VOL.13 NO.2 (published in Feb-2006)

Photo in Cover :A Demonstration Plant for Gasification of Sewage Sludge
(Installed in Nakagawa Sewage Works in Misato City, Saitama Prefecture)

VOL.13 NO.2 (published in Feb-2006)

Current Trend of Solvothermal Technology
-Such as Supercritical and Subcritical Water-

Yutaka FUKUSATO and Ken-ichi SHISHIDA
(Energy and Environmental Development Dept.)

(Abstract)

Solvothermal technologies have not become widely used because of the engineering limitations such as the durability of the reactor material, and the risk of reactor blockage with scale formation. However, numerous accomplishments of research and development have been accumulated, and many solutions of these issues are found. Because solvothermal technologies have strong possibilities not only in chemical syntheses but also the risk reduction of chemicals and the new production of energy and materials from solid waste and wet biomass, these technologies will make a breakthrough progress after surpassing the engineering limitations.

In this article, the properties of solvothermal fluids and today's engineering issues were described along with the development and prediction of the technologies.

Sludge Dewatering System at Water Purification Plants Using Freeze/Thaw Treatment

Yutaka FUKUSATO*,Takahiro YOSHII**,Shinji ITO*** and Atsuko SEO****
(*Energy and Environmental Development Dept.**Sewerage Engineering Dept.
***Energy Sales & Service Dept., Tokyo Gas Co., Ltd.
****Technology Research Institute, Research Dept.,Tokyo Gas Co., Ltd.)

(Abstract)

NFC system (New Freeze/thaw Concentration system) is an energy-saving and environment-friendly treatment that uses an ammonia absorption refrigerator whose energy source is the waste heat from a gas cogeneration system. This refrigerator uses only a quarter of the electricity used by the conventional electric compression refrigerator.

In this article, we reported on the demonstration test commissioned by Tokyo Metropolitan Government Bureau of Waterworks and Tokyo Gas Co., Ltd. We installed an NFC demonstration facility in the Purification Plant A in the Tokyo metropolitan area and achieved an excellent performance using sludge of four different purification plants from different riverheads throughout the year. We achieved improved dewatering and filtering speed when the mixing ratio of the volume of freeze/thaw sludge to that of untreated sludge was more than 25% in summer and 50% in winter. The system significantly reduces the power consumption of the dewatering treatment.

Denitrification in a Moving Bed up-flow Sand Filter (UNIFURO SAND FILTER)

Masahiko OKUDA,Tomoyuki DOI and Masaharu SAKAGAMI
(Sewage Engineering Dept.)

(Abstract)

Recently, the nitrogen removal technology involving bioreactors has been developed, and is being applied to sewage treatment. However, its application is limited due to the high costs for construction and operation, and the requirement for a large space, compared with the conventional activated sludge process, particularly in urban areas where land space is restricted. This study aimed at developing a new denitrification process with a different angle, and undertook to add a denitrification capability to a sand filter. The result is a system that combines a moving-bed up-flow sand filter with a capability for simultaneous removals of nitrogen and suspended solids (SS).

Demonstration tests were conducted for evaluating the nitrogen removal of the moving-bed up-flow sand filter, adding methanol to the secondary effluent as the source of carbon. Tests were carried out with the filtration speed of 245~400m/day (average of 300m/day), and the nitrate nitrogen (NO3-N) concentration of the specimen at 15mg/L. The results established that almost total denitrification was achieved, proving that the technology is capable of simultaneous removals of nitrogen and SS (suspended solids) by integrating the sand filtration (denitrification) with the conventional activated sludge process (single-stage carbon oxidation and nitrification process), while saving land space and operating costs over existing technologies.

This was the fruit of the joint study with the Sewage Bureau of the Metropolis of Tokyo and Takuma (fiscal year 2002 through 2004).

Development of Catalytic Tar Steam Reforming Technology in Biomass Gasification Processes

Kazuhiro SATO,Hirotaka DOHI and Takaaki SHINODA
(Research Center)

(Abstract)

The decomposition of tar by catalytic steam reforming was examined as the treatment of the tar generated in the CFB (Circulating Fluidized-Bed) gasification process of the biomass. In order to study the tar reforming characteristics using the newly developed Ni/MgO・CaO catalyst, we chose a simulated gas containing naphthalene as tar for the basic experiment. Afterward, we applied this catalyst to the gasification process of dried sewage sludge, a biomass.

