ISO 11520-2:2001
(Main)Agricultural grain driers — Determination of drying performance — Part 2: Additional procedures and crop-specific requirements
Agricultural grain driers — Determination of drying performance — Part 2: Additional procedures and crop-specific requirements
This part of ISO 11520 specifies additional procedures and gives guidance for testing and evaluating the drying performance of continuous-flow and batch grain driers for specific grain crops including wheat, barley, oats, maize, rice, sorghum and rape. It supplements the general procedures given in ISO 11520-1 based on drying only wheat over the limited range of moisture content of 20 % to 15 % wet basis. Methods and data are given for a) determining the evaporation rate of driers when drying grain crops under steady state conditions, and b) correcting the main drier performance characteristics, including evaporation rate, grain flow rate, drying time and specific energy and fuel consumption, to reference and other ambient conditions. Procedures are specified for sampling input and output grain to assess changes in grain quality.
Séchoirs à grains agricoles — Détermination des performances de séchage — Partie 2: Modes opératoires supplémentaires et exigences spécifiques à la récolte
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 11520-2
First edition
2001-02-01
Agricultural grain driers — Determination of
drying performance —
Part 2:
Additional procedures and crop-specific
requirements
Séchoirs à grains agricoles — Détermination des performances de
séchage —
Partie 2: Modes opératoires supplémentaires et exigences spécifiques à la
récolte
Reference number
ISO 11520-2:2001(E)
©
ISO 2001
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ISO 11520-2:2001(E)
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ISO 11520-2:2001(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative reference .1
3 Terms and definitions .1
4 Symbols and abbreviated terms .4
5 Test procedure.5
5.1 General.5
5.2 Test period.5
5.3 Frequency of sampling grain.5
5.4 Moisture removal .6
5.5 Grain dampening .7
5.6 Procedure for a multi-pass test.7
6 Grain quality.8
6.1 General.8
6.2 Input grain .8
6.3 Output grain .9
7 Methods of correction of test results .10
7.1 General.10
7.2 Evaporation rate.10
7.3 Mass flow rate of grain.13
7.4 Corrected drying time .13
7.5 Specific thermal energy, total energy and fuel consumption .13
8 Test report .14
Annex A (informative) Grain moisture content and sampling .15
Annex B (informative) Moisture removal in specific crops.19
Annex C (normative) Testing reduction in grain germination.20
Annex D (normative) Tables for correction of drier performance.21
Annex E (informative) Airflow calculations .99
Bibliography.102
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ISO 11520-2:2001(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this part of ISO 11520 may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 11520-2 was prepared by Technical Committee ISO/TC 23, Tractors and machinery for
agriculture and forestry, Subcommittee SC 7, Equipment for harvesting and conservation.
ISO 11520 consists of the following parts, under the general title Agricultural grain driers — Determination of drying
performance:
� Part 1: General
� Part 2: Additional procedures and crop-specific requirements
Annexes C and D form a normative part of this part of ISO 11520. Annexes A, B and E are for information only.
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ISO 11520-2:2001(E)
Introduction
ISO 11520-1 covers only those methods for evaluating the drying performance of continuous-flow and batch grain
driers to be used when drying rewetted wheat with a moisture content in the range 20 % to 15 % wet basis.
The methods specified in this part of ISO 11520 take account of the following factors:
� a greater range in input and output moisture contents;
� other crops apart from wheat;
� the impracticality of rewetting (dampening) some grains and of differing thermal characteristics.
For correcting the observed evaporation rates to those to be expected at different reference ambient and specified
grain conditions, the correction formulae given in ISO 11520-1 are augmented by a series of tables from which
correction factors are found by interpolation.
The methods specified are for determining the water evaporation rate which the machines concerned are able to
achieve when drying wheat and other grains under the steady-state conditions prevailing during the tests. Methods
for correcting observed performance to other input and reference ambient conditions are also specified.
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INTERNATIONAL STANDARD ISO 11520-2:2001(E)
Agricultural grain driers — Determination of drying performance —
Part 2:
Additional procedures and crop-specific requirements
1 Scope
This part of ISO 11520 specifies additional procedures and gives guidance for testing and evaluating the drying
performance of continuous-flow and batch grain driers for specific grain crops including wheat, barley, oats, maize,
rice, sorghum and rape. It supplements the general procedures given in ISO 11520-1 based on drying only wheat
over the limited range of moisture content of 20 % to 15 % wet basis.
