Incineration-Vitrification of chlorinated organic waste by the SHIVA process.
F.Lemort, C.Girold, L.Bruguiere, O.Pinet
Commissariat à l’Énergie Atomique (CEA), Valrhô/Marcoule
BP 171, 30207 Bagnols-sur-Cèze Cedex, France
Incineration represents a promising weight and volume reduction technique for hazardous
organic waste and its application is very useful in proper disposal of radioactive wastes. In the
case the incineration is followed by a vitrification process, the volume reduction can be
sensibly increased and the hazardous elements such as radionuclide or heavy metals are
immobilized in a long-lasting matrix. The SHIVA process (the French acronym for Advanced
Hybrid System for Incineration and Vitrification) has been developed in order to gather the
incineration and the vitrification in a unique reactor and to produce a glass containing the
mineral charge of the waste. This paper reminds the principle of the SHIVA process and
presents the first results obtained in the case of the treatment of chlorinated organic waste.
Introduction
The Commissariat à l’Energie Atomique (CEA) has pursued a broad research and
development for a number of years concerning the disposal chlorinated organic wastes
produced by work in confined atmosphere such as glove boxes. The first studies were
performed through the incineration that led to the development of the IRIS facility based on a
two-step incineration process offering a significant volume reduction through the production
of ashes having a very low carbon content. These ashes can be treated for the recovery of
various valuable elements (uranium, plutonium, ..) if it is necessary or directly vitrified for
disposal. In this second case, it would be more interesting to treat the waste in order to vitrify
directly its mineral charge. The SHIVA process (French acronym for hybrid system for
advanced incineration vitrification) has been developed in order to reach this goal.
SHIVA is based on a unique reactor in which incineration of the burnable waste is performed
on the surface of a glass bath heated in a cold crucible. The reactor mainly consists of a
cylinder, a roof and a crucible, all made of stainless steel with a water jacket system. Two
means of heating are used:
-
arc plasma system in order to begin the melting of the glass and to perform the
incineration of the organic wastes together with the combustion of the gases
direct induction through the cold crucible in order to keep the glass melted.
The SHIVA Process
Often, the waste management pattern is in favour of the vitrification due to the volume
reduction, resulting in cost savings for transport and storage. Furthermore, it provides for
good radioactivity immobilization in a long-lasting matrix. One very interesting way is to
perform the incineration of the burnable wastes, the vitrification of their mineral charge and
the combustion of the off-gases in the same vessel. Significant advantages can be obtained by
supplying the waste directly into oxygen arc plasma [1] located above a glass bath heated by
direct induction in a cold crucible. The temperature is very high and so is the efficiency of the
combustion in the exited free oxygen rich atmosphere that also promotes to a good oxidation
of the glass.
Figure 1 describes the reactor in which the incineration vitrification is performed.
Waste
+
Glass
precursor
Ar/O2
Ar/O2
Cathode
Anode
Burned
gases
exhaust
Metallic
Cooled
Plasma
walls
Molten
glass
Glass
pouring
HF
Current
Inductor
Figure 1: Incineration vitrification reactor
-
Twin-torch transferred arc system
The twin-torch transferred arc system comprises two plasma torches of opposite polarity. The
cathode torch consists of a thoriated tungsten water cooled pointed electrode. Two water
cooled nozzles, feeding argon and oxygen, provide a shroud of plasma forming gas around the
cathode and confine the arc attachment to the cathode. The anode torch is similar to the
cathode one, however the anodic electrode is a high-purity water cooled button of copper.
-
The Reactor
The reactor mainly consists of a cylinder, a roof and a crucible, all made of stainless steel with
a water jacket system. The inside diameter of the combustion chamber is 600 mm and the
crucible diameter is 600 mm. The total height is about 800 mm. Two openings in the roof
allow the entry of the twin plasma torches with an angle between them from 70 to 20°.
Openings allow the feeding of the waste (solid and/or liquid) directly in the plasma zone.
-
The gas treatment
The gas treatment is almost the same that for the IRIS process. It is made up of:
o
o
o
o
A diluter leading to the cooling of the off-gas.
An electrostatic filter
A bag filter (to recover the last fraction of the dust)
A scrubbing column
The figure 2 gives a description of the whole process including the reactor followed by the
gas treatment.
