In view of the CWC chemical weapon and agent destruction efforts currently underway Dr. Martens has provided our family of professionals, a very important and timely article.
Federal Armed Forces Scientific Institute for Protection Technologies - NBC-Protection, Munster, Germany
ASA Newsletter 97-1 reported that the Troop Training Area Munster-North is still a place of discovery of old chemical munitions from the First and Second World Wars. Some other places are known around the country, but with limited numbers of findings. Moreover, the ground of large areas of the Munster site has been contaminated with arsenicals by the explosion in 1919 (see ASA 97-1), as well as by chemical weapon testing activities and open pit burning of mustard gas mixed with arsenic compounds used as antifreeze for winter use.
Since the end of several clean-up campaigns in 1956, the whole place was divided into "White Areas" free of CW residues, "Yellow Areas" with a moderate CW agent burden and "Red Areas" with heavy concentrations of arsenic compounds, buried failure batches of particular viscous mustard formulations and ruins from former buildings.
After about 70 tons of CW agents, particularly viscous mustard, had been assembled and taken into storage bunkers, it was decided to build a destruction plant based on incineration technologies. The incinerator began operations in 1980 and was taken over by the supervisory authorities at the turn of the year 1982 to 1983. Despite two periods of interruption caused by an explosion inside one of the combustion chambers and by a fire in the pre chamber, the plant has been in full function until today. And, certainly it will be needed for more than the next 10 years.
In addition to the first incinerator, a much larger toxic waste disposal plant is under construction. Both facilities are shown in Figure 1. It is designated for the remediation of contaminated soil and consists of the combination of a soil-washing (flotation) step followed by thermal destruction of the extracted contaminants in a Plasmox reactor. As a final product of the reactor, heavy metal residues, particularly arsenic, are incorporated in a glass-type slag.
Both installations are described in the following.
DESCRIPTION: THE FIRST INCINERATION PLANT
Chemical Agents and other Materials for Disposal
The chemical agents found on the German territory, particularly in the Munster region, are characterized by their large diversity. Artillery shells, bombs, mortar munitions and land mines contain CW agents such as: sulfur mustard (HD), nitrogen mustard (HN-3), phosgene (CG), Tabun (GA), chloroaceptophenone, Clark I and II and Adamsite. Sarin (GB) is only occasionally found in shells. In addition to chemical munitions from former German production, captured items from the Allies of both World Wars are completing the extensive assortment. Not only chemical agents are to be disposed of, but also large amounts of waste, which are produced by demilitarization and decontamination activities.
Destruction of Chemical Agents
The basis of the German chemical warfare disposal concept is the incineration of the separated chemical agent fillings at high temperatures, which results in the complete mineralization of the chemical compounds. The flue gases arising from the combustion are scrubbed with an aqueous solution of sodium hydroxide. Emissions leaving the stack are continuously monitored to prove that the stringent German environmental standards are met.
After the chemical munitions are dismantled (demilitarization) by removing the fuses and bursters with explosives, the chemical agents, the resulting contaminated waste and the empty shells are intermediately stored in polyethylene (PE) containers. These PE containers can be burned together with their combustible contents. Similarly, used protective suits, gloves, boots and exhausted active carbon filters contribute to the multiple volumes of solid and liquid material that has to be disposed of by incineration.
Viscous mustard was discovered particularly in the region of Munster and has poor solubility in any type of solvent. The limited solubility of this agent was the main reason for selecting a batch-type incineration technology.
The disposal of phosgene filled munitions is carried out using an absorption column followed by neutralization with sodium hydroxide.
The incineration plant in Munster was designed for a destruction capacity of approximately 100 tons per year, based on an average related to the amounts of chemical agents and contaminated waste, such as the emptied munition shells and used up protective material.
Incineration Plant Configuration
Allowing for the large variety of chemical agents and other materials, a two-stage batch type furnace was calculated to be the most favorable solution for a mixed-type of incineration. Primarily, this configuration was determined because it solved the viscous mustard problem.
