a comparatibe study regarding to pellets and briquettes

A Comparatibe Study Regarding to Pellets

and Briquettes Properties of Corn Cobs

Cosmin Spîrchez1, Aurel Lunguleasa2

Abstract

This paper aims to determine the physical properties (moisture content, density) and calorific ones (calorific value, ash

content) of pellets and briquettes made of corn. The results obtained indicated a good calorific value for pellets and

briquettes of corn, compared to wood. The biomass is a renewable energetic source by the fact that, it increases year by year, it is widely spread worldwide and it has low costs in comparison to the fossil fuels. The final conclusion of the paper

is that vegetable biomass is recognized due to energetic properties. The biomass represents a renewable source of energy.

This does not contribute to the problem of environment changing, because it recycles the carbon dioxide in the atmosphere. A general conclusion rise whole from the paper, respectively the vegetable biomass is a renewable material and briquettes

from it remains the best option of the combustible materials.

Keywords: ash content, briquettes, calorific value, pellets

1. INTRODUCTION

Biomass is a renewable energy source, by means of the fact that it grows year after year, it is widely spread

throughout the world and it incurs low costs compared to fossil fuels. Biomass resources, from which

combustion material is produced, can include waste resulting from the production of agriculture grains,

municipal waste, animal waste. Biomass is one of the forms of renewable energy sources which can be

converted into solid, liquid or gas energy fuel and which can generate energy as heat via combustion, as well

as electric energy via conversion processes [1].

Biomass in the form of plant mass is a complex compound and varies from one species to the other. It

includes all the forms of plant matter, that grows on the surface of the earth, in the water or on the water, as

well as substances produced by biological development.

In the last decades, the notion of energy biomass is frequently used for all plant origin matters that have the

potential to contribute to the production of energy.

Biomass contributes within the carbon cycle in nature, through the use of carbon dioxide. Carbon dioxide

participates in the photosynthesis processes during growth, as well as being the component that determines a

complete burn during combustion[4].

1 Corresponding author: Transilvania University of Brasov, Wood Processing and Wooden Products of Design

Department, 500068, Brasov, Romania, [email protected]

2 Transilvania University of Brasov, Wood Processing and Wood Products of Design Department, 500068, Brasov,

Romania, [email protected]

EurAsia Waste Management Symposium, 26-28 October 2020, İstanbul/Türkiye

By means of the elementary processes occurring during photosynthesis, approximately 1% of the energy

received from the Sun is transformed into chemical energy by plants during growth[10]. The solar energy

absorbed by the biomass constitutes the chemical structure of the biomass components.

Biomass is environmentally friendly and represents a neutral energy in terms of carbon dioxide emissions[7].

Carbon dioxide is absorbed by plants during growth and forms a closed circuit, because the quantity of

carbon dioxide that was absorbed by the plants during growth shall be equal to the same quantity which was

eliminated during the processes of complete combustion.

Biomass can be used in the combustion processes and, for the most part, this does not require very large

investments as is the case with hydroelectric energy, solar power, wind power, geothermal energy[9].

Biomass differs from the other forms of renewable energy sources via the fact that it represents a rich type of

raw material that can be transported by means of various conversion processes into gas, liquid or solid fuel.

Biomass is divided in 4 large categories described in the regulatory document SR EN 1496-1ː

- Forestry production: wood, waste from wood processing, sawmill waste, trees, shrub, scrapings,

bark, resulting from exploitation and trimming of forests;

- Waste resulting from agriculture production, from agriculture processes, grain waste, urban organic

waste;

- Energy grains: cultures from short term processing, starch cultures (corn, wheat, barley), sugar

cultures (sugar cane, sugar beet), fodder cultures (grass, alfalfa, clover), oil-seed cultures (sunflower, soy,

saffron);

- Aquatic plants: algae, water herbs, common water hyacinth, cane and reed mace.

2. INTRODUCTION

Establishing the effective density

The actual density has been established according to standard EN 15103.

