In the fields of industrial refrigeration, central air conditioning and waste heat utilization, LiBr absorption chiller are widely used due to their advantages of environmental protection, energy saving and stable operation. Careful operation and maintenance personnel or industry practitioners will find that many LiBr absorption chiller are equipped with two generators — an upper generator and a lower generator, among which the upper generator is usually a high-pressure generator and the lower generator is a low-pressure generator. This dual-generator design is not redundant, but a core feature of double-effect LiBr absorption chiller. Its core purpose is to realize double-effect cycle, greatly improve energy utilization efficiency, optimize unit operation performance, adapt to different working conditions, and it is also one of the most essential differences between double-effect LiBr absorption chiller and single-effect units.

To understand the role of dual generators, it is first necessary to clarify their working principle — the two generators do not operate independently, but work together and utilize heat energy in a stepped manner to form an efficient double-effect cycle system. Simply put, it allows the energy of the driving heat source to be fully utilized twice, achieving "one heat source, two effects", thus breaking through the energy efficiency bottleneck of single-effect units. Specifically, the upper generator (high-pressure generator), as the "first station" of the entire cycle, first receives high-temperature heat sources, such as high-temperature heat generated by industrial steam and gas combustion, and uses this high-temperature energy to heat the dilute lithium bromide solution in the unit. Under the action of high temperature, the dilute lithium bromide solution will evaporate rapidly to generate high-temperature refrigerant vapor, and at the same time, the dilute solution is concentrated into a medium-concentration lithium bromide solution, completing the first energy conversion.

Subsequently, the high-temperature refrigerant vapor generated by the upper generator will not be directly discharged, but will be transported to the lower generator (low-pressure generator) to continue to play a role as the "secondary heat source" of the lower generator. At this time, the medium-concentration lithium bromide solution flowing into the lower generator from the high-temperature heat exchanger will be heated again by this secondary heat source to further evaporate and generate low-temperature refrigerant vapor, while the medium-concentration solution is further concentrated into a concentrated solution, completing the second energy conversion. Finally, the concentrated solution will be transported to the absorber, combined with the refrigerant vapor to become a dilute solution again, and enter the next cycle, forming a complete double-effect cycle process.

The biggest advantage of this stepped heat energy utilization design is that it greatly improves the coefficient of performance (COP) of the unit, with remarkable energy-saving effect. Compared with single-effect LiBr absorption chiller that can only utilize the energy of the heat source once, the double-effect cycle of dual generators allows the energy of the heat source to be utilized twice, and the energy efficiency ratio can be increased by more than 30%. It is especially suitable for industrial production, large-scale central air conditioning and other scenarios with high energy efficiency requirements, which can not only reduce energy consumption, but also reduce the operation cost of enterprises.

In addition to improving energy efficiency, the dual-generator design can also effectively expand the operation range of the unit and adapt to different load and heat source conditions. LiBr absorption chiller are often used to recover and utilize low-grade energy such as industrial waste heat. The temperature of such energy fluctuates greatly. When facing high-temperature heat sources, single-generator units are prone to crystallization of lithium bromide solution, which affects the stable operation of the unit; through stepped heat exchange, dual generators can fully recover and utilize heat energy of different temperature levels, with high-temperature heat sources used for the upper generator and secondary waste heat used for the lower generator. This not only avoids the hidden danger of solution crystallization, but also improves the recovery and utilization rate of low-grade energy, achieving dual consideration of operation stability and energy saving.

In summary, the upper and lower dual-generator design of LiBr absorption chiller is an intelligent innovation based on the principle of stepped heat energy utilization. It not only achieves a qualitative improvement in the energy utilization efficiency of the unit, but also expands the operation conditions, improves the operation stability, and at the same time takes into account equipment utilization and cost control, becoming the core configuration of high-end LiBr absorption chiller. Understanding the working principle and advantages of dual generators can not only help operation and maintenance personnel better operate and maintain equipment, but also make us more clearly realize the core value of LiBr absorption chiller in energy conservation and consumption reduction, providing strong support for industrial green development.