Method and equipment for cooling generators

Abstract

According to the method, either CO2-free air or pure nitrogen N2 is pumped into the cooling circuit selectively depending on system parameters. To this end, the method ensures that the air injection rate is high enough that, under normal conditions, the hydrogen concentration in the tank and in the riser remains below 2% H2. On air injection, the oxygen O2 (>2 ppm) in the cooling water reacts with the copper in the cooling ducts and a layer of copper oxide forms on the inner walls of said ducts. No reaction is triggered by the injection of nitrogen N2. The CO2 content in the injection air and, at the same time, also the H2 content in the exhaust air are continuously measured and monitored, and an alarm is triggered if adjustable limit values are exceeded. The equipment for performing the method comprises an electronic control unit (65) with an input field and display as a control box, and a pump and a pipe circuit for drawing air in from the riser. The control unit (65) can evaluate all the measured data from the sensors and analysers connected to the pipe and can at least check the CO2 content in the supply air and the H2 content in the riser (13) and display the hydrogen leakage.

Claims

1. Installation for cooling cooling water-conducting copper pipes present in large electric generators cooled with hydrogen gas, by means of which installation a minimum quantity of CO.sub.2-free air can be pumped into the cooling circuit in a targeted manner depending on the oxygen content of the cooling water in the case of a high oxygen content or pure nitrogen N.sub.2 in the case of a low oxygen content, and whereby the critical air quantity ratio for the hydrogen H.sub.2 contained in the cooling circuit can be kept outside the range of 4-75% H.sub.2 in the air contained in the cooling water and thus outside the dangerous quantity ratio, with a connection to a stator cooling water system, wherein the system comprises a stator cooling water tank (2) with outgoing pipe (3) and riser tube (13), and wherein the outgoing pipe (3) leads the cooling water through pumps (4), heat exchangers (6), a filter (7) and thereafter optionally through an ion exchanger (9) back into the stator cooling water tank (2) or into the cooling channels of a stator winding in a generator (1), and wherein the installation includes an air injection system (60) with a control system with measuring instruments for the continuous measurement of CO.sub.2 in the incoming supply air and H.sub.2 in the outgoing exhaust air, and a control unit (65) with operating elements, wherein limit values can be entered for the CO.sub.2 concentration and also for the H.sub.2 concentration, above which an alarm can be output or measures can be initiated automatically, wherein the air injection system (60) is equipped with a plant-side valve (V11) via which oil- and dust-free air can be passed through the pipe (66) and then through a pressure sensor (PS1) and a flow meter (FS1), then through a CO.sub.2 and H.sub.2O separation column (61) then via a second pressure sensor (PS2) into a CO.sub.2 analyzer (62) and via a plant-side valve (V12) via a pipe (64) into the stator cooling water tank (2), and wherein from the riser tube (13) gas can be drawn off via a plant-side valve (V13) by means of a pump (PM) with a pump impeller (63), which can be fed via an H2 analyzer and a valve (14) into the pipe (66) and via the valve (V12) back via the pipe (64) into the stator cooling tank (2), and in that the control unit (65) is an electronic control unit (65) with an input field and display, which belongs to the plant as a control box and by means of which the measurement data of all connected sensors and analyzers of the system can be evaluated, at least the CO.sub.2 content of the injected air and the H.sub.2 content in the riser tube (13) can be measured, and by means of which an acoustic and optical alarm can be emitted when an adjustable limit value is exceeded.

2. Installation according to claim 1, characterized in that by means of the electronic control unit (65) an injection rate of air into the stator-cooling water system can be kept above 0.15 cfm, that the pressure sensors (PS1) and (PS2) have a measuring range of 0-100 psi, for measuring the pressure in the sucked-in air, and by means of the flow meter (FS) an air flow of 0.1-10 I/min can be measured.

3. Installation according to claim 1, characterized in that by means of the electronic control unit (65) and the CO.sub.2 analyzer (62) the CO.sub.2 content in the injected air can be measured and displayed in a measuring range of a CO.sub.2 concentration of 1-1000 ppm, and at a freely selectable value an acoustic and optical alarm can be emitted.