In order to establish the actual density of the pellets and briquettes made from corn cobs, 20 pieces of each

were taken into consideration. The endings were evened out through buffing so that the surface was smooth.

In order to establish the effective density, the following relation was used:

]/[4 3

2cmg

ld

mef

whereː

m- pellets mass, in g

d- pellets diameter, in cm

l-pellets length, in cm.

Establishing the bulk density of the pellets

In order to establish the bulk density of the pellets, a tapered container was used, having the following

dimensions: R= 45.31 mm, r = 23.435 mm, h = 99.06 mm.

In order to establish the bulk density, the following relation was used:

ρ bulk = 3 m/ h (R2 + r2 + R r) [g/cm3]

Establishing the caloric power

The process for establishing the caloric power for the pellets and briquettes made from corn cobs is almost

similar to that of coal (as solid fuel) and with little differences from that of liquid fuel (gasoline, diesel fuel

etc.) or gas fuel (methane gas, LPG, biogas etc.). Generally, the method for establishing the caloric value is

performed separately for solid fuel (ASTM D3286-96,) than for liquid or gas fuel.

The number of trials required by the regulatory documents and by other researchers is 5,8 or 10 trials

researched through experimental means (ASTM D3286-96, DIN 51900-1 2000). The experiments within the

paper have been performed on 5 samples (DIN 51900-1 2000).

The installation used for determining the caloric power of the pellets made from corn cobs was the

calorimeter with explosive combustion type XRY-1C, manufactured by Shanghai Changji Geological

A comparative study regarding to pellets and briquettes properties of corn cobs

Cosmin Spirchez, Aurel Lunguleasa

Instrument Co., in China. Before performing the actual trial, the ranging of the calorimetric bomb with

benzoic acid was performed, using the benzoic acid with a known value of the caloric power (usually 26 463

kJ/kg (1kJ/kg=1J/g), or with slight maximum value differences in relation to this value ±3%), in order to

determine the calorimetric coefficient k of the calorimetric installation.

PCSs=k ∙(tf-ti)ml-qs-qb [kJ/kg]

where:

k - calorimetric coefficient, determined by ranging with benzoic acid, expressed in kJ/degree;

tf – final temperature, in degrees;

ti – initial temperature, in degrees;

ml - mass of the pellets (briquettes) made from corn cobs, in g.

qs - heat consumed to burn the copper nickel wire thread, in kJ;

qb – heat obtained by burning the cotton thread, in kJ.

Figure.1 Installation for establishing the caloric power of pellets made from corn cobs

The net caloric power of the pellets (briquettes) made from corn cobs is established on the basis of the gross

caloric power, with the help of the following relation:

PCIi=PCSs-6·(U+9·h) [kJ/kg]

where:

PCSs –the high caloric power, in kJ/kg;

U- is the moisture content level of the wood sample, in kg/kg;

h –hydrogen content of the wood sample, approximately 3,6 %.

The procedure for establishing the caloric power of the pellets (briquettes) made from corn cobs refers first of

all to preparing the raw material and the installation, then to the actual process of determining it and finally to

obtaining the end result. Preparation of the material in view of testing consists of collecting a small part of

around 0,6-0,8 grams from the whole material, the sample being weighed with a precision of 0,0002 g. The

sample must be clean[3]. This sample is placed in a porcelain melting pot and inserted into a laboratory oven,

in view of drying, at a temperature of 103±2 oC.

The desiccated state of the pellet (briquette) made from corn cob obtained is verified by successive weighing

thereof, until the difference between two successive weighings is smaller than double the value of the

weighing precision, or covering at least 2 hours of maintaining the sample in the oven for a piece of that size.

