INCINERATION IN JAPAN DR. CHIAKI IZUMIKAWA Regulations in the environmental field are becoming severe and severe. At the same time, NIMBY syndrome is becoming stronger day by day. The cost of incineration and other conventional waste treatment, especially landfill is increasing. As a result, recycling is becoming to be available. However, a considerable amount of substances including resources are still landfilled as a waste and remaining capacity of landfill is decreasing rapidly. Therefore, waste minimization isnow strongly required. Incineration is still considered to be one of the effective and indispensable technologies in Japan and plays important roles in the waste treatment. Recently, it is considered that the recycling should play and will play a major part of the waste treatment as a method of waste minimization from the aspect of both environment and natural resources. This figure shows the remaining capacity of landfill in Japan. Japan is short of landfill and its situation is becoming severe because of NIMBY syndrome. Actually, it is very difficult to construct a landfill newly. According to the estimated remaining capacity of landfill for industrial hazardous waste, we will loose a landfill in 2007. Therefore, Japan should reduce the waste to prolong the life of landfill. Recycling is focused on as effective means of waste minimization. This figure shows that the recycling has a great benefit from the environmental aspect as well as natural resources. For example, recycled paper eliminates 40% of energy, 130% of waste, and 90% of air pollution comparing the paper from virgin resources. In case of aluminum, recycling can eliminate 90%of energy, 95% of solid waste, and 90% of air pollution compared one from virgin raw materials. In case of iron steel, it can eliminate 60 % of energy, 90% of solid waste, and 30% of air pollution. Landfill options for waste disposal is becoming to be unavailable. To solve this problem recycling and complete incineration technologies are strongly required minimizing the emission of toxic substances and energy consumption. Now 75% of MSW are incinerated. Combustion of the organic component of waste is an effective disposal method if the combustion is conducted properly. Recycling is increasing year by year and now 12% of MSW are recycled. Landfill is decreasing. (This is one of the incineration facilities for the MSW near from Tokyo. Photo) Incineration allows a drastic reduction of amount and volume, is also one of the best techniques for hazardous organic wastes and is widely used.
It can achieve a 75 per cent weight reduction and an 85 per cent volume reduction. The long-term cost of land disposal is likely to be greater than the short-term cost of incineration. If organic wastes escape from a landfill, expensive treatment of contaminated ground water or other remedial actions must be practiced in the future. Proper treatment by methods like incineration eliminates the long-term costs, although the short-term costs may be higher. Recently, incineration is becoming more popular due to the shortage of landfill sites. The preferred technologies are shifting from landfill ones to those that achieve waste destruction, elimination and recycling. A great effort is now being made on recovering resources such as paper, bottles, cans, and electrical consumer appliances etc. from the municipal solid waste to minimize the final disposal and increase the lifetime of landfill. However, seventy five percent of them are still incinerated. (This is an incineration facility for hazardous wastes. Photo) The plant is comprised of a rotary kiln, secondary and tertiary combustion chambers, a fixed bed furnace, a quencher, scrubbers, a wet electrostatic precipitator and a stack. The waste is transported mainly in tanker trucks or steel drums. The waste was checked, classified and registered in each shipment and stored for treatment. Primary classification is based on the results of characterization tests on the spot such as viscosity, flammability, ph and compatibility of the waste where solid material is allowed to settle and is removed from the liquid. Before sending the material to a storage tank, a mixing test is carried out to avoid unexpected problems caused by chemical reaction between the liquids in the storage tank and pipes. After the primary classification the chemical composition, heat value and flash point are measured and combustion tests are carried out prior to treatment. The results are used for determination of the optimum treatment method and the schedule. The blended mixture is charged into a rotary kiln by a ram and incinerated at 1,000 0 C at a feed rate of 4 t/h. Waste oil will be burned at the same time when the mixture has a low heat value. Combustion gas from the rotary kiln goes into a secondary combustion chamber, where acid and alkali are decomposed thermally at 800 0 C. Then waste oil is burned in a tertiary combustion chamber to raise the temperature to 1,000 0 C to decompose hazardous materials completely.
