Modelisation strategique de la gestion energetique d'une usine de pate kraft

This research project examines the problem of the economic assessment of the powerhouse operation of a paper mill. The case studied is that of a kraft mill located in a town of Quebec. In the context of this case study, the following energy retrofit projects are analysed: reduction of steam demand, steam exportation for a district heating network and cogeneration. The principal objective of this research project is to study how these energy improvement measures would affect the operation of the powerhouse as well as quantifying the potential economic profit to be incurred in the context of various configurations. In order to assist the analysis, an optimization model was developed. In addition, the influence of the principal data used for the analysis (prices of energy and steam demand reduction) will be studied.; The optimization approach involves the use of a MILP (mixed integer linear programming) multi-period optimization model based on some typical features of powerhouse operation optimization models. The model is similar to a network model with certain particularities. The decision variables include, among others, the distribution of the steam in the powerhouse, the consumption of fuels and the amount of energy (steam and electricity) used, bought and sold. The solution is limited mainly by the powerhouse operation constraints (equipment capacities, limits of provisioning, etc), the legal limits for the export of electricity and the satisfaction of steam and electricity demand of their various consumers. The model was coded in AMPL and the execution of the experiments was carried out with CPLEX in communication with a worksheet for the input and output of the data.; The experiments produced made it possible to verify that the economic profits to be gained with the mentioned projects depend on the powerhouse configuration. For example, district heating could produce an associated profit which would vary between 0.3 and 0.9 M{dollar}/year depending on the configuration considered. Also, the results showed that a reduction of the low pressure steam demand of 15% does not produce any profit for an installation with a back-pressure steam turbine. On the other hand, in the current installation this project would produce a 0.8 M{dollar}/year reduction in fuel costs and in an installation with a condensing turbine it would produce revenue from the sale of electricity of approximately 1 M{dollar}/year. Although a priori we suspected that changing a part of the medium pressure steam demand to low pressure could increase the generation of electricity, the results make it possible to reject this assumption in the context of the previous configurations. However, the experiments allowed the identification of another possible configuration involving a backpressure steam turbine combined with a condensing steam turbine. According to the obtained results, this configuration is the most economically profitable because the potential electricity production is the highest. In this case the reduction of the low pressure steam demand and also the change of the medium pressure steam demand to low pressure produce additional profits. The analysis of the seasonal variations showed that they have an important impact on the powerhouse profit and that to neglect them could result in an error of 30%.; The results of the sensitivity analysis showed that the factors which have the most important effect in the powerhouse profit are the biomass cost and the selling price of electricity. This highlights the importance of having a good estimate of these prices in order to calculate the viability of the investments in the powerhouse projects. Concerning the price of the biomass, knowledge of its sources and provisioning limits are critical in order to estimate the benefit of the energy retrofit measures in a precise way. The regression analysis provided functions which permit the study of scenarios different from the data input considered.; In conclusion, a...