Temperature difference between inlet and outlet water in the condensing steam turbine cycle
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For a condensing steam turbine designed with a steam consumption of 10 tons per hour, what is an appropriate temperature difference between the inlet and outlet of its circulating cooling water? We are currently facing a situation where the inlet temperature of the cooling water for the turbine condenser is 16 degrees, while the outlet temperature is 43 degrees; there is a significant difference between these two values. Normally, the temperature difference between the inlet and outlet of the cooling water should be within 10 degrees, which would be considered acceptable. This includes the cooling water for reciprocating compressor cylinders; half of the coolers are of this type. But this time the temperature difference between the inlet and outlet of the condenser is so high – could it be due to the pipe structure, slow flow rates, or the inlet and outlet pipes for the circulating water being installed in the wrong order? There are ninety more. Another issue is that our exhaust temperature, which should normally be 50 degrees, is now at 65 degrees; moreover, the vacuum level isn’t ideal either.
Turbine condensers generally use intermediate water, and all of this intermediate water must be returned to the circulating water system; therefore, there is no need to control its usage. In other words, the cooling water for turbine condensers is usually left at full flow, which increases the flow rate of the cooling water and reduces its residence time, thereby effectively slowing down the formation of scale. Once scaling occurs, the vacuum level drops and the exhaust temperature rises, which further exacerbates scaling on the cooling water side, creating a vicious cycle; therefore, it is better to keep the temperature difference low – we usually aim for around 6 degrees, or even lower. (Apart from the need to control the medium temperature)
I also think that for a regular cooler, it’s sufficient to keep the temperature difference between the inlet and outlet of the circulating water below 10 degrees. Our condenser inlet temperature is 16 degrees, and the outlet temperature reaches 43 degrees. I decided that the flow rate is too low. Originally, the exhaust temperature was 50 degrees and the vacuum level was 0.07; now the exhaust temperature is 65 degrees and the vacuum level is below 0.06. The sound coming from the entire machine seems quite muffled, giving the impression that it’s not working properly.
Reply to 2# yanran88: I think what you say is more credible than what our technicians say. I mentioned this issue to him, and he said it’s completely normal; I no longer know what’s normal – something is clearly wrong
Of course, it’s better to make it smaller, so that the turbine operates more efficiently (with appropriate vacuum levels and exhaust temperatures as well)
We generally keep it within 10 degrees; if it exceeds 10 degrees, we clean the circulating water filter, and that’s it! The exhaust temperature is generally between 44-50 degrees!
As a supplement, the vacuum level is generally between -0.06 and -0.08
Your unit’s exhaust temperature is 65 degrees; the corresponding exhaust pressure, or vacuum level, should be -0.072. This requires a much higher steam inlet flow rate than before, and it results in a vacuum level that is far from the optimal value for the condenser, so operation under such conditions is not feasible over the long term. The temperature difference in the circulating water depends on the heat exchange area of the condenser; if the flow rate is 10 T, a condenser with an area of 250 square units is generally sufficient. It’s fine as long as the end difference is no more than 15 degrees.
Reply to 1# play609: Your unit is in a dangerous condition; there is a possibility that the exhaust temperature will rise and the vacuum level will drop. It’s necessary to check the heat exchanger, as this could lead to a shutdown of the unit……
Is it a new machine? If it has been like this all along, there’s no doubt that the water circulation volume is insufficient. What is the exhaust pressure? The exhaust temperature is a bit high.
Check the condition of your exhaust pump and condenser; it’s very likely that the condenser is blocked