ES2704988T3 - Procedure for supplying a cooling medium in a secondary circuit - Google Patents

Abstract

Process for supplying a cooling medium with a regulated temperature flow in a secondary circuit (20), wherein the cooling medium in the secondary circuit (20) absorbs heat from one or more process coolers (22) and then gives heat to the primary water in a primary circuit (10) before it flows back to the process refrigerators (22); characterized in that at least two primary heat exchangers (12, 14) are provided for cooling the cooling medium; further in that a bypass conduit (26) in the secondary circuit (20) deviates after the output of the process refrigerators (22) to bypass the primary heat exchangers (12, 14); and the regulation of the temperature in the secondary circuit (20) in the flow to the process refrigerators (22), is done by adjusting the bypass flow.

Description

DESCRIPTION

Procedure for supplying a cooling medium in a secondary circuit

The present invention relates to a method for supplying a cooling medium with a regulated temperature flow in a secondary circuit, wherein the cooling medium in the secondary circuit absorbs heat from one or more process coolers and then transfers heat to the primary water in a primary circuit before it flows back to the process cooler. In addition, the invention relates to a device for the implementation of the method according to the invention, wherein the device comprises one or more process coolers in the secondary circuit, as well as at least one temperature sensor in the flow to the cooler. process. The application WO 2011/149487 discloses a device with the characteristics of the general concept of claim 7.

In many processes from the technical point of view of the process, it is necessary to dissipate heat from appliances or parts of an installation. For this purpose, primary water is frequently used, which, particularly in industrial scale processes, is available as return cooling water, river water or seawater. From the point of view of the control of the process, it is desirable that the refrigeration of the apparatuses or of the pieces of installation is carried out as much as possible in constant temperatures. From the point of view of safety and environmental care, it must be avoided that, for example, in cases of spills, harmful substances may eventually reach natural waters. These requirements can be met when the primary water does not come into direct contact with the devices that must be cooled, using instead a cooling medium in a closed intermediate circuit, also called secondary circuit. The cooling medium is chosen according to the respective requirements. A usual cooling medium is water, other examples are water-glycol or methanol mixtures.

The refrigerant circulates in the secondary circuit with a certain temperature flow to one or several process coolers and there absorbs heat from the process, thereby heating it. To achieve that the cooling medium returns to the desired temperature flow, it is supplied to one or more heat exchangers, in which said medium is cooled by primary water. The primary water circuit, for example return cooling water, river water or seawater is called the primary circuit. Correspondingly, heat exchangers, in which the cooling medium is cooled by the primary water, are called primary heat exchangers.

The division of refrigeration in a primary circuit in which primary water circulates, and in a secondary circuit in which a cooling medium circulates is an established technique and offers several advantages. In the case of a spill in an appliance or in a process cooler, the harmful substances may eventually enter the cooling medium, while the primary water in the primary circuit remains free of contamination. On the other hand, due to the fact that the secondary circuit is closed, process coolers become less dirty in the installation than, for example, in cases where direct cooling with river water is carried out.

This procedure also makes it possible to adjust a desired value for the flow of temperature towards the process coolers, independently of the variations in primary water that may be caused by the time of day or the season of the year. In general, in terms of number and dimensional design, the primary heat exchangers are designed so that in a high load case, they can extract sufficient heat from the cooling medium. To define the case of high load, a state is taken as reference in which the temperature difference between the cooling medium that enters the heat exchanger and the primary water that enters, has a minimum admissible value determined. Given a given value for the cooling medium that enters, a maximum admissible value for the primary water that enters is deduced from it. For this reason, in central Europe the case of high load is usually in the summer months, in which the river water can reach, for example, temperatures of 28 ° C or more.

In contrast to the above, we speak of a case of reduced load when the temperature difference between the cooling medium that enters the heat exchanger and the primary water that enters, adopts high values. In Central Europe, this is usually the case in the winter months, when the temperature of the river water can drop, for example, to values of 4 ° C or lower. Hereinafter, a case of reduced load is mentioned when only little heat must be transmitted from the cooling medium in the secondary circuit to the primary water; for example, when an installation does not work at its maximum capacity or when it is completely disconnected, so that in the primary refrigerators less heat is transmitted from the cooling medium to the primary water. In these cases, maintaining the temperature flow of the refrigerant medium to the process coolers at the same value as in the case of high load, less primary water is needed, so that the primary water flow is usually reduced towards the primary heat exchangers. This way of proceeding is disadvantageous in the sense that in case of reduced load due to the reduced circulation speed, the primary heat exchangers tend from the primary water side to fouling, to the so-called biocorrosion. In addition, a regulation of the flow of temperature towards the thermal refrigerators through the inflow of primary water towards the primary heat exchangers is slow. The invention has as its object to provide a method for cooling of this kind, in which the fouling of primary heat exchangers is reduced and with which the flow of temperature towards the process coolers can be regulated rapidly and robustly.

