Treatment of waste

Abstract

A method for the treatment of waste by plasma treating the waste to destroy the hazardous organic components and to yield a slag and an off-gas by plasma treating the waste in the presence of added oxygen gas in a transferred-arc plasma treatment unit, followed by directing off-gas from the plasma treatment unit to a thermal oxidizer combustion chamber.

Claims

1. A method for the treatment of waste in a waste treatment system comprising a plasma treatment unit and an off-gas treatment system in communication with the plasma treatment unit, the waste comprising one or more hazardous organic components, the method comprising: plasma treating said waste in the plasma treatment unit to destroy the hazardous organic components and to yield a slag and an off-gas; wherein the one of more hazardous organic components are selected from persistent organic pollutants (POPs), ozone depleting substances (ODSs) and persistent, bioaccumulative and toxic (PBT) pollutants, and combinations of two or more thereof; wherein the waste comprises: (i) a soil and/or aggregate material; and (ii) an oil component which is a waste oil; and wherein, before plasma treating the waste, the waste comprises the one or more hazardous organic components and from 10 to 40% water by weight of the waste, wherein the plasma treatment is carried out in the presence of an oxidant in addition to the water present in the waste, namely, in the presence of a large amount of added oxygen gas of at least 20% by weight of the total weight of the waste, wherein the plasma treatment unit is a transferred-arc plasma treatment unit comprising: a reaction chamber having a base portion for holding the waste; a first electrode arranged above the waste and not in contact with the waste; and a second electrode in electrical contact with the base portion so that, in use, a plasma arc generated between the first and second electrodes passes through the waste; and the process further comprising directing the off-gas from the plasma treatment unit to a thermal oxidizer combustion chamber separate from the plasma treatment unit and combusting the off-gas at a temperature above 1100° C. in the thermal oxidizer combustion chamber; wherein the off-gas treatment system comprises the thermal oxidizer combustion chamber, filters, and a scrubber.

2. The method according to claim 1, wherein the waste is treated in a continuous process and the waste forms a waste stream.

3. The method according to claim 1, wherein the method comprises a step of blending (i) the soil and/or aggregate material, and (ii) the oil component to provide a substantially homogenous waste stream.

4. The method according to claim 1, wherein the waste oil is one or more of crude oil, diesel fuel, fuel oils and lubricants.

5. The method according to claim 2, wherein before the step of plasma treating the waste, the one or more hazardous organic components is contained in: (i) the soil and/or aggregate material; and/or (ii) the oil component; and/or (iii) the waste stream.

6. The method according to claim 1 wherein the oxygen gas is added in an amount of from 25 to 35% by weight of the total weight of the waste.

7. The method according to claim 1, wherein the plasma treatment of the waste is carried out at a temperature of at least 1100° C.

8. The method according to claim 1, wherein the plasma treatment of the waste is carried out at a temperature of from 1100° C. to 1800 C.

9. The method according to claim 1, wherein the hazardous organic component comprises said persistent organic pollutants (POPs).

10. The method according to claim 1, wherein the hazardous organic component is polychlorinated biphenyls (PCBs).

11. The method according to claim 1, wherein the method comprises retrieving a solid vitrified slag and/or an off-gas following the plasma treating of the waste.

12. The method according to claim 1, wherein the method comprises a step of adding of one or more of SiO.sub.2, CaO and Al.sub.2O.sub.3 to the waste.

13. The method according to claim 12, wherein the SiO.sub.2:CaO:Al.sub.2O.sub.3 are added to provide a ratio of SiO.sub.2:CaO:Al.sub.2O.sub.3 in the waste of: from 50 to 70% by weight SiO.sub.2; from 20 to 30% by weight CaO; and from 10 to 20% by weight Al.sub.2O.sub.3.

14. The method according to claim 1, wherein before the step of plasma treating the waste, the one or more hazardous organic components is contained in: (i) the soil and/or aggregate material; and/or (ii) the oil component.

15. The method according to claim 1 wherein the plasma treatment is carried out in the presence of oxygen gas in an amount from 20% to 40% by weight of the total weight of the waste.

16. The method of claim 1 wherein the directing the off-gas from the plasma treatment unit to the thermal oxidizer combustion chamber comprises ducting the off-gas directly from the plasma treatment unit to the combustion chamber via an off-gas duct.

Description

(1) The invention will now be discussed further with reference to the figures, provided purely by way of example, in which:

(2) FIG. 1 shows a schematic of the furnace chamber that can be used in the present invention.

