OPTIMIZATION OF COGENERATION PLANT FOR APPLICATIONS IN FOOD INDUSTRY

Abstract

Cogeneration systems represent an effective solution for optimizing energy performance of users with contemporary thermal and electrical energy demand. An energy audit of an industrial pasta factory equipped with a cogeneration system natural gas fuelled has carried out along last two years. This CHP plant, with a 650 kWe capacity, currently covers a relevant fraction of the electric and high-temperature heat loads during peak hours, while it is switched off during off-peak hours because of the much lower electricity price. Heat content of flue gases is recovered by two cascaded gas-diathermic oil and diathermic oil- water heat exchangers; the superheated water obtained is then supplied to the pasta dryers. A detailed plant description and an energetic and economic analysis are provided, that indicate margins for improvement of the current CHP system based on maximizing heat recovery. The existing plant only achieves heat recovery at high temperature (from exhaust gas), while a fraction of the thermal demand is associated with low temperature heat uses. Then a first retrofit hypothesis includes an additional low temperature heat recovery from the cooling jacket water and the lubrication oil circuits of the prime mover. As the above solution allows to achieve only minor benefits, from an economic viewpoint, a second and more comprehensive retrofit hypothesis was made, based on the use of a CHP gas turbine. Once sized the turbine to cover the whole heat demand of the pasta factory, energetic and economic analyses revealed the convenience of this second retrofit scheme compared to the existing lay-out.