WO2004032308A1 - Cooling method - Google Patents

Abstract

The invention relates to a method for the intensive cooling of machines (1) which release heat internally, whereby the cooling occurs as required by the heat balance in so far as economically possible with a conventional cooling circuit and in a second or optionally further cooling stage with provided cooling sources and, where further necessary for the heat balance, the cooling occurs with artificial refrigeration units, whereby the series of the individual cooling stages is dependent on the temperature level of the provided conventional and artificial cooling and refrigeration units.

Description

Cooling process

It is known to cool machines with internal heat generation, for example electrical machines with fresh air. However, the inside of the electrical machine is constantly exposed to dust and moisture from the fresh air drawn in, which can lead to contamination and cooling problems (source 1). For this reason, efforts are being made to cool larger electrical machines, for example electrical generators in a closed system, with air (magazine <Turbomachinery International-, vol. 40, No. 7 1999, pp. 32-34). The cooling medium air is preferably circulated through the machine with a fan located on the shaft of the generator, where it heats up, in order then to be recooled to the required temperature in a cooler. In order to improve the cooling especially at high specific outputs and to reduce the energy expenditure for the circulation of the cooling medium by low internal friction, it is also known to use hydrogen as a gaseous cooling medium under pressure (source 3).

In contrast to fresh air cooling, indirect cooling is associated with an additional temperature difference on the air cooler. In addition, the air cooler is usually supplied with cooling water from a closed cooling circuit, which in turn is recooled indirectly with cooling tower water via a heat exchanger. Two temperature differences add up, which can lead to inadequate cooling of the electrical machine, especially in warmer areas or with high specific outputs. This leads to an accelerated aging of the insulation materials and ultimately to a shortened service life of the electrical machine. In order to minimize these effects, the heat exchangers are designed with the smallest possible temperature difference of 2 to 5 Kelvin, which leads to a large surface area and expensive equipment.

For example, if it is a gas or gas and steam turbine power plant, up to now there was a decrease in gas turbine power with rising outside temperatures, so that at the same time a smaller amount of heat had to be dissipated from the electric generator. However, there are now technical possibilities to accelerate the gas turbine output, particularly in the warmer season, so that, contrary to the earlier inverse dependence on the outside air temperature and gas turbine output, a higher amount of heat must also be removed from the generator in the warmer season. The easiest way to achieve this is to reduce the temperature level of the cooling air in the electrical machine, but this is often required at a level that is below. the prevailing outside temperature. This is no longer possible with conventional cooling based on the principles listed above. An obvious solution would be to recool the electrical machine with an artificial cooling system. The disadvantage of this method is the energy consumption for generating the artificial refrigeration in the form of electrical drive energy for a compression refrigeration system, or in the form of heat, for example for an adsorption refrigeration system. In addition, chillers require additional space, are subject to constant wear and tear as compression chillers, have to be serviced regularly, mostly contain non-environmentally friendly refrigerants, reduce the availability of the main process. It is particularly negative that the amount of heat to be dissipated from the chiller, which is much larger than the previous one, since it is made up of the cooling capacity and the drive energy to be used, must also be dissipated via the conventional cooling circuit, which is subject to an expansion for this purpose.

The invention specified in claim 1 is based on the problem of cooling machines with internal heat development, for example electrical machines, with as little effort as possible, preferably independently of the outside air temperature.

This goal is achieved by a possibly multi-stage cooling of the cooling medium circulated in the machine to be cooled, first, if necessary according to the heat balance, with a conventional cooling circuit to an economic level, and then with a cooling source that may be present anyway, and / or if necessary after the heat balance, additionally with an artificial cooling system.

The advantages that can be achieved with the invention are, in particular, that the energy and equipment costs are kept as low as possible, an artificial cooling system, if necessary, is as small as possible, and if necessary the normal operation of the main process can be maintained with the conventional cooling circuit , and the amount of heat dissipated from the machine to be cooled and any existing artificial refrigeration system is returned to the overall process, so that there is no reduction in the efficiency of the overall system due to the more intensive cooling, but rather an increase. An advantageous embodiment of the invention is specified in claim 2. The development according to claim 2 makes it possible to use the fuel stream, for example, taken from a pipeline with an almost constant low soil temperature, as the most effective cooling source.

