Designing a tobacco curing station

1. Decide the appropriate total capacity of the curing station taking in account the following:
-How much tobacco will be cured this season .

( kgs of dry tobacco per season & confirm it with the acreage of your farmers)

-How much tobacco is forecasted to be cured next year.

-How much tobacco is forecasted to be cured the year after.

The size of the curing station should be big enough to cure this season’s tobacco, with possibility to expand at least to the forecasted tobacco curing need of 2 years later.

Decide the capacity of the curing station in kgs of dry tobacco per season then in racks or boxes & then in size & number of barns.

Take as an average: Dry leaf production – 2.500-3.000 kgs dry leaf per hectare .

When curing with Rack barns:

– ~ 7 kgs dry tobacco per rack , per cure x ~10 cures in a season = ~ 70 kgs dry /rack /season.

When curing with big Box barns

– ~180 kgs dry per box ,per cure x ~10 cures in a season = ~ 1800 kgs dry / big box /season.

2. Decide the appropriate type of the barns i.e. Rack or Box barn.

When tobacco leaves are hand harvested it is more economical & efficient to select Rack barns.

When tobacco leaves are harvested by automatic harvesters it is more efficient to select Box barns.

3. Decide the appropriate size of the barns taking in account the following :

– The best size of the barn is the one that can be loaded with one farmer’s tobacco.

Loading tobacco from many farmers in one barn , may not give uniform curing.

If farmers are not that big, or barns are of bigger size, you can compromise & load tobacco from 2 farmers or even 3 knowing that you will not get the best possible cure.

-Have in mind that the bigger size barns are cheaper (per kg of dry tobacco)

i.e. a 120 rack barn can cure twice as much tobacco than a 60 rack barn with only 40 % higher price.

The box barns are ~10-15% more expensive than the rack barns of the same capacity due to the higher cost of the boxes.

The rack barns are extendible .

The Box barns are not extendible.

-Have in mind that the smaller barns are relatively more expensive ( when comparing dry leaf production/ barn’s price) than the bigger ones but they have the possibility of expanding to bigger size whenever you like. So if you plan to gradually increase the size of your farmers & the curing station in the near future ,it may be a good idea to get more smaller barns right now & start expanding them gradually whenever you decide. This gives you the advantage of constructing the whole curing station right away with all infrastructure ready with smaller barns & simply you enlarge as many rack barns as you want whenever you want to without having to make a new infrastructure (concrete pads, shades, road ,electrical& fuel connections ,etc) that it may be difficult & more costly to construct later.

2. Decide alternatively the style of the curing station according to your budget:

-Simple curing station with the barns (only) mounted on non insulated concrete base, simple shades with removable cloth cover & dirt roads.

-A better curing station with flat concrete, permanent metal shades & paved station’s road .

– State of the art curing station with raised level under the metal shades & paved road on lower level to facilitate unloading of green tobacco from the trucks & loading the green tobacco in the barns ,standby genset, central control station with monitoring of curing & dry tobacco warehouse.

3. Decide the basic design (layout) of the curing station:

– Barns in 2 rows facing each other with the access road in between.( ideal for a fe up to hundreds of barns).

– All barns in 1 row with the access road in their front .(good for narrow plots).

– Barns in 2 rows backing each other with 2 access roads on both barn’s front sides (usually when barns are hot water with solid fuel firing).

– A combination of the above.

4. Decide the fuel to fire:

In big curing stations with several barns we should prefer the cheapest fuel easily available in the area in order to minimize the tobacco curing cost no matter if the installation may require some bigger initial investment .

In small installations and mainly in first time installations we usually select the easier to get fuel ,the cheaper barn to purchase and the easier installation to run and service .

Installations with Diesel or Gas fired Barns are in general ~10%-15% cheaper & faster to make than installations with solid fuel firing and need less follow up during their operation.

When firing solid fuels ( coal ,wood ,biomass ,pellets ) or heavy oil , the barns are hot water supplied i.e. they do not have individual burners on their heat exchangers but their heat exchangers(radiators) are fed with hot water supplied from a central boiler that burns the cheap fuels to heat water which is distributed through piping to several barns (always more than 3 or 4 ) .

The cost of the boiler ,pumps, piping etc (in order to produce the necessary hot water) is added on the cost of barns which makes the cost per barn ~10-15% higher than barns with individual gas or diesel burners .

The cheap cost of solid fuels may soon pay back this investment’s initial cost difference so it is worth of making a feasibility study consulting our Ventobacco well proven curing costs comparison data.

5. Select the appropriate location to build the curing station taking in account the availability of:

–Land ( flat land ,close to the tobacco fields, of enough size to allow possible expansion of the station in the future & possible construction of a warehouse.) The ideal length & width depends on your station’s layout so have in mind par.1 of this text when selecting the land.

–Access road (s),

–Fuel, Electricity & water.

Curing station should be build close to the tobacco fields so tobacco does not have to travel big distances to reach the curing station. (As a rule of thumb distance of less than an hour drive is considered acceptable).

6.Calculate the cost of the curing station.

