Chilled Aeration Research Articles

Economic and Technical Feasibility of Grain Chilling in Brazil

Grain quality is critical due to the more stringent food-safety demands. Chilled aeration has become a popular technology for preventing grain spoilage during storage, mainly in warmer regions. However, a limiting factor in broad-scale adoption of chilling is the general belief that this technology is much more expensive than other post-harvest methods, such as the aeration with ambient air. In this work, ambient and chilled aeration were simulated considering the three major grain-producing regions in Brazil. Also, three storage capacities (95, 5000, 10500 t), five-grain types (corn, coffee, rice, bean, soybean), and two storage periods (beginning at the first and the last months of the harvest period) were used in the study, totalling 180 simulation scenarios. Based on these simulations a comparative cash flow analysis was performed aiming at evaluating the influence of the product, storage period, region, and silo size on the costs and profits from using these technologies. Results were strongly affected by the weather patterns of the studied regions, market values of grain, storage sizes, and fan operation hours. Chilled aeration should be economically competitive with ambient aeration, and the two technologies appeared as low-risk investments in Brazil, achieving average profits for 20 years by considering the time of money of US$ 68 and 59.4 million, respectively. Considering the technical factors, chilling presented higher energy consumption, but showed a greater potential for reducing grain temperatures and resulted in grain dry matter losses around 58% smaller than those verified when using ambient air.

Chilled Aeration to Control Pests and Maintain Grain Quality during Summer Storage of Wheat in the North Central Region of Kansas

Abstract.Chilled aeration allows grain to be cooled, independent of ambient conditions, to “safe” temperatures at which insects, fungi, and spoilage development are reduced to a minimum. The objective of this research was to evaluate the advantages of using grain chilling to preserve the quality of grain and reduce post-harvest losses caused by insects and fungi, compared to the conventional aeration and storage strategies used during summer storage in central Kansas. The research trials were developed at a farmer’s cooperative in central Kansas in 2015 and 2016 on low-moisture wheat harvested during the summer of 2015 and 2016, respectively, and stored in two 1,350 metric ton (t) steel silos in which one was chilled and the other was used as a control managed by the cooperative. Temperature of the grain inside each silo was monitored with temperature cables. Variables evaluated were: moisture content (MC), grain and flour quality, insect-pest development and reproduction rate, insect fragments per 500 g of grain, and fungi presence. In 2015, the chilling treatment reduced the grain temperature from 28°C to 17°C in approximately 175 h, while in 2016 it took 245 h to reach about the same temperature with an initial grain temperature of 39°C. Grain temperatures below 25°C were not achieved in the control silo during the summer using ambient aeration. Minimum variation of MC was observed in the Chilled silo while ambient aeration reduced the moisture content by 0.5%. Reproduction rates of the red flour beetle and lesser grain borer were significantly reduced by chilling temperatures lower than 17°C. Lower temperatures also reduced insect populations detected in probe traps and insect damaged kernels. Insect fragments and fungi presence had no significant increase throughout the trials in either of the silos. No clear evidence of flour quality being better preserved at lower temperatures was detected. The energy cost of running the grain chiller was between 0.26-0.32 $/t higher than ambient aeration. Keywords: Ambient aeration, Grain chilling, Grain quality, Stored-product fungi, Stored-product insects, Summer storage, Wheat.

Chilled aeration to control pests and maintain grain quality during the summer storage of wheat in north central region of Kansas.

