JP2008267667A - Absorbent for absorption chiller/heater and absorption chiller/heater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an absorbent for an absorption chiller/heater, maintaining corrosion restraining effect of copper used as a heat transfer pipe of the absorption chiller/heater. <P>SOLUTION: This absorbent for the absorption chiller/heater using water as a coolant and a lithium bromide aqueous solution as an absorbent is characterized in that the absorbent is made of a lithium bromide aqueous solution at least containing 2,5-dimercaptothiadiazol. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an absorption liquid for an absorption chiller-heater and an absorption chiller-heater that use water as a refrigerant and an aqueous lithium bromide solution as an absorption liquid.

  Absorption-type hot / cold water heaters are the mainstream heat source equipment for medium- and large-scale air conditioning in buildings because they do not use chlorofluorocarbon gas, which causes ozone layer destruction, can be cooled and heated by a single unit, and can handle various types of energy. It has become.

  This absorption chiller / heater has a generator (regenerator) having a heating source, a condenser having a cooling water system, an evaporator having a cooling water system, an absorber having a cooling water system, a heat exchanger, a solution and a refrigerant. A pump or the like is provided, water is used as a refrigerant, and an aqueous lithium bromide solution is used as an absorbing liquid, and the cooling or heating ability is exhibited by circulating the equipment.

Since the aqueous solution of lithium bromide is highly corrosive, it is common to add a corrosion inhibitor called an inhibitor in order to suppress the corrosion of the equipment mainly composed of carbon steel and copper. Oxygen hydrochloric acid such as molybdenum hydrochloric acid, nitric acid hydrochloric acid, and chromic hydrochloric acid is known as an inhibitor mainly intended to prevent corrosion. In a steam-fired absorption chiller / heater with a high copper usage ratio, it is also known to add benzotriazole (hereinafter referred to as BTA) to an aqueous lithium bromide solution in addition to the oxygen hydrochloric acid. (For example, refer to Patent Documents 1 and 2). In an actual machine, a surfactant (2-ethyl-1-hexanol) is added to the aqueous lithium bromide solution to improve the heat transfer performance.
Japanese Examined Patent Publication No. 62-26357 Japanese Patent Publication No. 60-29872

  However, in an absorption chiller / heater using an absorption liquid containing oxygen hydrochloric acid and BTA, BTA is extracted into a surfactant (2-ethyl-1-hexanol) added to the lithium bromide aqueous solution as the operation time elapses. As a result, the concentration decreased and the corrosion inhibition effect on copper gradually decreased, and copper corrosion could not be effectively prevented.

  The objective of this invention is providing the absorption liquid for absorption type cold / hot water machines which can maintain the corrosion inhibitory effect of copper.

  Another object of the present invention is to provide an absorption chiller / heater capable of simplifying management such as replenishment of a copper corrosion inhibitor.

  In order to achieve the above object, an invention according to claim 1 of the present invention is an absorption liquid for an absorption chiller-heater using water as a refrigerant and an aqueous lithium bromide solution as the absorption liquid. It consists of a lithium bromide aqueous solution containing 5-dimercaptothiadiazole.

The invention according to claim 2 of the present invention is characterized in that, in claim 1, the aqueous lithium bromide solution contains 1 × 10 ⁻⁵ mol / liter or more of 2,5-dimercaptothiadiazole.

  The invention according to claim 3 of the present invention is characterized in that, in claim 1 or 2, it contains oxygen hydrochloric acid and an alkali in addition to 2,5-dimercaptothiadiazole.

  Further, the invention according to claim 4 of the present invention is an absorption chiller / heater using water as a refrigerant and an aqueous lithium bromide solution as an absorbent, and a bromide containing at least 2,5-dimercaptothiadiazole as the absorbent. A lithium aqueous solution is used.