The gas from the tertiary combustion chamber is quenched to 70 0 C or 80 0 C in a cooling tower by spraying a high volume of water. HCl and SOx are removed in a subsequent two stage scrubbing system, which is where the slaked lime slurry and the solution of caustic soda are sprayed. Before exiting the stack, the gas is introduced into the wet electrostatic precipitator, where particulate and water droplets are trapped and removed. It has recently reported that 80 0 C 90% of total amount of dioxins generated in Japan is from MSW incinerators. During the eighties the mechanisms of dioxin formation were revealed. On this basis considerable improvements of the burning process and flue gas cleaning have been introduced and innovative technologies are investigated to achieve complete combustion for the minimization of dioxin generation and detoxification of ash. According to the information from IAWG, considerable amount of dioxins are synthesized in the old gas treatment systems. However, improved technologies can reduce it drastically. The most important parameters for dioxin formation are organic carbon, chlorine, oxygen, temperature, time and catalyst. Principally incineration practices address the three T s : time, temperature, and turbulence. The wastes, as gases, must be exposed to a temperature high enough to allow complete oxidation of the organic materials. The waste gases must have some period of time exposed to these maximum temperatures, and the gases must be mixed well enough so that each molecule is exposed to enough oxygen molecules to allow complete oxidation. (This figure shows the relationship between dioxin concentration and combustion temperature.) According these data, combustion temperature must be maintained higher than 800 0 C (This figure shows the relation between dioxin concentration and CO concentration in exhaust gas.) The concentration of CO must be kept under 100 ppm at the exit of stack. This indicates a complete combustion decreases the dioxin formation. (This figure shows the relationship between dioxin concentration and the temperature of filter.) This means that filter must be operated at a temperature below 200 0 C. There are almost two thousand MSW incinerators in Japan and the effect of MSW incineration is great. (This figure shows a number of incinerators that generate a certain dioxin concentration.)
The small size and batch-operated incinerators tend to generate a considerable amount of dioxins. Japanese dioxin guideline with the requirements for combustion conditions for new facilities ensures that discharge concentrations of 0.1 ng/nm 3 can be obtained. The combustion conditions are listed in this table. Temperature is >850 0 C for at least 2 seconds with CO concentration at exit of stack <30 ppm at 12% oxygen, with the injection of activated carbon in the flue gas stream and with fabric filters at a temperature <200 0 C. (The table shows the new criteria for dioxin emission.) According to the estimation, the new guideline could achieve 86% of reduction in 5 years, 98% of reduction in 10 years, and 99.6% reduction in 20 years. Incineration of MSW generates approximately 10% of bottom ash and 3 % of fly ash. These are fly ashes from various MSW incinerators. Fly ash contains hazardous components such as heavy metals and dioxins. (The table shows the chemical composition of three kinds of fly ashes from MSW incinerators.) These contain copper, lead, zinc, cadmium, mercury, chlorine, and others. The content of lead, for instance, is between 0.2 and 1.25%, copper between 0.06 and 0.18%, mercury between 1 and 151 ppm and cadmium content is 100 ppm depending on the quality of waste and incineration process. They contain a considerable amount of calcium and chlorine. Calcium is injected in a form of slaked lime to eliminate hydrochloride from an exhaust gas. Excess lime raises a ph of fly ash and promotes lead leaching when the ash is landfilled. Chlorine ions also enhance the leaching of heavy metals. Earth alkali metals and some metals such as Fe, Cu, Ni, Cu and Al tend to remain in the bottom ash during incineration, whereas Na, K, toxic heavy metals, halogens and S are easily volatilized and go into the fly ash. Heavy metals, especially their chloride compounds have a higher vapor pressure and tend to be volatilized at lower temperature. For example, metal lead has a vapor pressure of 10-3 atm at 1000 degrees in centigrade, whereas leadchloride has a vapor pressure of 1 atm at 1000 degrees, it means leadchloride exists in a form of vapor.