After more than 40 years of storage in the ground, the mustard containers had corroded and the mustard itself turned into viscous lumps. The mustard containers were almost completely destroyed by corrosion and showed mustard concentrations of about 25% from inside to as little as 0.1% at the outside. The viscous mustard consists of a matrix of wax or chlorinated rubber with several sulfur mustard analogs and various arsenical compounds, such as phenyl dichloroarsine. These facts led to the choice of an incineration technology with a preliminary evaporation step for the inherent portion of volatile CW agents and other components, followed by high temperature combustion of the vaporized compounds in an afterburner chamber and a final alkaline flue gas scrub. Arsenic compounds are eliminated from the scrubber sewage by precipitation as ferric arsenate.
The isolated chemical agents and also their metal casings are supplied in 30-liter polyethylene drums and, first, stored in an intermediate storage area designed to hold a week's supply. Contaminated waste is provided in the same way.
Before incineration the chemicals are analyzed for the presence of arsenicals. Based on analytical results, batches are put together with regard to achieve the most effective sewage and effluent air purification results.
The process flow within the incineration plant is depicted in the functional diagram, Figure 2. The polyethylene barrels are placed on a charging wagon that is equipped with fire-proof stones. Once the lids have been removed from the drums, using a pull-cable mechanism, the wagon is moved into the first furnace chamber (evaporation chamber) via an airlock. Compared with the ambient air a negative pressure of 0.5 - 1.0 mbar prevails throughout the charging area, so that contaminations cannot get outside.
Evaporation and Main Combustion Chamber
Inside the evaporation chamber, the chemical agents are vaporized and subjected to partial pyrolysis at 300oC in an inert gas atmosphere environment (nitrogen, plus CO2 and H2O produced by stoichiometric combustion of fuel oil). In the case of viscous mustard, this process takes more than 12 hours in order to prevent a sudden and violent combustion or deflagration. By the suction of the central fan, the vapor fraction is moved into the main combustion chamber (afterburner), which is lined with fire-proof stones, and completely combusted at temperatures of 1000 - 1200oC. A residence time of two seconds in this chamber is sufficient to achieve total oxidation. Sulfur mustard (HD) is combusted with the formation of carbon dioxide (CO2) and water, besides sulfur dioxide (SO2) and hydrogen chloride (HCl), which, as environmental burdens, have to be eliminated from the flue gas. Arsenic compounds end up in the flue gas as arsenic oxide (As2O3) and require the final water treatment step. The main combustion chamber and the burn-out chamber are fired with heating oil via an ultrasonic burner. The charging wagon, containing the low volatile organic chemical residues and metal parts, is moved into the burn-out chamber, where especially the metal parts, e.g., the emptied munitions shells, are completely annealed at 1000oC. Subsequently the remains of the wagon are treated as special inorganic waste and/or metal scrap. The exhaust gas of the burn-out chamber is also fed into the main combustion chamber.
Flue Gas Quenching and Scrubbing
The flue gas is rapidly cooled down to 80oC by injection of cooling water and subsequently washed with water in two packed scrubbing towers in a line (each tower is six m high). Caustic soda solution is added to keep the pH value in the effluent solution at a constant level. The afore mentioned contaminants are neutralized both in this way and, considering SO2, oxidized in a reaction tank with hydrogen peroxide (H2O2). This process produces sodium sulfate and sodium chloride, both of which are non-toxic but cause a salt load to the sewage system. Similarly arsenic oxide is transformed to sodium arsenate that subsequently is eliminated by precipitation.
After passage through a demister, which retains small droplets that have been carried over, the flue gas is released to the open air through the stack. SO2, HCl, NOx (nitrogen oxides) and hydrocarbon emission rates are monitored at the stack and recorded continuously in the central operation control room. Dust and arsenic are separated isokinetically from the waste air by a dust probe and subjected to chemical analysis by atomic absorption spectroscopy.
Inorganic arsenic salts are hazardous compounds, which are regulated by a relatively low threshold level of one ppm As in the water effluent. Ferric arsenate (FeAsO4), with very low solubility in water (pKsp = 20.24), can be precipitated with the oxidation of the arsenic salts with H2O2 or KMnO4 solution, followed by the addition of ferric(III) chloride to previously collected batches of the scrubbing waters. The sludge material is dehydrated in a filter press and then filled into 200 L drums for final deposit in an underground waste dump (former salt mine).
Eventually the purified filtration waters are released into the municipal sewage system. In the future it is planned to combine the waste water of the first incineration plant with that of the second installation and to evaporate the liquids to dryness, thus reducing the salt load on the sewer system.