Chilled aeration allows to cool grain, independent of ambient conditions, to safe temperatures where insect, fungi, and spoilage is reduced to the minimum. The objective of this research was to evaluate the advantages of using grain chilling to preserve the quality of grain and reduce post-harvest losses, compared to conventional aeration and storage strategies used during the summer storage of wheat in Central Kansas, U.S.A. The research trials were developed in two 1,350 metric ton (t) steel silos in a Farmer’s Cooperative during the summer and fall of 2015 and 2016. One of the silos was chilled and the other was used as a control managed by the Cooperative. Variables evaluated were: grain temperature, moisture content (MC), grain quality, insect development and reproduction rate. The chilling treatment reduced the grain temperature from 28°C- 39°C to a minimum of 17°C- 17.6°C in less than 250 hours. Grain temperatures below 25°C were not possible during the summer using ambient aeration. Minimum variation of MC was observed in the Chilled silo while ambient aeration reduced the MC by 0.5%. Reproduction rates of RFB and LGB were significantly reduced by chilled temperatures lower than 17°C. Lower temperatures also reduced insects discovered in probe traps and insect damaged kernels (IDK). The energy cost of the grain chiller was between 0.26 US $/t- 0.32 US $/t higher than ambient aeration.

Technical and economic evaluation of ambient and chilled aeration strategies to maintain the quality of paddy rice during storage in a tropical climate: Presentation

Warm and moist conditions of some tropical climate regions make it difficult to use ambient aeration to cool stored grain, which contributes to pest problems and increases dependence on chemical control as part of grain management strategies. Grain chilling is a non-chemical alternative to cool grain stored under high risk climatic conditions. The objective of this research was to use computer simulation to evaluate the technical and economic viability of using grain chilling compared to four ambient aeration strategies developed for paddy rice stored under the tropical climatic conditions of the North Pacific coast of Costa Rica. The minimum grain temperature achieved through ambient aeration at the end of the six-month simulated storage period was 30.8°C, using an aeration strategy based on a grain-ambient temperature differential greater than 10°C. Grain chilling lowered the average grain temperature from 35°C to below 15°C in 117 hours and the maximum average temperature it registered after six months of storage was 15.5°C. The economic evaluation of the ambient aeration and chilling strategies determined that the operational costs of grain chilling were 1.83 US $/t lower than ambient aeration plus chemical control of pests. However, the initial cost of the grain chiller made the net present cost (NPC) of the grain chilling strategy 0.22 US $/t higher than the cost of ambient aeration plus chemical control over a 10-year analysis. Several potential financial options were analyzed to make the grain chiller economically feasible for a rice miller in Costa Rica.

Environmentally friendly technologies to maintain stored paddy rice quality

Exports of processed rice have been increasing every year, as well as legislative restrictions and consumer demand for certified chemical free rice, pressing the rice processing industry to new challenges. The objective of this work was the implementation of a Rice Quality Certification Program. The package includes the association of a rigorous sanitation program and safe environmentally friendly control measures. It was accomplished in a large paddy rice facility with 40 silos during the 2008/09 rice crop. Silo sanitation was done by washing with pressurized water the conveyor belt structure above the silo roof, around the externals walls and thorough aspiration of the aeration system. During silo filling, the lower and top portions of the rice grain were treated with a mixture of diatomaceous earth (DE) and powder deltamethrin. Artificial chilling was applied as soon as the top layer of the grain mass was leveled by insufflating cool air (6 to 8oC) with a large cooling machine through the aeration system. The grain mass temperature stabilized at about 12-14oC, and kept this range of temperature for about 60 d. As the temperature of the grain mass increased, mainly on the top layer, aeration was performed with natural air from the cold fronts during the winter months. After 8 months on storage the rice was free of external insects, as proved by the grain sampling just before processing. For the 2009/10 crop season, the rice quality program will be repeated on 60 silos with few adjustments. Keywords : Chilled aeration, Inert dust, Physical insect control, Rice quality maintenance.

