WO2015041569A1

WO2015041569A1 - Method for monitoring the condition of a condensate drain and device for implementing same

Info

Publication number: WO2015041569A1
Application number: PCT/RU2014/000335
Authority: WO
Inventors: Дмитрий Алексеевич САМСОНОВ
Original assignee: Дмитрий Алексеевич САМСОНОВ
Priority date: 2013-09-20
Filing date: 2014-05-12
Publication date: 2015-03-26
Also published as: RU2546907C1; RU2013142976A

Abstract

The invention can be used for monitoring the rational utilization of steam in heat exchangers. A method for monitoring the condition of a condensate drain includes measuring the temperature of a heating steam, the pressure of the heating steam, the temperature of the wall of a condensate pipe and the pressure in the condensate pipe, determining the mass flow rate of the heating steam and the diameter of the condensate pipe, and, according to the magnitude of the mass flow rate of the heating steam, first calculating a coefficient for the heat transferred from transient steam to the wall of the condensate pipe, and then calculating a coefficient for the heat transferred from the condensate to the wall of the condensate pipe, and then, based on the data regarding the pressure in the condensate pipe, calculating a saturation temperature corresponding to said pressure, then, using the ratio of the magnitude of the coefficient of heat transferred from the condensate to the wall of the condensate pipe to the magnitude of the coefficient of heat transferred from the transient steam to the wall of the condensate pipe and data regarding the temperature of the heating steam entering the heat exchanger and the saturation temperature corresponding to the pressure in the condensate pipe and the temperature of the wall of the condensate pipe, the efficiency of the condensate drain is calculated based on heat balance equations.

Description

Method for monitoring the status of the steam trap and device for its implementation

FIELD OF THE INVENTION

The invention relates to the field of power engineering, in particular to the task of energy conservation in steam consumption systems and can be used to control the rational use of steam in heat exchangers by determining the efficiency of a steam trap.

State of the art

At many industrial enterprises, water vapor is used as a process coolant, which, in most cases, is used in recuperative heat exchangers. Steam (called heating), giving up the heat of phase transition, condenses on the heat exchange surface. Then, the condensate that has formed accumulates in the steam trap and, passing through the nozzle of the steam trap, enters the condensate conduit through which it is transported to the boiler for reuse. The key device ensuring the completeness of condensation of the heating steam in the heat exchanger is a steam trap, which must hold the heating steam in the heat exchanger and pass only the liquid phase of the coolant through it. Over time, under the influence of contaminants adhering to the internal elements of the steam trap, erosion of the locking elements caused by the flow of the high-temperature vapor-liquid mixture, the steam trap loses its effectiveness, which is understood as the ratio of the mass of condensate passing through the nozzle of the steam trap per unit time to the mass of heating steam entering the heat exchanger for same unit of time. This indicator can be expressed as a percentage or fraction of a unit.

Monitoring the condition and efficiency of the steam trap is necessary to monitor the rational (full) use of heating steam in the heat exchanger. The steam trap, with the exception of rare cases, does not fail suddenly and completely. In most cases, a complete failure is preceded by a long (from a year to several years) period of operation in the mode of partial passage of heating steam, when the efficiency of the steam trap is within 9 (Н50%. It is very important to obtain information about the leakage of heating steam through the steam trap to the maximum possible earlier stage of malfunction. Water vapor is one of the most expensive coolants, therefore, control of its rational use is a very urgent task. If, according to the measurement results, the efficiency of the steam trap is, for example, 80%, then this steam trap must be replaced. However, to date, a malfunction of this level remains unnoticed by the operating personnel, and the steam trap continues to work for a long time, gradually losing its effectiveness more and more. As a result, untimely identification of faulty steam traps results in significant losses for the enterprise and, as a result, an increase in the cost of production.

Therefore, the creation of a method and device for monitoring the status of the steam trap is relevant.

A known method and device for monitoring the status of the steam trap described in patent US4456173 (A), 1984.06.26 and in patent US4468962 (A), 1984.09.04, based on measuring the flow rate and energy of the vapor phase of the coolant with a special hot-wire anemometer or similar device installed in the separator, mounted on a condensate line between the heat exchanger and the steam trap.

