Impact of process conditions on the density and durability of wheat, oat, canola, and barley straw briquettes

Energy Science & Engineering

2015

The quality and specific energy consumption (SEC) of the biomass pellets produced depend upon pelleting process conditions. The present study includes understanding the effect of feedstock moisture in the range of 28-38% (wet basis [w.b.]) and preheating in the range of 30-110°C at two die speeds of 40 and 60 Hz on the physical properties and SEC. A flat die pellet mill fitted with a 6 mm die was used in the present study. The physical properties of pellets such as moisture content, unit, bulk and tapped density, durability, and expansion ratio and SEC of the pelleting process are measured. The results indicate that the pellets produced have durability values in the range of 87-98%, and unit bulk and tapped density in the range of 670-1100, 375-575, and 420-620 kg/m 3 . Increasing the feedstock moisture content from 33% to 38% (w.b) decreased the unit, bulk and tapped density by about 30-40%. Increasing feedstock moisture content increased the expansion ratio and decreased the density values. A higher feedstock moisture content of 38% (w.b.) and higher preheating temperature of 110°C resulted in lower density and a higher expansion ratio, which can be attributed to flash off of moisture as the material extrudes out of the die. The SEC was in the range of 75-275 kWh/ton. Higher feedstock moisture content of 38% (w.b.) and a lower die speed of 40 Hz increased the SEC, whereas lower to medium preheating temperature (30-70°C), medium feedstock moisture content of 33% (w.b.), and a higher die speed of 60 Hz minimized the SEC to <100 kWh/ton.

Section: Resultsmentioning

confidence: 99%

“…Many researchers have worked on pelleting and briquetting of biomass by adjusting feedstock moisture content in the range of 7–23% (w.b.) . Some of the recent research articles published in 2014 have reported on pelleting raw, chemically and thermally pretreated biomass at moisture content >23% (w.b.)…”

Section: Introductionmentioning

confidence: 99%

High moisture corn stover pelleting in a flat die pellet mill fitted with a 6 mm die: physical properties and specific energy consumption

Energy Science & Engineering

2015

“…One major reason for different concentrations observed for different raw and thermally-pretreated biomass feedstock can be different chemical composition (i.e., woody biomass has higher fatty acids and lignin compared to herbaceous biomass). On the other hand, herbaceous biomasses are lower in lignin and free fatty acids [39,40]. Further research is needed to understand the chemistry behind different quantities of off-gas emissions from different biomass feedstocks.…”

Section: Discussionmentioning

confidence: 99%

Analysis on Storage Off-Gas Emissions from Woody, Herbaceous, and Torrefied Biomass

Lim

et al. 2015

Energies

Wood chips, torrefied wood chips, ground switchgrass, and wood pellets were tested for off-gas emissions during storage. Storage canisters with gas-collection ports were used to conduct experiments at room temperature of 20 °C and in a laboratory oven set at 40 °C . Commercially-produced wood pellets yielded the highest carbon monoxide (CO) emissions at both 20 and 40 °C (1600 and 13,000 ppmv), whereas torrefied wood chips emitted the lowest of about <200 and <2000 ppmv. Carbon dioxide (CO2) emissions from wood pellets were 3000 ppmv and 42,000 ppmv, whereas torrefied wood chips registered at about 2000 and 25,000 ppmv, at 20 and 40 °C at the end of 11 days of storage. CO emission factors (milligrams per kilogram of biomass) calculated were lowest for ground switchgrass and torrefied wood chips (2.68 and 4.86 mg/kg) whereas wood pellets had the highest CO of OPEN ACCESSEnergies 2015, 8 1746 about 10.60 mg/kg, respectively, at 40 °C after 11 days of storage. In the case of CO2, wood pellets recorded the lowest value of 55.46 mg/kg, whereas switchgrass recorded the highest value of 318.72 mg/kg. This study concludes that CO emission factor is highest for wood pellets, CO2 is highest for switchgrass and CH4 is negligible for all feedstocks except for wood pellets, which is about 0.374 mg/kg at the end of 11-day storage at 40 °C.

“…In lignocellulosic biomass, the presence of lignin within plant material helps to form pellets without adding any binders 18 . Woody biomass has higher lignin content (29-33%) when compared to a herbaceous biomass, which typically consists of 12-16% lignin 4,19 . At lower feedstock moisture contents of about 10-12% (w.b.…”

Section: Introductionmentioning

confidence: 99%

Method to Produce Durable Pellets at Lower Energy Consumption Using High Moisture Corn Stover and a Corn Starch Binder in a Flat Die Pellet Mill

Conner

Hoover

2016

JoVE

A major challenge in the production of pellets is the high cost associated with drying biomass from 30 to 10% (w.b.) moisture content. At Idaho National Laboratory, a high-moisture pelleting process was developed to reduce the drying cost. In this process the biomass pellets are produced at higher feedstock moisture contents than conventional methods, and the high moisture pellets produced are further dried in energy efficient dryers. This process helps to reduce the feedstock moisture content by about 5-10% during pelleting, which is mainly due to frictional heat developed in the die. The objective of this research was to explore how binder addition influences the pellet quality and energy consumption of the high-moisture pelleting process in a flat die pellet mill. In the present study, raw corn stover was pelleted at moistures of 33, 36, and 39% (w.b.) by addition of 0, 2, and 4% pure corn starch. The partially dried pellets produced were further dried in a laboratory oven at 70 °C for 3-4 hr to lower the pellet moisture to less than 9% (w.b.). The high moisture and dried pellets were evaluated for their physical properties, such as bulk density and durability. The results indicated that increasing the binder percentage to 4% improved pellet durability and reduced the specific energy consumption by 20-40% compared to pellets with no binder. At higher binder addition (4%), the reduction in feedstock moisture during pelleting was <4%, whereas the reduction was about 7-8% without the binder. With 4% binder and 33% (w.b.) feedstock moisture content, the bulk density and durability values observed of the dried pellets were >510 kg/m 3 and >98%, respectively, and the percent fine particles generated was reduced to <3%.