The Box(Bin) barns are Tobacco curing barns designed to cure tobacco densely loaded in boxes.
The most common size is the 10 box barn having a curing capacity ~ 2 tons of dry leaf per cure .
They are Indirect fired barns, with Upflow forced air recirculation.
Barn’s structure is similar to a container structure which is insulated to minimize heat losses.
The “container” is divided in 2 sections :
Curing room & Machine room separated by a separation wall .
Separation wall is leaving a free space at the lower part for the air supply ( lower plenum) and a free space at the upper part for the return air upper plenum).
The Curing room section is the front part of the container where the boxes full of tobacco are pushed on rails to touch well each other when in the barn so there are not air gaps in between the boxes in order to avoid air bypassing the tobacco mass.
The air is heated and recirculates through the tobacco in the boxes coming from the air furnace through the lower(supply) plenum & returning to the air furnace through the upper (return) plenum.
The lower air plenum includes the air distribution floor which is a slotted floor which helps distribute evenly the air through all barn’s surface .
On top of the front doors there are the air exhaust dampers(gravity dampers moving freely) which reject to the atmosphere a portion of the barn’s hot humid air .
The amount of rejected air is equal to the amount of fresh air sucked through the fresh air intake damper of the air furnace , it is heated from the heat exchanger and it’s amount depends on the opening of the automatically servocontrolled damper on the air furnace according to the required Wet bulb temperature (humidity level) during the different curing stages in the barn.
The Machine room section is the back part where the air furnace VCU
( heat exchanger , fan , electrical panel with curing controls & fresh air intake damper) is mounted
VCU heats and recirculates the air in the curing room through the supply & return plenums, one on top of the air furnace & the other under the air furnace.
The fresh air intake damper on the air furnace is sucking a controlled amount of fresh air ( through the curing control) which is heated and then mixed with the continuously recirculating in the barn air .
The air is pushed through the tobacco mass . A portion of this mixed air ( fresh heated & recirculating) after passing through the tobacco mass, picking some moisture from the heated tobacco , is exhausted to the atmosphere through the curing room’s front exhaust dampers.
The front exhaust dampers ( which are free moving) open a little or more pushed by the positive air pressure created by the fan when the air furnace’s fresh air damper opens a little or more .
The heat to the tobacco is supplied by the air furnace’s (VCU) heat exchanger which is either
-a stainless steel heat exchanger with Diesel or Gas pressure burner ,or :
-a hot water heating coil which is supplied with hot water through a servocontrolled valve taking order to open or close from the curing control’s Dry bulb thermostat .
Hot water is supplied to the VCU’s heating coils through insulated pipelines .
Hot water is produced in a client’s Hot water boiler firing coal .It is recirculating in the piping through a hot water recirculating pump.
Ventobacco ® factory made Box barns are made with galvanized Steel and polyurethane insulated panels .
The barns made by the Ventobacco licensed manufacturers in different countries can be constructed with different material according to the material availability in each country .
( All steel , Steel frame with concrete lower plenum ,bricks or ytong (hebel) & concrete , wood , retrofitted container structures ,etc. insulated with polyurethane sandwich panel insulation or glasswool or similar insulation or a combination of all above ) according to the material availability & cost on each market .
When home made barns ,no matter what material is used the internal barn’s sizes have to be respected so the size of the lower and upper air plenums are correct ( to keep the air velocities correct according to the air furnace’s air supply) and the internal width & length of the barn is correct so the boxes can get in properly .
The sides & roof thickness are not that important since they only alter the outside dimensions of the barn which have no effect on it’s operation.
When barn structure is made with bricks or Ytong & concrete , the cost of the barn’s structure is usually smaller than this of a metal barn since :
-the building material is usually found locally without added shipping cost and local labor’s cost is smaller than a metal factory’s labor cost.
– when several barns are required they can be build with common walls which saves the cost of 1 wall per barn .
On every case a good metal shop is needed because the boxes (bins) are made in steel either galvanized of painted .
2 Basic Designs of the barn:
-Barn tall complete with lower plenum built in.
This design is the most expensive since it is a complete barn that can sit on any flat surface without need of special foundation for the formation of the lower plenum .
( since a tall metal beam forms the lower plenum).
– Barn short without the lower plenum built in .( to sit on concrete beams ~ 12 m long )
This design is cheaper , easier to built ,easier to transport &faster to assemble on site.
It requires the customer to build the concrete beams which form the lower plenum where the barn will sit on .
Usually when barn’s price needs to be minimized , the short design is preferred and customer builts the lower plenum with concrete.
The loading flat concrete area in front of the barns can be built in at the same level with the lower plenum in order to ease box entrance in the barn.
All steel barn structures can be made either:
-Tall with lower plenum built in ,or
-Short to sit on concrete made lower plenum.
The steel barn structure can either be:
Modular frame & Panels ( Original Ventobacco retrofit design (box or rack))
with prefabricated frame modules made with galvanized tubes (which are bolted to each other to form the barn’s frame.
This frame supports the weight of all tobacco when loaded on racks besides the weight of the roof connectors and the roof.
