Farmer's Weekly (South Africa)
This tunnel farmer has gone loco
AWestern Cape farmer swears by old, converted, coal-burning locomotives for heating tunnels, and they cost less than conventional units.
A conventional coal-burning unit for heating tunnels costs about R120 000, which is a large capital outlay in anybody’s book, specially in a vegetable-production, under-plastic system where profit margins are relatively low.
Deon Rossouw, of Kilprug near Paarl, found a cheaper alternative when he decided to modify a locomotive for heating his tunnels. That was four years ago. Now he has four such units, heating tunnels with a total floor area of 4ha. He says his “locomotives” run more efficiently than the coal-burning heaters available on the market and cost less than a third of their price.
Rossouw bought his first Class 14 Garrett locomotive in Mossel Bay for R3 000 in 1984, and has subsequently installed another three smaller Class 24s at his English cucumber and cherry-tomato production tunnels. These were bought at De Aar, also for R3 000 each.
All the excess steel was cut off the locos, so only the boilers and fireboxes remained, before they were transported to Paarl by lowbed trucks. Transport costs to Paarl were R3 000 each for the 28-t Class 14 and the 22-t Class 24 machines, and the cost of the crane for unloading and positioning them was R1 500 for each unit.
CONVERSION
The conversion entailed rerouting the hot gas pipes where heat is exchanged with the water pipes. In the locomotive, these pipes only pass through the heat exchanger once before the gas is exhausted through the chimney stack. They have now been modified to pass through the exchanger three times, making the unit more efficient. Other changes involved the fitting of a blower fan at the firebox and an extractor fan at the chimney, coal feeders, tanks taps and pumps. The modification cost some R2 500 in labour and almost R20 000 in components.
“Fortunately I got hold of an ex-South African Railways artisan who had the know-how to do the conversion on the loco. He also gave us some valuable tips on operating it. He suggested that we put small amounts of horse dung in the water pipes when leaks develop. The fine particles settle in the places where the water seeps through, blocking it. He learnt this trick while working on locomotives in the Karoo.
“When leaks developed they would stop and collect donkey dung along the tracks and put it in the water,” he says.
The electrical installation that controls the whole unit cost R5 600 when it was completed. It has many back-up and safety systems. If anything goes wrong, it automatically shuts down.
If the automatic shutdown is overridden and the system is running manually, a siren goes off if there is a malfunction in any part of it. Total cost came to just over R35 000 per unit.
With the first unit, Rossouw ducted the hot air from the locos to the tunnels by means of large fans and plastic ducts, but the fans have high maintenance and electricity costs. Condensation on the bottom of the tunnel roofs is also high, and promotes crop diseases.
UNDER-FLOOR PIPES
In the newer installations, the tunnels are heated by water pipes running beneath the floors. “The closed-circuit system needs very little maintenance, humidity is lower, so disease problems are reduced, and the small water circulation pumps use very little electricity.
“The temperature in the tunnels is thermostatically controlled to remain between 15 and 18C. The water temperature has to be raised from about 6C by the boilers.”
The first boiler is lightly stoked so the water is preheated before entering the second one. This type of installation runs more economically than a single unit. Each boiler uses about 2t of coal a night, and costs a total of 33c/plant/month to heat the tunnels during the cold Cape winters. Only Grade A coal, which has an energy value of 28MJ/kg, is used.
This is more efficient than oil, diesel or electricity. Rossow says some farmers in the area use similar installations but burn wood instead of coal. However, large quantities of wood are required.
The only maintenance on the boilers is to flush out the coal dust from the circulation system with high-pressure hoses every week. The water is flushed out and replaced two or three times a year.