(3) FIG. 2 is a full schematic showing a configuration of the infrastructure that can be used in the present invention.

(4) FIG. 3 is a schematic of the feeding system for this system.

(5) A consistent numbering scheme has been adopted in the figures, wherein the numbers correspond to the following components: 1 Feed—waste containing hazardous organic component (in the examples, waste simulant used for the trials: 1,4 dichlorobenzene, topsoil, aggregate, quicklime, bauxite) 2 Water 3 Waste oil (Engine oil used for the R&D trials) 4 Inert gas (Nitrogen or Argon) 5 Oxidant (oxygen) 6 Plasma/inert gas (Nitrogen or Argon) 10 Primary electrode 11 Secondary electrode or electrodes 12 Feed port 13 Offgas duct 14 Main tap-hole (continuous overflow spout) 15 Secondary tap-hole 16a Refractory type 1 16b Refractory type 2 16c Refractory type 3 17 Thermally insulating electrically conducting hearth 18 Slag 19 Retained metal heel 20 Oxidizer 21 Natural gas inlet/dosing 22 Air inlet/dosing 23 Water inlet/dosing 24 Off gas cooling column (spray cooling tower) 25 Heat exchanger 26 Sorbent dosing system 27 Dosing/transporting air inlet 28 Bag house 29 Air pollution control residue 30 HEPA (high efficiency particulate air) filter 31 ID fan 32 Exhaust stack 40 cooling water 45 Roof of the furnace 50 Inlet of the furnace

(6) The invention will now be described with reference to a non-limiting example. It is noted that as the chemical structure of 1,4-Dichlorobenzene (C.sub.6H.sub.4Cl.sub.2) is similar to PCB's, this was used as a stimulant to avoid unnecessary operator content with real PCBs. 1,4-Dichlorobenzene is accepted throughout the literature as a stimulant.

(7) The plasma furnace used in the trial consisted of the following sections.

(8) A refractory-lined mild steel shell with an additional water cooling jacket in the upper shell area and a row of water cooled copper fingers at a nominal slag level in order to provide additional protection for the refractories at the slag line. The refractory is a cast alumina material, which contains >90% alumina and has a maximum service temperature limit of 1800° C. The furnace also has a 50 mm diameter horizontal tapping hole (100 mm above the furnace base in the centre of a tapping hole block). A 150 mm diameter steel bar in the base of the furnace acts as a return electrode for single electrode operation. The furnace has apertures in the upper shell region for pressure monitoring and for camera viewing. Thermocouple monitoring of refractory temperature are provided at 8 locations (K-type thermocouples) and in the return electrode at 2 locations (K-type).

(9) A conical refractory-lined mild steel roof with a water cooling jacket. The refractory is approximately 75 to 150 mm thick. There are 5 large apertures: a central port for single electrode work, four side ports for feeding and general access etc and a larger off-gas port. There is also a smaller camera port housing a small remote video camera in a protective case which allows for excellent viewing of the inside of the furnace. There are also 2 thermocouple holes for refractory temperature monitoring as above. The roof also provides location points for electrode manipulators and for the off gas ducting, which is connected with the thermal oxidiser, cooling tower, baghouse filter, high efficiency particulate air (HEPA) filters, induced draft (ID) fan, wet scrubber, stack etc.

(10) A steel support stand mounted on heavy-duty wheels and railway tracks for easy removal and installation of the furnace.

(11) Before starting the feeder, the plasma furnace needs to be pre-heated by the plasma electrode for about 3-4 hours, to ensure that the inner wall (high-temperature alumina refractory material) are hot enough, e.g. 900-1100° C. These temperatures can be estimated from the readings of thermocouples installed in the roof, shell, and bottom of the furnace. A camera, cooled by an argon gas purge, is installed to monitor the condition inside the feeding, plasma power is adjusted to match the feed rate, see Table 9. Temperatures in the furnace rise gradually until the melt pool is at 1400-1600° C.; at this point the heat input is matched by the heat loss to the cooling water and other losses, i.e. steady state conditions have been achieved as the temperatures plateau. (For commercial plant which has slag-overflow system, once the slag level reaches the desired height, e.g. 50 mm above the overflow port, the furnace is ready to be lanced to allow the molten slag to overflow continuously from the overflow port into a slag bin, which is changed periodically).