Evaluation of different temperature management strategies for suppression of Sitophilus zeamais (Motschulsky) in stored maize

Three years of experimental trials (2001–2003) were conducted in 12.7 t capacity pilot-scale bins to determine the survival, reproduction and suppression of Sitophilus zeamais Motschulsky under three temperature management strategies, no aeration (NA, control), ambient aeration (AA, ⩽23.9 °C), and chilled aeration (CA, ⩽18.3 °C) from May to November in Indiana, USA. One-way ANOVA indicated that the number of progeny for small adult populations of caged insects (0.14–0.28 insects per gram maize) embedded 0.6 m deep in the stored grain mass varied among temperature strategies for some, but not all of the storage periods. Progeny numbers in the CA strategy were significantly lower ( P<0.05) than those for the NA and AA strategies for periods with longer hours of grain temperature ⩽15.0 °C. There were no differences in progeny numbers between the NA and AA strategies for most of the storage periods. This may have been due to higher mortality, lower oviposition and fecundity from overcrowding of S. zeamais under the NA strategy caused by factors in the caged insect microclimate (e.g., rapid food depletion, heating, moisture, molding, and high CO 2 levels). Our results suggest that maintaining stored maize at temperatures ⩽15.0 °C for longer periods suppressed S. zeamais progeny more effectively than at ⩽18.3 °C. In addition, leaving the stored grain bulk unaerated early in the spring so it remained cool at ⩽15.0 °C due to winter aeration resulted in early suppression of S. zeamais progeny.

VALIDATION OF A FINITE–ELEMENT STORED GRAIN ECOSYSTEM MODEL

An axisymmetric finiteelement model was validated with respect to predicting the heat, mass, and momentumtransfer that occurred in upright corrugatedsteel storage bins due to conduction, diffusion, and natural convection usingrealistic boundary conditions. Hourly weather data that included hourly total solar radiation, wind speed, ambienttemperature, and relative humidity were used to model the corn temperature and moisture content during storage with noaeration, and with ambient and chilled aeration. Periods of aeration were simulated assuming a uniform airflow rate throughthe grain mass. Sixteen bins with a capacity of 11.7 t each and instrumented with temperature cables were available to validatethe model using two years of measured corn temperatures and moisture contents during summer storage. The averagestandard error between the experimental and predicted temperatures was 2.4C (1.1C to 5.7C range), and the standarderror between experimental and predicted moisture contents was 0.7 percentage points. The average standard error was 1.5Cin three nonaerated bins with sealed plenums when corn temperature was predicted as a function of the natural convectionequation. The predicted natural convection effect was not applicable unless the plenum was assumed sealed.

DEVELOPMENT OF A FINITE–ELEMENT STORED GRAIN ECOSYSTEM MODEL

An axisymmetric finite–element model was developed that predicts the heat, mass, and momentum transfer that occurred in upright corrugated steel storage structures due to conduction, diffusion, and natural convection using realistic boundary conditions. Weather data that included hourly total solar radiation, wind speed, ambient temperature, and relative humidity were used to model the temperature, moisture content, dry matter loss, and maize weevil development during storage with no aeration, and with ambient and chilled aeration. Periods of aeration were simulated assuming a uniform airflow rate through the grain mass. Heat and mass balances were used to calculate the temperature and absolute humidity in the headspace and plenum based on solar radiation, wind speed, ambient conditions, air infiltration, convective heat and mass transfer from the grain surface, and permeable boundaries that allowed natural convection currents to cross grain surfaces. A heat balance was used to estimate the wall temperature. The type of weather data in terms of solar radiation and frequency of data appear to be important when predicting the grain temperature, moisture content, dry matter loss, and maize weevil development.

A post-harvest economic model to evaluate grain chilling as an IPM technology

A spreadsheet model was developed to evaluate the economic costs of new post-harvest integrated pest management technologies, such as grain chilling, against traditional pest control methods, such as phosphine fumigation. The model considers 34 factors including electrical power consumption, capital investment cost, chemical costs, and less quantifiable factors such as worker safety, environmental issues, and changes in end-product value. When applied to the storage of popcorn, a high value speciality crop, and wheat, the annual operating costs of chilled aeration compared to phosphine fumigation with ambient aeration were up to 128 and 300% lower, respectively. The effect of high capital investment with low variable costs, as with chilled aeration, was compared to the low capital investment and high variable costs of phosphine fumigation using a multi-year Net Present Cost (NPC) model. For the case studies evaluated, the NPC of chilled aeration ranged from −122 to 197% of that for in-house fumigation with ambient aeration. Chilling of popcorn became economically feasible if a premium of less than one cent per retail bag could be obtained for popcorn labeled post-harvest pesticide-free. Chiller unit prices of US$ 80,000–90,000 were found to be a reasonable capital expenditure for this alternative integrated pest management technology.