Once the barn frame is bolted together ,the side & roof polyurethane sandwich panels are screwed on the frames with self tapping screws.
The side polyurethane panels do not support any weight but all loads are supported by the frame.
This construction allows :
– Retrofit from Box barn to Rack barn and vise -versa (the barn’s side frames can support the weight of the racks full of green tobacco).
– Easy assembling on site even by inexperienced labor .
– Disassembling of the complete barn at any time ( if customer needs to move it to some other place).
– Extension of the barn (to increase it’s size) by adding more modules .
– Use of thinner 40mm polyurethane sandwich panels with thin metal plates (0,4 or 0,5mm).
The side frame modules when totally assembled at the factory take more labor & shipping to the site takes more volume.
If site is far away & transport hard & expensive, it is recommended to ship the side frame square tubes cut & drilled but not welded to their final shape in order to save shipping volume & weld them on site using an assembling-welding table or use the following beam & panels structure.
Or Beams &Panels
– Cheaper & faster to build with less parts than the modular frame barn.
Can be completely made in the factory & shipped on special truck &
it can also be assembled on site
Made with horizontal galvanized or painted metal beams 3 or 4mm thick forming the lower & upper plenums where on the beam’s outer side the polyurethane panels slide to form the barn .
Since those beams are horizontal and there are not vertical beams
( besides the front doors frame’s vertical beams, the separation wall’s and back doors frame’s vertical beams), a part of the structure’s roof weight is supported by the polyurethane panels which have to be of increased thickness ( 50 mm min) with thicker metal plates on their both sides (0,6 -0,8 mm).
It may be easier, faster & cheaper for manufacturer to make this barn.
Most of box barns are made with beam & panels structure.
This structure has less frame parts & takes a ~10% less time to built.
It can be fully assembled in the factory & shipped assembled to the site if roads are big & low special truck available.
It can be shipped disassembled when site is far away from the manufacturing facility and be assembled on site.
It ‘s beams can be made in shorter parts to minimize weight & shipping length & these parts can be bolted together on site.
It cannot be retrofitted to rack barn since there are not vertical frames and just the polyurethane panels cannot support the weight of the racks full of tobacco.
It is hard to disassemble it after it has been assembled to move it to some other place.
Once it is assembled you have to transport it complete on special trucks.
This construction is similar to the previous construction made same as a shipping container ,usually preferred by manufacturers who are familiar with shipping container construction.
Walls & roof can be like a container’s walls insulated to the inside or outside with polyurethane panels or glasswool covered with metal sheets .
No matter what type of structure is followed ,the internal dimensions of the barn structure have to be followed in order to:
-Keep the air velocities correct to ensure uniform & efficient curing .
-permit to the boxes to enter the barn & fill the space in the curing room.
– leave the required distances from the sides of the barn .
There are cases where 40’ hi cube standard containers have been retrofitted to curing barns by opening the back side for the Machine room , adding a separation wall forming the upper & lower plenum , a distribution floor & insulating all structure.
In these cases narrower boxes were constructed and air furnaces were designed accordingly .
– Front doors
The front barn’s side (loading side) has the 2 loading doors.( container type doors) .
Doors need to be insulated to minimize heat losses and they must open wide enough to allow the boxes to get in the barn.
– Front dampers
On top of the front doors there are the 2 air exhaust dampers( gravity dampers) that move freely opening when the air furnace’s automatic damper opens ,closing when the furnaces auto damper closes .
CONSTRUCTION OF Ventobacco BOX BARNS locally by our licencees or appointed manufacturers.
In order to save shipping cost in some remoted areas where shipping may be very expensive ,Box barn structures can be made locally.
The barn structure can be made following any of the above mentioned designs with any suitable material after taking in account the following:
– Which material is best priced in the local market.
– Which construction minimizes the labor cost .( when labor cost is more significant than material’s cost)
– Which construction minimizes shipping cost ( a) raw material coming to the factory & b) barn shipped to the curing site).
– If curing site is far away from the factory ,select a barn type & design and organize your work in such a way that will allow you to make and assemble close to the curing site all parts that take big volume ,to minimize your transport (s) cost ( which in some cases can be very high per barn).
Boxes are made with galvanized or mild steel painted with antirust & enamel paint .
VV Boxes are standard in 2 sizes : Big box holding ~5 m3 of green tobacco & Small box holding ~ 4 m3 of green tobacco.
Both boxes have the same width (2.950 mm) with differences in height & depth so 10 big boxes or 12 small can get in the same barn structure .
Boxes can be custom -made in different height & depth according to client’s loading practices.
If you are going to use a box that is more or less wide than 2.950mm you have first to decide which box you are going to use and adapt your barn’s width to the width of the box or vise -versa .
The typical Powel big box includes an internal separator that permits a better & more uniform loading of the tobacco mass in the box minimizing loading mistakes.
Small boxes are of the same width ,but less deep and shorter than the big boxes and do not have the internal separator.
Boxes wheels are of good quality with good bearings to last for years .
Building 10 big boxes is faster than building 12 small and their cost is smaller since the wheels, ,tines and labor are less.
Loading tobacco in 10 boxes is faster than in 12 as well as moving them to the barns so usually clients prefer the big box.
