Animal fat represents a waste in abattoirs, butchers shops and kitchens. I'm interested to know if there are any concrete examples of its use for energy purposes (fuel for engines, boilers, biogas generation, etc.).
The company Agrokor Energija d.o.o. (http://www.agrokor.hr/hr/kompanije/agrokor-energija-d-o-o/) from Zagreb developed a biogas plant which partly uses the waste from meet industry as input material. I did not look deeply in their process, but I remember that they mentioned thermal processing of this kind of waste before the production of biogas.
I agree with Serena that waste to energy from offal is challenging. An energy balance analysis typically shows a negative number. I would suggest selling the fat to a rendering company (create your own company?). If the fat is heavily entrained in water, look at Electrocoagulation to remove larger fat particles. Sell the skimmings with the offal. The leftover effluent could be then an excellent feedstock for anaerobic digestion.
In Switzerland as in many other countries, (melted) animal fats ("of category 1" according to the regulations on animal by-products) are commonly used either for direct combustion or the production of biodiesel. Category 2 fats may be co-fermented in biogas plants (after pressure sterilisation), whereas "energetic rendering" is not the first priority and the "best use" for fats of category 3 (that can be used for feeding purposes).
The beef fat that I wish to treat comes from tanneries that transform beef skins in leather, so, it is not eatable. And the quantities are not so large. According to all opinions, the applicable techniques are: direct combustion, biodiesel and biogas.
biogas production will be more feasible option as for biodiesel production it will need cleaning and purity and cleaning will lead to extra cost of drying for biodiesel product process.