JP2013204982A - Method of monitoring contamination of cooling water line and method of controlling chemical feed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of discriminating whether the contamination of a cooling water line is caused by slime or a scale, and a method of feeding chemicals according to a result thereof.SOLUTION: In a method of monitoring the contamination of a cooling water system for circulating and supplying cooling water to a heat exchanger, the detection of fouling based on LTD or ATD of the heat exchanger and the detection of adhesion of slime by a slime sensor are executed, and whether the fouling is slime or a scale is discriminated according to the presence or absence of the adhesion of the slime by the slime sensor when the adhesion of fouling is detected on the basis of LTD or ATD.

Description

  The present invention relates to a method for monitoring contamination of a cooling water line in a refrigeration system and the like, and a method for controlling the cooling water line.

  In various factories, buildings, etc., water systems including various heat exchangers such as refrigerators are provided, and cooling water and the object to be cooled are brought into contact with each other through the heat exchanger to cool the object to be cooled (in some cases, latent heat is used). Including those that only take away).

  In recent years, in cooling water systems, cooling water has been operated at a higher concentration and lower flow rate in order to save water, but under such operating conditions, ions are generated along with the evaporation of cooling water. Ingredients may concentrate and scale may precipitate and adhere to the refrigerator. In addition, microorganisms may propagate in the cooling water and slime may adhere to the device.

  Due to the adhesion of dirt such as scale and slime, heat transfer from the cooled object to the cooling water is hindered. As a result, in the condenser, the amount of the object to be cooled decreases, the pressure rises, the temperature of the object to be cooled rises, the load on the compressor rises, and the high pressure cut (the compressor stops at a certain level or more). ) May occur. Moreover, since the refrigerating capacity is reduced and the power consumption is increased, the energy efficiency is lowered.

  For this reason, in the refrigerator, it is necessary to accurately estimate the adhesion state of dirt and appropriately add a scale inhibitor or a slime inhibitor to the cooling water according to the situation.

  As described in Patent Document 1, there are U value (overall heat transfer coefficient) and dirt coefficient as indices for knowing the heat exchange efficiency of the refrigerator, but the calculation is complicated. Further, it is difficult to determine whether or not the high pressure cut is reached immediately from only these values, not the unit [° C.]. Further, in order to make this determination, a measurement value in a normal state where dirt is not attached is necessary.

  For this reason, as described in Patent Document 2, an LTD (Leaving Temperature Difference) or ATD (Approach Temperature Difference) obtained by the following equation is actually used.

LTD = temperature after cooling of the cooled object−cooling water outlet temperature ATD = temperature after cooling of the cooled object−cooling water inlet temperature

  The temperature after cooling of the cooled object can be measured as the heat exchanger outlet temperature of the cooled object.

  Generally, in a compression refrigerator, if the heat exchange is insufficient, the temperature after cooling of the cooled object (condensation temperature in this case) rises, and if it exceeds a certain level, it causes a high-pressure cut and becomes inoperable. , ATD can determine the situation. That is, a relational expression of ATD = LTD + (cooling water outlet temperature−cooling water inlet temperature) is obtained from the above two formulas, and the ATD (or LTD) obtained from this is in units of temperature. By comparing the cooling body condensing temperature, it can be immediately determined whether or not a high pressure cut occurs.

  Since the ATD and LTD are strongly affected by load fluctuations in addition to dirt, Patent Document 2 corrects the LTD and ATD, and compares the corrected LTD value or the corrected ATD value with a reference value. And monitoring for heat exchanger fouling.

  In Patent Document 3, as a deposit detection device for detecting adhesion of slime in a cooling water system, a heating element and a temperature measuring element are inserted into a metal tube, and between the heating element and the temperature measuring element and the inner surface of the metal tube. A probe filled with a filler, an energization control unit for the heating element, and a determination unit for determining the adhesion of the deposit on the outer surface of the metal tube from the measured temperature of the temperature measuring unit, There is described a method for determining adhesion of an adhering substance to the outer surface of the metal tube based on a change in temperature measured by the temperature measuring element when the energization amount is changed.

