Regarding low-pressure saturated steam power generation, the issue of selecting generator sets

This post was last edited by gjn1970 on 2018-2-22 at 14:35. Energy of this level belongs to low-temperature waste heat. When utilizing such waste heat, priority should be given to applications that involve long-term operation at the same temperature level, that is, using this low-temperature heat to replace the secondary energy sources that were previously used, such as for air preheating, desalinated water heating, heating of process unit reboilers, and tank heating. Next, consideration should be given to applications that make use of this heat for part of the year, such as for heating purposes. Finally, advanced utilization methods such as heat pumps, refrigeration, and power generation should be considered. If power generation is the only purpose, the following factors need to be considered when deciding between a turbine and a screw expander: 1. Since the screw surfaces of a screw expander can withstand wear and impact from liquid particles, and there is a gap between these surfaces, the working medium can be superheated steam, saturated steam, a two-phase vapor-liquid mixture, or hot liquid. The working medium for a steam turbine can only be superheated steam or saturated steam. 2. Screw expansion engines have low requirements regarding the quality of the working medium. The relative motion between the screws, as well as between the screws and the casing, limits the growth of dirt. The remaining dirt that cannot be removed acts to reduce the gaps, thereby minimizing leakage losses and improving the efficiency of the unit. 3. The internal efficiency of the screw expansion engine remains almost unchanged when the pressure of the working medium fluctuates significantly. 4. Screw expansion engines require a low temperature of the working medium, generally kept below 250°C. The higher the temperature of the working medium used, the greater the clearance that must be provided during manufacturing to account for the expansion of the screw, which inevitably leads to a reduction in the efficiency of the unit. 5. Screw expansion engines require a low pressure of the working medium, which is generally kept below 1.5 MPa. Excessively high pressure of the working medium will increase the pressure difference between the inlet and outlet, exerting a large radial force on the screw and resulting in unacceptable mechanical deformation. Screw expansion engines present difficulties when using high-temperature and high-pressure working media; for example, when using the drain water from boilers with medium temperature and pressure or higher, it is necessary to reduce its temperature and pressure. 6. The outlet pressure of the screw expansion engine cannot be designed as a high vacuum, resulting in low thermal efficiency of the engine. Since the working medium still contains a large amount of heat when it is discharged, the thermal efficiency of screw expansion engines is at least 10% lower than that of steam turbines. Theoretically, the volume ratio of the working medium at the outlet and inlet of the screw expander should roughly equal the internal volume ratio. The internal volume ratio of screw compressors is generally not greater than 10. In summary, the investment cost for a screw expansion unit is definitely lower than that for a turbine; given the very low operating parameters, it is recommended to use a screw expansion unit.

Gas-condensing turbines are efficient and have a low failure rate; their use is recommended. 20 tons of steam can generate 2 megawatts of electricity, which is quite impressive.