Small-scale peanut shelling equipment has been designed and used to meet various needs and scales. A laboratory-scale sheller has been used by researchers to approximate the shelling outturns of a commercial shelling plant using 2 to 10 kg samples. A single commercial-sized sheller will have a shelling capacity up to 23 MT/hr. Commercial shelling operations utilize multiple shellers, each designed to shell a narrow range of peanut sizes. There are enterprises such as small seed processors or manufacturers in developing countries that need shelling equipment capable of processing 100 to 1000 kg of peanuts per hour with the capability of mechanically separating the hulls from the shelled material. A three-stage sheller was designed, fabricated, and tested to determine its throughput (kg/h), the efficiency of separating the hulls from the shelled peanut kernels, and sizing the shelled peanut kernels. The sheller had a maximum shelling rate in the first shelling stage of 1087 kg/h operating at 252 rpm. Approximately 93% of the peanuts were shelled in the first stage of shelling. An air velocity of 9.55 m/s was used to aspirate a mixed stream of peanuts and hulls and removed 97% of the hulls. The sheller was equipped with vibratory screens to separate the material into unshelled, edible sized peanut kernels, and oil stock.
Peanut shelling is the process by which the outer hull or shell of a peanut is broken and the kernel or seed is removed and separated. The process is accomplished by hand and mechanically. Hand shelling is a slow process, but results in a very high percentage of whole kernels. Mechanical shelling usually involves forcing the in-shell peanut (peanut pod) between a fixed surface and one moving parallel to that surface imparting a combination of shear and compressive forces on the peanut hull causing it to fracture, open, and extract the kernel. In large commercial shelling equipment, the shelling compartment contains a semi-cylindrical fixed shelling grate and a series of bars that rotate within the shelling grate enclosure. The clearance between the shelling grate and the sheller bars ranges from 1.90 to 3.49 cm and the opening in the shelling grate ranges from 0.56 to 1.27 cm depending on the peanut pod size (
Smaller scale shelling equipment has been designed and used to meet various needs and scales.
Meds and Foods for Kids (MFK) is an organization located in Cap Haitiens, Haiti that manufactures a ready-to-use therapeutic food (RUTF) for the treatment of severe childhood malnutrition from peanut paste. One of their objectives is to use locally grown peanuts in the production of the RUTF, thus helping improve the local economy. MFK and similar enterprises need shelling equipment capable of processing 100 to 1000 kg of peanuts per hour with the capability of mechanically separating the hulls from the shelled material.
The objective of this study was to evaluate the performance of a three-stage peanut sheller with aspiration and kernel sizing fabricated specifically for small scale peanut processing (Frank’s Designs for Peanuts, Mexico Beach, FL)
The throughput (kg/h) of each stage of the sheller,
The efficiency of removing hulls and light trash from the shelled product, and
The efficiency of separating shelled from unshelled peanuts.
A peanut sheller was designed and fabricated similar to the Model 4 sheller described by
Prototype peanut sheller for small-scale peanut processing operations consisting of a feed hopper, shelling chamber, hull aspiration, and two shaker sizers.
The shelling chamber was an open cylinder and concave design with three stages (
Cutaway view of small scale peanut sheller.
Physical dimensions of shelling cylinder and concave in small-scale prototype peanut sheller.
The primary differences between the Model 4 sample sheller (
As peanuts are shelled, the hulls, kernels, and small unshelled peanuts fall through the screen and into the aspiration chamber. The aspiration chamber is a rectangular section where air is flowing upward through a centrifugal fan and into a collection bin. The hulls and light material from the shelling chamber are lifted from the material stream and carried into the collection bin. The unshelled peanuts and the shelled kernels fall onto the top shaker screen equipped with 9.9 × 31 mm (22/64 × 1¼ in) slotted screen. The material larger than 9.9 mm should be mostly unshelled peanuts and is carried to the end of the screen and into a container. The material smaller than 9.9 mm falls through the screen onto a lower shaker/sizer screen equipped with 6.8 mm (17/64 in) round hole screen. The material falling through the 6.8 mm screen is predominantly small inedible peanut kernels and debris. The material riding to the end of the 6.8 mm screen is usually edible-sized whole and split peanut kernels.
