DE2924140C2 - Device for displaying the ingress of cooling water in a boiler feed water circuit - Google Patents

Description

The invention relates to a device for indicating the ingress of cooling water in a boiler feed water circuit.

In thermal power plants, the exhaust steam is usually converted into the liquid state in a heat exchanger and fed back into the boiler as boiler feed water. In many cases, saline river water is used as the coolant in the heat exchanger. Cooling water seeps into the boiler feed water circuit as a result of leaks in the heat exchanger. if increased corrosion occurs in this area or corrosion is induced on critical parts of the system. It is therefore necessary to detect even small amounts of cooling water in the feed water in order to be able to detect leaks in the heat exchanger at an early stage. Thus, the object is to provide a device of the type mentioned, which is sensitive enough to detect the boiler feed water quantity nor a cooling water ingress in the order of 10 ~ ^5, on the other hand, a simple design and is completely maintenance-free for long periods.

This object can be achieved with a device which is characterized in that a first sample stream taken from the boiler feed water circuit upstream of a heat exchanger fed with salt-containing cooling water is fed via a first cation exchanger of the H ⁺ type to a first conductivity measuring cell. Circuit after the heat exchanger, the second sample ^{stream taken via a second cation exchanger of the H +} type is fed to a second conductivity measuring cell and the sample streams are kept at the same temperature, and that the electrical outputs of the conductivity measuring cells are fed to a differential amplifier and the occurrence of a differential signal indicates an ingress of cooling water.

The structure and mode of operation in the device according to the invention are shown schematically on the basis of one in the figure illustrated embodiment explained below.

In line path 1 of a boiler feed water circuit a heat exchanger 2 is arranged, which is usually with salty river water as a coolant, for short

Kuhlwasser 3 called, is fed.

The boiler feed water used is treated high-purity water with a residual salt content of less than 2 μg / l and an addition of ammonia or hydrazine Commonly used as corrosion protection. Its conductivity is around 3 to 4 µS / cm. The electrical conductivity of the cooling water is depending on the salt content in the order of 500 μ5Λ: ιτι or above. Step into that Pipe system of the heat exchanger 2 leaks,

ίο for example due to point corrosion, so can cooling water 3 pass into the feed water circuit.

In order to be able to detect the ingress of even very small amounts of cooling water into the feed water circuit at an early stage, a first sample flow 4 is branched off from the boiler feed water circuit before entering the heat exchanger 2 and a second sample flow 4 'is branched off after exiting the heat exchanger 2. Both sample flows are branched off subjected to mutual temperature equalization in a further heat exchanger 5 and then each enter a cation exchanger with an ion exchange resin of the H ⁺ type. In the cation exchangers 6 and 6 ', the ammonia and the hydrazine are removed with the formation of water, while the salts possibly contained in the feed water are converted into their even better conductive acids. The sample streams 4 and 4 'emerging from the cation exchangers are passed through conductivity measuring cells 7 and T , which are also kept at the same temperature or are designed as double measuring cells. The signals picked up at the electrodes 8 and 8 'of the conductivity measuring cells 7 and T and corresponding to the conductivity of the respective sample stream are fed to a differential amplifier 9. If a difference signal occurs at the output of the amplifier 9, this is a sign that the second sample stream 4 'has taken up cooling water 3 containing salt in the heat exchanger 2.

With good temperature equalization along the entire path of the sample streams and with the use of modern amplification technology, the detection limit can be reduced to below 1 nS / cm, which corresponds to a sodium ion content of less than 0.1 μg Na + / I resulting from the ingress of cooling water. These values are sufficient to detect 20 l / h of cooling water in 4000 to 5000 m ^{3 of} boiler feed water. By using the difference method and good temperature compensation, other influences that change the conductivity of the sample streams are largely eliminated.

1 sheet of drawings

Claims (1)

Claim: Device for indicating a cooling water ingress in a boiler feed water circuit, characterized in that a first sample stream (4) taken from the boiler feed water circuit upstream of a heat exchanger (2) fed with salty cooling water (3) via a first cation exchanger (6) from the H + - Type is fed to a first conductivity measuring cell (7),
that a second sample stream (4 ') taken from the boiler feed water circuit after the heat exchanger (2) ^{is fed via a second cation exchanger (6') of the H +} type to a second conductivity measuring cell (7 ') and the sample stream (4, 4') are held au ^r the same temperature,
and that the electrical outputs of the conductivity measuring cell (7, T) are fed to a differential amplifier and that the occurrence of a differential signal indicates an ingress of cooling water.