JP 2003-322494 A JP-A-7-218188 JP 2010-101840

  In the method using LTD, ATD, correction LTD, and correction ATD as index values for estimating the fouling state of the heat exchanger, it cannot be determined whether the fouling is slime or scale, and accurate chemical injection cannot be performed.

  The present invention provides a cooling water line contamination monitoring method capable of determining whether the contamination of the cooling water line is slime or scale, and a chemical injection control method for performing chemical injection according to the result. With the goal.

  The cooling water line contamination monitoring method of the present invention is a method of monitoring the contamination of a cooling water system in which cooling water is circulated through a heat exchanger, and the adhesion detection of deposits based on LTD or ATD of the heat exchanger; The slime adhesion detection is performed by the slime sensor, and when the adhesion of the deposit is detected based on the LTD or ATD, the ratio between the slime and the scale in the deposit is determined according to the slime adhesion amount of the slime sensor. It is what.

  The chemical injection control method of the present invention performs sewage monitoring (detection of deposits) in the cooling water system by the method of the present invention, and based on this result, an antislime agent and / or a scale inhibitor is added to the cooling water system. It is characterized by.

  According to the contamination monitoring method of the cooling water line of the present invention, it is possible to accurately determine not only the detection of deposits on the cooling water system but also whether the deposits are slime or scale. Therefore, the slime and scale of the cooling water system can be accurately prevented (including suppression) by adding a slime inhibitor or a scale inhibitor to the cooling water system based on the determination result.

It is sectional drawing of the probe of the deposit | attachment detection apparatus which concerns on embodiment. It is a perspective view of the sensor of the deposit | attachment detection apparatus which concerns on embodiment. It is a circuit block diagram of an embodiment. It is an electricity supply pattern and a temperature change pattern figure. It is a temperature distribution figure in a pipe wall part.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a longitudinal sectional view in the vicinity of a probe of a slime adhesion detecting apparatus according to an embodiment. This slime adhesion detection device is described in Patent Document 3 (Japanese Patent Laid-Open No. 2010-101840).

  The probe 1 includes a metal tube 2 made of a corrosion-resistant metal such as brass and stainless steel whose base end side is open and its distal end side is closed, a heating element 3 and a temperature measuring body 4 disposed in the metal tube 2, and a metal tube 2. It has a filler 5 such as electrically insulating and thermally conductive magnesium oxide (magnesia) particles filled in a space between the inner peripheral surface and the heating element 3 and the temperature measuring element 4. The proximal end side of the probe 1 is sealed with a resin 14 such as an epoxy resin.

  The thickness of the metal tube 2 is preferably about 0.05 to 0.5 mm. The diameter of the metal tube 2 is preferably about 2 to 5 mm.

  As the heating element 3, a material in which a platinum thin film is formed on an insulating substrate is suitable. As the temperature measuring element 4, a thermocouple, a thermistor, or the like is suitable. However, the heating element 3 and the temperature measuring element 4 may be other than these.

  The heating element 3 is preferably disposed at the axial center of the metal tube 2. The temperature measuring body 4 is preferably provided so as to be in contact with the inner peripheral surface of the metal tube 2 between the heating element 3 and the inner peripheral surface of the metal tube 2.

  Of the lead wires 3a and 3b for energizing the heating element 3, one lead wire 3a extends to the outside of the probe 1, and the other lead wire 3b is connected to the metal tube 2 by soldering or the like. However, the lead wire 3b may extend to the outside of the probe 1 similarly to the lead wire 3a. The lead wire 3c is connected to the base end of the metal tube 2 by soldering or the like. Two lead wires 4 a and 4 b from the temperature measuring body 4 are drawn out of the probe 1. These lead wires are provided with an insulating coating.

