Impeller Huller FINAL
Impeller Huller FINAL
Impeller Huller FINAL
TECHNICAL BULLETIN
Vol. 7 No. 1 | ISSN 2243-8483 | 2018
DEVELOPMENT OF VILLAGE-LEVEL
RICE MILL WITH IMPELLER HULLER
ISSN: 2243-8483
Department of Agriculture
PHILIPPINE CENTER FOR POSTHARVEST DEVELOPMENT AND MECHANIZATION
CLSU Compound, Science City of Muñoz, Nueva Ecija, 2018
TABLE OF CONTENTS
Abstract 1
Introduction 1
Objectives 3
Methodology 3
Identifying the customer segment 3
Design of major components of the rice mill 3
Fabrication of the prototype unit 4
Performance testing 4
Financial analysis 5
Experimental design and statistical analysis 6
Results and Discussion 6
Design Aspect 6
Technology Breakthroughs 6
Development of new type of huller 6
Multi-functional rice mill 8
New design of aspirator 9
Accessibility of the hopper by the operator 9
Technical features of the developed rice mill technology 10
Capability to mill over dried and under dried rough rice 10
Installation of destoner to the already compact rice mill 11
Cost of milling and financial viability of the developed 14
technology
Conclusion and Recommendation 15
References 15
ABSTRACT
Rice mills play a vital role in the rice self-sufficiency program of the Philippine
government as these could affect the supply of rice in the market. The purpose of this
research was to develop a new type of village-level rice mill that could be used to address
the huge deficit of appropriate rice mill in the upland and remote areas. Test trials revealed
that the coefficient of hulling, coefficient of wholeness and hulling efficiency of the impeller
huller of the newly developed rice mill were 0.990, 0.877 and 86.8%, respectively.
Cost of milling was estimated at Php 0.87/kg with internal rate of return of 82.5%. The
developed rice mill technology can be used by farmers’ cooperatives and local entrepre-
neurs that are interested to engage in custom-milling or rice trading business, thus provid-
ing additional business opportunities in the rural areas.
INTRODUCTION
The low level of agricultural mechanization is highly evident on the limited rice mills
in the upland and remote areas in the Philippines (BPRE, 2007). Such problem is partly
caused by the high investment costs of the rice mill and the shed for the machine. A study
conducted by PHilMech in 2013 revealed that the total rice mill deficit in the country was
7,906 units of 1.5 mt/hr capacity (PHilMech, 2013; Bingabing, et al. 2013).
With such huge deficit, old kiskisan rice mill with under-runner disk huller continue to
operate in the country. However, kiskisan could only provide a milling recovery of 50 – 55 %
as compared to modern rice mills of 63 – 67 % (IRRI, 2012). The prevalent use of inefficient
rice mills like kiskisan could limit the available supply of rice in the country due to its low
milling recovery of 50 - 57 % as compared to rubber-roll type rice mills of 60 – 67 %. As
such, farmers are expected to get a lesser output of 12 % for using a kiskisan rice mill.
Majority of existing rice mills operating in the Philippines require three-phase electrical
lines (if not converted into engine-driven rice mill) that are not commonly available in the
barrio or rural areas. As such, the locations of these rice mills are situated along the national
highway where three-phase electrical lines are available. Hence, huge deficit of rice mill is
highly evident in the upland and remote areas.
Because of the growing demand for brown rice, rice mill for brown rice is highly needed
nowadays (Pabuayon, et al. 2011). However, the widely used village level compact rubber
roll rice mill is not capable of producing brown rice while modern rice mills can mill brown
rice but they are not available for custom milling, since these are highly dedicated to the
business milling operations of the rice mill owners while some modern rice mills require
minimum of 100 bags of 50 kilogram before accepting milling for brown rice.
In the early 1980s, a new type of hulling mechanism for rice mill has been developed
in Japan using impeller huller, but not yet been used for large scale commercial milling
(Aveyire, 2008). The impeller huller removes the hull of palay by rotating it with impeller
blades that accelerates radially through centrifugal force and dehulls palay with the aid of
frictional force and impact force when palay passes through the blades and the liner surface
of the impeller housing (Aveyire, 2008). Results of various studies revealed that the physical
characteristics of long grain are appropriate for impeller-type huller (Shitanda, et al. 2001).
