| Abstract: | Generator temperatures in ammonia absorption systems at subfreezing evaporator conditions have been optimized to use the minimum volume of biogas required to operate two-stage dual-fluid cycles. In this dual-fluid cycle, a LiBr---H2O absorption system is used at the first stage with ammonia absorption systems at the second stage. Three different refrigerant-absorbent combinations (NH3---H2O, NH3---NaSCN, NH3---LiNO3) were selected for this study. The absorber at the second stage is cooled by the low temperature water-refrigerant from the evaporator at the first stage. Lowering the absorber temperature reduces the heat input to the generator, which lowers the generating temperature and improves the performance of the absorption systems at the second stage. The optimum generator temperatures and performance coefficients of the systems at the first and second stages and the overall two-stage dual-fluid cycles are presented graphically. A comparative study between the three ammonia systems used in the two-stage dual-fluid cycle has been carried out. |
