steam intake is controlled by an electromagnetic valve to achieve closed-loop temperature control (temperature control accuracy ±2-3℃). 3. Advantages and Disadvantages Analysis - Advantages: ① Extremely high heat exchange efficiency, large latent heat of steam, and fast material heating speed (3-5 times faster than hot water heating); ② The operating cost is low. Steam can be supplied centrally in the factory or produced by small boilers, and the energy cost is much lower than the electricity cost. ③ It has good temperature uniformity, with steam evenly distributed within the jacket and no risk of local overheating. It is suitable for processes with high requirements for temperature uniformity (such as cooking food sauces). - Disadvantages: ① High initial investment, requiring a steam boiler (including boiler approval, installation, and annual inspection), which is difficult for small enterprises to afford; ② The upper limit of temperature is limited. The steam temperature is determined by the pressure. The maximum temperature of conventional steam is ≤160℃ (1.0MPa), which cannot meet the requirements of high-temperature processes. ③ Regular maintenance of the steam trap is required. If the steam trap is clogged or fails, the condensate water will remain in the jacket, causing a sudden drop in heat exchange efficiency and even leading to "water hammer" (condensate water being pushed by steam and hitting the jacket wall, generating noise and equipment damage). 4. Applicable scenarios - Temperature requirements: Medium and low-temperature processes (50-160℃); - Industry and Materials: Food processing (sauce and jam preparation), Pharmaceutical preparations (preheating of oral liquid before sterilization), chemical industry (dissolution with common solvents, reaction of low-boiling-point materials); - Equipment compatibility: It is preferred to be matched with "full jacket" agitator tanks (full jacket has a large heat exchange area and is suitable for uniform steam distribution). It is not suitable for high-pressure scenarios (steam pressure is usually ≤1.0MPa, and the jacket does not require special pressure-resistant design).

Ii. Electric Heating: The preferred choice for small capacity with flexible installation and precise temperature control. 1. Core Principle: Using electrical energy as the source, it is heated indirectly through the process of "electric heating elements heating the heat transfer medium → medium transferring heat to the tank wall". Fill the jacket with heat transfer oil (or water, but oil has better heat resistance), and insert the flange-type electric heating tube (mostly made of 316L stainless steel, anti-corrosion) into the heat transfer medium of the jacket. After being powered on, the electric heating tube heats up, first heating the heat-conducting medium in the jacket to the target temperature. Then, through the medium circulation (natural convection or forced circulation, some equipment is equipped with a small circulation pump), the heat is transferred to the tank wall, ultimately heating the material. 2. Core components - Heating elements: 316L stainless steel electric heating tubes (power is matched according to the size of the tank. 1000L tanks are usually equipped with 3-6kW electric heating tubes, with multiple groups connected in parallel for easy power adjustment). "Anti-dry burning design" is required (if the medium leaks, the temperature of the electric heating tube will rise sharply, triggering the thermal relay to cut off the power). - Heat transfer medium: Usually high-temperature heat transfer oil (with a temperature resistance of 200-300℃, such as 320 # heat transfer oil), avoid water (water has a low boiling point and is prone to scaling and clogging the jacket at high temperatures); - Temperature control system: Dual temperature sensors (respectively detecting the temperature of the heat transfer medium and the material), digital display temperature controller or PLC, which can precisely control the start and stop of the electric heating tube, with a temperature control accuracy of ±1℃ (much higher than steam heating). - Safety components: Thermal relay (power off when the electric heating tube is overloaded or dry-burned), temperature fuse (melts at extreme high temperatures to cut off the power supply), medium level gauge (monitors whether the heat transfer medium is sufficient to prevent dry-burning). 3. Advantages and Disadvantages Analysis - Advantages: ① Flexible installation, no need for external boilers or steam pipes, only 220V/380V power supply is required, suitable for laboratories, small workshops or scenarios without steam sources; ② The temperature control accuracy is extremely high, which can meet the requirements of processes in the pharmaceutical, electronic and other industries that are sensitive to temperature fluctuations (for example, enzyme preparation reactions require a constant temperature of 37℃±0.5℃). ③ The equipment is compact in size, has few supporting components (no boiler or steam trap), occupies a small area and is easy to maintain. - Disadvantages: ① High operating costs. The efficiency of converting electrical energy into thermal energy is approximately 85% to 90%, and the heat transfer medium dissipates heat quickly. The long-term operating electricity cost is much higher than that of steam or heat transfer oil furnaces. ② The heating efficiency is limited by capacity. For large-capacity tanks (≥5000L), multiple sets of electric heating tubes are required. The limited space in the jacket leads to poor medium circulation, resulting in a slow heating rate (2-3 times slower than steam heating). Electric heating tubes are prone to scaling. If the purity of the heat transfer medium is low or they operate at high temperatures for a long time, a scaling layer will form on the surface of the electric heating tubes, affecting the heat transfer efficiency. Therefore, the electric heating tubes need to be disassembled, cleaned or replaced regularly. 