  FIG. 2 is a perspective view of a sensor having the probe 1. A probe 1 protrudes from the center of the front end surface of the substantially cylindrical casing 6. Baffles 7 a and 7 b are provided in proximity to the probe 1 and only on one side as viewed from the probe 1. In the form of FIG. 2 (a), the baffle 7a is a baffle portion 8a whose one end side is a semi-cylindrical shape (a curved plate shape whose arc length is ½ of the circumference), and the other end side. The base 6 a is fitted with the casing 6, and the baffle 8 a is fixed so as to surround one side of the probe 1. The baffle 8 a protrudes from the tip of the casing 6 in a direction parallel to the probe 1 and the same length as the probe 1. The distance between the baffle portion 8a and the center of the probe 1 is substantially equal to the radius of the casing 6, and is, for example, about 3 to 10 times the outer diameter of the probe 1. The length of the arc of the baffle 8a is not limited to ½ of the circumference, but if the length of the arc is too large, the liquid around the probe 1 stays and the liquid is not exchanged. Since the detection cannot be performed and the influence of the flow velocity cannot be sufficiently suppressed if it is too small, it is preferable to set to 1/3 to 1/2 of the circumference.

  The shape of the baffle portion 8a is not limited to a semi-cylindrical shape, and may be a semi-columnar shape or a flat plate shape (not shown) as shown in FIG. 2 (b). If the distance is too short, deposits such as slime may cause bridging between the baffle portion 8b and the probe 1, and if the distance is too long, the influence of the flow velocity may not be sufficiently suppressed. A curved plate shape is preferred as shown in FIG.

  FIG. 3 shows the configuration of a measurement unit having an energization control means for the heating element 3 of the probe 1 and a determination means for processing the output signal of the temperature measuring element 4 to determine the adhesion state of the deposit. I will explain.

  The measuring unit 10 includes a current output unit 11 that outputs a current to the heating element 3, a temperature input unit 12 that inputs a temperature signal from the temperature measuring unit 4 and converts it into a digital signal, and a signal from the temperature input unit 12. , And a current value to be output by the current output unit 11 based on the temperature information of the temperature measuring element, and a calculation unit 13 that performs slime adhesion determination. The arithmetic unit 13 is an arithmetic processing circuit configured by a microcomputer (μ-CPU) or a large scale integrated circuit (LSI). The arithmetic unit 13 periodically increases the value of the energization current to the heating element 3, and based on the temperature data from the temperature measuring element 4, the calculation unit 13 detects the increase in heat transfer resistance caused by the deposits attached to the surface of the probe 1. Judgment status of deposits is determined.

  In order to observe the generation state of the slime in the water system using this adhering matter detection device, the probe 1 is immersed in the water of the water system, and the baffle 7 is located upstream of the probe 1 in the water flow direction. To place. Then, as shown in FIG. 4, the heating element 3 is energized in pulses, the measured temperature of the temperature measuring element 4 is detected, the amount of slime attached to the probe 1 is determined based on this result, and the slime in the water system The occurrence status (ease of occurrence) of the event is determined.

As shown in FIG. 4, when energization of the heating element 3 is started, the heat generated by the heating element 3 is transferred to the temperature measuring element 4, whereby the temperature detected by the temperature measuring element 4 starts to rise from T ₁ . The temperature detected by the temperature measuring element 4 rises until the amount of heat generated from the heating element 3 and the amount of heat released from the surface of the probe 1 are balanced.

The energization time t ₁ is selected so that the temperature detected by the temperature measuring element 4 is sufficient to reach the equilibrium temperature T ₂ . The time t ₁ may be determined by performing a pre-operation test. However, if t ₁ is excessively long, the real-time property of the measurement becomes poor, so the temperature rises to a temperature that can be substantially regarded as an equilibrium temperature (for example, a temperature at which the difference from the final equilibrium temperature is within 0.1 ° C.). the time required for temperature may be set as t _1. For normal, _{t 1} is preferably about 5 to 60 seconds, especially 5 to 20 seconds.

