The promotion of the use of indirect drying equipment with energy saving and environmental protection features is an important trend in the development of drying technology. This article focuses on the technical innovations such as the working principle and structural characteristics of the energy-efficient tube bundle dryer.
The new tube drying machine developed by Northeastern University Shenyang Yitong Venture Technology Co., Ltd. has greatly increased the thermal efficiency, 30% higher drying strength than conventional tube dryers, and the energy consumption of the equipment has reached the advanced level of similar products in China. It requires 1.2-1.5 tons of water per 1 kg of water evaporated. 1.3 kilograms of steam.
The core tube of the dryer is made of high-quality boiler steel pipe (GB3087). The advanced expansion joint technology completely solves the defect that the traditional welding process is prone to fracture at the weld seam. Both ends of the semi-axis turning, the precise coaxiality greatly improves the service life of the main bearing of the tube bundle and the smooth running of the tube bundle. According to the material drying characteristic curve design, the lifting uniform distribution tube blade can make different materials achieve the best drying effect.
1 Lifting even-distribution type shovel----completely mixed state The tube bundle dryer belongs to the stirring-type conduction heat exchanger dryer, which overcomes the above thermal resistance and guarantees a good drying effect. The key factor is the degree of stirring and mixing in the drying process. Since the law of the movement of the material inside the dryer is difficult to accurately describe, the particle coverage factor fR is generally determined by the actually measured data of the actually operating dryer.
Ordinary tube-bundle dryer - incompletely mixed state In an ordinary tube-bundle dryer, push-pull plates, tipping blades, and unloading shovel plates are distributed along the length direction. The main effect on the mixing state is the tipping blade. The type is lifting blade. The material began to fall at about 120°C and contacted with the heating surface of the tube bundle. After 4 contact processes, the material was removed from the heating wall to the material bed at the bottom of the dryer. This kind of blade will cause the stratification of the gas, and it will increase with the decrease of the number of rotation of the rotor and the increase of the diameter of the rotor. The advantage of using this blade is that the inner wall of the dryer is easy to clean, but the filling rate of the dryer is low, between 0.1-0.2.
New tube dryer - completely mixed state In the new tube dryer, the lifted uniform shovel is designed according to the drying characteristic of the material, enabling the material to fall at various angles of rotation, and the contact with the heating wall surface of the tube bundle is rotating. From all angles, so that the material tends to be completely mixed. Improves tube surface utilization and particle coverage factor fR According to the drying characteristics of the material, in the drying process, due to the change in water content, the state and properties of the material will also change accordingly, so the form of the shovel plate should be along the length Take several spade forms in the direction. In addition, the shape and angle of the same type of shovel blade should also be changed to ensure that the material is evenly distributed across the entire cross-section and the gas stratification is destroyed.
The new tube dryers are respectively arranged along the length direction of the pushing shovel plate, the tipping shovel plate, the equalizing shovel plate, and the unloading shovel plate. The main function of the mixing state is the tipping shovel plate and the uniform shovel blade. The type is: Lifting shovel board. This blade ensures that the material is well poured and spreads evenly over the entire cross section of the rotor.
According to the measured values, the tube bundle surface utilization rate is increased by more than 20% compared with the conventional tube bundle dryer, and the fR is increased by more than 30% compared with the conventional tube bundle dryer.
In addition, the relationship between the quantity, shape and filling factor of the shovel plate should be when the material on the shovel plate is the largest, and the material stored in the dryer should just cover the bare part of the shovel plate.
The number of shovel plates is related to the diameter of the rotor. Research at the Drying Institute of Tohoku University shows that the relationship between the general number and the rotor is: n=(10~14)D (D is the diameter of the rotor). The relationship between the height hR of the blade and the diameter of the rotor is shown in the following table:
2 siphon helium ---- non-condensing water retention hopper-type scoop bucket - suitable for high-speed equipment in the condensate discharge mechanism, the common tube dryer is a spoon-type hopper, this hopper with the tube bundle rotation, The condensed water in the head enters the mouth of the bucket. When the mouth is facing upwards beyond the horizontal axis, the condensed water that falls into the bucket is discharged through the hollow shaft.
