RU2152245C1 - Heat-and-mass exchange apparatus - Google Patents

Abstract

FIELD: chemical engineering. SUBSTANCE: heat-and-mass exchange apparatus has cylindrical casing with gas supplying and gas discharge branch pipes positioned in its upper part and liquid supplying and discharge branch pipes positioned in its lower part. Apparatus is further provided with rotating shaft carrying transverse continuous disks and separating annular walls, which are axially aligned with casing and shaft and arranged successively in alternation. Gas dynamic, hydrodynamic or contact sealing members are extending along outer diameter of separating walls. Packs of annular contact disks are positioned between disks and separating walls. Contact disks are arranged in spaced relation to casing, shaft and one to the other, and are partially immersed into liquid to form Z-shaped radial-axial, sequential-parallel flow of gas streams. Heat-and-mass exchange process is effectuated under continuous liquid film flow condition so as to provide for contact engagement between gas flow and liquid flow, with liquid flowing in the form of film over surfaces of rotating disks. EFFECT: increased efficiency by widened gas and liquid flow contact surface and simplified construction. 6 dwg

Description

 The invention relates to processes and apparatuses of chemical engineering and can be used in the energy, oil and gas, chemical, food and other industries for wet gas purification, absorption, rectification (distillation), etc. to processes in the gas-liquid system.

 A device is widely known from the prior art for carrying out a heat and mass transfer process by contacting a gas stream with a liquid stream flowing on the surface of a liquid droplet or film in hollow (non-nozzle) plate (cascade), packed film columns (see A. N. Planovsky , P. I. Nikolaev. Processes and Apparatuses of Chemical and Petrochemical Technology. M., Chemistry, 1972, S. 322, 323, 329-331, 373). The intensity of heat and mass transfer is determined by the velocities of the gas and liquid flows and largely depends on the size and shape of the contacting surface, however, an increase (development) of the latter leads to an increase in hydraulic resistance, entrainment of liquid droplets, and complication of the design and dimensions of heat and mass transfer apparatuses.

 Close to the invention is a device for carrying out heat and mass transfer processes by contacting a gas stream with a liquid stream flowing in the form of a film on the surface of rotating disks partially immersed in a liquid (see Aut. St. USSR 223766, class B 01 D 45 / 10, 1968). The main disadvantage of this device is that the intensity of contact interaction (gas flow with a liquid - a film on the surface of the disks) is determined by the gas flow rate and the rotational speed of the disks, the increase of which is limited by the possibility of film breakdown and droplet entrainment.

 Heat and mass transfer apparatuses are known, comprising a housing with a gas channel and nozzles for supplying and discharging gas, the lower part of which is filled with liquid, and a horizontal shaft installed in the housing with disks partially immersed in the liquid, which is equipped with a drive for rotation (see Auth. St. USSR 262096, class B 01 J 8/10, 1970; Aut. St. USSR 971437, class B 01 D 45/18, 1981). Moreover, the implementation of the disks in the form of grids or blades provides the axial flow of the gas stream at a sufficiently high speed, but does not allow the development of the phase contact surface.

 A heat and mass transfer apparatus is also known, comprising a housing with a gas channel and nozzles for supplying and discharging gas, in the lower part of which there is a bath with liquid, and a rotating horizontal shaft with a drive equipped with disks partially immersed in liquid (see Auth. USSR 223766, class B 01 D 45/10, 1968). The shaft in this unit is installed across the gas channel, i.e. in a plane directed across the gas flow, which increases the gas-liquid contact surface and forms a longitudinal flow around the disks with low hydraulic resistance, but limits the device’s functionality, since it does not allow its effective use for mass transfer processes requiring extended gas-liquid contact .

 Closest to the invention is a mechanical film heat and mass transfer apparatus (see V. M. Ramm, "Gas Absorption", Moscow, "Chemistry", 1976, p. 321-322), containing a cylindrical body equipped with a ring separation partitions forming sections. In each section, a solid disk is fixed on the shaft, to each of which packets of annular contact disks are mounted on each side, installed with a gap relative to the housing, shaft and each other. In the upper part of the body there are pipes for supplying and discharging gas, and in the lower part there are pipes for supplying and discharging liquid. The shaft is equipped with a drive for rotation. The contact discs are partially immersed in liquid. Such a device of the apparatus forms a zigzag radial-axial gas channel in the upper part of the body, and a liquid channel in the lower part, which, in principle, allows it to be used effectively for heat and mass transfer processes requiring extended contact of the gas with the liquid film.

