DK174314B1 - Method of thermal monitoring and protection of boilers - Google Patents

Description

DK 174314 B1

Description 1 The invention relates to a direct-acting monitoring and protection method for boilers, where the boiler room e.g. is made up of membrane walls. The protection and monitoring are based on external measurement of the temperature difference between e.g. membrane fin material and boiler tubes. On boiler types where no membrane walls are used, other 5 measuring points can be used if, through an increased temperature difference, they reflect an increased thermal load. Based on the temperature difference, the boiler load and thus thermal effect can be determined, since for a given boiler design and load, there is a very specific relationship between e.g. the temperature of the membrane material and the boiler tubes temperature. Thus, a large temperature difference will usually indicate a high thermal load, whereas a small temperature difference will usually indicate a small thermal load of the boiler.

The temperature difference between e.g. the fin material and the pipe, together with the actual boiler pressure and the degree of load, are the variable values from which the thermal load of the boiler material is continuously determined. Temperature differences between the fins and the tube as well as the absolute temperature on both the fins and tubes are measured using a two-point surface sensors. The sensor is designed as a leaf spring with surface sensors attached to the two ends of the leaf springs. The length of the sensor, and thus the leaf springs, is adjusted to the tube and fin size, so that the sensor achieves the best possible contact with the 20 measuring points. By means of the glued wedge-shaped guide washers, leaf spring is distributed downwardly against the pipe and the diaphragm respectively. In order to achieve a safe and good point contact and thus high heat conduction between the sensor and the boiler material, the spring is pressed into a weak U-profile.

Boilers are typically constructed with a radiation boiler compartment made up of vertically positioned water-filled boiler pipes which, by means of fins or welded flat material, form a gas-tight membrane and a space where the combustion of the selected fuel can take place, see fig. 1. The fuel can thus be oil, gas or coal. The radiant heat from the combustion heats the fin and boiler pipe materials which will cause vapor formation in the pipes. The steam generated is typically used as process heat or as a propellant in rotary machines, including for electricity generation.

One of the main causes of water pipe boiler failures is material stress due to local overheating and over-firing, uncontrolled temperature increase and overload.

35 Failure of the boiler's water-filled pipes often requires stops for repair for long periods, since the extent of the damage has often spread to several areas of the boiler. Since boiler failures often have very unfortunate operational aspects, many efforts have been made over the course of time to improve reliability. Thus, the legislation requires double independent water level protection against low water level and double protection against an undesirably high 40 boiler pressure.

Although the boiler's absolute material temperatures and temperature difference cause damage and thus provide the best indication of the boiler's load and condition, it has not been the practice to measure critical temperatures and temperature over time, but solely to monitor the and the protection of 45 2 DK 174314 B1 1 automatic boiler systems by indirect methods through the water level protection and pressure monitoring.

Industrial boilers have over the years tried several measures to obtain safe combustion and surface temperature measurements in boiler rooms. Apart from infrared surface temperature measurements, see United States Patent No. 5,355,845, surface temperatures are measured using thermo sensors mounted on the pipes in the boiler room, where they are exposed to extreme heat and corrosion impacts and therefore have only a limited lifetime and are very costly. to install.

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In the invention, the cold side of the pipe wall is measured exclusively. By measuring on the cold side of the boiler, in addition to a significant increase in the life of the sensors, it is also possible to use affordable materials and to make the installation work considerably easier, since no installation must be done in the boiler room but exclusively from the outside of the boiler. Measurement on the outside of the boiler gives an accurate picture of the effects the boiler is subject to, for a given boiler, a certain ratio between the temperature that can be measured on the inside and outside of the membrane and pipes prevails.

A ratio which, in addition to the degree of purity of the boiler, can be determined from the degree of load, see that in fig. 7 depicted temperature gradients. The primary measurement value is the difference temperature between the fin and the pipe wall, since at normal water level on the boiler and the amount of energy supplied it gives a direct picture of the heat transfer capacity and thus of the boiler's purity on both the water side and the flue gas side as well as the adverse effects of the boiler. subject to load variations.

25 By measuring difference temperatures between fines and pipes, a measure of the thermal stress effect to which the boiler is subjected is obtained through the temperature difference. Stress influences that, in addition to the heat supplied, in the form of fuel oil, are influenced by the boiler's heat transfer ability and thus purity and design. Since it is usually the thermal stress influences that cause boiler failure and damage, the differential temperature measurements provide between find and pipe a number of advantages over other indirect or direct measurements.

The invention will be explained in more detail below with reference to the drawing, in which: Figure 1 shows a boiler compartment made up of vertically positioned evaporator pipes assembled by means of welded fins to form a gas-tight combustion chamber.