After having decided all above add the cost of infrastructure & barns

Infrastructure:

-Land ,fence ,roads ,concrete barn bases , shades , fuel tanks & piping ,electrical control room & electrical lines, waterlines, standby genset & possibly warehouse.

Barns:

-Purchase , transport & assembling -training cost.

NOTE: depending on the country’s cost of the different available energy sources (fuel & electricity) select a barn type that has the minimum possible consumption of the expensive energy source. i.e. If electricity is expensive & fuel cheap in the country , select a barn type that will be very efficient in electrical consumption primarily.

BASIC FIGURES TO REMEMBER:

Most of the tobacco areas can cure easily 10 or 12 times per season.

( to simplify calculations consider 10).

Each rack can cure around 7 kgs dry per cure = ~70 kgs dry per season.

One hectare of tobacco usually produces ~ 2400 -3500 kgs dry tobacco = 3.000 kgs dry average. ( Adapt this figure to your local conditions )
One 60 rack barn can cure ~ 420 kgs dry( 500 kgs max) per cure =~ 4.200 kgs dry per season.
One 60 rack barn is good for ~ 1,25 hectares of tobacco field.
(when farmers become experienced 60 r barn will be good only for 1 hectare)

One 120 rack barn costs only~ 40 % more than a 60 rack barn.

One 120 rack barn can cure ~ 840 kgs dry (1000 kgs max) per cure =~ 8.200 kgs dry per season.
One 120 rack barn is good for ~ 2,5 hectares of tobacco field.
(when farmers become experienced 120 r barn will be good only for 2 hectares)

All Ventobacco barns are easily & cheaply extendible to 180 rack size.

One 180 rack barn can cure ~ 1.250 kgs (1500 kgs max) dry per cure =~ 12.500 kgs dry per season.
One 180 rack barn is good for ~ 3,75 hectares of tobacco field.
One 10 box barn is good for ~ 4 hectares of tobacco field.
The sizes of our rack barns increase per 30 Racks starting from 60 Racks.

(30 racks cure 0,5 hectare of tobacco = 240 kgs dry per cure = 2.400 kgs dry per season)

BASIC INFORMATION ON THE PREPARATION OF A CURING STATION

– LAND

Buy or lease the land ( Consult our typical Curing stations Layouts to select a suitable land ).

Once you decide the land you may send to Vencon Varsos S.A. a sketch if you want our proposal for the barn’s installation.

This land must have access road(s) to ease tobacco transport in & out.

– DRAWINGS

Get a civil engineer & a mechanical- electrical engineer to design your Electrical & Fuel installation according to the local standards.

-ELECTRICITY

Bring electricity to your central electrical panel & insure a good grounding triangle.

From your Main Electrical panel you will supply power to the Electrical Panel of each barn.

Your Station’s Electrical Installation must be made by authorized electrician.

Ensure that the Electrical supply is enough for your Installation without power drops.

When calculating your electrical loads take in account that ~ 80% of the barns will be running the rest ~20% will be standby either loading or unloading tobacco.

Add ~10% for your other small electrical demands( lights etc).

NOTE:

-3 phase x 380 Volts ( or other) electrical supply is always much cheaper both in Installation & running costs than a Single phase electrical supply.

Power required when 3 Ph x 380 Volts

~ 6 Amps / phase per barn .(60 r barn & 90 r barn)

~ 8 Amps / phase per barn .(120r barn & 150r barn)

~ 11 Amps / phase per barn .(180 r barn & 210 r barn)

~ 15 Amps / phase per barn .(240 r barn , 270 r barn and 10 box barns).

– GENSET

If you forecast Electrical power shortages during the Curing season , get a Genset capable of running at least half or more of the barns of your Curing Station.

NOTE : In some cases ,where Fuel is cheap & Electricity expensive or unreliable ,it may be cheaper to run the Curing station from a Genset instead of buying Electricity from the Public Power Corporation.

– WATER

Bring a water line to the land.

If pressure is not 3-4 Atm. make a water tank of ~ 6 tons where from through a pressure pump you will send water to the barns .

– FUEL

If you are firing Diesel oil.

Make 1 or more central diesel tanks or make 1 diesel tank per barn with a total capacity enough for~ 2 weeks or more operation.

Each barn will consume fuel according to it’s curing capacity ; i.e. from ~250 lts ( 60 r barn ) up to 800 lts( 240r or 10 box barn ) per week.

If you are firing LPGas

Make 1 or more central gas tanks or make 1 LPG tank per barn with a total capacity enough for~ 2 weeks or more operation.

Each barn will consume fuel according to it’s curing capacity ;i.e. from ~200 kgs ( 60 r barn ) up to 750 kgs ( 240r or 10 box barn ) per week.

If you are firing Natural Gas.

Bring the Natural Gas lines to each barn respecting the recommended size of gas piping.

Each burner when firing will need ~5 Nm3 per hour ( 60 r barn) up to 18 Nm3 /hour (the biggest size barns)

If you are firing Coal or Wood or Biomass

Bring the Hot water lines ( supply-return) from the boiler room to each barn respecting the recommended size of water piping.

