Reduction of Organic Emissions by Using a Multistage Drying System for Wood-Based Biomasses

Spets, Jukka-Pekka; Ahtila, Pekka

doi:10.1081/drt-120030000

Cited by 16 publications

(10 citation statements)

References 16 publications

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“…Product and air flow in the same direction; exhaust air from stage 1 reheated and used in stage 2. [9] The dryer inlet air temperature per-stage is set equal to that of the optimal sorption system for equivalence. Also, the results are compared with those for two-stage adsorption drying systems with the same adsorbent in each stage: zeolite-zeolite, alumina-alumina, and silica-silica.…”

Section: Comparison With Existing Alternative Systemsmentioning

confidence: 99%

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A Mixed Integer Formulation for Energy-efficient Multistage Adsorption Dryer Design

Atuonwu

Straten

Deventer³

et al. 2012

Drying Technology

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This work presents a mixed integer nonlinear programming (MINLP) formulation for the design of energy-efficient multistage adsorption dryers within constraints on product temperature and moisture content. Apart from optimizing temperatures and flows, the aim is to select the most efficient adsorbent per stage and product to air flow configuration. Superstructure models consisting of commonly used adsorbents such as zeolite, alumina, and silica-gel are developed and optimized for a two-stage, low-temperature, adsorption drying system. Results show that the optimal configuration is a hybrid system with zeolite as the first-stage adsorbent and silica-gel as the second-stage adsorbent in counter-current flow between drying air and product. A specific energy consumption of 2,275 kJ/kg is achieved, which reduces to 1,730 kJ/kg with heat recovery by a heat exchanger. Compared to a conventional two-stage dryer at the same drying temperature, this represents a 59% reduction in energy consumption. The optimal system ensures the exhaust air temperature of the first-stage regenerator is high enough to regenerate the secondstage adsorbent so no utility energy is spent in the second stage. A higher second-stage adsorbent wheel speed favors energy performance as it becomes optimized for energy recovery while the first is optimized for dehumidification. Although this work considers three candidate adsorbents in a two-stage system, the same reasoning can be applied to systems with more stages and adsorbents. The developed superstructure optimization methodology can, by extension, be applied to optimize multistage hybrid drying systems in general for any objective. INTRODUCTIONDrying is an important unit operation applied in a wide range of process industries. It is an energy-intensive process that accounts for as much as 15% of industrial energy consumption [1] and thus is a major contributor to greenhouse gas emissions and the associated negative environmental impacts. [2] For convective dryers, which constitute over 85% of all industrial dryers, [3] the energy-related operating costs amount to about five times the capital costs. [2]

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Section: Comparison With Existing Alternative Systemsmentioning

confidence: 99%

“…[9] In conventional multistage drying systems, the exhaust air from the earlier drying stages is reheated (to regain drying capacity lost due to moisture uptake) and reused in subsequent stages. The inlet air temperature per stage required to achieve the same moisture removal from a product is reduced as compared to a single stage dryer.…”

Section: Introductionmentioning

confidence: 99%

A Mixed Integer Formulation for Energy-efficient Multistage Adsorption Dryer Design

Atuonwu

Straten

Deventer³

et al. 2012

Drying Technology

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“…The potential of increasing drying efficiency with the development of two-, three-or multi-stage dryers has been shown in earlier studies. These studies focus on the use of lower drying temperatures and exhaust air recycling systems, as well as adapting drying techniques to the drying rate, for example, a technique for drying below the fiber saturation point [10,[15][16][17][18][19][20]. Frodeson et al (2013) have shown, based on industrial data, that pellet plants have the potential to increase their drying capacity as well as their energy efficiency by implementing a two-step drying technique [17].…”

Section: Introductionmentioning

confidence: 99%

The Potential for a Pellet Plant to Become a Biorefinery

et al. 2019

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The use of bioenergy has increased globally in recent years, as has the utilization of biomaterials for various new product solutions through various biorefinery concepts. In this study, we introduce the concept of using a mechanical dewatering press in combination with thermal drying in a pellet plant. The purpose of the study is to increase the understanding of the effects a mechanical dewatering press has in a pellet production chain and investigate whether a pellet plant could thus become a biorefinery. The evaluations in this study are based on industrial data and initial tests at the university. The results show that the concept of using the mechanical dewatering press together with a packed moving bed dryer reduces energy use by 50%, compared to using only a packed moving bed dryer. The press water could be used as a raw material for biogas, bioplastics, and biohydrogen. Hence, this study points out the possibilities of a pellet plant increasing the efficiency of the drying step, while moving towards becoming a biorefinery.

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“…The excess steam condensate will, on the other hand, need wastewater treatment as it can contain terpenes, fatty acids, formaldehyde and other types of contamination, depending on type of biomass and drying conditions. These organic compounds are released from the biomass as it is heated [7] [8] [9] [10] [4]. A further benefit of steam drying is that since there is no oxygen present in the dryer no oxidation can occur, this in turn leads to a minimal risk of ignition during operation [6].…”

Section: Introductionmentioning

confidence: 99%

Energy performance of an industrial superheated steam heat pump flash dryer for drying of bio-fuel

Renström

Johansson-Cider

Brunzell

2018

Proceedings of 21th International Drying Symposium

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Drying is an energy demanding industrial process and methods for reducing the energy consumption of drying is of interest to industry as well as society. This article presents the drying system of a biofuel factory. Steam is used as the refrigerant. Superheated steam is used as drying gas in a flash dryer with 28.8 tons/h dewatering capacity. The system includes an energy recovering water heat pump that receives its heat from the excess drying steam and heats the dryer. The SMER of the drying process ranges between 3 and 4 and the COP of the heat pump process ranges between 4 and 5.5 during one production season of peat drying. Variations in performance can be explained by variations in inlet moisture content and production rate. The example of this drying system shows the feasibility of drying in superheated steam, heat pump drying and water as refrigerant in high-temperature heat pumps.

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Reduction of Organic Emissions by Using a Multistage Drying System for Wood-Based Biomasses

Cited by 16 publications

References 16 publications

A Mixed Integer Formulation for Energy-efficient Multistage Adsorption Dryer Design

A Mixed Integer Formulation for Energy-efficient Multistage Adsorption Dryer Design

The Potential for a Pellet Plant to Become a Biorefinery

Energy performance of an industrial superheated steam heat pump flash dryer for drying of bio-fuel

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