RU2619326C1 - Method for hydrodynamic cleaning of plate exchangers and plate exchanger for method implementation - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: method for hydrodynamic cleaning of plate heat exchangers, made in the form of sections consisting of two connected plates with spherical recesses on their working surfaces, recesses of one plate enter the notches of the other plate, including the creation of a turbulized flow with individual self-organizing pulsating vortex structures under the action of the heat carrier main flow in the recesses, as well as of an additional jet bypass flow formed due to the bypass of a part of the main flow through bypass channels made in the meridian plane of recesses, from the increased pressure zones on the walls of the recesses adjacent to their outlet edges to the reduced pressure zones in the bottom of adjacent recesses.

EFFECT: as a result of complex hydrodynamic effect of single self-organizing pulsating vortex structures and jet bypass flow, continuous cleaning of the heat exchanger plate is performed, and its service life is increased, geometric parameters of tear-off holes on the plates, location and size of bypass channels are determined.

8 cl, 4 dwg

Description

The invention relates to a power system, and in particular to methods of hydrodynamic internal cleaning of contaminants of plate heat exchangers and can be used in energy, chemical, metallurgical and other industries.

It is known that during operation on the heat exchange surfaces of plate heat exchangers, foreign formations appear in the form of deposits - contaminants that add additional thermal resistance, clutter the passage section of the matrix channels and, as a result, lead to a change in the thermohydraulic characteristics of the surface. As noted in the work // Heat exchangers and cooling systems for gas turbine and combined installations: Textbook for universities / V.L. Ivanov, A.I. Leontiev, E.A. Manushin, M.I. Osipov. Ed. A.I. Leontiev. - M.: Publishing House of MSTU. N.E. Bauman, 2003 .-- 592 p. fractions of various substances entering the coolant are the main cause of pollution. This can be dust of various compositions, soot, ash in the solid or liquid phase, oil vapors, corrosion products, and with liquid coolants, salts dissolved in them. Physically, the process of pollution is explained by the influence of the following factors: molecular attraction, collision of particles with the surface and their subsequent adhesion; the action of thermophoresis forces (a surface superheated with respect to the flow repels particles, and supercooled - attracts) and electrostatic forces; possible occurrence of chemical reactions in the layer of primary deposits (under the influence of temperature, pressure, humidity); content of condensable vapors of oil and other substances.

If the working surfaces of the plate heat exchanger are contaminated, the flow conditions of the heat carrier and heat transfer are worsened, which leads to a decrease in the power of the heat exchanger. The first is expressed in an increase in pressure loss in the heat exchanger, in the second case, the temperature of the heated circuit decreases or the temperature of the cooled circuit at the outlet of the heat exchanger increases. As a result, heat losses increase. In most cases, it is necessary to deal with scale and deposits of iron oxides (or other iron compounds), as well as with their joint action. So, in the work Slepchenok B.C., Bystrov V.D., Zak M.L., Paley E.L. “Heating boilers of low power” // “News of heat supply”, 2004, No. 9, p. 24-33. using the Alfa Laval plate heat exchanger operating example installed on one of the central heating plants of the State Unitary Enterprise “Fuel and Energy Complex St. Petersburg” in St. Petersburg, it was shown that the thermal efficiency of the plate heat exchanger decreased: after the first year of operation - 5%; after the second ~ 15%; after the third - more than 25%.

It is known to use surface heat exchange intensifiers in plate heat exchangers in the form of systems of spherical indentations of a detachable type made on the plates by means of stamping. The use of spherical recesses can improve the efficiency of heat exchangers not only by increasing the heat transfer of the heat exchange surfaces of the plates, but also by reducing the intensity of their contamination as a result of turbulence in the heat carrier flow, as noted in the work // Guide to heat exchangers: In 2 vols. T. 2 / S. 74. Per. from English under the editorship of O.G. Martynenko et al. - M.: Energoatomizdat, 1987 .-- 352 p. The appearance of turbulence is due to the action of vortex structures arising in spherical recesses. Many small particles of pollution simply do not remain on the walls of the equipment, but are washed off during operation. But larger particles accumulate in the bottom of the spherical recesses and on the initially smooth surface of the plates between them, forming pollution and scale on the working elements during the long-term operation of the heat exchanger. Therefore, conducting periodic washes is a necessary condition for reliable and efficient operation of flat heat exchangers of this design. The shape of the stampings, the depth, the pitch and their shape are the main parameters that determine the thermal, hydraulic and mechanical efficiency of the plate heat exchanger specified by the technical operating conditions for each individual case. The results of the study of heat exchange equipment with spherical recesses are presented in the work of Popov, I.A. Hydrodynamics and heat transfer of external and internal free convective vertical flows with intensification. Intensification of heat transfer: monograph / Ed. ed. Yu.F. Gortyshova. - Kazan: Center for Innovative Technologies, 2007. - 326 p. However, this paper does not address issues related to cleaning flat heat exchangers with spherical recesses on the plates.

