While developing a new-generation stoker-type waste incinerator that reduces environmental burden and lowers costs, we have been embodying individual technologies that have been developed into newly built plants. The waste treatment plant of Senboku Environmental Improvement Cooperative Division #2, inaugurated in February 2003, has achieved low air ratio combustion (air ratio : roughly 1.35) and simultaneous reductions in NOx and CO concentrations by the introduction of excel-stoker and the re-burning system. A waste incinerator of Kashihara city completed in September of the same year has succeeded in obtaining stabilized combustion by adopting excel-stoker and a advanced-fuzzy control system. In each case, the advantages of new technologies have been fully utilized.
We have introduced to a commercial operation of an MSW incinerator a dry scrubber that uses BICAR to treat exhaust gases. BICAR is a new reagent of the sodium family that has been proven by demonstration tests with MSW incinerators to possess superior acid gas removing capability from exhaust gases. At the stoichiometric ratio of 1.3, removal rates of 98% for HCL and 90% for SOx have been achieved, approximately the same level as proven in the demonstration tests. In addition, the consumption of anti-elusion agent has been reduced by roughly 50% compared with slaked lime injection.
A total system that can effectively extract energy from sludge with minimum heat loss can be built by gasifying sewage sludge and mixing the product gas with natural gas for power generation, and using the waste heat for drying sewage sludge.
With this in mind, we have undertaken to develop a gasification system in order to attain highly efficient energy conversion of the sewage sludge. The characteristics of our gasification system show the follows. The gasifier takes a wide range of fuels, using CFB system that excels in mixing and temperature control. Gasification is done by blown air under atmospheric pressure at 800~900°C. It employs high-temperature dust removal and tar cracking by catalyst, producing unique ash-and-tar free gas.
For our current research, we have built a CFB gasification plant (fuel heat input:100kWth), and carried out gasification tests. We have conducted a continuous operation over 50 hours and achieved the results of approx. 90% carbon conversion rete and around 60% cold gas efficiency, with the gas calorific value of 4~5MJ/Nm3 at furnace outlet. The Results we have obtained so far are described in the foregoing article
The off-gas released from the carbon-black production process is called "Tail Gas". It has a low calorific value of 2,000kj/m3N, and does not burn unsustained.
The preceding article introduces the carbon-black production process, and explains the combustion technology that induces the tail gas to burn by itself while limiting the NOx concentration below 100ppm. It further discusses the points of note when using the tail gas for power generation to recover its thermal energy.
Takuma has a long history of supplying coal - fired boilers to all branches of industry. Coal is an abundantly available fossil fuel, and is an effective and economical energy source for power generation.
The preceding article introduces our latest supply of a coal-firing boiler of the spreader and traveling stoker type to Thai Fermentation Industry Co., Ltd. in Thailand.
The dewatering system described in this article utilizes condensation by freezing using ammonia absorption freezer. By using CGS waste heat as energy source, the system saves electricity as it consumes only one quarter of electric power expended by the traditional freezer with electric compressor. This article reports on the pre-coating process by which a part of raw sludge is condensed through freezing and melting, utilizing the above process, and the condensed(treated)sludge is coated on the filter cloth of the dewatering machine. The untreated raw sludge is then filtered through this pre-coated filter. We have confirmed that this improves the dewatering capacity by speeding up the filtering speed, and reduces maintenance needs by preventing filter clogging and improving cake removal. It has proven to be a practical improvement for the treating process by reducing operational as well as initial costs.
Lately, effective use of molten and solidified residues from MSW and sewage sludge is being pursued. An effective utilization requires the constant safety assurance of the slag. The quality control of the slag is difficult at present as the analyses of its heavy metals leachate and concentration take roughly a week.
In order to achieve quality control of the slag, we have examined a fast, on-site measuring of its lead concentration through the use of small energy-dispersion fluorescent X-ray analyzer.
The result has assured us that the lead concentration of the slag can be accurately determined in roughly 30minutes, requiring only simple pre-treatments such as drying and crushing. We have also confirmed that the lead concentration of the bottom ash and the soil can be measured by this method.