The investigation of IAWG revealed the behavior of lead and cadmium in the incineration process. It shows that about 30% of lead contained in the waste are volatilized in the incineration process and are recovered in a fly ash. About 90% of cadmium are volatilized and contaminate fly ash. [This figure shows the chemical properties of the bottom, boiler (one of fly ash), and ESP ash (one of fly ash)]. Yellow part means to be soluble and blue part insoluble. About 49% of zinc existed in bottom ash could be soluble, whereas 81% of zinc in ESP ash could be soluble, 51% of lead in bottom ash is soluble, whereas 94% of lead in ESP ash is soluble. Cadmium is more soluble. These facts mean the fly ash has more unfavorable properties than the bottom ash from the environmental aspect. Fly ash is likely to contaminate groundwater or soil when it is landfilled. Therefore, fly ash has more difficulties in the treatment. In addition, the fly ash contains much amount of salts, sodium chloride and potassium chloride. These salts promote metal leaching especially in the acid ph region. This phenomenon is important considering acid rain. Thirty-six million tn/y of MSW are incinerated in Japan and approximately 10 W % of bottom ash and 5 W % of fly ash are generated from an incinerator. In 1992, the legislation was revised and fly ash from an incineration process has to be treated by certain methods in order to comply with the new requirements. Fly ash, which contains toxic heavy metals and dioxins, must be treated using cement solidification, vitrification, chemical stabilization or acid and solvent extraction methods prior to landfilling. By means of cement s/s method, metal ions and other toxic substances may be incorporated into the crystal structure of the cement minerals. It is more economical than other treatment method and has been widely used before. Various vitrification processes are becoming commercially available for the destruction and/or immobilization of hazardous wastes.
In the last decade some combined vitrification processes have been developed. As a common feature the mineral components are melted and glassified. Fly ash with or without bottom ash is heated to over 1,300 0 C with fuel oil or electricity and then vitrified and reduced in volume. Simultaneously, toxic dioxins are destroyed at the high temperatures. Volume reduction also reduces the landfill problem. With these advantages vitrification processes have been introduced as a treatment method of fly ash for MSW reducing the problems of dioxins, toxic heavy metals and landfilling. I show here some of vitrification processes that are commercially used in Japan, plasma type and arc one that use electricity, and surface melting type that use fuel oil. Various chelating agents are currently used to stabilize chemically. However, very toxic dioxins cannot be destroyed by this technology. In addition, treated wastes may not be stable forever considering biological reactions after landfill. Acid and solvent extraction method is not economically available. Considering the existence of toxic dioxins, vitrification treatment, which can decompose them at high temperature, is superior to the other methods. In addition, vitrification is also superior for both volume reduction and resistance to leaching. However, low boiling point metals such as cadmium, lead, zinc and mercury, especially their chloride compounds, will be volatilized during vitrification and generate fly ash again with high concentrations of heavy metals. Our studies revealed the behavior of toxic metals in the vitrification system. At a temperature of 1300 degrees most of mercury and arsenic go into exhaust gas passing fabric filter, whereas most of lead and cadmium go into the fly ash. About 40% of zinc and copper remain in a slag and remaining 60%of them are volatilized and go into the fly ash. The rate of volatilization is strongly depending on the melting temperature and depending on the metals. The volatilization rates are increasing with the increase of the temperature. Almost all of lead is volatilized at a temperature of 1000 degrees
Amount of zinc in a slag is decreasing with increasing temperature. And the investigation by X-ray diffraction revealed that metals are volatilized in the form of chlorides, oxide, sulfates and silicates. Even very toxic dioxins can be decomposed into carbon dioxide, sodium or calcium chloride and water and can be completely detoxified. On the other hand, heavy metals cannot be decomposed any more. Metal-bearing wastes have to be carefully treated because heavy metals could be leached out under uncontrolled conditions when disposed in a landfill. Most heavy metals before being mined exist underground under reducing conditions and are naturally stabilized in the form of sulfides with low solubilities. Heavy metals disposed of into the earth after consumption are not stable. On the other hand, they do not influence the environment as long as they are utilized. Heavy metals, therefore, have to be recycled and utilized forever. However, recycling will be realized only when the metal content is high enough. If it is low, it will be discarded and the concentration will then be sometimes high enough to influence the environment. This is the great problem concerning metal-bearing wastes. In this case, stabilization or recycling is required. Recycling is more ideal considering that it is managed by humans and that there is no chance to affect the environment. Consequently, heavy metals should be principally recovered and recycled forever from the viewpoint of protecting the environment as well as natural resources. From this standpoint, a technology to recover heavy metals from toxic vitrification fly ash was developed. Commercial plant is now under construction and the operation will start in 2002. The main feature of the process is to solve the waste problem by complete recovering of over 99.9 % of the heavy metals for recycling without making any new waste requiring further treatment. The process recovers all of the heavy metals from the vitrification fly ash and does not generate any more waste except the effluent water that meets Japanese effluent standards.