It is known that various methods can be used to clean up impurities and scale from the heat exchange surfaces of plate heat exchangers: mechanical, chemical, and hydrodynamic. These are the most common cleaning methods, but there are also electrohydropulse and ultrasonic methods, which are rarely used due to their high cost. Depending on how much pollution and composition they are, as well as what the design of the heat exchanger is, the condition of its heat exchange surfaces and one of three main cleaning methods is chosen.

A hydrodynamic method for cleaning hydrodynamic contaminants and scale of heat-exchange equipment (see RF patent 2366881, IPC F28G 7/00, F28G 9/00, publ. September 10, 2009), which ensures effective cleaning of both tubular non-separable, is selected as a prototype. and plate-type collapsible heat exchangers with heat transfer intensifiers on their working surfaces.

The hydrodynamic cleaning method allows the mechanical destruction of various deposits and their simultaneous removal by high-speed water flow. This type of work requires the use of hydrodynamic plants with special nozzles and disassembly of the heat exchanger (with the exception of tubular structures, for which this is not necessary). In the process of hydrodynamic cleaning, any types of scale and deposits are removed, cleaning is carried out completely, almost "to metal", which slows down the new formation of scale and significantly increases the efficiency of the equipment and as a result reduces the energy consumption of the enterprise as a whole. Objects of hydrodynamic cleaning are not damaged, the result is an increase in the resource of the equipment being cleaned while the process is ecologically clean. This gives a clear advantage over mechanical and chemical cleaning methods.

However, in the method of hydrodynamic cleaning selected as a prototype, it is necessary to use special expensive equipment with hydrodynamic nozzles to supply a jet of water under high pressure, reaching 400 MPa, and at a speed of up to 350 m / s. Buying such equipment is not always cost-effective. In addition, after hydrodynamic washing of a collapsible plate heat exchanger, it is supposed to replace its seals, which are the elements of the heat exchanger most vulnerable to contamination. This method cannot be applicable for cleaning welded or soldered models of plate heat exchangers, widely used in energy and heat engineering.

The problem to which the invention is directed, is to develop a simple and cheap method of hydrodynamic continuous cleaning from pollution of plate heat exchangers of various designs with spherical "tear-off" recesses on their working surfaces.

The technical result, which the invention is aimed at, is to improve the quality of cleaning from contaminants and increase the life of the heat exchange equipment.

The technical result is achieved by the fact that in the method of hydrodynamic cleaning of plate heat exchangers made in the form of sections consisting of two connected plates with spherical recesses on their working surfaces, the recesses of one plate enter the recesses of the other plate, including creating under the influence of the main coolant flow in the recesses turbulent flow with single self-organizing pulsating vortex structures, new is that part of the aforementioned main coolant flow they are passed from the pressure zones in each recess to the low pressure zones of adjacent recesses, thereby forming an additional jet bypass flow in the direction of movement of the aforementioned main coolant flow.

Part of the main flow is passed from the high-pressure zones located on the walls of the recesses adjacent to their outlet edges to the low-pressure zones in the bottom of adjacent recesses.

The technical result is achieved by the fact that in a plate heat exchanger made in the form of sections, consisting of two connected plates with spherical recesses on their working surfaces, the recesses of one plate enter the recesses of the other plate, the sections have power connections to each other inside the heat exchanger, new is that between adjacent recesses in their meridional plane, bypass channels are made connecting high pressure zones in each recess with low pressure zones in adjacent recesses.