4. Installation according to claim 1, characterized in that the installation can be used on stator cooling water systems with low oxygen content, without CO.sub.2 removal, in that pure nitrogen N.sub.2 can be blown into the stator cooling water system instead of air, and the hydrogen leakage can be measured and displayed.

5. Installation according to claim 1, characterized in that the electronic control unit (65) includes an app for sending acoustic alarms.

6. Installation according to claim 1, characterized in that by means of the electronic control unit (65) all data measured by the connected measuring devices can be read out via cable or wirelessly to one or more CPUs.

Description

(1) Such an installation is shown in the figures using a schematic representation. Their components and their function as well as the procedure carried out with them are described and explained in detail.

(2) It shows:

(3) FIG. 1: A schematic of a conventional generator cooling system with its components, in order to be able to show more clearly later the difference of the system according to the invention to it and the process operated with it;

(4) FIG. 2: The scheme of a generator with copper rods with their the basic structure of the cooling circuit and the storage tank;

(5) FIG. 3: The scheme of a generator with copper rods with their cooling circuit and the storage tank, the vent riser and the connected system according to the invention for carrying out the method;

(6) FIG. 4: A diagram of a CO.sub.2 separator for air.

(7) First of all, the diagram according to FIG. 1 shows conventional cooling of a generator by means of water. In principle, it is about the cooling of the copper rods 16, 17 in FIG. 1. These copper rods are penetrated lengthwise by cooling channels. Lines made of Teflon are connected to these cooling channels 16, 17 as supply lines 22 and as discharge lines 24. There is a water tank 30, which is approx. ⅔ filled with water in the picture, while space 50 for gas or air is present above the water level. Cooling water can be fed to the tank via a valve 60. The cooling water flows down through the line 19 and then flows through a pump 34, a heat exchanger 36 and a filter 38, after which it is fed into the cooling channels 16, 17 via the distributor 20 and the supply lines 22 connected to it. After heat has been absorbed, it flows on the other side of the cooling channels via the discharge lines 24 and a collector 26 via the line 28 back into the tank 30. The generator or its copper rods are flushed with hydrogen gas H.sub.2 from the outside. In the process, a small proportion of hydrogen H.sub.2 inevitably diffuses through the Teflon hoses 22 and 24 into the interior of the cooling water. This hydrogen is then carried along by the cooling water and reaches the tank 30 and escapes from this via the riser. In addition, according to the state of the art, air is pumped into the cooling water. This proportion of air is deliberately kept low so that the volume flow remains below 4.25 litres/min. According to the common doctrine, only such a small proportion of air ensures that the hydrogen content in the cooling water can be reliably monitored.

(8) FIG. 2 schematically shows a structure of a cooling system for a water-cooled generator 1. From a water tank 2, water is pumped via the line 3 through the pumps 4 and their associated electric motors 5 through a heat exchanger 6, in which heat is extracted from the water so that cool water then flows through a filter 7. After the filter 7, a water line 8 branches off into an ion exchanger 9, which water is then returned to the water tank 2 via the return line 10. This secondary flow is usually constant and serves to remove possible impurities, including CO.sub.2, copper oxides, etc. Because the generator is flushed with hydrogen gas inside its housing, and a small proportion of hydrogen inevitably penetrates the cooling water through the Teflon hoses, this is fed back into the tank 2 together with the cooling water, which absorbed heat inside the generator. From there, the hydrogen escapes from the tank 2 via a long riser 13 into the atmosphere.

(9) FIG. 3 shows the essential components of the installation according to the invention for carrying out the method, interconnected with a cooling system as just presented. A riser 13 leads upwards from the cooling water tank 2. Through this, hydrogen separated from the cooling water is released into the atmosphere. According to the new concept, an injection module is used which is encompassed by a dashed line in FIG. 3 and denoted overall by 60. The core of this concept is that CO.sub.2-free air is supplied to the cooling circuit air, and this to a much greater extent than previously practiced, namely with an injection rate of more than 70 cm.sup.3/s. Up to now, this injection rate was chosen empirically and kept rather low. Compressed air DL, provided by the power plant, is pumped into the plant via a valve V1, which is present on the power plant side, via a further V11 belonging to the plant. With a pressure sensor PS1 for a range 0-100 psi, with a typical operating regime of 70 psi inlet and 50 psi outlet, the pressure of the sucked air is continuously measured, and the air flow rate is measured with a flow meter FS1 of 0-10 l/min.

