This paper presents studies carried out in a pilot-scale plant for recovery of waste heat from a flue gas which has been built in a lignite-fired power plant. The purpose of the studies was to check the operation of the heat recovery system in a pilot scale, while the purpose of the plant was recovery of waste heat from the flue gas in the form of hot water with a temperature of approx. 90 °C. The main part of the test rig was a condensing heat exchanger designed and built on the basis of laboratory tests conducted by the authors of this paper. Tests conducted on the pilot-scale plant concerned the thermal and flow parameters of the condensing heat exchanger as well as the impact of the volumetric flow rate of the flue gas and the cooling water on the heat flux recovered. Results show that the system with a condensing heat exchanger for recovery of low-temperature waste heat from the flue gas enables the recovery of much higher heat flux as compared with conventional systems without a condensing heat exchanger.

Sorghum produces allelopathic compounds, including total phenolic compounds and sorgoleone, which exhibit a phytotoxic effect on weeds. The field study, carried out in 2016-2017, was designed as an one-factor experiment, in the randomized block design, in four replications, with Sucrosorgo 506, Rona 1, KWS Freya, KWS Juno, and KWS Sammos, to assess the impact of allelochemicals on weeds. Weed infestation was determined at the beginning of July. Individual weed species were collected from two random places in each plot and weighed. The aim of the laboratory study was to evaluate the total content of phenolic compounds, and sorgoleone in the early stages of plant development (5, 10, and 15 days after emergence) in varieties Rona 1, KWS Freya, KWS Juno, KWS Sammos, Farmsorgo 180, GK Aron, PR 845F, Sucrosorgo 506 and PR849F. The total content of phenolic compounds was determined using the colorimetric method, and the sorgoleone HPLC technique on a Flexar chromatographic set. The highest value of sorgoleone was observed in 15-day-old seedlings of KWS Juno, the lowest in 5-day-old seedlings of Sucrosorgo 506, the highest levels of total phenolic compounds in 5-day-old seedlings of PR 845F, the lowest in 15-day-old seedlings of Farmsorgo 180. The results do not fully confirm the beneficial effect of allelopathic compounds on reducing weed infestation, however, it is important to emphasize the diversity of cultivars used. The statistically insignificant results indicated that most varieties of sorghum plants do not exhibit a significant decrease in yield.