This method does not allow to reliably determine the state of the steam trap, since droplets of condensate will inevitably fall on the sensitive element of the device that measures the flow rate of the steam, introducing significant distortions into the result of the measurement of the flow rate of the steam.

A known method is presented in patents, for example, US5069247 (A), 1991.12.03 or GB2231407 (A), 1990.1 1.14, based on the use of a condensate level sensor mounted on a condensate pipe between the heat exchanger and the steam trap. The level sensor is located in a special pocket or chamber and determines the level of condensate by measuring the conductivity of its environment, whether it is condensate or steam.

The disadvantage of this method is the ability to diagnose only two extreme states of the steam trap: “good” and “faulty”. Moreover, the condition of the steam trap is “faulty” is diagnosed only with a mass fraction of passage steam of the order of 50% or more. The known method described in patent US4249697 (A), 1981.02.10, based on measuring the temperature difference between the body of the steam trap and the wall of the condensate pipe. If the temperature difference is less than a predetermined value, then the steam trap is considered defective.

The disadvantage of this method is the ability to diagnose only two extreme states of the steam trap: “good” and “faulty”. This method works satisfactorily when the pressure drop before and after the valve of the steam trap reaches a significant value. With a small pressure drop before and after the valve of the steam trap, the temperature difference between the body of the steam trap and the wall of the steam trap will be small. In the event that the steam trap is operational, the sensor may mislead the observer, signaling a malfunction.

The known method described in patent EP1831767 (B1), 2011.06.29, based on the registration of the acoustic signal generated by the flow of the medium during its flow at high speed through the nozzle of the steam trap and additional control of the temperature of the steam entering the steam trap or leaving the steam trap.

The disadvantage of this method is the ability to diagnose only two extreme states of the steam trap: “good” and “faulty”. Also, in the event of a change in the pressure drop across the valve of the steam trap, the nature and intensity of the acoustic signal will change, which can lead to a false positive of this monitoring system of the steam trap. As a protection against this situation, the tolerance limits for the acoustic signal can be extended, however, this entails a significant decrease in the sensitivity of this monitoring system.

The closest to the method for monitoring the status of the steam trap according to the technical nature and the achieved result, selected as a prototype, is the method described in patent US8050875 (B2), 2011.11.01, based on measuring the temperature of the wall of the condensate pipe and the flow of coolant leaving the steam trap, and comparing these temperatures with the temperature of the heating steam. Also, this method involves the use of pressure sensors located on the steam pipe, steam trap and condensate pipe. The disadvantage of this method is the ability to diagnose only two extreme states of the steam trap: “good” and “faulty”.

The closest to the device for monitoring the status of the steam trap in terms of technical nature and the achieved result, selected as a prototype, is the device described in patent US8050875 (B2), 2011.11.01, which includes heat carrier temperature sensors installed in the steam line, inside the steam trap (or its wall), on the wall of the condensate pipe, and inside the condensate pipe at the outlet of the steam trap. Also in this device are pressure sensors installed in the heat exchanger, in the steam trap and in the condensate conduit.

The disadvantage of this device is the possibility of its successful use for diagnosing only two extreme conditions of the steam trap: “good” and “faulty”.

SUMMARY OF THE INVENTION

The problem solved by the invention is the improvement of the method and device for monitoring the status of the steam trap.

The technical result from the use of the invention lies in the possibility of determining the efficiency of the steam trap.

This result is achieved by the fact that in the method for monitoring the status of the steam trap, including measuring the temperature of the heating steam, the pressure of the heating steam, the wall temperature of the condensate pipe and the pressure in the condensate pipe, the mass flow rate of the heating steam and the diameter of the condensate pipe are additionally determined, then the coefficient is first calculated from the mass flow rate of the heating steam heat transfer from passing steam to the wall of the condensate pipe, and then calculate the heat transfer coefficient from condensate to the wall of the condensate then, based on the pressure data in the condensate pipe, the saturation temperature corresponding to this pressure is calculated, then using the ratio of the heat transfer coefficient from the condensate to the wall of the condensate pipe to the value of the heat transfer coefficient from the passing steam to the wall of the condensate pipe and data on the temperature of the heating steam entering the heat exchanger , the saturation temperature corresponding to the pressure in the condensate line, and the wall temperature condensate pipeline, calculate the efficiency of the steam trap according to the heat balance equations.