The husked ratio performance of rubber-roll huller is highly dependent on the size and
shape of palay unlike the impeller huller with almost the same performance (maximum
husking energy efficiency) for both long and short grain samples. Rubber-roll type huller
has higher system cracked ratio compared to impeller huller for both short and long palay
samples due to the existence of shearing force when palay passes through two rubber-rolls
operating at different speeds that tends to stretch the grain between the rolls.
Rice mills for the farmers and for small business milling operation is highly needed in
the country particularly in the remote and upland areas. Total volume of palay retained by
farmers for home consumption was estimated at 22 % of the total volume of rice production.
Given this production volume, the total estimated rice mill deficit in the upland and remote
areas in the country is about 2,000 units of 300 kg/hr capacity. Therefore, the development
of a new type of village-level compact rice mill that is appropriate for upland and remote
areas is imperative to address the rice mill deficit in the upland and remote areas of the
country.
General:
This project aimed to develop a technically feasible and economically viable
village-level impeller-type rice mill.
Specific:
METHODOLOGY
In the eventual introduction of a new type and design of rice mill in the country, the
initial question was, what are the basic features of this new impeller rice mill technology
that can address specific problems of farmers in the upland and remote areas that warrant
its desirability in the market. To address this issue, the conduct of one-on-one interview/
consultation with farmers, rice traders, millers, and even policy makers involved in the rice
mechanization program of the Department of Agriculture was undertaken. All the inputs
gathered have served as basis in the design and development of the different features of
the new rice mill technology.
Basic design parameters that affect the hulling efficiency of the rice mill that
includes the speed and type of materials used in the impeller blades, the clearance
between the tip of the blade and the impeller lining, and other parameters were
thoroughly analyzed using laboratory prototype model. Likewise, the principle
of operation of the impeller huller was studied based on available published
technical papers, and some of these were validated through a laboratory setup.
The concept of the new design was drawn through CAD software featuring the detailed
parts and components of the impeller rice mill machine. The laboratory setup of the
impeller huller, the aspirator, whitener and de-stoner were all fabricated and tested at the
PHilMech fabrication shop to determine their performance. Debugging and modifications
were conducted until the desired performances of each component were achieved.
The upscale model of the final design of the different parts and components
of the new impeller-rice mill were again drawn through CAD software. The CAD
drawings have served as reference in the fabrication of the final prototype unit and
to clearly visualize the final design of the impeller rice mill as one machine in three
dimensional perspectives. The fabrication of the different parts and components
of the impeller rice mill were all undertaken at the fabrication shop of PHilMech.
Performance testing
The standard laboratory method of test for a rice mill (PAES 207:2000) was strictly
followed during the laboratory and field trials to establish the technical performance
of the developed rice mill such as the input capacity, output capacity, milling capacity,
milling recovery, coefficient of hulling, coefficient of wholeness, percent head rice,
percent broken rice and percent brewers (PAES. 2001). Per PAES 207:200, the formula
in getting the milling capacity, milling recovery and hulling efficiency, are as follows:
The performance of the developed impeller huller was also compared with the
performance of the rubber-roll huller of a single-pass compact rice mill currently installed
at PHilMech.
The results of series of test trials have served as bases in modifying the ini-
tial design to further improve the performance of the rice mill, safety, ease of opera-
tion, and most importantly, the financial viability of the developed rice mill technology.
The final prototype unit was also pilot tested in Catalanacan Multi-Purpose Coop-
erative in Catalanacan, Science City of Munoz, Nueva Ecija, Philippines for two months.
Financial analysis
Based on the actual technical performance of the rice mill, the milling cost or simply
the total cost of producing one kilogram output was estimated. As such, it is expected
that the computed milling cost shall be less than the average or minimum prevailing
milling fee in the country to realize economic benefits of operating the technology.
where; I0 is the initial investment costs in the year 0 (the first year during which the
project is constructed) and I1 ~ Im are the additional investment costs for maintenance and
operating costs during the entire project life period from year 1 (the second year) to year m.
B1 ~ Bm are the annual net incomes for the entire operation period (the entire project life
period) from year 1 (the second year) to year m. By solving the above equality, the value of
r or commonly known as the Internal Rate of Return (IRR) is obtained.
The data gathered were consolidated and analyzed using Analysis of Variance
(ANOVA) to determine the differences among group means on the different designs
and components of the developed rice mill technology. Each test trials had two
repetitions while the collection of samples for laboratory analysis had two replicates.
Statistical analysis was performed using Statgraphics Plus, a statistic package
software that performs and explains basic and advanced statistical functions.
