Experimental Investigation of Mildly Pressurized Torrefaction in Air and Nitrogen

Nhuchhen, Daya Ram; Basu, Prabir

doi:10.1021/ef4022202

Cited by 44 publications

(24 citation statements)

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“…They obtained optimum temperature, particle size and residence time as 290 C, 24 mm and 10 h, respectively. Nhuchhen and Basu (2014) investigated mildly pressurized (200-600 kPa) torrefaction on poplar wood in air and nitrogen in batch reactors with the view to replace nitrogen with air in full-scale industrial setups. They were assisted by the response surface methodology (RSM) method and they developed a correlation to predict mass loss.…”

Section: What We Know From Literaturementioning

confidence: 99%

Biomass torrefaction as an emerging technology to aid in energy production

Mamvura

Danha

2020

Heliyon

116

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Biomass torrefaction has gained widespread attention due to its benefits as a standalone process to improve biomass properties to be at par or similar to those for coal in electricity generation or as a pretreatment step before pyrolysis and gasification processes. It has also found application in other processes like steel production where it is aiming to replace coal or work alongside coal by co-firing the coal with biomass at certain proportions. There have been a lot of papers on biomass torrefaction review, but this paper tried to look at a different angle to show other aspects of torrefaction and how it links to other technologies as well as the chemistry behind it. Overall, the process has seen a big shift in the technology it utilizes, and the hope is that it will make the process more viable and applicable in future.The focus starts from the raw biomass, how it is analysed and the different analysis that are performed to determine relevant information about biomass properties. There are different reactors that are used but to date there is not a preferred one as they have their pros and cons. However, the focus mostly is the process not which reactor to use as they have all not shown any significant differences. The main product of the process, torrefied biomass determines the efficiency and how it can be applied to other technologies. To date, biomass torrefaction is for co-firing with coal for energy generation and as a pretreatment step for pyrolysis and gasification. Due to varying types of biomass in different countries, the technology has not yet reached its full potential, but the hope is it will with calls for use of renewable sources of energy.Other areas like modelling torrefaction of biomass have not been looked at in this review. However, the paper sets the foundations for such detailed reviews.

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Section: What We Know From Literaturementioning

confidence: 99%

Biomass torrefaction as an emerging technology to aid in energy production

Mamvura

Danha

2020

Heliyon

116

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“…Experimental mean residence time (in minutes) can be determined using Equation (1). Solids flow rate and holdup were measured experimentally.…”

Section: Measurementsmentioning

confidence: 99%

“…[1] The process of torrefaction has been developed in order to minimize these limitations, thus enhancing biomass fuel qualities and producing an improved solid biomass with properties similar to coal. [2] Torrefaction is a slow heating process that is usually carried out in an inert environment and at atmospheric pressure within a narrow temperature range of 200-300 8C.…”

Section: Introductionmentioning

confidence: 99%

“…The use of biomass resources is often limited by their physical properties, including their high moisture content, low bulk density, and fibrous nature; and their chemical properties, such as their hydrophilic nature, low heating value, and high O/C and H/C ratios . The process of torrefaction has been developed in order to minimize these limitations, thus enhancing biomass fuel qualities and producing an improved solid biomass with properties similar to coal …”

Section: Introductionmentioning

confidence: 99%

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Investigation into mean residence time and filling factor in flighted rotary torrefier

2016

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Torrefaction can upgrade the properties of biomass, making it similar to coal. This study develops an innovative indirectly heated two-stage rotating drum-type torrefier where biomass moves due to the rotation of inclined cylindrical reactors. The rotary reactors consist of three rectangular flights placed axially along the reactor. This paper mainly investigates the mean residence time and filling factor of reactors operated at steady and plug flow conditions. Semi-empirical expressions using dimensionless correction constants for the mean residence time and the filling factor were proposed. Experiments keeping a constant solid flow rate at the dryer inlet were conducted in order to measure filling factor and mean residence time at different angular speeds and inclinations of reactors (dryer and torrefier). Mean residence times of 5.8 min at 8 rpm and 38, and of 27.5 min at 4 rpm and 18 were found in the dryer (diameter: 64 mm, length: 610 mm), whereas they were 4.7 and 21.4 min in the torrefier (diameter: 100 mm, length: 762 mm) at respective operating conditions. Filling factors of 3.0 % at 8 rpm and 38, and 14.3 % at 4 rpm and 18 were found in the dryer, whereas they were 0.8 % and 3.6 % in the torrefier at the corresponding angular speed and inclination. Measured and predicted mean residence times were also compared and validated against those of other investigators. The proposed expressions, which include the effects of different operating and geometrical parameters, have strong predictive power and may be useful in scaling-up a rotary torrefier.

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“…For instance, we confirmed that an elevated-pressure of 1.0 MPa induces selfheating at below 100˚C, while atmospheric pressure (0.1 MPa) does not [20], indicating that ambient pressure is highly relevant to the initiating temperature of self-heating. In addition, a few studies have reported that torrefaction under elevated pressure improves fuel properties such as fuel ratio and energy density [21,22]. These previous studies imply that the ambient pressure in self-heating torrefaction is associated with the chemical properties of the resulting char as well as the torrefaction temperature.…”

Section: Introductionmentioning

confidence: 98%

Role of ambient pressure in self-heating torrefaction of dairy cattle manure

et al. 2020

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This paper describes the role of ambient pressure in self-heating torrefaction of livestock manure. We explored the initiating temperatures required to cause self-heating of wet dairy cattle manure at different ambient pressures (0.1, 0.4, 0.7, and 1.0 MPa). Then, we conducted proximate, elemental, and calorific analyses of biochar torrefied at 210, 250, and 290˚C. The results showed that self-heating was induced at 155˚C or higher for 0.1 MPa and at 115˚C or lower for 0.4 MPa or higher. The decrease of the initiating temperature at elevated pressure was due not only to more oxygen, but also to the retention of moisture that can promote chemical oxidation of manure. Biochar yields decreased with increasing torrefaction temperature and pressure, and the yield difference at 0.1 and 1.0 MPa was more substantial at lower temperatures: a 29.8, 16.4, and 9.4% difference at 210, 250, and 290˚C, respectively. Proximate and elemental analyses showed that elevated pressure promotes devolatilization, deoxygenation, and coalification compared to atmospheric pressure; its impact, however, was less at higher temperatures as the torrefaction temperature became more dominant. Calorific analysis revealed that elevated pressure can increase the higher heating value (HHV) on a dry and ash-free basis at 210˚C because of the increase in carbon content, but its impact is limited at 250 and 290˚C. Meanwhile, the HHV on a dry basis exhibited the opposite trend due primarily to an enlargement of ash content. The present study revealed that ambient pressure considerably affects the initiating temperature of self-heating and the chemical properties of biochar at a low torrefaction temperature.

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Experimental Investigation of Mildly Pressurized Torrefaction in Air and Nitrogen

Cited by 44 publications

References 43 publications

Biomass torrefaction as an emerging technology to aid in energy production

Biomass torrefaction as an emerging technology to aid in energy production

Investigation into mean residence time and filling factor in flighted rotary torrefier

Role of ambient pressure in self-heating torrefaction of dairy cattle manure

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