Masakatsu Hiraoka

Pilot plant study on sewage sludge pyrolysis—I

A pilot plant study was carried out on drying-pyrolysis process in order to put the sludge pyrolysis process with multiple hearth furnace to a practical use. Additional studies were carried out on a direct pyrolysis process and incineration process in order to compare these three thermal processings. The samples in this study were 5 dewatered cakes obtained from various sewage treatment plants and from various dewatering methods. The pilot plant for the experiments of this study consisted of a four-shaft indirect steam dryer with a total heating area of 10.1 m/sup 2/, a four hearth furnace with a total hearth area of 1.63 m/sup 2/ and its incidental facilities. The results of the study are presented.

Combined process of pyrolysis and combustion for sludge disposal.

A combined process of pyrolysis and combustion of sewage sludge was examined by use of a double hearth incinerator. The effectiveness of the introduction of a pyrolysis stage to incineration was investigated and compared with the usual sludge incineration. The behavior of heavy metals and other toxic or unburnt gases was analyzed in connection with the pyrolysis temperature, showing the effectiveness of this process for the prevention of air pollution. Pyrolysis a t low temperature minimized the vaporization of heavy metals contained in the sludge without sacrificing the reduction of bulk density. The analyses of heavy metals caught in the particulates and scrubbed water suggested that much of the vaporized metals escape as fumes. An adequate temperature control may suppress nitrogen oxide emission.

SYSTEM IDENTIFICATION AND CONTROL OF ACTIVATED SLUDGE PROCESS BY USE OF AUTOREGRESSIVE MODEL

ABSTRACT He experimented the system identification and control of an activated sludge process by using an autoregressive model in an real wastewater treatment plant. The control system used in this experiment was a cooperative type based on a combination of conventional PI control and autoregressive model. In system identification, we constructed an autoregressive model from the process data that was obtained by changing manipulated variables such as return sludge flow rate, excess sludge flow rate, and air flow rate in terms of noise. We confirmed the validity of this model from its analytical results, and observed through control simulation that the model could dynamically control treated sewage quality. Next, by using this model and optimum feedback gain, we experimented control performance to check treated sewage quality for approximately one month in a real wastewater treatment plant. As a result, we confirmed that control by the autoregressive model operates exactly the way we initially anticipated. Thus, it was clarified that cooperative-type control systems are effective for suppressing fluctuations in treated sewage quality.

AUTOMATIC MEASUREMENT AND ANALYSIS OF PROCESS DATA IN A COMBINED WASTEWATER TREATMENT PLANT

ABSTRACT For automatic control, even for manual control, the reliability of measurements is a prior condition. The authors installed automatic measuring instruments in a combined wastewater treatment plant which treated 80,000 m 3 sewage per day and gathered data every fifteen minutes for a year. In this paper the results from these experiments are presented. Measured items and their sampling points were flow rate, UV, SS, pH at the outlet of the primary settling tank, air flow rate, MLSS, temperature, three DO concentrations along the flow in the aeration tank, flow rate and SS of the return and excess sludge and rainfall intensity. The discussions in this paper are as follows, (1) verification of instruments, (2) data collection and pretreatment and (3) analysis of data.

STATISTICAL ANALYSIS OF ACTIVATED SLUDGE PROCESS DYNAMICS IN A COMBINED WASTEWATER TREATMENT PLANT

ABSTRACT On the basis of the results of analyzing the dynamic behavior of an activated sludge process, the authors have considered that its control systems must be constructed hierarchically and concluded that a statistical model is suitable for expressing short-time variation. In this paper, the results of applying an AR model (which belong to the statistical models) to an activated sludge process of a combined wastewater treatment plant are presented. First, by a one point prediction and the response of system variables using white noise, the fabricated AR model was tested. Next, the effects of its own noise on the variables of the system to the variation of controlled variables were calculated by using this model. As a result, it was judged that the model was adequate, and fully expressed the dynamics of the process objectives.

Overview of MSWI residue Recycling by Thermal Processes

Abstract The melting technology reduces the volume of incinerator residues, bottom ash and fly ash, making the melted slag stable and non-toxic. Moreover, this type of treatment allows the melted slag to be used as a resource again. In Japan, the melting process was developed in the 1980s and has been in practical operation at around 24 municipal solid waste (MSW) incineration facilities including scheduled ones. By the melting process, PCDDs/PCDFs in residues are decomposed at temperature of approximately 1,400°C in the furnace and heavy metals are concentrated in the fly ash of melting process. The drafting of an ‘effective reuse manual’ is introduced, aiming at promoting the safe reuse of incinerator residues, by setting reprocessing technologies, reuse standards and their evaluation methods.

A Study on Catalyst Preparation of Dioxin Decomposition

著者等はダイオキシンの再合成が極めて低いとされている貴金属触媒においても触媒に含まれている炭素によりダイオキシンが合成されている例を確認した。この炭素は触媒作成工程で付着したもので, 工程を改良することによりダイオキシンを合成することのない触媒を作成することができた。

AUTOMATIC MEASUREMENT AND STATISTICAL ANALYSIS OF OPERATION DATA ON DRYING FLUIDIZED-BED INCINERATION PLANT

ABSTRACT A new data acquisition system was developed for a drying fluidized-bed incineration plant to get the continuous collection of operating data. A statistical model of each process was then prepared to analyze the characteristics of the whole process. From the results of the analysis employing an autoregressiye model (AR model), it was confirmed that the dryer sludge feed quantity, the height of the dryer weirs, and the condenser exhaust gas extraction flow rate are the major parameters affecting the dried sludge moisture content, the dryer exhaust gas humidity and the dryer disc shaft rotational torque in the drying process. Moreover, in the incineration process, it was confirmed that the dewatered sludge feed quantity, and the condenser exhaust gas extraction flow rate are important parameters affecting the sand bed temperature, the freeboard temperature, CO and NOx concentration in the exhaust gas. From the foregoing results, it was judged that the drying and incineration processes can be expressed by a combination of the two AR models.

Modeling and Control of the Activated Sludge Process by Use of Autoregressive Model

Abstract The authors have insisted that the control systems must be constructed hierarchically. In the bottom level of this system, the statistical model is suitable to express the dynamics of the activated sludge process. In this paper, it is shown that an AR model which belongs to the statistical model is applicable to the activated sludge process in the combined wastewater treatment plant. Next, it is discussed how to change the manipulated variables on purpose to clearly determine the effects of the manipulated variables, because the manipulated variables are generally maintained almost constant in the actual plants.

Dust Removal with a Perforated Plate Tower

多孔板塔の集塵効率を測定し, 湿式集塵装置としての多孔板塔の性能を解析した. Flg. 1 (a),(b) に示す実験装置を用いて一段および多段スクラッバーの集塵効率におよぼす因子と効事の関係を研究した。この実験の因子として堰高さ. ガス量, 液量液ガス比それに多孔板段数が選ばれた. その結果はFigs (4),(5),(6),(7).(8) に示すとおりで, 多孔板塔をスクラッバーとして使用する場合. 液ガス比は0.3/m3・gas以上を必要としよう。実験結果をFuksの理論を基にしたモデルにより解析した。