What Is The Role of A Dry Cooler in An ORC System?

In the Organic Rankine Cycle (ORC) system, the Dry Cooler is the key heat dissipation equipment, and its core role is to efficiently dissipate the residual heat released by the workmasses in the ORC system to the external environment to ensure the stable operation of the cycle process.

The ORC system realizes energy conversion through the phase change of organic substances (e.g. R245fa, pentane, etc.), and the process is as follows:

Evaporation stage: the low-temperature and low-pressure liquid substance absorbs the waste heat (e.g. industrial waste heat, geothermal heat, etc.), and evaporates into the high-temperature and high-pressure gaseous substance;

Expansion stage: the gaseous substance pushes the turbine (or the expander) to perform the work, and drives the generator to generate electricity;

Condensation stage: after performing the work, the pressure and temperature of substance are reduced, and it becomes low-pressure gas state. Condensation stage: after the work done, the pressure and temperature of the workpiece is reduced to a low-pressure gaseous state, which needs to be released in the condenser to release the remaining heat and condense into a liquid state;

Pressurization stage: the liquid workpiece is pressurized by the pump and re-enters the evaporator to complete the cycle.

Among them, the dry cooler is essentially the “condenser” of the ORC system, which is responsible for completing the heat dissipation task in the “condensation stage” -- cooling the gaseous material into a liquid state through the heat exchange between the air and the material. Through the heat exchange between the air and the work material, the gaseous work material is cooled to liquid state, providing low temperature and low pressure work material for the next cycle.

The efficiency of the dry cooler's heat dissipation directly affects the condensing temperature and pressure:

Insufficient heat dissipation results in a high condensing temperature of the mass, which can lead to a high back pressure in the system and a loss of the expander's efficiency (or even inability to function properly);

Excessive heat dissipation (e.g., low ambient temperatures) may result in an overcooled mass, but the dry cooler can usually be used to control condensing temperatures by adjusting the airflow (e.g., a variable-speed blower) to maintain it within the design range.

ORC systems are often used in remote areas (e.g., geothermal power plants, desert photovoltaic and solar thermal projects) or water-scarce environments. Dry coolers use air as the cooling medium and do not need to consume water resources, which avoids the dependence of traditional water-cooled condensers on a water source, making ORC systems more practical in scenarios of drought, high altitude, and so on.

In ORC system, the condenser can also be water-cooled (e.g. cooling tower), but the advantages of dry cooler are:

No water source required: suitable for water-scarce areas, reducing the dependence on the environment;

Simple maintenance: no clogging and scaling problems of the water pipeline, reducing the cost of chemical treatments (e.g. water softening);

Flexible installation: the number of fin tube bundles and fans can be designed according to the layout of the site, to adapt to the different heat dissipation needs.