!

Torrefaction Technology for Biomass Pretreatment Process

นายนิมิต นิพทัธธ์รรมกลุ ผูป้ระสานงานโครงการ

2

Overview

- Global Warming - Decrease Power Generation of Nuclear Power Plant - 2020 Policy of EU

- Logistic cost depends on diesel price.

Wood Pellet Cost Distribution

32%

35%

33%Raw Mat.ProcessLogistic

Renewables 2013 Global Status Report

Wood Pellet Association of Canada

3

Overview

an interesting option to improve biomass properties to getmore uniformity. Densification by means of pelletization is

considered to be a proven technology to improve biomassproperties for its conversion into heat and power. Pelletsfrom torrefied biomass are attractive with respect to heatingvalue, grindability, combustion nature, storage, transportand handling which make them attractive as replacementfor coal in existing power stations. Energy research CentreNetherlands (ECN) [20,26,27] developed the so-called BO2

process (in initial literature also referred to as the TOPprocess) in which pellets are processed with torrefiedbiomass. Compared to non-torrefied pellets BO2 pellets showbetter hydrophobic behavior, strength and higher density.

The main characteristics of different pellets are shown inTable 3 [27].

The BO2 process combines torrefaction and pelletizationand according to Fig. 14 torrefaction is introduced into thesystem as a unit after drying and before size reduction incomparison to a typical biomass pelletization process [20]. Thetorrefaction process consists of several steps such as drying,torrefaction and cooling. The pelletization process comprisesthe steps of drying, size reduction, steam pre-conditioning,densification and cooling. Combining the torrefaction andpelletization process leads to the introduction of torrefaction

in the pelletization step and the removal of the steam pre-

conditioning from the pelletization step.Currently ECN operates a 50e100 kg/h pilot plant where

biomass pellets are produced from a broad range of biomassstreams, such as wood chips, agricultural residues andvarious residues from the food and feed processing industry[51]. These so-called 2nd generation pellets have superiorproperties in terms of high energy density (1.5e2! conven-tional pellets), excellent grindability and water resistantnature (eliminating/reducing biological degradation andspontaneous heating, and enabling outdoor storage).

4.2. Torrefaction and gasification

Torrefaction is mainly used as pre-treatment technology toupgrade the biomass to a higher quality biofuel. This biofuelcan be used in other conversion methods to produce bio-energy. The main application of torrefied biomass (wood) isas a renewable fuel for combustion or gasification. Prins et al.[2] studied the possibility of more efficient biomass gasifica-tion via torrefaction in different systems; air-blown circu-lating fluidized bed gasification of wood, wood torrefaction

and circulating fluidized bed gasification of torrefied wood,and wood torrefaction integrated with entrained flow gasifi-cation of torrefied wood.

Themain idea behind combining biomass torrefaction andgasification is that the heat produced during gasification in theform of steam is recovered for application in the torrefactionstage. The advantages of torrefaction as a pre-treatment priorto gasification in three concepts are compared with eachother. In Fig. 15aec [2] three different gasification schemes arepresented.

" Fig. 15a shows biomass (wood) gasification in circulatingfluidized bed (CFB). The CFB gasifier is operated below1000 #C at atmospheric conditions to avoid problems withash softening and melting. Air is used as gasifying medium.The steam is exported at 280 #C at 45 bar.

Table 3 e Properties of wood, torrefied biomass, woodand BO2 pellets [27].

Properties Unit Wood Torrefiedbiomass

Wood pellets TOP pellets

Low High Low High

Moisture %wt 35% 3% 10% 7% 5% 1%LHVNormal MJ/kg 10.5 19.9 15.6 16.2 19.9 21.6Dry MJ/kg 17.7 20.4 17.7 17.7 20.4 22.7Mass

densitykg/m3 550 230 500 650 750 850

Energydensity

GJ/m3 5.8 4.6 7.8 10.5 14.9 18.4

Fig. 14 e Pelletization, torrefaction and TOP process schemes [20].

b i om a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 7 4 8e3 7 6 2 3757

Biomass upgrading by torrefaction for the production of biofuels: A review

4

Torrefaction Technology

Biomass Torrefaction

Torrefaction is used as a pre-treatment step for biomass conversion techniques such as gasification and co-firing. The thermal treatment not only destructs the fibrous structure and tenacity of biomass, but is also known to increase the calorific value. Also after torrefaction the biomass has more hydrophobic characteristics that make storage of torrefied biomass more attractive above non-torrefied biomass, because of the rotting behavior.

Biomass upgrading by torrefaction for the production of biofuels

Torrefaction 250 ˚C

1M 1E

Biomass

0.3M 0.1E

Torrefied Gases

0.7M 0.9E

Torrefied Biomass

1.3 E/M1 E/M

5

Torrefaction Technology

6

Value PropositionsValue Propositions - เชื<อเพลิงชีวมวลความรอ้นสงู

- สามารถเก็บรกัษาไดม้ากกว่า 1ปี

- ป้องกนัความชื<นไดดี้

- ตน้ทนุการขนส่งลดลง

- ลดตน้ทนุ Operating Cost

โรงไฟฟ้าถ่านหินแบบ Co–firing

34

Figure 5 total chain costs white pellets versus black pellets More recent studies on the production and logistical costs of torrefied pellets confirm the fact that

higher conversion costs on the side of torrefied pellets are almost fully compensated by lower logistic

and handling costs - especially when looking at a supply chain including ocean shipping. In the case of

the KEMA study16 (Figure 5) these were 8.6 €/GJ for white Pellets and 8.8 €/GJ delivered for torrefied

pellets.

Figure 6 cost comparison wood pellets versus torrefied wood pellets 16 KEMA, 2012, presentation

US

$/G

J wood pellet torrefied pellet

IEA bioenergy task 40 Possible effect of torrefaction on biomass trade (IEA bioenergy)

1 ton

0.75 ton

1.4 m3

0.68 m3

7

Pretreatment of the biomass using torrefaction is considered the optimum solution since torrefied material, particularly pelletized torrefied wood, is very similar to fossil coal and burns cleaner. Several large research projects are under way to speed up the development of torrefied pellets, both in Canada and Europe. The target is set for large-scale introduction of torrefied pellets around 2014-2015.

8