After drying, the samples are kept in the desiccator for cooling without changing the humidity content until


they are inserted in the calorimetric bomb. Preparation of the installation in view of performing the trial refers

to checking the quantity of water in the calorimeter of the Cu tank (so that it exceeds by 1-2 mm the lid of the

calorimetric bomb), the agitator A of the water Ap in the tank, the computer software C, the outer calorimeter

thermometer T and the level of gas pressure in the oxygen tank Bo. The test sample 1 is tied to the cotton

thread 2 and is inserted into the melting pot of the bomb 3. The spiral copper nickel thread is tied 4 to the

sample and the cotton thread, after which the protection lid is positioned correctly 5. The melting pot is

connected to the lid of the calorimetric bomb 6 by two electrodes 7 and 8, which continue with the electric

wires connecting the calorimetric bomb 9 and 10. By screwing the lid of the bomb, the bomb is coupled 11 by

means of the nozzle 12 to the oxygen tank Bo, thereby inserting 30 atmospheres. The bomb is inserted in the

calorimeter of the installation Cu, the two electric wires are connected, the lid of the calorimeter is closed and

the thermostat is inserted T for determining the temperature (Fig.2).

Figure 2. Calorimetric bomb section

Subsequently, the computer software is accessed, filling in the type of test (establishing or ranging), the name

of the sample, the mass of the sample, that of the copper nickel and cotton thread, as well as other required

data [8]. Afterwards, the operation for establishing the caloric power is initiated, by selecting and activating

the "START" button in the computer program displayed on the monitor (F). From this moment forward the

actual test starts for establishing the caloric power.

Figure 3. Description of the process for establishing the caloric power of pellets and briquettes made from corn cobs.

The final result of the process of burning the wood biomass is expressed by the caloric power, notion

designating the amount of heat obtained upon burning the mass unit. For the inflammable materials with a

high content of water and oxygen, such as wood biomass, two types of caloric power can be distinguished,

namely the high caloric power (PCS) and the low caloric power (PCI) [2]. PCS is established directly with the

calorimetric bomb, where the water vapours formed by burning hydrogen from the wood, as well as those



formed by water decomposition, condense in the container of the bomb, releasing around 2 510,4 kJ (600

kcal) for each kilogram of condensed water vapours (the so-called condensation heat). PCS cannot be used

practically, because the water vapours are evacuated through the chimney and only PCI remains to be actually

used. The test includes three distinct stages (Fig. 3), namely:

The initial stage ("fore"), which has the purpose of establishing water temperature variations within the

calorimetric container, due to the heat exchange with the exterior before combustion[6]. During this period,

usually lasting 5 minutes, the temperature is displayed and measures from one minute to the next are taken

with the precision thermocouple. The last temperature level measured in the initial stage actually represents

the first temperature level in the main stage. The temperature levels recorded in this stage are generally six in

total. After recoding the sixth value the material ignites and it is displayed in the menu tab (” Burning

time”).

The main stage ("main"), begins by igniting the sample and consequently leads to an increase in the water

temperature level in the calorimetric container, due to the combustion of the pellet particle and the generation

of heat. In order to establish the final temperature level, the temperature value is displayed minute by minute.

The final temperature level is given by the maximum temperature value, because after decrease thereof, this

means that the calorimetric container no longer receives heat from the bomb. The values recorded during this

stage vary depending on the duration of the burning process of the inflammable material within the

calorimetric bomb [6]. The number of values can vary between 19-42 temperature values recorded during this

stage.

The final stage ("after"), has the purpose of establishing the average water temperature variation in the

calorimetric container, due to the heat exchange with the exterior, after burning. As in the first stage, the

temperature is displayed every half minute, for 4-5 minutes, on average recording 8-10 values for temperature

variation.

Establishing the ash content

The process of establishing the ash content was performed according to European standards CEN/TS

14780ː2005ːE and CEN/TS 14775ː2004.

The analytic balance with the measuring field ranging between 0.001 g – 100 g is used. The mass of the

empty melting pot shall be determined, as well as the mass of the melting pot with the sample which is to be

analysed.

The sample weighed will be inserted in the burning oven and heated to a temperature of 750 ºC +-10 ºC. After

reaching the temperature level mentioned, the samples are then inserted in the burning oven for 60 minutes,

after which they will be taken out and left to cool for 5 minutes (Fig.4).

