Energy analysis of a pasta factory and application of cogeneration

The energy production factor has become increasingly important following the trend within energy markets toward ever greater margins for optimisation. In the light of this fact, energy analysis provides a useful tool for determining the consumption of individual process phases in order to devise comprehensive intervention strategies aimed at more rational energy usage. The application of cogeneration to food-production processes is likewise of great interest, due to the opportunity it affords for improving the overall energy performance of facilities. The present study is concerned with the application of the above technologies to a pasta factory, beginning with a thorough energy analysis of the existing installation to select the most appropriate type of cogeneration system, and the development of a project to accommodate its anticipated future expansion in years to come. The factory in question consists of a line for the production of short dried pasta shapes having a capacity of 2,000 kg/h. Production runs continuously from Monday to Friday, and the process requires both electrical and thermal energy (in the form of superheated water at 130°C). Thermal analysis For the thermal analysis, mass and energy balances were determined by measuring the moisture and temperature of product exiting the individual loads within the drying process, and using the values for temperature and humidity of the machines recorded by the supervision system by means of capacitive/resistive sensors. The factory produces forty-seven different types of short dried pasta shapes, which can be roughly classified into two groups according to their specific volume: "short pasta" and "soup pasta". The experimental analysis was conducted on the above two groups as well as on "bowtie" and "protein-enriched corkscrew" pasta shapes which, due to their lower throughput and special recipes, are better able to highlight any differences in thermal demand. Next, the thermal demand for each of the above four types of pasta was determined and, based upon the contribution of each group to the total annual output of the factory, a weighted average of the thermal requirements of the individual process loads was computed, and found to be 288.7 kcal/kg. Electrical analysis For the electrical analysis, the various loads within the plant were identified and suitable reduction coefficients estimated, partly on the basis of experience and partly based on graphs obtained from tests with current probes on the electrical panels. These graphs indicated that during certain work cycles the load does not always absorb maximum power, and so these cycles were monitored to better understand the functioning of the individual machines. The results of the electrical analysis were used to estimate the contribution of each load to the total consumption, and hence identify the process phases that incurred the highest electrical expenditure. The average monthly consumption was found to be 123,793 kWh which, for a monthly pasta output of 665,448 kg, again estimated using a weighted average, gave an overall specific energy consumption of 0.186 kWh/kg. Application of cogeneration After determining the overall energy consumption of the pasta factory in its present state, the feasibility of installing a cogeneration plant was evaluated, with the pasta factory divided into 4 production lines having a total capacity of 7,000 kg/h, and assuming 7,000 working h/year. On the basis of the assumptions made and the results of a market survey, the system chosen was a natural gas-fuelled reciprocating Otto cycle engine with 1,105 kWe rated power, connected in parallel to the electricity supply grid, and an auxiliary boiler. The cogenerator was slightly undersized to ensure it would always operate at full load, for maximum efficiency. An economic analysis and profitability analysis were carried out to ascertain that the savings accrued over the life time of the system could reimburse the investment cost. The Pay-Back Period (PBP) was found to be 29 months, and the resultant Net Present Value (NPV) indicates that the project is viable, with the annual revenues sufficient to both pay back the interest and recover the initial outlay before the end of the useful life of the investment.