Method for monitoring a mechanical seal within a rotating machine

Abstract

The invention relates to a method for monitoring a mechanical seal within a rotating machine, in particular a pump, with at least one temperature sensor arranged within the machine for detecting the ambient temperature and / or at least one component of the mechanical seal, wherein the rotational speed of the rotating machine is estimated by means of the at least one temperature measurement value and at least one further operating parameter of the mechanical seal.

Description

[0001] The invention relates to a method for monitoring a mechanical seal within a rotating machine.

[0002] Mechanical seals are used in pumps, among other applications, to seal the rotating pump shaft against a housing. The main components of a mechanical seal are two sliding parts: a sliding ring fixed to the shaft and a stationary counter ring fixed to the housing. The sliding ring is typically axially displaceable on the rotating shaft. The facing sliding surfaces between the two parts are—depending on the type of mechanical seal—usually flat and generally made of carbon-graphite materials, metal, ceramic, plastic, or resin-bonded carbon. The distance between the sliding surfaces is called the sealing gap.

[0003] The function, service life, and reliability of a mechanical seal depend significantly on the conditions (state) at the seal contact. Assessing and monitoring this state allows for an estimation of the seal's remaining service life (often referred to as remaining useful lifetime, RUL) and thus forms the basis for predictive maintenance.

[0004] The condition of a mechanical seal depends significantly on the temperature or temperature profile in the area of ​​the seal contact. In-situ measurements of the condition at the contact, i.e., the temperature at the contact, are only possible in a laboratory with considerable measurement effort, but are virtually impossible in field operation. Therefore, such measurements, e.g., of the temperature, must be carried out on adjacent elements / components. For example, a temperature measurement can be taken outside the seal contact at or in the stationary mating ring of the seal, e.g., as described in the as yet unpublished German patent application 102023109020.8.

[0005] Besides temperature, rotational speed is an important operating parameter that significantly influences the condition of the mechanical seal. It largely determines the frictional work generated in the contact and thus the heat generation at the seal contact. Furthermore, the time integral of the rotational speed represents the important parameter of the seal's sliding path. In practice, however, measuring the rotational speed is not feasible in many applications, for example, due to space constraints or cost considerations.

[0006] Therefore, a way is being sought to determine the rotational speed as a function of known operating parameters of a mechanical seal.

[0007] This problem is solved by a method according to the features of claim 1. Advantageous embodiments of the method are the subject of the dependent claims.

[0008] According to the invention, a method for monitoring a mechanical seal within a rotating machine, in particular a pump, is proposed, wherein the rotating machine or mechanical seal comprises at least one temperature sensor arranged within the machine for detecting at least one temperature value in the immediate vicinity of the mechanical seal. Additionally or alternatively, the at least one temperature sensor can also detect a temperature value of at least one component of the mechanical seal. Typically, the mechanical seal is surrounded by a fluid; however, when the mechanical seal is used within a pump, for example, a portion of the pumped medium can be directed to the sealing chamber and surround the mechanical seal.

[0009] Measuring the temperature in the vicinity of the mechanical seal can be achieved, for example, by using a temperature sensor to detect the fluid temperature within the seal area. It is also conceivable that temperature sensors are installed within individual components of the mechanical seal to directly measure the temperature of the respective component.

[0010] Based on at least one temperature measurement, and in combination with at least one other operating parameter of the mechanical seal, the rotational speed of the rotating machine, and thus of the rotating mechanical ring, should be estimated. Possible operating parameters of the mechanical seal include pressure measurements in the area of ​​the mechanical seal, such as the pressure on the high-pressure and / or low-pressure side, or any differential pressure between the high- and low-pressure sides of the mechanical seal. The differential pressure directly influences the force with which the two rings, i.e., the mechanical ring and the mating ring, are pressed against each other in the area of ​​their contact surfaces.

