Techno-economic feasibility assessment of a diesel exhaust heat recovery system to preheat mine intake air in remote cold climate regions

Underground mines in Arctic and Subarctic regions require the preheating of mine intake air during winter.The cold fresh air of those remote areas can be as severe as
40℃ and commonly needs to be heated to around+3℃.This extensive amount of heating is usually provided by employing large-size air heaters,fueled by diesel,propane,natural gas,or heavy oil,leading to high energy costs and large carbon footprints.At the same time,the thermal energy content of a diesel generator sets(gen-sets)exhaust is known to be one-third of the total heating value of its combusted fuel.Exhaust heat recovery from diesel gen-sets is a growing technology that seeks to mitigate the energy costs by capturing and redirecting this commonly rejected exhaust heat to other applications such as space heating or pre-heating of the mine intake air.The present study investigated the possibility of employing a simple system based on off-theshelf heat exchanger technology,which can recover the waste heat from the exhaust of the power generation units(diesel gen-sets)in an off-grid,cold,remote mine in Canada for heating of the mine intake air.Data from a real mine was used for the analysis along with environmental data of three different location-scenarios with distinct climates.After developing a thermodynamic model,the heat savings were calculated,and an economic feasibility evaluation was performed.The proposed system was found highly viable with annual savings of up to C$6.7 million and capable enough to provide an average of around 75%of the heating demand for mine intake air,leading to a payback period of about eleven months or less for all scenarios.Deployment of seasonal thermal energy storage has also been recommended to mitigate the mismatch between supply and demand,mainly in summertime,possibly allowing the system to eliminate fuel costs for intake air heating.

Effects of sustained cold and heat stress on energy intake, growth and mitochondrial function of broiler chickens

To study the correlation of broiler chickens with energy intake, growth and mitochondrial function which exposed to sustained cold and heat stress and to find out the comfortable temperature, 288 broiler chickens（21-day with（748±26） g, 144 males and 144 females） were divided randomly into six temperature-controlled chambers. Each chamber contained six cages including eight AA broilers per cage, each cage as a repeat. After acclimation for one week（temperature, 21℃; relative humidity, 60%）, the temperature of each chamber was adjusted（finished within 1 h） respectively to 10, 14, 18, 22, 26, or 30℃（RH, 60%） for a 14-day experimental period. After treatment, gross energy intake（GEI）, metabolizable energy intake（MEI）, the ratio of MEI/BW, metabolizability, average daily gain（ADG）, the concentration of liver mitochondria protein and cytochrome c oxidase（CCO） were measured respectively. Our results confirmed that when the temperature over 26℃ for 14 days, GEI, MEI and CCO activities were decreased significantly（P〈0.05）, but the concentration of liver mitochondria protein was increased and metabolizability of broilers was not influenced（P〉0.05）. Compared with treatment for 14 days, the ratio of MEI/body weight（BW） were also decreased when the temperature over 26℃ after temperature stress for 7 days（P〈0.05）, meanwhile mitochondrial protein concentration was increased at 10℃ and CCO activity was not affected（P〉0.05）. Additionally at 22℃, the ADG reached the maximal value. When kept in uncomfortable temperatures for a long time, the ADG and CCO activities of broiler were reduced, which was accompanied by mitochondrial hyperplasia. In summary, our study focused on the performance of broilers during sustained cold and heat environmental temperatures ranging from 10 to 30℃. From the point of view of energy utilization, moreover, 22 to 26℃ is comfortable for 28–42 day s broilers. And these could provide the theoretical basis on the high efficient production.