Henrik Holmberg

• D.Sc. (Tech)
• Professor (Associate) at Aalto University

Thermal energy storage (TES) offers a practical solution for reducing industrial operation costs by load-shifting heat demands within industrial processes. In the integrated Thermomechanical pulping process, TES systems within the Energy Hub can provide heat for the paper machine, aiming to minimize electricity costs during peak hours. This strateg...

Preface Novel high-performance veneer products by effective drying and nano-coating (VERYCOAT) was performed in 2019-2022. The project was funded by Business Finland with collaboration with industry partners. The research partners were VTT and Aalto University's departments Bioproduct and Biosystems and machine design. The industry partners are sho...

Thermo-mechanical Pulping (TMP) is one of the most energy-intensive industries where most of the electrical energy is consumed in the refining process. This paper proposes the energy-saving refining optimization strategy by integrating the machine learning algorithm and heuristic optimization method. First, refining specific energy consumption (RSE...

Data from two thermo-mechanical pulp mills are collected to simulate the refining process using deep learning. A multilayer perceptron neural network is utilized for pattern recognition of the refining variables. Results show the impressive capability of artificial intelligence methods in refining energy simulation so that the correlation coefficie...

A refining model is developed to analyses the refining process’s energy efficiency based on the refining variables. A simulation model is obtained for longer-term refining energy analysis by further developing the MATLAB Thermo-Mechanical Pulping Simulink toolbox. This model is utilized to predict two essential variables for refining energy efficie...

Thermo-mechanical pulping (TMP) as a subdivision of the refiner-based mechanical pulping is one of the most energy-intensive processes in which the main procedure is carried out during the refining process. In this study, a simulation model is developed to estimate the energy efficiency of the refining process for the long-term period. A Simulation...

In the pulping industry, thermo-mechanical pulping (TMP) as a subdivision of the refiner-based mechanical pulping is one of the most energy-intensive processes where the core of the process is attributed to the refining process. In this study, to simulate the refining unit of the TMP process under different operational states, the idea of machine l...

Soot sludge is a waste stream formed in the fuel oil gasification of formic acid and hydrogen peroxide production. The soot sludge has a high moisture content (95%) and is presently combusted with heavy fuel oil in order to dispose of the sludge. Experimental tests earlier conducted by the authors have shown that the sludge can be convectively drie...

In this article, we show how a revised district heat network control strategy can be employed to utilize the storage capabilities of the network. An optimization problem is formulated, with minimum operating costs as the objective. Allowing the district heat supply temperature to vary freely within given boundaries results in approximately 2% reduc...

This study examines the energy and mass balances of algae cultivation and different post-processing pathways. Flue gases and excess heat from a combined heat and power (CHP) plant are used in algae cultivation, with nutrients from municipal wastewater. In the studied pathways, algae are cultivated in open ponds and photobioreactors with or without...

Drying woody biomass holds the potential to improve the energy efficiency of certain processes, such as in CHP plants. Drying can also be a necessary unit process in several energy conversion processes (e.g. in biomass gasification). Belt dryers are typically used for drying when low temperature air ( 100–110 °C) is used. This article aims to produ...

In recirculating aquaculture, a bacterial biofilter is applied to convert ammonium, excreted by the fish, to the non-toxic nitrate. Unfortunately, nitrifying bacteria produce off-flavor compounds that lower fish quality. We investigated, by calculations and estimations, possibilities to replace the biofilter by autotrophic organisms that incorporat...

Traditional pulp and paper industry is in transition due to increased competition and changes in consumption habits. Advanced biorefining is seen as one option to create new business opportunities. This article presents a microalgae-utilizing biorefinery which is integrated into a traditional pulp and paper mill and which produces high-value algal...

This study examines energy and mass balances of algae cultivation and different post-processing pathways. Flue gases and excess heat from a combined heat and power (CHP) plant are used in algae cultivation, alongside with nutrients from municipal wastewaters. In the studied cases, algae are cultivated in open ponds and photobioreactors with or with...

Soot sludge is formed in the production of formic acid. Currently, this waste is combusted together with heavy fuel oil in a boiler. The current theoretical lower heating value of the sludge is − 23.8 MJ/kgd.b.. Drying of sludge increases the heating value, and decreases oil use. Drying of pure sludge in a fixed bed is impossible in practice and th...

The European Union's goal is to increase the share of renewable energy sources to 20 per cent and that of liquid biofuels for transport to at least 10 per cent by 2020. Liquid biofuels for transport are, for example, biodiesel and bioethanol. Their use is not assumed to increase CO2-emissions in the atmosphere. However, production processes of tran...

Drying of wood chips at a power plant site increases the lower heating value and decreases composting and dry matter losses in long-term storage. In this study, experimentally measured drying curves for wood chips are produced to study the drying kinetics of the chips. Drying curves have been used to assess whether or not wood chip drying in a batc...

20% of the Finnish district heating (DH) power plant fuels are wood-based and the share is increasing. The wood fuel demand probably exceeds the potential supply in the future. The wood fuel drying with waste heat is one profitable opportunity to gain more wood fuel. If the drying energy can be produced with lower primary energy use than combusting...

In a combined heat and power plant (CHP plant), heat and power are produced simultaneously in the same power plant process. The CHP technology reduces total fuel consumption compared to a situation where heat and electricity are produced separately. For condensing power plants the exergy loss is usually calculated by multiplying the entropy generat...