Figure 2: Description of the SHIVA process
-
Operating Parameters
For the treatment of each kind of waste, the crucible receives about 30kg of glass frit, which
composition is to be chosen according to the kind of waste to be treated. The frit is first
melted with the torches up to the moment when the quantity of melted glass is enough to
ensure continued melting by induction. At this moment, the inductor is switched on to
complete the melting of the glass bath. The temperature of the glass in the middle of the bath
is held around 1200°C for an arc intensity of 200A and a voltage of 100V (this voltage
increases up to 250V during feeding). The power of the high frequency generator (300 KHz)
is maintained around 60kW. Then, the waste is processed by direct feeding in the plasma. As
the plasma column radiation is very important, the waste generally ignites as early as it is
introduced in the furnace and burns in the oxidizing atmosphere. With a moderate feeding
flowrate of about 10 kg/h (depending on the waste), a perfect combustion is achieved in the
oxygen plasma, on the surface of the bath, without accumulation. Glass pouring is possible
after treatment. After each run, the products in each module of the installation are sampled
and a material balance is made; it shows a good transfer in the glass of the mineral elements
of the waste.
The SHIVA process has a number of advantages:
-
Continuous feed of homogeneous waste and good combustion efficiency
very compact process achieving the incineration and the vitrification of waste in a
unique vessel
the plasma torches allow to initiate the melting of the glass
The cold crucible technology avoids the corrosion
Production of glass that constitutes an ultimate disposal product with a maximal
reduction volume….
The chlorinated organic wastes treatment
The treatment of the wastes requires a specific preparation in order to be able to feed the
reactor. To steps are necessary to reach the goal of the incineration-vitrification:



The preparation of the load
The feeding
The incineration-vitrification
In addition, it is interesting to performed the phosphation of the dust as it has been made
regarding the incineration by the IRIS process.
Composition of the waste and phosphatation
Incineration-vitrification tests were performed on technological wastes with a mean
composition representative of the actual waste stream, comprising 10 wt% cellulose, 8%
polyethylene, 17% neoprene, 17% latex, and 48% PVC. The feed rate was about 3 kg·h-1.
Phosphorus that is introduced together with pink PVC is used to convert the chlorides to
phosphates as it has been performed in incineration processes (IRIS) [2]
The composition of the blended waste stream was analyzed, and the main elements are
indicated in Table 1. Phosphorus was not present in sufficient quantities for zinc
phosphatation, as it accounted for only 0.05 wt% of the waste feed. The values in the table are
only averages for multiple waste batches. The “other” column (0.7 wt%) includes a variety of
minor elements (Na, Mg, Cr, etc.).
Element
C
H
N
O
Cl
S
K
Ca
Zn
Al
Si
P
Other
wt%
57.9
7.8
0.3
9.3
22.2
0.4
0.1
0.2
0.6
0.2
0.3
0.6
0.7
Table 1: Waste feed stream composition (wt%)
The test that was previously performed about the incineration of the wastes through the IRIS
process showed that the ash composition [3] was largely constant but that phosphatation
occurred in the afterburner [4] leading to obtain very stable dust. The table 2 gives the
composition of the dusts that are obtained without and with phosphorus addition.
Element
Zn
Cl
P
C
Si
Al
Ca
K
Without P additive
47.4
51.4
0.3
0.1
0.2
0.1
0.1
-
With P additive
26.9
0.2
24.9
0.2
0.1
0
0
4.2
Table 2: Particle matter composition (wt%)
In heat treated wastes without phosphorus additives, zinc was found exclusively as zinc
chloride (ZnCl2 constituted about 99 wt% of the particle matter); the analysis results without
P additive in Table II account for virtually all the material weight. Conversely, the results
obtained with the Phosphorus additive reveal a major weight deficit due the fact that oxygen
was not analyzed: phosphorus was found mainly as phosphate, and oxygen could account for
over 40 wt% of the particle matter. Although the analyses were performed using different
protocols with different material batches, and some caution is necessary in comparing the
results, the effectiveness of the phosphorus additive is indisputable: the chloride content was
reduced to virtually to zero. A qualitative comparison of the particle matter confirmed this
observation: the particles became liquid and highly corrosive in air in the first case, but
remained dry and stable in the second.
The experience acquired about the incineration has to be used on SHIVA in order to transform
the chlorides into phosphates and then to protect the facility. Then, phosphorus was also
added through the pink PVC in the same proportion.
Preparation of the load
The wastes coming from the gloves boxes are made of different kind of plastics and metals
and the mixture has to be prepared before treatment. The first operation consists to sort the
mixture in order to separate the plastics and metals. This can be performed manually or thanks
to an X-ray inspection. Then, a shredding of the first components lead to obtain thin fragment
that are brought up to an homogenizer. Downstream, the waste is sent up to the feeding
hopper before being introduced into the process.
This kind of preparation has been previously tested for the incineration of the waste and is
implemented at the valduc centre for the industrial application of the alpha incinerator. In
addition to the previous description, an automatic extraction of small metal parts has been
implemented in this facility to prevent dysfonctionement
The feeding
The introduction of the waste is performed thanks to a screw connected to a feeding hopper
ensuring a continuous and steady feeding rate. The regulation is carried out with weight
sensor inducing the speed of the screw. By this way, the waste drops directly in the plasma.
