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Vermiculite is a naturally occurring mineral. When crushed, graded and fed into a hot furnace (1200ºC or 2,200ºF), the vermiculite expands to produce a lightweight particle that is then used in a range of horticultural and industrial applications. The process requires a very rapid heat transfer to the particles to promote as large an increase in particle size as possible to give low densities. Historically, vertical shaft and rotary kilns have been used to exfoliate vermiculite.
The TORBED processor has shown itself to have unique capabilities in this industrial mineral processing application in producing higher quality,lighter and more consistent product with lower energy consumption. High heat and mass transfer and precision of control with the TORBED processors have provided these advantages. Most important, the TORBED process provides more saleable product per unit of raw material fed i.e., a higher yield.
TORBED processors have been successfully installed in 18 major production plants in Europe, Japan and the United States of America.Throughputs vary according to raw material grading but typically range from 1-5 tonnes per hour. The oldest Operational TORBED was sold to British Gypsum in 1989. Regularly refurbished, it has now completed 35 years of service.
The ability of TORBED reactors to carry out flash processing of fine powders with particle retention times of often less than 50milliseconds has led to the development of novel products and processes. Flash calcining is used both in industrial mineral processing and industrial catalyst processing. This ability was developed at pilot scale (up to 300kg/h). Subsequently and a 1.5m diameter TORBED Reactor was successfully commissioned in 1999/2000 for the flash processing of sub 5-micron ore, producing white paint dye from a clay feedstock for the then English China Clays (now Imerys). This reactor uses a direct gas injection technique whereby natural gas is mixed and combusted directly in the process chamber base allows intense high temperature calcination reactions to be undertaken.
Multiple dense phase conveying injectors are used to distribute the raw material feed around and into the TORBED Reactor’s process chamber. The finished product is carried out of the TORBED Reactor in the exhaust gas stream and collected in a bag house after gas and solid cooling.
The ability to heat the fine particulate feed from ambient to more than 1,000ºC in milliseconds provides a process environment where high surface area products are routinely produced. It is not uncommon for a tenfold increase in particle surface area to be achieved.
These abilities, amongst others, distinguish the Torftech technology from traditional calciners such as rotary kilns.
Torftech’s first dryer for industrial biomass processing was installed at Sappi in Mastricht in 2002.This three-stage TORBED drier is used to dry 6 tonnes per hour of paper sludge from 60% moisture to 5% moisture, removing 3.5 tonnes per hour of water using a stream of waste heat at 110ºC. Replacing a (significantly larger) industrial belt drier used for the same purpose, the TORBED achieved greater availability and reduced cost by avoiding maintenance needs and being capable of remote operation. The dried paper sludge is used as animal bedding, ensuring that a waste stream that would otherwise rot and create carbon emissions is put to use.
Other large-scale dryers have followed. Eleven of these machines have been installed across Poland and Belarus, principally drying sawdust and waste wood chip for the commercial biomass pellet market. At maximum capacity, the largest are capable of drying 10T per hour of feedstock at 50% moisture to 12% moisture, removing 4.3T of water per hour. The evenness of processing in a TORBED dryer ensures that the feedstock does not become discoloured.
These dryers can also be used in the first phase of more complex industrial biomass processing and also as apart of industrial sludge treatment processes (as described below).
Building on our experience at SAPPI and with calcining, this plant embraces the circular economy and uses more than one process, drying paper sludge and the calcining it, providing heat both for industrial purposes and to dry the sludge. The ash from the calcination is a useful cementitious mineral capable of use as a cement substitute in concrete. As a final stage of the combined process, a mixture of air and process gas is mixed with the calcined mineral, which adsorbs CO2 from the gas stream. This is a practical example of Torftech’s technology being used to de-carbonize a foundation industry.
Torftech’s first dry gas scrubbing project was in the Aluminium Industry.
