The CombiTech process can treat all „soft“ waste materials, that means any kind of plastics and organic waste and convert them into energy. Accordingly the initial waste volume will be reduced to less that 10% of its original volume and thus comes close the “zero waste” target. The simultaneous generation and sale of energy- rich gas and/or the resulting electricity and the recovery
of recyclable materials from the waste stream such as glass, metals and certain valuable plastics fractions not only cover the operating costs but result in considerable profits. Accordingly waste treatment is no longer a heavy cost burden for any municipality but rather a very interesting highly profit center. The project has been based on the assumption that the plant will treat 150.000 t/year of fresh waste plus 50.000 t/year old waste from the existing landfill, thus gradually removing it and recovering and rehabilitating the land and reducing the contamination of the area. The ratio of fresh waste and landfill waste can be varied to a certain extent. The most obvious advantages of a BioTech plant are:
- the biological and chemical processes take place in closed tanks, so that no environmental affects like smell or ground water contamination will occur, i.e. CombiTech plants can be installed close to populated neighbourhoods. Reference plants in Germany can prove this fact!
- A CombiTech plant produces an energy-rich gas and subsequently electricity; accordingly municipal garbage is turned from an expensive waste product into a valuable raw material which will reduce the import of problematic fossil fuels. The generated electricity is usually considered “renewable” so that the plant profits from favourable subsidies as well as from additional income from sale of CO2 emission certificates.
- A CombiTech plant can treat without problem mixed unsegregated municipal waste. A separate waste collection (organics/inert residues) is not required.
- A CombiTech plant can also accept sewage sludge as input material, which offers a cheap an efficient way of disposal with additional energy output
The proposed waste treatment plant consists of two parts, the first part for treating the organic fraction by anaerobic digestion (BioTech) and the second part for treating all the “soft” residues such as the plastics, the celullose/lignin fraction and possibly the non digestable compost substrate fraction from the digestion plant, which are not accessible to the biological attack of bacteria by a new and specific liquification and gasification process (SRS). In this way a maximum energy efficiency is obtained and the entire waste is treated/converted except for the mineral fraction (stones, sand, broken glass, batteries) which does not exceed 10% of the input quantity.
3 Products from CombiTech Process
The most important products resulting from the CombiTech process are:
a) Biogas is an inflamable gas which consists 65 - 70% of methane (practically natural gas). About 25
% are inert CO2. The calorific value of biogas is in the order of 6,5 kW h per standard m³. This gas like natural gas may be used directly in an industrial plant (such as ceramic, brick, cement, chemical plants etc.). It can also be purified and used as gaseous fuel for vehicles or may fed into the city gas grid. But the most frequent use is the immediate conversion into electricity in a local CHP power plant. b) The SRS process as second stage generates synthesis gas consisting of hydrogen and carbon
monoxide (H2 + CO). Due to the liquifaction in the initial process stage toxic ingredients like chlorine, mercury and other
heavy metals are converted into insoluble salts by simple chemical buffering reactions so that they can be safely eliminated in form of sediments. In addition lignin/cellulose is converted into organic salts so that no more tar forming agents are available. Accordingly the resulting synthesis gas is absolutely free from tar and toxic contaminants!. The synthesis gas is converted into electricity in the same CHP plants like the biogas. c) The proposed technology, apart from electricity also generates substantial quantities of excess of high and moderate temperature heat (95 °C from cooling water of the CHP unit as well as 500 °C from exhaust flue gas). In case no consumer of thermal energy is available in the vicinity, this excess heat may be
converted into absorption cooling energy, and here again into moderate temperature cooling energy (- 5°C for example for air conditioning etc. ) as well as deep freeze cooling energy (- 25 °C for cold stores and similar). d) The SRS technology allows to extract any metal 100%, even smallest particles which are normally not detected by rag pickers. The sale of such recycled metals, especially non-ferrous metals, with current metal prices will substantially increase the overall revenues.
4 Outline of the CombiTech Technology
4.1 Introduction
Municipal Household W aste is a very problematic substance due to its heterogeneity and inconsistency. It consists of an undefined mixture of organic material with varying degrees of inert materials. Thus a plant for treating of household waste requires a high degree of flexibility
The basic advantage of the CombiTech process is, that it can treat such a great variety of household or industrial refuse without expensive presorting. A manual presorting however is possible to extract valuable input materials (such as paper, PET-bottles, metals, glass) which may be marketed for cash. But valuable residual materials, especially ferrous and non-ferrous metals are also recovered more or less completely from the subsequent W LE process which may provide considerable additional income. The BIOTECH process may treat without modifications such a wide variety of refuse:
- organic household waste in various compositions
- industrial waste (organic and paper, from food and canning industries for example)
- agricultural wastes such as remains from olive pressing, from canning of citrus fruit, from grapes after pressing, etc.
- agricultural animal waste and manure
- waste from the gastronomic industry
- slaughter houses waste
- sludge from settling tanks and wastewater treatment plants
- garden trimmings
There is no specific requirement for purity or composition of the input waste. In order to reduce initial investment costs, a manual pre-sorting of the waste has been envisaged. Few unskilled persons are required on a continuous conveyor belt to eliminate those particles like metal, plastics, paper etc. which may be suitable for recycling. They may be recruited from the scavengers which actually search the waste landfill sites, thus further guaranteeing them their income. This manual presorting can never be 100% effective. Still about 10 - 15% of inert material will remain undetected in the waste, which will be eliminated by the process technology.Remaining heavy particles like batteries, stones, glass will be automatically eliminated from the process after dissolving the waste in water by gravity separation, and small quantities of remaining plastics will be sieved off so that the obtained compost maintains highest standards for agricultural applications.
4.2 BioTech Process (Anaerobic Digestion)
4.2.1 Preparation
Garbage is delivered by truck into the preparation building. This building is equipped with exhaust fans and bio-filters, which assure that no smells escape into the environment. The waste is directly emptied into a storage area. This stock can bridge a one-day-delivery of waste. The waste is taken up with a pay loader which is equipped with a crusher shovel. W hile emptying the waste out of the shovel it passes the grinding equipment set at 150 mm. This will just open plastic bags and other packaging material so that the waste becomes accessible for further treatment. The loosened waste stream passes a coarse screening machine(> 80 mm). The oversize practically contains no organic material and
will pass a sorting conveyors, where a certain amount of recyclables such as paper, metals, different
plastic, glass, may be sorted out, while the remaining bulk of inert material shall be sent to to the second process stage, the W LE process line. The undersize material from the screen (< 80 mm) will contain the bulk of the organic material but still approx. 20 – 30% non organics. This material passes a magnetic metal separators before it is crushed once again to about 25 mm and then transported to the turbo-dissolver tank. Water is added and by imposing high shearing forces, the organic material is disintegrated down to fibre size to form a pasty slip, while the inert materials are practically not affected. Heavy components like broken glass, batteries, stones, metal parts etc. are sinking to the bottom and are discharged from the slurry via steep
worm conveyor. They are eliminated via a double valve lock. The slurry is gradually emptied onto a vibrating dewatering screen. The non- disintegrated inert materials are then compacted and dewatered in a pressworm separator. The screened slurry passes a sand separation tank. The remaining slurry, now practically pure organic material, is collected in an underground reservoir and then pumped
to the buffer tank holding a storage capacity of 2 – 3 days in order to assure a certain homogenisation of various input materials
