Description
Drying of grain is done for various reasons – but primarily drying is done to be able to get crops off the field earlier.
By getting your crops off the field earlier you achieve the following:
a) You increase your harvesting days – so you’re able to harvest longer, using the same combines – so instead of purchasing new or bigger combines, you’re able to utilize your existing equipment better, making. It also allows you to plant more fields, as you have more time to harvest them – reducing your cashflow requirements when expanding your farming operations.
b) You’re able to get your crops off the field earlier – which is especially important, if you’re doing multi-cropping – when it’s crucial to have your crop off of the field so that you can get your next crop in the ground.
c) It allows you to start delivering grain earlier – allowing you to take advantage of better market prices for earlier deliveries – as in typical years, the grain prices start to fall as soon as the majority of the crop comes in.
d) Specifically on maize – the wetter you are able to harvest, the less harvesting losses you have – less ear drop, and less kernel shedding, meaning you leave less of your profit back on the field
How do I size my dryer?
Dryers are usually sized – based on your harvesting capability – for a continuous harvesting operation, you need to have a dryer that is able to dry, as much as you have harvested for that day, so that you aren’t creating a bottle neck in your operation at the dryer, because you can’t offload grain coming in from the field, because the dryer isn’t keeping up with your harvesting rate. Most dryers are rather easy to expand – so it’s not a neccesity to start with an oversized dryer. Because dryers are expensive pieces of equipment, ABC Hansen suggests that you size your dryer, based on a continuous 24 hour operation – all commercial dryers are designed to be able to run 24 hours – so if you’re harvesting 500 tons a day, size your dryer at around 20-25 tons per hour (500t / 24 hours) and not at 80 tons per hour (500t / 8hours.
The second factor to take into consideration is the percentage that you want to dry – what is the wettest that you’ll be taking off your grain from the field. In the US – farmers regularly harvest at moisture contents of up to 24% – usually out of neccesity – from incoming winter weather – but typically corn isn’t harvested at over 22%. Most dryers capacities will be specified, based on some assumptions. These assumptions are usually:
i) Maize/Corn
ii) Incoming moisture content 20%
iii) Drying to 15% (thus 5% moisture reduction in dryer)
iv) Drying temperature 120ºC – all heat (no cooling)
v) Relative humidity during drying period – 50%
vi) Ambient air temperatures 20ºC
Some manufacturers may also indicate capacities based on wheat depending on the manufacturer’s major markets – and care should be taken when comparing capacities based on wheat and corn – wheat dries much easier than maize, because of the much smaller kernel size – so when comparing – make sure to compare the same commodities, when assessing capacities and fuel consumption.
What is it going to cost me to dry?
We’re not going to give values for the inputs that are used for drying – but rather just the quantities – as pricing on fuels change significantly over time – but the below should give you a good idea of what the costs will be (all based on maize)
1) Fuel cost – as a rule of thumb – you’re going to be expending approximately the following:
a) Natural gas – approximately 0.9m³ of gas per percentage point dried, per ton of grain (thus when drying grain by 5% – you will be using [0.9m³ x 5% x 1T]=4.5m³ of gas
b) Diesel – approximately 1liter of diesel per percentage point dried, per ton of grain (thus when drying grain by 5% – you will be using [1lt x 5% x 1T] = 5 liters of diesel
c) Wood – approximately 3kg of wood per perentage point dried, per ton of grain thus when drying grain by 5% – you will be using [3kg x 5% x 1T] = 15 kg’s of wood
* Note – wood is a wide term – and not all woods are the same – and the quanties are dependant on wood density, wood moisture content, percentage of green material)
The amounts used are indicative, and some dryers could be a bit more efficient, or less efficient, but usually not more than 5% either way.
The amount of fuel used is primarily a factor of energy density – to be technical – you need approximately 32.7 megajoules of energy to dry 1 ton of grain by 1%. For example, 1 liter of diesel contains 45 megajoules of energy – and then there is an approximate loss of 12% of the energy – on the burner and ambient heat loss, and heat loss through the heat exchanger. A cubic meter of natural gas contains 40 megajoules of energy – but losses are lower, due to the natural gas burners not having to pass through heat exchangers.
What dryer should I use?
There are multiple ways to dry your grain – the simplest – being to dry aerate your grain, or to do in-bin drying (see HERE for more info on these types of drying). For larger producers though, continuous dryers are a neccesity, as in-bin, batch type drying doesn’t allow for high enought throughput rates, and doesn’t always allow you to harvest at high moisture contents. Also any grain above 20% moisture should not be dried in-silo, as there are risks of spoilage in the silo at such high moisture contents.
Most dryers today, are what is known as mixed flow dryers, which basically mean that there is a mix of grain and air that is moving continuously through the drying collumn – which results in low resistance of airflow through the dryer, as all of the grain is constantly moving in a cascading motion, which allows for air flow over the grain particles on all sides during the time it spends in the dryer.
Most mix flow dryers will be built in sections – and are usually rather easy to expand, by just stacking another section on top of the existing section – and optimal drying can be achieved by being able to control the heat of the air into each section.
Typically you would start with the hottest air in the top section, and then gradually decrease the air temperature as you get to the lower sections, with the last section just blowing ambient air through the grain, to allow the grain to cool off before exiting the dryer. By reducing the heat in each section, you’re able to reduce stress/heat fracturing of the grain, while also allowing the grain time to temper (for the heat to reach the centre of the kernel, allowing for drying of the entire kernel, not just the outer shell). Drying at too high heat, for too long periods cause the grain structure to crack, resulting in high breakage of the grain – and lower gradings at the end user.
Most modern dryers are equiped with sophisticated control systems, which automatically measure moisture content of grain entering the silo, temperatures in the different sections, moisture content and temperature of grain exiting the dryer, as well as dryer fill levels – and they use this automation to make sure that you get consistant results from the dryer – based on your parameters – on the moisture content and temperatures.
Continuous dryers are never installed as standalone units – as the handling requirements on the dryers are high. As a minimum, when installing a dryer you will need
a) A pre-cleaner – it is best to preclean grain before drying – because you want to remove as much foreign material as possible from the grain before drying – you don’t want to expend fuel and energy drying leaves and chaff etc. It’s also important to have clean grain, as dirty grain can block up drying channels in the dryer.
b) A wet silo – this is usually a buffer silo – that is installed after the cleaner – where the high moisture grain is stored temporarily – which feeds into the dryer continuously – you don’t want to offload to your silo complex at the same capacity as your dryer, as dryers are usually rather low capacity, compared to handling systems, and dryers work best when fed a consistent steady flow of grain. The size of the wet silo, is usually approximately the size of your dryers capacity – based on a 24 hour operation – hence if you have a 20TPH dryer – you should look at a 48-T-500T wet bin – which will allow the dryer to work continuosly for 24 hours on the grain that is in the wet bin.
c) When planning on a drying facility – it is also going to be important to plan the silo complex, that you are able to offload grain – while you are drying – so your silo complex needs to be set up, to allow for loading and unloading grain at the same time.
d) The silo that the grain enters into after the dryer – needs to be an aerated silo, so that you’re able to push ambient air through the warm (though it is cooled in the dryer, it is still warmer than ambient) grain, and cool it off as quickly as possible, to prevent condensation in the silo (for more about aeration and condensation in silos see HERE)
ABC Hansen offers a range of dryers – depending on application, customer preference and heat sources – from a range of suppliers from the US, Europe and South America.