The equipment was powered by three 0.75 kW electric motors, one each for the aspiration fan, the sheller cylinder, and the eccentric mechanism for the shaker/sizers. The sheller was driven by a V-belt on an adjustable speed sheave.
Tests to evaluate the sheller were conducted in two phases. The purpose of the first phase was to determine the proper damper position in the hull aspiration system to remove the hulls from the shelled peanuts without removing excessive amounts of peanut kernels. The purpose of the second phase of testing was to determine the shelling rate of each stage of the sheller. Peanuts used in this study consisted of a mixture of runner cultivars made up of predominantly Georgia 06G (
In the first phase, 16-kg samples of cleaned, unshelled runner type peanuts placed in the feed hopper of the sheller’s first stage. Power was applied to the sheller and all motors allowed to reach full speed. The air velocity in the rectangular section of the aspiration chamber was measured using a hot wire anemometer (Model HHF42, Omega Engineering, INC., Stamford, CT). The hopper gate to the sheller was opened, allowing the peanuts to flow into the sheller’s first stage. The equipment was run until all of the peanuts had passed through the 1st stage and the screens clear. The unshelled peanuts were then hand sorted and passed through the 2nd stage. After the 2nd stage was cleared, the remaining unshelled peanuts were passed through the 3rd stage. The weights of the sample, aspirated material, material riding the 9.9 mm slotted screen (+10 mm), material riding the 6.8 mm round screen (+7 mm), and the material fall through the 6.8 mm round screen (−7 mm) were recorded. A subsample of the aspirated material was collected from the collection bin and hand sorted into hulls, unshelled peanuts, and shelled peanut kernels and weighed. The screened material (+10 mm, +7 mm, and −7 mm) was subsampled and sorted into shelled, unshelled, and hulls and each component weighed. The aspiration airflow rate was changed by partially closing the in-line damper. Tests were replicated three times at five damper settings for a total of 15 aspiration tests.
Using the results of the aspiration tests, the aspiration airflow rate was set to minimize peanut kernels aspirated into the hull system and minimize the hulls in the shelled material. A sample was placed in the 1st stage hopper, power applied to the equipment, and all motors allowed to reach full speed. The hopper gate was opened, a stopwatch timer started, and all of the material was allowed to flow through the 1st stage sheller. When material stopped falling from the sheller onto the top shaker/sizer, the stopwatch timer was stopped and elapsed time recorded. The rpm of the shelling cylinder was measured by placing the measuring tip of a handheld tachometer on the end of the sheller driveshaft while the sheller was operating under load. The screened and sized material was weighed. The +10 mm material was subsampled, and the subsample sorted into unshelled, shelled whole kernels, shelled split kernels, and hulls. Each component was weighed, and then added back to the original +10 mm material. The +10 mm material was then shelled through the 2nd stage, recording the time required to shell the material. Again, the screened material from shelling the 2nd stage was weighed. The resulting +10 mm material was subsampled, sorted, and component weights recorded, then shelled through the 3rd stage. The sheller rpm was changed by adjusting the variable speed sheave and the tests repeated. Three samples were shelled at each of four different speeds ranging from approximately 210 to 340 rpm.
The air velocity in the hull aspiration section of the sheller ranged from 3.85 to 12.50 m/s depending on the position of the damper in the outlet of the aspiration system (
Increasing the order of the regression equation to a quadratic resulted in a slightly improved R2 = 0.944 (
The percent hulls (H) aspirated from the peanut stream increased exponentially from 60 and asymptotically approached 100% as the air velocity increased from 4 to 12 m/s (
Air velocity (m/s) as a function of the position of the damper installed in the hull aspiration duct (0 = closed, 100% = open).