(12) The off-gas leaving the plasma furnace is a mixture of argon, N.sub.2, NO.sub.x, CO, CO.sub.2, O.sub.2, HCl and particulates at temperatures of 900-1200° C. This mixture is combusted in the thermal oxidiser at above 1100° C. for two seconds gas phase residence time.

(13) After the combustion stage, the gases are cooled to 300-400° C. by passing a spraying cooling system and a heat exchanger. At this temperature, hydrated lime powder is injected to the off-gas stream to react with HCl gas, if necessary. The carry-over particulates and any excess lime are separated in the off-gas bag house filter and collected in a drum. Particulate-free off-gas is further cleaned by high-efficiency particulate absorbing (HEPA) filters and wet scrubber then monitored by CEMS before being emitted to atmosphere via a stack.

(14) The feeding system was modified to allow all the three streams (solid, water and engine oil) to be fed into the furnace simultaneously, with minimum cross-effects on their flowrates. Preferably the three components meet just before being introduced into the furnace to form a continuous waste stream. Alternatively, separate feeds can be used to form the waste stream in the furnace. Argon was introduced to the feeding pipe as well, to cool down the water/engine oil feeding pipe during the furnace warming-up and cooling-down periods, and to force the solid mixture to move forward to the furnace. Oxygen was fed into the furnace by joining in one of argon pipe. FIG. 2 is a simplified schematic of the modified feeding system.

(15) For each trial, the furnace was heated from room temperature to approximately 1200° C. before starting to feed. This took about 3 to 4 hours. The heat added to the furnace was imparted on the refractory material and the shell resulting in increases in thermal mass and temperature. The mode of heat transfer was dynamic in that a part of the heat added was removed by cooling water. When the furnace losses to water-cooled elements reached about 80 kW and stabilised, it meant that the furnace was in quasi-steady state. Starting to feed materials from steady state, ensured that the materials were melted quickly, and therefore avoided the formation of “cold wall” or “feed pile”; this was considered to be more representative of continuous processing conditions.

(16) During feeding, the feed rates were maintained as constant as possible, and the formulation of simulated wastes. The slag level within the furnace would increase because of continuous feeding; however, the plasma arc length was adjusted to be in the range of 100 to 200 mm. Consequently the voltage of the plasma changed from 160 to 250 volt. By changing the set-point of the plasma current, the plasma power was easily controlled to match the feed-rate of the simulants, i.e. 110 to 130 kW for processing 40 kg/h simulated wastes.

(17) After delivering all the feed required for each trial (typically 130 to 200 kg), the slag level reached the desired height, e.g. 200 to 300 mm. Following feeding the charge was soaked for about 20 minutes (equivalent to normal steady state residence time) to allow all materials fed into the furnace to melt and be treated, while plasma power was maintained at 90 to 110 kW (to compensate the heat loss from the plasma furnace to all elements of the plasma furnace, i.e. including non water-cooled parts).

(18) Then the team prepared to lance the tap hole of the furnace, in order to tap the slag out to a tray.

(19) When the tapped lava-like slag naturally cooled down in the tray, it formed a dense slag monolith. After mechanical fracture, the size could be reduced to less than 150 mm. This slag was vitreous and dense and, subject to qualification, could be considered as an inert waste for the purposes of disposal and/or re-use, and hence could be used in construction or for road surfacing material.

(20) The components and their fractions in the simulants were as follows, see Table 1 (unit: wt/wt).

(21) TABLE-US-00001 TABLE 1 Components of PCB waste simulants Components Fractions 1,4-Dichlorobenzene (C.sub.6H.sub.4Cl.sub.2) 0.1-1.2% Comma 15W-40 Super Mineral Engine  7.5% Water 12.5% Topsoil 50.0% Aggregate Balance Total 100.0% 

(22) For the topsoil, the average values of the main components were obtained from literature, see Table 2 (unit: wt/wt).

(23) TABLE-US-00002 TABLE 2 A typical composition for top soil Organi SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO K.sub.2O Na.sub.2O Total 7.68% 66.60 12.91 3.48% 3.28% 1.84% 2.56% 1.64% 100.00

(24) From the literature, organics in topsoil can be represented by C.sub.9H.sub.11NO.sub.3.

(25) The components of aggregate are based on the following two assumptions:

(26) Assumption 1:

(27) Aggregate is made from cement, sand and stone only, and their fractions are as follows, see Table 3 (unit: wt/wt).