4. Applicable scenarios - Temperature requirements: Low to medium-high temperatures (50-250℃, depending on the temperature resistance of the heat transfer oil); - Industry and Materials: Laboratory small-scale/medium-scale trials (such as small-scale sample preparation), pharmaceutical industry (precise temperature-controlled synthetic reactions), small-scale production without steam sources (such as heating of cosmetic pastes); - Equipment compatibility: Suitable for small-capacity agitator tanks (≤5000L). The jacket needs to be "sealed" (to prevent leakage of the heat transfer medium), and it is preferred to be paired with a "half-tube jacket" (the half-tube jacket has good pressure resistance and can withstand the high-temperature expansion pressure of the heat transfer oil).

Iii. Heat Transfer Oil Heating: The Only Reliable Choice for High-temperature Processes 1. Core Principle: Using high-temperature heat transfer oil as the heat medium, heating is achieved through a closed cycle of "heating the heat transfer oil in the heating furnace → transporting the hot oil by the circulating pump → releasing heat from the jacket → recirculating the cold oil". The external heat transfer oil furnace (fuel oil/gas/electric heating type) heats the heat transfer oil to 200-320℃ (depending on the type of heat transfer oil, for example, the maximum temperature resistance of 320 # heat transfer oil is 320℃), and the high-temperature circulating pump presses the hot oil into the jacket of the stirring tank. When the hot oil flows in the jacket, it transfers heat to the material through the tank wall. The cooled heat transfer oil flows back from the jacket outlet to the heating furnace, is reheated and then enters the next cycle. 2. Core component - Heat transfer Oil heating System Thermal oil furnace (core equipment, oil/gas furnaces suitable for large-capacity tanks, electric heating furnaces suitable for small-capacity tanks), high-temperature circulating pump (temperature resistance ≥350℃, ensuring forced circulation of thermal oil in the system and avoiding local overheating), expansion tank (balancing the volume of high-temperature expansion of thermal oil, discharging air and moisture in the system (To prevent the oxidation and deterioration of heat transfer oil), oil storage tank (for storing heat transfer oil when the system is shut down); - Jacket and pipes: The jacket should preferably be a "half-pipe jacket" (the half-pipe is welded to the outer wall of the tank, with strong pressure resistance, capable of withstanding the high temperature and high pressure of the heat transfer oil, and avoiding cracking of the full jacket due to thermal expansion and contraction). The pipes should be made of seamless steel pipes (with a temperature resistance of ≥350℃) and insulated (to reduce heat loss). - Temperature control and safety system: Heat transfer oil temperature sensor, material temperature sensor (dual temperature control to prevent heat transfer oil or material from overheating), pressure sensor (monitoring the pressure of the circulation system), explosion-proof valve (automatic pressure relief in case of heat transfer oil leakage and fire), heat transfer oil leakage detector (to prevent leakage from causing safety accidents). 3. Advantages and Disadvantages Analysis - Advantages: ① High upper limit of temperature, capable of achieving high-temperature heating from 160 to 320℃, making it the only method that can meet the requirements of high-temperature chemical processes (such as resin polymerization and coating curing); ② It has good temperature stability. The temperature fluctuation of the heat transfer oil during circulation is small (±1℃), and there is no problem of sudden temperature drop caused by steam condensation water. It is suitable for long-term constant-temperature processes. ③ It is compatible with large-capacity tanks. The forced circulation heat transfer oil can evenly cover the large jacket, and the heat exchange efficiency is stable (the heating rate of a 10,000L tank can reach 5-8℃/h). - Disadvantages: ① High initial investment, requiring the installation of systems such as heat transfer oil furnaces, circulating pumps, and expansion tanks, with equipment costs 30% to 50% higher than steam heating. ② The maintenance cost is high. The heat transfer oil needs to be replaced every 3 to 5 years (it is prone to oxidation and deterioration at high temperatures, affecting the heat transfer efficiency), and the system needs to be cleaned regularly (to avoid coking and blockage of the pipes). ③ The safety risk is high. The heat transfer oil is flammable (flash point ≥180℃). If the pipeline leaks or overheats, it is easy to cause a fire. Explosion-proof design and regular safety inspections are required. 4. Applicable scenarios - Temperature requirements: High-temperature processes (160-320℃); - Industry and Materials: Chemical industry (resin synthesis, polymerization of polymer materials, asphalt heating), Building materials industry (preheating of ceramic slurry before drying), Pharmaceutical industry (high-temperature sterilization or solvent distillation); - Equipment compatibility: Suitable for medium and large capacity tanks (≥5000L), it must be equipped with a "half-tube jacket" (pressure-resistant and resistant to thermal expansion and contraction), and the workshop needs to undergo explosion-proof treatment (such as explosion-proof lamps, explosion-proof motors).