The percent of hulls and peanut kernels aspirated as a function of air velocity in the hull aspiration chamber.
Similarly, the percent kernels aspirated (K) with the hulls increased exponentially from 0 to 0.7% and can be estimated as a function of air velocity (
If a velocity, V, of zero is substituted in
Rearranging
Selecting the appropriate shelling grate sizes is crucial to efficient peanut shelling. On average, 92.8% of the peanuts were shelled in the first stage using a 9.9 mm shelling grate and 6.5% were shelled in the second stage using a 9.1 mm shelling grate. More than 99% of the peanuts were shelled in the first two stages with only 0.7% of the peanuts being shelled in the third stage. These data confirmed that the procedure used to select the shelling grate sizes was appropriate and resulted in efficient peanut shelling.
Similarly, screen sizes for the vibratory sizing screens were selected to separate unshelled, whole edible sized kernels, edible sized split kernels, and small-sized peanuts normally used as oilstock (
Characterization of material riding and falling through screens to separate material after each stage of shelling.
Shelling capacity averaged 1087, 242, and 20 kg/h for the first, second, and third stage shellers respectively. The shelling capacity (kg/h) of the first two stages increased with increasing speed (rpm) until an optimum sheller speed (rpm0) was reached, and then the throughput decreased as the speed increased (
Shelling capacity (kg/h) of each sheller stage as a function sheller speed (rpm).
Regression parameters to estimate shelling capacity (kg/h) for each sheller stage as a function of sheller speed (rpm) using a three parameter lognormal functiona.
In a small production system, similar to that used by MFK in Haiti, a series of shelling grate sizes might be maintained on site so that the optimum sizes for each stage of the sheller could be used. The size of the shelling grate should be determined using a method similar to the method used evaluating the shelling characteristics for the Uniform Peanut Performance Tests (
All peanuts are processed through the first stage, and the unshelled peanuts are separated by the vibratory screens and by hand. The unshelled from the first stage would then be accumulated and loaded into the second stage and shelled. In a similar fashion, the peanuts not shelled in the second stage would be sorted and fed back into the third stage.
This sheller is intended for use in developing countries and small capacity processors. In developing areas, capital for equipment is scarce, but labor is readily available. Therefore, this particular sheller was designed to maintain relatively low initial capital expenditure for equipment, and utilize the local population for hand labor to sort peanuts. To further reduce the cost of the equipment, a sheller could be fabricated with a single shelling chamber and peanuts processed through the single stage sheller with the first stage shelling grate installed. The unshelled could be sorted and accumulated until the batch has been processed. Then a smaller grate installed in the sheller, and the unshelled previously collected shelled. The process could be repeated until all the peanuts are shelled.
As demand for product increases, additional equipment can be purchased and upgraded to include improved sorting of shelled and unshelled, automatic recirculation of unshelled to the next stage, and size sorting of shelled kernels.
A three-stage peanut sheller based on designs originally developed for shelling and evaluating peanut samples for commercial shelling operations, was scaled up, fabricated and tested. The maximum shelling capacity through the first stage was 1087 kg/h with an average of 93% of the peanuts being shelled in the first stage. Regression equations were developed to estimate the sheller throughput as a function of sheller speed. Methods established and used the Uniform Peanut Performance Tests for selecting the appropriate grate sizes were used successfully in these studies. Tests also determined that the air velocity for aspirating and separating the peanut hulls from the shelled peanuts was 9.55 m/s. These tests showed that the sheller was suitable for small commercial shelling operations.
The authors gratefully acknowledge the work of agricultural research technicians Mr. Clyde Johnson and John Gardner, and student employee Mr. Trey Rice in completing this research. The authors also acknowledge the support of Mr. James Rhoads, formerly of MFK Haiti, for making the authors aware of the need for this type of equipment. The authors are grateful for Mr. Frank Nolin, owner of Frank’s Designs for Peanuts, LLC for providing the prototype sheller for testing.