The embodiment according to claim 3 makes it possible to use the fresh water, which is already present in a process, which is taken from a line, for example, at floor temperature and is used as make-up water for a cooling or steaming process, or as injection water in a gas turbine process or otherwise. There is usually a proportionality between the need for cold and the amount of cold.

The advantage of the embodiment according to claim 4 is that the drive energy and / or the working medium for artificial refrigeration systems are taken from the actual main process with as little loss as possible and, if necessary, are also fed back into it. This eliminates the need for additional equipment, prime movers and new working media, and simplifies operation and maintenance.

The embodiment according to claim 5 leads to a reduction in the required cooling capacity and to an increase in the efficiency of the overall process.

The development according to claim 6 makes it possible to control the temperature level in the machine to be cooled in proportion to the internal pressure of the gaseous cooling medium, that is, to be able to work with suitable temperature levels for cold sources.

The configuration according to claim 7 ensures that media involved in the heat exchange, for example high-pressure fuel gas and a cooling medium, do not mix with one another in the event of a leak in the heat exchanger, so that it is also prevented without an intermediate circuit that dangerous situations arise in the machine to be cooled , An embodiment of the invention is shown in the drawing and will be described in more detail below. 1 shows the closed cooling system of an electrical machine 1. This consists of fans 2 and a combined recooler 3, 4 for the circulated heated cooling air 5. The recooler consists of two parts, a precooler 3 and an aftercooler 4. The precooler 3 is connected to a conventional cooling circuit, essentially consisting of a circulation pump 6 and an intercooler 7. The aftercooler 4 is connected to an additional cooling circuit, consisting of a circulation pump 8 and a gas preheater 9, the latter being of a safety design.

The electrical machine 1 is cooled as follows. At an outside temperature of 33 ° C, the cooling air 5 is circulated by fans 2 through the machine 1, absorbing the heat released inside and heating up from about 30 to 65 ° C. Then the cooling air 5 in the combined recooler 3, 4 is cooled again in two stages. In the pre-cooler 3 there is a recooling to approx. 40 to 38 ° C with a conventional cooling circuit, through which a cooling medium with a temperature of 35 ° C is conveyed by means of a circulation pump 6 and its heat in an intermediate cooler 7 to an open one, not shown here Emits cooling circuit. The cooling air 5 is then cooled to 30 ° C. in the aftercooler 4. For this purpose, an intermediate cooling circuit with a cooling medium at 10 ° C., which uses the fuel gas of the drive machine of the electric generator 1 at a temperature of 2 ° C. in a gas preheater 9 as a cold source. So that the heat exchanger 9 does not leak, the high-pressure fuel gas does not penetrate into the cooling circuit, leakage gases are carried over into the electric generator 1 and ultimately the intermediate cooling circuit, which is designed for a lower pressure, ruptures, the gas preheater 9 becomes a double pipe - Safety heat exchanger implemented.

The cooling air is thus cooled 3 K below the outside air temperature without an artificial cold source. Preheating the fuel gas from 2 to 27 ° C using waste heat from the process leads to fuel savings and an equivalent increase in efficiency of the gas turbine. The preheating of the fuel gas with waste heat from the process replaces the heat usually used for this purpose from a separate boiler heated with fuel gas. The drive energy required for the second circulation pump 8 is incomparably smaller than that for a compression refrigeration system with the same cooling capacity. Cooling the cooling air 5 below 30 ° C would be possible if the fuel gas had a temperature lower than 2 ° C. This can be achieved using the Joule-Thomson effect if the fuel gas is throttled isenthalpically in front of the gas preheater 9. An even higher cooling is achieved with a polytropic expansion of the natural gas in a turbine. The mechanical energy released in the process can be used to drive a generator 1. If the available pressure drop is not sufficient, the natural gas can be artificially expanded under the combustion pressure of the gas turbine and then compressed again to the combustion pressure with the drive energy of the expansion turbine and possibly additional drive energy in a compressor located on a shaft. If the freezing point is undershot, an antifreeze must serve as the cooling medium in the after-cooling circuit. If the cooling is too deep, the expansion can take place in several stages with intermediate heating of the fuel gas. With this method, the heat balance can possibly be fully absorbed, ie all the heat released in the electrical machine 1 can be supplied to the fuel gas. The corresponding increase in efficiency would be particularly high, a pre-cooling system could be omitted.