[0011] Another operating parameter that can be considered is a mechanical preload force, for example, a preload on the mechanical seal components using a spring or other mechanical aids. Furthermore, it is conceivable that any characteristic properties of the fluid flowing around the mechanical seal could be used as operating parameters. These characteristic properties could include the fluid density, the dynamic viscosity of the fluid, or the specific heat capacity or thermal conductivity of the fluid. Vapor pressure can also be relevant.

[0012] Furthermore, it is conceivable to consider material parameters of the sealing components as operating parameters of the mechanical seal, such as the material density, specific heat capacity, or thermal conductivity of the sealing material used, i.e., the material of the sliding and counter rings. The Young's modulus, Poisson's ratio, or coefficient of thermal expansion for the rotating sliding ring or the stationary counter ring can also be relevant. Finally, surface properties at the seal contact point and of the surfaces of the sealing components that are in contact with the fluid can also be important. These include, for example, surface roughness or an effective coefficient of friction.

[0013] Taking into account one or more of the aforementioned operating parameters and one or more temperature measurements, a sufficiently accurate estimation of the rotational speed of the mechanical seal can be made. By evaluating the temperature and rotational speed profiles over time, it is then possible to analyze the condition of the mechanical seal and, preferably, to estimate its service life.

[0014] Several approaches are conceivable for determining the rotational speed. An implicit or explicit approach is possible. The latter is advantageously based on attempting to calculate the current rotational speed using an explicit functional equation that includes one or more temperature measurements as well as one or more of the aforementioned operating parameters. For example, such an explicit function could be defined using all available parameters of the mechanical seal that can be determined during machine operation. Preferably, the explicit function includes a pressure value and at least one, preferably all, of the following temperature measurements as functional parameters: the temperature of the fluid to be sealed at the mechanical seal, the ambient air temperature at the housing and / or component temperatures of the sliding and / or counter ring, as well as temperatures of one or more adjacent housing or counter-support components.

[0015] The explicit function can be predefined and stored in memory for machine operation. Determining the explicit function can be done beforehand, for example, through experimental investigations. During the investigation, the rotational speed is measured using sensors, and a mathematical relationship is defined based on the machine's operating parameters. Various methods are available for finding the function. For example, regression analysis is one possibility. More complex mappings are also conceivable, such as those using neural networks, radial basis functions, or approaches like kriging.

[0016] An alternative to experimental investigations for determining the function are modeling and simulation-supported approaches. Here, virtual experiments are used to try to define a suitable function for estimating the rotational speed.

[0017] One advantage of the explicit approach to calculating rotational speed lies in the ability to easily model transient processes. If typically transient information from the input variables, such as the time derivative, is also considered as input variables for the rotational speed prediction formula, then it is potentially possible to estimate even highly transient rotational speeds.

[0018] Instead of an explicit approach, an implicit approach can also be used to estimate the rotational speed. Particularly preferred is estimation of the rotational speed by thermal balancing of the mechanical seal. Such an approach is based on the premise that a thermal equilibrium exists, such that the sum of the heat flows across the surfaces of the sealing rings of the mechanical seal is identical to the heat loss generated in the sealing gap.

[0019] The heat generated in the sealing gap depends significantly on the mechanical friction between the contact surfaces of the sliding and mating rings, as well as on the shear of the fluid in the sealing gap. Both heat generation mechanisms, mechanical and hydrodynamic, are substantially influenced by the rotational speed of the mechanical seal. By balancing the generated heat and the heat flows exiting the surfaces of the mechanical seal components, a rotational speed can be determined for which the condition of thermal equilibrium is met. The rotational speed determined in this way corresponds to the estimated rotational speed of the mechanical seal.

[0020] Advantageously, the heat released in the sealing gap is defined as a function of both mechanical and hydrodynamic power losses. The mechanical power loss depends primarily on the preload of the mechanical seal, the pressure differential between the high- and low-pressure sides of the seal, the coefficient of friction of the contact surfaces, and the rotational speed. In addition to the mechanical power loss, there is a hydrodynamic component, determined by viscous shear effects in the sealing gap. Accordingly, the viscosity of the fluid is taken into account, and more complex thermomechanical deformations of the sealing rings, as well as thermodynamically possible phase transitions of the fluid in the sealing gap, can be determined and considered.