(10) The water and CO.sub.2 content is separated in an aggregate 61. Another pressure sensor PS2 follows. Then the air flows through a CO.sub.2 analyzing device. This one is able to display the CO.sub.2 concentration from 0-1000 ppm. This CO.sub.2 analyzing device 62 checks the cleaning effect of the CO.sub.2 remover in order to guarantee CO.sub.2-free air. The cooling air relieved of CO.sub.2 then goes via the system-side valve V12 and then via a generator-side valve V2 via the line 64 to the cooling water tank 2. From this the cooling water enriched with CO.sub.2-free air is finally pumped into the cooling channels in the copper rods of the generator 1. The injected air is not only used to enrich the cooling water with oxygen, but also some of the hydrogen H.sub.2 is removed from the tank 2. This hydrogen-air mixture is drained off via the riser tube 13. Gas is withdrawn from the riser tube 13 and conveyed through the generator-side valve V3 and the system-side valve V13 via the pump wheel 63 and via a flow sensor FS2 to an H.sub.2 analyzing device 67. The flow rate is kept lower here than in the air injection. The system can also be used for systems with a low oxygen content, in a simplified version even without CO.sub.2 removal, by blowing in pure nitrogen N.sub.2 instead of air.

(11) As can also be seen from FIG. 3, electrical lines lead from all system components, namely from the pressure sensor PS1, from the flow meter FS1, from the unit 61 for the H.sub.2O/CO.sub.2 check, from the On/Off switch E, from the second pressure sensor PS2, from the CO.sub.2-analyzing device 62, from the analyzing device 67, from the second flow meter FS2, from the pump PM for the flow of the cooling water and from the gas flow meter FS3 in the riser tube 13 to a central electronic control unit 65, which processes the data from all these components and transmits it to one associated display, whereby on this electronic control unit 65, desired parameters can be put in via an associated control panel for the control unit 65 as required, for example system-typical limit values. The illustrated valves V11 to V14 can optionally be electronically controllable solenoid valves in order to couple or uncouple the entire injection module 60 to or from a cooling system via the central electronic control unit 65, if necessary.

(12) Newly, according to this cooling concept, air is pumped into the cooling water to a much greater extent, in order to achieve a volume flow of at least more than 5 litres/min. The volume flow of the air which has been cleaned of CO.sub.2 and which is blown in is in fact sufficiently high in the context of a still acceptably large hydrogen leak to safely avoid an explosive mixture with hydrogen. If the leak is larger, the generator 1 has to be switched off for repairs anyway. This large volume flow of air differs from the common solutions that work with a volume flow of <4.25 litres/min. The sufficiently accurate detection of the H.sub.2 content in the air for continuous monitoring is possible with new H.sub.2 measuring devices which can even detect the smallest concentrations of H.sub.2 in the air. This makes it possible to ensure that no explosive gas mixture is present in the cooling water tank 2 and the riser tube 13.

(13) During several chemical cleanings on systems with a high oxygen content, one of the problems was the penetration of CO.sub.2 into the stator cooling water system SCWS by the Stator-Leakage-Monitoring-System SLMS. The SLMS is equipped with a CO.sub.2 remover, but in practice this often suffers from non-functioning or malfunction and provides incorrect feedback. Therefore, a really functioning CO.sub.2-free air injection, preferably in combination with a really functioning hydrogen leakage monitoring system, is impressive, because the monitoring systems currently installed also often do not work satisfactorily.

(14) As already mentioned, all data from the air inlet system and the H.sub.2 analyzer 67 go to an electrical control unit 65 in a switch box. This creates a control box. In this at least the hydrogen leak rate is calculated and the most important parameters and alarms are displayed. The data storage can be set up on a permanent memory or USB stick as well as via a possible online data transfer to a server. The hydrogen leak rate can be calculated from the amount of air that is injected into the system and the concentration of hydrogen in the air that leaves the system using the following formula.

