Vapor Compression Report

Vapor Compression (VC) (Figure 7): a working fluid is evaporated at the condenser (by condensing another fluid, such as the top product from a distillation or stripping column). The working fluid is then compressed to a higher temperature (saturation) condensed in the reboiler (often determined by the specific conditions and materials within a process) and cooled down by expansion over a throttle valve to a (saturation) temperature below the condenser temperature. One of the most important design variables when using a vapor compression heat pump is the choice of an adequate working fluid. An example that can be seen in industry the ethylene-ethane separation using propylene as working fluid (Bruinsma & Spoelstra, 2010)

Thermo-acoustic heat

This energy serves to evaporate the working fluid out of the absorption medium at a high pressure. The absorption medium’s pressure is then reduced via an expansion device as it flows to the absorber. Within the absorber the working fluid is absorbed (P0/T1) back into the medium. This is an exothermic process, meaning usable heat is released at an intermediate temperature. Lastly, the pressure of the mix is increased with a pump and flow back to the generator (where thermal energy is provided in the first place).

Refrigeration cycle (Figure 10): when thermal energy is provided at the generator, the refrigerant is evaporated out of the absorption medium. The gas then flows to the condenser, where it releases usable heat as it changes from the gaseous phase to the liquid one. The liquid refrigerant’s pressure is then lowered inside an expansion device as it moves to the evaporator. At this point (P0/T0), heat is added to the refrigerant and it evaporates back to the gas phase. This implies that waste heat can be utilized as a viable energy sources, but it is also possible to use the evaporation stage for cooling the surrounding environment or other relevant streams. The

Table 2 Advantages and disadvantages of different types of heat pumps

Type of Heat Pump Advantages Disadvantages

Vapor Recompression Proven technology with very good performance

Simpler process (when compared to traditional compression)

Recycle of produced vapour within the system (no need for external working fluid)

Low operating cost

Ease of design and operation Potential for high investment cost (although this is largely dependent on design)

Potentially long payback times (unacceptable for industry deployment)

Use of high grade energy (electricity / mechanical work)

Possibility of leakage is a concern

Vapour Compression Proven at industrial scale (mature technology)

No major modifications to processes with implementation

Useful with corrosive and fouling components

Option to drive with mechanical energy or electrical energy

Acceptable efficiencies (up to 60% of Carnot’s limit) Design dependent on the ability of the heat exchange fluid to meet stringent operational, environmental and safety