FIG. 2 shows the sensor mounting on the membrane wall. FIG. 3 shows the structure of the temperature sensor itself • fig. 4 shows the control chip which ensures good contact between the sensor element and the measuring point.

FIG. 5 shows the system structure and its integration with the boiler's existing control system.

FIG. 6. shows the logical system structure.

FIG. 7 shows the temperature difference between e.g. the find and pipe material in relation to the boiler load rating.

3 DK 174314 B1 1 In fig. Figure 1 shows the structure of the membrane pipe walls in the vertical boiler type. The individual tubes (2) forming here the boiler room (1) are connected by means of welded fins (3), thereby creating gas density ten in the surroundings. The construction shown here, seen from the top, is provided on the outside with insulation (4) as well as a protective cover-plate (5).

In FIG. 2 shows a section through the membrane wall and a sensor. The sensor, shown here mounted in between the two glued control pieces (3), consists of a leaf spring (4) on which thermocouples (5) are built into the ends. The length of the leaf spring is adjusted 10 according to the dimensions of the membrane wall (1,2), so that the spring force from the leaf spring presses the thermocouples against the acid chips with a force which ensures good contact between the sensors and the measuring points on the pipe (2) and the fins (1), respectively. ). An electrical conduit (6) which is conductively connected to the thermocouples is passed through the leaf spring (4) and secured to it by means of a heat-resistant glue 15 (7). The wire (6) serves to pass the measured signals from the thermocouples to the signal processing unit, which will subsequently be referred to as the TIP module.

FIG. 3 shows the structure of the differential temperature sensor itself. The two sensor elements (3), with electrical wires (4), are selected from the temperature range to be measured and may be of any suitable type. The sensor element itself is fastened by means of heat-resistant glue to a heat-insulating layer (2) which is again glued to the leaf spring (1). The leaf spring (1) can be made of any suitable material which can ensure a good spring tension. In cases where the leaf spring is made of fibers, or other non-heat conductive material, the heat-insulating layer 25 can be omitted, thus simplifying the structure of the sensor.

FIG. 4 shows the configuration of the control chip. The control chips ensure a fixation of the temperature sensor and ensure that, through the spring tension, a good heat-conducting contact between the sensor elements and the boiler material is obtained at the selected measuring point. In addition, a secure contact is produced through the wedge-shaped configuration of the control piece core (2) and the sensor guide (3). The control pieces may be made of any suitable material which allows attachment to the boiler material with heat resistant glue.

FIG. 5 shows the system assembly with the boiler's existing control panel (4).

The system hardware consists of signal acquisition, signal processing, recording, monitoring and interaction with the boiler's existing control systems (4). In the TIP module (3), the signals from a number of difference temperature sensors (2), pressure sensors (7) and load sensors (8) are processed.

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FIG. 6 shows the logical structure of the TIP module: The central unit of the TIP module is the microprocessor (1) which can be a standard PLC unit with sufficient computational capacity to process the incoming signals, relative to the determined parameters stored in the ROM ( 2) and RAM (3) based on experience and the boiler 45 design and operation form. In the input module (4), the analog input signals are converted to digital signals and in the output module the necessary conversions are made so that the boiler's existing control panel can be communicated.

Claims (6)

Patent claims: 1. The boiler is secured by the method through continuous determination of the thermal load conditions. The thermal load conditions are determined using a microprocessor and calculation program. CHARACTERISTICS by, based on temperature measurements of e.g. the external temperature difference between the pipe and the fin material, or other areas of the boiler where an increased load results in an increased difference temperature, to calculate the thermal load and thereby to monitor and protect the boiler from harmful thermal effects. 2. The surface measurement is FEATURED by taking place exclusively on the 25 cold side of the diaphragm wall and using an elastically deformable differential temperature sensor as well as fixing and control pieces which together ensure a good contact and thus heat conduction between sensor and measuring points. Continuous contact is ensured by the deformed sensor seeking to straighten, thus creating a force effect towards the bottom of the wedge-shaped control pieces and thus to the measuring point. 3. The sensor is FEATURED by being determined in terms of length from the distance between the measuring points, so that the force applied down to the measuring point becomes the greatest possible. 35 4. The sensor is FEATURED for a structure that ensures good heat conduction between measuring point and sensor. Apart from the actual measurement point, isolate the actual sensing element from the surroundings, thus ensuring minimal heat conduction. 5. The method is FEATURED by being capable of being used for monitoring and protection of equipment other than boilers in particular. 6. The control with the sensor is FEATURED by being able to mount other surfaces in a special embodiment where a safe contact and surface temperature measurements are required without mounting of fixed sensor requiring the use of heat and cutting tools and where it is possible to replace feel without the use of tools.