In this study, a novel fifth-generation district heating (DH) model was proposed that implements the energy-prosumer concept of bilateral heat trading (BHT) process between the DH network and the building. The newly proposed BHT model can be characterized by the feature of using the low temperature of DH return pipe’s water. The technical feasibility of the proposed BHT model was evaluated through operation simulation analysis based on the actual operation data of the hybrid pilot system combined with the fuel cell and heat pump and the annual hourly temperature profile of the existing DH return pipe. The main objective of this study is to examine the technical feasibility of the interconnection operation model with the existing DHN as an alternative to overcome the limitations of the current fuel cell cogeneration model, which suffers from the low production volume caused by the high initial investment cost. From the simulation results, it was confirmed that considerable operational benefit, more than 30% in terms of primary energy savings, can be achieved with the proposed model, and compared to the stand-alone model of the fuel cell cogeneration system for the building, it can provide a more flexible technical environment to improve the system utilization rate by about 40%.
The simultaneous firing characteristics of woodchips and spent mushroom substrates (SMS) were studied in a stoker-type industrial boiler. The type of spent substrate intended for combustion consisted of oyster mushrooms. SMS from mushroom farms generally have a high water content. Dryers are therefore used for combustion. The moisture content of SMS was reduced to achieve low moisture to combust sufficiently at about 20%. First, the basic characteristics of the boiler were confirmed by conducting a woodchip combustion test under various operating loads of 30, 50, 70, and 100%. Thereafter, a simultaneous combustion test of woodchips and SMS was performed. During the experiment, exhaust gas concentrations in the boiler combustion chamber were measured, such as the temperature of oxygen (O2), carbon monoxide (CO), and nitrogen oxides (NOx). In addition, industrial and basic analyses were performed on woodchips and SMS. The main differences in the fuel analysis results between woodchips and SMS were ash, nitrogen, sulfur content and net calorific value. According to the analysis, the nitrogen content of SMS was 2.6%, which was 8.7 times higher than that of woodchips, and the ash content was also 14.8%, which was 18.5 times that of woodchips. As a result of the combustion experiment, the woodchip experiment revealed that the values of O2 and CO decreased and the combustion chamber temperature increased as the amount of fuel increased. Due to higher combustion temperature, thermal NOx also increased. When comparing this combustion test with the co-firing test, there was no significant difference in O2, CO, and combustion chamber temperature. However, with regard to the NOx value, the results showed a sharp increase from 64 ppm to 135 ppm. Although the NOx value increased, SMS had enough heat to be burned as fuel. Therefore, the utility of various agricultural byproducts as fuel has prospects for achieving an effective approach to energy cost reduction.
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