After being left out in the open air for 5 minutes, the melting pots with the burnt material shall be inserted in

the desiccator until completely cold [17]. After reaching room temperature, the melting pots with the burnt

material shall be weighed, establishing the mass of the melting pot with residue after incineration.

The ash content of the sample is calculated as a ratio between the mass of the residue obtained after

incineration and the initial mass of the sample analysed.

A = (m3-m1)/(m2 – m1) * 100 [%]

where:

m1 – mass of the empty melting pot;

m2 – mass with the sample;

m3- mass of the melting pot with the residue, after incineration.

3. RESULTS AND DISCUSSION

The moisture content level for the pellets made from corn cobs was 9% and for the briquettes made from corn

cobs it was 10%.

The values of the actual density for the four types (D20, D200, D400 of pellets and briquettes vary from 829

kg/m3 to 1255 kg/m3.

In Fig. 4 the graphic representation of the values for the actual density is displayed for pellets and briquettes

made from corn cobs.


Figure 4. The values of the bulk density for the four types of pellets

The values of the bulk density for the four types of pellets vary from 635.1 kg/m3 to 714.4 kg/m3.

In Fig. 5 the graphic representation of the bulk density values is displayed for the four types of pellets.

Figure 5. The values of the bulk density for the four types of pellets

The values of the gross caloric power vary from 19867 kJ/kg to 19902 kJ/kg.

The values of the net calorific power vary from 19305 kJ/kg to 19819 kJ/kg.

In Fig. 6 the graphic representation of the values for the high caloric power is displayed for pellets and

briquettes made from corn cobs.

635,1

675,1685,3

714,4

580

600

620

640

660

680

700

720

740

D20 D200 D400 D500

Bu

lk d

en

sity (

kg

/m3

)

829

11001137

11521255

0

200

400

600

800

1000

1200

1400

Briquettes D20 D200 D400 D500

Eff

ective

de

nsity (

kg

/m3

)



Figure 6. The values for the gross caloric power for pellets and briquettes made from corn cobs.

The values of the burnt ash content vary from 2.22% to 2.6%.

In Fig.7 the graphic representation of the values for the burnt ash content is displayed for pellets and

briquettes made from corn cobs.

Figure 7. The values for the burnt ash content for pellets and briquettes made from corn cobs.

4. CONCLUSIONS

- Biomass is the most widely spread resource which includes, alongside wood biomass, wood

processing residues and agricultural residues;

- The value of the minimum actual density is, for briquettes, 829 kg/m3, and the maximum value of

1255 kg/m3 is for D500 type pellets;

- The value of the bulk density is minimum 635.1 kg/m3 for D20 and the maximum value of 714.4

kg/m3 is for D500 type pellets.

19902

1981919867

19305

19000

19100

19200

19300

19400

19500

19600

19700

19800

19900

20000

Gross calorific

pellets

Net calorific

pellets

Gross calorific

briquettes

Net calorific

briquettes

Ca

lori

fic p

ow

er(k

J/k

g)


- The value of the high caloric power and the low caloric power is greater in the case of pellets than

for briquettes made from corn cobs, due to the level of compression;

- The value of the ash content, for pellets made from corn cobs, as well as for briquettes made from

corn cobs, is lower than 6% according to standards.

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BIOGRAPHY

Cosmin Spirchez is a lecturer university at Transilvania University of Brasov. Phd in

industrial engineering since 2010. Area of interestː Wood processing, tools for wood industry, devices for wood industry, wood construction, wood biomass. Has 2 patents and

has published over 100 articles, 5 books. Responsable and member in the research projects.

Member in the Cost FP 1407working group from May 2015.Participant at exhibitions in wood industry field (Hanovra-Germany, Bucharest, Brasov).

He may be contacted at [email protected]

mailto:[email protected]

a comparatibe study regarding to pellets and briquettes

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