The specified result is achieved by the fact that the steam trap pressure monitoring device entering the heat exchanger, the temperature sensor of the heating steam entering the heat exchanger, the wall temperature sensor of the condensate pipe, the pressure sensor in the condensate pipe and a computing module are additionally equipped with a heating steam flow sensor entering the heat exchanger.

The method is as follows.

1. Data on the temperature, pressure and flow rate of the heating steam entering the heat exchanger, on the temperature of the condensate pipe wall and pressure in the condensate pipe, are received from the sensors in the computing module for processing. Data on the diameter of the condensate pipe is entered into the memory of the computing module at the initial setup stage of the device for monitoring the status of the steam trap.

2. Based on the known mass flow rate of the heating steam entering the heat exchanger, the heat transfer coefficient from the passing steam to the wall of the condensate pipe is calculated.

3. Based on the known mass flow rate of the heating steam entering the heat exchanger, the heat transfer coefficient from the condensate to the wall of the condensate pipe is calculated.

4. Based on the data on the pressure in the condensate line, the saturation temperature corresponding to this pressure is calculated.

5. Using the ratio of the coefficient of heat transfer from the condensate to the wall of the condensate pipe to the value of the coefficient of heat transfer from the passing steam to the wall of the condensate pipe, as well as data on the temperature of the heating steam entering the heat exchanger, the saturation temperature at the pressure in the condensate pipe and the temperature of the wall of the condensate pipe, the efficiency of the condensate drain is calculated.

List of drawings

The invention is illustrated by the figures of the drawings, which depict: b

figure 1 - diagram of a device for monitoring the status of the steam trap with temperature and steam pressure sensors installed on the steam line; figure 2 - diagram of a device for monitoring the status of the steam trap with temperature and steam pressure sensors mounted on a heat exchanger; fig.Z is a diagram of a section of a condensate pipe with an installed temperature sensor of the wall of the condensate pipe;

DETAILED DESCRIPTION OF THE INVENTION

The physical principle of the patented method for monitoring the status of the steam trap is as follows.

It is known that the steam trap is a batch device - in a serviceable steam trap, the shutoff valve is alternately open or closed, the temperature of the condensate pipe wall behind the steam trap is determined by the temperature of the throttled condensate and secondary boiling steam. When the shut-off valve is worn or broken, this valve is in the open position. In this case, the period of the breakthrough of the high temperature steam (called span steam) is replaced by the period of condensate discharge accumulated during this time in the body of the steam trap. When condensate is throttled through the nozzle of a steam trap, its temperature decreases due to the formation of secondary boiling steam. A film of relatively cold condensate moves along the inner surface of the wall of the condensate pipe, cooling it. After a certain period of time, overflow steam again enters the condensate pipe through the nozzle of the steam trap. Due to the small diameter of the condensate pipe, the passage of steam moves at high speed. There is a breakdown of the condensate film from the wall of the condensate pipe and heating of this wall. Then a new portion of throttled condensate enters the condensate line and the cycle repeats. Thus, the temperature of the wall of the condensate pipe near the steam trap changes cyclically in time. Since the wall of the condensate line and temperature sensors have some thermal inertia, the wall temperature in this case can be considered quasistationary. The value of the wall temperature of the condensate pipe depends on the ratio of the mass flow rates of the high-temperature span steam and the low-temperature condensate. Knowing the value of the heat transfer coefficient from the passage steam to the wall of the condensate pipe and the value of the heat transfer coefficient from condensate to the wall of the condensate pipe, the temperature of this wall, the pressure in the condensate pipe, the saturation temperature at the pressure in the condensate pipe, and the temperature of the passage steam (which is equal to the temperature of the heating steam that has passed the throttling process to pressure in the condensate line), it is possible to calculate the mass flow rate of the condensate and the mass flow rate of the passing steam and thus determine the efficiency ndensatootvodchika.