The entrance of the bypass channels is made on the walls adjacent to the output edges of the recesses, and the exit from them is made in the bottom of adjacent recesses.

а радиус скругления кромок выемок - R=0,5 d, где d - диаметр выемки.The relative step between the axes of the recesses made on the working surfaces of the plates is

and the radius of rounding of the edges of the recesses is R = 0.5 d, where d is the diameter of the recess.

где d_к.п - диаметр канала перепуска.The relative diameter of the bypass channels in the recesses

where d _{K. p} - diameter of the bypass channel.

All bypass channels in the recesses are made at an angle of 50 ° to the axis of the recesses.

где

и

- площади канала перепуска на входе и выходе из него.The bypass channels are made in confuser shape in the direction of low pressure zones with a degree of confuser

Where

and

- the area of the bypass channel at the entrance and exit from it.

In FIG. Figure 1 shows sections of a plate heat exchanger with spherical recesses, in the meridional plane of which there are inlet and outlet bypass channels connecting the zone of increased pressure on the wall of the recess adjacent to the outlet edge to the zone of reduced pressure in the bottom of the adjacent recess.

In FIG. 2 shows a section of sections of a plate heat exchanger in the plane of the meridional section of the recesses.

In FIG. 3 shows a diagram of the distribution of the pressure coefficient C _p in the plane of the meridional section of a spherical recess.

In FIG. Figure 4 shows a graph of changes in heat transfer in the plane of the meridional section of a spherical recess.

Where:

1 - the upper plate sections of the plate heat exchanger;

2 - lower plates of the same sections;

3 - spherical recesses "tear-off" type;

4 - input bypass channel in each recess;

5 - output bypass channel to each adjacent recess;

6 - input edge of the spherical "tear-off" recess - the edge of the half of the recess through which the main coolant flow enters into it;

7 - the output edge of the spherical "tear-off" recess - the edge of the half of the recess, through which the main coolant flow exits from it;

"A", "c", "d" - the internal cavity of the recesses made in the upper plate of the section;

"B", "g", "e" - the internal cavity of the recesses made in the bottom plate of the section;

d is the diameter of the spherical recess;

R is the radius of the spherical recess;

d _K.p - diameter of the bypass channels;

t is the step between the axes of adjacent recesses made on the working surfaces of the plates;

h is the maximum depth of the excavation;

S is the distance between the sections of the plate heat exchanger.

- направление движения основного потока теплоносителя;

- the direction of motion of the main flow of the coolant;

- направление движения дополнительного струйного байпасного течения через каналы перепуска, возникающего под действием части основного потока теплоносителя;

- the direction of movement of the additional jet bypass flow through the bypass channels that occurs under the action of part of the main coolant flow;

The method of hydrodynamic cleaning of plate heat exchangers is as follows. When the heat carrier (air, another gas or liquid) is supplied to the plate heat exchanger, the main heat carrier flow is formed, which moves (the direction is shown by large arrows) along the sections formed by the upper 1 and lower 2 plates, on the working surfaces of which “tear-off” spherical recesses 3 are made, located in a specific order (see Fig. 1 and 2). The structure of the aforementioned main coolant flow is determined by the geometrical and operating conditions of the flow around the "tear-off" spherical recesses 3. Both plates in each section (see Fig. 2) are connected by spot welding so that the recesses of the upper plate 1 enter the recesses of the lower plate 2. When hit of the aforementioned main flow of the coolant into the spherical "tear-off" recesses 3 in them arise single self-organizing pulsating vortex structures that turbulence the aforementioned main flow and eyes ayut recesses of fines impurities. Part of the aforementioned main coolant flow (see FIG. 2) is passed through the bypass input channel 4 of each recess and the bypass output channel 5 in the adjacent recess from the pressure zones on the walls adjacent to the output edges 7 (see FIG. 1) of the recesses 3 , in the zone of reduced pressure in the bottom of adjacent recesses of both plates. Moreover, under the action of the resulting pressure drop on the walls and in the bottom of the recesses (see Fig. 3), an additional bypass flow is formed in the direction of movement of the aforementioned main coolant flow. The jets of the additional bypass flow (the direction is shown by small arrows) destroy large fractions of contaminants in the bottom of the recesses 3. As a result of the combined action of a turbulent flow with individual self-organizing pulsating vortex structures and an additional jet bypass flow arising in spherical recesses under the action of the aforementioned main coolant flow, pollution removed from the working surfaces of the plate heat exchanger, which prevents the formation of n Kipi. In this case, the process occurs continuously throughout the entire working cycle of the heat exchanger. It was experimentally established (see Fig. 4) that the proposed hydrodynamic cleaning method does not significantly affect the thermohydraulic characteristics of the plate heat exchanger. This is due to increased turbulence of the aforementioned main coolant flow in spherical heat transfer intensifiers on the working surfaces of the plates. The present invention allows for the implementation of a simple, effective and cheap method of continuous hydrodynamic cleaning of plate heat exchangers of various designs.

