ORC Power System
Solutions
The solutions for the ORC Power System on-site are mainly determined by the type of heat sink(water-cooled、air-cooled、evaporation-cooled), the type of heat source(hot water/steam,hot gas/flue gas),electricity characteristics(Low or high voltage) and whether the installation site is the explosion-proof area . The following are some layouts of different solutions for the ORC Power System
(1) Water-Cooled ORC
Recommended if water cooling tower or extraction of cold water(well, river) is available. Benefits: (1) Good thermal efficiency, less working fluid required, longer lifespan, lower price；(2) Low cleaning and maintenance fee, long lifespan for water-cooled system
(2) Air-cooled ORC
Recommended only if cooling water isn't available on the installation site. Disadvantages: (1) Fan, which consumes energy, is required as the substitution for the cooling water (2) Lower thermal efficiency due to increased cooling temperature. (3) About double or triple of working fluid required , compared with water-cooled ORC.
(1)(2)(3) combined increased the price of the system.
(3) Evaporation-cooled ORC
The Evaporation-cooled ORC utilizes the evaporation of water on the heat pipe to dissipate heat , thereby decreasing the condensing temperature and increasing the thermal efficiency. Although the cooling water required is around 1/3 to 1/2 that of water-cooled ORC, the amount of refilled water to compensate for the evaporation is slightly greater than that of water-cooled ORC.。Furthermore, the large area of heat pipe necessitated, high price of the evaporation units, and double to triple amount of working fluid required all makes the ORC systems expensive. What's worse, since cooling water evaporates from the heat pipe directly, problems like fouling and corrosion leads to frequent need for maintenance and high expenses, thereby reducing the lifespan of the ORC system.
(4) Hot water/Hot oil/ Low Pressure Steam ORC
Owing to the high power density and high cleanliness, hot water, hot oil, and low pressure steam can be used directly in the evaporator of ORC, therefore significantly cutting down the installation fee on-site.
(5) Hot gas/Flue gas ORC
Because the power density of hot gas and flue gas are low, heat is usually extracted indirectly. (For instance, we can design an economizer in the flue where we want to extract heat. The heat extracted will then be directed into the evaporator of the ORC as a heat source.。These additional devices contributes to the higher price of the system.
(6) Combined ORC(ORC+Steam Turbine)
The combined ORC, which is the combination of the back pressure steam tubine and the ORC, using high pressure steam as the heat source, is recommended if the thermal efficiency of the high pressure steam i still high. In the combined ORC, the high pressure steam first go throgh the steam turbine, and the exahust steam will then be directed to the evaporator of the ORC as the heat source. The steam after the evaporator will turn into water and flow to the pipe system of the manufacturing process, meaning that the steam is reusable. In other words, this comined system first use the waste pressure, and then use the waste heat to generate electricity. To wrap up, the high thermal efficiency, renewable cooling water makes combined ORC a profitable investment.