  According to the present invention, the absorbing solution contains at least 2,5-dimercaptothiadiazole, which is not extracted during operation into the surfactant 2-ethyl-1-hexanol. Therefore, the time-dependent fall of a 2, 5- dimercapto thiadiazole density | concentration can be prevented, and the density | concentration of a 2, 5- dimercapto thiadiazole can be maintained in the appropriate range. In addition, 2,5-dimercaptothiadiazole is used in combination with oxyacid salt, an inhibitor of carbon copper, and added to lithium bromide absorbing solution that is high in temperature and high concentration, effectively preventing absorption chiller water corrosion. can do.

  In addition, since the concentration of inhibitors (2,5-dimercaptothiadiazole and oxyacid salt) can be maintained appropriately over a long period of time, it is necessary to frequently manage the concentration of inhibitors (2,5-dimercaptothiadiazole and oxyacid salt) It is possible to provide an absorption-type cold / hot water machine that does not have any.

  An embodiment in which the present invention is applied to a steam-fired double-effect absorption refrigerator will be described below with reference to the drawings.

  FIG. 1 is an explanatory diagram showing an absorption spectrum of an absorption chiller / heater absorption liquid according to one embodiment of the present invention, and FIG. 2 shows copper in the absorption chiller / heater absorption liquid according to one embodiment of the present invention. FIG. 3 is an explanatory diagram showing an anodic polarization curve of copper in a conventional aqueous solution of lithium bromide containing BTA for explaining the present invention, and FIG. 4 explains the present invention. FIG. 5 is a schematic diagram showing the structure and cycle flow of a double-effect absorption refrigerator that is an application target of the present invention.

  In FIG. 5, the double-effect absorption refrigerator includes a high-temperature regenerator 1a, a low-temperature regenerator 1b, a condenser 2, an evaporator 3, an absorber 4, a heat exchanger 5, and an absorption liquid (odor) between these devices. Lithium chloride aqueous solution) 6, 6 a, 6 b and pumps 8 a, 8 b for circulating the refrigerant 7, and each device operates as follows.

  Evaporator 3: Cold water 10 passes through the tubes of the evaporator tube group 9 of the evaporator 3, and the refrigerant 7 supplied from the refrigerant pump 8b is sprayed from the spray nozzle 11 to the outside of the tube. Remove heat from cold water 10.

  Absorber 4: The absorbing liquid has a significantly lower vapor pressure than water at the same temperature, and absorbs the refrigerant vapor generated in the evaporator 3. The heat generated at this time is cooled by the cooling water 13 flowing in the tubes of the absorber tube group 12.

  Regenerators 1a and 1b: The diluted absorbent 6b whose concentration has been reduced by absorbing the refrigerant vapor in the absorber 4 is partly sent to the high-temperature regenerator 1a by the solution circulation pump 8a and overheated by the steam (or gas burner). And concentrated. The high-temperature steam 14 generated by heating serves as a heating source for the low-temperature regenerator 1b, and heats and concentrates the diluted absorbent 6b having a reduced concentration. The concentrated absorbents 6 a and 6 b are returned to the absorber 4 as the concentrated absorbent 6.

  Condenser 2: Refrigerant vapor (water vapor) emitted from the low-temperature regenerator 1b enters the condenser 2, is cooled by the cooling water 13 flowing in the condenser tube group 15, and becomes liquid refrigerant 7 and flows to the evaporator 3.

  Heat exchanger 5: A low-temperature diluted absorbent 6b from the absorber 4 toward the high-temperature regenerator 1a and the low-temperature regenerator 1b is supplied to the high-temperature regenerator 1a and a high-temperature rich absorbent 6a from the low-temperature regenerator 1b to the absorber 4 Heat exchange and increase thermal efficiency.

  Pumps 8a and 8b: The absorption liquid circulation pump 8a circulates the absorption liquid (lithium bromide aqueous solution), and the refrigerant pump 8b circulates the refrigerant (water).

  Here, the maximum temperature and concentration of the absorbing solution composed of the lithium bromide aqueous solution in the machine are 160 ° C. and 65 weight percent (hereinafter abbreviated as wt%), respectively.

