Working principle and process of ammonia absorption refrigeration

Ammonia absorption refrigeration technology: ㈠ Principle An absorption refrigeration unit consists of components such as a generator, condenser, evaporator, absorber, circulation pump, and throttle valve. The working media include the refrigerant used to produce cold, as well as the absorbent used to absorb and release the refrigerant; these two together form a working medium pair. The concentrated ammonia solution is heated in the generator, and a certain flow rate of refrigerant vapor is separated and sent to the condenser. The refrigerant vapor is cooled in the condenser and condensed into a liquid state ； The liquid refrigerant is throttled to reduce its pressure and then enters the evaporator, where it absorbs heat and evaporates, thereby producing a cooling effect; the refrigerant changes from a liquid state to a gas state before entering the absorber ； Additionally, the dilute solution flowing out of the generator passes through a heat exchanger and a throttling device to reduce its pressure before entering the absorber, where it absorbs the refrigerant vapor coming from the evaporator. The concentrated solution produced as a result of this absorption process is pressurized by a circulation pump; after absorbing heat in a heat exchanger and thus increasing in temperature, it returns to the generator, thus enabling continuous cooling. Ammonia absorption refrigeration uses naturally available substances such as water or ammonia as refrigerants, and it is harmless to the environment and the ozone layer ； Using thermal energy as the driving force, in addition to steam from boilers and heat generated by fuels, low-grade heat sources such as waste heat, excess heat, and solar energy can also be utilized. The same system can achieve both cooling and heating functions. Apart from the pumps and valves, the entire system consists mainly of heat exchangers; it operates quietly with minimal vibration ； At the same time, the refrigerator has a simple structure, is safe and reliable, and easy to install. In the current situation of energy shortages, strained power supply, and increasingly severe environmental problems, absorption refrigeration technology has attracted widespread attention due to its unique advantages. Currently, absorption refrigeration is evolving toward smaller size and higher efficiency. Research and development efforts in this field around the world focus on areas such as combined cycles, waste heat utilization, absorption heat pumps, studies of the mechanisms involved in absorption and generation processes, heat exchange structures and surfaces, surfactants and corrosion inhibitors, optimal design of units and economic analysis, as well as simulation of system characteristics. Absorption refrigeration has become one of the main development directions in refrigeration technology, with very broad prospects. (II) Process: The exhaust heat recovery refrigeration unit uses an ammonia solution as the working medium, and its operating cycle consists of six processes: generation, separation, condensation, throttling, evaporation, and absorption (see the process diagram attached). Refrigerant cycle: The exhaust gas is used to heat the generator; the resulting gas-liquid mixture is separated in a separator, from which a high-concentration refrigerant vapor is obtained. It is condensed into a liquid by the condenser and enters the liquid storage tank. The refrigerant liquid enters the evaporator to evaporate after being throttled and depressurized by a float valve. The evaporated refrigerant gas enters the absorber, where it is absorbed by the dilute solution to form a concentrated solution. This concentrated solution is then pumped through a solution heat exchanger, where it exchanges heat with the dilute solution coming from the generator, before being sent back to the generator for further heating. This process repeats itself, thus forming a refrigeration cycle. Solution circulation: The dilute solution separated by the separator enters the solution heat exchanger where it exchanges heat with the concentrated solution; thereafter, it is automatically regulated by a float valve to enter the absorber, where it absorbs the refrigerant and becomes concentrated solution. This concentrated solution is then pumped by a solution pump to the generator for heating. The resulting gas-liquid mixture enters a separator for separation, from which a dilute solution is obtained, thus forming a cycle of solution circulation.

This post was last edited by Chemical Gas Purification on 2010-8-20 at 14:35. Shandong Taishan Group has done well in its operations; it seems to have started by working on ship exhaust gases. We should promote all good technologies.

Could you provide a schematic diagram of the equipment process flow for systems using ammonia as a refrigerant? How does its layout compare to that of lithium bromide systems? The various components in lithium bromide systems are arranged compactly to form a single unit; I’m curious about what the structure looks like when ammonia is used as the refrigerant ?

Initially, the equipment was quite large and required a lot of space for installation; now there are those who use unit-based designs, which yield good results as they are more compact.

Comparison of the performance between ammonia water absorption refrigerators and vapor compression refrigerators. The coefficient of performance of the absorption refrigeration cycle, as well as the cooling coefficient of the vapor compression refrigeration cycle, are both key technical indicators used to evaluate the economic efficiency of these cycles. However, the two cannot be directly compared, as compression refrigerators consume work while absorption refrigerators consume thermal energy; work has a higher quality than thermal energy, and the cost of generating work is also higher. When comparing these two values, it is necessary to take into account the heat exchange conditions and efficiency in the steam systems of the power plant. Even so, the coefficient of performance of absorption chillers remains lower than that of compressive chillers, due to the presence of more thermally irreversible processes during the operation of absorption chiller systems. 　　Comparing the operating costs of the two systems, it seems that an absorption refrigeration system is more suitable at lower evaporation temperatures, especially when a high-temperature heating medium is available. This is because it is possible to use a single-stage absorption refrigeration system to achieve low temperatures that would require a two-stage compression system. 　　Features of ammonia-water absorption refrigerators Compared with other types of refrigerators, ammonia-water absorption refrigerators have the following features: (1) They use steam or hot water as heat sources, which facilitates the comprehensive utilization of waste heat; they are particularly suitable for use in refrigeration equipment in the chemical, metallurgical, and light industry sectors ； 　　(2) Using ammonia as a refrigerant, low temperatures below 0°C can be achieved ； 　　(3) Apart from the pump, the entire system consists of heat exchange equipment such as towers and tanks; it has a simple structure, making it easy to manufacture ； 　　(4) It has low vibration and noise levels, allowing it to be installed outdoors, which reduces construction costs ； 　　(5) When the load is adjusted within the range of 30–100%, there is no significant change in the economic efficiency of the device ； 　　(6) Simple maintenance, easy to operate, and easy to manage ； 　　(7) Ammonia is inexpensive and readily available ； 　　(8) Causes no damage to the atmospheric ozone layer ； 　　(9) Corrosive to copper and copper alloys (except phosphor bronze) ； 　　(10) High consumption of steel and cooling water ； 　　(11) Lower thermal coefficient ； 　　(12) Since the boiling points of ammonia and water are relatively close, distillation and condensation equipment must be added to the system in order to increase the ammonia concentration.