Entropy and Entransy Dissipation Analysis of a Basic Organic Rankine Cycles (ORCs) to Recover Low-Grade Waste Heat Using Mixture Working Fluids.

Mixture working fluids can reduce effectively energy loss at heat sources and heat sinks, and therefore enhance the organic Rankine cycle (ORC) performance. The entropy and entransy dissipation analyses of a basic ORC system to recover low-grade waste heat using three mixture working fluids (R245fa/R227ea, R245fa/R152a and R245fa/pentane) have been investigated in this study. The basic ORC includes four components: an expander, a condenser, a pump and an evaporator. The heat source temperature is 120 °C while the condenser temperature is 20 °C. The effects of four operating parameters (evaporator outlet temperature, condenser temperature, pinch point temperature difference, degree of superheat), as well as the mass fraction, on entransy dissipation and entropy generation were examined. Results demonstrated that the entransy dissipation is insensitive to the mass fraction of R245fa. The entropy generation distributions at the evaporator for R245/pentane, R245fa/R152a and R245fa/R227ea are in ranges of 66-74%, 68-80% and 66-75%, respectively, with the corresponding entropy generation at the condenser ranges of 13-21%, 4-17% and 11-21%, respectively, while those at the expander for R245/pentane, R245fa/R152a and R245fa/R227ea are approaching 13%, 15% and 14%, respectively. The optimal mass fraction of R245fa for the minimum entropy generation is 0.6 using R245fa/R152a.

Hydrothermal liquefaction of cellulose in ammonia/water.

In order to obtain the N-containing organics from cellulose under mild conditions, hydrothermal liquefaction of cellulose in the presence of ammonia was conducted in this study. The results showed that the increasing reaction temperature and prolonging time facilitated the conversion of cellulose in hydrothermal liquefaction (HTL) with NH3·H2O and decreased the amount of solid residue. Reaction temperature showed more influence than reaction time on solid residue formation. The components of bio-oil were significantly affected by reaction temperature and reaction time. Electrospray ionization-Fourier transform-ion cyclotron resonance-mass spectrometry (ESI FT-ICR MS) provided an insight for understanding the distribution of the different kinds of N-heterocycle compounds in the bio-oil. The possible reaction pathway of N-heterocycle compounds formation from cellulose during hydrothermal liquefaction with NH3·H2O was proposed.

Dewatering of sewage sludge via thermal hydrolysis with ammonia-treated Fenton iron sludge as skeleton material.

In this study, the alkaline hydrothermal ferric carbon (AHFC), which was prepared by hydrothermal liquefaction method using Fenton iron sludge with NH3·H2O, was used as a skeleton materials for the dewatering of sewage sludge (SS) via thermal hydrolysis. NH2 functional group presented in the AHFC and nano-sized γ-Fe2O3 was anchored on the surface of AHFC. The NH2 functional group notably promoted thermal hydrolysis of SS from the increasing of TOC and TN value. γ-Fe2O3 showed adsorption effect to the water, resulting in decline of the dewatering rate of SS in present condition. When 100% of AHFC was added, dewatering rate of SS was decreased by 19.93% (at 160 °C), 4.50% (at 180 °C) and 8.34% (at 200 °C) respectively. 3D-EEM results showed that the degree of hydrolysis was deepened when AHFC was added for the intensity of soluble microbial products decline. AHFC promoted the decomposition of protein to form heterocycle compounds in the resulting cake according to in situ FTIR results. The nano γ-Fe2O3 catalysis to cake also can be observed for the activation energy was lower than blank in the range of 40˜60%. The study demonstrated concept and the effectiveness the reuse/recycle of the Fenton iron sludge for dewatering of SS.