Said object is solved by a method according to the invention according to claim 1, as well as by means of a device according to the invention according to claim 7. Advantageous improvements of the invention are indicated in the respective related claims 2 to 6. In the procedure , according to the invention, for supplying a cooling medium with a regulated temperature flow to a secondary circuit; the refrigerant in the secondary circuit absorbs heat from one or more process coolers and then transfers heat to the primary water in a primary circuit, before it flows back to the process coolers. At least two primary heat exchangers are provided for cooling the cooling medium. After the output of the process coolers, and prior to entry to the primary heat exchangers, a bypass line extends in the secondary circuit to bypass the primary heat exchangers. The bypass line flows into the line of the secondary circuit, from the primary heat exchangers to the process coolers. According to the invention, the regulation of the temperature flow to the process refrigerators in the secondary circuit is carried out by adjusting the bypass flow. By "temperature flow" is hereinafter meant the temperature in the secondary circuit in the flow to the process coolers. The section of the secondary circuit between the branch line inlet in the secondary circuit and the first process heat exchanger is called "flow to the process coolers". The section of the secondary circuit that lies between the output of the at least one process heat exchanger and the derivation of the bypass line is called "divergence". In the case of a plurality of process heat exchangers, the section of the secondary circuit located between the confluence of the output conduits of the process heat exchangers and the derivation of the bypass conduit is called "output".

In a preferred embodiment of the invention, a temperature sensor is located in the flow to the process coolers, and the bypass line is provided with an adjusting element with the help of which the flow of temperature to the process cooler can be regulated. in the secondary circuit. Various temperature sensors can also be provided in the flow to the process coolers, for example to perform a redundant measurement. Suitable temperature sensors, for example thermoelements, detect the temperature of the circulating cooling medium and make available a value that is transmitted to a regulation system.

In another configuration according to the invention, at the outlet of the secondary circuit, one or more temperature sensors are located, and the bypass line is provided with an adjustment element with the help of which the flow of temperature towards the cooling unit can be regulated. process in the secondary circuit.

The appropriate adjustment elements allow to adjust between a minimum value and a maximum value, the flow through the bypass conduit. Preferably, the minimum value is equal to zero, which means a completely closed bypass conduit. The maximum value corresponds preferably to a completely open bypass line. Between the extreme values, discretional values for the flow can be adjusted, preferably continuously, not stepwise. The adjustment elements are known to the person skilled in the art, for example, flaps, ball valves or three-way valves.

In a preferred embodiment, a regulation system is provided, which has a theoretical value for the temperature flow. From a comparison of the theoretical value with the temperature flow detected by the temperature sensor, the regulation system generates an output signal to transmit it to the adjustment element. The temperature of the cooling medium circulating through the bypass line is higher than the temperature of the cooling medium that flows from the primary heat exchangers to the process coolers. Therefore, the regulation provides for reducing the current through the bypass line, in the case of a very high temperature flow compared to the theoretical value; and correspondingly in the case of a very low temperature flow compared to the theoretical value, increase the current through the bypass conduit.

In another embodiment according to the invention, a regulation system is provided, which has a theoretical value for the outlet temperature. From a comparison of the theoretical value with the output temperature detected by the temperature sensor, the regulation system generates an output signal to transmit it to the adjustment element. Also in this configuration, the regulation provides for reducing the current through the bypass line, in the case of a very high outlet temperature compared to the theoretical value; and correspondingly in the case of a very low outlet temperature compared to the theoretical value, increase the current through the bypass line.

The flow of the cooling medium through the bypass conduit can also be influenced by the provision of adjustment elements in the conduits through which the cooling medium goes towards the primary heat exchangers or through which it leaves the primary heat exchangers, which adjust correspondingly in their degrees of opening. A regulation of the shunt flow by the influence of an adjustment element on the shunt conduit is however simpler to perform and therefore is preferred. With regard to the regulation system, it can be an independent device, for example, a compact controller that is computer-connected with the temperature sensor and with the adjustment element. The adjustment system can also be implemented in combination with an adjustment element, for example in the form of a control valve. Alternatively, the regulation system can also be integrated into a higher system for process control, for example in a process control system.

