Here, we propose a double-effect adsorption chiller with a zeolite adsorbent (FAM-Z01) for utilization of waste heat. The FAM-Z01 adsorbent has the potential to recover waste heat in low temperatures ranging from 353 to 333 K and shows good potential in the adsorption chiller in terms of the high cooling output. A double-effect adsorption chiller could provide a higher Coefficient Of Performance (COP) than that of a single-effect chiller. In this paper, we developed a measuring method for the amount of adsorption in the first and second adsorber in a double-effect adsorption chiller and measured the adsorption and desorption rate based on the volumetric method. We calculated the COP of the adsorption chiller with the quantity of adsorbent obtained in the experiment. In the experiments, the quantity of adsorbent in the first adsorber was 0.14 g-H 2O/g-Ads at the pressure 20 kPa and a desorption temperature over 100 ℃. The amount of adsorbent in the second adsorber was equal to that of the first adsorber. By analyzing the COP with the experimental results, the COP value was calculated to be over 1.0 ( –) at any desorption temperature. The COP of the double-effect cycle was higher than that of single-effect cycle.
In response to increasing energy consumption since the Industrial Revolution, the amount of industrial waste heat has been rising. Energy-cascading technologies have been developed to save on energy consumption. In particular, the development of advanced technologies to utilize low-temperature heat energy below 373 K would be beneficial in terms of reducing waste heat emissions. Recently, adsorption chillers have been receiving much attention. The adsorption chiller is one of the most advanced pieces of equipment that has the potential to collect or upgrade waste heat at low- temperatures. An adsorption chiller can store waste heat at temperatures less than 353 K and supply cooling energy at levels around 283 K [
The most significant problem is that the coefficient of performance (COP) per unit is considerably smaller than that of an absorption chiller. The COP of an adsorption chiller is less than 1.0. The maximum value is approximately 0.65 at 358 K for a regenerative heat source. Adsorption chillers have a realistic heat loss between the adsorption steps and desorption steps. This is because adsorption chiller was a batch type for a chiller cycle. A previous study of an adsorption chiller proposed a high adsorption capacity of adsorbent as well as designed an adsorber for a heat exchanger in a combined cycle. In this study, we pay attention to a double-effect adsorption chiller cycle.
in the heat exchanger tube of the B2 adsorber. The FAM-Z01 on adsorber B2 is desorbed by condensation heat from B1 (first adsorber). Because the double-effect cycle obtained a heat cooling output from the first and second adsorber approaching the input desorption heat for the first adsorber, the cycle COP was expected to have much higher value than a single-effect cycle.
In general, the adsorption quantity was large because the desorption temperature was high in the adsorption chiller [
In previous reports, the adsorbent for a double-effect adsorption chiller cycle has been silica gel. Recently, Marlinda published papers that refer to the feasibility of a double-effect adsorption chiller for numerical analysis. As a result, a double-effect cycle can be operated at the heat source temperature of 90˚C [
In this paper, adsorption isotherm and adsorption/desorption rate characteristics of a double-effect cycle with FAM-Z01 have been investigated. We have determined the behavior of the first and second adsorbers based on the assumption that a double effect cycle was operated. The volumetric method was employed to evaluate the influence of the desorption temperature and the adsorption bed thickness for the adsorption/ desorption rate. In the desorption step for the second adsorber, the amount of adsorption in the second adsorber, while H2O vapor was supplied, was determined using an estimate of the pressure and temperature of the first adsorber. We evaluated that the characteristic of COP with a double-effect adsorption chiller cycle was based on the amount of adsorption from experimental results.
FAM-Z01 of zeolite Adsorbent made by Mitsubishi Plastics, Inc. was selected for this study. FAM-Z01 was developed for adsorption chillers. The adsorption isotherms of water on FAM-Z01 are available for low temperature exhaust heat at approximately 60˚C.
In this experiment, the sample diameter was under 5 μm. Before the experiment, an adsorbent sample was out gassed at 90˚C for 24 h inside vacuum.
This experiment for the evaluation of the amount of adsorbent and rate at which it adsorbs is measured using a static volumetric method.
