SDCS Regenerator Heat Exchanger Volumetric Flow Effect

Figure 6.14 shows the impact of regenerator heat exchanger water volumetric flow on regenerator performance. The volumetric flow range investigated was 0.5-3.5 L min^-1. This range was selected because it covers a typical volumetric flow of a SOFC WHR circuit. Figure 6.14a shows that as the water volumetric flow increases from 0.5 to 3.5 L min^-1, both the moisture addition rate and latent (regenerator) effectiveness increase from 0.06061 to 0.3565 g s^-1 and 30.17 to 37.97 % respectively. Over the range investigated, the temperature of the desiccant solution entering the regenerator HMX core was 41-51 °C. An increase in desiccant solution temperature results in an increase in mass transfer from the solution to the air.

Figure 6.14b demonstrates that as water volumetric flow is increased, the regenerator thermal input increases from 659.2 to 1749 W, however the water temperature difference across the regenerator plate heat exchanger (PX 2) decreases from 18.88 to 7.16 °C. The selection of a suitable regenerator heat exchanger water volumetric flow will be dependent upon achieving a hot water flow temperature from the SOFC CHP system that will facilitate effective desiccant solution regeneration. Testing of the SOFC CHP system is presented in Chap. 7.

Across all regenerator tests, the maximum calculated relative uncertainties in the regenerator MAR and n_L are ±7.8 and ± 22.8 % respectively. Next, Sect. 6.3.2.6 concludes the regenerator component analysis and discusses the implications for tri-generation system integration.

Fig. 6.14 SDCS regenerator performance with heat exchanger volumetric water flow

Section 6.3.2 has provided the results and analysis from the SDCS regenerator component evaluation. The results and analysis show regeneration of a potassium formate solution at a 0.65-0.7 solution mass concentration is possible with a hot water flow temperature as low as 45 °C and improves as the hot water flow temperature increases. Regenerator performance improves with a lower inlet air temperature and relative humidity. As a result, the work in this thesis considers extract room air as the regenerator inlet air stream for tri-generation system integration. Regenerator capacity is greater with increasing volumetric air and desiccant solution flow. However, increasing these variables demonstrates an increase in the required regenerator thermal input. For effective tri-generation system integration this needs to be balanced against the available thermal input from the SOFC CHP system. Furthermore, regenerator capacity is greater with increasing hot water flow temperature and water volumetric flow in the heating circuit. A maximum moisture addition rate of 0.4331 g s^-1 has been achieved, with a regenerator thermal input of 1588 W. The latent (regenerator) effectiveness is in the range of 15-40 %. During tri-generation system integration, the performance of the regenerator will be largely dictated by the available thermal energy from the SOFC CHP system. To ensure balanced SDCS operation, this will inform the permissible moisture removal rate that the dehumidifier should be operated at.

Next, Sect. 6.3.3 presents the results and analysis for the complete SDCS operating in a balanced manner.