Resorption Thermal Transformer Generator Design

Samuel Hinmers,Michel Van Der Pal,George H Atkinson,Robert E Critoph

doi:10.3390/en15062058

Samuel Hinmers, Michel Van Der Pal + Show 2 more

Open Access

https://doi.org/10.3390/en15062058

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Abstract

This work takes an empirical and evidence-based approach in the development of a resorption thermal transformer. It presents the initial modelling conducted to understand key performance parameters (coefficient of performance and specific mean power) before discussing a preliminary design. Experimental results from large temperature jump and isosteric heating tests have identified the importance of heat transfer in ammonia-salt systems. Both the heat transfer resistance between the salt composite adsorbent and the tube side wall, and the heat transfer from the heat transfer fluid to the tube side wall are key to realising resorption systems. The successful performance of a laboratory-scale prototype will depend on the reduction in these heat transfer resistances, and improvements may be key in future prototype machines. A sorption reactor is sized and presented, which can be scaled for length depending on the desired power output. The reactor design presented was derived using data on reaction kinetics constants and heat of reaction for calcium chloride reacting with ammonia that were obtained experimentally. The data enabled accurate modelling to realise an optimised design of a reactor, focusing on key performance indicators such as the coefficient of performance (COP) and the system power density. This design presents a basis for a demonstrator that can be used to collect and publish dynamic data and to calculate a real COP for resorption system.

Highlights

The UK government has set out a roadmap for transitioning towards a hydrogen economy [1]
The first step is to derive an active fraction; the salt is assumed to have an active fraction of salt that is accessible to the ammonia and capable of reacting, which is the percentage of the stoichiometric mass reacting that is observable over the cycle time
large temperature jump (LTJ) testing has identified the reaction kinetics and equilibrium data for calcium chloride reacting with ammonia, as per the two reactions: CaCl2·8NH3 CaCl2·4NH3; and CaCl2·4NH3 CaCl2·2NH3

Summary

Introduction

The UK government has set out a roadmap for transitioning towards a hydrogen economy [1]. Resorption transformers can be used to recover and upgrade low-grade waste heat from industrial processes—which would otherwise be lost—and subsequently reused within the processes on site. This will be essential for many industries where valorising this waste heat in district heating networks will not be possible due to the remoteness of industrial sites. Contemporary experimental work tends to use either a gravimetric suspension balance test cell, or large-temperature-jump testing. This is applied to a model, often based upon the methods presented in the 1990s. This paper will first consider the material and testing methods before an overview of the methods used to model and understand the reaction behaviour

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