The main features of a different sample tested are recorded in
The adsorption and desorption rates with a double-effect adsorption cycle were evaluated based on the thickness of the adsorbent packed bed, so the thickness of the samples in this experiment were adjusted to change the packed bed area on the reaction cell for the remaining samples of the same weight.
First, the temperature of the reaction cell was set at 120˚C. The reaction cell and the H2O chamber were degassed for 12 h. After that, all the valves were closed. Second, the H2O vapor evaporating from evaporator 1 was introduced to the H2O chamber, and the pressure was increased to the required pressure for adsorption. The temperature of the reaction cell was set at the appropriate adsorption temperature. The valve between the reactor and H2O chamber was opened, and the H2O vapor was introduced to the reactor. The pressure of the H2O chamber reduced along with the rate of adsorption. The pressure change was measured by a data-logger. The duration of time taken for the pressure of the H2O chamber to change was equal to the time required for adsorption equilibrium. Then, the valve was closed. Subsequently, the desorption step was initiated. The temperature of the reaction cell was raised to the desorption temperature. The pressure of the H2O chamber was either set to 20 kPa (first adsorber) or 4.2 kPa (second adsorber) with the use of a vacuum pump and evaporator 1. The pressure of the H2O chamber was raised to correspond to the pressure required for desorption. The time required for the pressure of the H2O chamber to change occurred at the same time the desorption equilibrium was reached. When the rate of the first adsorber desorption was evaluated, the desorption heat was supplied by a medium heat at a high desorption temperature. However, when the rate of the desorption of the second adsorber was evaluated, the desorption heat was supplied by the condensation of the H2O vapor. The
Adsorption step | Desorption step | ||
---|---|---|---|
1st adsorber | 2nd adsorber | ||
Tank volume [L] | 13 | ||
Tank pressure [kPa] | 1.07, 1.40, 1.75 | 20 | 4.23 |
Sample weight [g] | 0.12 | ||
Sample thickness [μm] | 50 - 100, 100 - 125, 180 - 200 | ||
Adsorber temperature [˚C] | 30 | 120, 110, 100, 90, 80 | 60, 58, 56 |
Heat supply type | Liquid | Liquid | Vapor |
pressure of the H2O vapor provided by evaporator 2 was set at the first adsorber desorption pressure. When the desorption step was started, the H2O vapor was introduced to the reaction chamber with a reaction cell.
The amount of adsorption and the rates of desorption in this experiment were as follow:
In this section, we evaluated the desorption rate for the first adsorber in a double-effect cycle. In this experiment, the adsorption step was conducted at 30˚C, 1.0 kPa. Next, the H2O chamber pressure was set at 20 kPa, which was equal to saturated H2O vapor pressure at 60˚C.
After the adsorption step at 1.0 kPa and 30 kPa was completed, the valves were closed. The H2O chamber pressure was set at 4.2 kPa. The H2O vapor condensation heat was the desorption heat of the sample introduced to the reactor chamber. The H2O chamber could be set at any pressure by changing the evaporator 2 temperature.
desorption rate was same for both the supplied heat form conditions. The packed bed temperature change was under 0.5˚C for the duration of time because the effect of the supplied heat form was very small.
The coefficient of performance was calculated for a double effect adsorption cycle using the experimental quantity of adsorption and desorption. It was expected that the coefficient of performance for an adsorption chiller was capable of influencing realistic heat values for an adsorber heat exchanger. In this study, this value was investigated only for the adsorbent and the H2O refrigerant for realistic heat. The value referred to was from Mitsubishi Plastics, Inc [
In this study, a double-effect adsorption chiller cycle with FAM-Z01 was evaluated. From the experimental study, we obtained the following results.
1) A double-effect adsorption chiller cycle can be operated at the desorption temperature of 100˚C. At this temperature, the quantity of adsorption was 0.14 g/g for the first and the second adsorbers.
2) The COP was calculated from the quantity of adsorption for the experiment and the result was 1.1 at the desorption temperature 100˚C.
Esaki, T., Kobayashi, N. and Matsuda, T. (2016) Evaluation of the Characteristic of Adsorption in a Double- Effect Adsorption Chiller with FAM-Z01. Journal of Materials Science and Chemical Engineering, 4, 8-19. http://dx.doi.org/10.4236/msce.2016.410002