Smaller boxes are used when harvesting tobacco with light harvesters that cannot handle the increased weight of the big box full of tobacco.
Boxes take a big shipping volume .
They can be totally assembled (welded ) in the factory which is economical only when curing site is close to the factory.
Alternatively to minimize their shipping volume and shipping cost:
They can be constructed bolted (with bolts & nuts) which takes more manufacturing time ,
The final weldings of the 3 sides can be done after transporting them to destination .( using a box assembling model-table).
Air distribution floor
Typical press-cut or perforated or slotted galvanized steel leaving ~ 8 % open surface .
Indicative type SUKUP .
Metal floor can also be build in factory by bending metal stripes leaving a small distance in between them so the total open surface does not exceed ~2,5m2 on a 10b barn.
Distribution floor can be made with other locally found material that may be cheaper (like wood) leaving an open surface as above.
The floor is not supporting any weight (besides a person’s weight that is pushing the boxes in the barn).
The purpose of this floor is to help the airflow in the curing room to be distributed in all barn’s floor surface without leaving curing room areas with less or more flow, so all tobacco in the boxes gets the same air flow.
The boxes ,when full of tobacco, ensure a good air distribution , so the use of air distribution floor when all boxes are equally loaded ( same weight i.e. leaf density) is not that important .
When barn’s air furnace supplies lots of air and farmer is exoerienced weighting each box so it is loaded with same amount of tobacco the distribution floor the distribution floor may not be needed since the dense tobacco mass is doing the distribution job.
NOTE: if some of the boxes are not equally loaded ( which can easily happen when boxes weight is not measured to be equal or with inexperienced farmers), the air flow will find the easier way to go , a lot of air will pass through the less dense box leaving all rest boxes with poor air circulation which will result badly cured leaf ,swelled stems etc.
Anyhow it is recommended with new customers to use a distribution floor .
10 b Barn Size
The typical common size ( 10 big box barn
( or 12 small) ) has a heat exchanger of 100.000 kcal/hr & 10 hp fan motor .
It takes a leaf volume of ~ 51 m3 of tobacco and it is designed to cure in~ 6 days.
The density of tobacco mass in the boxes depends on several factors like the leaf position, the leaf growing practices & conditions , the leaf maturity & quality etc.
When loading the boxes with leaves of lower plant position less density is followed. Density is increasing as leaves are harvested from upper plant positions . Maximum density when loading tips.
The 10 b barn with 10 hp motor is the ideal size & barn to start with in a new area where there is a potential for big tobacco curing needs in the future.
It is a barn that has extra power useful in first time curing in box barns to gain the required experience to decide the most suitable & practical size for the specific area .
First curings give the necessary information to both client & us whether a bigger size barn or an even bigger sized box could satisfy better the curing demands of the customer, increase the curing capacity of the barn , lower the investment cost or the curing cost, etc.
IMPORTANT POINTS on BARN’s structure & BOX construction.
-Construct your barn structure prototype carefully to ensure that all parts are properly made and when bolted –welded they fit where they are supposed to.
-Construct your box prototype carefully to ensure that all parts are properly made and when bolted –welded they fit where they are supposed to.
-Preventing air leaks ( from the barn structure to the atmosphere as well as in between the boxes and the sides of the barns)is very important for the performance of the barn.
Barn is designed so whatever air is exhausted to the atmosphere it is exhausted from the front exhaust dampers located on top of the front doors.
– Make all frame parts ,beams ,front doors ,separation wall etc to attach well to each other when assembled &
-Take care to prevent any air leaks when assembling the insulating panels on frames in order to ensure that all air will pass through the tobacco and will not escape out of the structure.
Use acrylic sealant or other suitable to prevent air leaks from insulating panel joints, from panel joints on frames & from lower & upper plenums.
– Curing room’s length is about 35 cms longer than what the 10 boxes need when they get in the barn so when boxes are overpacked with green tobacco and their doors may be bended they will all get in the barn .In order to prevent air bypassing from the space next to the front doors a piece of sponge (afrolex or similar) is welded on the front doors inner side .
– In order to prevent air bypassing the boxes from the sidewall clearance a rubber gasket is placed on the side panels.
– Make well all box parts so when box is assembled-welded it will be square.
– Ensure that when boxes are placed one next to the other in the barn there is not any gap between them to ensure that there will be no air bypassing through them during curing.
– Check that the proper distance of box’s wheel to barn’s side is followed to ensure that the boxes will easily get & travel in the barn.
The Air furnace:
The air furnace (VCU) is located in the barn’s machine room sitting on the lower(supply)insulated air plenum.
The upper return plenum is insulated, mounted on top of the air furnace.
The complete air furnace is supplied by Vencon Varsos SA. either completely assembled or disassembled in parts to save shipping volume.
It is designed so it can be mounted on either steel or brick barn ,tall or short with built in plenum or plenum made with concrete beams.
The Air furnace is built in a insulated casing as well as the upper and lower plenums.
The typical 10b hot water VCU frame size is 1,5m wide x1,3m deep x 2,05m high insulated on the out sides with 4cms polyurethane panels.
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