Thermomechanical converters - Steam engine cycles and combined. Cogeneration

Steam-driven power plants (SMP), which originate from steam thermodynamic cycles, correspond to the most powerful engines. These are machines that use external heat supplied either by combustion or by a nuclear reaction. They are found in large conventional or nuclear power plants, where their output exceeds one gigawatt. They are also found in more modest sizes on industrial sites, operating in a wide range of industrial processes at powers ranging from a hundred kilowatts to several hundred megawatts.

The basic cycles, known as Rankine cycles, are close to Carnot cycles, which a priori is a guarantee of efficiency, confirmed by experience. However, for technical reasons, some modifications have been made, leading to a deterioration in efficiency, offset by certain improvements.

Since, as with all thermal machines, there is a great deal of waste heat from these steam-powered installations, it is vital to recover this heat. It can be used as a thermal input for many industrial processes, or for residential or tertiary heating via heat networks. There are two types of VMI energy production: mechanical (or electrical) and thermal. This is known as total energy production or cogeneration. Typical installation cases are presented in this document, together with an energy analysis followed by a thermo-economic analysis of the benefits of such production.

In the article [BE 8 051] , the loss of exhaust energy from combustion turbines (TAC) was highlighted. Given the relatively low thermal level required for conventional VMI operation, the external heat input, usually produced by combustion or nuclear reaction, can be replaced by the enthalpy input of TAC exhaust gases. In terms of the cycle, the coupling of these two machines results in the combination of a Joule cycle with a Hirn cycle. This gives rise to so-called combined-cycle plants, which are currently the most efficient of all thermal machines.