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The goal of the study was to develop an optimization methodology combining a cost model, a 2-D heat transfer model, and load variation, executable in a feasible time in a personal computer. The objective function to maximize is the annual net cash flow. For this purpose, the cogeneration plant performance is determined at different load points as a function of the condenser performance using IPSEpro process simulation software. This data is then used to implement the calculation process to obtain the objective function value. Due to the computationally heavy heat transfer model, and each objective function evaluation requiring multiple runs, one per load point, improving optimizer performance was given particular attention. A novel hybridization of cuckoo search and a greedy differential evolution strategy was created for this; the new algorithm is shown to perform better than either of its parent algorithms or other benchmarks, finding optimal solution reliably, and within approximately half the number of function evaluations as required by the parent algorithms.

Finland has the greatest forest cover of European countries and thus considerable raw material potential for wood pellet market development. Wood pellet production and consumption volumes in the country have increased steadily during the last decades. The aim of this paper is to present an overview of the current status of the Finnish wood pellet business and discuss the main opportunities and challenges facing future development of the industry. The paper collects and revises data on the Finnish wood pellet market based on the results of a survey of nearly 60 wood pellet experts. The results show that neglect of policy support and a lack of suitable regulation are the key factors inhibiting Finnish wood pellet industry development. Currently, wood pellets are not economically competitive with other fuels. However, Finnish wood pellet markets seem promising if challenges such as high raw material costs and competitiveness with other fuels, especially for household users, are addressed. The country has the potential to become a more important producer and consumer on European wood pellet markets if effective policy support and a suitable regulatory framework are formulated. Post-print / final draft

Wood-fired combined heat and power (CHP) plants are a proven technology for producing domestic, carbon-neutral heat and power in Nordic countries. One drawback of CHP plants is the low capacity factors due to varying heat loads. In the current economic environment, uncertainty over energy prices creates also uncertainty over investment profitability. Hydrothermal carbonization (HTC) is a promising thermochemical conversion technology for producing an improved, more versatile wood-based fuel. Integrating HTC with a CHP plant allows simplifying the HTC process and extending the CHP plant operating time. An integrated polygeneration plant producing three energy products is also less sensitive to price changes in any one product. This study compares three integration cases chosen from the previous paper, and the case of separate stand-alone plants. The best economic performance is obtained using pressurized hot water from the CHP plant boiler drum as HTC process water. This has the poorest efficiency, but allows the greatest cost reduction in the HTC process and longest CHP plant operating time. The result demonstrates the suitability of CHP plants for integration with a HTC process, and the importance of economic and operational analysis considering annual load variations in sufficient detail.