Phase change heat storage can solve some new energy intermittent and waste heat recovery problems, but heat storage is needed to act as this energy hub. Since the direct contact heat accumulator has the advantages of simple structure, large heat transfer area, and small heat transfer resistance, it is a good choice for improving energy storage rate. Although a great deal of research has been done on phase change materials and heat accumulators over the years, a systematic review of direct-contact heat accumulators is lacking. This paper reviews the related research on direct contact heat storage, aiming to summarize the research work on direct contact phase change heat storage systems. Various phase change materials (PCMs) for direct contact systems are analyzed, and the study of PCM melting crystallization behavior, heat transfer coefficients and system performance in direct contact systems is summarized, as well as the improvement methods for direct contact vessels and PCMs. It provides a useful reference for future research on direct-contact heat storage systems.

A novel integrated rotary reactor for NOx reduction by CO and air preheating (iNA reactor) was proposed. NOx removal performance was investigated in a fixed-bed reactor, which was used to simulate the working conditions change in iNA reactor. Lab-synthesized Cu/FeCeOx were used as catalyst. Two different modes were tested with iNA reactor: short cycles and long cycles. Excellent NOx removal efficiencies of over 95% and 90% for short cycles and long cycles were observed in iNA reactor. Moreover, compared with the constant-temperature rotary reactor, better H2O and SO2 resistances were also found in iNA reactor. The reaction mechanism was proposed based on in-situ DRIFT study. NOx was stored as nitrates in the adsorption zone, and then decomposed rapidly by both high temperatures and CO, leading to the deep catalyst regeneration. Therefore, temperature swinging and the feed of CO were key to having high iNA reactor performance for NOx removal.