RU2017618C1 - Condensation unit for film casting machine - Google Patents

Abstract

FIELD: production of polymer films. SUBSTANCE: condensation unit for film casting machine is provided with vortical apparatus for mixing and additional fan. Suction line of the last is connected to the lower drying channel. Force-line connected to tangential inlet pipe of vortical apparatus and to the inlet pipe of upper drying channel. Outlet pipe of upper channel is connected to axial inlet pipe of vortical apparatus. Its inlet end is connected to the entrance into condenser. This enables to increase degree of fumes condensation of solvent owing to presence of vortical apparatus, to increase the flow speed in lower drying channel. EFFECT: increased output of casting machine. 1 dwg

Description

 The invention relates to the production of polymer films and can be used for the recovery of volatile solvents removed in the process of film formation.

 Known condensation installation for a casting machine containing fans, condensers, heaters (see Podgorodetskiy E.K. Technology for the production of films from high molecular compounds, M., Art, 1953, p. 131).

The steam-air mixture from the drying channel of the casting machine is supplied by the fan to the heat exchanger. Passing through the tubes of the heat exchanger, the steam-air mixture is cooled to 0 - -10 ^о С due to the cold air coming from the condenser and passing between the tubes.

A disadvantage of the known installation is the large surface of the heat exchanger (approximately equal to the surface of the condenser), which is a consequence of the small value of the coefficient of the heat exchanger (3-4 W / m ² K) from the cold air flow to the tube wall and from it to the steam-air mixture. Therefore, the increase in productivity of the casting machine is limited by the dimensions of the capacitors and the large mass.

 The closest in technical essence and the achieved effect to the invention is a condensation installation for a tape casting machine, containing fans, a condenser and a heater, connected by pipelines to the upper and lower channels of the casting machine (see ed. St. USSR N 1234204, class B 29 C 41/46, 1986).

A disadvantage of the known device is that the steam-air mixture of drying the casting channel of the machine is fed to a suction fan, and then under pressure at a temperature of 40-50 ^{° C} is supplied to the condenser. In this installation, a two-stage condenser system is used, connected in series along the steam-air mixture, in the first stage of which there is cooling and partial condensation of the solvent vapor, in the second stage, more complete condensation. This leads to the limitation of increasing the productivity of the casting machine, since it requires increasing the dimensions of the capacitor and its metal consumption.

 The objective of the invention is to increase the productivity of the installation.

 The problem is achieved in that in a condensation installation to a tape casting machine, containing fans, condensers and heaters connected by pipelines to the upper and lower channels of the casting machine, according to the invention, a vortex mixing apparatus and an additional fan are installed, the suction line of which is connected to the lower drying channel, discharge - with the tangential inlet pipe of the vortex apparatus and the inlet pipe of the upper drying channel, the outlet pipe of which is connected to sevym inlet of the vortex device, and the output end of the first unit is connected to the input of the condenser.

Increasing the degree of condensation of solvent vapors is achieved due to the fact that the established before the condenser, in the course of the vapor-air mixture, a vortex mixing apparatus by contact interacting streams of heated steam mixture at 40-50 ^{° C} is sucked by the discharge fan lines.

As a result of mixing of different streams of vapor temperature decreases to 5-6 ^{° C,} the surface of the capacitor is input at a higher speed more cold flow than in the prior art. At the same time, by introducing an additional fan into the suction line from the lower drying channel, the condensing unit according to the invention makes it possible to increase the flow velocity in the lower drying channel of the casting machine from 1.3 to 2.5-3.0 m / s, while maintaining the flow velocity in the upper drying channel is 0.5-0.7 m / s. An independent system for controlling the speed of the vapor-air mixture in both drying channels of the casting machine allows, by increasing the heat exchange from the flow and to the film, to accelerate the drying process and increase the productivity of the installation and casting machine according to the invention.

 In addition, when the vapor-air mixture is injected into the vortex mixing apparatus and further into the condenser, the rarefaction in it decreases, which in turn reduces the amount of air suction from the atmosphere. According to technology, nitrogen is supplied to the vapor-air mixture to maintain the oxygen concentration not higher than 12%. Reducing the suction of air from the atmosphere allows you to reduce the amount of nitrogen supplied to the stream of vapor-air mixture, which is energetically beneficial.

 The drawing shows a schematic diagram of a condensing unit.

 The condensation unit is designed for a casting machine containing the upper 1 and lower 2 drying channels. The lower drying channel 2 by the discharge line is connected by an air duct with a 3 m air heater to the fan discharge line. The suction line of the lower drying channel 2 is connected to the suction line of the additional fan 5, the discharge line of which is connected by an air duct to the entrance to the upper drying channel 1 and to the tangential nozzle 6 in the vortex mixing apparatus 7. The tangential nozzle 8 of the vortex apparatus 7 is connected by an air duct to the discharge line of the fan 4 The axial pipe 9 is connected by an air duct to the outlet of the upper drying channel 1. The output open end of the vortex mixing apparatus 7 is connected by an air duct to the inlet of the condenser 10. The outlet of the steam-air mixture from the condenser 10 is connected to the suction line of the fan 4. The annular space of the condenser 10 is connected by the brine inlet and outlet piping to the refrigeration station 11. The prepared solution for the outflow of the substrate is fed into the die 12 of the casting machine.

 Condensation unit operates as follows.