  As described above, in the absorption refrigerator, the performance depends on how the evaporator 3 increases the evaporation efficiency of the refrigerant and how efficiently the generated refrigerant vapor is absorbed by the absorber 4 in the concentrated absorbent. The efficiency of the evaporator 3 depends on the pressure in the machine, and the efficiency of the absorber 4 depends on the wettability of the heat transfer tube group and the absorbing liquid. For this reason, a surfactant is added to the absorption liquid, and the absorption liquid temperature is high, and therefore, it is selected from higher alcohols such as n-octyl alcohol and 2-ethyl-1-hexanol.

  The absorption liquid is composed of a refrigerant, an absorbent and an inhibitor, water as a refrigerant, lithium bromide (LiBr) aqueous solution as an absorbent, and 2,5-dimercaptothiadiazole (2, 5-dimethylcaptodiadiazol (hereinafter referred to as DMTDA) is used, and corrosion protection of carbon copper is added. Further, 2-ethyl-1-hexanol is also added as a surfactant for improving the heat transfer performance.

  In general, the ratio at which a substance in an aqueous solution is present in an organic solvent is called a distribution ratio. The smaller this value, the smaller the amount extracted into the organic solvent. In the case of two phases of 2-ethyl-1-hexanol and the absorption liquid, the distribution ratio of BTA is 3.76, whereas 2,5-dimercaptothiadiazole is as small as 0.2, and the cold water heater is in operation. In the absorbent without being extracted into 2-ethyl-1-hexanol which is a surfactant. Accordingly, it is possible to prevent the deterioration of the corrosion inhibition effect on copper over time.

  FIG. 3 shows the copper concentration in a 3 mol / liter (hereinafter abbreviated as mol / l) lithium bromide solution containing BTA before and after the addition of 2-ethyl-1-hexanol, with the current density on the vertical axis and the potential on the horizontal axis. FIG. 3 is an explanatory diagram showing an anodic polarization curve. In FIG. 3, curve A is only 3 mol / l lithium bromide aqueous solution, curve B is when 0.005 mol / l BTA is added, and curve C is 0.005 mol / l. 1 BTA and 2-ethyl-1-hexanol were added and stirred, and then the aqueous lithium bromide solution containing BTA was separated. The aqueous solution of lithium bromide alone increases the anode current due to active dissolution of copper at a potential higher than about −0.4 volts (hereinafter referred to as V vs SSE) at the reference electrode of Ag / AgCl (silver / silver chloride). In the case of containing, the anode current is greatly reduced, and the dissolution of copper is suppressed. However, in curve B, it can be seen that the anode current increased again and the corrosion inhibition effect was significantly reduced.

  FIG. 4 is an explanatory diagram showing an absorption spectrum of a 3 mol / l lithium bromide aqueous solution containing 0.005 mol / l BTA before and after the addition of 2-ethyl-1-hexanol, with the vertical axis representing absorbance and the horizontal axis representing wavelength. Before the addition of 2-ethyl-1-hexanol in curve A, an absorption peak of BTA exists in the vicinity of 270 nanometers (hereinafter abbreviated as nm), and the absorbance is 0.95. On the other hand, after the addition of 2 ethyl-1-hexanol in the curve (b), it was greatly reduced to 0.2, indicating that BTA was transferred from the aqueous lithium bromide solution to 2 ethyl-1-hexanol.

  FIG. 1 is an explanatory diagram showing absorption spectra of a 3 mol / l lithium bromide aqueous solution containing 0.0004 mol / l DMTDA before and after addition of 2-ethyl-1-hexanol, with the vertical axis representing absorbance and the horizontal axis representing wavelength. The absorption peak of DMTDA is close to 320 nm, and the absorbance is almost the same before and after the addition of 2-ethyl-1-hexanol in curve I. DMTDA is in 2-ethyl-1-hexanol. It turns out that it is not extracted.

