JP5131081B2 - Heat exchanger scale removal method and apparatus - Google Patents

Description

  The present invention relates to a heat exchanger descaling method and apparatus applied as a preheater of a geothermal binary power generation system, for example.

  The geothermal binary power generation system described above is a system in which a geothermal fluid (steam or hot water) is passed through a heat exchanger, a binary medium having a low boiling point is evaporated, a steam turbine is driven, and power generation is performed (for example, non-power generation). Patent Document 1).

  As is well known, the geothermal fluid pumped from the production well contains various dissolved components such as silica and calcium carbonate, depending on the geology of the well. When the air and water are separated into water, the dissolved components are deposited as the pressure and pH change. Therefore, when a heat exchanger (preheater) is operated using geothermal hot water as a heat source, the precipitate of the dissolved component (mineral substance) becomes a scale as the temperature of the hot water decreases with the heat exchange with the heated fluid. It becomes deposited on the heat transfer tubes of the exchanger (multi-tubular shell-and-tube heat exchanger). In particular, in the preheater of a binary power generation system that preheats a low boiling point binary medium using geothermal hot water as a heat source, the function and durability of the heat exchanger are reduced due to the deposition of scales, making it impossible to operate geothermal power smoothly. Cause problems.

Therefore, conventionally, as a measure for scaling of the heat exchanger, the scale is dissolved and removed by injecting the chemical into the heat exchanger from the outside at a relatively short cycle (for example, once a month). As for heat exchangers that use geothermal hot water as a heat source, the pH adjusted cleaning liquid is injected and circulated through the heat transfer tubes through which the hot water flows, so that the scales deposited and deposited on the tube walls of the heat transfer tubes are dissolved and separated. A scale removal method is known (see, for example, Patent Document 1).
Shigeto Yamada, 1 other, “Small Geothermal Binary Power Generation System”, Fuji Times, Fuji Electric Holding Co., Ltd., 2005, vol78, No2, p136-139, [0nline], [searched July 30, 2008], Internet <URL: http://www.fujielectric.co.jp/company/jihou_archives/pdf/78-02/FEJ-78-02-136-2005.pdf JP-A 64-75895

  By the way, the scale removal method disclosed in Patent Document 1 includes a cleaning facility for injecting a cleaning liquid into the heat exchanger, and when the scale is removed, the operation mode of the heat exchanger is switched from the heat utilization operation to the scale removal operation. Therefore, the cleaning liquid is poured from the cleaning equipment into the heat transfer tube of the heat exchanger and circulated to clean and remove the scale that has adhered and accumulated.

  For this reason, a cleaning liquid storage facility for injecting the cleaning liquid separately from the heat exchanger, and replenishment management of the cleaning liquid are required. Also, during the scale removal operation, it is necessary to stop the heat utilization operation of the heat exchanger by stopping the flow of hot water as the heat source. During this scale removal operation, the operation of the binary power plant is stopped. There must be.

  The present invention has been made in view of the above points, and the object of the present invention is to use the heat in a state where the heat utilization operation is continued without using any chemicals such as a cleaning liquid and without stopping the operation of the heat exchanger. It is an object of the present invention to provide a novel heat exchanger scale removal method and apparatus capable of separating and collecting scales deposited and deposited on a heat transfer tube of an exchanger.

This invention is a scaling measure for a counter-flow heat exchanger that heats the heated fluid by causing the hot water and the heated fluid to flow countercurrently using geothermal hot water as a heat source,
According to the method of removing scale deposited and deposited on the heat exchanger tube of the heat exchanger according to the present invention, the flow of hot water passing through the heat exchanger tube of the heat exchanger is temporarily "opposite flow" when removing scale from the flow of the heated fluid. ”To“ Parallel flow ”, a sudden temperature change (heat shock) is applied to the heat transfer tube, and the scale fragments separated from the tube wall of the heat transfer tube due to the difference in thermal expansion between the heat transfer tube and the scale due to this temperature change Is collected along the hot water line downstream of the heat exchanger (claim 1).

  In addition, the scale removing device of the present invention that implements the scale removing method has a flow of hot water introduced from the hot water line to the heat exchanger at the time of scale removal with respect to the flow of the heated fluid flowing through the heat exchanger. Channel switching means that reverses the direction from “opposite flow” to “parallel flow”, and the scale debris separated from the heat exchanger tube and discharged from the heat exchanger, is captured in the downstream hot water line. The scale collection means to be recovered and the operation control means to periodically switch the flow of hot water from “counterflow” to “parallel flow” and then return to “counterflow” again during operation of the heat exchanger. (Claim 2).

  Further, as the scale collecting means, a container with a cleaning circuit containing a strainer for capturing the scale is bypass-connected to the piping of the hot water line via a gate valve (Claim 3).