The steam-air mixture from the drying channels 1 and 2 of the casting machine is fed into the suction lines of the fans 4 and 5, and then, under the pressure of the fans, it moves to the tangential nozzles 6 and 8 of the vortex displacement apparatus 7, twists in the annular space and moves to the output end. In this case, the air-vapor mixture is sucked through the axial pipe 9 from the upper drying channel 1 of the casting machine. Passing through the tubes further condenser 10, steam mixture is cooled from 5-6 to ^about -13 C by a cold brine, coming from the cooling station 1 at a temperature ^of -23 C and passes between the tubes in countercurrent with the vapor-air mixture. When the vapor-air mixture is cooled in the condenser 10 to a temperature of (-12) - (- 15) ^о С, the complete condensation of solvent vapors occurs. From the condenser 10, the cooled air is supplied through the air duct to the suction line of the fan 4, on the discharge line of which it is divided into two streams. One stream is fed to a vortex mixing apparatus 7 via tangential conduit 8 passes through another heater 3 is heated to 80-100 ^{° C} and held at the lower pressure inlet of the drying channel 2. From the bottom outlet of the drying duct 2, air is supplied to the auxiliary fan suction line 5, on the discharge line of which it is divided into two streams. One stream is supplied to the vortex mixing apparatus 7 through the tangential pipe 6, the other passes into the discharge pipe of the upper drying channel 1.

 Additionally installed fan 5 due to the vacuum created in the lower drying channel 2, increases the speed of the vapor-air mixture in the channel section from 1.3 to 2-2.5 m / s.

,, где W - количество испаряемых растворителей;
F - площадь испарения;
τ - время испарения.The drying rate of the film-forming solution applied to the mirror layer of the machine tape is determined by the expression
U =

,, where W is the amount of evaporated solvents;
F is the area of evaporation;
τ is the evaporation time.

, (1) где β_p - коэффициент массообмена;
Р_нас - давление насыщенных паров растворителей при tч;
Р_о - давление паров растворителей в пароазотной смеси;
t₂ - температура теплоносителя в сушильном канале;
l - длина активной части ленты;
b - ширина формирующейся пленки или
V =

=

, (2) где W/l - удельная норма растворителей на погонный метр пленки (кг/п.м.), зависящая от сорта пленки, толщины основы, скорости движения ленты.The speed of the tape V of the casting machine, i.e. its performance is related to the amount of evaporated solvents W by the following expression
V =

, (1) where β _p is the mass transfer coefficient;
P _us - pressure of saturated vapor of solvents at tч;
P _about - vapor pressure of solvents in a vapor-nitrogen mixture;
t ₂ is the temperature of the coolant in the drying channel;
l is the length of the active part of the tape;
b is the width of the forming film or
V =

=

, (2) where W / l is the specific rate of solvents per linear meter of film (kg / lm), depending on the type of film, the thickness of the substrate, and the speed of the tape.

 To increase the productivity of the casting machine for a given length l = const, it is necessary to increase the completeness of solvent return, and this can be achieved only due to a higher degree of condensation of solvent vapors in the capacitors. Equation (2) expresses the relationship connecting the ebb rate of the machine with the rate of evaporation of solvent vapor from the free surface of the film.

(3) или Nu_D=0.018 Re^0.8·Pz $\genfrac{}{}{0ex}{}{\text{0}}{\text{D}}$ ^.33 (4) где Pz_D=

; Rl =

; (5)
P_SD - диффузионное число Прандтля;
Rl - число Рейнольдса;
d_э - эквивалентный диаметр сушильного канала;
К_р - коэффициент диффузии;
V - скорость движения паровоздушной смеси в канале;
ν - кинематическая вязкость протока паровоздушной смеси.In turn, an increase in the speed of the tape leads to an increase in the specific rate of solvents W / l; according to equation (2) in this case, it is necessary to increase the drying speed U or the mass transfer coefficient β _p , where the Nusselt diffusion criterion Nu _D is determined by the expression Nu _D =

(3) or Nu _D = 0.018 Re ^0.8 · Pz $\genfrac{}{}{0ex}{}{\text{0}}{\text{D}}$ ^.33 (4) where Pz _D =

; Rl =

; (5)
P _SD is the diffusion Prandtl number;
Rl is the Reynolds number;
d _e is the equivalent diameter of the drying channel;
To _p - diffusion coefficient;
V is the velocity of the vapor-air mixture in the channel;
ν is the kinematic viscosity of the duct of the vapor-air mixture.

Equations (3) - (5) show that in order to increase the mass transfer coefficient β _p in the drying channel of the casting machine, it is necessary to increase the speed of the vapor-air mixture v.

 In the invention, by installing an additional fan 5, the speed of the steam-air mixture in the lower drying channel 2 is increased, which ensures an increase in the drying speed of the film and ultimately leads to an increase in the productivity of the casting machine.

 In this condensation unit, a higher degree of condensation of solvent vapor (from 70 to 92%) allows you to increase the speed of the tape of casting machines by 1.7 times. On casting machines with a tape length of 28-30 m, the belt speed increases from 2.1 to 3.7 m / min, i.e. the productivity of casting machines increases by about 1.7 times with the same geometric parameters.

 Thus, the present invention, by reducing the temperature of the vapor-air medium in front of the condenser, increases the completeness of solvent condensation, which ultimately leads to an increase in the productivity of the casting machine.

Claims (1)

 CONDENSATION UNIT FOR TAPE CASTING MACHINE, containing fans, condenser and air heater, connected by pipelines to the upper and lower channels of the casting machine, characterized in that it is equipped with a vortex mixing apparatus with tangential and axial inlet nozzles and an additional fan, while the suction line of the additional fan with the lower drying channel, discharge - with the tangential inlet pipe of the vortex apparatus and the inlet pipe of the upper drying channel, outlet discharge pipe which is connected with the axial inlet of the vortex device, and the output end of the vortex device connected to the input capacitor.

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