In a preferred embodiment of the method according to the present invention, the primary heat exchangers are designed in terms of number and dimensional design for a high load case. In a case of reduced load, the cooling capacity of the primary circuit is adapted by disconnecting one or more primary heat exchangers, where at least one primary heat exchanger remains in operation. The terms "high load case" or "reduced load case" are defined as operating states as defined above.

In another preferred variant, the primary heat exchangers are designed so that in a case of reduced load, a heat exchanger is sufficient to cool the cooling medium until reaching the desired temperature flow, using for this a maximum admissible temperature difference between the input and the primary water outlet. For the case of high load, more heat exchangers are provided, which are preferably also designed individually for a maximum admissible temperature difference between the primary water inlet and outlet, and which are, overall, suitable for the difference of minimum temperature in the case of high load. The maximum permissible temperature difference between the primary water inlet and outlet is often officially determined, for example at a value of 15 K. By this measure, the primary water can be efficiently used in a variable load range in total quantities. seasons of the year and the minimum quantities of primary water required can be dramatically reduced.

The bypass line, in terms of its capacity, is preferably designed so that the regulation range of the regulating duct is sufficient to regulate the flow of temperature in the secondary circuit without complications, before the disconnection and connection of an exchanger primary thermal

In the design of the bypass duct, it is also preferably considered that changes in the temperature of the primary water caused by the time of day can only be compensated by regulating the current through the bypass line. A connection or disconnection of primary heat exchangers is not foreseen for this case.

In a particularly preferred manner, the flow of primary water through the primary heat exchanger (s) remains essentially constant. In this case, the flow is not actively regulated, but instead results from the pressure difference between the primary heat exchanger inlet and outlet, on the primary water side. In case of variations in this pressure difference, there are also variations in the flow rate. If the temperature of the primary water falls, or if the amount of heat that must be extracted from the cooling medium is reduced, for example by a reduction in the flow rate of the coolant through a primary heat exchanger or by a reduction in the temperature of the medium refrigerant at the exit of the process refrigerators; then the temperature of the cooling medium at the outlet of this primary heat exchanger decreases. Correspondingly, the outlet temperature of the cooling medium increases, in the event of an increase in the primary water temperature and / or an increase in the amount of heat that must be extracted from the cooling medium.

In another preferred embodiment of the invention, the adaptation of capacity through the connection or disconnection of primary heat exchangers is carried out in such a way that the pressure loss of the primary water during circulation through the primary heat exchangers found in operation, respectively reaches at least 300 mbar, preferably preferably at least 800 mbar. In this way, the probability that sediments form on the primary water side is significantly reduced.

The at least two primary heat exchangers can be interconnected in different ways. Preferably, the primary heat exchangers are connected in parallel, both on the side of the primary circuit, as well as on the side of the secondary circuit.

As primary heat exchangers, all types of heat exchangers known to those skilled in the art can be used for this purpose, preferably heat exchangers of plate or heat exchangers with tube bundles are implemented, particularly preferably sealed or welded plate heat exchangers. Particularly preferred plate heat exchangers are designed, in general, for high pressure loss. This is advantageous when the shunt must be carried out without additional conveyors such as pumps.

In a preferred configuration of the process according to the invention, as regards primary water, it is return cooling water, river water, sea water or saline water. By "return cooling water" is meant here water that has been cooled in a processing plant by an installation such as a cooling tower or a return cooling installation.

In contrast to the method known by the state of the art, the invention offers numerous advantages. The provision of at least two primary heat exchangers, which together provide the necessary cooling capacity in the case of high load; but that in case of reduced load they can be partially disconnected, it allows the individual primary heat exchangers to be operated with a practically constant circulation of the primary water side, which prevents a premature biocorrosion. In addition, this offers the possibility to alternately connect or disconnect the primary heat exchangers, which allows easy inspection and eventually maintenance and cleaning. Beyond this, the minimum quantities of primary water necessary for the provision of cooling capacity are also considerably reduced. Another advantage to be considered is that a regulation of the temperature flow with the aid of the bypass flow is fundamentally simpler, quicker and more robust to implement than a regulation by means of the primary water flow, such as that applied in the state of the art.

In the following, the invention is explained in detail by means of the drawings, in which the drawings are to be understood as basic representations. They do not represent any limitation of the invention, for example, as regards the number, type or interconnections of the heat exchangers. They show:

Figure 1: a basic scheme of a cooling system according to the state of the art;

Figure 2: a basic scheme of a cooling system according to the invention;

Figure 3: a basic scheme of a cooling system according to the invention, with a series circuit of primary heat exchangers on the secondary side;

Figure 4: a basic scheme of a cooling system according to the invention, with a flexible interconnection of primary heat exchangers on the primary side;

Figure 5: the development in time of the primary water temperature and the number of primary heat exchangers that are in operation.