[0021] The heat flows transferred to the environment via the surfaces of the sliding and counter rings depend significantly on the temperature levels established within the rings, as well as on the speed-dependent flow and temperature field of the fluids at the rings. One possible definition of the heat flows is based on the mean temperature of the exchange surfaces between the rings and the surrounding fluid, and a speed-dependent heat transfer coefficient at these exchange surfaces. The dependencies of the aforementioned heat flows on operating parameters can be obtained from coupled fluid or structural mechanics simulations. The use of so-called "conjugate heat transfer" simulations is possible.

[0022] In this way, dependencies, models, or mathematical functions can be determined for both the heat flows and the power loss within the sealing gap, including the rotational speed of the mechanical seal as one parameter. By balancing these three functions, the rotational speed at which thermal equilibrium exists can be determined. The rotational speed is therefore estimated using an implicit approach. Determining the rotational speed at thermal equilibrium can be done analytically or through graphical / numerical evaluation. The latter method is based on a heat balance curve that defines the heat balance as a function of the rotational speed. The zero crossing of the heat flow balance curve corresponds to the estimated rotational speed at thermal equilibrium.

[0023] In addition to the method according to the invention, the present invention also relates to a rotating machine with an integral mechanical seal and a processor unit for carrying out the method according to the invention. The rotating machine thus has the same advantages and properties as those already described above with reference to the method according to the invention. Therefore, a repetitive description is omitted.

[0024] Further advantages and features of the invention will be illustrated below with reference to figures. These show: Fig. 1: a representation of a heat balance curve for the graphical determination of the rotational speed, and Fig. 2: a schematic representation of the sliding and counter rings of a mechanical seal with the resulting heat flows.

[0025] The function, service life, and reliability of a mechanical seal depend significantly on the condition of the seal contact. Assessing and monitoring this condition (condition monitoring) allows for predictions about the remaining service life of the seal and thus forms the basis for predictive maintenance. Besides temperature, rotational speed is an important operating parameter for determining the seal's condition. It significantly influences the frictional work generated in the contact and thus the heat generated at the seal contact. Furthermore, the time integral of the rotational speed represents the important parameter of the seal's sliding displacement. However, since measuring the rotational speed is not feasible in many applications, for example, due to space constraints or cost considerations, it must be determined by other means.

[0026] The invention therefore describes a method for estimating the rotational speed of a mechanical seal using temperature measurements and other necessary operating parameters (besides the rotational speed). Two possible evaluation approaches for the measured temperatures of mechanical seal components and other operating parameters are described below, which allow for a sufficiently accurate estimation of the rotational speed. The first described variant is an implicit approach, the principle of which is based on a thermal balance of mechanical seal components. The second possibility is an explicit approach that uses a direct modeling of the rotational speed as an explicit function of known quantities. Implicit approach

[0027] In the thermal equilibrium of the mechanical seal rings, the heat output generated in the sealing contact must be identical to the sum of the heat flows across the surfaces of the mechanical seal rings. The thermal control area boundaries are defined, for example, at the outer surfaces of the mechanical seal rings. However, this approach can be used generally for any control area boundaries over which the heat flows can be estimated as a function of the unknown rotational speed using available measurement data. Additionally, the heat source in the sealing gap must also be determined as a function of the unknown rotational speed using available measurement data. This evaluation approach therefore requires an a priori model of the mechanical seal components, in which all thermally relevant effects must be represented.

[0028] These thermally relevant effects include, for example, heat flows across the selected control volume boundaries. The dependence of these heat flows on operating parameters can be obtained from coupled fluid and structural mechanics simulations (CHT - Conjugate Heat Transfer Simulations). In this context, the influence of rotational speed on the resulting flow around the sealing components is particularly relevant and relatively application-specific (depending on the fluid volume around the seal).

