CA1168889A

CA1168889A - Monitoring the superheated state of steam

Info

Publication number: CA1168889A
Application number: CA000397661A
Authority: CA
Inventors: Bobby L. Day
Original assignee: Brown Boveri Reaktor GmbH
Current assignee: ABB Reaktor GmbH
Priority date: 1981-03-07
Filing date: 1982-03-05
Publication date: 1984-06-12
Also published as: DE3108782A1; DE3108782C2

Abstract

Abstract A temperature measurement-independent process and apparatus for determining the degree of superheat in steam by comparing the saturation pressure corresponding to the superheated steam temperature with the pressure of the steam.

Description

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Monitoring the Superheated State of Steam Background of the Invention This invention concerns a method and apparatus for monitoriny the superheated state of steam.
The use of superheated steam is necessary in many manufac-turing 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.
The precise monitoring of this condition is desirable, so that the 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, of the type described in U.S. 3447509 (Sprague), the absence of superheat can lead to severe damage to the ; 15 turbine valves and the turbine.
There exists the possibility of determining the degree of superheat by comparing the steam temperature in the piping - to the turbine with the saturation temperature of the fluid flowing. However, since it is difficult to determine the exact saturation temperature, this method would lead to inexact results.
Brief Summarv of the Invention _ ` The purpose oE this invention is therefore to provide a reliable and -temperature measurement independent method and apparatus for the simple and direct monitoring of the

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superheated state of steam, with which more precise results are produced.

This problem is solved pursuant to the invention by deter-mining the saturation pressure of water in indirect contact S with the steam, corresponding to the steam -temperature, comparing this saturation pressure with the steam pressure, and using the difference of these pressure values as an index for the degree of superheat of the steam.

By this method and apparatus, the superheated state of the steam is monitored while avoiding an uncertain saturation temperature measurement by means of a simple differential pressure measurement.

In a device for implementing this method, a previously evacuated tube is partially filled with water, and sealed at one end. The sealed end of this tube extends into a steam pipel with the water in the end region extending into the steam piping leaving an empty volume to hold a steam cushion formed at the saturation pressure correspondinq to the steam temperature in the piping. The open end of this tube is connected to the measurement chamber of a differ-ential pressure-measuring transducer. Another tube connected directly to the steam piping opens into a second measurement chamber.

The sealed end of the measurement tube is preferably specially formed to maximize the surface to volume ratio thus promoting a more rapid temperature change of the liquid in the end region of the measurement tube in order to improve the transient time response of the device.

With such a device, 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.

Thus, in accordance with one aspect of the present invention there is provided apparatus for determining the degree of - 2a ~ ~ 8~

superheat in steam comprising a first tube partially filled with water ancl closed at one end, the closed end of which extends into a steam pipe containing steam, a water level existing in the closed end above which steam is formed in contact with the water in a previously evacuated space, means to transmit pressure in the first tube to a first measurement chamber, 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 the steam in khe pipe.

In accordance with a further aspect of the present invention there is provided a method of monitoring the degree of superheat of steam comprising, determining and measuring the saturation pressure corresponding to the temperature of the steam, determining and measurinq the steam pressure and comparing these pressures to indicate the degree of superheat of the steam.

Brief Description of the Drawing Figure 1 is a schematic representation of the inventive l ~ fi ~

apparatus.
Detailed Description of the Drawing Referring to the drawing, superheated steam 2 flows in pipeline 1 from a steam generator, not shown, to a point of use, also not shown. A tube 5, one end of which is sealed 8, extends into steam piping 1. The other end of tube 5 is connected to a first measurement chamber 3 of a differen-tial pressure-measuring transducer 4. The tube 5 is filled with water to the 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 piping 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 tube 5 and occupies the space above the water level 6. The heat transfer from the steam 2 to the water in tube 5 extending into steam piping 1 results in the formation of steam in contact with the water at the saturation pressure corres-ponding to the steam temperature in piping 1. This pressureis transmitted to first measurement chamber 3. Since the tube 9 is connected directly to the steam piping 1 it will sense and transmit the steam pressure in piping 1 to second measurement chamber 10. The difference between the saturated pressure corresponding to the steam temperature in piping 1 and the steam pressure in this piping provides information on the degree of superheat of the steam to be monitored.
This data therefore can be used as the basis of control and regulatory functions in the steam generating system.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for determining the degree of superheat in steam comprising a first tube partially filled with water and closed at one end, the closed end of which extends into a steam pipe containing steam, a water level existing in the closed end above which steam is formed in contact with the water in a previously evacuated space, means to transmit pressure in the first tube to a first measurement chamber, 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 the steam in the pipe.

2. The apparatus of Claim 1 in which the sealed end of the first tube has a maximized surface to volume ratio with respect to the remainder of the first tube.

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