а радиус скругления кромок выемок - R=0,5d, где d - диаметр выемки. Расстояние между секциями S (см. фиг. 2) пластинчатого теплообменника и их количество определяются индивидуально в зависимости от условий эксплуатации теплообменного оборудования.Plate heat exchanger for the implementation of the proposed method for its hydrodynamic cleaning works as follows. The main coolant flow (the direction is shown by large arrows) moves along the sections formed by the upper 1 and lower 2 plates, on the working surfaces of which are made “detachable” spherical recesses 3 located in a certain order (see Fig. 1 and 2). Both plates in each section (see Fig. 2) are connected by spot welding so that the recesses of the upper plate 1 enter into the recesses of the lower plate 2, and the sections themselves have power connections between themselves inside the heat exchanger. When the aforementioned main flow of the coolant enters the spherical "tear-off" recesses 3, single self-organizing pulsating vortex structures appear in them, which turbulence the aforementioned main flow and clean the recesses from small fractions of contaminants. In this case, a pressure gradient arises on the walls of the recesses and in their bottom part. It was experimentally established that the zone of increased pressure due to the inhibition of the main flow of the coolant entering the spherical recess is formed on its wall adjacent to the outlet edge 7 (see Fig. 1). A zone of reduced pressure is created in the bottom of the same recess and is caused by the rotation of the flow and its acceleration when creating a single self-organizing pulsating vortex structure in the recess. In order to reduce the hydraulic resistance of the recesses, a rounding of their input 6 and output 7 edges is used. The maximum and minimum values of the measured static pressure in the zones of high and low pressure are fixed in the plane of the meridional section of the recess. At the same time, the basic geometric parameters of the “tear-off” type spherical recesses were experimentally determined: the relative pitch between the axes of adjacent recesses made on the plates was

and the radius of rounding of the edges of the recesses is R = 0.5d, where d is the diameter of the recess. The distance between the sections S (see Fig. 2) of the plate heat exchanger and their number are determined individually depending on the operating conditions of the heat exchange equipment.

в плоскости меридионального сечения выемки, где P_i - статическое давление на стенках и в донной части сферической выемки в точках замера; Р_∞, ρ_∞, и W_∞ - статическое давление, плотность и скорость набегающего основного потока теплоносителя соответственно; х - осевая координата в плоскости меридионального сечения сферической выемки. Эксперименты проводились в скоростном диапазоне

течения теплоносителя - воздуха, соответствующему рабочему процессу в пластинчатых теплообменниках. Из графика видно, что в зоне повышенного давления С_р=0,25, а в зоне пониженного давления - С_р=0,09. Отношение этих значений составляет 2,78, что предопределяет перепад давления на стенках и в донной части сферической выемки. Установленный перепад давления реализуется в пластинчатом теплообменнике, где осуществляется предлагаемый способ гидродинамической очистки путем создания дополнительного струйного байпасного течения, показанного на фиг. 2 маленькими стрелками. С этой целью в зонах повышенного давления на стенках выемок 3, примыкающих к их выходным кромкам 7, и пониженного давления в донной части смежных выемок обеих пластин 1 и 2, в их меридиональной плоскости выполнены входные каналы перепуска 4 в каждой выемке и выходные каналы перепуска 5 в смежные выемки. Под действием перепада давления часть вышеупомянутого основного потока образует дополнительное байпасное течение, траектория движения последнего имеет следующий вид: из внутренней полости «а» выемки верхней пластины 1 через входной канал перепуска 4 струя байпасного течения попадает в зону пониженного давления во внутренней полости «б» смежной выемки нижней пластины 2 одноименной секции пластинчатого теплообменника. Затем из этой выемки струя байпасного течения через выходной канал перепуска 5 попадает в зону пониженного давления во внутренней полости «в» смежной выемки верхней пластины 1. В последующих смежных выемках происходит аналогичный процесс последовательного движения струй байпасного течения во внутренние полости выемок: «в» - «г», «г» - «д», «д» - «е». Были установлены оптимальные размеры и места расположения каналов перепуска в сферических «отрывных» выемках обеих пластин для всех секций пластинчатого теплообменника: относительный диаметр каналов перепуска в выемках