 However, in such devices, a contradiction arises between the efficiency of organizing the process of heat and mass transfer and its constructive implementation.

 So from the point of view of increasing the efficiency of the process of heat and mass transfer in devices of this type, it is necessary to ensure minimum axial gaps between the extreme (in packages) annular contact disks and the dividing ring partitions not involved in the process of heat and mass transfer (since the latter are fixed in the housing and their the surface is not covered by a film of liquid), i.e., the size of these gaps should be equal to no more than half the value of the optimal gaps between the ring contact disks. At the same time, from the point of view of ensuring the manufacturability and manufacture of such devices and their operation, as practice shows, when installing, as a rule, 10-16 dividing ring partitions, these gaps should be 3-6 times greater than the optimal gaps between the ring contact disks, which in turn leads to an overflow of up to 50% of gas through these "technological" gaps, bypassing the process of heat and mass transfer on the contact disks and, as a result, the loss of efficiency of these devices.

 Hence, a significant drawback of such devices is their structural complexity, relatively low manufacturability and assembly, caused by problems of high precision manufacturing, sequential installation and accurate fixation relative to each other with predetermined axial clearances (taking into account manufacturing, assembly and temperature expansion errors): on the shaft - continuous disks with packages of annular contact disks, and in the case - dividing annular partitions, which leads to an increase in dimensions (axial by more than 40-60%), mass s design and cost of devices (60-200%) up to the loss of their competitiveness.

 The invention is directed to the creation of a compact, highly efficient, technologically advanced, cheap contact heat and mass transfer apparatus with higher specific productivity and wide functionality by reducing gas flow over "technological" gaps, increasing the surface of effective contact interaction of gas with a liquid film, and organizing more intense heat and mass transfer during contact interaction of a gas with a liquid film.

 The solution to this problem is provided by the fact that in the heat and mass transfer apparatus containing a cylindrical body, in the upper part of which there are nozzles for supplying and discharging gas, and in the lower part there are nozzles for supplying and discharging liquid, equipped with dividing ring partitions forming sections in each of which a transverse solid disk is mounted on a rotating shaft, to each of which are attached packets of annular contact disks, which are installed with a gap relative to the housing, shaft and each other partially immersed in a liquid, which together form a zigzag radial-axial, sequentially parallel flow of gas flows, according to the invention, the annular separation partitions are fixed between the packages of annular contact disks coaxially to the shaft with the possibility of joint rotation with it, and are installed on the outer diameter of the separation annular partitions ( gas-dynamic, hydrodynamic or contact) seals.

The claimed design \ heat and mass transfer apparatus provides:
- additional involvement of the surfaces of the separating annular partitions in the process of heat and mass transfer (due to the performance of the functions of the surfaces of the contact disks during their joint rotation), which increases the efficiency of the apparatus by 5-20%;
- 5–15 times reduces or completely eliminates gas overflow along “technological” gaps between sections (in the area of annular partition walls);
- significantly simplifies the design of the apparatus, reduces by 30-80% their length and weight, by 60 - 200% the cost of their manufacture.

 Thus, the proposed technical solution allows to increase the surface of effective contact interaction of gas with a liquid film, provides the possibility of organizing more intensive processes of heat and mass transfer, and, as a result, an increase in the specific productivity of devices of this type, and together provides a significantly higher efficiency of various processes heat and mass transfer over a wide range of combination of regime parameters and thermophysical properties of two different interacting nitrogen media (gas and liquid), with a continuous flow of a liquid film (absorption, distillation, gas purification) in horizontal devices with rotating disks that determine the minimum dimensions of the device, it can be used in technological schemes with various liquid and gaseous substances, for example, for air purification from solid particles and impurities, rectification of oil and gas products, absorption of hydrocarbon vapors (phenol, formaldehyde, gasoline, etc.) from air, distillation in an ethanol-water system, etc., instead of towing columns with high hydraulic resistance.

