1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 3986 : Part 2 : 1998 I
2、CS 65.040.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Methods of test for drying performance of agricultural grain dryers Part 2. Additional procedures and crop specific requirementsThis British Standard, having been prepared under the direction of the Engineering Secto
3、r Board, was published under the authority of the Standards Board and comes into effect on 15 June 1998 BSI 1998 The following BSI references relate to the work on this standard: Committee reference AGE/23 Draft for comment 96/709873 DC ISBN 0 580 29527 3 BS 3986 : Part 2 : 1998 Amendments issued si
4、nce publication Amd. No. Date Text affected Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee AGE/23, Equipment for harvesting and conservation, upon which the following bodies were represented: Agricultural Engineers Assoc
5、iation British Agricultural other crops as well as 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 correct
6、ion formulae given in BS 3896 : Part 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 stea
7、dy state conditions prevailing during the tests. Methods for correcting observed performance to other input and reference ambient conditions are also specified. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for t
8、heir correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 72, an inside back cover and a back cover. BSI 1998 1 BS 3986 : Part 2 : 1
9、998 1 Scope This Part of BS 3986 specifies additional procedures and gives guidance for testing and evaluating the drying performance of continuous-flow and batch grain dryers for specific grain crops including wheat, barley, oats, maize, rice, sorghum and rape. It supplements the general procedures
10、 given in BS 3986 : Part 1 that are based on drying only wheat over a limited range of moisture content of 20 % to 15 % wet basis. Methods and data are given for: a) determining the evaporation rate of dryers when drying grain crops under steady state conditions; and b) correcting the main dryer per
11、formance characteristics, including evaporation rate, grain flow rate, drying time and specific energy and fuel consumption, to reference and other ambient conditions. Procedures are given for sampling input and output grain to assess changes in grain quality. 2 References 2.1 Normative references T
12、his Part of BS 3986 incorporates, by dated or undated reference, provisions from other publications. These normative references are made at the appropriate places in the text and the cited publications are listed on the inside back cover. For dated references, only the edition cited applies; any sub
13、sequent amendments to or revisions of the cited publication apply to this Part of BS 3986 only when incorporated in the reference by amendment or revision. For undated references the latest edition of the cited publication applies, together with any amendments. 2.2 Informative references This Part o
14、f BS 3986 refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions. 3 Definitions For the purposes of this standard, the fol
15、lowing definitions apply, supplementing the definitions given in BS 3986 : Part 1. 3.1 reference ambient conditions The ambient conditions of temperature, relative humidity and barometric pressure to which the results of a dryer test shall be corrected. 3.2 airflow rate The volume of air flowing in
16、unit time per unit volume of grain. This value is also the number of air changes per unit of time. NOTE. There are several ways of expressing airflow rate but for comparison between dryers and crops it is convenient to express airflow rate in this way. 3.3 drying period The period during which dryin
17、g air passes through the grain. 3.4 cooling period The period during which ambient or near-ambient air passes through the grain. 3.5 tempering The process by which partially dried grain is held in temporary storage for a number of hours without ventilation, allowing equalization of moisture content
18、within the grain kernel with minimal stress cracking. NOTE. When drying rice, a common practice is to cool it to within 28C 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 The process by which hot grain is take
19、n directly from a dryer 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. 3.7 test period A period during which a continuous-flow dryer operating a
20、t a single steady state for at least one residence time, or a batch dryer 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. Th
21、e 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 p
22、rotein 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 (
23、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. 3.13 rice Grain of Oryza sativa L.2 BSI 1998 BS 3986 : Part 2 : 1998 3.14 paddy or rough rice Rice with the hull or
24、 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 or white rice. The 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 remove
25、d 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 grain or a broken grain with length equal to or greater than three-quarters of the average length of a whole or unbroken
