RU2624982C1 - Method of hardness scaling control on heat units walls and device for its implementation - Google Patents

Abstract

FIELD: heating system.

SUBSTANCE: method is based on measuring the scaling thickness on the walls of the heat unit by comparing the electrical resistances of the water layers with scaling and clean water in the heat unit vessel. The current values of the measured scaling thicknesses are differentiated in time. The fact of the beginning of scale deposits and the growth of scale are fixed with the possibility of establishing a critical level of scale formation rate. The device contains an electrical resistance bridge with five electrodes placed in an aqueous medium. Three balancing resistances of the bridge are formed by the resistance of the water layers between the first and second electrodes, between the second and third and as well as the fourth and fifth electrodes. The fourth shoulder is formed between the fifth electrode and the metal wall. The wall is connected to one of the poles of the power source. The third and fifth electrodes are combined and connected to its other pole. The output diagonal of the resistance bridge formed between the second and fifth electrodes is connected to the input of the differentiating link, which is provided with a threshold circuit at the output.

EFFECT: improving the control accuracy and manufacturability.

4 cl, 2 dwg

Description

The invention relates to the field of heat engineering, in particular to measuring and controlling the thickness of scale deposits on the inner walls of heat generating units.

Scale deposits on the working surfaces of the latter reduce the efficiency and the level of their safety in operation.

Currently, the problem of combating scale is solved by organizing periodic cleaning of equipment, completing a water treatment system and developing measures of a constructive nature. Cleaning, as a rule, is carried out manually, they involve dangerous and inefficient labor, are not economically efficient, and the schedule of periodic cleanings may not coincide with the real need for them, since deposits form unevenly and depend on many factors. In practice, water treatment does not always save from scale due to salt “leakage” and, in addition, is accompanied by large financial and time costs. Constructive measures are also expensive. At the same time, the quality of the operation of heat generating units is evaluated by metering devices: heat meters, flow meters, and pressure gauges. However, they have low accuracy and cannot fundamentally indicate: where and when in the thermal circuit critical levels of scale have been reached.

Known methods and devices for measuring the thickness of deposits based on non-destructive testing methods: eddy current (1), acoustic (2) and other types. The disadvantages of the solutions in accordance with (1) and (2) are the low sensitivity of control and reduced manufacturability due to the need for periodic calibration of measurements.

Closest to this invention is a method and apparatus for determining scaling according to the patent (3), taken as a prototype. The principle of operation of the prototype is based on a point-by-point comparison of two values of electrical resistance to direct current between the electrodes placed inside the capacitance before scale deposits and after. Since the specific resistance of the scale is significantly higher than water, the difference of these resistances carries information about the thickness of the scale deposited on the electrodes. This solution allows you to measure the thickness of deposits on the inner walls of boilers and pipes. However, it has limited capabilities, since monitoring at a point does not give an objective assessment of scale formation in the entire heat generator. A large set of measurements is needed even in a small area. In addition, from the description of the prototype patent it follows that when measuring thicknesses of the working range of the prototype (1-5) mm, the relative error is depending on the conditions (10-60)%. Such restrictions when controlling deposits, for example, in thermal boilers are unacceptable. So, according to the “Rules for the Design and Safe Operation of Steam and Water Boilers” (4), the maximum scale thickness during operation of the boiler with a capacity of up to 0.7 tons of steam per hour should not exceed 0.5 mm. Boilers with higher productivity should be equipped with water treatment systems, and the scale thickness for them is not regulated, since according to the requirements it is believed that there should be no scale. Indeed, during control there is no need to measure the absent scale, it is more important to catch the beginning of the dangerous scale formation process in time to take appropriate measures, which is contained in such a process parameter as the growth rate (or descent) of the scale.

The foregoing allows us to conclude that the known technical solutions cannot be reliably applied to control the scale thickness in boilers and, most importantly, in the initial stage of its occurrence and growth, when high measurement accuracy is required.

The aim of the invention is to improve the accuracy and manufacturability of control over a non-scale mode of operation of boiler units.

The proposed method for controlling scale formation on the inner walls of heat generating units is achieved by controlling by measuring the thickness of the scale by comparing the electrical resistances of the water layers with scale and just water, and, in addition, according to the invention, the fact of the onset of scale deposition and its growth is recorded by differentiating the current values with time the measured scale thickness with the establishment of its unacceptable level. Known devices do not possess the necessary qualities due to the low sensitivity and susceptibility to interference when measuring small scale thickness. The main obstacle to the measurements of the above analogues and prototype is the unstable electrical conductivity of water, often depending on changes in the concentration of non-scale-forming salts, alkalinity, etc. Water resistance is included in the measuring circuit and in the case of small resistance of fine scale can have a decisive influence on the measurement result.

In order to increase the noise immunity, an adequate implementation of the proposed method consists in the fact that the electrical resistance of the microlayer of the scale thickness is measured using a bridge circuit composed of three balancing resistors that reflect the resistance of the sections of the water medium of the heat generating unit, and a fourth one representing the total resistance of the scale microlayer on the wall of the latter with adjacent water, with the addition of a differentiating unit, made, for example, on an operational amplifier connected to the output diagonal of the resistance bridge, and a threshold circuit connected to the output of the differentiating link. In addition, the electrodes, with which a resistance bridge is formed in the tank, are made of materials with reduced adhesion to scale-forming salts.