(28) TABLE-US-00003 TABLE 3 The assumption of the components in aggregate Materials in aggregate Cement Sand Stone Total Fractions 19% 31% 50% 100%

(29) Assumption 2:

(30) The components in cement, sand and stone are as follows, see Table 4 (unit: wt/wt).

(31) TABLE-US-00004 TABLE 4 Components in cement, sand and stone Materials in aggregate Organics SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO K.sub.2O Na.sub.2O Total Cement 0.00% 22.45%   5.10%   4.08%   64.29%    2.04%   1.02%   1.02%   100.00%   Sand 0.00% 100% 0% 0% 0% 0% 0% 0% 100% Stone 0.00%  30% 0% 0% 50%  20%  0% 0% 100%

(32) By combining the figures in Table 3 and Table 4, the fractions of the components in the solid aggregate mixture can be calculated and the results are shown in Table 5 (unit: wt/wt).

(33) TABLE-US-00005 TABLE 5 Calculated fractions of the components in aggregate Materials Organics SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO K.sub.2O Na.sub.2O Total Aggregate 0.00% 50.56% 0.96% 0.76% 36.98% 10.36% 0.19% 0.19% 100.00%

(34) Assuming the concentration of 1,4-Dichlorobenzene is 1.00%, the final composition of the simulant waste can be obtained by combining the data in Tables 1, 2 and 5. The results are shown in Table 6 (unit: wt/wt). These results were used as the basis of process calculation in this report.

(35) TABLE-US-00006 TABLE 6 Final compositions in a simulant waste Components Fractions C.sub.6H.sub.4Cl.sub.2 1.00% C.sub.12H.sub.26 7.50% H.sub.2O 12.50% C.sub.9H.sub.11NO.sub.3 3.84% SiO.sub.2 47.96% Al.sub.2O.sub.3 6.73% Fe.sub.2O.sub.3 1.96% CaO 12.36% MgO 3.93% K.sub.2O 1.34% Na.sub.2O 0.88% Total 100.00%

(36) In order to achieve the beneficial effects of the balance of SiO.sub.2, CaO and Al.sub.2O.sub.3, the amount of flux materials were “back-calculated”. The components of final blended feed are shown in the last column of Table 7. Note this is based on the assumption that the concentration of 1,4-Dichlorobenzene in raw simulant waste is 1.00%. The fractions of the raw simulant waste and the blended materials are shown in Table 8.

(37) TABLE-US-00007 TABLE 7 Comparisons of raw simulant waste and blended feeding materials “Top three” Final “top In raw In raw three” after simulant simulant adding flux Finally in the waste waste materials blended materials Components (wt/wt) (wt/wt) (wt/wt) (wt/wt) C.sub.6H.sub.4Cl.sub.2 1.00% 0.91% C.sub.12H.sub.26 7.50% 6.84% H.sub.2O 12.50% 11.40% C.sub.9H.sub.11NO.sub.3 3.84% 3.51% SiO.sub.2 47.96% 71.52% 62.56% 43.76% Al.sub.2O.sub.3 6.73% 10.04% 13.20% 9.23% Fe.sub.2O.sub.3 1.96% 1.79% CaO 12.36% 18.44% 24.24% 16.96% MgO 3.93% 3.58% K.sub.2O 1.34% 1.22% Na.sub.2O 0.88% 0.80% Total 100.00% 100.00% 100.00% 100.00%

(38) TABLE-US-00008 TABLE 8 The fractions of the seven streams in a simulant waste Streams Fractions 1,4-dichlorobenzene 0.91% (variable) Engine oil 6.84% Water 11.40%  Dry topsoil (<5 mm) 45.62%  Dry aggregate (<5 mm) 26.46% (variable) Flux (quicklime CaO) 5.68% Flux (Bauxite Al.sub.2O.sub.3) 3.09% Total 100.00% 

(39) The concentration of 1,4-Dichlorobenzene used for the four trials may vary slightly, e.g. from 0.1 to 1.2% w/w (1,000 ppm-12,000 ppm) in simulant wastes. To balance this variation, we adjusted the concentration of aggregate accordingly while retaining the concentrations of all other streams, i.e. water, engine oil, topsoil and flux materials. Therefore, in Table 8, the fractions of 1,4-Dichlorobenzene and aggregate are marked as “variable”.

(40) Assuming the feed-rate of the simulant waste (its components are listed in Table 8) is 806 kg/h (i.e. commercial 6,000 tpy plant scale), oxygen (used as oxidant) flow-rate is 257 kg/h.