где d_к.п - диаметр канала перепуска; все каналы перепуска в выемках выполнены под углом 50° к оси выемок для повышения эффективности действия дополнительного струйного байпасного течения. Для повышения кинетической энергии струй дополнительного байпасного течения, прокачиваемого через каналы перепуска, последние выполнены конфузорной формы в направлении зон пониженного давления со степенью конфузорности

где

и

- площади канала перепуска на входе и выходе из него.In FIG. 3 shows a diagram of the distribution of the coefficient of static pressure

in the plane of the meridional section of the recess, where P _i is the static pressure on the walls and in the bottom of the spherical recess at the measuring points; P _∞ , ρ _∞ , and W _∞ are the static pressure, density and speed of the incident main coolant flow, respectively; x is the axial coordinate in the plane of the meridional section of the spherical recess. The experiments were carried out in the speed range

heat carrier flow - air, corresponding to the working process in plate heat exchangers. The graph shows that in the zone of high pressure With _p = 0.25, and in the zone of low pressure - With _p = 0.09. The ratio of these values is 2.78, which determines the pressure drop on the walls and in the bottom of the spherical recess. The established pressure difference is realized in a plate heat exchanger, where the proposed method of hydrodynamic cleaning is carried out by creating an additional jet bypass flow, shown in FIG. 2 small arrows. To this end, in the zones of increased pressure on the walls of the recesses 3 adjacent to their outlet edges 7 and of reduced pressure in the bottom of the adjacent recesses of both plates 1 and 2, inlet channels 4 in each recess and outlet channels 5 are made in their meridional plane into adjacent recesses. Under the action of the pressure drop, part of the aforementioned main flow forms an additional bypass flow, the trajectory of the latter has the following form: from the inner cavity "a" of the recess of the upper plate 1 through the inlet channel of the bypass 4, the bypass stream enters the reduced pressure zone in the inner cavity "b" adjacent recesses of the lower plate 2 of the same section of the plate heat exchanger. Then, from this recess, the bypass stream through the outlet bypass channel 5 enters the reduced pressure zone in the inner cavity “c” of the adjacent recess of the upper plate 1. In subsequent adjacent recesses, a similar process of sequential movement of the bypass stream jets into the internal cavities of the recesses occurs: “in” - “G”, “g” - “d”, “d” - “e”. The optimal sizes and locations of the bypass channels in the spherical "tear-off" recesses of both plates for all sections of the plate heat exchanger were established: the relative diameter of the bypass channels in the recesses

where d _{K. p} - diameter of the bypass channel; all bypass channels in the recesses are made at an angle of 50 ° to the axis of the recesses to increase the efficiency of the additional jet bypass flow. To increase the kinetic energy of the jets of an additional bypass flow pumped through the bypass channels, the latter are made in confuser shape in the direction of low pressure zones with a degree of confuser

Where

and

- the area of the bypass channel at the entrance and exit from it.

As a result of the hydrodynamic effect of the jet bypass flow, large fractions of contaminants settling in the bottom of the spherical recesses are destroyed and further removed from the recesses and from the working surfaces of the plates by the combined action of individual self-organizing pulsating vortex structures and jet bypass flow arising in detached spherical recesses the action of the aforementioned main coolant flow. Cleaning the plate heat exchanger with spherical recesses on the working surfaces of the plates from contamination and protecting the plates from scale in the proposed method is continuous due to the movement of the main flow of the coolant.

