GB2117515A

GB2117515A - Monitoring the degree of superheat of steam

Info

Publication number: GB2117515A
Application number: GB08208764A
Authority: GB
Inventors: Bobby L Day
Original assignee: Brown Boveri Reaktor GmbH
Current assignee: ABB Reaktor GmbH
Priority date: 1982-03-25
Filing date: 1982-03-25
Publication date: 1983-10-12
Also published as: GB2117515B

Abstract

A temperature measurement- independent apparatus for determining the degree of superheat of steam in a pipe (1) comprises a tube (5) having a closed end (8) disposed in the pipe (1) and partially filled with water so that steam at a saturation pressure corresponding to the superheated steam temperature is formed in a space (7). Such pressure is communicated by the pipe (5) to a chamber (3) of a differential pressure transducer (4) and compared with the pressure of the steam in the pipe (1), which is communicated with a chamber (10) of the transducer (4) by a tube (9). <IMAGE>

Description

SPECIFICATION Monitoring the degree of superheat of steam This invention relates to methods of and apparatus for monitoring the degree of superheat of steam.

The use of superheated steam is necessary in many manufacturing processes and in the generation of energy. In this context, steam is understood to have a temperature above the saturation temperature corresponding to the steam pressure. Precise monitoring of this condition is desirable, so that, for example, equipment using superheated dry steam will not be damaged by wet steam or entrained water droplets. Thus, for example, in a power plant which is fed with superheated steam produced in a straight tube steam generator with shell-side boiling and comprising a turbine and turbine valves, of the type described in US Patent No. 3 447 509 (Sprague), the absence of superheating can lead to severe damage to the turbine valves and the turbine.

The degree of superheat could be determined by comparing the steam temperature in a pipeline or piping to the turbine with the saturation temperature of the flowing fluid. However, since it is difficult to determine the exact saturation temperature, such a method would lead to inexact results.

According to a first aspect of this invention there is provided apparatus for monitoring the degree of superheat of steam, the apparatus comprising a tube which is closed at one end, the closed end of the tube extending into a steam pipe which, in use, contains steam, and the tube being partially filled with water such that a water level exists in the closed end, above which level steam is formed, in use, in contact with the water in a previously evacuated space, a first measurement chamber arranged to be subjected to the pressure in the tube, means to transmit pressure in the steam pipe to a second measurement chamber, and means to compare the pressures in the measurement chambers to determine the degree of superheat of steam in the pipe.

According to a second aspect of this invention there is provided a method of monitoring the degree of superheat of steam, the method comprising determining the saturation pressure corresponding to the temperature of the steam, determining the steam pressure, and comparing said pressures to indicate the degree of superheat of the steam.

An embodiment of this invention described below provides for the simple and direct monitoring of the degree of superheat of steam in such a manner that precise results may be produced. Thus, the degree of superheat is monitored by means of a simple differential pressure measurement, avoiding the need for an uncertain saturation temperature mea surement.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawing, the sole figure of which is a schematic representation of apparatus embodying the invention.

Referring to the drawing, superheated steam 2 flows in a pipeline or piping 1 from a steam generator (not shown) to a point of use (not shown).

A tube 5, one end 8 of which is sealed, extends into the steam pipeline 1. The other end of the tube 5 is connected to a first measurement chamber 3 of a differential pressure-measuring transducer 4. The tube 5 is filled with water to a level 6, after prior evacuation, leaving an empty space 7 above the level 6 at the sealed end 8. A second tube 9, communicating with the superheated steam 2 in the pipeline 1, is connected to a second measurement chamber 10 of the differential pressure-measuring transducer 4. In operation, steam is formed in the sealed end 8 of the tube 5 and forms a steam cushion that occupies the space 7 above the water level 6.

Heat transfer from the steam 2 to the water in the tube 5 extending into the steam pipeline 1 results in the formation of steam in contact with the water at a saturation pressure corresponding to the temperature of the steam in the pipeline 1. This pressure is transmitted to the first measurement chamber 3.

Since the tube 9 is connected directly to the steam pipeline 1 it will sense and transmit the steam pressure in the pipeline 1 to the second measurement chamber 10. The difference between the saturated pressure corresponding to the steam temperature in the pipeline 1 and the steam pressure in the pipeline 1 provides information on the degree of superheat of the steam to be monitored. This data can be used as the basis of control and regulatory functions in the steam generating system. With such an arrangement, the degree of superheat can be monitored reliably, since the comparison of two pressure measurements can be carried out in a simple and direct manner.

The sealed end 8 of the measurement tube 5 is preferably (as shown) specially formed to maximise its surface to volume ratio with respect to the reminder of the tube, thus promoting a more rapid temperature change of the liquid in the end region of the measurement tube 5 in order to improve the transient time response of the device.

