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Title:
METHOD AND APPARATUS FOR CONTROLLING THE TRACE HEATING OF A PIPE
Document Type and Number:
WIPO Patent Application WO/2012/152986
Kind Code:
A1
Abstract:
The invention relates to a method and apparatus for controlling the trace heating of a pipe. The material conveyed in the pipe is heated with a heating cable (2) attached to the pipe and the temperature of the pipe (1) is monitored by a temperature sensor (5) attached to the pipe, on the basis of which measurement data is controlled the supply of electricity to the heating cable. The rate of change of the temperature indicated by the temperature sensor (5) is monitored by means of a program-controlled processor (7) and the rate of change is compared with a predetermined reference value. If a fall in the temperature is observed which is more rapid than the predetermined rate of change, or if despite heating with a heating cable the temperature does not increase at least at the predetermined rate of change, this observation is determined as flow taking place in the pipe and the supply of electricity to the heating cable is cut off.

Inventors:
PIIRAINEN, Aarni (Syväojankatu 3, Kajaani, FI-87700, FI)
PIIRAINEN, Toni (Syväojankatu 3, Kajaani, FI-87700, FI)
Application Number:
FI2012/050354
Publication Date:
November 15, 2012
Filing Date:
April 11, 2012
Export Citation:
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Assignee:
PLANRAY OY (Syväojankatu 3, Kajaani, FI-87700, FI)
PIIRAINEN, Aarni (Syväojankatu 3, Kajaani, FI-87700, FI)
PIIRAINEN, Toni (Syväojankatu 3, Kajaani, FI-87700, FI)
International Classes:
H05B1/02; H05B3/56; F17D1/18; G05D23/19
Foreign References:
US5900179A1999-05-04
US6005228A1999-12-21
US20100084393A12010-04-08
CN201594196U2010-09-29
US4859834A1989-08-22
US5064604A1991-11-12
JPH11118554A1999-04-30
Attorney, Agent or Firm:
LEITZINGER OY (Tammasaarenkatu 1, Helsinki, FI-00180, FI)
Download PDF:
Claims:
Claims

1. A method for controlling the trace heating of a pipe, in which method the material conveyed in the pipe is heated with a heating cable (2) attached to the pipe and the temperature of the pipe (1) is monitored by a temperature sensor (5) attached to the pipe, on the basis of which measurement data is controlled the supply of electricity to the heating cable, characterised in that a program-controlled processor (7) monitors the rate of change of the temperature indicated by the temperature sensor (5) and compares the rate of change with a predetermined reference value, and that if a more rapid fall in the temperature is observed than the predetermined rate of change, or if despite heating with a heating cable the temperature does not increase at least at the predetermined rate of change, this observation is determined as flow taking place in the pipe and the supply of electricity to the heating cable is cut off.

2. A method as claimed in claim 1, characterised in that the ending of the flow of the material in the pipe is detected with an algorithm of the processor (7) program, by means of which

- the falling of the temperature indicated by the temperature sensor (5) compared with the temperature measured at the beginning of the flow is monitored, and when the fall in the temperature has been detected,

- the supply of electricity is connected to the heating cable (2) and the reacting of the temperature sensor (5) is monitored, whereby a rise in temperature which is more rapid than the predetermined rate of rise is interpreted as the ending of flow, and

- the supply of electricity is continued under the control of the temperature sensor (5) and the program-controlled processor (7).

3. A method as claimed in claim 1, characterised in that the ending of the flow of the material in the pipe is detected with an algorithm of the processor (7) program, by means of which - the angular coefficient of the heating of the heating cable (2) is monitored with a temperature sensor (9) connected to the heating cable and

- the said angular coefficient is compared with the temperature indicated by the temperature sensor (5) connected to the pipe and - should the temperature of the pipe rise at least at the predetermined rate of rise with respect to the said angular coefficient, this is interpreted as the flow having ended, and

- the supply of electricity is continued under the control of the temperature sensor (4, 5) and the program-controlled processor (7).

4. An apparatus for controlling the trace heating of a pipe, the apparatus comprising a heating cable (2) attached to the pipe (1), a temperature sensor (5) attached to the outer surface of the pipe and a control device (3, 7) to which the temperature sensor (5) is connected and which controls the supply of electricity to the heating cable (2) on the basis of the measurement data obtained from the temperature sensor (5), characterised in that the control device (3, 7) comprises a program-controlled processor (7), the program of which is provided with an algorithm for detecting the flow of material in the pipe (1) on the basis of the rate of change of the temperature de- tected by the temperature sensor (5), and that the control device (3, 7) is equipped with a switch (8) which is controlled to switch the supply of electricity off from the heating cable (2) when the flow in the pipe (1) is detected by means of the said algorithm. 5. An apparatus as claimed in claim 4, characterised in that the processor program is provided with an algorithm by means of which is detected the ending of the material flow in the pipe by monitoring the falling of the temperature indicated by the temperature sensor (5) compared with the temperature measured at the beginning of the flow and by monitoring the reacting of the temperature sensor (5) when the control device (3, 7) switches on the supply of electricity to the heating cable as a response to the said detection of the fall in temperature.

6. An apparatus as claimed in claim 4 or 5, characterised in that a temperature sensor (9) is connected to the heating cable, and that the micro- processor (7) is arranged to monitor the angular coefficient of the heating of the heating cable (2) and to compare it with the temperature indicated by the temperature sensor (5) connected to the pipe.