In a tubular photobioreactor, a degassing column is often used for oxygen removal and carbon dioxide addition. The column may limit growth because the conditions are optimal only right after the degassing zone. In the present study, we tested continuous oxygen removal and nutrient delivery by placing a porous membrane tube inside a photobioreactor...

In this study biomass-based energy production was introduced to an urban city area of Helsinki, Finland. The study compared two cases in integration with a municipality: (1) biomass fuelled small-scale CHP (combined heat and power)-plant and (2) a biorefinery. The comparison was made according to primary energy consumption, primary energy factors,...

The biorefinery concept produces high value products such as omega 3 fatty acids, bio-fertilisers, biomethane also heat and electricity. The goal of this paper is to evaluate the economic and technological factors of a microalgal biorefinery when it’s integrated into an existing pulp and paper mill in Finland. Energy efficiency and the economic fac...

A problem arises in integrated production plants, where several products are produced simultaneously, when different plants are evaluated in respect to their own energy efficiency indicators. Energy efficiency is measured as the ratio of energy input to products produced. In a mill that produces pulp and paper products, heat, electricity, and liqui...

The improvement of energy efficiency is seen as one of the most promising measures for reducing global emissions and dependence on fossil fuels. One opportunity for boosting the energy efficiency is to enhance the utilization of excess heat. The excess heat means waste energy which is not exploited in any manner. Most of the excess heat is generate...

This paper studies allocation of fuel costs and CO2-emissions to heat and power in a CHP plant producing heat to an integrated pulp and paper mill and electricity to the liberalized electricity markets (or to the mill by the market price). The CHP plant and the mill are considered to be two separate economical units and both the mill and the CHP pl...

This paper introduces a new type of contact drying method that has been developed at Aalto University in Finland. The paper also presents experimental results from tests with the new drying method. The drying system consists of a hot upper plate, a cold bottom plate, a vacuum inside the drying chamber and a mechanical press. An experimental drying...

In complicated systems, such as a highly integrated industrial plant with its own energy production, estimating the value of energy conservation is not so straightforward. Often, heat is priced using different kinds of methods for allocating the fuel cost to heat and electricity. However, there is no consistent way to valuate the process steam in i...

Bark has a heterogeneous particle size distribution and an irregular particle shape. For this reason, drying models usually give only rough estimations of the drying rate, and drying tests are needed to define the drying rate precisely. In this study, normal drying curves and a characteristic drying curve are experimentally determined for bark that...

A problem arises in integrated production plants, where several products are produced simultaneously, when different plants are evaluated in respect to their own energy efficiency indicators. Energy efficiency is measured as the ratio of energy input to products produced. In a mill that produces pulp and paper products, heat, electricity, and liqui...

All real processes generate entropy and the power/exergy loss is usually determined by means of the Gouy-Stodola law. If the system only exchanges heat at the environmental temperature, the Gouy-Stodola law gives the correct loss of power. However, most industrial processes exchange heat at higher or lower temperatures than the actual environmental...

All real processes generate entropy and the power/exergy loss is usually determined by means of the Gouy-Stodola law. If the system only exchanges heat at the environmental temperature, the Gouy-Stodola law gives the correct power loss. However, most industrial processes exchange heat at higher or lower temperatures than the actual environmental te...

Energy efficiency studies are normally carried out using the specific energy consumption, SEC, which describes the ratio between the total energy used and a useful output of the process, usually measured in physical units such as tons of product (for example GJ/t) (EC, 2008). The total energy used is the difference between the energy inputs and the...

In Book: Energy Use. Visions and Technology Opportunities in Finland. 2007. ISBN 978-951-37-4742-8

The primary aim of this article is to present a simulation model for a bark dryer integrated into a combined heat and power plant. The same model can be used for the model-based control of the dryer. The secondary aim is to evaluate how useful the control is from an economic point of view. Results show that the final fuel moisture content can be st...

The calculation of heat consumption is based on the First Law and it gives quantitative information about the energy used in drying. However, it does not pay any attention to the quality of the energy used in drying. To take into account the quality of the energy, attention must be paid to the Second Law, too. Especially in those cases where the en...

The moisture content of wood-based biofuels (bark, forest residues, and waste wood) used by the forest industry typically varies between 50 and -%. The high moisture content considerably decreases the power production of the power plant. The main target of this paper is to compare the drying costs of two alternative drying systems: multi-stage dryi...

Drying of solid particles is generally divided into three periods: a short initial heating period, a constant drying rate period, and a falling drying rate period. Drying in a fixed under various drying conditions was experimentally studied. The main goals of the measurements were to calculate the heat transfer coefficient based on the measured val...

Bio fuel plays an important role in the energy production of the forest industry. The initial moisture of the fuel typically varies between 50 - 63 w-%. A multi stage drying concept has been developed for the drying of wet bio fuel. To adjust the temperature levels in the multi stage drying system there must be a simple and fast method to define th...

At Helsinki University of Technology, a new kind of contact drying method for veneer has been developed. The drying system consists of the hot upper plate, cold bottom plate, vacuum inside the drying chamber and a mechanical press. The goal of the paper is to present experimental results of the drying time of the veneer when the contact drying meth...

This thesis presents the results of a research project in which the enhancement of the CHP production by means of biofuel drying at an integrated pulp and paper mill has been explored. Instead of high temperature flue gas drying the use of low-temperature secondary heat as drying energy has been studied. The drying system considered in this thesis...