Methods and data are given for
a) determining the evaporation rate of driers when drying grain crops under steady state conditions, and
b) correcting the main drier performance characteristics, including evaporation rate, grain flow rate, drying time
and specific energy and fuel consumption, to reference and other ambient conditions.
Procedures are specified for sampling input and output grain to assess changes in grain quality.
2 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of
this part of ISO 11520. For dated references, subsequent amendments to, or revisions of, any of these publications
do not apply. However, parties to agreements based on this part of ISO 11520 are encouraged to investigate the
possibility of applying the most recent edition of the normative document indicated below. For undated references,
the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of
currently valid International Standards.
ISO 11520-1:1997, Agricultural grain driers — Determination of drying performance — Part 1: General.
3 Terms and definitions
For the purposes of this part of ISO 11520, the terms and definitions given in ISO 11520-1 and the following apply.
3.1
reference ambient conditions
ambient conditions of temperature, relative humidity and barometric pressure to which the results of a drier test are
to be corrected
3.2
airflow rate
volume of air flowing in unit time per unit volume of grain (this value is also the number of air changes per unit of
time)
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ISO 11520-2:2001(E)
NOTE There are several ways of expressing airflow rate, but for comparison between driers and crops it is convenient to
express it in this way.
3.3
drying period
period during which drying air passes through grain
3.4
cooling period
period during which ambient or near-ambient air passes through grain
3.5
tempering
process by which partially dried grain is held in temporary storage for a number of hours without ventilation,
allowing equalization of moisture content within the grain kernel with minimal stress cracking
NOTE When drying rice, a common practice is to cool it to within 2 °C of ambient prior to tempering for a minimum of 4 h.
One or more further drying, cooling and tempering cycles may be given.
3.6
dryeration
process by which hot grain is taken directly from a drier and allowed to temper for a minimum of 4 h before being
cooled slowly so as to extract additional moisture without using additional fossil fuel
NOTE The hot grain referred to is usually maize or rice, sorghum, soybeans or wheat.
3.7
test period
period during which a continuous-flow drier operating at a single steady state for at least one residence time, or a
batch drier completing a single full cycle of drying and cooling, is monitored to enable its thermodynamic
performance to be assessed
NOTE In multi-pass drying there may be several test periods.
3.8
wheat
grain of the genus Triticum, of which the commercially important species are T. aestivum (breadwheat), T. durum
and T. compactum (club wheat)
3.9
barley
grain of Hordeum sativum or H. vulgare
3.10
oats
grain of Avena sativa L.
3.11
naked oats
grain of Avena nuda L., which readily loses the husk at threshing
NOTE Naked oats have a high protein and oil content and the loss of husk makes the kernels prone to rancidity.
3.12
maize
grain of Zea mays L.
NOTE This is commonly referred to as corn in North America and some other countries. There are about seven different
types of maize distinguished at the “convar” level of classification (between species and cultivar) and within each type there are
hybrids having different drying properties. The most widely grown type is the convar indentata commonly known as “dent corn”.
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ISO 11520-2:2001(E)
3.13
rice
grain of OryzasativaL.
3.14
paddy rice
rough rice
rice with the hull or husk still intact
3.15
brown rice
rice kernel from which the hull or husk has been removed during the milling process
3.16
milled rice
white rice
white grain or kernel remaining after the removal of the husk or hull and of the bran (whitening); the embryo or
germ may be totally or partly removed and part of the bran may still remain on the grain
NOTE For some end uses, rice may be dried in the milled condition.
3.17
head rice
for brown and milled rice, either a whole or broken grain with length greater than or equal to three-quarters of the
average length of a whole or unbroken grain
3.18
full head rice
unbroken head rice
3.19
broken rice
either brown or milled rice grain which has less than three-quarters of the average length of a full head grain
3.20
sorghum
grain of Sorghum vulgare Pers
NOTE Types of cultivated grain sorghum include kaffir corn, milo and durra (Africa), feteritas (Sudan), shallu, jowar,
cholum and “Indian millet” (India), and kaoliang (China).
