Corn cob dry

Corn Cob Commercial Utilization

Corn cobs are an abundant source of thermal energy for producing heat, power, fuels and

many chemicals too (Kaliyan & Vance, 2008). Historically, corn cobs have been used for whole

array of different products, from small modifications of its original physical and chemical

properties to highly industrialized goods. For instance, The Andersons Inc. located in Indiana has

long processed cobs for many agrichemical and commercial applications such as abrasives,

absorbents, activated carbon, asphalt shingle and roofing, chemical waste absorbent, concrete

additive, feedstock for petrochemical industry (xylitol, furfural, oxalic acid), fermentation

substrates, fertilizer diluents, food fiber source, carriers for chemicals such as herbicide,

insecticide and pesticides, insulating materials, plastic extenders, and many more products

(Anderson Inc). Recently, studies are exploring the use of corn cob for its energy content mainly

for ethanol fermentation, co-firing and as a feedstock in thermochemical conversion

technologies, thus potentially broadening the demand and importance of this so called “farm

residue”.

Further work to refine specific systems of utilizing corn cobs would be of great benefit to

agriculture, finding markets and alternative uses of material for farmers’ profits. Economic

comparison between storage options and deterioration during storage will influence cobs value

and cost of storage. In energy systems, cob costs need to include dry matter loss and changes of

moisture content, whereas if the cobs are being stored for chemical production then mass loss but
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even more important, compositional changes will be a factor determining cob storing and

handling.

Ethanol sector has rapidly grown in the last decade, reaching close to 11 billion gallons in

2009 (Renewable Fuel Association). Private and public sector are strongly supporting the

development of this renewable fuel as it has a number of advantages in terms of social, economic

and environmental aspects. Currently, ethanol is mainly produced from the corn kernel, but it is

envisioned to be also produced from lignocellulosic, such as corn stover, switchgrass, woody

biomass, etc. The new regulations proposed by Environmental Protection Agency establishes the

production of 36 billion gallon of renewable fuels, in which 16 billion gallons will come from

cellulosic biofuels, in which the cellulose fermentation pathway would be one of the major

contributors (EPA, 2009).

Decades ago, corn cobs have been used for drying seed and more recently as an energy

source. The seed industry and farmers tried to benefit from cobs barely used before and find a

new use for the material that could let them save money on drying operations (Dahlberg R.

1977). In the past, many cob burners and gasifiers were proposed to be used. The energy content

of corn cobs is around 18.4 MJ/kg (high heating value), comparable to other cellulosic materials

such as wood, and even cobs have 6% more energy than shelled corn and 11% more than

cornstalks (Dahlberg, 1977). He also claimed that from kernel with 35% moisture and 66%

efficient drier, there is enough energy in the cob to dry the corresponding kernels under average

corn-belt drying conditions. Many seed plants had implemented different types of burners, and
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have successfully decreased drying expenses; however, problems in cob handling and burners

prevented the technology from being extensively adopted.

Main problems were focused on material handling, particulate matter emission (very fine

ash). Also, corrosion caused by water vapor in combination with sulfur and chlorides producing

acids, difficulties for temperature control, greater maintenance required than conventional natural

gas burners, and slag formation at high temperature (950ºC) where minerals components melt

and solidify as green glass-like substance. These problems highlighted by Dahlberg (1977)

which prevented cobs from replacing natural gas for seed companies in drier facilities.

Furthermore, natural gas could be easily hooked on and it is a relatively cheap source of energy.

Other problems associated with this types of seed dryers were tar material condensation

at low temperature (below 300ºC), which would plug pipes, fans, burners and valves.

Approaches to solving tar condensation were to burn the producer gas at high temperature before

it condense, use down-draft gasifiers in order to oxidize and burn tars, or cool down the gas to

condense the tar and burn the gas once it has been cleaned.

A latter more sophisticated approach to solve many of the problems with cobs burners

was the use of gasifiers or pyrolysis units to produce low energy gas (in comparison to methane).

If utilized within short distances, low BTU values for the gas wouldn’t be detrimental; but it is

still a problem that adds to the cost (heat content of 150 BTU/cu. ft vs. natural gas 1000 BTU/cu.

ft).

Morey et al. (1984) proposed that a farmer with 200 ha requires approximately 50 tons of

cobs to dry his corn with average yielding. Cob piles in farm drying operations are a feasible
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alternative system to be used in the same season or, depending on the conditions, dried and

stored for later use.