(41) Oxygen flowrates were determined to be excessive in order to completely destroy the organic chemicals, e.g. engine oil and 1,4-Dichlorobenzene, and to reduce the electricity power requirement as much as possible. As a result of this, the unit melting energy required was only 0.22 kWh/kg, which was much lower than those of many other solid waste systems (typically 0.5 to 0.8 kWh/kg).

(42) Table 9 lists the relevant figures.

(43) TABLE-US-00009 TABLE 9 Calculated oxygen and electricity requirements Feed-rate of simulants (kg/h) 25 30 35 40 45 50 O.sub.2 flow-rate (kg/h) 7.97 9.56 11.15 12.74 14.34 15.93 O.sub.2 flow-rate (l/min) at NTP 92.93 111.52 130.10 148.69 167.28 185.86 Theoretical melting energy required 0.22 0.22 0.22 0.22 0.22 0.22 (kWh/kg) Melting power required (kW) 5.57 6.68 7.80 8.91 10.03 11.14 Hot-Wall Furnace heat loss (kW) 80.00 80.00 80.00 80.00 80.00 80.00 Plasma power required (kW) 85.57 86.68 87.80 88.91 90.03 91.14

(44) For operation safety and environmental protection reasons, the simulant wastes were stored in completely sealed drums and blended using a driven tumbling machine.

(45) During operation, the furnace is designed to work under a slight negative pressure, i.e. −60 to −120 Pa, to avoid the release of fumes and the egress of off-gas, by the use of an induced draft fan. The off-gas is designed to be fully oxidised in a thermal oxidiser. The particulates in the off-gas are collected in a baghouse filter followed by a high efficiency particulate air (HEPA) filter before it is discharged into the atmosphere.

(46) The only “waste” from the plant is the particulates collected from the Thermal Oxidiser and the Baghouse Filter. The main components in the particulates are NaCl and KCl, which can be used as road salt, subject to qualification.

(47) The results of the trials are set out in the following table.

(48) TABLE-US-00010 Trials No Trial 1 Trial 2 Trial 3 Trial 4 Date 17/11/2009 19/11/2009 01/12/2009 08/01/2010 Formulation by fraction (w/w) 1,4-dichlorobenzene 0.100% 0.912% 0.200% 1.200% Engine oil  6.84%  6.84%  6.84%  6.84% Water 11.40% 11.40% 11.40% 11.40% Dry topsoil (<5 mm) 45.62% 45.62% 45.62% 45.62% Dry aggregate (<5 mm) 27.27% 26.46% 27.17% 26.17% Flux (quicklime CaO)  5.68%  5.68%  5.68%  5.68% Flux (Bauxite Al.sub.2O.sub.3)  3.09%  3.09%  3.09%  3.09% Total 100.00%  100.00%  100.00%  100.00%  Formulation by weight per 25-litre drum 1,4-dichlorobenzene (kg) 0.020 0.182 0.040 0.240 Engine oil (kg) 1.37 1.37 1.37 1.37 Water (kg) 2.28 2.28 2.28 2.28 Dry topsoil (<5 mm) (kg) 9.12 9.12 9.12 9.12 Dry aggregate (<5 mm) (kg) 5.45 5.29 5.43 5.23 Flux (quicklime CaO) (kg) 1.14 1.14 1.14 1.14 Flux (Bauxite Al.sub.2O.sub.3) (kg) 0.62 0.62 0.62 0.62 Materials per drum including engine oil & 20.00 20.00 20.00 20.00 water (kg) Materials processed No. of drums processed 6.0 10.0 8.0 6.0 Total solid materials processed in the trial 98.10 163.51 130.80 98.10 (kg) Process data Pro-loaded carbon before the trial (kg) 0.92 0.00 0.50 0.50 Pro-loaded pig iron before the trial (kg) 11.69 0.00 8.44 0.00 Pro-loaded slag before the trial (kg) 0.00 75.00 82.35 75.00 Feeding time in the trial (hour) 4.12 5.25 4.10 3.57 Average feed-rate of solid in the trial (kg/h) 23.83 31.14 31.90 27.51 Average feed-rate of simulant in the trial 30.21 38.34 38.86 34.34 (kg/h) Actual water consumed in the trial (kg) 19.35 26.51 20.71 18.01 Actual engine oil consumed (kg) 6.90 11.26 7.80 6.35 Actual simulant (solid + engine oil + water) 124.35 201.27 159.31 122.47 processed (kg) Actual oxygen consumed in the trial (from 49.40 67.05 52.36 45.55 MFC) (kg) Average current when feeding (A) 624 541 564 656 Average voltage when feeding (V) 173 185 193 160 Average power when feeding (kW) 108 100 109 105 Heat loss when feeding (kW) 77 77 77 77 Unit energy for melting (actually in the trial) 0.25 0.12 0.20 0.23 (kWh/kg) Slag (predicted from HSC modeling) (kg) 103.61 228.21 213.35 166.92 Slag (generated approximately) (kg) 89.02 155.00 180.00 178.00 Particulates (predicted from HSC modeling) 1.10 1.83 1.47 1.10 (kg) Particulates (generated approximately) (kg) 3.50 5.83 4.67 3.50 Analysis results on 1,4-dichlorobenzene In slag (μg/kg) <5 <5 <5 <5 In particulates before combustion chamber N/A 63 N/A 29 (μg/kg) In particulates after combustion chamber N/A <5 <5 <5 (μg/kg) In off-gas before combustion chamber N/A N/A N/A <8.12 (mg/Nm3) Destruction & removal efficiency (slag basis) 99.99963%   99.99996%   99.99972%   99.99994%  

