Avoiding landfill by incineration20 March 2006
Cape Produce Company have installed a R5 million incinerator as part of an ambitious scheme to reduce tannery waste by 90%, in a way that meets South Africa's strict (but usually unenforced) air pollution laws, and generates a saleable byproduct (steam) in the process.
Tannery manager Peter Howard believes CPC's incinerator project is the first of its kind anywhere. If it performs to expectations, he thinks it will become widely used, perhaps standard practice, especially where landfill is prohibitively expensive.
The project goes back to 1996, when the Port Elizabeth hazardous waste dump operator, Waste-Tech, increased their charges from R50 to R650/ton. CPC were generating 400 tons/month at the time.
'Initially, our goal was to reduce the water content, so we started drying the waste', he said. 'Co-incidentally Waste-Tech were operating a medical waste incinerator, so we asked them to investigate whether the waste would burn. They reported failure, but we suspected that they weren't motivated.
'We then built ourselves a Dutch oven, similar to those used by the timber mills, and established that the waste burned quite well when mixed with coal. At the time, we were operating coal boilers so we squeezed the waste into brickets and added it to the coal feeding the boiler. The authorities then stopped us burning the waste in the boiler.'
In the meantime, CPC had approached a Boksburg company, which made incinerators for abattoirs, for a demonstration which was carried out at Leeuwkop Prison in Johannesburg. 'We arrived with a load of compressed blocks of beamhouse solids', Howard said. 'The incinerator was adjacent to the abattoir (in the kitchen area), staffed with long-term prisoners mostly in for violent crimes, many of them armed with flaying knives. It wasn't a comfortable time.'
'The prisoners behaved, but the waste didn't. The blocks were charring on the outside, forming a clinker, and refused to burn. They tried breaking them up with long rakes, still to no real effect, until that is the temperature reached 800ºC, at which point they burst into flames and continued burning. The warder in charge gazed at them with wonder and asked if we had 'more of that stuff', Howard said. 'I think he could see himself having gallons of diesel to sell for his own account.'
By now, two years had elapsed, with no end in sight. 'The next step was more difficult', Howard said. 'We had to then apply for a permit to build and operate an incinerator and scrub the emissions to DEAT (Department of Environmental Affairs and Tourism) specifications. Two court cases and R500,000 in consultancy fees later, in July this year we secured a one-year temporary permit to proceed.'
The resulting system includes a 'fairly unremarkable' 450m
3 fluidised bed incinerator, which will incinerate around 15 tons/day. The emissions are fed to the scrubbing equipment, which includes a quench tower to address particulates and a packed column where the gasses are passed through a caustic solution. The quench tower and the packed column are both constructed from stainless steel, and are the most expensive parts of the system.
The incinerator burns waste at temperatures between 850°C and 1,000°C. The hot gas passes through a boiler on the way to scrubbing where the heat is used to produce steam.
One of the permit conditions was to install a weather monitoring station and to record levels of SO 2 and H 2S for three months prior to commissioning. The system was built in the former boiler building and was fired up in September.
In the final configuration of the system, all five of the tannery's waste streams - screenings, clarifier, centrifuge, hair and the pallets which come with imported raw hides (which must be destroyed in terms of veterinary regulations) - are collected and mixed before incineration.
The waste is thrown into a specially designed device, which looks similar to a clarifier. A circulating bridge mixes the waste while moving it to a conveyor which then transports it to the incinerator feeder. The system is automated, regulating the feed rate based on the continuous monitoring of the temperature inside the incinerator.
'The downside, for us, has been that there are no references anywhere', Howard said. 'We've had to pay school fees - from Sub-A. For instance, it was estimated we would need around 20kg of caustic soda a day to keep the scrubbing water at around pH9. Initial results indicate that this will be closer to 200kg a day.'
Has it been worth it? 'We've ended up with ground-breaking but expensive technology to handle waste disposal', he said. 'The reason we persisted with it, fought for permission, paid the cost, was that we believed - still believe - that the costs of fuel and disposal will continue to rise, and that environmental legislation will be enforced, and we wanted to be ahead of the game.
'Our beamhouse waste has a calorific value equivalent to 90% that of coal, which allows us to use it as fuel for the boiler. Together with the disposal savings, it gives an acceptable payback.
But the real reason for going ahead is [CPC managing director] Benji Lapiner's philosophy of independence and long-term cost control.
'In fact, when the DEAT gave us permission to proceed, Waste-Tech cut their charges, which are now R260/ton. Also, some of our competitors continue to dispose illegally, because the laws are not being enforced. On top of everything else, there has been a major downturn in the tanning industry. It may not have been the right financial decision at the time - that's difficult to gauge - but pioneering technology is often difficult to justify. One thing's for sure, we're better placed to deal with whatever the future holds.'