RU2751468C2 - Heat exchanger operation method - Google Patents

Abstract

FIELD: geothermal energy.

SUBSTANCE: invention relates to geothermal energy and can be used to operate heat exchangers in a mode without salt deposition and with minimal corrosion of its internal surface. The essence of the invention consists in periodically changing the direction of the flows of geothermal and cold heated water in the corresponding circuits of the heat exchanger to the opposite one, while maintaining their countercurrent movement. The period of change in the flow direction is determined by the readings of the salt deposition sensors installed on the geothermal water supply and discharge pipelines directly adjacent to the primary circuit of the heat exchanger.

EFFECT: invention provides an increase in the efficiency of the use of the heat exchanger by preventing the formation of the solid phase of calcium carbonate and reducing the corrosion of the equipment.

1 cl, 3 dwg

Description

The invention relates to geothermal energy and can be used for the operation of heat exchangers in a mode without salt deposition and with minimal corrosion of its inner surface.

A known method of operating heat exchangers using geothermal waters, excluding the deposition of calcium carbonate on the heat exchange surface in the primary circuit. The method consists in maintaining the pressure in the equipment above the equilibrium value, at which no solid phase of calcium carbonate is released in geothermal water [1, 2]. This method of operating the heat exchanger has disadvantages. High pressure at the mouth of a geothermal well leads to a decrease in its flow rate, as well as to an increase in the acidity of the water solution due to the increased content of carbon dioxide in it.

There is also known a method of operating heat exchangers using geothermal waters, excluding the formation of a solid phase of calcium carbonate on the heat exchange surface in the primary circuit by maintaining equilibrium parameters of pressure and temperature of geothermal water in it [3]. However, with sharp changes in the mode of consumption of thermal energy by consumers, it is not always possible to avoid the process of scaling in the primary circuit. This is due both to a sharp change in hot water consumption at different times of the day, and to pressure fluctuations in the primary circuit of the heat exchanger. As a result, the temperature of the heat exchange surface changes, which leads to the formation of a solid phase of calcium carbonate in the primary circuit [4]. As a result, there is a sharp deterioration in the operation of the heat exchanger, requiring repair work with the shutdown of thermal distribution stations at geothermal wells.

The proposed technical solution is aimed at increasing the efficiency of using the heat exchanger by preventing the formation of a solid phase of calcium carbonate and reducing equipment corrosion.

The problem is solved due to the fact that in the method of operating the heat exchanger, which includes the supply of geothermal water to the primary circuit, heated water in counterflow to the secondary circuit, regulation of the water flow in both circuits using stop valves, the direction of flows of geothermal and cold heated water in the corresponding circuits periodically changes on the opposite, while the time of the period of changing the direction of flows is selected according to the readings of the scaling sensors installed on the pipelines for supplying and removing geothermal water directly at the entrance to the heat exchanger. At the same time, the countercurrent movement of water flows in the heat exchanger circuits remains unchanged with all changes.

The essence of the invention is illustrated by drawings.

FIG. 1 is a graph of the equilibrium values of pressure and temperature of geothermal water at which the water is stable, i.e. does not dissolve and does not release a solid phase of calcium carbonate.

FIG. 2 is a diagram of the connection of the heat exchanger through the shut-off valves to the geothermal well and to the water source in the secondary circuit.

FIG. 3 - distribution of water temperature in the heat exchanger circuits along its length.

For each geothermal well, there are water parameters at which it does not dissolve and does not release a solid phase of calcium carbonate [2]. For example, in FIG. 1 shows a line of equilibrium values of pressure and temperature of water solution of well 27 T (Makhachkala, RD). The operation of the heat exchanger at the parameters of pressure and temperature of geothermal water above the equilibrium line, on the one hand, reduces the flow rate of the well, and on the other hand, leads to an increase in the corrosive activity of water due to the presence of aggressive carbon dioxide in it. Moreover, the higher the operating parameters of the heat exchanger from the equilibrium line, the higher the corrosion of the equipment. Operating the heat exchanger below the equilibrium line results in calcium carbonate deposits on its inner surface. In practice, in order to exclude salt deposition on the heat exchange surface, the operation of heat exchangers is carried out at pressure parameters higher than the equilibrium value, which reduces the efficiency of using heat exchangers by reducing the flow rate of the well and corrosion of its inner surface.

