Single-effect ammonia/lithium nitrate heat pump-transformer: A technology for process heat recycling

Abstract

The modeled operating characteristics of a single-effect ammonia/lithium nitrate absorption heat pump-transformer (type III absorption heat pump) are presented and compared to other working pair options and absorption heat pump cycles. Heat and mass balance equations are given. The effect of cycle operating parameters is shown on cycle thermal efficiency and solution pump power. It is shown that the ammonia/lithium nitrate working pair would achieve a performance a little less efficient than a water/lithium bromide system. Ratios of useful heat delivered to driving heat of nearly 2 are shown, with this system, to be achievable over a wide range of operating conditions. Ammonia/lithium nitrate has practical advantages over water lithium bromide in relation to corrosion, construction materials, and operating pressures. Both working mixtures have high viscosities in the absorbent/refrigerant solutions. However, an ammonia/lithium nitrate system has much higher available pressure drops for the economizer allowing the designer greater leeway in the use of enhanced heat exchange techniques. Costs and payback are commented upon.