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Organic Rankine Cycle (ORC) Process for Power Generation

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Low heat and low emissions are a thing of the future through a technology developed by Turboden, now part of Mitsubishi Heavy Industries group company. The Organic Rankine Cycle (ORC) converts thermal energy into electricity utilizing FCs (Fluorocarbons), silicon fluids, FHCs (hydrofluorocarbons), old and new generation refrigerants in a closed loop system rather than high-pressure steam requiring boilers to produce steam from water. 

Besides the economic advantage, the organic fluids do not deplete atmospheric ozone. The basic principle is an external heat source transfers thermal energy into the refrigerant causing it to vaporize. High-pressure refrigerant vapor flows into the turbine, where it expands and causes it to spin. The turbine turns the generator producing electrical power. Cooling water extracts thermal energy from the low-pressure refrigerant vapor to condense it back into liquid. Then the liquid refrigerant is pumped back into the evaporator to restart the cycle.

The heat source for the evaporator/heat exchanger to evaporate the organic fluid (refrigerant) can be provided by multiple sources, such as renewables (biomass, geothermal energy, solar energy), traditional fuels and waste heat from industrial processes, waste incinerators, engines or gas turbines, etc.

The organic fluid has a lower boiling point and a higher vapor pressure compared to water. As a result, it can use low-temperature heat sources to produce electricity without harmful emissions. The majority of turbines are different types of axial turbines ranging from 2 to 6 stages reaching up to 20 MW of power and in some cases exceeding isentropic efficiency of 90%.

The Inspection procedures of ORC systems are similar to the inspection of steam turbines. There should be permanent vibration monitoring and alarm set as per OEM specifications, as well as overspeed testing on an annual basis.

The organic fluid should be sampled quarterly and spectrographically analyzed and results trended. The undercover inspection should be completed based on performance monitoring and not extend five years for the first inspection. The visual inspection should be focused on examining any leaks from the seals. These turbines have special seals manufactured on recessed hydropad technology. This technology is specifically designed for the double pressurized O-ring pusher seal working with oil barrier fluids. The recess technology optimizes the liquid film thickness formation.

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