Chilled versus ambient aeration and fumigation of stored popcorn part 2: Pest management

During the summer of 1994, a prototype grain chiller was tested to determine its efficacy as a pest management tool and its economic competitiveness with conventional pest management techniques. Four popcorn bins (121.5 tonnes) at a commercial facility were utilized. Two bins were managed using traditional ambient aeration and fumigation. The remaining two bins were managed with chilled aeration. Insect probe, larval, and pheromone traps were placed in each bin and monitored weekly. Significantly fewer Plodia interpunctella (Hübner) were trapped in the chilled aeration bins compared to the traditionally managed popcorn bins. Very few insect species were found in the probe traps, with the exception of hairy fungus beetles, Typhaea stercorea (L.) in July and August. Fewer beetles were found in the chilled bins when compared to the traditionally managed bins. Costs of chilled aeration (0.11 cents/kg) were competitive with the costs of conventional pest management practices (fumigation and ambient aeration) (0.096–0.17 cents/kg).

Chilled versus ambient aeration and fumigation of stored popcorn part 1: Temperature management

During the summer of 1994, four commercial 121.5 tonne corrugated steel bins of stored popcorn were evaluated for chemical-free pest management and conditioning. Two of the bins were managed conventionally with intensive aeration for moisture conditioning and calendar-based fumigation treatments for pest control. In the other two bins grain temperatures were managed with the Purdue prototype grain chiller. They were monitored and chilled only as needed throughout the summer. The average grain temperature in the core of the chilled bins was 11.3 °C, which was well below the critical 15–17 °C limit for most insect development. The average temperature along the south wall of the two bins was maintained at 17.5 °C. Grain temperatures in the bins conditioned with ambient aeration never dropped below 23 °C, and thus were on average 6–18 ° higher during the same period. Electrical operating costs of chilled aeration were 0.11 cents per kg of popcorn.

Temperature management of the maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), in three locations in the United States

A new simulation model was used to quantify the effect of eight common stored maize management practices on dry matter loss and Sitophilus zeamais Motsch. development using ambient weather conditions for Indianapolis, Indiana; Columbia, South Carolina; and Amarillo, Texas. For each location, good, normal, and poor storage years were identified and evaluated. No aeration was found to be ineffective and undesirable for control of dry matter loss and S. zeamais development in all situations. Fall-chilled aeration proved to be the most effective aeration strategy for all locations and years. However, Indianapolis showed the least benefit compared to ambient fall aeration, while Columbia benefited most. Although only continuous ambient fall aeration was investigated, the results showed that controlling the aeration process holds promise in optimizing this technique. The use of spring warm-up aeration increased the rate of quality deterioration while summer rechilling improved insect control with little increase in dry matter loss. A combination of controlled ambient aeration in the fall and chilled aeration during summer storage has significant potential as a non-chemical preventative pest management technique for all locations and years. Residual pesticides and fumigation of properly cooled maize storages should not be necessary in the United States.

Comparison of Conventional and Chilled Aeration of Grains Under Texas Conditions

Conventional and chilled aeration of rice and corn were investigated for Texas conditions using the simulation model AERATE. Of four conventional aeration strategies, continuous aeration performed best since it results in the smallest moisture losses and moisture gradients in the commercial rice and corn silos investigated. Chilled aeration utilizes a refrigeration system to control the bin inlet air conditions. It is able to prevent moisture losses and to maintain the average grain temperatures 15 C (25 F) below that of conventionally-aerated rice and corn during the summer months.