The waste treatment
A first experiment was carried out during height hours. The following table summarises the
main running parameters record during the treatment.
Parameter
Feeding rate
Plasma torches
HF generator
Electrostatic
precipitator
Gas
A
V
O2
Ar
P
F
Ui
Uf
CO
NOx
Value
3 kg.h-1
220A
230V
10NM3.h-1
5.5NM3.h-1
100kW
283Hz
65kV
40kV
< 100 ppm
< 1000ppm
Table 3: Main running parameters of the SHIVA process
(Ui: initial value, Uf: final value)
The main results
The observations performed during the treatment show clearly a good behaviour of the
process with parameters remaining steady. The only technological difficulty occurs on the
introduction of the waste with the appearance of periodic clogging. Some improvements are
going to be made to ensure a very continuous feeding.
After the experiment, some deposits were removed from the facility. The following table
gives their amount for the treatment of 33kg of wastes:
Location of
Weight (g)
Weight % of
deposits
initial load
Reactor
930
2.8
Connexion to
500
1.5
filter
Cold point
30
0.1
Filter
1041
3.15
Table 4: Amount of deposits removed from the facility
The cold point is located directly under the inlet of the diluter. At this place, the deposits are
liquids.
Some analyses have been performed on each of these deposits. The table 5 gives the results.
Element
Reactor Connexion
Filter
Cold point
1.55
1.3
1
0.64
C
18.4
30.5
26
38
Cl
1.4
0.53
0.62
0.63
S
4.6
5.1
11.5
2.15
P
6
3.75
9.5
2.95
Na
2
1.75
3.25
0.55
K
1.25
0.35
0.25
0.3
Mg
6.2
3.6
1.25
1.05
Ca
18.5
15.6
20
3.8
Zn
16.5
3.6
1.9
1.6
Al
4.3
2.1
1.9
1.25
Si
0.9
1.4
1.5
Sb
1.3
3
0.1
2.9
Ni
6.4
15.9
1.1
26
Fe
1.6
3.4
0.15
5.8
Cr
1.6
0.75
0.25
0.15
Ba
1.45
1.45
3.1
1.96
B
4.8
4.2
15.7
8.9
O
Table 5: Analysis (weight %) of the deposits coming from the different locations
The analysis of the glass has not been performed. The main conclusion coming from the
results indicated in Table 3 are:
- All the deposits have low carbon content. The combustion of the waste is the totally
achieved.
- The deposits contain phosphorus and essentially the dust removed from the filter. This
shows the feasibility of the phosphatation.
- The deposits have high chlorine content even in the filter. The phosphatation of the dust is
not totally achieved. Despite of this observation, the dust containing around 26% weight has a
good behaviour (remain dry).
- All the deposits contain boron that comes from the volatilisation of the glass and essentially
during the melting of the glass.
- The composition of the liquid deposits removed from the cold point shows corrosion
products (Fe-Ni-Cr).
According to the table 4, the amount of the dusts represents around 7% of the initial load
made up of 75% of CHON that are transformed into gases. This suggests that if all the dust
comes from the waste, the mineral charge of the 33kg of waste representing 8250 g of dust is
introduced in the glass with an efficiency of around 70%. By considering that a part of the
dust comes from the volatilisation of the glass (B in table 5), this amount could be a
minimum. In addition, in the case it will be possible to recycle the dust recovered from the
filter in a colder area of the glass, this efficiency could be sensibly increased.
All these observations show a feasibility for the treatment of organics chlorinated wastes by
the SHIVA process. However, some improvements have to be made in order to enhance the
phosphatation of the dust and to eliminate cold point in the connexion between the reactor and
the filter.
References
[1]
C.Girold, R.Cartier, J.P.Taupiac, J.M. Baronnet
Incineration/vitrification of surrogate radioactive wastes under transferred arc plasma
Waste Solidification-Stabilisation Processes,1995, Nancy, France
[2]
F.lemort, JP.Charvillat
Incineration of chlorinated organic nuclear waste: in situ substitution of phosphates for
chlorides, ICEM 99 Conference, September 26-30, 1999, Nagoya, Japan
[3]
A.Jouan, JP.Moncouyoux, R.Boen, R.Cartier, JJ.Vincent and T.Longuet
Incineration Processes for Radioactive Waste with High Alpha Contamination: New
Development. Proceeding of IT3 Conference pp. 209-210, May 8-12, 1995, Bellevue,
Washington, USA.
[4]
H.Rouault, R.Cartier, R.Boen, T.Longuet
Phosphorus: In situ Treatment for ZnCl2 Formed by Incineration of Organic Waste.
Proceedings of IT3 Conference, pp. 225-228, May 11-15, 1998, Salt Lake City, Utah,
USA.