Description:
Method and apparatus for controlling the trace heating of a pipe

The invention relates to a method for controlling the trace heating of a pipe, in which method the material conveyed in the pipe is heated with a heating cable attached to the pipe and the temperature of the pipe is monitored by a temperature sensor attached to the pipe, on the basis of which measurement data is controlled the supply of electricity to the heating cable.

The invention also relates to an apparatus for controlling the trace heating of a pipe, the apparatus comprising a heating cable attached to the pipe, a temperature sensor attached to the outer surface of the pipe and a control device to which the temperature sensor is connected and which controls the supply of electricity to the heating cable on the basis of the measurement data obtained from the temperature sensor.

The most common applications of such method and apparatus are industrial plants (chemistry, wood processing, metal), where heating is required for maintaining the process temperature and/or for keeping the material conveyed in the pipe molten and/or plastic in order that the material will not solidify. The material may be water, resin, oil, chemical pulp, or the like.

The problem with known trace heatings is unnecessary energy consumption during flow. When there is flow in the pipe, the temperature may fall below the set value, whereupon the regulating devices usually attempt to heat the pipe unnecessarily with full power, because the flowing material will remain isothermal and plastic irrespective of the heating. This is a very common occurrence which consumes considerable amounts of electricity because the circuits used for heating pipes may be long and powerful. The aim of the invention is to solve the above-mentioned problem. According to the invention, the problem is solved by means of the method disclosed in the accompanying claim 1 and by means of the apparatus disclosed in claim 4. The dependent claims disclose preferred embodiments of the invention.

The basic idea of the solution according to the invention is to observe the flow taking place in the pipe without separate flow sensors, only by means of temperature measurement, whereupon unnecessary heating may be discontinued during the flow to save electricity. When the flow stops, the control apparatus resumes the heating of the pipe in the usual manner. From the patent publication CN101033993 (A) is known a sensor device for measuring flow data. This sensor device includes point heating arranged for the measurement. The flow data is not used directly for controlling the heating of the pipe. In the invention is not, however, required a separate sensor device with point heating, and the flow data is used directly for controlling the heating of the pipe, in order to save electricity by discontinuing heating during flow.

The invention is illustrated in the following with reference to the accompanying drawing, in which

Figure 1 shows an embodiment of a trace heating apparatus by means of which the controlling of trace heating according to the invention can be carried out. The apparatus comprises a heating cable 2 attached to the outer surface of the pipe 1, to which cable the control device 3, 7 supplies electricity through a switch 8 and a wire 4. The heating cable 2 is attached directly to the outer surface of the pipe 1. In some applications, it is possible to place the heating cable inside the pipe. On the outer surface of the pipe 1 is attached a tem- perature sensor 5 which is connected with a wire 6 to the control device 3, 7 for transmitting measurement data to the microprocessor 7. The temperature sensor 5 is separate from the cable 2. The microprocessor 7 program is provided with an algorithm by means of which is detected the ending and beginning of the material flow in the pipe 1 by observing temperature changes, as disclosed below. The control device 3, 7 controls the supply of electricity to the heating cable 2 on the basis of the measurement data obtained from the temperature sensor 5.

The switch 8 is a relay, contactor or semiconductor relay. The semiconductor relay can be, for example, a Triac component by means of which the power supplied to the heating cable 2 can be cut down by 10-100%, and thus the temperature can be controlled accurately.

When the temperature indicated by the temperature sensor 5 falls below the set value (e.g. +60 °C), the power regulation algorithm of the microproces- sor 7 attempts to increase the temperature back to the set value by increasing the power supplied to the heating cable 2. If the flow of material in the pipe starts, it brings about a rapid decrease in temperature. If there is no flow in the pipe 1, the power increase should be indicated as an increase in temperature on the temperature sensor 5 at the previously measured speed (the average angular coefficient of temperature increase has been measured during previous heating times). If the temperature does not increase despite the power increase, this is interpreted as flow. On the other hand, a sudden downward change in temperature indicates the moment when flow starts in a simple manner without an attempt to increase the power.

The ending of the flow can thus be detected by monitoring the rate of change of the temperature indicated by the temperature sensor 5 and comparing it with a predetermined reference value. If the temperature falls more rapidly than at the predetermined rate of change, it is determined as flow taking place in the pipe. Alternatively, if despite heating with a specified output, the temperature does not increase at the predetermined rate of change, it is determined as flow taking place in the pipe. Both of these can thus be used separately or together for detecting the flow. When the flow is detected, the supply of electricity to the heating cable 2 is cut off. During the flow, the temperature in the pipe remains more or less constant and no essential changes would take place even if it was heated. Heating can, therefore, be cut off for the whole duration of the flow.

The ending of the flow can be detected when the temperature begins to de- crease from the temperature measured at the beginning of the flow, in which case test heating is carried out. If the temperature of the pipe reacts to the test heating, it may be presumed that the flow has ended and heating will be continued normally. For detecting the ending of the flow can also be utilised a temperature sensor 9 placed on the surface of the cable, which is con- nected by a wire 10 to the control device 3, 7 for transmitting the measurement data to the microprocessor 7. The angular coefficient of the heating of the cable can then be monitored and compared with the temperature of the pipe measured with the sensor 5. Should the temperature of the pipe not react to the heating of the cable 2 in the predetermined manner, it may be presumed that the flow is still on. On the other hand, if the processor 7 detects the temperature sensor 5 to react in such a way that the temperature rises more rapidly than at the predetermined rate of increase, this will be interpreted as the flow having ended. In this case, the supply of electricity is continued under the control of the temperature sensor 5 and the program- controlled processor 7.