Heat Pumps for Drying

Background

Drying processes are widely used in industry, including the food, paper, chemicals, and ceramics industries, as well as in commercial laundries and in household applications, such as white goods. The Handbook of Industrial Drying describes at least 15 different dryer types and identifies more than 20 different industrial drying sectors, making it challenging to generalize about drying technologies.

Drying processes make a significant contribution to energy consumption, accounting for 10-25% of industrial energy consumption. To this day, drying continues to be the main process used in industrial preservation for a large number of products. Industrialization has helped to optimize drying processes, which are conducted under varying, but controlled conditions. However, the basic principle of drying remains the same as it was thousands of years ago, with convective dryers continuing to be the most commonly used type of dryer.

Industrial convective drying plants are mainly operated by burning fossil fuels and product waste. The moisture extracted from the material to be dried is, in most cases, released into the environment in pure gaseous form, or with a drying medium (e.g. air, steam).  This exhaust air contains high amounts of energy, which is often only partially utilised by heat recovery. Modern industrial drying processes are either an open loop system using heated ambient air, or closed loop systems that re-circulate the drying air.

Heat pumps offer an opportunity to utilize a heat source at low temperatures (at the evaporator) and supply a heat sink at a higher temperature (condenser). In the case of a closed loop drying system, the combined heating and cooling load is used for the recovery of drying energy, which is essentially the latent heat from the water evaporation, returning this energy back into the drying process in the form of dehumidified and re-heated drying air.

Objectives

The use of heat pumps in drying processes show great energy savings potential for the numerous industries reliant on drying processes. Annex 59 will thus explore and evaluate the potential that can be unlocked in a range of applications. Furthermore, the Annex shall seek to undertake the following:

• Collate relevant data of the state of the art of drying processes equipped with heat pumps 
• Analyse drying processes at a theoretical level to find the optimal process design (e.g. lowering temperatures), in-process operation (drying time) as well as in heat pump design and integration.
• Gather experience from demonstration projects through monitoring and simulation of the entire drying system
• Make recommendations regarding the design of heat pump drying systems, taking into account performance compared with conventional dryers
• Highlight and review the most promising dryer concepts that can integrate heat pumps

Target audience

• Heat pump manufacturers of industrial and small-scale heat pumps as well as component manufacturers
• Manufacturers of white goods
• Plant engineers and dryer manufacturers
• End users in the industrial sectors addressed
• Policy makers

Contact Person

Dr. Michael Lauermann,  michael.Lauermann@ait.ac.at

Participating Countries

Austria (Operating Agent), China, Germany, Norway, USA, Sweden, Switzerland