Handling of Straw

Large-scale straw handling for energy purposes has developed into an independent discipline in agriculture
with attachments in which particularly large farms and machine pools invest.

After combine harvesting, the straw is left on the earth in swaths. The straw should be removed as quickly as possible so that the treatment of the soil
preparation can begin thereby establishing next year’s crop. The thickness of the straw swath has increased considerable over the recent years, because
the combine harvester swath width has been considerably increased.
This is an immediate advantage in respect of the baling capacity, but it may be problematic to dry the straw after rainfall.
The following calculation is based on a straw yield of 3 tonnes per ha, a field size of 4 ha, and a transport distance of 1,000 m from the field to the
farmer’s storage. Big bales are currently delivered from the storage to district heating plants etc. during the year depending on crop delivery contracts.
Straw that has not been baled into big bales is used primarily in the farmer’s farm-scale boiler.



 

 


Baling/Chaff cutting of Straw


The following baling/chaff cutters are examples of baling/cutting types used in agriculture:

• Small baler
• Round baler
• Medium-size baler
• Big baler
• Chaff cutter

The small baler typically has a tunnel dimension of 46 x 36 cm and a bale length of 80 cm. The weight of the bale is approx. 12 kg, and the bale
density is 90-100 kg/m3 /ref. 17/. Previously, is was the most widely used type of baler, but is now used only to a small extent for baling of straw for
bedding and for burning in small farmscale boilers.
The round baler has been in the market for approx. 25 years. The commonest type of baler bales into a width of 120 cm and a diameter of 150

 

 


...cm. The average bale weight is 244 kg, and the bale density is approx. 110 kg/m3 /ref. 17/. There is also a type of baler designed for round bales
of 150 cm width and 180 cm diameter. That was the type that was first marketed, but now it is only seldom seen.
The interest for the round baler was great when it was marketed, but has declined over the last many years.

The round baler is primarily used for baling of straw for feeding and bedding purposes, and for burning in straw-fired farm-scale boilers.
The medium-size baler has gained a firm foothold in agriculture for the baling of straw for feeding and bedding purposes, and for burning in
farm-scale boilers. It was marketed some years after the big baler, probably because the bale dimension is more suitable for agricultural purposes.
The baler tunnel dimension is typically 80 x 80 cm and the bale length is 240 cm. The weight of the bale is approx. 235 kg, and the density is approx. 140 kg/m3. However, balers with other tunnel dimensions and bale lengths from 120 to 200 cm are also manufactured. The baler often is equipped with a chaff cutter, thereby increasing the bale density to approx. 165 kg/m3. Chaffed straw is a better bedding material, and this is the
major reason why the baler is equipped with a chaff cutter.
The big baler has been in the market for approx. 20 years. It is the only bale size that is accepted by the district heating-, CHP-, and power plants. The baler tunnel dimension is approx. 120 x 130 cm, and the bale length is approx. 240 cm/ref. 18/. The bale length may however be adjusted
from 110 to 275 cm, but for reasons of road transport, a bale length of approx. 240 cm is most suitable. The bale density has increased over the
years due to the technological development of the baler. The average bale density is 139 kg/m3 , and the average
weight of bale is 523 kg.
The introduction of other baler types that conform to a width of 120 cm and a length of 240 cm, which is the most
important requirements by the plants, has been tried. These balers produce a bale height of less than 130 cm.
They can be equipped with a chaff cutter which means that the bale density may be increased to approx. 170 kg/m3 /ref. 18/. However, these
baler types have not gained ground and are therefore not widely used.
The baler is used primarily for baling of straw for heating-, CHP-, and power plants and for large farm-scale
boilers.
Chaff cutting of straw for the use at heating-, CHP-, and power plants in bulk (without having been baled) has been tried, but it requires a reconstruction
of receptacle and feeding facilities of the plants. The storage facilities on the farms also should undergo adjustments, since storage in the field without
cover causes losses and decrease in value.
For the chaff cutting of straw from the field a towed or self-propelled chaff cutter and a cutter loader may be used. The cutter loader is equip-ped with a chaff cutter, and the system thus makes out an all-in-one unit that both cuts, transports and unloads the straw . By using a chaff
cutter, a suitable number of trailers can be used for the further transport of the chaffed straw to the destination.
One of the greatest problems connected with chaffed straw is though that the volume weight by transporting is very low, i.e., 45-50 kg/m3
. However, by storage by loader tractor or straw blower with adjuster fan, the volume weight is 70-80 kg/m3, though. The baling capacity depends on the choice of technology which Figure 9 clearly illustrates.
The gross capacity that includes all operations in connection with the baling is lowest when the straw is baled by a small baler and round baler, and it is highest when using a big baler.
The chaff cutter capacity (selfpropelled) is considerably higher than that of the round baler, but also lower than that of the big baler. The capacity
of the newest and largest selfpropelled chaff cutters is considerably higher than stated here.