The disadvantage of this kind of bucket is that there is always water in a certain horizontal plane of the tube bundle, steam exists only in the upper tube, and the condensed water in the lower tube cannot be discharged in time, which affects the steam utilization rate and thermal efficiency. At the same time, in the process of discharging the condensate, it is inevitable to take part of the steam and increase the steam loss.
Siphon pick - suitable for low-speed equipment The new tube dryer replaces the common scoop-type spade bucket with a siphon, which uses the pressure difference between the vapor pressure inside the heat exchanger and the trap. The condensate flows through the bottom of the heat exchanger. The nozzle is continuously discharged. The gap between the nozzle and the bottom wall is generally controlled at 5-10mm. The diameter of the pipe is determined by the amount of condensing water. Generally, the small cylinder adopts a DN15mm and the large cylinder adopts a siphon tube of DN20-25mm; the other end is fixed in the inlet. Steam turbine components.
The siphon hydrazine not only reduces the loss of steam, but more importantly there is no condensate water remaining in the bilge pipe at the bottom of the bundle. The actual heating and drying area is greatly increased, and the utilization rate of steam is increased. And this kind of bucket, in the timely discharge of condensate, basically no steam loss.
3 Jet technology ---- increase the heat transfer coefficient of the inlet section The way of entering the steam is improved from the ordinary filling mode to the jet entry mode. This is the application of the free jet enhanced heat transfer technology in the steam heat transfer. At the entrance of the wet material, the steam velocity is higher than that of other parts, thus forming a partial pulse flow of steam. On the one hand, a jet is formed on the end tube sheet, which improves the heat transfer effect of the end tube sheet, and also the layer of the inlet section. The flow state is changed to a turbulent state, which means that the increase of the steam velocity increases the local heat transfer coefficient.
Convection Heat Transfer Rate Equation: Newton's Cooling Law Based on "rate equals pushing force divided by resistance", it also equals a coefficient multiplied by the driving force.
Thermal fluid dQ =ds α(T-TW )
Cold fluid dQ =ds α (tW-t)
Where: α: local convection heat transfer coefficient; general use average convection heat transfer coefficient Q = α S Δt m
Δt m — average heat transfer temperature difference Due to the effect of local jets, the local heat transfer coefficient is correspondingly increased, and thus the heat transfer amount is increased.
The new tube drying machine developed by Northeastern University Shenyang Yitong Venture Technology Co., Ltd. has greatly increased the thermal efficiency, 30% higher drying strength than conventional tube dryers, and the energy consumption of the equipment has reached the advanced level of similar products in China. It requires 1.2-1.5 tons of water per 1 kg of water evaporated. 1.3 kilograms of steam.
The core tube of the dryer is made of high-quality boiler steel pipe (GB3087). The advanced expansion joint technology completely solves the defect that the traditional welding process is prone to fracture at the weld seam. Both ends of the semi-axis turning, the precise coaxiality greatly improves the service life of the main bearing of the tube bundle and the smooth running of the tube bundle. According to the material drying characteristic curve design, the lifting uniform distribution tube blade can make different materials achieve the best drying effect.
1 Lifting even-distribution type shovel----completely mixed state The tube bundle dryer belongs to the stirring-type conduction heat exchanger dryer, which overcomes the above thermal resistance and guarantees a good drying effect. The key factor is the degree of stirring and mixing in the drying process. Since the law of the movement of the material inside the dryer is difficult to accurately describe, the particle coverage factor fR is generally determined by the actually measured data of the actually operating dryer.
Ordinary tube-bundle dryer - incompletely mixed state In an ordinary tube-bundle dryer, push-pull plates, tipping blades, and unloading shovel plates are distributed along the length direction. The main effect on the mixing state is the tipping blade. The type is lifting blade. The material began to fall at about 120°C and contacted with the heating surface of the tube bundle. After 4 contact processes, the material was removed from the heating wall to the material bed at the bottom of the dryer. This kind of blade will cause the stratification of the gas, and it will increase with the decrease of the number of rotation of the rotor and the increase of the diameter of the rotor. The advantage of using this blade is that the inner wall of the dryer is easy to clean, but the filling rate of the dryer is low, between 0.1-0.2.