The method of operating a heat exchanger in a mode without scale deposition and with minimal corrosion of its inner surface is carried out as follows. With closed valves 3 and 5 and open valves 4 and 6 (Fig. 2), through line 1, geothermal water is supplied to the primary circuit of the heat exchanger and is discharged through line 2. At the same time, with closed valves 11 and 13 and open 10 and 12, through line 8 into the secondary heated water is supplied in a countercurrent flow and is removed through line 9. In practice, the deposition of calcium carbonate salts is mainly observed at the beginning of the heat exchange surface of the primary circuit due to the high temperature of geothermal water (see Fig. 1 and Fig. 3), at which water prone to precipitation of a solid phase of calcium carbonate from the solution. As it moves along the heat exchanger path, the geothermal water solution enters a state of equilibrium and, at the end of the heat exchange surface, enters a state of maximum aggression, i.e. into a state in which the dissolution of previously formed deposits, if any, occurs [5]. The presence of deposits at the beginning of the heat exchange surface of the primary circuit is recorded by the scale sensor 14 (Fig. 2). In the presence of deposits with a thickness of more than 1-2 mm, the direction of movement of geothermal and cold heated water is changed in the corresponding circuits of the heat exchanger. For this, valves 4 and 6 are closed and 3 and 5 open (Fig. 2). In this case, through line 1, geothermal water is supplied to the primary circuit of the heat exchanger and is discharged through line 2 in the opposite direction. At the same time, valves 10 and 12 are closed, and 11 and 13 are opened. In this case, the heated water in the secondary circuit through line 8 is supplied in a countercurrent flow and is discharged through line 9 also in the opposite direction (opposite to the original direction). FIG. 3 shows the change in the temperature distribution in the circuits along the heat exchanger path. Solid lines - temperature lines of geothermal (1) and heated (2) water, respectively, in the primary and secondary circuits along the length of the heat exchanger. Dashed lines - lines of water temperature in the primary (1) and secondary (2) circuits of the heat exchanger after changing the operating mode of the heat exchanger. As seen in FIG. 1 and 3, a change in the operating modes of the heat exchanger contributes to the dissolution of previously formed deposits in the primary circuit, which keeps the operation of the heat exchanger in a state of repair.

Thus, due to the periodic change in the direction of movement of geothermal and cold heated water in the corresponding circuits of the heat exchanger in counterflow with the help of shut-off valves, the efficiency of using the heat exchanger in the mode without scale deposition increases for the uninterrupted supply of heat energy to consumers.

Sources of information

1. Alkhasov A.B. Geothermal energy: problems, resources, technologies. - M .: Fizmatlit, 2008 .-- S. 100-107.

2. Akhmedov G.Ya. Problems of salt deposition in the use of geothermal waters for hot heat water supply // Promyshlennaya energetika. - No. 9. - 2009.

3. Akhmedov G.Ya. Operation of geothermal heat supply systems in a regime without salt deposition // Industrial energy. - 2010. - No. 4. - S. 54-59.

4. Akhmedov G.Ya. Solid deposits of calcium carbonate in geothermal systems // Alternative energy and ecology. - 2010. - No. 11. - S. 81-86.

5. Pat. 2528776, RF, IPC F28G 9/00. The method of cleaning the heat exchanger from carbonate deposits declared. / Akhmedov G.Ya. Publ. 09/20/2014, Bul. No. 26. - 5 p.

6. Pat. 2387950 RF, IPC G01B 7/06. Method and device for determining the thickness of salt deposition / Akhmedov G.Ya. Publ. 04/27/2010. Bul. No. 12. - 7 p.

7. Akhmedov G.Ya. On some methods of scaling control in geothermal energy / Industrial energy. - 2010. - No. 6. - S. 58-62.

Claims (1)

A method of operating a heat exchanger, including the supply of geothermal water to the primary circuit, heated water in counterflow to the secondary circuit, regulation of the water flow in both circuits using stop valves, characterized in that the direction of the flows of geothermal and cold heated water in the corresponding circuits periodically, keeping their countercurrent movement , changes to the opposite, while the time of the period of changing the direction of flows is selected according to the readings of the scaling sensors installed on the pipelines for supplying and removing geothermal water directly at the inlet and outlet of the primary circuit of the heat exchanger.

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