Design aspect
Based on individual interviews with key players of the rice milling industry (farmer-rice
producers, rice traders, millers and policy makers), it was suggested that the envisioned
rice mill technology should have a smaller capacity of about 250 - 350 kg/hr than the
current single-pass, two stage compact rice mill with milling capacity of 450 - 500 kg/
hr. A smaller capacity was highly recommended so that this will not compete but rather
complement with existing traditional rubber-roll compact rice mills. A smaller capacity
rice mill was highly recommended by the stakeholders to suit the level of operation of
farmer’s cooperative in the upland and remote areas including the rice mill requirement
of small grains businessmen for their rice trading or custom milling business operations.
As such, the following features of the new rice mill technology were fully considered
in the overall design: (1) the utilization of single-phase electric motor so that this can
be easily installed in the villages or remote areas with no rice mill currently operating
in their locality; (2) a compact design but with capacity of 300 - 400 kg/hr to reduce
working space and minimize additional investment of the shed for the rice mill;
and, (3) all parts and components of the rice mill should be locally readily available.
Technology breakthroughs
A new type of huller was successfully developed using impeller huller as illustrated
in Figure 1. It dehulls rough rice as it slides to the rotating blades, and as it is thrown and
slides to the impeller lining. Rough rice is rotated by the blades, moved in radial direction
by centrifugal force, and received vertical and frictional forces from the blade surface.
Based on technical reports, 20 - 50% of rough rice are dehulled as it slides at the impeller
blades through the application of frictional force (MAFF, 1995), though such data cannot be
confirmed due to the absence of high speed camera in the laboratory. From the rotating
impeller blades, rough rice is then thrown and slides to the lining of the impeller for further
dehulling given the application of impact force and frictional force, respectively. Therefore,
when rough rice slides at the surface of the blades and at the lining of the impeller, it
The performance of the developed impeller huller was compared with the
rubber-roll huller of Satake single-pass, two stage compact rice mill that is currently
installed at PHilMech using newly harvested Rc216 rice variety is shown in Table-1.
Test results revealed that the coefficient of hulling of the impeller huller is significantly
higher with 0.98 as compared with rubber-roll huller of 0.88 and as such, the
coefficient of wholeness of rubber-roll is significantly higher than the impeller.
However, in terms of hulling efficiency that accounts both the degree of hulling and
wholeness of the brown rice, there is no significant difference between the rubber-roll and
impeller huller. The milling capacity of the impeller huller is 337 kg/hr is within the desired
capacity and expectedly lower than the single pass rubber-roll compact rice mill of 540 kg/hr.
Table 1. Technical performance of the developed compact impeller huller with existing
rubber-roll type huller, 2015
PARAMETERS RUBBER-ROLL IMPELLER
Coeff. of hulling 0.88a 0.98b
Coeff. of wholeness 0.85a 0.76b
Hulling efficiency (%) 74.61a 74.41a
Hulling recovery (%) 78.98a 78.00a
Milling capacity (kg/h) 535.90a 337.25b
Note: Means across rows having the same super script are not significantly different at 5% level.
However, the laboratory trials have not established the optimum revolution of the
impeller blades that could provide the highest hulling efficiency given a type of materials used
in the impeller blades. The result of the laboratory trials, however, confirmed the findings
of Shitanda for the utilization of ABS plastic for the impeller blades (Shitanda, et al., 2001)
given its high coefficient of friction that yields higher hulling efficiency than PLA (MAFF, 1995).
The rice mill was also designed to produce not only white rice but also brown rice by us-
ing the whitener as second stage of hulling. Results of laboratory test trials revealed that the
impeller huller is capable of producing ‘coefficient of hulling’ of as high as 0.99, by setting the
rotation of the impeller blades to 2,400 rpm. The ‘coefficient of hulling’ measures the abil-
ity of the machine to remove rice hulls (PAES, 2001). However, it was observed that a higher
‘coefficient of hulling’ could provide a higher percent of ‘broken grains’ given a higher im-
peller force applied to the rough rice as it impact to the impeller lining. As such, the rotation
of the impeller blades is set to 2,000 rpm to reduce the impeller force to get a coefficient
of hulling of 0.90 - 0.94 thereby achieving higher coefficient of wholeness of 0.85 – 0.91.
In line with this, the whitener was designed for two major functions: (1) to remove the
bran of the brown rice for the production of white rice; and (2) to serve as second stage huller
for the complete removal of hull for the production of brown rice. Note that based on labo-
ratory test trials, rubber-roll-type hullers could provide only a coefficient of hulling of 0.85
and as such, the utilization of the new design of whitener for such purpose is not possible.
