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The article aims to find a solution for the energy efficiency improvements in variable speed-controlled parallel pumping systems with lesser initial data and without additional flow metering and start-up measurements. This paper introduces a new control strategy for variable speed-controlled parallel pumps based on flow rate estimation and pump operation analysis utilizing variable speed drives. The energy-saving potential of the new control strategy is studied with simulations and laboratory measurements. The energy consumption of the parallel pumps using the new control strategy is compared with the traditional rotational speed control strategy of parallel pumps. The benefit of the new control strategy is the opportunity to operate variable speed-controlled parallel pumps in a region which suggests improved energy efficiency and lower risk of mechanical failure of the controlled pumps compared with traditional control. The article concludes by discussing the implications of the findings for different applications and varying system conditions.

Sustainability and energy efficiency have become important factors for many industrial processes, including chemical pulping. Recently complex back-end heat recovery solutions have been applied to biomass-fired boilers, lowering stack temperatures and recovering some of the latent heat of the moisture by condensation. Modern kraft recovery boiler flue gas offers still unutilized heat recovery possibilities. Scrubbers have been used, but the focus has been on gas cleaning; heat recovery implementations remain simple. The goal of this study is to evaluate the potential to increase the power generation and efficiency of chemical pulping by improved back-end heat recovery from the recovery boiler. Different configurations of heat recovery schemes and different heat sink options are considered, including heat pumps. IPSEpro simulation software is used to model the boiler and steam cycle of a modern Nordic pulp mill. When heat pumps are used to upgrade some of the recovered low-grade heat, up to +23 MW gross and +16.7 MW net power generation increase was observed when the whole pulp mill in addition to the boiler and steam cycle is considered as heat consumer. Combustion air humidification proved to yield a benefit only when assuming the largest heat sink scenario for the pulp mill.

The forest industry is a significant emitter of CO2 and thus it needs to transform toward​ a more sustainable operation in order to contribute to tackling climate change. This paper looks at the progress, tools, possibilities, and barriers of Finnish and Swedish forest industries in achieving deep decarbonization. Finland and Sweden have set ambitious national targets to reach net negative greenhouse gas emissions. The role of the forest industry in reaching national targets in these countries remains unclear even if significant fossil CO2 emission reduction and efficiency improvement has occurred. If the forest industries in these countries fulfill their planned future visions, their contribution to meeting the targets will be substantial. This study identified the largest CO2 emitting sectors in the forest industry. They are for both countries, arranged by size, transport including non-road mobile machinery, on-site energy production, fossil fuel use in processes (lime kilns and dryers), and purchased electricity. Viable decarbonization measures exist for key fossil CO2 emissions sources, but several technical, economic, and political barriers are hindering their implementation. Fuel switching from fossil energy sources to bio-based alternatives is the main tool in the decarbonization of the forest sector in both countries, but also electrification of e.g. transport, provides emission reduction opportunities. The forest industry has a high and sustainable potential to become carbon-negative by investing in bioenergy with carbon capture and storage (BECCS) but achieving net-zero emissions might not be realistic without changes in policies and suitable incentives.

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.

Abstract Chemical quantitative characterization of biomass is relevant for waste to energy recovery technologies. In the present work, selected agroindustry solid residues from coffee crops – parchment and coffee shrub, i.e., stem, branches and leaves – were characterized. Properties such proximate, ultimate and biochemical composition, energy content, and thermogravimetric analysis, were evaluated. Results showed high values of higher heating value and volatile matter content. The silica contents are small for all samples. Additionally, the high content of extractives and lignin, reveal that these residual biomasses are more suitable for charcoal than cellulose pulp production. The extensive residue characterization provided valuable data that helped in outcome of the evaluation of different conversion technologies as being an environmentally friendly alternative, contributing to sustainable, reliable, carbon-neutral form of modern energy and upgrade the large quantity of waste generated by the coffee industry into energetically valued residues, by improving their management.