EP0136180A2

EP0136180A2 - Method for measuring coke oven wall temperatures

Info

Publication number: EP0136180A2
Application number: EP84306595A
Authority: EP
Inventors: Daniel Kwasnoski; John H. Gerdes, Jr.; James B. Lynn
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1983-09-29
Filing date: 1984-09-27
Publication date: 1985-04-03
Also published as: JPS6097246A; CA1229001A; EP0136180A3

Abstract

A method of measuring the temperature of slot type coke oven walls by measuring the temperature of selected portions of the irradiant hot coke mass as it is pushed from the coke oven.

Description

This invention relates to slot type coke ovens and more particularly to a method for measuring the temperature of coke oven walls as the coke is being removed from the coke oven with a radiation pyrometer positioned externally of the coke oven.
U.S. Patent No. 3,501,380 issued March 17, 1980 describes a method and apparatus for measuring the temperature of the coke oven walls by reflecting the radiant energy emitted by the coke oven walls to a radiation pyrometer positioned outside the coke oven on the arm of the pusher ram.
British Patent Application No. 2,073,408 published October 14, 1981 describes a method and apparatus for monitoring the temperature of the coke as it is removed from a coke oven using an optical pyrometer mounted on the coke guide car which pyrometer scans the surface of the hot coke as it emerges from the coke oven.
U.S. Patent No. 4,344,819 issued August 17, 1982 and assigned to Applicants' assignee, describes a method for determining the level of coke in a coke oven during the pushing operation by using a plurality of optical pyrometers mounted on the coke guide which provide vertical coke temperature profile data and oven wall temperatures.
While the three patents are examples of the prior art relating to the use of optical pyrometers to try to accurately measure the temperature of the coke oven walls, prior methods have not been satisfactory in practice. In Column 1, Lines 58-66 of the above mentioned U.S. Patent No. 3,501,380 it is stated, "Attempts have been made in the past to measure the temperature of the coke as it moves through the coke guide when it is pushed out of the coke oven. This technique has not proven entirely satisfactory because the radiation pyrometer is sited on the rapidly cooling coke as it emerges from the oven and the temperatures measured do not provide an accurate temperature profile of the coke oven walls."
It is an object of this invention to provide a method for accurately determining the temperature of coke oven walls at the end of the coking cycle.
It is a further object of this invention to provide a method for improving the accuracy of temperature measurements made by an optical pyrometer mounted on a guide.
The foregoing objects may be achieved by a method of using an optical pyrometer to focus on successive areas of the irradiant hot coke mass as it emerges from the coke oven which areas are no greater than 2.54 mm (0.1 inch) in diameter and recording only the highest temperature signals measured by the optical pyrometer during predetermined time intervals.
In the accompanying drawings:

Figure 1 is a fragmentary isometric view illustrating the scanning position of the optical pyrometer used for the method of this invention.
Figure lA is a time-temperature plot of the coke temperatures being read by the optical pyrometer as it scans the surface of the coke mass as shown in Figure 1.
Figure 2 is a sectional view showing the field of view of the optical pyrometer using the method of this invention.

