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Abstract Mathematical models of circulating fluidized bed (CFB) combustion systems vary from simple lumped models to full-scale 3D models with multi-phase flow fields. Models help to predict the behavior of the boiler under new operating conditions and to understand the underlying phenomena. Is it more important to make experiments or models? The answer is both. The real values can be assessed with the help of experiments and refined models. Is a complex model always better than a simple one? A simple model can be more easily modified and better adapted to the actual use. A 1,5-dimensional model of a CFB furnace is the simplest possible model that takes into account the most important heat transfer and flow features. Of these solids circulation is the most important factor that determines the amount of heat transfer at the furnace walls. Consequently, regulating the solids circulation is the fundamental means of load control in CFB furnaces. One dimensional model takes into account only the vertical flow direction, but 1,5-dimensional model considers solids circulation inside the furnace as well. The internal circulation is up to 2 times greater than the circulation around the solids separator and return in CFB combustors. 1,5-dimensional model is also called the core-annulus model. The furnace is considered as a cylinder with an annular space around it. The hot solids flow upwards along the cylinder and downwards along the annular space. In this study, a core-annulus model is implemented using a commercial IPSEpro software. The developed model consists of several modules. The mathematical principles of each module is described. The software is also presented briefly. The new model is applied to study the behavior of a large biomass boiler. The model inputs include mass flows of fuel and air, fuel type and parameters regarding the solids amount, size and distribution. In addition to inputs for the design operation, other scenarios are considered such as partial load and burning of different fuels. Strengths and weaknesses of the model are also assessed and pathways of future research are reviewed.

Abstract 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.

International trade in biomass for energy is growing and wood pellets have become a very successful internationally traded bioenergy-based commodity. Russian wood pellets have captured an important share of European markets. The wood pellets are mainly transported to European markets by sea. The paper addresses challenges facing wood pellet logistics in Northwest Russia, through the ports of St. Petersburg, Vyborg, and Ust-Luga, focusing on options for seaborne transportation of pellets from producer to consumer from the economic, environmental and regulatory perspectives. The study shows that seaborne transportation of Russian wood pellets faces many constraints and without improvements in all stages of the wood pellet transportation chain through Northwest Russian seaports, the future for Russian wood pellet exports to Europe does not seem promising from the economic and environmental perspectives. Optimal logistics-related decisions require analysis of each specific situation, with detailed study of the investment and production capacities of the individual companies involved. Better knowledge of the respective stages of the wood pellet transportation chain and full consideration of the environmental aspects involved will enable effective optimization actions to be taken. This study represents a starting point for further discussion of possible improvements to seaborne wood pellet transportation to European consumers.