For example in power plants fresh water is sometimes consumed in considerable quantities. The blowdown and evaporation water is replaced in steam and cooling processes. Spray water can be used in gas turbine processes. This is taken from a pipe laid in the ground or from other clean sources and has almost floor temperature, which only fluctuates by approx. This provides a better cooling option than with cooling water cooled in the ambient air, which has not been used before. The waste heat transferred to the fresh water benefits the main process and increases its efficiency.

Instead of or in addition to the gas preheater 9, an artificial cooling system could also cool the post-cooling circuit. Usual compression, absorption or adsorption refrigeration systems can be supplied with drive energy from the process. For example, mechanical energy could be used directly as a compressor drive without the detour via electrical energy. The thermal energy for an absorption or adsorption process can also be taken directly from the main process. Like the latter, a steam jet cooling process would be almost wear-free, the motive steam of which, for example, can be removed from the waste heat boiler of a gas turbine process and the condensate can be fed back to the main process.

The cooling air 5 itself can also be used as the cooling medium, which can dissipate the heat via process stages such as compression, throttling / expansion, similarly as described for the fuel gas.

It is particularly useful to return the heat released from the cold generating systems to the main process. A cooling process allows this to be done at the required temperature level. In such an application, a refrigerator works as a <heat pump. Possible heat sinks in a power plant are, for example, the fuel gas or the condensate fed back into the boiler.

For the sake of completeness, it should be pointed out that the proposed method can be used for any machine or system which releases heat inside.

In addition to gases, liquids as well as the gaseous or liquid fuel itself can of course also serve as the cooling medium and refrigerant. The internal cooling system can also be designed to be open, but this would have the known disadvantages.

Furthermore, a heat exchanger such as the gas preheater 9 could also be included in the internal cooling circuit of the machine 1 to be cooled, so that a temperature difference due to / and an intermediate cooling circuit would be eliminated. A safety heat exchanger 9 would guarantee that the fuel would not enter the machine 1 even if the heat exchanger 9 leaked. Ultimately, the cooling would also be possible by means of cooling channels built into the parts of the machine 1 to be cooled, without additional cooling medium 5, by means of the cooling or cooling media of conventional cooling circuits, cold sources which are present anyway, and, if the heat balance is required, circulating additional artificial cooling systems.

Claims

Claims. 1. A method for cooling internal heat-releasing machines (1), consisting of a closed cooling circuit with an internal cooling medium (5), and an external recooling circuit, characterized in that the cooling, if necessary according to the heat balance, is economically justifiable with a conventional cooling circuit, and in a second or, if necessary, further cooling stages with existing cold sources, and if necessary according to the heat balance, additionally with artificial cooling systems, the order of the individual cooling stages depending on the respective temperature level of the existing and artificial cold sources , 2. The method according to claim 1, characterized in that as the already existing cold source, for example in a gas turbine power plant, the fuel is used at ground temperature or with artificially lowered temperature by relaxation or throttling. 3. The method according to claim 1 or 2, characterized in that as an already existing cold source, for example in a gas turbine, steam turbine or combined cycle power plant, the fresh water supplied to the process is used at soil temperature. 4. The method according to any one of claims i to 3, characterized in that compression refrigeration systems, absorption or adsorption refrigeration systems or steam jet systems are used as artificial refrigeration systems, the drive energy and / or working medium are removed from the actual process with as little loss as possible and, if appropriate, also supplied to it again becomes. 5. The method according to any one of claims 1 to 4, characterized in that the amount of heat to be dissipated from artificial refrigeration systems is fed back to the actual process, for example the condensate in a steam turbine power plant or the fuel in a gas turbine power plant at a required temperature level. 6. Locking according to one of claims 1 to 5, characterized in that a gaseous cooling medium (5) located in the machine to be cooled is kept under a pressure which is favorable for the cooling process. 7. The method according to any one of claims 1 to 6, characterized in that the heat between safety or other reasons immiscible media is transmitted with safety heat exchangers (9).