When the energization of the heating element 3 is stopped, the temperature detected by the temperature measuring element 4 starts to decrease by radiating heat from the probe 1 to the surrounding water. The energization-stopping time period t _2, previously selected as the detected temperature of the temperature sensing element 4 even if the slime is attached to the probe 1 is sufficient time to reach approximately equal equilibrium temperature T ₁ of the ambient temperature . The time t ₂ may be determined by performing a pre-operation test. However, if too long a t _2, since the real-time measurement becomes poor, required to decrease to a temperature which can be regarded as substantially equilibrium temperature (e.g., temperature difference between the water temperature is within 0.1 ° C.) time may be set as t _2. Usually, t2 is preferably about ₂₀ to 300 seconds, particularly about 60 to 300 seconds.

In the fourth drawing are zero energization amount at t ₂ hours period, but may be energized a constant current i ₂ traces than the current amount i ₁ of t ₁ hour period. However, i ₂ = 0 is preferable.

If the water temperature of the water does not vary, when no adhered slime probe 1, both the one energization time t ₁ before the start of the measurement temperature T _1, and the measured temperature T ₂ of the current supply time t ₁ the end is Constant over time. It is preferable to set the amount of current supplied to the heating element 3 so that the difference between T ₂ and T ₁ is of the order of 5 to 20 ° C..

In a state where slime adheres to the probe 1, the measured temperature T _{2 at the} end of the energization time t ₁ is higher than when the slime does not adhere to the probe 1. This is because heat transfer from the probe 1 to water is inhibited by slime, and the detailed mechanism will be described next.

Accordingly, the temperatures T ₁ and T ₂ are measured over time while the pulse energization shown in FIG. 4 is repeated, and the change from T ₁ and T ₂ (T ₂ −T ₁ ) over time to the probe 1 is measured. It is possible to detect the presence and amount of slime adhesion.

A calculation formula for obtaining the adhesion thickness of the slime from the above temperatures T ₁ and T ₂ is as follows. This equation is based on the heat transfer model shown in FIG.

In FIG. 5, Tw (water temperature) is _{T 1.} Ts (sensor surface temperature), when the thermal conductivity of the internal sensor is smaller in negligible compared to kf can be a value equal to T _2. The items on the right side other than Tw and Ts are constants obtained from the shape of the sensor, the resistance value of the heating element, the energization amount, and the like.

For example, for the heat flux q, the electrical resistance value R of the heating element 3, the energization current value i to the heating element 3, the length L of the heating element 3 in the probe longitudinal direction, and the radius r ₁ of the metal tube 2 are Can be calculated.

Thus, by measuring the T ₁ and T _2, it is possible to measure the thickness of the slime (sensor surface deposits).

  However, in order to consider the laminar boundary film heat transfer coefficient as a constant, it is necessary to make the thickness of the laminar boundary film constant. For that purpose, the flow rate of water in which the sensor is immersed is constant, or the laminar boundary It is necessary to make the fluctuation of the film heat transfer coefficient more than a negligible speed value. When the baffle 7 is provided as shown in FIG. 2, the laminar boundary film becomes thin, and high-precision measurement is possible.

  Next, the adhering matter detection (estimation of the contamination state of the heat exchanger) based on LTD or ATD will be described.

  This adhering matter detection method is the method described in Patent Document 2 (Japanese Patent Laid-Open No. 7-218188).

  In order to carry out this method for estimating the contamination state of the heat exchanger, the inlet temperature and outlet temperature of the cooling water of the heat exchanger such as a refrigerator and the temperature after cooling of the cooled object (corresponding to the outlet temperature) are measured. First, the LTD value or the ATD value is obtained by the following equation (I) or (II).