Lead and some heavy metals are recovered under acid conditions as a lead product while zinc and the other heavy metals are recovered in a zinc product under alkaline conditions. The process, called MRG Process, comprises pre-treatment, leaching, neutralization, sulfurization and wastewater treatment and is equipped with reaction tanks, pumps, filter presses and an automatic control system. Vitrification fly ashes are slurred 20 % solid concentration with water and are pumped to a leaching tank, where heavy metals such as zinc, copper, cadmium, etc. are leached out with sulfuric acid and then lead, tin and antimony are recovered by filtering. The Filtrate is sent to a neutralization tank where caustic soda is added by adjusting the ph to approximately 8 and the hydroxides of zinc, copper and cadmium are precipitated. A trace amount of heavy metals still remain in the solution even after neutralization. Sodium hydrosulfide is then added to precipitate and remove the remaining heavy metals. The ph of the effluent water from the process is automatically regulated and the COD (Chemical Oxygen Demand) is checked before being released into the environment. Thus, the process detoxifies vitrification fly ash and recovers heavy metals that are recyclable for smelters. Also the effluent water meets strict environmental requirements and can be released into the environment. (This is a pilot plant that we successfully used.) Lead product is sent to a lead smelter where various metals are extracted and purified. Zinc product is sent to a zinc refinery to be used again as a pure metal. An innovative technology, that treats undesirable wastes containing heavy metals, chlorides and dioxins, was developed by a Japanese cement company. Various wastes are utilized as a raw material in a cement kiln to produce Eco-cement. Toxic chemical components could be destroyed at a temperature of 1450 0 C. Bottom ash, fly ash, sewerage sludge and other wastes are fed into a cement kiln with additives such as limestone, silica and iron ore to adjust the chemical components. Eco-cement has a shorter setting time than Portland cement. The compressive strength is similar to that of the High Early Strength Cement. Eco-cement contains chlorine and can be used in the field of non-steel plain concrete, concrete blocks and cement fiber boards and marine structures. If the chlorine content is enough low, it can be widely used like Portland cement.
The kiln dust from the Eco-cement Process contains 2 0 C 4%Cu, 1 0 C 2%Pb and 0.5 0 C 1%Zn with a slight amount of other toxic heavy metals as well as ca.60% sodium and potassium chlorides as a result of volatilization. It is very similar to vitrification fly ash and can be treated by the MRG process like vitrification fly ash of MSW. The total system in combination with the Eco-cement Process and MRG Process will solve the MSW related problems ofzero Emission. A commercial plant is now under construction and the operation will begin in 2002. I show you the studies on the metal recovery from automotive shredder residue(asr) using a thermal decomposition and physical separation technologies. ASR, that contains plastics, ferrous and nonferrous metals, is currently landfilled without any treatment. However, it has both a resource value and an environmental contamination risk. To solve the problem, we have been working on the recovery from the ASR. We decomposed ASR thermally in a rotary kiln prior to physical separation. Thermal decomposition successfully achieved great volume reduction of ASR and liberation of each component for subsequent separation without oxidation of metals. (This is a pilot plant of physical separation for ASR.) (This is one of the equipment, separating and recovering copper.) (This is a copper product recovered from ASR.) Recently, gasification/vitrification processes have developed as an innovative technology for coming century. Some commercial-scale plants are under construction. The gasification/vitrification process principally consists of shredding solid waste, magnetic separation, screening of pyrolysis char with separation metals, pyrolytic degassing, gasification of char, clean gas production, energetic utilization and melting residues. This technology is expected as one of treatment method of coming century to contribute to the minimization of dioxin and NOx emission, reduction and detoxification of residues, utilization of energy and metals, and cost reduction. Waste is fed to a pyrolytic gasification furnace, where organic materials are decomposed thermally and generated fuel gas that is used for power generation. Metals are recovered from a residue and separated char from residue and melted in a vitrification furnace with air or oxygen, sometimes fuel gas generated from waste are used for the vitrification. Many gasification/vitrification processes are proposed. Rotary kiln, fluidized bed furnace and shaft are used as a gasification process.
(This is one of gasification/vitrification processes.) Any way, industrial clustering is very important to treat the waste effectively utilizing the waste of other industries instead of conventional raw materials prior to considering a use of incineration. If the principal industries such as steel industries, nonferrous industries, cement industries, energy suppliers and transportation are integrated each other or with other industries, many kinds of wastes can be treated and utilized as raw materials. Therefore, industrial clustering is the key point to proceed nationwide recycling and waste treatment effectively and economically. Waste minimization and development of waste technologies are strongly required to achieve sustainable development around the world. Think globally, act locally!