  FIG. 2 shows the anodic polarization curve of copper in a 3 mol / l aqueous lithium bromide solution containing 0.005 mol / l DMTDA before and after the addition of 2-ethyl-1-hexanol, with the current density on the vertical axis and the potential on the horizontal axis. In the same figure, curve A represents DMTDA before addition of 2 ethyl-1-hexanol, and curve B represents DMTDA after addition of 2 ethyl-1-hexanol. From this figure, it can be seen that in the case of DMTDA, there is no significant difference in the anode current before and after the addition of 2-ethyl-1-hexanol, and even if 2-ethyl-1-hexanol is added to the absorbent, the corrosion inhibition effect on copper does not change.

Table 1 summarizes the current density in the case where a constant potential of −0.005 V vs. SSE on the conventional polarization curve is applied to copper in relation to the concentration of DMTDA. The measurement conditions for the polarization curve are the same as in FIG. As is apparent from this table, DMTDA has a sufficiently low current density due to corrosion of copper even after addition of 2-ethyl-1-hexanol, if the concentration is 1 × 10 ⁻⁵ or more, compared to conventional BTA. It turns out that the corrosion inhibitory effect is exhibited.

  Next, the results of measuring the copper ion concentration and the DMTDA concentration during operation using a steam-fired double-effect absorption refrigerator will be described.

Using a steam-fired double-effect absorption refrigerator having a freezing capacity of 30 RT (freezing ton), 0.25 wt% LiOH (lithium hydroxide), 0.02 wt% Li ₂ MoO ₄ (molybdenum) in a 55 wt% lithium bromide aqueous solution 200 kg of an absorbing solution to which 0.08 wt% DMTDA was added was sealed in the apparatus, and 784 kpa of steam was supplied to operate at full load for 1000 hours. During the test, the copper ion concentration and DMTDA concentration in the absorbent during operation were measured. As a comparative example, a 30 RT steam-fired double-effect absorption refrigerator in which an absorption liquid added with 0.05 wt% BTA instead of DMTDA was enclosed was tested under the same conditions. Table 2 shows the results.

  As is apparent from Table 2, the absorption refrigerator according to the present invention effectively suppressed the corrosion of copper as a constituent material, and as a result, the copper ion eluted in the absorbing solution due to corrosion was determined as the lower limit of quantification of the analytical method. It can be reduced to:

It is explanatory drawing which shows the absorption spectrum of the absorption liquid for absorption type cold / hot water machines which becomes one Example of this invention. It is explanatory drawing which shows the anodic polarization curve of copper in the absorption liquid for absorption type cold / hot water machines which becomes one Example of this invention. In order to demonstrate this invention, it is explanatory drawing which shows the anodic polarization curve of copper in the lithium bromide aqueous solution containing the conventional BTA. It is explanatory drawing which shows the absorption spectrum of the lithium bromide aqueous solution containing the conventional BTA in order to demonstrate this invention. It is the schematic of the structure and cycle flow of the double effect absorption refrigerator used as the application object of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Regenerator 2 Condenser 3 Evaporator 4 Absorber 5 Heat exchanger 6, 6a, 6b Absorbent liquid 7 Refrigerant 8a, 8b Pump 9 Evaporator tube group 10 Cold water 11 Spray nozzle 12 Cooling tube 13 Cooling water 14 High temperature refrigerant Steam 15 Cooling pipe

Claims (4)

  In an absorption liquid for an absorption chiller / heater using water as a refrigerant and an aqueous lithium bromide solution as the absorption liquid, the absorption liquid is composed of an aqueous lithium bromide solution containing at least 2,5-dimercaptothiadiazole. Absorption liquid for absorption cold / hot water machine. 2. The absorption liquid for an absorption chiller / heater according to claim 1, wherein the aqueous lithium bromide solution contains 1 × 10 ⁻⁵ mol / liter or more of 2,5-dimercaptothiadiazole.   The absorption liquid for an absorption chiller-heater according to claim 1 or 2, further comprising an oxyacid salt and an alkali in addition to 2,5-dimercaptothiadiazole.   In an absorption chiller / heater using water as a refrigerant and an aqueous lithium bromide solution as an absorbing liquid, an absorbing cold / hot water characterized in that an aqueous lithium bromide solution containing at least 2,5-dimercaptothiadiazole is used as the absorbing liquid. Water machine.

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