Disposal Balance and Costs
The first incineration plant is in full operation on five days weekly (eight hour shifts) and is kept in a stand by mode through the weekends and on holidays.
The throughput of the incineration plant depends considerably on the type of treated material. For sulfur mustard it amounts between 25 and 35 kg per hour.
Since the beginning of the CW agent disposal program in 1980 until the end of 1996 about 122 tons of chemical agent have been destroyed. The disposal balance for contaminated waste stands somewhere about 935 tons. All together about 28 million DM have been invested in the infrastructure facilities of the plant in its present configuration. The facility was designed and constructed by the Lurgi Company in Frankfurt am Main/Germany. The operational costs per year amount to approximately 2.8 million DM, including the wages for the crew of 10 people.
Taking into account all cost factors, the price for the destruction of 1 kg of sulfur mustard may reach 350 DM. Consequently the disposal of this chemical agent, as an example, is about 10 times more expensive than its production.
THE SECOND INCINERATION PLANT
The large scale soil contamination with arsenicals and viscous mustard residues on the terrain of the Troop Training Area Munster-North, particularly in the “Red Areas”, and occurrences located in other German Federal States, led to the initiative to build a soil remediation plant in Munster.
It seemed inadequate and uneconomical to employ a thermal disposal technology on the whole quantity of the removed, but not uniformly contaminated, soil. Based on the lessons learned from the arsenic-related problems of the first incinerator, the decision was made for a preliminary extraction of arsenic compounds and other contaminants from the excavated soil. Subsequent to this clean-up step, the accumulated but concentrated contaminants are to be treated thermally in a high-temperature plasma reactor.
Preliminary results received with a pilot plant demonstrated a successful clean-up of sandy soil, with a reduction of the arsenic concentration to below 20 mg/kg of dry soil. The effectiveness of contaminant separation from the soil matrix depends on combined operation of mechanical washing (attrition) and flotation steps. Moreover, the application of auxiliary additives in very specific formulations is required. The clean-up yield for a typical sandy soil was about 90%, which means that the contaminating compounds have been isolated as flotation concentrate, together with the fine soil fraction, 10% of the original material. The cleaned soil can be back filled on to the sites of previous excavation.
The plasma reactor consists of an internal centrifuge in which the hazardous waste material is heated up by melting torches, producing a plasma arc with a temperature of about 20,000oC. Under this condition, the filling of the centrifuge is turned over at temperatures about 1600oC within four hours into a molten slag. The liquid slag is released after the rotor stops and the slag solidifies to a glassy material with nonleachable characteristics (with respect to the attack of water from atmospheric precipitation).
In the course of the plasma treatment any organic components in the material are at first pyrolyzed and then oxidized in the presence of oxygen, ending with usual pollutants like SO2 and HCl. The arsenic compounds are oxidized to arsenic oxide (As2O3), which is partially kept in the glass-like slag. Another portion of the arsenic oxide will be removed by a multi-stage flue gas scrubber, similar to that of the first incineration plant.
The waste water of the off-gas cleaning system will be treated in a water evaporation unit. Thus, no waste water will be released into the sewers. Due to its arsenic contents, the dry residue from the evaporator has to be disposed of in a hazardous waste dump site.
The main contractor for development and construction of the second incineration plant in Munster is the Mannesmann Anlagenbau, Dsseldorf/Germany.
Owing to the existence of an incineration plant that is earmarked for the destruction of CW agents, Germany is in compliance with the Chemical Weapons Convention. Moreover, after completion of the second facility, even the chemical residues contaminating the ground from the two World Wars can be disposed of safely.
Editors Note:All of us wish to thank Dr. Martens for his very well written and exceptionally timely article on the experience of the Federal Armed Forces Scientific Institute for Protection Technologies with their CW destruction facilities in Munster, Germany. This experience with the world’s longest running, full-scale operational CW destruction facility, which is being shared with us, will help provide our worldwide family documentation needed to initiate and/or help influence the decisions for destruction of their own or others’ abandoned stocks of chemical munitions.
For additional information on the Munster facilities and on the many varied tasks of the Federal Armed Forces Scientific Institute for Protection Technologies - NBC Protection, please see ASA Newsletters 97-1 and 97-2.
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