New tube dryer - completely mixed state In the new tube dryer, the lifted uniform shovel is designed according to the drying characteristic of the material, enabling the material to fall at various angles of rotation, and the contact with the heating wall surface of the tube bundle is rotating. From all angles, so that the material tends to be completely mixed. Improves tube surface utilization and particle coverage factor fR According to the drying characteristics of the material, in the drying process, due to the change in water content, the state and properties of the material will also change accordingly, so the form of the shovel plate should be along the length Take several spade forms in the direction. In addition, the shape and angle of the same type of shovel blade should also be changed to ensure that the material is evenly distributed across the entire cross-section and the gas stratification is destroyed.
The new tube dryers are respectively arranged along the length direction of the pushing shovel plate, the tipping shovel plate, the equalizing shovel plate, and the unloading shovel plate. The main function of the mixing state is the tipping shovel plate and the uniform shovel blade. The type is: Lifting shovel board. This blade ensures that the material is well poured and spreads evenly over the entire cross section of the rotor.
According to the measured values, the tube bundle surface utilization rate is increased by more than 20% compared with the conventional tube bundle dryer, and the fR is increased by more than 30% compared with the conventional tube bundle dryer.
In addition, the relationship between the quantity, shape and filling factor of the shovel plate should be when the material on the shovel plate is the largest, and the material stored in the dryer should just cover the bare part of the shovel plate.
The number of shovel plates is related to the diameter of the rotor. Research at the Drying Institute of Tohoku University shows that the relationship between the general number and the rotor is: n=(10~14)D (D is the diameter of the rotor). The relationship between the height hR of the blade and the diameter of the rotor is shown in the following table:
2 siphon helium ---- non-condensing water retention hopper-type scoop bucket - suitable for high-speed equipment in the condensate discharge mechanism, the common tube dryer is a spoon-type hopper, this hopper with the tube bundle rotation, The condensed water in the head enters the mouth of the bucket. When the mouth is facing upwards beyond the horizontal axis, the condensed water that falls into the bucket is discharged through the hollow shaft.
The disadvantage of this kind of bucket is that there is always water in a certain horizontal plane of the tube bundle, steam exists only in the upper tube, and the condensed water in the lower tube cannot be discharged in time, which affects the steam utilization rate and thermal efficiency. At the same time, in the process of discharging the condensate, it is inevitable to take part of the steam and increase the steam loss.
Siphon pick - suitable for low-speed equipment The new tube dryer replaces the common scoop-type spade bucket with a siphon, which uses the pressure difference between the vapor pressure inside the heat exchanger and the trap. The condensate flows through the bottom of the heat exchanger. The nozzle is continuously discharged. The gap between the nozzle and the bottom wall is generally controlled at 5-10mm. The diameter of the pipe is determined by the amount of condensing water. Generally, the small cylinder adopts a DN15mm and the large cylinder adopts a siphon tube of DN20-25mm; the other end is fixed in the inlet. Steam turbine components.
The siphon hydrazine not only reduces the loss of steam, but more importantly there is no condensate water remaining in the bilge pipe at the bottom of the bundle. The actual heating and drying area is greatly increased, and the utilization rate of steam is increased. And this kind of bucket, in the timely discharge of condensate, basically no steam loss.
3 Jet technology ---- increase the heat transfer coefficient of the inlet section The way of entering the steam is improved from the ordinary filling mode to the jet entry mode. This is the application of the free jet enhanced heat transfer technology in the steam heat transfer. At the entrance of the wet material, the steam velocity is higher than that of other parts, thus forming a partial pulse flow of steam. On the one hand, a jet is formed on the end tube sheet, which improves the heat transfer effect of the end tube sheet, and also the layer of the inlet section. The flow state is changed to a turbulent state, which means that the increase of the steam velocity increases the local heat transfer coefficient.
Convection Heat Transfer Rate Equation: Newton's Cooling Law Based on "rate equals pushing force divided by resistance", it also equals a coefficient multiplied by the driving force.
Thermal fluid dQ =ds α(T-TW )
Cold fluid dQ =ds α (tW-t)
Where: α: local convection heat transfer coefficient; general use average convection heat transfer coefficient Q = α S Δt m
Δt m — average heat transfer temperature difference Due to the effect of local jets, the local heat transfer coefficient is correspondingly increased, and thus the heat transfer amount is increased.