Page 164 - Low Temperature Energy Systems with Applications of Renewable Energy

154 Low-Temperature Energy Systems with Applications of Renewable Energy

Ukraine is among the top ten producers of wheat and corn, where 60% of the steppe
region of agricultural land is taken up with the cultivation of grain crops, one of the
largest amounts in the world. For the year 2018, the wheat and corn harvest in Ukraine
amounted to 24.5 and 35.5 million tons, respectively. The harvested crops are subject
to technological processing, storage for local use, and exportation. The moisture
content of the collected grain is 10e30% higher than the equilibrium value, which
necessitates its drying to improve the quality and shelf life. Readers unfamiliar with
crop drying processes, may refer to Ref. [45] which presents the fundamentals, but
without any discussion of the use of heat pumps, which is our main purpose in this
section.
Furthermore, 20e90% of the total cost of agricultural grain output resides in the
cost of processing the harvest, which mainly involves the most power-consuming pro-
cess of heat-and-moisture treatment; up to 80% of the harvest is subject to this form of
processing. Also, the constant growth of prices for traditional energy sources together
with the increase in grain production volumes leads manufacturers (1) to increase the
energy efficiency of technological processes of drying, (2) to use secondary energy re-
sources, and (3) to develop optimal schemes of heat-and-moisture treatment using
alternative energy sources.
Performing the drying process in a timely and proper manner not only raises the
quality of the grain during storage, but also improves its food characteristics. By main-
taining optimal drying methods, further ripeness of grain is achieved, the degree of
maturity is aligned, uniform distribution of moisture is established, and the appearance
and other technical characteristics are improved. The process of heat-and-moisture
treatment leads to the destruction of pests and microorganisms, and in some cases,
improves the technical properties of defective grain. Grain drying technology for food-
stuffs determines the grade of flour being obtained, the quality of the cereals, and the
“shelf life” for their storage. Seed and feed grain drying has its own characteristics.
Processes for seed grain are done at low temperature and require special technological
parameters of the drying processes, which depend on their intended purpose.
The use of grain as a ready-made agricultural product necessitates its heat-and-
moisture treatment to a certain level of humidity. When wheat grain is used in the
domestic market it is enough to dry it to 16e17% moisture. However, when grains
are exported or used as seed material for long-term storage, the final humidity should
be 11e14%, assuming an initial humidity of 19e35%, depending on the grade and
subsequent special purpose. The main methods of drying grain are by convection, con-
duction, electricity, sorption, and infrared rays. The selection of the most effective
method depends on the purpose of grain, its volume, and technical parameters of
the heat-and-moisture treatment process.
The drying processes make up 90% of the energy consumption for converting the
harvested grain into a finished product. The most cost effective and, consequently, the
main method of drying is by convection. Convective drying has its specific features
and is characterized as either high temperature (drying agent 80 C) or low temper-

ature (25e80 C). Since the 1980s, high-temperature heat-and-moisture processing
has been mainly used for feed grain and low-grade grain. In most cases, low-
temperature drying methods are used for food types of grain. This is because grain