  According to the scale removing method and apparatus of the present invention described above, the flow of hot water flowing through the heat transfer tube of the heat exchanger is reversed from the “countercurrent flow” to the “parallel flow” with respect to the flow of the heated fluid. By applying a sudden temperature change (heat shock) to the heat transfer tube, the thermal expansion coefficient of the heat transfer tube (stainless steel) and the scale (silicon dioxide, etc.) deposited on the tube wall of the heat transfer tube A shear stress based on the difference acts to cause the scale to peel from the heat transfer tube. Then, the debris of the scale peeled off from the heat transfer tube wall is captured and collected by a scale collector located in the hot water line piping downstream from the heat exchanger, so that the cleaning chemicals are used as in the conventional scale cleaning method. The scale can be effectively removed without using the.

  This eliminates the need for cleaning liquid injection equipment and cleaning liquid replenishment as in the conventional method. Moreover, the scale can be removed by simply switching the flow of hot water that passes through the heat transfer tube from the "counter flow" to the "parallel flow" while the heat exchanger continues to operate. It is not necessary to stop the operation of the geothermal binary power generation system.

  Hereinafter, an embodiment of a scale removing apparatus according to the present invention will be described based on examples shown in FIGS. 1 to 4, taking a binary medium preheater applied to a geothermal binary power generation system as an example. 1 is a peripheral piping system including a heat exchanger (preheater) and ancillary equipment used for scale removal, FIGS. 2 and 3 are flow sheets in a steady operation state and a scale removal operation state, respectively. These are the structure of a scale collector in FIG. 1, and a piping system diagram.

  First, in FIG. 1, 1 is a heat exchanger, 2 is a hot water line on the heat source side, 3 is a heated fluid line, 4 is a scale collector, and 5 is an operation control unit. The geothermal hot water (heat source of the heat exchanger 1) collected from the well and separated into steam flows, and the low-boiling binary medium (for example, isopentane) flows to the heated fluid line 3 to heat between the two. Exchange.

  Here, the illustrated heat exchanger 1 is a multi-tubular shell-and-tube heat exchanger, and a plurality of heat transfer tubes 1c are laid between the left and right headers 1a and 1b inside the shell. Thus, a flow path for hot water and a fluid to be heated is defined. The left and right headers 1a and 1b of the heat exchanger 1 are connected to the upstream and downstream pipelines of the hot water line 2 via three-way valves (motor valves) 6A and 6B, respectively.

  The hot water line 2 has a first flow piped so as to bypass the heat exchanger 1 across the branch ports of the three-way valves 6A and 6B connected to the headers 1a and 1b of the heat exchanger 1. An on-off valve (motor-operated valve) 7 is provided to bypass the heat exchanger 1 across the path switching line 2a and the left header 1a of the heat exchanger 1 and the downstream line of the hot water line 2. A second flow path switching line 2b is provided.

  On the other hand, the scale collector 4 has a structure in which a strainer 4b made of a cylindrical wire net that captures scale debris is built in an airtight container 4a as shown in FIG. 1 is connected to a hot water line 2 on the downstream side of 1 via a bypass pipe 2 c, and the scale collector 4 is sandwiched between the inlet and outlet sides of the bypass pipe 2 c and the middle of the hot water line 2. Gate valves (motor valves) 8A, 8B, and 8C are connected. The container 4a of the scale collector 4 is provided with a backwashing type cleaning circuit 9 through a water supply cock 9a for cleaning water (fresh water) and a drain cock 9b.

  The three-way valves 6A and 6B and the on-off valves 7 and 8A to 8C are switched and turned on / off as described below based on a command given from the operation control unit (for example, a programmable controller) 5.

  Next, the states of the steady operation and the scale removal operation of the heat exchanger 1 will be described based on FIGS. 3 and 4, respectively. In FIGS. 3 and 4, Δ for the ports of various valves represents an “open” state, and ▲ represents a “closed” state.

  First, in the steady operation state shown in FIG. 3, hot water (geothermal hot water) supplied from the hot water line 2 flows into the left header 1a of the heat exchanger 1 through the three-way valve 6A, and from here the heat transfer pipe 1c passes through the arrow. After flowing in the A direction and entering the right header 1b, it flows so as to flow out downstream of the hot water line 2 through the three-way valve 6B. During this steady operation, the gate closing valves 8A and 8B arranged on the inlet and outlet sides of the scale collector 4 are closed, and the hot water discharged from the heat exchanger 1 passes through the gate valve 8C in an open state. To flow downstream.