The extract ductwork that draws fumes away from the smelting pots in an aluminium smelting plant contains levels of contaminants that need to be removed from the exhaust before discharge to atmosphere. The TORBED process is used as a reactor to contact alumina with the exhaust gas stream to adsorb the pollutants prior to discharge. A TORBED processor can be employed in a single or two-stage assembly providing unique adsorption properties. The low pressure drop across TORBED processors is important because the volumes of gases to be processed are high at 200,000 nm3/h (117,500 acfm) per TORBED processor and the particle size range that is used in the processor is small and substantially un-graded. The use of venturi reactors, fluidized beds and reactant recycling systems had been explored, but these methods usually lead to increased processing time and/or significant pressure drops across the system which waste considerable amounts of energy. In some instances, up to 20 times more reactant would have been needed to scrub the exhaust gases. These technologies also call for large ancillary processing plants with additional capital expenditure.
After construction of a 5000mm prototype in 1993, a 6000mm(20 ft) diameter two-stage reactor was installed and commissioned in early 1994. The results were sufficiently favourable that New Zealand Aluminium Smelters Ltd decided to proceed with a new scrubbing plant based on thirteen 6000mm (20 ft) diameter TORBED reactors. These were installed in1995/6 and the plant is achieving the best world standards. A further 6 such units were commissioned at Comalco’s Bell Bay smelter in Tasmania in 1997.
The ability of TORBED reactors to handle wide variations in feed shape, size and quality is being applied tothe controlled combustion of a variety of materials including carbon, shredded wood waste, organics and hydrocarbons, acting variously as an industrial waste combuster or the source of heat for a biomass-fuelled power station.
One such application that relies on the absolute precision of the TORBED processors is the processing of Spent Pot Lining (“SPL”) from the aluminium smelting industry. The refractory lined “pots” in which aluminium is smelted are removed from service when they have reached the end of their useful life and the spent refractory lining and carbon cathode are broken up and removed from the pot as Spent Pot Lining (SPL) so that a new lining and carbon cathode can be installed. The material that is removed is often classified as a toxicwaste. SPL contains a mixture of refractory, carbon and other contaminants including fluxes and cyanide. Comalco Aluminium Ltd of Australia commenced a development programme in 1987 to process SPL to produce a waste stream that is non-hazardous. To thermally dissociate the cyanide in the SPL, processing of the material was attempted in various calcination devices including a rotary kiln, fluidised bed and transport reactor without success. A TORBED reactor proved to be successful. In 1990, a plant capable of processing 3,000 tonnes per year of SPL was commissioned. The process has proved to be as effective as predicted and by the end of1994, the plant capacity was increased to 10,000 tonnes per year.This is a well-proven industrial application of the Torftech technology.
The Torftech technology was identified as being one capable of satisfying the need for the controlled combustion of shredded wood waste. Pilot trials were successfully completed and two 5MWtcombustors were installed in 1999 in the Netherlands. These processors were required also to handle tramp feed materials including door handles, hinges,nails and other metal and incombustible materials. This was Torftech’s first industrial biomass processing plant, offering a practical, compact alternative to conventional fluidized bed combustion technologies . Subsequent installations have included the combustion of rice husks, where the TORBED processors control of temperature allowed production of amorphous silica ash without significant traces of crystoballite.
Extending the work done on biomass combustion, Torbed processors have been used as industrial gasifiers, processing waste wood, straw and miscellaneous biomass. Unlike combustion, gasification does not result in full carbon burn-out, producing biochar together with residual ash. Biochar produced by a TORBED gasifier has been used commercially for soil remediation. Tests by the university of Leeds identified the surface area of biochar produced from straw in a TORBED gasifier has a surface area of 463 m2/g. This can be significantly increased if activated with either CO2 or KOH. Then TORBED gasifier offers a compact and highly effective alternative to updraft, downdraft or fluidized bed gasifiers.
In 1993, a pilot plant capable of processing 150 kg/h of oil-contaminated solids was fully tested at BP’s Sunbury laboratories. A consortium of oil and gas exploration companies then funded the further development of a TORBED processor as a transportable de-oiling plant for eventual offshore use. This plant demonstrated the capability of stripping hydrocarbons from solids in a controllable manner.
When recycling machine shop (“swarf”) and other metal wastes such as mill scale, it is a problem when these contain cutting oil and a coolant since the wastes cannot be added directly to a remelting process without serious disruption of the molten metal from the steam and explosive vapours that are generated.