[0029] If, for a given seal and a given operating condition, all heats are formulated (numerically or analytically) and balanced as a function of the remaining unknown rotational speed, then a heat balance curve follows, whose zero crossings are the solution of the thermal balance and thus correspond to the possible rotational speeds.

[0030] Fig. Figure 1 shows an example of such a heat balance curve, in which the heat flow balance is plotted against the rotational speed of the mechanical seal.

[0031] One possible, but not exclusive, execution of the evaluation is described below. The sliding and counter rings 1, 2 of a mechanical seal are considered, as shown in Fig. 2. A heat source Q_in is modeled in contact 3. In the steady-state thermal equilibrium of the rings, Q_in must be equal to the sum of all heat fluxes exchanged across the outer edges, which are in Fig. 2 are indicated by the arrows 4. The sum of the heat flows emitted via the edges of the sliding ring is denoted as Q_ring, the sum of the heat flows emitted via the edges of the opposing ring as Q_gegen. For thermal equilibrium, the following must hold: 0=Q_in+Q_ring+Q_against Q_ein, Q_ring and Q_gegen can be represented as functions of the following parameters: i) the fluid temperatures inside Tf_i (e.g. on the high-pressure side of the seal) and outside Tf_a (e.g. on the low-pressure side of the seal), ii) the pressures of the fluids inside p_i and outside p_a, iii) the (mechanical) preload F_before the sealing contact 3, iv) of the fluids and thus their properties inside (e.g. density rhof_i, dynamic viscosity muf_i, specific heat capacity cpf_i, thermal conductivity lambdaf_i, vapor pressure pvap_i) and outside (correspondingly with index a), v) the material parameters of the sealing rings (e.g. for rotating sliding ring 1: Density rho_r, specific heat capacity cp_r, thermal conductivity lambda_r, Young's modulus E_r, Poisson's ratio Poisson's ratio, coefficient of thermal expansion alpha_r, for stationary counter-ring 2 corresponding quantities with index -g), vi) the surface properties in the sealing contact 3 and in exchange with the fluids (e.g. effective coefficient of friction mu_fric), vii) the rotational speed n.

[0032] The heat Q_in released at contact 3 increases primarily with the mechanical power loss in the frictional contact, which in turn increases with increasing preload F_vor, increasing pressure difference p_i - p_a, increasing coefficient of friction mu_fric, and increasing rotational speed n. In addition to the mechanical power loss, there is a hydrodynamic component due to viscous shear action in the contact gap 3, which increases with the viscosity of the fluid muf_i or muf_a. Complex thermomechanically induced deformation of the sealing rings 1, 2, as well as a possible phase transition of the internal fluid in the sealing gap 3, also influence the mechanical and hydrodynamic power loss. These complex relationships can be determined, for example, using specialized tribological modeling and simulation software focusing on the sealing rings 1, 2 and the sliding contact 3. The coefficient of friction mu_fric can be determined experimentally using tribometers.

[0033] The heat fluxes Q_ring and Q_gegen transferred from rings 1 and 2 to the surroundings beyond their boundaries depend primarily on the temperature levels established within rings 1 and 2, and on the flow and temperature fields of the fluids at rings 1 and 2, which are significantly dependent on the rotational speed n. One possible formulation for Q_ring and Q_gegen is based on their mean temperature, their exchange surface area with the fluid, and the respective rotational speed-dependent heat transfer coefficients at these exchange surfaces.

[0034] For the modeling and estimation of Q_ein, Q_ring and Q_gegen, the method disclosed in DE 10 2023 127 926.2 can be used, the disclosure of which is fully incorporated here. Explicit approach

[0035] The explicit approach attempts to directly predict the rotational speed based on all available and known parameters during operation, such as the pressure of the fluid being sealed at the mechanical seal, the ambient temperature, and the temperatures of other components of the mechanical seal. The prediction method can be derived from multiple sources / methods, each requiring prior development work.