Здесь

- число Нуссельта, определенное по температуре в точках замера, где: α - коэффициент теплоотдачи; X - коэффициент теплопроводности среды; d - характерный размер. Кроме этого: Nu_max - число Нуссельта, определенное в точке на внутренней поверхности выемки, где была зафиксирована ее максимальная теплоотдача. Также на фиг. 4 используются следующие обозначения: W_∞ - скорость набегающего основного потока теплоносителя; x - осевая координата в плоскости меридионального сечения сферической выемки; сплошная линия

- изменение местной теплоотдачи в сферической выемке без каналов перепуска; значок

- изменение местной теплоотдачи в сферической выемке с каналами перепуска при наличии струйного байпасного течения.It was experimentally established that, in a plate heat exchanger, where the proposed method of hydrodynamic cleaning will be used, the thermohydraulic characteristics of the heat exchanger will practically not change. In FIG. 4 shows a graph of changes in local heat transfer in the plane of the meridional section of the “tear-off” spherical recess in the form of a dependence

Here

is the Nusselt number determined by the temperature at the measuring points, where: α is the heat transfer coefficient; X is the thermal conductivity of the medium; d is the characteristic size. In addition: Nu _max is the Nusselt number determined at a point on the inner surface of the recess where its maximum heat transfer was recorded. Also in FIG. 4, the following notation is used: W _∞ is the speed of the incident main flow of the coolant; x is the axial coordinate in the plane of the meridional section of the spherical recess; solid line

- change in local heat transfer in a spherical recess without bypass channels; icon

- change in local heat transfer in a spherical recess with bypass channels in the presence of a jet bypass flow.

Comparison of the obtained experimental data showed their good convergence. The maximum discrepancy between the results did not exceed 6%, which lies within the accuracy of conducting thermotechnical experiments.

Thus, the present invention will allow for a process of continuous hydrodynamic cleaning from contamination of plate heat exchangers with spherical recesses on their working surfaces during operation. This is achieved due to the complex effect of a turbulized flow with individual self-organizing pulsating vortex structures and an additional bypass jet flow arising in spherical recesses under the action of the main coolant flow. As a result, the thermal, hydraulic and mechanical efficiency of plate heat exchangers specified by the technical operating conditions is ensured with a longer service life at a lower financial cost.

Claims (8)

1. The method of hydrodynamic cleaning of plate heat exchangers made in the form of sections consisting of two connected plates with spherical recesses on their working surfaces, the recesses of one plate enter the recesses of the other plate, including the creation of a turbulent flow with single self-organizing pulsating under the action of the main coolant flow in the recesses vortex structures, characterized in that part of the aforementioned main flow of the coolant is passed from the zones of high pressure into Doi recess in the reduced pressure zone adjacent recesses forming the supplemental jetting bypass flow in the direction of the aforementioned primary coolant flow. 2. The method according to p. 1, characterized in that the bypass part of the main stream is carried out from high pressure zones located on the walls of the recesses adjacent to their outlet edges, to the low pressure zone in the bottom of adjacent recesses. 3. A plate heat exchanger made in the form of sections consisting of two connected plates with spherical recesses on their working surfaces, the recesses of one plate enter the recesses of the other plate, the sections have power connections between each other inside the heat exchanger, characterized in that between adjacent recesses in them on the meridional plane, bypass channels are made connecting high pressure zones in each recess with low pressure zones in adjacent recesses. 4. The plate heat exchanger according to claim 3, characterized in that the input of the bypass channels is made on the walls adjacent to the output edges of the recesses, and the outlet is made in the bottom of adjacent recesses. 5. The plate heat exchanger according to claim 3, characterized in that the relative pitch between the axes of the recesses made on the working surfaces of the plates is

and the radius of rounding of the edges of the recesses is R = 0.5d, where d is the diameter of the recess. 6. The plate heat exchanger according to claim 3, characterized in that the relative diameter of the bypass channels in the recesses

where d _{K. p} - diameter of the bypass channel. 7. The plate heat exchanger according to claim 3, characterized in that all the bypass channels in the recesses are made at an angle of 50 ° to the axis of the recesses. 8. The plate heat exchanger according to claim 3, characterized in that the bypass channels are made in confuser shape in the direction of the zones of reduced pressure with a degree of confuser

where

and

- the area of the bypass channel at the entrance and exit from it.

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