RU2528776C1 - Method of cleaning heat exchanger from carbonate deposits - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: method of cleaning heat exchanger from carbonate deposits is provided, comprising feeding of geothermal water with a concentration of carbon dioxide above the equilibrium value, which is generated by increasing the total, respectively, and the partial pressure of carbon dioxide in the cleaned heat exchanger. The cleaned heat exchanger is connected in series to the clean the heat exchanger, and from the geothermal water before feeding to the clean heat exchanger a part of carbon dioxide is removed to the equilibrium value and fed into the geothermal water before feeding to the cleaned heat exchanger, the partial pressure of carbon dioxide in the cleaned heat exchanger is maintained at a level above the equilibrium value.

EFFECT: invention enables to improve the efficiency of cleaning the heat exchanger and to avoid heat loss of geothermal water used for hot water supply.

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Description

The invention relates to geothermal energy and can be used to clean geothermal equipment from carbonate deposits.

Known methods of mechanical (hydromechanical) cleaning of surfaces of various equipment from solid deposits of calcium carbonate [1, 2]. Cleaning is carried out with a special cleaning tool - scrapers, gear crowns, roller nozzles, centrifugal cones, and the cleaned deposits are removed by a fluid stream. The application of these methods is facilitated in the case of loose deposits with a density of 1500-1900 kg / m ³ with open access to the surface being cleaned. Removing dense solid deposits in hard-to-reach places is expensive and mechanical damage to the walls of the equipment being cleaned is possible during the cleaning process. The disadvantages of these methods also include the costs of installation and dismantling and simple equipment during cleaning.

There is also a method of cleaning equipment from carbonate deposits using various chemicals, mainly acid-containing [3, 4]. The greatest effect is obtained, as you know, the use of hydrochloric, sulfuric, nitric acids. Most often, acid washing is carried out with a solution of hydrochloric acid, which forms soluble salts when interacting with all deposits. The disadvantages of this method are: high consumption of acids, corrosion of equipment during cleaning, environmental pollution, as well as additional costs for installation and dismantling and simple equipment during cleaning.

Closest to the claimed invention is a method of cleaning geothermal equipment by dissolving carbonate deposits with carbon dioxide contained in geothermal water [5]. For this, in the equipment being cleaned, the partial pressure of carbon dioxide is maintained above the equilibrium value, which creates aggressive carbon dioxide in the water solution.

Aggressive carbon dioxide, increasing the acidity of the solution, converts solid calcium carbonate to a solution of water in the form of a highly soluble salt of calcium bicarbonate.

In this method, the partial pressure of carbon dioxide is increased by increasing the total pressure in the equipment being cleaned. However, when cleaning the heat-exchange equipment by this method, heat losses of geothermal water occur due to the presence of a layer of deposits on the heat-exchange surface, and therefore the potential of geothermal water is used with low efficiency. Since the equipment cleaning process takes considerable time (due to the low acidity of the solution of geothermal water used for cleaning), heat losses increase in proportion to the cleaning time.

The technical solution of the proposed method is to increase the efficiency of cleaning the geothermal heat exchanger from carbonate deposits.

The problem is solved due to the fact that in the method for cleaning the heat exchanger from carbonate deposits, which includes supplying geothermal water with a carbon dioxide concentration higher than the equilibrium value, which is created by increasing the total, respectively, and partial pressure of carbon dioxide in the cleaned heat exchanger, the cleaned heat exchanger is connected in series to a clean heat exchanger, and part of the carbon dioxide is removed from the geothermal water before being fed to a clean heat exchanger to an equilibrium value and served in geothermal water entering the cleaned heat exchanger, while the partial pressure of carbon dioxide in the cleaned heat exchanger is maintained at a level above the equilibrium value.

The invention is illustrated by drawings and data on the solubility of solid deposits of calcium carbonate in geothermal water wells. 27T (Makhachkala, Republic of Dagestan) presented in the table. Figure 1 - equilibrium parameters of water well. 27T, in which it does not emit and does not dissolve the solid phase of calcium carbonate, and in Fig.2 - connection diagram of the cleaned heat exchanger to a clean heat exchanger.

