Approved destruction technologies for ozone-depleting substances
According to Article 5.1 of the Montreal Protocol, the Parties to the Protocol approve the list of destruction technologies for ozone-depleting substances. The first version of the list was released as Annex II to the report on the Fourth Meeting of the Parties (November 23–25, 1992, Copenhagen, Denmark). With amendments adopted by decisions V/26, VII/35, XIV/6 and XXX/6, the list of the destruction technologies is as follows (click for PDF):
| Technology | Applicability | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Concentrated Sources | Dilute Sources | ||||||||||
| Annex A | Annex B | Annex C | Annex E | Annex F | Annex F | ||||||
| Group 1 | Group 2 | Group 1 | Group 2 | Group 3 | Group 1 | Group 1 | Group 1 | Group 2 | Group 1 | ||
| Primary CFCs | Halons | Other CFCs | Carbon Tetrachloride | Methyl Chloroform | HCFCs | Methyl Bromide | HFCs | HFC-23 | ODSs | HFCs | |
| DRE* | 99.99% | 99.99% | 99.99% | 99.99% | 99.99% | 99.99% | 99.99% | 99.99% | 99.99% | 95% | 95% |
| Cement Kilns | Approved | Not approved | Approved | Approved | Approved | Approved | Not determined | Approved | Not determined | ||
| Gaseous/Fume Oxidation | Approved | Not determined | Approved | Approved | Approved | Approved | Not determined | Approved | Approved | ||
| Liquid Injection Incineration | Approved | Approved | Approved | Approved | Approved | Approved | Not determined | Approved | Approved | ||
| Municipal Solid Waste Incineration | Approved | Approved | |||||||||
| Porous Thermal Reactor | Approved | Not determined | Approved | Approved | Approved | Approved | Not determined | Approved | Not determined | ||
| Reactor Crackin | Approved | Not approved | Approved | Approved | Approved | Approved | Not approved | Approved | Approved | ||
| Rotary Kiln Incineration | Approved | Approved | Approved | Approved | Approved | Approved | Not determined | Approved | Approved | Approved | Approved |
| Rotary Kiln Incineration | Approved | Approved | Approved | Approved | Approved | Approved | Not determined | Approved | Approved | ||
| Inductively Coupled Radio Frequency Plasma | Approved | Approved | Approved | Approved | Approved | Approved | Not determined | Not determined | Not determined | ||
| Microwave Plasma | Approved | Not determined | Approved | Approved | Approved | Approved | Not determined | Not determined | Not determined | ||
| Nitrogen Plasma Arc | Approved | Not determined | Approved | Approved | Approved | Approved | Not determined | Approved | Approved | ||
| Portable Plasma Arc | Approved | Not determined | Approved | Approved | Approved | Approved | Not determined | Approved | Not determined | ||
| Chemical Reaction with H2 and CO2 | Approved | Approved | Approved | Approved | Approved | Approved | Not determined | Approved | Approved | ||
| Gas Phase Catalytic Dehalogenation | Approved | Not determined | Approved | Approved | Approved | Approved | Not determined | Approved | Not determined | ||
| Superheated Steam Reactor | Approved | Not determined | Approved | Approved | Approved | Approved | Not determined | Approved | Approved | ||
| Thermal Reaction with Methane | Approved | Approved | Approved | Approved | Approved | Approved | Not determined | Not determined | Not determined | ||
| Thermal Decay of Methyl Bromide | Not determined | Not determined | Not determined | Not determined | Not determined | Not determined | Approved | Not determined | Not determined | ||
* — Destruction & Removal Efficiency
Concentrated sources refer to virgin, recovered and reclaimed ozone-depleting substances.
Dilute sources refer to ozone-depleting substances in solid materials (for example, foam).
Brief overview of destruction technologies
The destruction technologies can be divided into three groups:
Incineration technologies
Reactor cracking
Cracking is a high-temperature decomposition of chemical compounds into products with lesser molecular weight.
Waste gases and recovered refrigerants are burnt with oxygen and hydrogen resulting in hydrofluoric (HF) and hydrochloric (HCl) acids, carbon dioxide (CO2), water (H2O), and a small amount of chlorine. In a heat exchanger, the decomposed products are cooled and acid gases are purified. The generated 55% hydrofluoric and 33% hydrochloric acids can be used for commercial purposes. Waste waters are processed at a water treatment plant. When acid residuals are removed, waste gas consists of CO2, O2, and water vapor. The process does not generate any solid wastes.
Gaseous/fume oxidation
Waste refrigerants and vapors (mostly persistent organic pollutants) are thermally destroyed in fire-resistant combustion chambers. The fume stream is heated with external fuels such as natural gas or fuel oil. The residence time of most refrigerants is 1–2 seconds at approximately 1,100°C.
Rotary kiln incineration
Rotary kilns are used to destroy hazardous substances of all forms and kinds: gaseous, solid, liquid, sludge wastes. As fuel, they use natural gas, fuel oil, or liquid wastes with high caloric power.