1. Apparatus for monitoring the degree of superheat of steam, the apparatus comprising a tube which is closed at one end, the closed end of the tube extending into a steam pipe which, in use, contains steam, and the tube being partially filled with water such that a water level exists in the closed end, above which level steam is formed, in use, in contact with the water in a previously evacuated space, a first measurement chamber arranged to be subjected to the pressure in the tube, means to transmit pressure in the steam pipe to a second measurement chamber, and means to compare the pressures in the measurement chambers to deter mine the degree of superheat of steam in the pipe.

2. Apparatus according to claim 1, in which the sealed end of the tube has a maximised surface to volume ratio with respect to the remainder of the tube.

3. Apparatus for monitoring the degree of super heat of steam, the apparatus being substantially as herein described with reference to the accompany ing drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Monitoring the degree of superheat of steam This invention relates to methods of and apparatus for monitoring the degree of superheat of steam. The use of superheated steam is necessary in many manufacturing processes and in the generation of energy. In this context, steam is understood to have a temperature above the saturation temperature corresponding to the steam pressure. Precise monitoring of this condition is desirable, so that, for example, equipment using superheated dry steam will not be damaged by wet steam or entrained water droplets. Thus, for example, in a power plant which is fed with superheated steam produced in a straight tube steam generator with shell-side boiling and comprising a turbine and turbine valves, of the type described in US Patent No. 3 447 509 (Sprague), the absence of superheating can lead to severe damage to the turbine valves and the turbine. The degree of superheat could be determined by comparing the steam temperature in a pipeline or piping to the turbine with the saturation temperature of the flowing fluid. However, since it is difficult to determine the exact saturation temperature, such a method would lead to inexact results. According to a first aspect of this invention there is provided apparatus for monitoring the degree of superheat of steam, the apparatus comprising a tube which is closed at one end, the closed end of the tube extending into a steam pipe which, in use, contains steam, and the tube being partially filled with water such that a water level exists in the closed end, above which level steam is formed, in use, in contact with the water in a previously evacuated space, a first measurement chamber arranged to be subjected to the pressure in the tube, means to transmit pressure in the steam pipe to a second measurement chamber, and means to compare the pressures in the measurement chambers to determine the degree of superheat of steam in the pipe. According to a second aspect of this invention there is provided a method of monitoring the degree of superheat of steam, the method comprising determining the saturation pressure corresponding to the temperature of the steam, determining the steam pressure, and comparing said pressures to indicate the degree of superheat of the steam. An embodiment of this invention described below provides for the simple and direct monitoring of the degree of superheat of steam in such a manner that precise results may be produced. Thus, the degree of superheat is monitored by means of a simple differential pressure measurement, avoiding the need for an uncertain saturation temperature mea surement. The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawing, the sole figure of which is a schematic representation of apparatus embodying the invention. Referring to the drawing, superheated steam 2 flows in a pipeline or piping 1 from a steam generator (not shown) to a point of use (not shown). A tube 5, one end 8 of which is sealed, extends into the steam pipeline 1. The other end of the tube 5 is connected to a first measurement chamber 3 of a differential pressure-measuring transducer 4. The tube 5 is filled with water to a level 6, after prior evacuation, leaving an empty space 7 above the level 6 at the sealed end 8. A second tube 9, communicating with the superheated steam 2 in the pipeline 1, is connected to a second measurement chamber 10 of the differential pressure-measuring transducer 4. In operation, steam is formed in the sealed end 8 of the tube 5 and forms a steam cushion that occupies the space 7 above the water level 6. Heat transfer from the steam 2 to the water in the tube 5 extending into the steam pipeline 1 results in the formation of steam in contact with the water at a saturation pressure corresponding to the temperature of the steam in the pipeline 1. This pressure is transmitted to the first measurement chamber 3. Since the tube 9 is connected directly to the steam pipeline 1 it will sense and transmit the steam pressure in the pipeline 1 to the second measurement chamber 10. The difference between the saturated pressure corresponding to the steam temperature in the pipeline 1 and the steam pressure in the pipeline 1 provides information on the degree of superheat of the steam to be monitored. This data can be used as the basis of control and regulatory functions in the steam generating system. With such an arrangement, the degree of superheat can be monitored reliably, since the comparison of two pressure measurements can be carried out in a simple and direct manner. The sealed end 8 of the measurement tube 5 is preferably (as shown) specially formed to maximise its surface to volume ratio with respect to the reminder of the tube, thus promoting a more rapid temperature change of the liquid in the end region of the measurement tube 5 in order to improve the transient time response of the device. CLAIMS

4. A method of monitoring the degree of superheat of steam, the method comprising determining the saturation pressure corresponding to the temperature of the steam, determining the steam pressure, and comparing said pressures to indicate the degree of superheat of the steam.

5. A method of monitoring the degree of superheat of steam, the method comprising being substantially as herein described with reference to the accompanying drawing.