Thermal energy

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I was recently watching a lovely program about energy production on discovery, when a intriguing question invaded my mind.

Our major type of power plants all operate upon burning a fuel and transferring that thermal energy into a fluid medium such as water that in turn uses some of that thermal energy and converts it into kinetic energy and thus can spin a turbine's blades. But after this cyclical process there is another process happening as well, that is the cooling side. The amount of thermal energy that can be transformed into kinetic energy is dependent on the difference between the temperature of the fluid, so in order to maximize the amount of kinetic energy it is useful to cool the primary fluid. You cool it through a few means, but the most common i have seen is the evaporation method. That is using another fluid to absorb thermal energy after the turbine phase of the primary part. The easiest way to release the absorbed thermal energy is to evaporate the secondary steam up a cooling tower, where some of it falls back down but a lot of it is released into the atmosphere.

So my question is, why don't we use that steam to turn another turbine? It seems to me that there is a lot of wasted energy within the system because of the secondary systems lack of turbine, and its blatant loss of energy to the environment. Why wouldn't you use pressure in maybe 3 or 4 systems to remove the thermal energy from the first? I'm sure there is some sort of thermal energy maximum that is present within the systems, and because of the maximum there is an optimal temperature to keep the fluid.

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You've used the thermal energy to create high pressure, and have expended that in the turbine. What's left over is hot, but at atmosphere. There's nothing left that is extractable from a turbine. Thermodynamics tells us that all engines reject heat; we can't use it all to do work. You could use the leftover hot steam to heat things up, or drive some other kind of thermodynamic engine and extract some more energy that way — adding a secondary use is called co-generation.

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An example of atmosphere-pressure heat-to-motion transformation

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