This invention is based upon the discovery that it is possible to indirectly obtain an accurate measurement of the temperature of coke oven walls by measuring the temperature of selected portions of the irradiant coke mass as it emerges from the coke oven during the pushing operation. These temperature measurements provide useful information to the operator relating to the functioning and operation of the coke oven.
As the hot coke mass emerges from the oven, much of the coke surface will be cooled immediately by the ambient air. The surface of the coke mass contains many cracks or crevices which provide a source of temperatures which are more directly related to the temperatures of the coke oven walls.
As best illustrated in Figure 1, the irradiant hot coke mass 1 has a fractured surface having a substantially planar outer surface 2 separated by cracks or crevices 3. As the coke is pushed from the oven, it moves past an optical pyrometer 4 in the direction of the arrow. The optical pyrometer 4 may be mounted on the coke guide as described in U.S. 4,344,819 assigned to the present applicant. The optical pyrometer 4 is directed perpendicular to the planar outer surfaces 2 and focuses on a narrow spot along the straight scanning line 5 shown in Figure 1. If desired, a plurality of optical pyrometers may be positioned vertically to measure the temperature along several parallel scanning lines 5 separated vertically. It has been observed that five pyrometers vertically spaced an equal distance apart give the best temperature measurement for the coke oven wall.
As shown in Figure 2, if the field of view of the optical pyrometer is kept under 2.54 mm (0.1 inch), the optical pyrometer will be able to read the temperature of the coke in the crack or crevice 3 rather than on the planar surface 2. With such a technique, the only radiation that is translated into temperature values is that emitted from the confines of this small field of view. A spot this 2.54 mm (0.1 inch) size can obtain the radiation within the cracks or crevices of the coke mass, where heat loss is minimal, exclusive of the outer surface where heat loss to the ambient air is significant.
In Figure lA is a graphical temperature profile corresponding to what the pyrometer 4 has measured up to the position shown, representing a definite time interval or distance. The maximum temperature value of this profile is identified by the peak 6. If the frequency of the recording of the peak value is once during the indicated time span, then this peak value 6 is the only one to represent the temperature for the corresponding length of the coke mass as shown. If the frequency of recording is twice for this time span, then the temperature value 7 of a second crevice is included. A greater frequency will result in inclusion of the cooler temperature values of the outer surfaces.
A special handling of the temperature signals is desired, where only the highest analog signal in a given time frame is converted to a digital value and recorded, and all lower values are discarded. In data logging parlance this technique is referred to as "peak sense and hold." Assuming that all the pieces of coke in the moving coke mass have cooled outer surface areas of about 30.48 cm² (12 square inches), the frequency of digitizing and recording values of the continuous analog signal can be no greater than five times per second, in order to insure that all recorded values represent only those within the crevices. Of course, a distribution of coke pieces having cooled outer surface areas of less than 30.48 cm² (12 square inches) can tolerate a higher digitizing frequency and still avoid including these cooler areas. The system that we prefer to use digitizes only every 0.5 to 1.0 second.
Even with the above techniques, the values obtained will still be somewhat depressed from true values because of some slight cooling, but experience and trials have shown that the deviation from true values is small enough to show that the technique is practical. Tests using thermocouples inserted into the coke mass in the plane perpendicular to the heating wall have shown that after the normal heat soaking time of only an hour the temperature gradient from the center of the mass to the wall interface is only about 17°C. (30°F.) and is reduced to about 6 to 11°C. (10 to 20°F.) in the subsequent hour of heat soaking. This shrinking of the gradient is observed when the center temperature approaches 1093°C. (2000°F.). Therefore, when the center temperature exceeds 1093°C. (2000°F.), it can be expected that the coke close to the wall is roughly only 6 to 11°C. (10 to 20°F.) higher, depending on the soaking time. Using this relationship and comparing the center mass temperatures with the results of the coke guide pyrometer, the error of the pyrometer with the designated spot size was determined to be only 28 to 33°C. (50 to 60°F.). This deviation has been shown to be fairly consistent, and represents only a 2.5 percent difference which can be compensated for by calibration of the pyrometer or by processing of the recorded temperature data.
Tests with an optical pyrometer focusing on a larger spot of 6.35 mm (0.25 inch) in diameter which greatly diminishes its chances of isolating a crevice, have shown that deviations are between 56 and 67°C. (100 and 120°F.) below expected values.
Using the above techniques to obtain an accurate thermal profile over the whole plane of a coke oven wall requires several pyrometers aligned vertically over the height of the coke guide. An alternate arrangement might use fiber optics to transmit the viewed radiation to infrared photocells at a location out of direct line of sight. The choice may depend upon the structure of the coke guide. The continuous signals from the pyrometers or photocells are transmitted by wire to a multiplexer which scans the parallel signals at a very fast rate. These signals are processed by a data processor which uses the "peak sense and hold" technique at the correct frequency (less than once every 0.2 second). The data are coded by a manual or automatic input to identify the oven and time of measurement. The data collected are stored onboard the coke guide machine temporarily, then transferred to a computer for specified processing and permanent storage.
An additional feature may be an automatic activator for the data processor. Experience has taught that coke temperatures are always above 815°C. (1500°F.). Therefore, the data processor is programmed to begin recording values only when two or three of the sensors view radiation translated to temperatures greater than 815°C. (1500°F.). This guarantees that the beginning of measurements corresponds to the beginning emergence of the coke mass from the coke oven.

Claims

1. A method for indirectly measuring the temperature of coke oven walls, wherein surface temperatures of a coke mass emerging from the coke oven are measured, characterized by measuring the highest temperatures of selected portions of the irradiant hot coke mass as it emerges from the coke oven, said portions being no greater than 2.54 mm (0.1 inch) in diameter.

2. A method according to claim 1, characterized in that the temperatures of said selected portions are measured by an optical pyrometer.

3. A method according to claim 1 or 2, characterized in that said selected portions are at several vertical levels.

4. A method according to any one of claims 1 to 3, characterized in that said selected portions are along parallel lines at several vertical levels.

5. A method according to any one of the preceding claims, characterized in that said selected portions are at five vertical levels.

6. A method according to any one of the preceding claims, characterized in that the temperature is measured by an optical pyrometer directed perpendicular to the planar surface of said coke mass.

7. A method according to any one of the preceding claims, characterized in that only the highest temperatures in predetermined intervals during the pushing of the coke mass are recorded.