Figure 1 shows a cooling system according to the state of the art, in which in a secondary circuit 20 a cooling medium circulates towards process coolers 22, there it absorbs heat and in a primary heat exchanger 12 it gives heat to the primary water in a circuit 10, before it flows back to the process coolers. The process coolers can have different construction designs, for example plate heat exchangers, with tube bundles, or spirals, or coatings of tubes or containers for cooling. The temperature flow of the cooling medium is detected before the process coolers 22 with the aid of a temperature sensor, and regulated by the regulating system 24 on the basis of a certain theoretical value. The amount of primary water in the primary circuit 10 functions as a theoretical value for regulation.

A preferred embodiment of the method according to the invention is shown in FIG. The cooling medium leaving the process coolers 22 is conducted through two primary heat exchangers 12, 14, where the medium gives heat to the primary water in the primary circuit 10. In the preferred case, represented, the primary heat exchangers they are connected in parallel, both on the side of the primary circuit, and also on the side of the secondary circuit. Between the outlet of the cooling medium from the process coolers 22 and their entry into the primary heat exchanger 12, 14 a bypass line 26 extends, which after the exit of the cooling medium from the primary heat exchangers returns to flow into the circuit secondary 20. The regulation 24 of the temperature flow of the cooling medium to the process refrigerators 22 occurs by adjusting the current in the bypass line. In the case of high load, both primary heat exchangers 12 and 14 are in operation, while in the case of reduced load reaches the capacity of a primary heat exchanger for sufficient cooling of the cooling medium in the secondary circuit 20. In this case , by closing the respective valve in the secondary circuit, one of the primary heat exchangers is disconnected.

A further preferred embodiment of the method according to the invention is shown in FIG. 3. In this example, the primary heat exchangers 12 and 14 are interconnected in parallel on the side of the primary circuit, and in series on the side of the secondary circuit. To be able to disconnect the primary heat exchangers 12 and 14 in the case of reduced load, sections are provided in the secondary circuit that can be connected or disconnected by means of valves.

Figure 4 shows another preferred embodiment of the method according to the invention, in which the primary heat exchangers 12, 14 are connected parallel to the secondary side. On the side of the primary circuit, the interconnection remains flexible. By means of corresponding opening and closing of the exemplified valves, a series circuit or a parallel circuit can be realized on the primary side. In addition, the primary heat exchangers 12, 14 can be switched off reciprocally by closing the corresponding valves in the secondary circuit.

The representations are merely illustrative. As long as the regulation of the temperature flow in the secondary circuit is made by adjusting the derivation flow, the configurations and interconnections that differ from the representations, should also be considered as disclosed by the present invention.

Particularly the number of heat exchangers represented in the drawings is merely exemplary and not restrictive. It is advantageous when more than two primary heat exchangers are provided. While more primary heat exchangers are available, the individual connection or disconnection of the primary heat exchangers is more flexible to make an optimal adaptation to the current load case. On the other hand, this also increases the investment costs. Preferably two to three primary heat exchangers are provided.

A selection criterion for the number of primary heat exchangers can be derived from the primary water temperature gradients. Preferably, the optimum number of primary heat exchangers is estimated by the quotient of the maximum admissible temperature difference and conventional temperature difference in the case of high load. For example, for the German town of Ludwigshafen am Rhein (Port of Louis of the Rhine), the official maximum admissible temperature difference between the primary water inlet and the outlet reaches 15 K, using river water as primary water. In addition, the water that is driven back to the river must not exceed a value of 33 ° C. In case of high load in the summer months, in which the river water can reach temperatures of 28 ° C, between the primary water inlet and outlet, common temperature differences of 5 K are thus common. a ratio of 15 K / 5 K = 3. For this reason three primary heat exchangers are advantageously provided, which are designed so that each of the three heat exchangers can extract only the amount of heat required from the cooling medium in the secondary circuit, when the maximum admissible temperature difference of 15 K is extracted.