  In this steady operation state, in the shell of the heat exchanger 1, hot water (hot water flow A) and heated fluid (heated fluid flow B) flow in a “counterflow” manner to exchange heat, and heat exchange at a low temperature state. The heated fluid flowing into the vessel 1 is heated to flow out and flows out.Here, the specification example of the heat exchanger 1 is expressed by numerical values, where the hot water inlet temperature is 150 ° C. and the heated fluid inlet temperature is 38 ° C. The outlet temperature of the hot water by the “counterflow” is 110 ° C., and the outlet temperature of the fluid to be heated is 100 ° C. Then, if this steady operation is continued for a long time, mineral components dissolved in the geothermal hot water (silica, Calcium carbonate, etc.) precipitates and becomes the core of the scale and adheres to the tube wall of the heat transfer tube (stainless steel) 1c, and the scale grows as the operation time continues to generate a strong deposit. In such a state, the heat exchanger 1 Thermal performance, in addition to the durability is lowered, predetermined hot water flow flowing through the heat exchanger can not maintain thinned cross section of the heat transfer tube 1c.

  Therefore, in this embodiment, the heat exchanger 1 is changed from the steady operation to the scale removal operation at a predetermined cycle (depending on the properties of the hot water, for example, once a month) from the operation control unit 5 shown in FIG. Issue a control command to switch. Thereby, the flow path of the hot water introduced into the heat exchanger 1 from the hot water line 2 is switched as represented by the flow sheet of FIG. That is, hot water flows from the branch port of the three-way valve 6A into the right header 1b of the heat exchanger 1 through the channel switching pipe line 2a and the branch port of the three-way valve 6B, and in the direction opposite to that in FIG. After flowing through 1c, it enters the left header 1a, and further flows out from here through the flow path switching line 2b and the on-off valve 7 to the downstream line of the hot water line 2. As the scale removal operation is started, the gate valves 8A and 8B attached to the scale collector 4 are “open” and the gate valve 8C is “closed”, and the hot water flowing out of the heat exchanger 1 is collected by the scale. It flows through the vessel 4.

  Thus, when the operation mode of the heat exchanger 1 is switched from the steady operation of FIG. 3 to the scale removal operation, the flow direction of the hot water flowing through the heat transfer tube 1c of the heat exchanger 1 is illustrated as can be seen from the illustrated flow sheet. 3, the flow of the hot water flow A and the heated fluid flow B is reversed from “opposite flow” (see FIG. 3) to “parallel flow”. In this case, when examining how the temperature of the heat transfer tube 1c of the heat exchanger 1 changes as the hot water flow A is reversed, the temperature of the heat transfer tube 1c is shorter at the hot water inlet side than in FIG. It decreases rapidly by about 15 ° C over time, and conversely increases by 25 ° C on the hot water outlet side (verified).

  The rapid temperature change of the heat transfer tube 1c is generated when the flow of hot water is switched from "counterflow" to "parallel flow", and this rapid temperature change adheres to and accumulates on the heat transfer tube 1c and the heat transfer tube. It acts as a heat shock as described below on the scale.

That is, if the material of the heat transfer tube 1c is stainless steel and the component of the scale adhered and deposited on the heat transfer tube 1c is silica (silicon oxide), the thermal expansion coefficient of the stainless steel is 16.7 × 10 ⁻⁶ / ° C. The expansion coefficient is 1.8 × 10 ⁻⁶ / ° C., and the difference in thermal expansion coefficient between the two is very large. Moreover, about the actual machine of the heat exchanger 1, the tube length of the heat transfer tube 1c is 6 m, and the temperature of the heat transfer tube 1c accompanying the reversal of the “opposite flow” / “parallel flow” of the hot water flow changes by an average of 25 ° C. in the entire length region. Then, the amount of change in thermal expansion in the length direction of the heat transfer tube 1c is 2.5 mm, whereas the amount of change in thermal expansion of silica deposited and deposited over the entire length of the heat transfer tube 1c is only 0.3 mm. is there. Due to the difference in the amount of thermal expansion, a shearing stress acts on the interface between the heat transfer tube and the scale as the hot water flow is reversed, so that the scale is mechanically separated from the tube wall of the heat transfer tube. become. In this case, the operation of the heat exchanger 1 is switched from the steady operation to the scale removal operation at an early stage (the scale is deposited in a porous state) before the scale grows into a strong multilayer deposit. By applying a heat shock, the scale easily peels off from the heat transfer tube, and the peeled scale also becomes fine debris.

  On the other hand, the scale fragments peeled off from the tube wall (inner wall) of the heat transfer tube 1c flowed out of the heat exchanger 1 in a form accompanying the flow of hot water, and then bypassed to the downstream pipe line of the hot water line 2. It flows into the scale collector 4 where it is captured by the strainer 4b built in the container 4a. In this case, the scale fragments peeled off from the heat transfer tube 1c of the heat exchanger 1 flow out intermittently from the heat exchanger.