3.21
rape (canola)
seeds of Brassica napus or B. campestris (also known as B. rapa)
NOTE Canola and rapeseed are both members of the same botanical family. The designation “canola” has been
established by Canada and is applicable to varieties that meet the canola standard for the level of erucic acid and
glucosinolates in the seed. From the drying performance point of view, there is no evidence of any difference in drying rates or
drying characteristics between rapeseed and canola.
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ISO 11520-2:2001(E)
4 Symbols and abbreviated terms
These are given in Table 1.
Table 1 — Symbols and abbreviated terms
Symbol Description Unit
B rated output kg/s
E water evaporation kg
E water evaporation rate kg/s
�
F fuel consumption kg/s
G holding capacity of drier kg
J specific fuel consumption kg/kg
K factor for correcting evaporation (defined in 7.2.3) —
M moisture content of grain, wet basis (m.c.w.b) %
N anticipated number of test periods dimensionless
Q specific heat consumption J/kg
S specific energy consumption J/kg
3
V volumetric capacity of drier m
W energy consumption J
3
q air volume flow rate m /s
v
c coefficients in Equation E.1 —
1.3
d coefficients in Equation E.2 —
1.3
–1 –1
c specific heat of air at constant pressure kJ�kg �K
pa
–1 –1
c specific heat of water vapour at constant pressure kJ�kg �K
pw
d depth of grain bed m
2
f face area at point of air entry to grain bed m
h specific enthalpy J/kg
i coefficient in Equation E.3 —
m mass of grain in a single batch or passing through a continuous-flow drier in a kg
test run
m� mass flow of grain kg/s
n exponent in Equation E.3 —
p pressure or pressure drop Pa
s(y) standard error of mean of variable y —
t duration of test period s
3
� density kg/m
� grain residence time in drier s
Other subscripts
e electrical
f final, at drier exit
i initial, at drier inlet
o observed value
—
s corrected value at reference or specified conditions
p predicted (for model)
sys drier system of ducts and plenum chambers
t thermal
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ISO 11520-2:2001(E)
5 Test procedure
5.1 General
This clause shall be used in conjunction with clause 7 of ISO 11520-1:1997.
NOTE For the general principle of the tests, test equipment and preparation for testing, see clauses 5, 6 and 7 respectively
of ISO 11520-1:1997
Driers are most often used to dry grain which is physiologically ripe and for which the variation in moisture content
(m.c.) at harvest is largely a function of ambient weather conditions. For the purposes of a drier test, such grain can
normally be rewetted artificially and the test itself conducted more conveniently outside the harvest period. One
advantage of this is that the variation in moisture content of the wet grain is usually very small, i.e. less than
� 0,5 % wet basis (w.b.). This is important for minimizing uncertainty in the results.
However, some crops (e.g. maize in France) are harvested at moisture conditions in excess of those to which the
grain can reasonably be rewetted and the test has to be conducted during the harvest. In these cases there may be
considerable variation in the moisture content of the wet grain and residence times may be large.
Clause B.4 of ISO 11520-1:1997 prescribes procedures for estimating the uncertainty (or level of confidence) in
derived performance measures. Variation in ingoing moisture content is an important component of the
determination of uncertainty. The uncertainty in determination of the evaporation rate and related quantities
increases if too little moisture reduction is achieved (see annex A). A moisture reduction of more than four
percentage points is therefore advisable. Provisions are given in 5.4.
5.2 Test period
The test period shall normally be a minimum of one residence time in a continuous flow drier or one drying and
cooling cycle in a batch drier.
ISO 11520-1 does not make a direct requirement of the length of the test period, although experience has shown
that, for a continuous-flow drier, 1 h is normally sufficient provided that
a) 1,5 residence times are allowed for stabilization, and
b) sampling of the input grain begins prior to the start of the test period, so that the initial moisture content of the
grain that will leave the drier during the test period is known.
Where good estimates of the mass flow rate and the measured capacity are available, calculate the residence time
using the formulae given in 10.2.2 of ISO 11520-1:1997. For these formulae, the rated output, B (in kilograms per
second), may be used in place of the observed mass flow of grain q . Otherwise, Table 2 may be used to provide a
m
guide to the expected residence time.