For each geothermal well, there are water parameters at which it does not dissolve and release the solid phase of calcium carbonate [6]. For example, figure 1 shows a line of equilibrium values of pressure and water temperature of a well 27 T. At points with parameters of pressure and water temperature above the equilibrium line, the solid phase of calcium carbonate dissolves in the form of calcium bicarbonate

CaCO ₃ + CO ₂ + H ₂ O = Ca (HCO ₃ ) ₂

Moreover, the higher the point is located from the equilibrium line, the higher the dissolution rate (see table). Conversely, at points located below the equilibrium line, a solid phase of calcium carbonate is released from the water. Using a graph of the equilibrium water parameters of the operated well and a clean heat exchanger, it is possible to clean the heat exchanger with solid deposits of calcium carbonate without losing the thermal potential of the geothermal water of this well.

Table The dissolution rate of CaCO ₃ deposits in the well. 27T (t = 99 ° C) No. Re The total pressure in the system P, MPa The density of deposits ρ, kg / m ³ The rate of dissolution of deposits υ, mm / day one 200,000 0.75 2700 0.4 2 50,000 0.75 2200 0.3-0.4 3 200,000 0.55 2700 0.1-0.15 four 50,000 0.55 2200 0.05-0.1 5 50,000 0.45 2200 0-0.01

The method is as follows. On line 1 (figure 2), geothermal water with a pressure P ₁ not lower than the equilibrium value enters the first circuit of a clean heat exchanger 2. Next, water with a pressure P ₂ exceeding the equilibrium value at a given temperature is fed through line 3 to the cleaned heat exchanger 4 and is discharged from it with a pressure of P ₃ corresponding to not lower than the equilibrium value at the temperature of water outlet from the system being cleaned. At the same time, in countercurrent, cold fresh water is supplied to the second circuit of the cleaned heat exchanger 4 through line 6. Next, cold water through line 7 is supplied to the second circuit of the heat exchanger 2 and is removed from it to the consumer through line 8.

On line 1, part of the carbon dioxide is discharged from geothermal water in front of heat exchanger 2 and through line 9, pump 10 is fed into geothermal water on line 3 in front of the heat exchanger being cleaned 4. This process reduces the acidity of the water solution supplied to clean heat exchanger 2, thereby reducing its internal corrosion the walls. At the same time, the supply of carbon dioxide to geothermal water, previously cooled in a clean heat exchanger 2, on line 3 increases its acidity before being fed to the cleaned heat exchanger 4, thereby increasing the dissolution rate of the deposits.

Pure heat exchanger 2 allows you to utilize the heat of geothermal water and contributes to greater solubility of carbon dioxide in geothermal water supplied to the cleaned heat exchanger 4.

If it is necessary to increase the flow of geothermal water through a clean heat exchanger 2 (for example, in winter), a line 11 with shutoff valves 12 is provided parallel to the heat exchanger 4.

Thus, the serial connection of the cleaned heat exchanger to a clean heat exchanger, the decrease in the partial pressure of carbon dioxide in a clean heat exchanger and its increase in the cleaned heat exchanger can improve the efficiency of cleaning the heat exchanger from carbonate deposits and eliminate heat loss from geothermal water.

Information sources

1. RF pat. 20003390, class B08B 9/04, publ. 11/30/93.

2. RF pat. 2177377, cl. B08B 9/045, publ. 27.12.2001.

3. RF pat. 2078058, class C02F 5/14, publ. 04/27/1997.

4. RF Pat. 2177458, cl. C02F 5/14, C23F 14/02, publ. 12/27/2001.

5. Akhmedov G.Ya. On the formation and dissolution of carbonate deposits in geothermal systems // Alternative Energy and Ecology. 2010. No. 7. S.128-133.

6. Akhmedov G.Ya. Problems of scaling when using geothermal water for hot heat supply // Industrial Energy, 2009. No. 9 P.50-54.

Claims (1)

A method of cleaning the heat exchanger from carbonate deposits, including the supply of geothermal water with a carbon dioxide concentration above the equilibrium value, which is created by increasing the total, respectively, and partial pressure of carbon dioxide in the cleaned heat exchanger, characterized in that the cleaned heat exchanger is connected in series to a clean heat exchanger, and from of geothermal water before being fed into a clean heat exchanger, part of the carbon dioxide is removed to an equilibrium value and fed into geothermal water before supply to the cleaned heat exchanger, while the partial pressure of carbon dioxide in the cleaned heat exchanger is maintained at a level above the equilibrium value.

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