  Therefore, in the actual scale removal operation control, the time for reversing the flow of hot water to “parallel flow” (see FIG. 4) is set to 30 minutes, for example. The hot water is “counterflowed” (see FIG. 3). On the other hand, after the reversal of the flow of the hot water is completed, the scale collector 4 continuously flows the hot water flowing out of the heat exchanger 1 for about one hour, and the scale mixed in the hot water during this period. Make sure that debris is collected. When a predetermined time elapses, the gate valves 8A, 8B, 8C attached to the scale collector 4 are returned to the steady operation state of FIG.

  The scale fragments collected by the strainer 4b of the scale collector 4 open the cocks 9a and 9b with the gate valves 8A and 8B closed, and allow cleaning water (fresh water) to flow from the backwash circuit 9. Thereby, the scale fragments collected inside the strainer 4b are discharged and collected to the outside through the drain cock 9b.

  In the illustrated embodiment, the three-way valves 6A and 6B are connected to the left and right headers 1a and 1b of the heat exchanger 1, and the flow path switching pipe line 2a is piped between the branch ports. Instead of using a three-way valve, two sets of gate valves can be used in combination on the inlet and outlet sides of the heat exchanger.

  In addition, regarding the control of the scale removal operation in which the hot water flowing through the heat exchanger 1 is switched from the “counter flow” to the “parallel flow”, the scale removal operation is executed periodically at a rate of about once a month. As described above, when the geothermal hot water properties (scale components, precipitation amount) are not stable over a long period of time and fluctuate from time to time, the scale removal operation should be performed using the following control method. Is also possible.

  That is, as the growth of the scale deposited and deposited on the tube wall of the heat transfer tube 1c of the heat exchanger 1 proceeds, the flow passage cross section of the heat transfer tube 1c gradually narrows and the flow rate of hot water flowing through the heat transfer tube 1c decreases. Therefore, the flow rate of the hot water flowing out from the heat exchanger 1 is constantly monitored, and when the flow rate drops below a predetermined level, an alarm signal is given to the operation control unit 5 to switch the operation mode from the steady operation to the scale removal operation. . Thereby, scale removal can be appropriately performed according to the scale adhesion state of the heat exchanger that changes depending on the properties of the geothermal hot water.

The surrounding piping system figure which shows the scale removal apparatus of the heat exchanger by the Example of this invention Detailed structure of scale collector in Fig. 1 and its surrounding piping system diagram Flow sheet showing the steady operation state of FIG. Flow sheet showing the scale removal operation state of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat exchanger 1a, 1b Header 1c Heat transfer pipe 2 Hot water line 2a, 2b Flow path switching line 2c Bypass line of scale collector 3 Heated fluid line 4 Scale collector 4a Container 4b Strainer 5 Operation control part 6A, 6B Three-way valve 7, 8A-8C Gate valve 9 Cleaning circuit for scale collector

Claims (3)

For counter flow heat exchangers that use geothermal hot water as a heat source to constantly flow hot water and the fluid to be heated against each other and heat the heated fluid, on the wall of the heat exchanger tube of the heat exchanger that flows hot water A method for removing the deposited and accumulated scale,
When the scale is removed, the flow of hot water that passes through the heat transfer tubes of the heat exchanger is reversed from “opposite flow” to “parallel flow”, and a temperature change is applied to the heat transfer tubes. The heat exchanger is characterized in that the scale debris separated from the heat transfer tube wall due to the difference in thermal expansion between the heat transfer tube and the scale is collected along the hot water line downstream of the heat exchanger. Scale removal method.   It is a scale removal apparatus of the heat exchanger which implements the scale removal method of Claim 1, Comprising: With respect to the flow of the to-be-heated fluid which flows into a heat exchanger, it is from a hot water line to a heat exchanger at the time of scale removal. Flow path switching means that reverses the flow direction of the hot water to be introduced from “opposite flow” to “parallel flow”, and the scale fragments peeled off from the heat transfer tubes of the heat exchanger and discharged from the heat exchanger on the downstream side The scale collection means that captures and collects in the middle of the water line and the flow of hot water during the operation of the heat exchanger are periodically switched from "counterflow" to "parallel flow" and then changed to "counterflow" again. A scale removal device for a heat exchanger, characterized by comprising a return operation control means.   3. The scale removing apparatus according to claim 2, wherein the scale collecting means is a container with a cleaning circuit incorporating a scale capturing strainer, and is bypass-connected to the piping of the hot water line via a gate valve. Heat exchanger scale remover.

Images