It should be noted that in order to calculate the heat transfer coefficient from passing steam to the wall of the condensate pipe and the heat transfer coefficient from condensate to the wall of the condensate pipe, the mass flow rate of heating steam entering the heat exchanger is used. To simplify, the statement is used that the speed of the passage of steam and condensate in the condensate pipeline directly and directly depends on the mass flow rate of the heating steam entering the heat exchanger. This statement is close enough to the true picture of the physical process taking place in the condensate pipe behind the steam trap.

In many cases, the flow rate of heating steam is measured for a group of heat exchangers and the installation of an individual flow meter on each heat exchanger is impossible or impractical. In this case, to calculate the heat transfer coefficient from the passing steam to the wall of the condensate pipe and the heat transfer coefficient from the condensate to the wall of the condensate pipe, the calculated (as a fraction of the total flow rate of heating steam entering the group of heat exchangers) or the design value of the flow of heating steam for each heat exchanger can be used. This will not cause a significant decrease in the accuracy of monitoring the state of the steam trap, since the heat balance equations that determine the efficiency of the steam trap use the ratio of the heat transfer coefficient from the condensate to the wall of the condensate pipe to the value of the heat transfer coefficient from the passing steam to the wall of the condensate pipe.

In the case of a further simplification of the method for monitoring the state of the condensate drain, the heat transfer coefficient from the passing steam to the wall of the condensate pipe and the heat transfer coefficient from condensate to the wall of the condensate pipe can not be determined by calculation, but can be presented in the form of predetermined values (or immediately their ratios) stored in the computational memory module. However, in this case, the accuracy of state monitoring the condensate drain will decrease due to the fact that for different values of the flow rate of the heating steam, the ratio of the heat transfer coefficient from the condensate to the wall of the condensate pipe to the value of the heat transfer coefficient from the passing steam to the wall of the condensate pipe.

An example of a specific implementation of the method.

The method can be implemented using a steam trap monitoring device, the circuit of which is shown in FIG. one.

The device consists of a temperature sensor heating steam 1; heating steam pressure sensor 2; heating steam flow sensor 3; the temperature sensor of the wall of the condensate line 4; pressure sensor in the condensate line 5; connected to the computing module b.

The diagram also shows the steam line 7; heat exchanger 8; steam trap 9; condensate line 10; pipeline transporting the heated coolant 11.

The device for monitoring the status of the steam trap operates as follows. The sensors /, 2, 3, are installed on the steam line 7, and the sensors 4 and 5 are installed on the condensate line 10. Data received from these sensors, via a wired or wireless channel 12, is input to the computational module 6. In the computational module 6, according to predetermined algorithms (heat balance equations), the efficiency of the steam trap is calculated.

Information about the current state of the steam trap can be displayed on a display installed on the control panel, or transmitted via a wired or wireless channel to the dispatcher’s personal computer, where this information is displayed on a personal computer display or further processed. Thus, the device for monitoring the status of the steam trap can be integrated into the automated process control system (ACS TP) of the enterprise.

The computing module is based on a modern microprocessor device, for example, such as Atmel AVR ATmega 1284Р or similar.

To measure the temperature of the heating steam entering the heat exchanger, its pressure and flow rate, as well as the pressure in the condensate pipe, various sensors widely manufactured by industry. Sensors /, 2 for measuring the temperature and pressure of the heating steam entering the heat exchanger can be installed both on the steam line 7 and on the heat exchanger 8 (Fig. 2).

The wall temperature of the condensate pipe can be measured using thermocouples, thermistors, and other sensors designed to measure surface temperature. The temperature sensor must be securely mounted on the surface of the wall of the condensate pipe or mounted in the wall. To exclude the effects of ambient temperature, the surface section of the condensate line 10 together with the sensor 4 should be covered with thermal insulation 13 (Fig. 3).