Figure 1 illustrates the proposed method, figure 2 shows a diagram of a device that implements this method.

The reference numbers in FIG. 1 and 2 reflect: 1 - bridge of resistances; 2 - differentiating link; 3 - threshold circuit; 4, 5, 6, 7 - resistance of the shoulders of the bridge of resistances 1, of which 4, 5, 7 - balancing, formed by water 8 in the tank of the heat exchanger, 6 - the shoulder with the resistance formed by water 8 and the deposition of scale 9 on the wall 10 of the tank; 11 - electrodes in the amount of 5 units, with which the resistances of the balancing arms of the resistance bridge 1 are formed. One of the electrodes of the arm 6 is the wall of the heat generator 10. It should be noted that it doesn’t matter which bridge arm will be used as the measuring one, according to theory, it can be anything. And in this regard, the figures show one of four possible circuit versions. The conclusions of the wires from the capacity of the heat generator carried through the transition connectors 12.

The proposed method can be explained on the operation of the device for its implementation. The electrodes 11 are placed in the aqueous medium 8 of the capacity of the heat generator: a pipe, a drum, etc., on the walls 10 of which there is initially no scum 9. The formed bridge of resistances 1 is balanced by known methods. Balancing is not needed here for measuring purposes, but to bring the resistance bridge 1 to operating mode. After that, the heat unit is included in the work. The signal levels at the outputs of the bridge 1 and node 2 are equal to zero. If, in this case, a change in water resistance 8 occurs, then this change will affect equally all the shoulders of the bridge circuit 1, and the signal at the mentioned outputs will remain unchanged. In the case of the start of the scale formation process, only the resistance of the arm 6 will begin to change, the rest will remain unchanged, since their electrodes are coated with low adhesion material and no scale forms on them. An unbalance current occurs in the output diagonal of the bridge of resistances 1, and a signal is generated at the output of the differentiating link 2, the level of which will reflect the current scale formation rate. Possible interference from the mutual shunting of the electrodes through water can be reduced by spacing them apart. Since the signal from the diagonal of the resistance bridge 1 can be weak in level, the differentiating link 2 at the output is equipped with an amplifier. The optimal circuitry solution for this link in this case should be in the form of an operational amplifier with differentiating properties.

A nonzero value of this signal means an increase in scale, and if the thickness of the scale exceeds the critical level set at the reference input of the threshold circuit 3, it works, generating an alarm signal, according to which appropriate measures are taken. Such measures include adjusting the dosing device when using chelators, connecting and adjusting ultrasonic, magnetic and other anti-scale devices of non-reactive action, or conducting an audit of the water treatment system.

The proposed invention compares favorably with the prototype in that

- a new quality of control has been created: an assessment of scale formation, i.e. the growth rate of scale deposits, which allows you to quickly take measures to stabilize or reduce it. Estimates for a signal without differentiation in time are uninformative, since the temporal dynamics of changes in the scale formation process is lost;

- improved control accuracy by creating a bridge circuit for measuring scale resistance using a certain set of electrodes coated with a material of reduced adhesion immersed in an aqueous medium;

- improved manufacturability and reliability of control of scale formation by expanding the control zone due to the spatial placement of several electrodes and their dimensions (instead of one "point", as in the prototype), and averaging the measurement results.

INFORMATION SOURCES

1. RF patent No. 2487343, MKI G01N 27/72, G01B 7/06, 07/10/2013.

2. RF patent RU 02098754 C1, MKI G01B / 02, 12.10.1997.

3. RF patent No. 2387950, MKI G01B 7/06, 04/27/2010.

4. Rules for the design and safe operation of steam and hot water boilers. PB 10-574-03. M., PIO MBT, 2003.

Claims (4)

1. A method of controlling scale formation on the walls of a heat generating unit, based on measuring the thickness of scale deposits by comparing the electrical resistances of water layers with scale deposits and simply water in the capacity of a heat generator, characterized in that the current values of the measured scale thickness are differentiated in time, record the fact of the onset of deposits and growth scale with the ability to establish a critical level of scale formation rate. 2. A device for controlling scale formation on the walls of a heat generating unit, comprising means for generating and comparing the electrical resistances of the aqueous medium in the capacity of the heat generating unit and scale on its walls, characterized in that the said means is made in the form of an electrical resistance bridge with five electrodes placed in this aqueous medium, three balancing resistances are formed by the resistances of the water layers, respectively, between the first and second electrodes, between the second and third and also the fourth and fifth elec by rods, the fourth arm is formed between the fifth electrode and the metal wall, the latter is connected to one of the poles of the power source, the electrodes of the third and fifth are combined and connected to its other pole, the output diagonal of the resistance bridge formed between the second and fifth electrodes is connected to the input of the differentiating link which is equipped with an output threshold circuit. 3. The device according to p. 2, characterized in that the differentiating element is made as part of an operational amplifier. 4. The device according to claim 2, characterized in that the surfaces of said electrodes are made of materials with reduced adhesion.

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