(49) The concentration of 1,4-dichlorobenzene in every slag sample was less than limit of detection (i.e. 5 μg/kg), which means the minimum destruction and removal efficiency (DRE) is 99.99963%.

(50) DRE is calculated as the mass emission rate of the selected hydrocarbon divided by the mass input rate of this same hydrocarbon. The calculation of DRE is as follows (Trial 3 is used as an example):

(51) Step 1: Calculate the concentration of 1,4-dichlorobenzene in simulants, which is defined as C.sub.in (unit: μg/kg).

(52) $C_{\mathrm{in}}=\frac{\mathrm{Mass}\mathrm{of}1A-\mathrm{dichlorobenzene}\mathrm{in}\mu g}{\mathrm{Mass}\mathrm{of}\left(\mathrm{Engine}\mathrm{oil}+\mathrm{Water}+\mathrm{Solid}\mathrm{Materials}\right)\mathrm{in}\mathrm{kg}}=\frac{0.04\times 8\times {10}^9}{7.80+20.71+130.80}=2008664\mu g/\mathrm{kg}$

(53) Step 2: Determine the concentration of 1,4-dichlorobenzene in slag, which is defined as C.sub.out (unit: μg/kg). As this concentration is in slag less than limit of detection (5 μg/kg), we choose 5 μg/kg as a safe margin, i.e.
C.sub.out=5 μg/kg

(54) Step 3: Define and calculate DRE
DRE×100%=[(0.04×8×10.sup.9)−(5*180)]/[0.04×8×10.sup.9]×100%=99.99972%

(55) The concentrations of 1,4-dichlorobenzene in particulates collected between the combustion chamber and the plasma furnace off-gas exit were 63 and 29 μg/kg respectively in Trials 2 & 4. These high concentrations (compared to those in slag) might be caused by carry-over of feeding materials, i.e. “short-circuit” from the feeding pot to the off-gas exit duct, or by short residence time, and can be improved by modifying the feeding method of solid materials, e.g. using oxygen to blow the feed to the furnace. Commercially, it would also be possible to recycle this secondary waste back to the plasma furnace.

(56) By contrast, after the combustion chamber, the concentrations of 1,4-dichlorobenzene in particulates were below 5 μg/kg. This confirms that the combustion chamber assisted in destroying the majority of the remaining 1,4-dichlorobenzene by combusting it in oxygen-excess atmosphere and is therefore an essential part of the off-gas train.

(57) The off-gas from Trial 4 was measured. The results show that the concentrations of 1,4-dichlorobenzene in the off-gas immediately exiting from the plasma furnace (before entering into the Combustion Chamber), sampled at different feeding stages, were lower than 8.12 mg/(N)m3, i.e. 6.5 ppm. In all cases the detected concentrations of dichlorobenzene compounds were below the quoted LOD for the analysis technique employed, as denoted by the ‘<’ symbol.

(58) During the feeding time of Trial 3, i.e. 4.1 hours, totally 0.320 kg of 1,4-dichlorobenzene was fed into the furnace. During the period, the total amount of 1,4-dichlorobenzene escaped into the off-gas duct (e.g. “shortcut” from feeding pipe to off-gas duct directly) was calculated and the result was 389.5 mg, which equaled to 0.12% of total input 1,4-dichlorobenzene.