 The drawing schematically shows a General view of the heat and mass transfer apparatus.

 The heat and mass transfer apparatus (see Fig. 1-5) contains a cylindrical housing 1, in which a horizontal shaft 2 is mounted rotatably with transverse solid disks 3 fixed to it, to which are laterally (for example, on couplers 4 with spacer washers 5 (see Fig. 2)) attached are packages 6, assembled from ring contact disks 7, which can be made, for example, smooth, rough, perforated, ribbed, mesh, etc. Ring contact disks 7 are installed with a gap relative to the housing shaft and each other. Between the packages of annular contact disks 6, annular partition walls 8 are installed and fixed coaxially to the shaft 2, equipped with an outer diameter of seals 9 (hydrodynamic, gasdynamic (see Fig. 3) or contact (see Fig. 4, 5)), forming sections 10 A gas channel 11, longitudinal relative to the shaft 2, is formed in the upper part of the housing 1 with nozzles 12 and 13 for supplying and discharging gas, and in the lower part of the housing 1, a liquid channel 14 is formed with inlet and outlet nozzles 15 and 16 for supplying and discharging liquid, which liquid filled Tew.

 The gas channel 11 is formed by the gaps between the casing and the transverse solid disks 3, the annular contact disks 7 and the dividing ring partitions 8, forming a multi-pass zigzag radial-axial, sequentially parallel flow of gas flow. Similarly, a liquid channel 14 is formed in the lower part of the housing. The rotation of the horizontal shaft 2 with solid disks 3, ring contact disks 7 and separation ring partitions 8 is provided by a drive (not shown in the drawing).

 The process of heat and mass transfer is as follows.

The gas flow enters the gas channel 11 through the nozzle 12, passes through the cavity of the first (in the direction of the gas) section 10, then along the radial gaps between the (transverse) partitions of the first packet of rotating ring contact disks 7 and disks 3 and 8, entering into contact interaction with a stream of liquid flowing in the form of a film from the surface of the rotating disks 3, 7 and 8, which during rotation are partially immersed in the wetting liquid from the liquid channel 14, then the gas is turned around 180 ^o and enters the radial gaps between the partition kami of the second package of rotating annular contact disks, etc. before it leaves the device through the pipe 16.

In this case, the contact interaction of the phases occurs with a radial gas flow, which, flowing along the apparatus as a whole in the axial direction, with a sequential transition from the cavities of one packet of radial clearances - the gas channel 11 travels through the cavity (the next, along the gas flow) section 10 the next one, changes its (radial) direction of movement in the opposite direction, flowing around the contact elements (rotating disks 7, 3, 8) - on both sides with a speed W _r , i.e., it makes a multi-pass, zigzag rad within the gas channel 11 axial-axial, serial-parallel movement.

 The continuous flow of the liquid film along the surface of the rotating disks 7 (3.8) and the implementation of the centrifugal separating effect due to the rotation of the gas flow eliminates the possibility of droplet formation, which leads to a decrease in the dimensions of the apparatus, since there is no need to create a significant separation space. In addition, the presence of convective fluid flows in the flowing film arising at a certain rotational speed of the disks 7 under conditions of a rather complicated cross-mixed organization of the relative motion of the phase flows, in combination with an allowable range of gas flow velocities in the zone of contact interaction of the phases of the gas-liquid system (t .e. with radial flow in the gaps between the transverse solid disks 3, the annular contact disks 7 and the dividing ring partitions 8), causes an increase in the coefficients eploperedachi and mass transfer during the transition phase material through the contact surface in various processes.

 The installation of dividing ring partitions 8 (with seals in the outer diameter) on the shaft between the packages of ring contact disks 6 allows not only to drastically simplify the design of the heat and mass transfer apparatus, but also to ensure high manufacturability of assembly and disassembly of devices without special high-precision equipment, to increase their operational characteristics .

