Page 145 - Low Temperature Energy Systems with Applications of Renewable Energy

Heat pumps in the drying 4
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industry

4.1 Introduction and overview of drying using heat
pumps

One of the main thrusts of this book is the use of heat pumps for a broad range of
applications. Currently the range of heat pump capacities are typically from 1 to
5 MWth, with the highest thermal power of a single heat pump being 35 MWth.

Heat pumps are capable of providing working fluids at temperatures up to 100 C
for many applications including heating, hot water supply, and various technological

needs in industry. Using heat pumps for applications above 100 C is problematic, and
the industry has obstacles to overcome in this area. Even with these limitations, more
than 10 million heat pumps units, from very small to very large, have been installed so
far in Europe.
The main obstacles limiting the use of heat pumps in industry are high initial capital
cost which might lead to uneconomic returns on investment and perceived risk on the
part of industrialists who may view heat pump technology as new and not sufficiently
proven in commerce and having limited examples of successful applications. Thus, to
expand the adoption of heat pumps for a wide application of technologies, it is neces-
sary to remove structural barriers in industry; apply intensive energy saving method-
ology; integrate capabilities and responsibilities in their implementation from an
overall system perspective that will optimize industrial processes and commercial
applications.
Figure 4.1 shows the wide spectrum of thermal demand (heat energy) in various in-
dustries. The demand is broken down into heat over temperature bands. Of this huge
energy demand, heat pumps provide 174 TWh-th or 8.7% of all industrial needs [1,2].
According to Ref. [3], among the first applications of heat pumps for drying and
dehydration was the work of Sulzer on the dehydration and drying of underground
cavities in Germany in 1943 and a grain dryer developed in the USA in 1950. A
significant part of the work involving the use of heat pumps is connected not
only with convection drying, but also with freeze-drying [4,5], in which refrigerating
equipment is used to freeze the product. Particularly important drying materials with
heat pumps are described in Refs. [6e11]. The most famous and widespread appli-
cation of heat pumps in convection drying is the drying of wood (sawn timber) in
chambers with closed air circulation and condensation moisture removal.
There is no doubt that drying is one of the most energy intensive industrial pro-
cesses. In developed countries, about 10% of fuel consumption is used for drying
various products of industry [12]. One of the common processes of drying plants is

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Written by Andriy and Oleksandr Redko; edited by Ronald DiPippo.
Low-Temperature Energy Systems with Applications of Renewable Energy
https://doi.org/10.1016/B978-0-12-816249-1.00004-2
Copyright © 2020 Elsevier Inc. All rights reserved.