26、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 (Af
27、rica), 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
28、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. 4 Symbols and unit
29、s Symbol Quantity Units B rated output kg/s E water evaporation kg E9 water evaporation rate kg/s F fuel consumption kg/s G holding capacity of dryer kg J specific fuel consumption kg/kg K factor for correcting evaporation (defined in 7.2.2) M moisture content of grain, wet basis (m.c.w.b) % N antic
30、ipated number of test periods dimensionless Q specific heat consumption J/kg S specific energy consumption J/kg V volumetric capacity of dryer m 3 W energy consumption J a air volume flow rate m 3 /s c 1.3 coefficients in equation E.1 d 1.3 coefficients in equation E.2 c pa specific heat of air at c
31、onstant pressure kJkg 21 K 21 c pw specific heat of water vapour at constant pressure kJkg 21 K 21 d depth of grain bed m f face area at point of air entry to grain bed m 2 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 d
32、ryer in a test run kg m9 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 r density kg/m 3 t grain residence time in dryer s Subscripts e electrical f final; at dryer exit i initial, at dryer inlet
33、 o observed value s corrected value at reference or specified conditions p predicted (for model) sys dryer system of ducts and plenum chambers t thermal BSI 1998 3 BS 3986 : Part 2 : 1998 Table 1. Guide to dryer residence times Moisture removed Specific heat energy consumption Residence time, h Spec
34、ific air volume flow rate, m 3 s 21 m 23 0.3 3.0 Drying air temperature, % w.b. MJ/kg water evaporated 408C9 0 8 C 1408C4 0 8 C9 0 8 C 1408C 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 Test procedure 5.1 General This clause shall be used in conjunction with
35、 clause 7 of BS 3986 : Part 1. NOTE 1. For the general principle of the tests, test equipment and preparation for test, see clauses 3, 5 and 6 respectively of BS 3986 : Part 1 : 1998 NOTE 2. Dryers are most often used to dry grain which is physiologically ripe and for which the variation in moisture
36、 content at harvest is largely a function of ambient weather conditions. For the purposes of a dryer test, such grain can normally be rewetted artificially and the test itself be conducted more conveniently outside the harvest period. One advantage of this is that the variation in moisture content o
37、f the wet grain is usually very small, i.e. less than 0.5 % w.b. This is important to 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 conduct
38、ed 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 BS 3986 : Part 1 : 1998 prescribes procedures for estimating the uncertainty (or level of confidence) in derived performance measures. Va
39、riation 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 p
40、oints is therefore advisable. Prescriptions for specific crops are given in 5.4. 5.2 Test period NOTE 1. See also clauses 7.5.3, 7.5.4 and 7.6 of BS 3986 : Part 1 : 1998. The test period shall normally be a minimum of one residence time in a continuous-flow dryer or one drying and cooling cycle in a
41、 batch dryer. NOTE 2. BS 3986 : Part 1 does not make a direct prescription of the length of the test period although experience has shown that, for a continuous-flow dryer, 1 h is normally sufficient provided that: a) 1.5 residence times are allowed for stabilization; and b) sampling of the input gr
42、ain begins prior to the start of the test period, so that the initial moisture content of the grain which will leave the dryer during the test period is known. Where good estimates of the mass flow rate and the measured capacity are available, calculate the residence time by either formulae (4a) or
43、(4b) given in 8.2.2 of BS 3986 : Part 1 : 1998. NOTE 2. For these formulae, the rated output, B (in kg/s) may be used in place of the observed mass flow of grain, m9 fo . Otherwise table 1 may be used to provide a guide to the residence time to be expected. Table 1 gives a guide to approximate resid
44、ence times (in h) 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 dryers Unless the range of variation in moisture contents of input grain is
45、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 dryer at a frequency such that they are spaced evenly over the test period. NOTE 1. Clause 7.1.3 of BS 3986 : Part 1 : 1998 specifies sampling both ingoing and
46、outgoing grain streams at a frequency which will provide 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 % w.b., but are not adequat
47、e 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). NOTE 2. Ingoing samples will need to correspond to the grain exiting from the dryer during the test period (see 7.1.3.1 of BS 3986 : Pa
48、rt 1 : 1998). 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. 5.3.2 Batch dryers Because of the greater variability of moisture content which might occur in the output stream from a batch dryer, a minimum of 50 samples of the output grain shall be taken.