Table 2 gives a guide to approximate residence times (in hours) for combinations of airflow, drying air temperature,
moisture removed and specific energy consumption, calculated for a final moisture content of 15 %.
5.3 Frequency of sampling grain
5.3.1 Continuous flow driers
Unless the range of variation in the moisture content of input grain is known to be less than 1 % w.b. (see annex A),
take a minimum of 20 samples from the ingoing and outgoing grain streams of a continuous-flow drier at a
frequency such that they are spaced evenly over the test period.
Clause 7 of ISO 11520-1:1997 requires sampling of both ingoing and outgoing grain streams at a frequency
providing at least 12 samples of each, spaced evenly over the test period. For rewetted wheat in which the range of
variation is less than 1 % w.b., these prescriptions have given good accuracy for drying from 20 % w.b. to 15 %
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ISO 11520-2:2001(E)
w.b., but are not adequate for all crops. The aim is to reduce the standard error of the mean to ensure an accuracy
of estimation of the evaporation rate of ��5 % (see annex A and Figure A.2).
Ingoing samples will need to correspond to the grain exiting from the drier during the test period (see 7.1 of
ISO 11520-1:1997). Some grain samples taken will therefore later be found to be unnecessary, although their
additional use in rapid moisture tests may well have given essential information on the progress of stabilization.
Table 2 — Guide to drier residence times
Moisture Specific heat energy Residence time
removed consumption h
Specific air volume flow rate
3 –1 –3
m ·s ·m
0,3 3,0
Drying air temperature
o o o o o o
% w.b. MJ/kg water evaporated 40C90 C 140C40C90 C 140 C
5 4 7 4 2 0,6 0,2 0,1
10 17 7 5 1,4 0,5 0,4
25 4 34 13 9 3 1,1 0,7
10 85 33 23 7 3 2
5.3.2 Batch driers
Because of the greater variability of moisture content that might occur in the output stream from a batch drier, a
minimum of 50 samples of the output grain shall be taken.
5.4 Moisture removal
Except for multi-pass drying, a minimum of four percentage points of moisture content shall be removed in each
test period. To maintain reasonable accuracy on the estimation of evaporation rate (see annex A), this minimum
shall be increased in line with the variability in the ingoing moisture content in accordance with Table 3 or
Figure A.3.
Moisture content prescriptions for specific crops are discussed in annex B.
Table 3 — Minimum moisture removals
Range in ingoing Minimum moisture removal
moisture content
%w.b. % w.b.
0,5 4
15
28
310
419
523
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ISO 11520-2:2001(E)
5.5 Grain dampening
Unless it is freshly harvested (i.e. less than 6 wk from harvest), cereal grain shall not exceed 17 % m.c.w.b. before
dampening, and shall not have received more than one drying treatment.
The procedure for dampening is described in 6.3.2 of ISO 11520-1:1997.
Experience has shown that Canadian varieties of wheat, barley and canola can be dampened to 25 % w.b., 25 %
w.b. and 20 % w.b., respectively.
5.6 Procedure for a multi-pass test
5.6.1 General
This procedure specifies the additional steps necessary for a multi-pass test.
5.6.2 Quantity of grain
Calculate the minimum quantity of grain for one test using the formula given in 7.2 of ISO 11520-1:1997, with the
difference that, in this case, N represents the number of passes and t is the time for each pass. If more than one
multi-pass test is to be conducted, multiply the formula by the number of such tests.
5.6.3 Outline procedure for continuous flow driers
Fill the drier, run it as for a single pass, and direct the output grain to a discard store. At the start of the test period,
direct the output grain to the test period store. When the test period is complete, direct the output grain to a buffer
store and continue drying without adjustment until all the grain has passed through the drier.
o
Cool the grain that is in both the test period store and the buffer store to within 2 C of ambient temperature, and
temper it for 4 h.
Fill the drier with the grain from the previous test period and sample the input grain for use in calculating
evaporation during the previous test period. Restart the drier, direct the grain to the discard store and continue
sampling the input. When the test period store is emptied, switch to feeding from the buffer store.
When the moisture content of the drier output grain has stabilized, start a new test period by switching the grain to
the test period store. When the test period is complete, direct the output grain to a new buffer store and continue
drying until all the grain has passed through the drier.