 

 


Manpower Required
The manpower required for the bailing and transport of the straw to the storage on the farm varies with the type of bale and technique that is used during loading, unloading, and transport. The manpower required for the handling of small bales is thus 72 minutes per tonne when loading unloading by
hand. This is almost 3 times as much as required for the handling of round bales and 5½ times more than required for the handling of big bales,
see Figure 10. By mounting a bale chute on the bailer and by loading directly on to the transporting vehicle, the manpower may be reduced,
though, to approx. 45 minutes per tonne for small bales.
The manpower required for chaff cutting of the straw or for the handling of medium-sized bales is the same,
i.e., 17 minutes per tonne. By handling of big bales, the manpower required is only 13 minutes per tonne, though. This very drastic reduction of
the manpower required and the great physical labour saving is the principal cause of small bales having been almost outdistanced by round bales,
medium-sized bales, and big bales.

 

 


Transporting Straw to Storage

When transporting straw, various techniques and methods are used depending on the local conditions.
Small bales are loaded in the field by hand, bale fork, bale loader, bale chute, or bale gun. Back on the farm, the bales are unloaded by hand
directly into the storage or an elevator or bale conveyor. The bales can also be dumped and then by hand placed
on an elevator or bale conveyor. If an elevator is used, the bales shall be stacked by hand, and if a bale conveyor is used, it can partly distribute
the bales in the storage. The bale conveyor is particularly fitted for lofts.
Flat cars or special V-shaped straw vehicles are used. They will contain from 75 to 250 straw bales.
Round bales are loaded by frontend loader, loader tractor, trencher or the like. The same machinery is used for unloading in the storage. The frontend
loader is the most used machine both in field and in storage. Depending on the front-end loader design, lifting capacity, and the local conditions, one or two bales are handled at a time. Most often, only one bale is handled at a time. For transport, reconstructed trucks or truck trailers are used, but also ordinary farm trailers or specially designed vehicles are used. Usually, the tractor is only towing one trailer, and it will contain from 8 to 14 bales .

Medium-sized bales are loaded and unloaded by front-end loader, trencher, loader tractor or the like. The front-end loader is the most used machine
for both loading in the field and for unloading in the storage or at the straw stack. One or two bales are handled at a time depending on the
front-end loader equipment and lifting capacity. Reconstructed trucks, truck trailers, flat cars, or specially designed vehicles are used for the transport.
The size of the loads varies from 12 to 45 bales, but most often load will hold approx. 24 bales.Big bales are loaded and unloaded by
front-end loader, trencher, loader tractor, telescope loader or the like. The telescope loader is suitable for unloading,
because it can reach high up when storing in stacks. The front-end loader is the commonest. Depending on the front-end loader equipment and
lifting capacity, the tractor load capacity and stability, and the local conditions, one or two bales are handled at a time. The capacity is highest, when
handling two bales at a time, but it is a severe load on the tractor front axle, and the stability of the tractor is decreased dramatically if not a balancing
weight is mounted on the back of the tractor.
Reconstructed trucks or truck trailers are widely used. The size of the load varies from 6 to 18 bales. Over long distances, the tractor is often
towing two trailers so that the size of the truckload attains 24 bales per trail.



 

 


Delivery to Plant
During the heating season, the straw is usually delivered to the plant in accordance with a crop delivery contract.
It may be a direct agreement with the farmer, an association of straw producers, or a contractor. This
agreement includes, e.g., delivery dates, quantities to be supplied, contracted prices, and quality criteria. By farmer transport, either a tractor or a
truck is used. The farmer loads and transports the straw to the plant, and the plant personnel unloads it either by forklift truck, overhead travelling
crane or the like. When transporting by haulage contractor, the farmer or the haulage contractor loads the truck, the haulage contractor travels to the
plant where the plant personnel unloads by forklift truck, overhead travelling crane or the like. In certain cases, there are sometimes more people involved
in haulage by contractor than in transporting by the farmer which may result in waiting time for some persons, e.g., the driver. The driver often
uses part of the waiting time for mounting or dismounting straps around the load. By transporting by tractor, the rate of speed is considerably
lower than that required by haulage by haulage contractor, and consequently the capacity is lower. Figures 12 and 13 show the manpower required
and the capacity when delivering big bales to the plant /ref. 19/. The figures clearly show that the manpower requirement increases, and the
capacity decreases with increasing transport distance. It is also obvious that the manpower required is greater and the capacity lower when transporting
by tractor than by haulage contractor, and that the differences increase with increasing transport distance.
When transporting by truck, there are almost always loaded 12 bales on the truck and 12 bales on the truck trailer distributed in two layers. This is
also seen by tractor transport, but load sizes of 16 or 20 bales is widely used, particularly for transport over short distances.
Plants unloading by crane, often require that the bales are arrangement accurately on the vehicles, and that the bales should have a specified
dimension and not exceed a certain weight. In connection with the delivery, only big bales have been mentioned, because the plants are upgraded
for this size of bales and handling technique. At a long view, also other methods ought to be analysed and large-scale tested, like e.g. straw pellets, whose volume weight is much higher.

 

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