Figure 5 schematically represents the development over time of the temperature of the primary water T (discontinuous curve) and the number of primary heat exchangers N that are in operation (solid lines, right scale), in a time period of 12 months This exemplary representation is based on the fact that the amount of heat that must be dissipated from the secondary circuit remains constant throughout the observed period. As primary water, river water is used, which in the winter months of December and January has the lowest temperature, for example 4 ° C. The maximum permissible temperature difference can be completely removed, so that it reaches a primary heat exchanger for sufficient cooling of the cooling medium in the secondary circuit. As soon as the river water exceeds a value from which, considering a certain range of variation, the maximum admissible temperature difference can no longer be guaranteed, another primary heat exchanger is put into operation. In the case of a given range of variation of 3 K, and a maximum value of 33 ° C for the water delivered in the river, a value of 15 ° C results, from which the second heat exchanger is put into operation primary. In the example according to figure 5, this is the case in mid-April. At the beginning of June, the temperature of the river water increases to a value from which the third primary heat exchanger is needed to, on the one hand, dissipate the necessary amount of heat reliably, and on the other hand not to exceed the maximum value of 33 ° C. During the summer months of June, July and August, three primary heat exchangers work, until the temperature of the river water drops again enough to reach two primary heat exchangers, in the example at the beginning of September. At the end of October, the temperature of the river water drops further, for example below 15 ° C, so that it only reaches a primary heat exchanger again.

The method according to the invention makes it possible to provide cooling capacities in a flexible manner, according to current requirements. In the example shown in figure 5, a primary heat exchanger is in operation for five and a half months, two primary heat exchangers for three and a half months and three primary heat exchangers for three months. In comparison with a design purely for the case of high loading, by the method according to the invention it is possible to drastically reduce the amount of primary water required.

On the primary water side, an essentially constant quantity of water circulates through each primary heat exchanger, which prevents fouling and biocorrosion. Except in the summer months, heat exchangers that are out of operation can be maintained and cleaned without affecting the operation of the facilities in the secondary circuit. Assuming that in the installations according to the state of the art, in which primary heat exchangers designed only for the case of high load are arranged, in which in the case of reduced load, the amount of primary water is reduced, the installation must be disconnected once a year for approximately 3 days because of soiling; Through the According to the invention, the capacity of the installation can be increased by about 1%. In the case of frequent or long disconnection periods, the economic advantage increases correspondingly.

Claims (7)

1. Process for supplying a cooling medium with a regulated temperature flow in a secondary circuit (20), wherein the cooling medium in the secondary circuit (20) absorbs heat from one or more process coolers (22) and then yields heat to the primary water in a primary circuit (10) before it flows back to the process refrigerators (22); characterized in that at least two primary heat exchangers (12, 14) are provided for cooling the cooling medium; further in that a bypass conduit (26) in the secondary circuit (20) deviates after the output of the process refrigerators (22) to bypass the primary heat exchangers (12, 14); and the regulation of the temperature in the secondary circuit (20) in the flow to the process refrigerators (22), is done by adjusting the bypass flow. The method according to claim 1, wherein the number and dimensions of the primary heat exchangers (12, 14) are designed for a high load case; and in a case of reduced load, the cooling capacity of the primary circuit (10) is adapted by disconnecting one or more primary heat exchangers (12, 14), where at least one primary heat exchanger remains in operation. Method according to claim 2, wherein the capacity adaptation is carried out in such a way that the pressure loss of the primary water through the primary heat exchangers (12, 14) which are in operation, reaches respectively at least 300 mbar , preferably at least 800 mbar. Method according to one of claims 1 to 3, wherein the primary heat exchangers (12, 14) are designed for a maximum permissible temperature difference between the primary water inlet and the primary water outlet. Method according to one of claims 1 to 4, wherein the primary heat exchangers (12, 14) are connected in parallel on both the primary circuit side (10) and the secondary circuit side (20). Method according to one of Claims 1 to 5, in which primary heat exchangers (12, 14) use plate heat exchangers or heat exchangers with tube bundles, particularly sealed or welded plate heat exchangers. Device for implementing the method according to at least one of claims 1 to 6, comprising one or more process coolers (22) in the secondary circuit (20), as well as at least one temperature sensor in the flow to the process coolers (22); wherein at least two primary heat exchangers (12, 14) are provided, in which the cooling medium of the secondary circuit (20) can yield heat to the primary water of the primary circuit (10); and wherein also a bypass conduit (26) is provided, which in the secondary circuit (20) is diverted after the output of the process refrigerators (22) to bypass the primary heat exchangers (12, 14) and that it is provided with an adjustment element with the help of which the temperature in the secondary circuit (20) can be regulated in the flow to the process cooler (22); characterized in that the primary heat exchangers (12, 14) are connected in parallel, both on the side of the primary circuit (10), and also on the side of the secondary circuit (20).