Systems and methods for estimating total dissolved solids in boiler water, and steam boilers

Abstract

A system (12) for estimating the total dissolved solids (TDS) concentration in boiler water is described, the system comprising a sensor (14) having a transmitter configured to transmit an RF or microwave signal to the boiler water and a receiver configured to receive a reflected signal from the reflection of the RF or microwave signal by the boiler water, and an analysis module (16) configured to determine a conductivity value in the boiler water based on the reflected signal and to determine the TDS concentration in the boiler water based on the conductivity. A corresponding method is also described.

Description

Technical Field

[0001] The present disclosure relates to systems and methods for estimating total dissolved solids in boiler water.

Background Art

[0002] When a boiler generates steam, any impurities in the boiler feed water that do not boil with the steam concentrate in the boiler water.

[0003] As the total dissolved solids (TDS) become increasingly concentrated, steam bubbles tend to become more stable and thus do not burst when they reach the surface of the boiler. At some point (depending on boiler pressure, size, and steam load), a significant portion of the steam space in the boiler is filled with bubbles and the bubbles are carried to the main steam pipe.

[0004] This is undesirable because the steam is not only overly wet when it exits the boiler but also contains boiler water with high levels of dissolved solids and possibly suspended solids. These solids can contaminate control valves, heat exchangers, and steam traps.

[0005] TDS is derived from dissolved organic and inorganic substances in the boiler feed water. In particular, common salt components in the boiler feed water include calcium, sodium, chloride, potassium, phosphate, and nitrate.

[0006] To avoid performance and safety issues in the boiler, it is necessary to measure, monitor, and control the TDS concentration in the boiler water.

Summary of the Invention

[0007] According to one aspect, a system for estimating the total dissolved solids (TDS) concentration in boiler water is provided. The system includes a transmitter configured to transmit an RF or microwave signal to the boiler water, a sensor having a receiver configured to receive a reflected signal from the reflection of the RF or microwave signal by the boiler water, and an analysis module configured to determine a conductivity value in the boiler water based on the reflected signal and determine the TDS concentration in the boiler water based on the conductivity.

[0008] The analysis module may be further configured to determine a reflection coefficient based on the reflected signal and determine a conductivity value based on the reflection coefficient.

[0009] The system may further include a control module configured to determine whether the TDS concentration exceeds a threshold and take measures when the TDS concentration exceeds the threshold.

[0010] The control module may output a warning to an operator when the TDS concentration exceeds the threshold.

[0011] The control module may open a blowdown control valve to reduce the TDS concentration when the TDS concentration exceeds the threshold.

[0012] The sensor may be an open-ended coaxial probe. The probe may be a high-pressure and high-temperature probe.

[0013] The analysis module may include a vector network analyzer.

[0014] According to another aspect, a steam boiler including the aforementioned system is provided.

[0015] According to another aspect, a method for estimating the total dissolved solids (TDS) concentration in boiler water is provided, the method including transmitting an RF or microwave signal to the boiler water, receiving a reflected signal from the reflection of the RF or microwave signal by the boiler water, determining a conductivity value in the boiler water based on the reflected signal, and determining the TDS concentration in the boiler water based on the conductivity.

[0016] The method may further include determining a reflection coefficient based on the reflected signal, and the conductivity value is determined based on the reflection coefficient.

[0017] The RF signal or microwave signal may be transmitted and received using a sensor probe.

[0018] The sensor probe may be an open-ended coaxial probe. Alternatively, the RF or microwave signal may be transmitted and received using a coaxial transmission line, or may be transmitted and received using a resonant cavity measurement system. The resonant cavity measurement system may be connected to a blowdown line.

[0019] The method may further include determining whether the TDS concentration exceeds a threshold value, and taking measures when the TDS concentration exceeds the threshold value.

[0020] The measures may include giving a warning to the operator.

[0021] The measures may include opening a blowdown control valve to reduce the TDS concentration.

[0022] For a better understanding of the present invention and to more clearly show how the present invention can be put into practice, reference is now made, by way of example, to the accompanying drawings.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0024] FIG. 1 shows a schematic view of a steam boiler plant 2. The steam boiler plant 2 includes a steam boiler 4. The steam boiler 4 is connected to a feed water line 6 and a main steam pipe 8. Water 10 is pumped from a feed water tank to the boiler 4 by a feed water pump (not shown). Thereafter, the water 10 is heated in the boiler 4 to form steam. This steam is discharged through the main steam pipe 8 and transported to a point of use.

[0025] A TDS monitoring system 12 according to an embodiment of the present invention is provided in the steam boiler 4. The system 12 includes a sensor probe 14 connected to an analysis module 16. The output from the analysis module 16 is supplied to a control module 18. This control module 18 may be used to control a blowdown valve 20, or may be used to take other measures.

[0026] As shown in FIGS. 2(a) and 2(b), the sensor probe 14 may be an open-ended coaxial probe. This open-ended coaxial probe includes an inner conductor 22 and an outer conductor 24, which are concentrically arranged and separated from each other by a dielectric material 26. The dielectric material 26 is arranged between the inner conductor 22 and the outer conductor 24 so that the inner conductor 22 and the outer conductor 24 are electrically insulated from each other.