Another critical component of the rice mill is the aspirator that separates rice hulls
with brown rice and unhulled rice. With the initial amount of airflow coming from the
impeller huller, the utilization of traditional design of aspirator is no longer applicable,
thus, necessitating the development of a new design that is compatible with the impeller
huller. The aspirator was carefully designed to provide the desired quality of milled
rice and at the same time, minimize quantitative losses (Figure 3). The application
of excessive airflow in the aspirator could throw not only rice hulls but includes brown
rice to the cyclone, resulting to high incidence of quantitative losses. On the other
hand, the application of less airflow to the aspirator than the required could mix rice
hulls with the brown rice, resulting to the high mixture of unhulled rice with milled rice.
During laboratory test trials, it was observed that the brown rice and rice hulls can
be thrown upward by the impeller blades towards the aspirator. Given the impeller force
from the impeller blades, the huller of the machine can be placed below the aspirator to
The new impeller rice mill was designed with the following components as shown in
Figure 6, namely: (1) impeller huller, (2) aspirator, (3) whitener; and (4) destoner and grader.
Likewise, the rice mill technology is also equipped with the following primary components:
(1) a blower that is incorporated at the aspirator; (2) blower to suck bran from the whitener
; (3) input hopper that serves as storage bins for rough rice or rough rice before flowing
gravitationally to the impeller huller; (4) two 5-hp electric motors that serve as the prime-
movers of the major components of the rice mill; (5) cyclone to control dust pollution; and,
(6) control panel that contains the “on” and “off” push bottom switches of the impeller
huller, whitener, blower, aspirator, and destoner including the installation of emergency
switch and contactors for ease of operation and to ensure the safety of the operator as well
as to protect the electric motors from breaking down.
The major and primary components of the rice mill are lodged in a mainframe with a
leveler installed at the bottom of the main frame of the rice mill unit. As emphasized in
the previous section, the final design of the impeller rice mill was a product of series of
laboratory trials and “trial and error” method to achieve the desired performance of the
rice mill.
Laboratory trials were conducted to test the performance of the impeller huller
using Rc 222 rice variety at different moisture contents (Table 2). It was observed that
paddy samples with moisture content of 20 %, 16 %, 14 % and 10 % could yield hulling
efficiency of 72.1 %, 74.0 %, 74.9 %, and 75.3 % and hulling recovery of 79.0 %, 76.0 %, 79.9
% and 77.5 %, respectively.
Note: Means across rows having the same super script are not significantly different at 5% level.
The results of test trial revealed that the impeller huller is capable of milling
palay with moisture contents of 10-20 % without significantly affecting hulling
recovery of brown rice. Such distinct feature of the impeller huller technology
will fully address the problem of farmers in over drying or under drying their palay
with moisture content of 12-16% as they heavily rely on sun drying and without any
moisture meter at hand. Traditional rice mills like rubber-roll type require rough rice
to be dried at 14% to get higher milling recovery and hulling efficiency (MAFF, 1995).
After the short pilot-testing, the project collaborator suggested the installation of a
destoner and mini-grader in the new rice mill technology given the fact that farmers are
drying their produce in the highway, wherein the accumulation of tiny stones during
drying cannot be avoided. As such, a new destoner was designed and developed with
the inclusion of mini-grader to separate brewers with milled rice. The design of the
destoner (Figure 5) was made small but still matched the capacity of the rice mill so that
it can be incorporated to the current dimension of the already compact small rice mill.
Figure 5. Design of de-stoner and mini-grader of the developed rice mill, 2015
The connection of each component of the impeller mill for brown rice and white
rice can be more explained with the process flow as shown in Figure 7. As designed,
rough rice is fed to the feeding hopper 1 and when the feed shutter is opened, rough
rice flows directly to the impeller huller. The volume of rough rice that enters to the
impeller huller is controlled by an inlet control mechanism. The rice hull is detached and
separate from the brown rice through the impeller huller and the aspirator, respectively.
From the aspirator, rice hull goes directly to the rice hull cyclone. Brown rice then
proceeds to the whitener to remove the bran from the endosperm. The milled rice then
automatically fell to the de-stoner to remove tiny stones. Brewers then will be separated
from milled rice once the milled rice passes through the mini-grader. Brown rice can be
produced by adjusting the shaft speed of the impeller huller through the transmission
assembly and by loosening the discharge valve of the whitener. The entire operation
is centralized by an automated control panel disposed conveniently by the operator.