[0036] Experimental investigations with a known (measured) rotational speed can be used to try to find ways to predict the rotational speed with all other quantities known later in operation, especially temperatures of the mechanical seal components, e.g. regressions, but also more complex models such as neural networks, radial basis functions, kriging, etc.

[0037] Another possibility is a modeling and simulation-supported approach in which virtual experiments are carried out in order to derive a rotational speed estimate from the results, as in the experimental approach.

[0038] One advantage of the explicit approach lies in the ability to more easily model transient processes. If typical transient information from the input variables, such as the time derivative, is also considered as input variables for the speed prediction rule, then it is potentially possible to estimate even highly transient speeds. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102023109020.8

[0004] DE 10 2023 127 926.2

[0034]

Claims

[1] Method for monitoring a mechanical seal within a rotating machine, in particular a pump, with at least one temperature sensor arranged within the machine for detecting a temperature in the vicinity of the mechanical seal and / or at least one component of the mechanical seal, wherein the rotational speed of the rotating machine is estimated by means of the at least one temperature measurement value and at least one further operating parameter of the mechanical seal. [2] Method according to claim 1, characterized by , that a state of the mechanical seal is determined using the estimated rotational speed and at least one measured value from at least one temperature sensor. [3] Method according to any of the preceding claims, characterized by, that at least one further operating parameter of the mechanical seal for estimating the rotational speed is a pressure value of the fluid surrounding the mechanical seal, in particular the pressure difference of the fluid between the high and low pressure sides of the mechanical seal, and / or the preload force of a mechanical preload of the mechanical seal and / or one or more characteristic sizes or properties of the fluid surrounding the mechanical seal and / or one or more material parameters of the sealing components and / or a surface property of the mechanical seal components (1, 2) in the sealing contact of the mechanical seal. [4] Method according to any of the preceding claims, characterized by that the rotational speed is modeled by an explicit function, whereby the explicit function is determined experimentally in advance through preliminary tests or by a simulation-based approach through virtual tests. [5] Method according to claim 4, characterized by that the experimental determination of the explicit function is carried out by regression analysis and / or by mapping via neural network, radial basis functions or kriging. [6] Method according to claim 4 or 5, characterized by , that the explicit function takes into account at least the pressure and at least one temperature measurement, in particular one or more of the following temperature measurements: Temperature of the fluid surrounding the mechanical seal, the ambient air temperature at the housing of the rotating machine and / or the component temperatures of the sliding and / or counter ring or one or more adjacent housing or counter-support components. [7] Method according to any one of the preceding claims 1 to 3, characterized by, that the rotational speed is estimated by balancing the heat flows occurring in the area of ​​the mechanical seal, which are dependent on the rotational speed, whereby at least one temperature measurement value and at least one further operating parameter of the mechanical seal are taken into account for the determination of the heat flows. [8] Method according to claim 7, characterized by , that for the calculation the heat released in the sealing gap (3) (Q_in) is compared with the sum of the heat flows (Q_ring, Q_against) exchanged over the outer surfaces of the sealing components (1, 2). [9] Method according to claim 8, characterized by , that the heat (Q_in) released in the sealing gap (3) is defined as a function of the mechanically and hydrodynamically caused power loss. [10] Method according to claim 8 or 9, characterized by, that the exchanged heat flows (Q_ring, Q_gegen) are defined as a function of the temperature of the mechanical seal components (1, 2), the exchange surface of the mechanical seal components (1, 2) with the fluid and the speed-dependent heat transfer coefficients at the exchange surfaces of the mechanical seal components (1,2). [11] Method according to one of claims 9 or 10, characterized by that the dependencies are determined in advance using tribological modeling. [12] Rotating machine with a mechanical seal and a processor unit for carrying out the method according to one of the preceding claims.

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