As hydrofluoric acid can harm kilns, this technology is applied only to wastes containing up to 1% of fluorine and requires environmental monitoring.
Liquid injection incineration
Liquid injection incinerators usually have one chamber with one or more waste feeding systems, and allow feeding flammable liquids or flammable liquid wastes, including sludges and slurries. Injection of liquid wastes through atomizers supplies optimum suspended mixture with air to an incinerator. To improve the ignition potential of the waste mixture, extra fuel (fuel oil or natural gas) can be supplied to a combustion chamber from a feeder vessel.
Municipal solid waste incineration
Solid wastes are destroyed in incinerators that use either auxiliary fuel (for non-processed solid wastes) or fuel of mechanically homogenized solid wastes.
Cement kilns
As cement kilns generate much heat energy, they are used to destroy contaminated fuel and other hazardous substances. Most cement kilns are suitable for controlled feeding of refrigerants but the decision must be taken on an individual basis.
Porous thermal reactor
ODS and other industrial waste gases are decomposed in porous thermal reactors at high temperatures in an oxidizing atmosphere with a continuous supply of auxiliary gas. As the process requires appropriate heat transfer, the porous structure ensures even heat distribution and reduction of a reactor volume.
Plasma technologies
Argon plasma arc
Argon plasma stream directly destructs waste (PLASCON technology).
Argon ionized by a direct current of 150 kW generates a plasma stream at 10,000°C. Wastes are quickly heated in a reaction chamber up to 2,500°C and in approximately 20 milliseconds pyrolysis begins and the waste is vaporized. Oxygen converts all the evolving carbon into carbon dioxide, and hydrogen prevents from generation of CF4.
Inductively coupled radio frequency plasma
Vapor and gaseous refrigerants are heated by a plasma stream and destroyed in a high-temperature reactor (2,000°C) in 2 seconds. The generated acid gases are destroyed through cooling and scrubbing. The technology is used for commercial purposes due to its high destruction efficiency and a small amount of generated dioxins.
Nitrogen plasma arc
CFC, HCFC, and HFC are destroyed by high-temperature nitrogen plasma created by a direct current plasma torch with water-heated electrodes. As against pressurized liquefied gases that can be fed into a reactor from a stock tank, liquids first should be located in a pressure vessel and then be fed into an evaporator by compressed air. Carbon oxide is oxidized in a diffusion-furnace tube. HCFC and HFC react with vapor and decompose into carbon oxide (CO), hydrofluoric (HF) and hydrochloric (HCl) acids. Then air oxidizes carbon oxide in a diffusion-furnace tube to generate carbon dioxide. Lime-water absorbs hazardous acid gases (HCl and HF) in a gas scrubber.
Microwave plasma
This technology feeds 2.45 GHz microwave energy at low pressure and low temperature to generate plasma in a gas flow in a dielectric tube. The capacity of a unit can reach 50 kW. In a coaxial resonator of a special design, microwaves generate a strong electric field thus creating high-temperature plasma under the atmospheric pressure. Molecules ionize and decompose at a minimum temperature of 5,700°C.
Acid gases (HCl, HF) are de-acidified by caustic lime, and CO is combusted with air to generate CO2. The process features high electrical efficiency. Argon is used only to initiate the plasma but the process requires no gas.
Portable plasma arc
A portable plasma arc for ODS destruction was developed by ASADA, a Japanese company. The plant requires high capital investments (approximately USD 150,000 excluding expenses for the creation of necessary infrastructure: installation of power lines, etc.) and maintenance expenditures (USD 30–50,000 per year). The minimum capacity is 1–2 kg per hour (3.6–7.2 tons per year). The average ODS destruction cost is USD 25 per kg.
Non-incineration technologies
Gas phase catalytic dehalogenation
Hitachi Corp., a Japanese company, developed a technology for ODS destruction with metal oxide catalyst at 400°C and atmospheric pressure. The generated hydrofluoric and hydrochloric acids are absorbed by calcimine. The technology is used to destruct persistent organic pollutants (polychlorinated biphenyls) and is suitable for the destruction of ODS but not on a commercial scale.
Superheated steam reactor
A superheated steam reactor destructs ODS in a vapor phase under very high temperatures. When mixed with ODS, vapor and air are pre-heated up to approximately 500°C and fed into a tubular reactor with walls that are electrically heated up to 800–1,000°C. The process generates HF, HCl, CO2. Exhaust gas is fed into a scrubber to be quenched with a calcium hydroxide solution to neutralize the acid gases.
Chemical reaction with H2 and CO2
The process of ODS and HFC decomposition operates at a temperature of 300–1,000°C and pressure of 1–30 atm. and generates pure HF, HCl, CO, and H2O, i.e. requested commercial products that can be sold to cover destruction expenses.
Thermal reaction with methane
The reaction of methane and ODS occurs in a plug-flow reactor at atmospheric pressure and temperature up to 800°C. Weak bonds in ODS molecules are destroyed producing radicals that react with methane.