[0027] As shown in FIG. 2(b), the sensor probe 14 is inserted into an opening formed in the wall 28 of the steam boiler 4 so as to be immersed in the boiler water 10. The sensor probe 14 may be a high-pressure and high-temperature probe capable of withstanding the conditions in the steam boiler 4. The outer conductor 24 may form a flange 28 that abuts against the inner surface of the wall 28.

[0028] As described above, the sensor probe 14 is connected to the analysis module 16 via the probe connection cable 17. In this embodiment, the analysis module 16 includes a vector network analyzer (VNA). The VNA includes a signal source that generates an RF (Radio Frequency) or microwave signal, and this RF or microwave signal is transmitted to the sensor probe 14.

[0029] The RF or microwave signal forms an electromagnetic field between the inner conductor 22 and the outer conductor 24, and as shown by step S2 in FIG. 3, this electromagnetic field is transmitted into the boiler water 10 and reflected by the boiler water. The VNA further includes a receiver, and in step S4, it receives the reflected signal from the sensor probe 14 after reflection by the boiler water 10.

[0030] In step S6, the analysis module 16 determines the conductivity value in the boiler water 10. This is determined by calculating the reflection coefficient based on the ratio of the amplitude of the reflected signal to the amplitude of the transmitted signal (i.e., the incident signal). It has been found that the amplitude of the reflected signal depends on the conductivity of the boiler water 10. Therefore, the analysis module 16 can then determine the conductivity of the boiler water 10 from the reflection coefficient. Then, in step S10, the analysis module 16 determines the TDS concentration from the conductivity.

[0031] The correlations between the reflection coefficient and the conductivity and between the conductivity and the TDS concentration may be determined empirically. The method may be repeated with signals having different frequencies to improve accuracy.

[0032] As described above, the output from the analysis module 16 may be supplied to the control module 18, which can take measures according to the current TDS concentration. In particular, the control module 18 may open the blowdown valve 20 to discharge the water 10 from the boiler 4, and then the water 10 is replaced with fresh feed water to reduce the TDS concentration of the boiler water in the boiler 4. This measure may be taken when the current TDS concentration exceeds a threshold value.

[0033] In other embodiments, the control module 18 may give a warning such as an audible warning or a visual warning, and function as a prompt for a human operator to take measures to reduce the TDS concentration. For example, the operator may manually open the blowdown valve 20. In other embodiments, the output from the analysis module 16 may simply be displayed to the operator to enable the operator to monitor and control the TDS concentration. It will be understood that the analysis module 16 and the control module 18 may be embodied by a single unit (e.g., a processor) and distinguished only by their functionality.

[0034] In other examples, RF or microwave signals may be transmitted and received using a coaxial transmission line, or may be transmitted and received using a resonant cavity measurement system. The resonant cavity measurement system may be connected to the blowdown line.

[0035] The present invention is not limited to the embodiments described herein and may be modified or adapted without departing from the scope of the present invention.

Claims

1. A system for estimating the total dissolved solids (TDS) concentration in boiler water, comprising: a sensor having a transmitter configured to transmit an RF or microwave signal to the boiler water and a receiver configured to receive a reflected signal from the reflection of the RF or microwave signal by the boiler water; an analysis module configured to determine a conductivity value in the boiler water based on the reflected signal and to determine a TDS concentration in the boiler water based on the conductivity; A system comprising the above.

2. The system according to claim 1, wherein the analysis module is further configured to determine a reflection coefficient based on the reflected signal and to determine the conductivity value based on the reflection coefficient.

3. The system according to claim 1 or 2, further comprising a control module configured to determine whether the TDS concentration exceeds a threshold value and to take measures when the TDS concentration exceeds the threshold value.

4. The system according to claim 3, wherein the control module outputs a warning to an operator when the TDS concentration exceeds the threshold value.

5. The system according to claim 3 or 4, wherein the control module opens a blowdown control valve to reduce the TDS concentration when the TDS concentration exceeds the threshold value.

6. The system according to any one of claims 1 to 5, wherein the sensor is an open-ended coaxial probe.

7. The system according to any one of claims 1 to 6, wherein the analysis module comprises a vector network analyzer.

8. A steam boiler comprising the system according to any one of claims 1 to 7.

9. A method for estimating the total dissolved solids (TDS) concentration in boiler water, comprising: transmitting an RF or microwave signal to the boiler water; receiving a reflected signal from the reflection of the RF or microwave signal by the boiler water; determining a conductivity value in the boiler water based on the reflected signal; determining a TDS concentration in the boiler water based on the conductivity; A method including the above.

10. further comprising determining a reflection coefficient based on the reflected signal; and the conductivity value is determined based on the reflection coefficient. The method according to claim 9.

11. The method according to claim 9 or 10, wherein the RF or microwave signal is transmitted and received using a sensor probe. **Claim 12** The method according to claim 11, wherein the sensor probe is an open-ended coaxial probe. **Claim 13** Determining whether the TDS concentration exceeds a threshold value; Taking measures when the TDS concentration exceeds the threshold value; The method according to any one of claims 9 to 12, further comprising: **Claim 14** The method according to claim 13, wherein the measure includes giving a warning to an operator. **Claim 15** The method according to claim 13 or 14, wherein the measure includes opening a blowdown control valve to reduce the TDS concentration.

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