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INDUSTRIAL PLANT FOR ENERGY RECOVERY BY PYROLYTIC COMBUSTION OF WASTES PRODUCED IN TEXTILE PLANTS

Ziel

The conversion of waste from 4 textile factories into heat by pyrolytic combustion thereby optimizing energy recovery and minimising environmental impact and construction of an integrated energy system for the same factories.
Measurements were taken over a six-month period following the installation of the plant. The following problems emerged :
(i) the heat lost in raising the incinerator to its operating temperature (using LPG as fuel, in accordance with standard practice) averages 2000 kJ per kg of waste consumed;
(ii) the total heat recovered from 2000 kg of incinerated waste is about 30000 MJ.
(iii) the electricity consumed by the plant (other than by the heat exchanger oil pumps) is about 0.15 kWh/kg of incinerated waste.
Overall, the project has demonstrated that :
a) the system is technically viable provided it uses materials suited to the incinerator's operating conditions;
b) its economic viability depends on how much it would otherwise cost to process the waste (which must be in excess of Lit 180/kg) and the cost of alternative conventional fuel (at least Lit 400000/TOE);
c) the plant's capacity should preferably be at least 3000 kg of waste incinerated per day.
The project has shown that:
a) the technology involved is efficient in burning textile waste, keeping within the limits laid down for emissions into the atmosphere;
b) the thermal energy recovered is 25-30% less than expected. This is chiefly due to :
(i) the heat required to bring the refractory in the combustion and post-combustion chambers up to operating temperature : this heat is subsequently lost during night cooling;
(ii) the thermal energy contained in the carbon residue in the combustion chamber : this too is lost during the night;
c) electricity consumption is about 30% greater than expected, because of the extra power absorbed by the fume ventilator and because the pump which circulates the fume scrubber solution also absorbs power;
d) the heat which has to be supplied to the incinerator from conventional fuel is some 40% greater than estimated.
The following conclusions may be drawn from the project as a whole :
1) Atmospheric emissions from the plant are comparable to those from a conventional oil-fired heat generator.
2) The processing capacity of the plant tested was too small for it to be economically viable.
3) To improve the plant's economics, it should consist of two combustion chambers and a single post-combustion chamber, so as to double the quantity of waste processed, with minimal effect on the capital cost of the plant.
The demonstration plant has the capacity to process some 2000 kg per day of textile waste consisting of a mixture of synthetic and cellulose fibres (net calorific value 25000 - 27000 kJ/kg).
Provision is also made for recovering some of the heat in the waste gases from the incinerator (temperature 1000 1100 deg.C) using a fumes/oil heat exchange unit (oil temperature 200 - 260 deg.C) with a rated potential of 930 thermal kW.
Waste is burned in a steel pyrolytic furnace to which a post-combustion chamber has been added to burn gases completely at 1100 or 1200 C.
The plant will substitute 185 TOE/y without noxious emissions and limited solid residues.
The plant is composed of :
- feeder of nap or woven yarn waste
- inlet channel to the pyrolitic chamber
- pyrolitic chamber
- afterburning chamber with auxiliary LPG burner
- stack
- diathermic oil heat recoverer
- flue gas NOx absorbtion tower
- draught fan
- combustion controllers and regulators.
Nap or woven yarn waste is stored ina hopper which feeds the pyrolitic chamber by the means of a screw feeder and an inlet channel.
In the pyrolitic chamber (volume 6,2 m3) nap is gassified at a temperature between 350 deg.C. and 500 deg.C. where compound molecules forming nap crack and a flammable gas is produced.
The flammable gas is then fired in the afterburning chamber (volume 6,3 m3) equipped with an auxiliary LPG burner used only if the temperature drops below 900 deg.C.
Exhaust passes through the diathermic oil heat exchanger where heat is recovered from the hot gases and exits at about 280 deg.C./300 deg.C. A flue gas absorbtion tower eliminates remaining pollutants present and further lowers NOx concentration before feeding exhaust to the stack and successively to the atmosphere.
The plant is equipped with automatic controlling equipment that regulates the flow of nap and air into the pyrolitic chamber in function of the oxygen content of exhaust.

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Koordinator

Consorzio Generale Fibre Olimpia Sima Sersin
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Via Milano 8
50045 Montemurlo
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