(15) $H2\left(\mathrm{leakage}\right)=\frac{(-\mathrm{Air}\left(\mathrm{blown}\mathrm{in}\right)*H2\left(\mathrm{measured}\right)}{(H2\left(\mathrm{measured}\right)-H2\left(\mathrm{purity}\right)}$$\begin{array}{cc}{H}_2\left(\mathrm{leakage}\right)& H_2\mathrm{leakage}\mathrm{rate}\\ \mathrm{Air}\left(\mathrm{blown}\right)& \mathrm{air}\mathrm{injection}\mathrm{rate}\\ (H_2\left(\mathrm{measured}\right)& \mathrm{measured}\mathrm{concentration}\mathrm{of}{H}_2\\ H_2\left(\mathrm{purity}\right)& H_2\text{-}\mathrm{purity}\mathrm{of}\mathrm{the}\mathrm{cooling}\mathrm{gas}\left(\mathrm{typically}95\text{-}99\%\right)\end{array}$

(16) What is special about this cooling concept is that it works with a deliberately higher air injection rate of >0.15 cfm or 70 cm.sup.3/s, and the risk of explosive gases in the ventilation line and the expansion tank is prevented, which is an essential safety feature. According to this new formula, the hydrogen purity of the hydrogen cooling gas is also included as a measured variable for calculating the amount of air injected.

(17) The installation can have a modular structure to provide either just the air inlet system or just the hydrogen leakage monitoring. Depending on the version, the hydrogen leakage monitoring system must have an air inlet system. It always includes the switch box with an electronic control unit 65 as a control box, with all the necessary connections for future expansions if only one of the two modular systems is installed. Depending on the design of the cooling water system, there are up to 20 cubic feet or 0.5663 m.sup.3 H.sub.2 leakages without causing an explosive mixture in the generator. These are medium-sized leaks that should or must obviously be repaired. For example, guide values and the indications to be implied from them are the following: Dense system: 0.2 cubic feet=0.005663 m.sup.3/day: 0.08% H.sub.2 in air Normal system: 1 cubic feet=0.02832 m.sup.3/day: 0.38% H.sub.2 in air 5 cubic feet=0.1416 m.sup.3/day: 1.91% H.sub.2 in air: an acoustic and visual ALARM is given due to the presence of potentially explosive gas mixtures! From 4% a mixture is explosive and therefore dangerous. With an alarm threshold of 1.91% H.sub.2 in the air, there is a safety margin of 100%. Average leakage: 20 cubic feet=0.5663 m.sup.3/day: 7.63% H.sub.2 in air Severe leakage: >50 cubic feet=1,416 m.sup.3/day: >19.07% H.sub.2 in air

(18) The electronic control unit 65 belonging to the installation includes the following functions, which can be called up via a control panel and shown on the associated display. Display of the air inlet flow Alarm or display of the CO.sub.2 concentration of the air injection Display of the hydrogen concentration in the vent line Calculation and display of the hydrogen leak rate Data storage via USB Potentially expandable for wireless data transmission to a server Triggers an acoustic and visual alarm in the event of: high CO.sub.2 injection into the stator cooling water system SCWS Malfunction of the air injection Hydrogen content reaches >2%
In the future, the installation for this stator cooling water system (SCWS) can be combined with a chemical instrumentation module.

(19) FIG. 4 shows a diagram of a CO.sub.2 separator for air in order to explain its function. The air to be cleaned flows through the inlet 70 into the absorber column T1. The air, i.e. the air polluted with CO.sub.2 and H.sub.2O, then flows from bottom to top through this absorber column T1. Typically, more than 50% of the air purified in this absorber column T1 is used in the regeneration column T2 for its regeneration, while the remaining air is CO.sub.2-free and can be drawn off via the check valve 71 and the connection 75 and is available for use. A solenoid four-way valve 72 is periodically changed from absorber column T1 to regeneration column T2 and vice versa. The regeneration can be assisted by a heater, for heating the regeneration column T2 or directly the regeneration gas by placing the column T2 under a negative pressure, and by releasing regeneration gas to ambient pressure, while the absorption in the column T1 is at an increased pressure level he follows.