Depending on the type of process and its required efficiency, compaction 9 can be performed:
- hydrodynamic or gasdynamic, for example labyrinth (see Fig. 3), which practically does not lead to an increase in the power of the electric drive for rotating the shaft 2;
- contact - with the installation of one or more (see figures 4, 5), for example, elastic rubber rings 17. The increase in the power of the electric drive for rotating the shaft 2 in this case is no more than 2-5% of the total power of the installation (if an order of magnitude greater positive effect);
- combined - with minimal ("zero") preloading the elastic seals 17 to the wall of the housing 1 (see Fig.6).

 We give evidence that the installation of annular partition walls with (even gas-dynamic) seals leads to a decrease in the proportion of bypass and an increase in the efficiency of the apparatus.

где: Σξ_к - сумма гидравлического сопротивления канала;
l_k - длина канала;
λ_тр - коэффициент трения;
d_эк - эквивалентный диаметр канала;
ω_к - скорость газа в канале;
ρ_г - плотность газа.The pressure drop between adjacent sections is Δp = P ₁ -P ₂

where: Σξ _k is the sum of the hydraulic resistance of the channel;
l _k is the length of the channel;
λ _Tr - coefficient of friction;
d _ek - equivalent diameter of the channel;
ω _to - gas velocity in the channel;
ρ _g is the density of the gas.

V = ω _k • f _k ,
where V is the volumetric gas flow in the channel;
f _to - the cross-sectional area of the channel (between the discs 3, 7, 8).

V_п= F_п•ω_п,
где ξ_п - коэффициент гидравлического сопротивления перепускного канала;
ω_п - скорость газа в перепуске;
V_п - объемный расход газа в перепускном канале.

V _p = F _p • ω _p ,
where ξ _p - coefficient of hydraulic resistance of the bypass channel;
ω _p - gas velocity in the bypass;
V _p - volumetric gas flow in the bypass channel.

На фиг. 6 приведена зависимость между коэффициентом эффективности контактной ступени (пакета контактных дисков) и долей перепуска газа по зазору (осевому или радиальному) между соседними секциями тепло- и массообменного аппарата.The proportion of gas bypass (D _p ) of gas between sections by the gap (bypass channel) in the (labyrinth) seal is determined as follows:

In FIG. Figure 6 shows the relationship between the coefficient of efficiency of the contact stage (package of contact disks) and the fraction of gas bypass gap (axial or radial) between adjacent sections of the heat and mass transfer apparatus.

From the graph (Fig. 6) it can be seen that with an increase in the percentage of bypass D _{p, the} efficiency of the contact element decreases and when D _p = 30 - 50%, it reduces the efficiency of these devices to 0.5 - 0.35.

In analogs, due to the spread in the accuracy of manufacturing parts, assembly errors and thermal expansions during operation (taking into account the mechanical operability of the system), the axial clearances between the dividing ring partitions and ring contact disks, as a rule, exceed the values of the optimal working clearances between the ring contact disks in 3 - 6 times, which leads to an increase in the proportion bypass _n D 50% or more, leading to a drop in the efficiency η of the contact elements from 0.7 to 0.35 and as a consequence is founded implicit cause of their lack of demand.

можно снизить в 5 - 10 раз и восстановить η от 0,35 до 0,65-0,69.When moving to the proposed devices with dividing ring partitions mounted on the shaft between the packages of ring contact disks and equipped with gas-dynamic seals in outer diameter, the value

can be reduced by 5-10 times and restore η from 0.35 to 0.65-0.69.

Obviously, when installing contact seals, the bypass fraction D _p will be close to zero, i.e., the efficiency η of the contact elements will be close to the maximum possible ~ 0.7.

Claims (1)

 A heat and mass transfer apparatus containing a cylindrical body, in the upper part of which there are nozzles for supplying and discharging gas, and in the lower part, nozzles for supplying and discharging liquids, equipped with dividing annular partitions forming sections, in each of which a transverse shaft is mounted on a rotating shaft a solid disk, each of which is attached to the sides of the packs of annular contact disks installed with a gap relative to the housing, shaft and each other and partially immersed in liquid, which together form they make a zigzag radial-axial, sequentially parallel flow of gas flows, characterized in that the annular separation partitions are fixed between the packages of annular contact disks coaxially with the shaft with the possibility of joint rotation with it, and seals are installed on the outer diameter of the separation annular partitions.

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