The information contained in this report makes it possible for the user to carry out an initial screening of applicative possibilities for the use of renewable sources in milk processing. Indeed, special attention was paid to the requirements of government analysts and/or agencies for agricultural development which are interested in identifying the energy carriers best suited to their countries' needs. Nonetheless, the results obtained with the methods outlined here should be considered approximate and valid only as a preliminary orientation. While the recommended evaluation methods and various information are based on experience with numerous experimental plant, they naturally do not take into account the peculiarities of each individual situation.
Within this context, one of the main goals of this report is to make possible for users to initially select one or two possible technical solutions without having to commission special studies. Later, these solutions can be more carefully evaluated by experts in the field.
Technologies for the use of renewable energy sources require a more advanced milk processing plants, since the autoproduction of energy requires equipment which (even in its simplest versions) is more complicated than normal processing plants. Consequently, it make sense to consider plant solution in which the energy-producing and milk-processing aspects are consistent with each other.
The energy currently required for the transformation of 1 t of milk varies from 30–600 thermal MJ and from 100–200 electric MJ (if condensed milk is not included). Consequently, total requirements (considering normal efficiencies for the production of electric energy) range from 400 to 1300 MJ/t of milk.
In other words, processing requires from 9.5 to 31 kg of oil equivalent per t of milk.
The present evaluation of the energy requirements of milk processing is based on the standard features of currently available plants. This decision was motivated by practical considerations connected with the difficulties involved in modifying commercial plants that are readily available on the market.
It should be emphasized, however, that commercial plants are not optimal from an energy standpoint. Consequently, their “redesign” (e.g., to limit electric energy requirements and allow for the use of hot water instead of steam) could facilitate the employment of renewable sources. In this light, studies on the various modifications that could be made to these plants would be enlightening.
Specifically, studies whose goals are the following should be undertaken to clarify possibilities for the use of renewable sources and encourage the development of milk processing centers in developing countries:
identification of various types of processing plants designed to reduce energy requirements to a minimum;
construction indications on the energy technologies to be employed;
detailed information about the possible combination of technologies related to i) and the various solutions in ii), in order to provide users with applicative examples for every climatic and social condition considered to be significant.
Consequently, the goal is to harmonize processing plant characteristics and requirements with energy supply while providing construction models for plant design.
Under present conditions, the most promising technologies that make use of renewable sources are those which:
rely on one single plant to meet thermal and electric requirements (so as to limit maintenance and investment costs);
can be produced on the semi-industrial level in developing countries (which would favor their development);
do not require a second plant in parallel to guarantee energy supply over time (again, to reduce investment costs).
Consequently, the following technologies are of interest: reciprocating steam engines, endothermal engines fed with renewable fuels (gasification gas, vegetable oils, etc.), all technologies for the recovery and limitation of energy consumption (e.g., plate-type exchangers for milk precooling, etc.).
Giving up the use of steam and electric energy (or their drastic reduction) would simplify plants considerably. The use of solar energy would also become a valid proposal if the milk containers utilized could be heated by hot water. The use of hot water (as opposed to steam or direct flame), however, requires different work schedules, since there is less thermal power available, and the plants' thermal inertia is increased.