Iv. Hot Water Heating: Exclusive for mild and safe low-temperature heat-sensitive materials. 1. Core principle: Using hot water as the heat medium, heating is achieved through the "sensible heat transfer" of hot water: An external hot water boiler (or electric heating water tank) heats the water to 40-95℃ (below the boiling point of water to avoid steam generation), and the hot water is then transported to the jacket by a circulating pump. When hot water flows in the jacket, it transfers heat to the material through the tank wall (after the hot water temperature drops by 3-5℃), and then flows back to the hot water boiler from the jacket outlet for reheating and recycling. 2. Core components - Hot water supply system: Hot water boiler (mostly electrically heated or gas-heated, with temperature controlled below 95℃ to prevent boiling), circulating pump (low head, large flow rate to ensure uniform hot water flow within the jacket); - Jacket and pipes: The jacket is selected as "full jacket" (with a large heat exchange area, suitable for uniform heating at low temperatures), and the pipes are made of ordinary steel pipes (no need for high-temperature resistance), which can be simply insulated (the hot water temperature is low, and the heat loss is small). - Temperature control system: Hot water temperature sensor, material temperature sensor (temperature control accuracy ±2℃), temperature control valve (regulating hot water intake and controlling heating rate); - Safety components: Level gauge (monitors the water level of the hot water boiler to prevent dry burning), relief valve (overflows when hot water expands to avoid system overpressure). 3. Advantages and Disadvantages Analysis - Advantages: ① Mild temperature, with a maximum temperature of ≤95℃, no risk of local overheating, suitable for heat-sensitive materials (such as milk, fruit juice, enzyme preparations), avoiding material denaturation or loss of activity due to high temperature; ② It has a high safety factor. Hot water is non-flammable and there is no high pressure. Even if there is a pipeline leak, it will not cause a safety accident. It is suitable for industries with extremely high safety requirements such as food and medicine. ③ It is clean and pollution-free. The hot water does not come into direct contact with the materials and can be recycled without contaminating the materials or generating harmful substances. It meets the hygiene standards of food grade (FDA) and pharmaceutical grade (GMP). - Disadvantages: ① Low heat exchange efficiency. The specific heat capacity of hot water (4.2kJ/kg·℃) is much lower than the latent heat of steam, and the heating rate is slow (the heating rate of a 1000L tank is only 1-2℃/h), which is not suitable for processes that require rapid heating. ② The upper limit of temperature is low, which cannot meet the process requirements above 100℃, and the application scenarios are limited. ③ It has a relatively high energy consumption. Hot water heating requires a continuous maintenance of water temperature, and the heat dissipation loss is greater than that of steam (even if it is insulated, the electricity or gas cost for long-term operation is still higher than that of steam). 4. Applicable scenarios - Temperature requirements: Low-temperature processes (40-95℃); - Industry and Materials: Food industry (milk preheating, juice blending, yogurt fermentation constant temperature), Pharmaceutical industry (oral liquid insulation, low-temperature reaction of biological preparations), cosmetics industry (gentle heating of face cream base materials); - Equipment compatibility: Suitable for small-capacity tanks (≤3000L), with priority given to "full jacket" (large heat exchange area to ensure low-temperature uniformity), and the inner wall of the tank body needs to be mirror-polished (Ra≤0.4μm, meeting hygiene and cleaning requirements).