The result of this basic experiment has confirmed that the newly developed catalyst shows a high naphthalene reforming activity at the low temperature of 750℃, and is stable for 100 hours at more than 800℃ even in a gas containing hydrogen sulfide. As a result of the application for gasification of the dried sewage sludge, 97% tar reforming efficiency was obtained at 800-850℃ in the presence of 200-300ppm sulfur, while more than 90% ammonia decomposition was observed at the same time. The results have shown that the newly developed Ni/MgO・CaO catalyst exhibits higher activity at low temperature and superior resistance to coking and sulfur poisoning compared with several commercial steam-reforming catalysts.

Development of High-efficiency Dust-Blowing Nozzle

Satoshi YOSHIMOTO
(Combustion and Core Technology Dept.)

(Abstract)

We have developed an air-injection nozzle suitable for blowing dust away from ceramic filters and bag filters. It is a de Laval nozzle with a low nozzle resistance encased in a cylinder with elongated holes downstream of the nozzle that straighten the injected air flow.

When used for blowing dust off ceramic filters, this combination can apply half again as much air pressure upon the filter surface under the same condition as a conventional nozzle. When used for a normal bag filter, it can save up to 25% of air consumption, with an excellent pressure-differential recovery.

Practical Application of New-type Laser O2 Analyzer

Yoshiji MATSUDA,Hiroyuki FUJIKAWA and Shin-ichi TSUJIMOTO
(Electrical and Instrumentation Dept.)

(Abstract)

We have initiated the real-time measurement of the O2 concentration in the exhaust gas and the real-time controlling of the secondary air, using laser technology. The demonstration test of the accelerated combustion technology was performed at an MSW incineration facility, and the commercial introduction that followed has proven successful. This will contribute enormously to the stable operation of the new-generation stoker-type incineration plant that features low excess air combustion, for which we are anticipating to receive orders.

Traditional laser O2 analyzers for exhaust gas, however, are very expensive and the application involves various restrictions, making their introduction difficult. We,therefore, have begun testing a new type of laser analyzer for application to MSW incinerators that is less expensive and easier to use. Tests were conducted for long-term continuous measurement, with air purging, in a high temperature atmosphere as well as under low oxygen.

In every phase of the test, the results have been successful, proving that its application to MSW incinerator is feasible.

Guangdong Shenyi Impregnating Plant

Kazuo OYAMA and Masatoshi MYOJO
(Amenity Engineering Dept.)

(Abstract)

This article reports on the impregnating plant that manufactures the prepreg material to produce insulated substrate for printed circuit board. The plant was delivered to the Guangdong Shenyi of China in October of 2005.

This plant consists of four impregnating lines, and the exhaust gas from all four lines is treated by a regenerative thermal deodorizer. A heat-transfer oil boiler is commonly used as the source of heat for the dryer, but this plant, our latest model, utilizes the waste heat from the regenerative deodorizer by means of a heat-transfer oil heater, reducing energy cost.

Basic Study on Influence of Residual Carbon while Heat-treating
PCDD/Fs in Fly Ash from MSWI

Takahiro MASUDA* and Yoshitaka KAKUTA**
(*Environmental Engineering Dept.
**Research Group of Recyclable Resources Assessment (TAKUMA endowed),
Graduate School of Engineering, Hokkaido University)

(Abstract)

In reducing PCDD/Fs by heat-treating the fly ash, it is important to inhibit the de novo formation of PCDD/Fs during the cooling process. In this study, we have assumed that the residual carbon is the main cause of de novo synthesis, and examined the relation between PCDD/Fs and the residual carbon. Using the MSWI fly ash that was heat-treated in an operating facility, we confirmed that the PCDD/Fs concentration and the residual carbon decreased when the heating temperature was raised. Additionally, in order to simulate the heat treatment process, the fly ash was heated at different temperatures and gas atmospheres. The heated fly ash was then placed in oxygen to promote de novo synthesis under quick cooling and slow cooling processes. As a result, a good correlation between PCDD/Fs and the residual carbon was found, establishing experimentally that the residual carbon is the dominant factor in PCDD/Fs formation by de novo synthesis.

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