Performance And Application Of A Novel Composite Adsorbent For Adsorption Chilling System Driven By Lower Pressure Waste Vapor

Solid adsorption refrigeration get more and more global attention for it can utilize efficiently the low grade thermal energy and does no harm to the environment. For the application of adsorption refrigeration, the chemical adsorption happened in composite adsorbent-ammonia is the best working pair at the freezing situation where the temperature is lower than 0oC. Composite adsorbent -ammonia working pair has the advantage of low evaporating temperature and it can be used to make ice comparison with the physical adsorbents using water as refrigerant. In recent researches, the chemical adsorption icemaker which utilizes the CaCl₂/expanded graphite-NH₃ as working pair has been reported. But there are five problems in the application of metal chloride. Firstly, the thermal conductivity of the calcium chloride and expanded graphite composite adsorbent is very low (thermal conductivity of composite adsorbent is only 0.1-0.2W·m-1K-1), can not quickly release the adsorption/desorption heat out of adsorber, this causes longer cycle time and decreases the cooling power of the adsorption refrigeration system. Secondly, there is serious performance decreasing phenomenon happened in repeated desorption/adsorption process, this decreases the adsorption capacity of adsorbent. Thirdly, in the designing of the adsorption system which use composite adsorbent-ammonia (calcium chloride and expanded graphite) as the working pair. The exhaust gas and cooling water are switched by the four-port valve, although this system is very simple but it would cause the corrosion problem between exhaust gas and steel tube wall. Fourthly, The heat pipe heating and cooling system can sovle the corrosion problem of the heating tube in the adsorber, but the pressure of the working fliud in the heat pipe always change between the positive and negative with the switch of the adsorber heating and cooling processes. This will shorten the living time of the swith valves in the adsorption system. Finally, the application field of the adsorption system is very narrow. for the field there have many waste lower pressure vapor, such as petrochemical plant and electric plant, they also need the chilling system, but there almost not have a adsorption chilling system applied in this field. Furthermore, a new type of composite adsorbent is developed in this paper, which is used in a novel adsorption chilling system diriven by the low pressure vapor. Based on this work, the main contents in this paper include as follows:1. A new kind of compound adsorbent which is composed of CaCl₂/expanded graphite adsorbent is studied in this paper. The expanded graphite will enhance the mass transfer of composite adsorbent by plenty of porous structure inside expanded graphite and solve the adsorption capacity deterioration happened in long term adsorption/desorption process. The consolidated compound adsorbent has a higher thermal conductivity because of consolidated technology is used in compound adsorber. For the powder composte adsorbent thermal conductivity is 0.1～0.2 W·m^-1·K^-1, the consolidated compound adsorbent with 20% expanded graphite thermal conductivity is 0.22～4.2 W·m^-1·K^-1 with different density of the composite adsorbent blocks. The thermal conductivity increased 2～10 times. So it is possible to decrease the cycle time and volume of adsorber using consolidated compound adsorbent. The composite adsorbent block porosity is 0.36～0.8, which is about 2.5 times of the calcium chloride. So the mass transfer performance is increased by the additive of the expanded graphite2. The iso-volume testing system is built in this paper to study the adsorption and desorption performance of the composite adsorbent with different adsorption temperature and desorption temperature. The experiment results show that the homogeneity of the composite adsorbent enfluence the adsorption performance of the composite adsorbent, the more homogeneous the composite adsorbent is, the better the adsorption performance is. The two reaction processes of the composite adsorbent with the ammonia are discriminated in this paper. The experiment shows that the desorption speed of both the two reaction process working at the same time is smaller than the sum of desorption The kinetic adsorption speed models are built in this paper, the adsorption performance at different working condition is studied of the composite adsorbent.3. A novel adsorption system driven by the lower pressure waste vapor is established in this paper, which structure is compact and excellent heat transfer performance. The composite adsorbent- ammonia working pairs is used in this adsorption system. The heating heat pipe is to heat the adsorber and the cooling system is to cool the adsorber. The corrosion problem between exhaust gas and steel tube wall is solved. The heat transfer performance is enhanced obviously because the heat transfer in phase change process happened in heat pipes is quite higher than convection heat transfer in traditional adsorber heat exchanger.The mass recovery tube is not installed between the two adsorbers, but is installed between the two evaporators. This structure can save the cooling power of the adsorption system and realize the completely chilling process.4. The test rig for testing the adsorption chiller machine performance is constructed. The speed of desorption and adsorption process is fastened. The cycle time for heating and cooling process is shortened. When adsorber temperature change from 35oC-120oC, the heating time or cooling time is 25 minutes which is decreased almost 100% compared with compound heat pipes type adsorber using same heat pipe working medium. The averaged cooling power is 11.4kW, SCP is 420W·kg ^-1. The adsorption speed of the adsorber is 3.5×10^-4 kg.kg^-1.s^-1, campared with the that value of 2.7×10^-4 kg.kg^-1.s^-1 of the adsorption system at the same working condition wich increased 30%。The heat transfer coefficients of the adsorber are 745.4 W.m^-2 and 832.6 W.m^-2. oC^-1 in the adsorption process and desorption process. These value increased 265%and 300% than those in the literature. The heat conductivity of the composite adsorbent in the adsorber is 0.72 W.m^-1. oC^-1 in the heating process and 0.56 W.m^-1. oC^-1 in the cooling process.5. The influence of the installion place of the mass reconvery tube on the adsorption performance is importantly studied in this paper. The experimental results show that, when the mass recovery tube is installed between the two evaporators, the cooling power in the evaporator is efficiently saved and the adsorption chilling system can continuely out the cooling power. Combination analysis of the theory and the experimental results, the shortcoming of the adsorption chilling system is found and the improvement method is get. Which are very useful for the next work of the adsorption system...