The data received at the input of the computing module can be obtained not only from sensors installed specifically for monitoring the status of the steam trap. As at least one of the sensors included in the device for monitoring the status of the steam trap, similar sensors used in the existing telemetry system of the technological process of the enterprise can be used. This will avoid duplication of various sensors, and will reduce the cost of the device for monitoring the status of the steam trap. For example, if the existing telemetry system of an enterprise’s technological process uses temperature sensors for heating steam entering the heat exchanger, then it is not necessary to install a separate temperature sensor for heating steam to operate the steam trap status monitor - the existing sensor can be connected to the device for monitoring the status of the steam trap and thus enter its composition.

The method is tested at the enterprise of heavy industry. Using the device, the following data were obtained from the sensors: the temperature of the heating steam was 180 ° C, the absolute pressure in the heat exchanger was 0.5 MPa, the absolute pressure in the condensate pipe was 0.15 MPa, the temperature of the wall of the condensate pipe was 118 ° C, the mass flow rate of heating steam was 0.2 kg / s. The diameter of the condensate pipe was determined to be 0.05 m. Using the data obtained, using the heat balance equations, the efficiency of the steam trap was determined, amounting to 82%. At first glance, the steam trap has a fairly high efficiency, and it is not necessary to replace it. However, an economic analysis shows that at a cost of 1 GJ of heat of about 300 rubles and the cost of a new steam trap about 45,000 rubles, the payback period for replacing a steam trap under these conditions is about 24 days (with a round-the-clock operation). As a result, a decision was made to replace this steam trap.

Thus, the use of the invention allows to identify inoperative steam traps at an early stage of the development of a malfunction. Using data on the cost of a unit of thermal energy, the average cost of a steam trap of a given capacity, its nominal efficiency guaranteed by the manufacturer and its average life, you can simply determine the threshold value of the efficiency of a steam trap, at which it is recommended to replace it.

As a result of the use of the invention, the replacement of faulty steam traps will be made more often and the annual costs of the enterprise for this purpose will increase. However, the economic effect of saving heating steam will exceed the increase in costs for more frequent replacement of steam traps.

The present invention meets the criterion of industrial applicability, since it has been tested on real heat exchangers equipped with various types of steam traps. Among other things, a significant positive feature of the invention is the possibility of its integration into an automated process control system of an enterprise.

It should be noted that the invention has the property of adaptability and allows you to monitor the status of the steam trap in a wide range of fluctuations in the parameters of the heating steam (such as temperature, pressure, flow). This allows you to provide the necessary reliability and accuracy of monitoring the status of the steam trap under various technological operating modes of the heat exchanger.

Claims

CLAIM

1. A method for monitoring the status of the steam trap, including measuring the temperature of the heating steam, the pressure of the heating steam, the temperature of the wall of the condensate pipe and the pressure in the condensate pipe, DIFFERENT in that it further determines the mass flow rate of the heating steam and the diameter of the condensate pipe, then the heat transfer coefficient is first calculated from the mass flow rate of the heating steam from the passage of steam to the wall of the condensate pipe, and then calculate the heat transfer coefficient from condensate to the wall of the condensate pipe, after that coming from the data on the pressure in the condensate pipe, the saturation temperature corresponding to this pressure is calculated, then using the ratio of the heat transfer coefficient from the condensate to the wall of the condensate pipe to the value of the heat transfer coefficient from the passing steam to the wall of the condensate pipe and the data on the temperature of the heating steam entering the heat exchanger, the saturation temperature, corresponding to the pressure in the condensate pipe, and the wall temperature of the condensate pipe, calculate the efficiency of the steam trap according to the equations pilaf balance.

2. A device for monitoring the status of the steam trap, including a pressure sensor for heating steam entering the heat exchanger, a temperature sensor for heating steam entering the heat exchanger, a temperature sensor for the wall of the condensate pipe, a pressure sensor in the condensate pipe and a computational module DISTINCTING IN that a heating steam flow sensor is additionally introduced, entering the heat exchanger.