LTD = cooled body outlet temperature−cooling water outlet temperature (I)
ATD = cooled body outlet temperature−cooling water inlet temperature (II)
In this temperature measurement, it is important to perform more accurate measurement. For example, it is preferable to employ the following method i) or, more precisely, the following measurement method ii).

i) When measuring by an operator, measure at one point at least three times (the higher the number of measurements, the better) and obtain the average value.

ii) Attach or insert a temperature sensor to the site to be measured, and take the measured value at regular intervals.

  After obtaining the LTD value or ATD value by the above formula (I) or (II), the corrected LTD value or the corrected ATD value is obtained by the following formula (III) or (IV).

Correction LTD = LTD × rated cooling water inlet / outlet temperature difference ÷ measured cooling water inlet / outlet temperature difference (III)
Correction ATD = ATD x rated cooling water inlet / outlet temperature difference ÷ actual cooling water inlet / outlet temperature difference (IV)
Here, the rated cooling water inlet / outlet temperature difference is the cooling water inlet / outlet temperature difference of the heat exchanger during 100% load (full load) operation. For example, in JIS B8621, the rated cooling water for a centrifugal refrigerator is rated. The entrance / exit temperature difference is 5 ° C.

  The corrected LTD value or ATD value calculated by the above formula (III) or (IV) reflects only the state of dirt adhesion. For example, by performing the following determination, the current dirt adhesion It is easy to grasp the situation, estimate the future state of dirt adhesion, and determine the appropriate cleaning time.

  A. In the refrigerator, the allowable limit value LTDf or ATDf of the LTD or ATD is obtained from the cooled object outlet temperature (refrigerant condensing temperature) that causes an operation stop such as high-pressure cut and the cooling water inlet / outlet temperature when the maximum load temperature is indicated. .

  B. The difference between the allowable limit value LTDf or ATDf and the current correction LTD or correction ATD is obtained, and it is determined how much room is left before the dirt adheres to the high pressure cut.

  C. The time required for this value to exceed the allowable limit value LTDf or ATDf is estimated from the transition of the correction LTD or the correction ATD (the slope of the graph plotting the measured values), and the necessity or timing of cleaning is determined.

  In a normal case, it is advantageous to set the cleaning time when the difference from the allowable limit value LTDf or ATDf is equal to or less than a predetermined value.

  The predetermined value is appropriately determined according to the scale and performance of the cooling water system to be cleaned, the cooling water temperature, and the like. In the case of a refrigerator, the predetermined value is about 8 to 15 ° C. Also in the case of a general heat exchanger, it is determined appropriately according to the temperature of the object to be cooled.

  Correct the LTD value or ATD value obtained from the difference between the cooled object outlet temperature and the cooling water outlet temperature or the cooling water inlet temperature by the ratio of the rated cooling water inlet / outlet temperature difference and the measured cooling water inlet / outlet temperature difference. Thus, the LTD value or ATD value when the current state is set to the rated state can be obtained.

  This corrected LTD value or ATD value is proportional to the stain coefficient, that is, the relationship of corrected LTD or corrected ATD = a × dirt coefficient + b, and accurately indicates only the dirt adhesion state.

  In one aspect of the present invention, the amount of deposits in the cooling water line is detected based on LTD or ATD by the method described in Patent Document 2, and FIGS. 1 to 4 described in Patent Document 3 are used. The slime adhesion amount is detected using the slime sensor shown in FIG. The slime detection by this slime sensor can detect slime adhesion at an early stage, and the slime sensor detects the slime earlier than the actual change in LTD or ATD. Therefore, when the slime sensor detects slime, the slime inhibitor is added according to the detected value. If deposits based on LTD or ATD are subsequently detected despite the addition of the anti-slime agent, it means that the scale has adhered, so the scale is added to the cooling water system according to the detected amount of deposit. Add inhibitor. Thereby, both slime and scale can be prevented accurately.