The distinct technical features of the technology with traditional rice mill are shown
in Table 3. The impeller design has successfully reduces the investment cost and space
requirement of the traditional rice mill, and hence become affordable to private small-scale
grain business and to the farmer’s cooperative as well. Most importantly, it can mill rice
paddy with moisture content of 10 - 18% and capable of producing both white rice and
brown rice, a distinct features not available to the current rice mill technology. It was ensured
during the design that all parts and components of the rice mill are locally available in the
market. The connection of the rice mill using household or single-phase electrical lines was
fully considered to ensure its easy installation in the countryside. Majority of traditional rice
mills requires three-phase electrical line that is not commonly available in the countryside.
Table 3. Technical features of the impeller rice mill as compared with traditional rice mill,
2015
FEATURES NEW IMPELLER RICE MILL TRADITONAL RICE MILL
Hulling mechanism Impeller Rubber-roll
Cost of rice mill with shed (Php) 320,000 600,000
Milling recovery (%) 62-65 62-65
Milling capacity (kg/hr) 250-300 450-500
Production of white rice / /
Production of brown rice / X
Can mill paddy at 10- 18% m.c. / X
Reduces Investment for the shed / X
Smaller space (60% less) / X
Connectivity to single- / X
phase electrical supply
Total cost per year (Php/yr) 156,979 Fixed cost + Variable cost
Cost of milling per kg output (P/kg) 0.87 Total cost per yr/Total annual cap.
Profit (P/kg) 0.88 Milling fee – Cost of milling
Payback period (Yr) 1.89 Investment cost/(Profit x Total
capacity)
Internal rate of return (%) 82.5 Refer to item III.3.2.e , page 6
Based on the technical performance of the developed rice mill technology, the financial
viability of the rice mill machine was analyzed. The results of the estimation (Table-4)
revealed that the total cost of milling per kilogram output is estimated at Php 0.87 which
is far below the existing milling fee of Php 1.75 - 2.25 per kg of milled rice. If the rice mill
shall be used for custom milling business, the estimated profit is about Php 0.88 per kg
even charging a minimum milling fee of Php 1.75/kg of milled rice. This is equivalent to
total projected annual net income of Php 158,558 for a total annual capacity of the rice mill
of 180,180 kg. From this, the estimated payback period is 1.89 years with internal rate of
return of 82.5 %.
Based on the results of the laboratory and field trials, the technical features of the
newly developed rice mill technology, are as follows:
• Ultra: milling capacity of 250 - 300 kg/hr and capable of producing both white rice
and brown rice, and can mill 10 - 18 % moisture content for the production of
brown rice which the traditional rice mill is not capable of doing.
• Compact: 60 % reduction in the space requirement of current rice mill technology;
• Efficient: Milling recovery of 62-65% for white rice and 72-78% for brown rice,
while the cost of milling is Php 0.87 per kg of milled rice which is far below the
prevailing milling fee of Php 1.75 - 2.50/kg; and
• Simple setup: Compatible with single-phase electrical lines and working space of
16 m2.
Given its capability to produce brown rice that can yield higher milling recovery
than white rice, which can be translated to additional rice supply in the country, the
developed technology could contribute in achieving food self-sufficiency in the country.
The newly developed rice mill technology is highly favorable for villages with no
existing rice mill installed in their areas as this can be easily connected to household or
single-phase electrical line. The technology can also be used by brown rice producers
and organic rice suppliers.
The developed rice mill technology can be used by farmer cooperative and local
entrepreneurs that are interested to engage in custom-milling or rice trading business
in the locality. As such, the new rice mill technology could provide additional business
opportunities in the locality other than limited to owning a tricycle or a jeep for transport
services or operating a small sari-sari store, the common businesses in the rural areas.
REFERENCES
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and Postharvest Mechanization Program (2011-2016)”, College, Laguna, Philippines:
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Bureau of Postharvest Research and Extension BPRE, 2007. “Postharvest Database and
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International Rice Research Institute, 2012. “Rice Milling Manual”. Manila, Philippines.
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ACKNOWLEDGMENT
The authors gratefully acknowledge the Philippine Council for Agriculture, Aquatic and
Natural Resources Research and Development (PCAARRD), Department of Science and
Technology (DOST) for funding this research project.