(59) The final emissions at the stack, after passing through the off-gas system (e.g. the combustion chamber, the baghouse filter, the wet scrubber). It should be noted that the emissions of both VOC and carbon monoxide are over release limits. The reason is that the combustion chamber was not hot enough. The temperature in the combustion chamber should be maintained at 1100° C. or above; however, due to the restriction of natural gas supply, the real temperature may be lower than 800° C.

(60) TABLE-US-00011 Sample 1 Sample 2 Sample 3 Pollutants (11:37-12:07) (12:46-13:16) (13:17-13:36) 1,2-Dichlorobenzene <4.48 <2.58 <8.12 1,3-Dichlorobenzene <4.48 <2.58 <8.12 1,4-Dichlorobenzene <4.48 <2.58 <8.12 Acetone <4.48 <2.58 <8.12 Methyl ethyl ketone <2.24 <1.29 <4.06 Styrene <2.24 <1.29 <4.06 Toluene <2.24 <1.29 <4.06 Notes: All concentrations expressed at 273 K, 101.3 kPa, dry gas (mg(N)m−3); The dichlorobenzene compounds were all analysed at the limit of detection (<10ug).

Process Gas Analysis (Sampling from the Exit of Plasma Furnace Off-Gas)

(61) TABLE-US-00012 Concentrations Release Mass at 273 K, Estimate Limit Emission 101.3 kPa, of Error (mg(N)m.sup.−3) Rate dry gas 2σ (WID- Pollutants (gs−1) (mg(N)m.sup.−3) (95%) % ELV) TPM.sup.1,2 0.0001 1.23 ±48 10 VOC (as carbon).sup.3 0.0035 58.1 ±10 10 Hydrogen <0.0001 0.23 ±8 10 Chloride.sup.2 Sulphur Dioxide.sup.2 0.0001 1.77 ±8 50 Hydrogen <0.0001 0.02 ±8 n/a Cyanide.sup.3 NO.sub.x (as NO.sub.2).sup.3 0.0009 14.58 ±10 400 Carbon 0.0477 791.5 ±10 50 Monoxide.sup.3 Notes: .sup.1Total Particulate Matter; .sup.2Duplicate test (sampling periods 11:50-12:50 & 13:20-13:40); .sup.3Continuous test (11:28-13:40); .sup.4Data is uncorrected for oxygen.

Ultimate Emissions Testing

(62) As demonstrated in the foregoing example, the trial results show simulated PCB wastes (containing 1,4-dichlorobenzene instead of real PCBs) can be successfully destroyed using a thermal plasma process over a broad range of compositions (e.g. 0.1˜1.2% w/w of 1,4-dichlorobenzene in simulated wastes) at high destruction and removal efficiency (DRE).

(63) The predicted specific melting energy, which was predicted at 0.22 kWh per kg of blended waste, by thermal modeling software, was confirmed in the trials and therefore endorsed the commercial operating model and the efficient characteristics of the process.

(64) All the concentrations of 1,4-dichlorobenzene (to simulate PCBs) in the slag generated in the four trials, was below the analytical limit of detection (LOD), i.e. 5 μg/kg, which means that slag-based DREs were higher than 99.99996%. This also means the slag material is suitable for compliant disposal or re-use (subject to qualification). This endorses the recovery, as opposed to disposal, calibre of the technology presented. The technology was also demonstrated to be robust and non-selective in terms of DREs. This performance is attributed to the thermochemical design of the system, high furnace operating temperatures, photo-catalytic character of the light, sharp temperature gradients and desirable time versus temperature history.

(65) The concentration of 1,4-dichlorobenzene in the raw off-gas from the plasma furnace was also below the limit of detection (LOD), i.e. 8.12 mg(N)m.sup.−3 (or 6.5 ppm), which equate to a low gas phase partitioning of 0.122% w/w of 1,4-dichlorobenzene. This was measured at the immediate furnace exit and was confirmed to be further lowered by the use of a conventional off-gas system after the plasma furnace. This confirms that the PCBs are being successfully destroyed as opposed to being simply displaced.

(66) Based on the results obtained from the trials, based on local unit cost assumptions, are estimated at £100 per tonne of PCB contaminated wastes, which after benchmarking, is confirmed to be highly competitive.

(67) The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.