The Air Pollution Control (APC) technology of waste incinerators has followed a different path than that of other furnaces due to the wide variety and the non-homogeneity in the constituents of the waste. It has developed by combining a number of control techniques and equipment. It continues to improve the current techniques and adopt the state-of-the-art technologies by meeting the ever-tightening air pollution regulations and the need to reduce the treatment cost and to raise the efficiency. In particular, several dry acid gas treatment methods (dry process) have been introduced mainly in Europe, where there is an acute race among the competing technologies.
In this article, we begin with the overview of the prevailing air pollution control technologies, mentioning the different filter media used mainly with the baghouse, and the catalytic de-NOx system (SCR). We then proceed to describe the trend of the new entries such as dry acid-gas treatment in which reaction products are re-circulated, the new system using alkaline agents, and the high-temperature filtration.
This paper describes an overview of the development of the dry sodium bicarbonate flue gas cleaning process in Europe. Solvay developed this process under the registered name NEUTREC, covering the flue gas cleaning as well as the treatment and recycling of flue gas cleaning residues. The use of sodium bicarbonate is now widely spread across Europe, with more than 150 users. It is recognized as a new-generation dry system, combining the simplicity of dry systems with a top-class efficiency traditionally associated with much more complicated systems.
Today Solvay is working in partnership with Takuma for the promotion of this process in Japan.
The next sections describe successively:
・the legislative evolution in Europe
・the process itself, from a technical point of view
・the business positioning
・the application fields and historical development
・some examples of plants equipped with this system.
The follow-up on the performance of the methane fermentation facility with the Kompogas process installed in CAMPO RECYCLE PLAZA Co., Ltd on March 2004 was conducted for more than one year.
We have found out that 70-80% of the feedstock fed into the digester was composed of biodegradable materials such as food and paper waste, while the rest was non-biodegradable material in the anaerobic digestion, such as plastic waste and so on. Over 70% of the organic substance in the feedstock was decomposed to yield 205m3N of biogas from one ton of feedstock. Furthermore, it was confirmed that about 60% of the electric power generated from the biogas was exported as surplus.
This article reports on the Amagasaki Municipal Incineration Plant No.2 that we completed and delivered to the city in March 2005.
In this facility, the heat generated from the incinerator is recovered thoroughly by generating electricity ; and the incineration residue, including the fly ash is melted in a plasma melting furnace for reuse.
In the performance test, both the incineration furnace and the melting furnace achieved their design throughput, with the power generation efficiency of 21.7%. Also, the results of the exhaust gas measurement and analysis, and the molten slag leachate test satisfied the regulation standards.
There is a tendency in the industrial factories today that the electric power demand rises while the steam demand goes down. The factories that already have co-generation systems of boiler-steam turbine often find it difficult to increase only the electric power output at high thermal efficiency by adding another co-generation system.
The preceding article describes the gas turbine re-powering system that combines the existing boiler-steam turbine system with a newly installed gas turbine. This enables to increase the electric power ratio without losing the thermal efficiency.
Oshima pyrolysis and melting plant for the treatment of MSW, ordered by the Oshima District Cooperative of Municipal Solid Waste Management, was finished in March 2003. The waste treated in this plant has high moisture contents near that of the design low-end calorific waste. Moreover, the plant operation has to be kept continuously at the maximum load and efficiency because the waste input is almost equal to its design capacity. In order to treat such high-moisture waste smoothly, the facility and the waste quality have been improved, accomplishing nearly full annual throughput in 2004. The number of operating days between the two units in the period was 577, and the total throughput reached 99.4% of the design capacity.
The features of the kiln-type plant, low air ratio (λ=1.2) combustion and stable heat recovery, have been accomplished even when the waste feed to the pyrolysis drum had to be interrupted for a short time due to problems in the waste feeding system.
Recently, night soil treatment plants (sludge treatment and recovery centers) are installing methane fermentation facilities and composting units for recovering resources.
Phosphorus, on the other hand, is not recovered widely even though it is considered a diminishing resource, while the material is being imported for food and fertilizer uses.
We have conducted demonstration tests of phosphorus recovery, and studied its application to night soil treatment facilities. The preceding article reports on the result of these tests.
Two treating methods, the MAP and the phosphorus crystallization process, were used, and both have been proven capable of stable phosphorus recovery. Furthermore, we have found out that the product granules of MAP can be de-watered to 30% water content simply by draining ; that it satisfies the qualification to be officially registered as a compound fertilizer material. MAP process has proven to produce an effective phosphate fertilizer that is easy to handle.
Looking for a method of recovering energy from biomass, we researched and experimented on the anaerobic biohydrogen production. At the beginning of this report, we summarized the findings from earlier studies that the metabolism of carbohydrates by hydrogen-producing microbes such as genus Clostridium and Enterobacter is important in anaerobic biohydrogen production, and that these microbes can be made dominant by a heat treatment of about 80℃ and by controlling pH and hydraulic retention time. Studies, however, of biohydrogen production from high-concentration substrates of real biomass, have not been conducted. Thereupon, we studied the characteristics of biohydrogen production using a simulated organic waste. At the batch experiments with the initial total solid concentration in the range of 2～10%, the optimum pH showed a tendency to shift from acid to neutral when the concentration increased, and the maximum hydrogen gas production yield was roughly 1.7mol-H2/mol-glucose at each test condition. At the continuous experiment using a substrate of the same 10% total solid concentration, a continuous production of the hydrogen gas was observed for 100 days, and the yield was 0.21mol-H2/mol-glucose.
When installing a mixer in a water tank of a wastewater treatment facility, it is important to choose one with a sufficient mixing capacity and low power consumption. We have developed a low-power vertical mixer that satisfies this requirement, and demonstrated its performance by testing it in an operating facility. The result has verified that it can attain the flow speed of more than 0.1m/s uniformly over the entire bottom area at the mixing power density of 3W/m3 compared with 6～10W/m3 of the conventional mixers. It has also proven to be capable of stabilized, uniform mixing under high MLSS (Mixed Liquor Suspended Solids) density and low water inflow.
In the meantime, we have built a computer model that simulates the fluid flow in the mixing tank and the mixing and stirring conditions for evaluating its performance, and compared them with the results of the test, verifying the analytical method.