Each barn will consume solid fuel according to it’s curing capacity and to the solid fuel’s heating value :

indicatively from ~400 kgs of coal ( 60 r barn ) up to 2.000 kgs ( the biggest size barns) per week.

-LINES IN THE CURING STATION

ELECTRICAL LINES from the main panel to each barn.

FRESH WATER LINES from the water supply to each barn.

HOT WATER LINES from the boiler to each barn ,or

DIESEL or GAS LINES from the tank(s) or main supply to each barn with filters & pressure regulators.

RUN A SIMPLE 2 WIRE CABLE (i.e.a telephone cable) from each barn to the control room where you can monitor the barns to a P/C.

– CONCRETE PADS

Prepare the concrete pads whereon the barns will be assembled .

Insulate your pads under the concrete with Styrofoam or equivalent to save fuel. Consult Vencon Varsos S.A. recommendations and our typical layouts .

– SHADES

Construct shades so tobacco & people do not stay under the sun or rain when loading -unloading the barnsin order to operatie efficiently the station with any weather.

– FENCE & MAIN ENTRANCE

Surround the land with fence & make one or 2 main entrances in order to control visitors.

– CONTROL ROOM wherefrom you can control and monitor the station’s operation & curing

– ELECTRIC ROOM where the main Electrical Panel will be mounted.

– GENSET ROOM where the genset will be mounted.

– WC .The people in a big curing station during the curing period may be a lot.

Example of designing a curing station with Rack barns .

We want to build a curing station in the middle of the tobacco area of …right next to the main road…..

We want to contract 80 farmers bringing their tobacco to the station.

Half of those farmers are 1 hectare farmers and the other half are 2 hectares.

We plan to grow( the best of ) them bigger to 3 hectares in the near future.

i.e. We want to build o curing station good for the 80 small farmers of today with the possibility to expand to 3 times more capability in the future.

TODAYS CAPACITY: 40 farmers x 1 hectare x 3000 kgs dry/hectare=120.000 kgs dry per season plus

40 farmers x 2 hectare x 3000 kgs dry/hectare=240.000 kgs dry per season

TOTAL 360.000 kgs dry tobacco per season TODAYS CAPACITY.

We can cure 10 times per season so the above dry quantity will be cured in 10 times

so we will need to cure 36.000 kgs dry per curing (per week).

Each rack can give ~7 kgs dry tobacco per curing so 36.000 kgs / 7kgs per rack=~5.150 Racks TOTAL TODAYS CAPACITY.

i.e 5.150 racks / 120 racks per medium size barn =

43 barns of 120 racks or 57 barns of 90 racks or 86 barns of 60 racks , or better a combination of the above.

The cheapest short term investment is to get the bigger barns & fill them with tobacco of 2 or 3 farmers .

Even cheaper would be to get less & even bigger barns i.e 150 r or 180 r.barns & fill them with more farmers tobacco.

If tobacco is uniform this can cure acceptably but usually it does not.

We have to think a little more & decide what barn size is in long term more economic to get.

If we want to do the cheapest possible curing station ,then the above solution is fine.

If we know that we are not going to expand the curing station in the near future the above solution is again fine.

But If we know that we are going to expand the curing station in the near future and we will need to get more barns next season ,then the above solution is not the best because we will compromise with quality this season & pay the cost of the more barns next season.

In such a case we should get more smaller barns right now, so we can have

– less farmers curing tobacco in one barn,&

– prepare all infrastructure right from the beginning.

– Enlarge as many and as much as we like next season.

Lets think a little more .

The 60 r barns are slightly bigger than necessary for the 1 hectare ( when inexperienced) farmers & small for the 2 hectare farmers.

The 90 r barns are good (slightly small) for the 2 hectare farmers but we may get 2 of the 1 hectare farmers in them or one 2h farmer that has not harvested enough tobacco to fill 120 racks.

The 120 r barns are slightly big for the 2 hectare farmers but we may fill them with tobacco from 2 farmers (one big & 1 small if needed).

To save some money & not get just one barn for one farmer we can get:

For the small farmers some 60 & some 90 barns so we can fill with one farmer’s tobacco the 60 r & with 2 farmers the 90 r barns.

For the big farmers some 90 rack and some 120 rack barns .

With these 3 sizes we have:

– the flexibility to fill the barns with the available tobacco( if farmers bring a little we fill the 60r,if more the 90r etc.)

– lower purchase cost than getting only the smaller size barns &

– the possibility to expand as many as we want next year (for those farmers who will prove good and we want to help them grow bigger).

-all infrastructure ready & we can increase (even double) the capacity of the curing station by simply adding extensions (one or more per barn) without need of building new barns, pads shades ,roads etc.

After having decided the number & size of the barns proceed to the desired layout so you can determine the ideal perimeter ,length & width of the plot.

Keep on following the above described steps & consult the basic barn & get the infrastructure prices to get a rough first idea of the cost.

Don’t hesitate to contact us for any further information you might need.