Experimental study on using 85 °C low-grade heat to generate

Abstract

A great amount of below 100 °C low-grade heat exists in wasted heat and renewable energy fields while generating above 100 °C steam consumes a huge quantity of energy in production. Using below 100 °C low-grade heat to generate steam could save energy and reduce carbon dioxide emissions. This work experimentally studies an ammonia-water absorption heat transformer that increases temperatures of 85 °C low-grade heat to generate below 120 °C steam. A temperature-distributed generation process is introduced, which can enlarge the temperature utilization spans of heat sources. A prototype is built, and performance is investigated. Results show that the prototype successfully uses 85 °C low-grade heat for steam generation. The output temperature fluctuation is ±0.4K, which meets the demand for most industrial applications. In addition, the prototype COP increases with the strong solution concentration in the experiment range, and the maximum COP is 0.33. System performance improvement results from the rise in ammonia generation quantity. However, the disadvantage of rising strong solution concentration is the absorption pressure increment, bringing the challenge for heat exchanger design. The maximum temperature lift of the prototype is 34.7K. Moreover, the performance of prototypes with different sizes is predicted based on the experimental data. The predicted practical COP of the 200 kW prototype is 0.36 when the output temperature is 119.7 °C, close to the simulation value of 0.38.