Rotary kilns have been used in the past to evaporate the oil and water from these wastes providing a clean feed stream to the remelting process.Because the feed stream has a widely varying quantity of cutting oil and water, the process needs very close control to prevent combustion of the oil in the drying process. A TORBED processor was shown to provide up to 8 times more throughput of clean dry metal per unit of energy input than rotary kiln-based techniques. The quality of the metal was found to be consistent and of higher purity with minimal oxidation.
A further extension of the use of TORBED processors for devolatilization was into industrial catalyst processing, where two processors were installed for a process to remove hydrocarbons, carbon and sulphur from spent catalysts to facilitate their recycling.
In the summer of 2000, a 1.8m diameter reactor was commissioned for the devolatilisation of up to 20 t/h of old asphalt coated road stone.The plant was opened formally in September 2000. The plant is designed to volatilise old asphalt (laden with PAHs) so that the road stone can be recoated and reused. The volatiles produced in the process are thermally oxidised directly in the upper part of the TORBED reactor.
40% of the machines that Torftech has sold have been to the food industry.
Approximately half of these have been for applications in the cereal and snack food industries that accounts for many of the household names amongst our clients.
With snack foods, most products available are either fried or “cooker extruded” before being dusted with oil and flavours. A trend toward lower fat and healthier eating snacks has allowed the development of new low-fat products, particularly based on expanded “half pellet” products.
For both snacks and cereals, the TORBED process has shown itself to have unique capabilities in producing higher quality, lighter and more consistent products with lower energy consumption. Indeed, some shapes of product can only be air expanded in a TORBED processor whose high heat and mass transfer and precision of control provide these advantages. The installation is quiet and compact. The TORBED process is in successful operation in several major production plants in Europe, Australasia, the Americas and the Middle East. Throughputs vary but typically range from 50-500 kg per hour.
Another significant application for Torbed processors has been drying. Nearly half the dryers that Torftech has sold have been to the food industry. Principally these have been used to dry starch powders. The example pictured opposite is used to dry potato starch. Other products dried include Carob powder, carrot flour, cheese, dextrin and distillate solids.
Traditionally spices have been pasteurised by steam orradiation. The former technique has limitations in terms of product quality and ultimate levels of pasteurisation. It has been found by extensive trials on a range of spices that much lower residual contamination can be achieved using the TORBED reactor with hot air as the process medium.The TORBED process has shown itself to have unique capabilities in these applications in producing higher quality, more consistent product at low energy consumption with low residual contamination levels. The process can rapidly be changed for different products and characteristics. The installation is quiet and compact. Full-scale production plants are in operation processing 300 – 400 kg/h of spices and other ingredients.
The final area of food application`, is coffee and cacoa, roasting or torrefaction, where a TORBED processor has been successfully used as an alternative to a rotary kiln. Machines for this purpose have been supplied in both the UK and continental Europe. This application of the TORBED has been extended to nuts being roasted for snack purposes.
Roasting with a TORWAVE offers many benefits to coffee roasters. Combining conventional hot air heating with microwave power offers total control over the roasting process. It is also an intense process, with time reductions of up to 80% compared to conventional roasting, without any of the downsides of traditional fast roasting.
The TORWAVE also unlocks new possibilities for coffee flavour and extraction with increased bean surface area. This is all done in a fully electric system, displacing any requirement for gas burners.
TORWAVE roasting is a green solution to get more out of your beans.
TORWAVE roasting happens throughout the whole of the bean simultaneously, allowing flavour development without overprocessing the outside or under-processing the inside.
The high intensity heat transfer in the TORWAVE leads to increased bloating and porosity of the coffee beans, increasing surface area by up to 20%.
Independent control of hot air and microwave power lets roasters precisely control the roast conditions and be flexible to get the most out of any bean
The TORWAVE processor can provide all of these benefits with a fully electrical system, allowing a move away from traditional gas fired roasters, reducing CO2 emissions.
Our processors have capabilities in a range of gas-solid contacting processes from high temperature flash calcination to low temperature drying across a diverse range of industries. Often our processors offer an alternative to less resource-efficient conventional technologies. Find out about some of the processes for which our technology has been used and see if we could assist you.
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