Repeat the procedure until all passes have been completed.
5.6.4 Outline procedure for batch driers
5.6.4.1 Grain stationary
A drier in which the grain remains stationary during drying shall be emptied between successive drying periods,
taking samples for moisture content at input and output as in a single-pass test.
The purpose of removing the grain during rest periods is to aid the process of moisture equalization and destroy
any moisture gradient.
5.6.4.2 Grain recirculating
A drier in which the grain is recirculating during drying shall not be emptied during rest periods. Moisture content at
the end and beginning of each test period shall be assessed on the basis of samples taken from the recirculating
grain stream.
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ISO 11520-2:2001(E)
6 Grain quality
6.1 General
It is assumed that good quality grain will be used in a drier test. It is therefore important that its properties exceed
the minimum national limits for the grain concerned. Where, as in the US and Canada, grain is categorized into
grades, the aim should be to use grain satisfying Grades 1 and 2.
NOTE A useful summary of cereal grain quality standards worldwide is given by Kent and Evers [1].
6.2 Input grain
6.2.1 All grains
Determine the moisture content of those samples taken from the input grain stream during the test period.
Record any relevant detail of grain origin or provenance, and the variety, hybrid or both.
Either
a) obtain a 2 kg sample of the input grain as specified in 6.3.1 of ISO 11520-1:1997, or,
b) if the grain is freshly harvested and there is no static bulk, take samples from the input grain stream additional
to those being taken to monitor moisture variation with time.
If the grain is to be dampened, obtain a 2 kg sample both before and after dampening.
Using a sample divider, remove from each 2 kg sample a 100 g subsample. Determine the moisture content of the
samples.
Dry the remainder of the 2 kg sample or samples with unheated air in a laboratory drier until moisture contents of
approximately 15 % w.b. and 10 % w.b. are reached for the cereal seeds and oilseed rape, respectively.
Determine the mass per hectolitre (bulk density) using a calibrated instrument (chondrometer).
Draw subsamples of sufficient size for the determination of mass per 1000 grains, and of purity and germination
using ISTA procedures [2].
NOTE 1 The ISTA procedures contain instructions for checking that the averaged results of purity and germination tests fall
within prescribed tolerances. If they do not, retest procedures are to be followed. It is particularly important to accurately assess
germination capacity because this property is a good guide to quality in general and can be a sensitive indicator of heat damage
during drying. (See also 6.2.2.)
NOTE 2 In barley, seed dormancy may be broken by drying.
6.2.2 Wheat for baking
Depression in germination (6.2.1) shall be taken as an indication of damage to baking quality.
NOTE A simple and rapid test for heat damage to protein has been shown to be a useful guide to baking quality.
6.2.3 Maize
From the remainder of the 2 kg sample, draw four samples each of 100 grains. Examine the individual kernels on a
grain viewer and count the number of cracked grains. Express the number of cracked grains as the mean of the
four samples.
NOTE Cracked grains reduce the value of maize for wet milling.
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ISO 11520-2:2001(E)
6.2.4 Rice
6.2.4.1 From the remainder of the 2 kg sample, draw four samples each of 100 grains. Carefully husk by hand,
examine the individual kernels on a grain viewer and count the number of cracked grains. Express the number of
cracked grains as the mean of the four samples.
6.2.4.2 From the remainder of the 2 kg sample, draw a further four samples each of 200 g and process
through a laboratory husker and whitener. From the output from this machine:
a) draw 100 g samples of brown rice and determine the number of broken grains;
b) take four samples each of 100 grains and determine the number of cracked grains as given in 6.2.4.1;
c) return the material to the remainder of the 200 g samples passed through the husker.
Separate sufficient whole grains of husked rice to determine the mass per 1 000 grains of the brown rice. Return
thegrains tothesample.
Using the laboratory whitener, mill the brown rice and separate the head rice and broken rice from the rest of the
grain materials. Weigh each component, in grams. Calculate the head milled rice recovery.
Draw four 100 grain samples of the milled rice and examine them for any damage such as scorching, gelatinization
or discoloration that may be due to excessive heat. Record the percentage of heat-damaged grains.
6.3 Output grain
6.3.1 All grains
D
...
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