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Strath Brown, the founder of Brown Engineering Group (initially J. S. Brown Industries), developed the tunnel concept in the 1970’s. Since then the systems have progressively been optimized and the efficiencies have increased to what they are today. A standard 30Ha tunnel now only requires as little as 0.7kg of coal per kg of dry tobacco produced and can run on 15KW per hour of electricity (20KVA Generator). As a comparison, conventional barns use between 3-4kg of coal per kg of dry tobacco. The savings on coal, electricity and labor make a tunnel a worthwhile investment.
A tobacco tunnel is a continuous system which means that hot air is blown into one side of the tunnel and is pushed through the tunnel to be exhausted at the end. Some of the moist air is returned to the heat exchanger room and mixed into the hot air stream so that the humidity is controlled in the tunnel.
Brown Engineering Group offers a range of tunnels from 10Ha to 120Ha with different configurations and options. We also have three types of heat-sources to choose from, a dry heat exchanger, a kettle and radiator system or a boiler and radiator system. We offer 4 layout options depending on the farmers building site and requirements:
- Single Pass or Straight tunnel
- Double Pass or Turnaround tunnel
- Triple Pass Tunnel
- Custom design
BEG provides all the drawings and equipment. A project manager is allocated to your project and will guide you through each step of the build.
The chongolo system, like the tunnel, is a continuous curing system where heat is introduced in one barn and only exhausted from the last barn after picking up as much moisture as possible throughout the system. Instead of moving the tobacco through the curing unit, doors in each barn are used to control the airflow through the system.
For a chongolo, Brown Engineering Group provides three standard options, 12Ha, 18Ha and 26Ha units. Each unit can use either a dry heat exchanger or a kettle and radiator system.
We supply all the drawings, steel work and electrics required for the unit including the vents, doors, roof, fans and heat exchanger. If a concrete roof is preferred, we will provide the design and required reinforcing. Alternatively, a corroboard ceiling can be used.
Conventional barns and downdraught barns are becoming less and less viable to cure tobacco. They are too inefficient, so it is becoming increasingly difficult to cover the cost of running them as margins on tobacco sales keep decreasing.
A solution Brown Engineering Group provides is to convert these older systems into chongololos or single heat source systems. Up to 16 furnaces can be replaced by a single dry heat exchanger or kettle and radiator.
We have standard designs or can offer custom designs to convert these old systems into more efficient chongololos or single heat source systems. We supply all the drawings, steel work and electrics required for the unit including the vents, doors, roof, fans and heat exchanger.
Sometimes a farm has an old system on it that is rundown or not working. Brown engineering can perform a survey and provide a quote to renovate the system. We will help you understand how the old system worked and can supply all the necessary equipment and drawings to modernize the unit and get it up and running again.
Curer Unit Equipment
We stock a vast array of curing unit equipment and spares. If we don’t have the equipment in stock, we should have the raw materials to make it up as soon as possible.
The technical sales representative at Brown Engineering will guide you through the calculations to ensure you know how many hectares your unit will be able to cure. We will go through the assumptions with you and will take into consideration your specific requirements and growing conditions on your farm.
The curer is sized for a single planting. If you do irrigated and dryland in one season, then it will be able to double the amount.
An example which shows some typical assumptions and the formulas used is shown below. The example considers a 30Ha tunnel. If you have 2 plantings in one season the tunnel will do 60Ha. However for regions with a thinner leaf or if a high wet bulb is used, curing time could be reduced to 6 days in the tunnel and 1 day in a green bay, which would mean that the same tunnel would be able to do 21 Trolleys per day which is 35Ha.
This is a question often asked. However, it must always be considered with the cost of the cure. Profit is selling price minus cost price. So, the ultimate goal is to get a high selling price and low-cost price per kg of tobacco.
All systems if run properly will give you a very good cure. A tunnel gives you the lowest cost price per kg of dry tobacco. It will cure very nicely if uniform tobacco is being loaded into the unit from day to day and a few basic curing principles are executed correctly.
The same applies to a chongololo as it is also a continuous system. It is a bit more expensive to run than a tunnel, but the advantage with the chong is that you can vary conditions slightly in each barn depending on the tobacco by adjusting some vents. This gives you a bit more control if the tobacco is not uniform.
Some of the best curing units are the single heat source units, where there is a fan in each barn that draws hot air from a common duct. There are four doors to control the amount of heat, the amount of ambient air, the return air and the exhaust. These systems are not continuous so they are not as efficient as a chongololo or tunnel but there is more control over the tobacco in each barn and the tobacco does not have to be uniform from day to day.
The initial cost per hectare is considered when you want to build a curing system. However, the running cost per hectare in the following seasons must also be considered to see which option has the best return on investment. A chongololo is a high-pressure system and uses large fans. An 18Ha chong at max uses about 13KW which is 0.72KW per hectare compared to a 30Ha tunnel which only uses about 10KW which is 0.33KW per hectare. This shows that a tunnel uses less than half the amount of power than a chong. If the electricity must be produced by a generator, the cost saving of a tunnel is even larger.
Another aspect to consider is the amount of scrap produced. Conventional barns or a chongololo that uses tier poles results in about 5% loss due to scrap. The tobacco is reaped into clips, stacked onto a trailer, lifted past tier poles into the barn. Then after curing tobacco is passed down through tier poles, stacked onto trays, carted to the shed then unloaded from the cart into stick bulks. For a trolley system, the tobacco is loaded onto the trolley and only touched again when it is unloaded into stick bulks. This reduces the amount that the tobacco is handled, and scrap loss can be as low as 0.3%.
A dry heat exchanger is one that does not use circulating water to transfer heat from a furnace to the air. A kettle and boiler use a pump to circulate hot water through a radiator. Fans blow through the radiator to heat up the air. A dry heat exchanger uses a steel shell around the furnace. Air is blown over the steel shell to pick up heat. The shell also incorporates ribs or pipes to increase the surface area for more heat to transfer to the air.
A kettle and a boiler look the same but operate slightly differently. They both use a pump to circulate hot water through a radiator. Fans blow through the radiator to heat up air.
A boiler is sealed by a pressure relief valve which means that when heat is supplied, the pressure increases in the boiler up to about 3 bar. This increase the boiling point of water in the boiler to about 130 degrees Celsius. The water that circulates through the radiators can reach 120 degrees Celsius. A kettle on the other hand is not sealed, it has a header tank which ensures the kettle is always full. The pressure does not increase in a kettle, so the boiling point of the water is only about 100 deg Celsius. This means that the water circulating through the radiators only reaches about 98 deg Celsius.
The advantage of not having a pressured system is that the steel plate used to make the kettle is lighter than that of the boiler. It also means that a kettle does not need a government inspection every 3rd year. These two points make it cheaper to buy and operate. With our new radiators, the water temperature of 98 deg Celsius through the radiator is enough to heat the air up to a maximum of about 85 degrees Celsius which is ample for tobacco curing.
The dry heat exchanger is seen as an economic short-term solution. A kettle or boiler is ideal for a long-term investment. Many boilers installed before 2005 are still in use today. The total power and efficiency of the three different systems are very similar. Please see the table below for a comparison.
Service & Backup
Before the curing season starts, Brown Engineering offers preseason unit inspections in Zimbabwe, Malawi and Zambia. Please contact us if you would be interested in this service.
During the season, we offer around the clock backup service with dedicated teams on call. We plan 6 months in advance and hold enough stock for any situation.
In 2018, 45m of a tunnel in headlands burnt down. The Brown Engineering teams responded and within 5 days the tunnel was operational again. The ceiling, the trusses and the roof had been replaced.