  In another aspect of the present invention, the deposit is detected based on the LTD or ATD, and the slime adhesion amount of the slime sensor when the deposit is detected is referred to. If the slime sensor does not detect slime, the deposit is a scale, so a scale inhibitor is added to the cooling water system. When the slime sensor detects slime and the detected amount of slime is an amount commensurate with the amount of deposit based on LTD or ATD, it is determined that the deposit is slime, and an anti-slime agent is added (for this reason) The correlation between the detection value of the slime sensor and the detection amount of slime adhesion based on LTD or ATD is obtained in advance). The slime sensor detects slime, but when the amount of slime detected by this slime sensor is less than the amount of adhesion detected based on LTD or ATD, both the slime and the scale are attached, so the slime inhibitor And a scale inhibitor. Furthermore, the ratio of the adhesion amount of slime and scale can be calculated, and the slime inhibitor and the scale inhibitor in an amount corresponding to the ratio can be added.

[Example 1]
In a refrigerator cooling water system having a 500 refrigeration ton turbo chiller, the LTD of the condenser was measured, and the corrected LTD was calculated by the method of Patent Document 2 above. Moreover, slime was detected using the slime sensor of the said patent document 3 shown in FIGS.

  When the corrected LTD increased to 8 ° C., the output value of the slime sensor increased by about 0.5 ° C., so that “Krinstream C-101” manufactured by Kurita Kogyo Co., Ltd. As a result of adding L, both the sensor output value of the slime adhesion detection device and the correction LTD decreased.

[Example 2]
In the same refrigerator cooling water system as in Example 1, the correction LTD increased to 8 ° C., but the slime sensor output value remained almost constant. For this reason, 11000 mg / L of “Taworkrin CS” manufactured by Kurita Kogyo Co., Ltd., which is a scale cleaning agent, was added to perform cleaning, and as a result, the correction LTD decreased to an appropriate value.

  According to these Examples 1 and 2, it was confirmed that accurate drug injection was possible according to the present invention.

DESCRIPTION OF SYMBOLS 1 Probe 2 Metal tube 3 Heating element 4 Temperature measuring element 5 Filler 7a, 7b Baffle

Claims (4)

In the method for monitoring the contamination of the cooling water system in which cooling water is circulated through the heat exchanger, adhesion detection based on the LTD or ATD of the heat exchanger and slime adhesion detection by the slime sensor are performed.
A contamination monitoring method for a cooling water line, characterized in that, when adhesion of an adhering matter is detected based on LTD or ATD, the ratio of the slime and the scale in the adhering matter is discriminated according to the slime adhering amount of the slime sensor. In Claim 1, the detection of the deposit based on the LTD or ATD is performed by measuring an inlet temperature and an outlet temperature of cooling water of the heat exchanger and a temperature after cooling of the object to be cooled. It is characterized in that it detects the adhered matter by obtaining the LTD value or ATD value by the formula (II) and then obtaining the corrected LTD value or the corrected ATD value by the following formula (III) or (IV). Monitoring method for cooling water lines.
LTD = temperature after cooling of the cooled object−cooling water outlet temperature (I)
ATD = temperature after cooling of the object to be cooled−cooling water inlet temperature (II)
Correction LTD = LTD x rated cooling water inlet / outlet temperature difference ÷ cooling water inlet / outlet temperature difference (III)
Correction ATD = ATD x rated cooling water inlet / outlet temperature difference ÷ cooling water inlet / outlet temperature difference (IV)   3. The probe according to claim 1, wherein the slime sensor has a heating element and a temperature measuring element inserted into a metal tube, and a filler is filled between the heating element and the temperature measuring element and the inner surface of the metal tube. And an energization control unit for the heating element, and a determination unit for determining adhesion of the deposit on the outer surface of the metal tube from the measured temperature of the temperature measuring element, and the energization amount to the heating element was changed. A contamination monitoring method for a cooling water line, characterized in that adhesion of the deposit on the outer surface of the metal tube is determined based on a change in temperature measured by the temperature measuring body.   4. The method according to claim 1, wherein deposits in the cooling water system are detected, and a slime inhibitor and / or a scale inhibitor is added to the cooling water system based on the detection result. Chemical injection control method.

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