Economizer Research Articles

Distribution of Polybrominated Dibenzo-p-dioxins and Dibenzofurans and Polybrominated Diphenyl Ethers in a Coal-fired Power Plant and Two Municipal Solid Waste Incinerators

In this study, the distributions of polybrominated dibenzo-p-dioxins (PBDD/Fs) and dibenzofurans and polybrominated diphenyl ethers (PBDEs) in the bottom residues of the combustion chambers (BR), the fly ashes from superheaters (SH), economizers (EC), semi-dry scrubbers (SDA), fabric filters (BF), fly-ash pits (FAP) and stack flue gases (SFG) of two municipal solid waste incinerators (MSWIs) and the bottom residue (BR), electrostatic dust precipitators (ESD), and stack flue gases (SFG) of a coal-fired power plant (TPP) were investigated. BR of combustion chambers exhibited the highest content of PBDEs and PBDD/Fs among all the units. The amount of PBDE mass found in bottom residues constituted 99.7% at MWSI-A, and 92.6% at MSWI-B and 75.1% at TPP of the total PBDE discharges, respectively; while the second highest PBDE mass observed in MSWI-A and MSWI-B was from SFG (0.146%) and EC (5.54%), respectively. In TPP, the PBDE distribution was 75.1% in BR, 12.5% in ESD, and 12.4% in SFG. The mean concentrations of PBDEs emitted from SFG of MSWI-A, and MSWI-B were 9.32 ng/Nm3, and 7.62 ng/Nm3, respectively; however, that of PBDE discharged from SFG of TPP was only 5.43 ng/Nm3. The dominant congener found from MSWI-A,MSWI-B and TPP, was BDE-209, accounting for 65.9%, 77.7%, and 77.6% of total PBDE concentrations in SFG, respectively; whereas BDE-206 (6.01%–6.36%) was the second highest congener. Meanwhile, the PBDE emission factors from the stack flue gases were 35.6 ± 10.9 μg/ton-waste at MWSI-A, 47.6 ± 29.4 μg/ton-waste at MSWI-B and 62.9 ± 10.9 μg/ton-coal at TPP of the total PBDEs, respectively; showing the PBDE emission rates and contributions of TPP to the ambient air are actually much higher than those of MSWIs, while the PBDE concentrations in SFG of TPP were lower than MSWIs’. Further investigations on the safety of BR reutilization and the impact of SFG from TPP are strongly advised.

Exergoeconomic analysis of a fluidized-bed coal combustor (FBCC) steam power plant

Exergoeconomic analysis has been used as a powerful tool to study and optimize various types of energy-related systems. This study deals with an exergoeconomic analysis of an FBCC steam power plant, located in the city of Izmir, Turkey using actual operational data. This plant consists of a ventilation fan (VF), an FBCC, a heat recovery steam generator (HRSG), a cyclone (CY), an economizer (ECO), an aspiration fan (AF), a pump (P) and a chimney (CH) as sub-systems. Quantitative exergy cost balance for each component and the whole FBCC plant is considered. The exergetic efficiency of this plant is calculated to be 20.28% at a steam mass flow rate of 1.861 kg/s. The highest exergy destruction rate occurs in the FBCC with an irreversibility rate of 89.2%, followed by HRSG, VF, ECO, AF, CH and P. The unit exergy cost and exergy cost of steam produced by the FBCC steam plant amount to 17.88 US$/GJ and 93.57 US$/h, respectively. This study demonstrates that exergoeconomic analysis can provide extra information than exergy analysis, while the results obtained from this analysis present cost-based information.

The Emission and Distribution of PCDD/Fs in Municipal Solid Waste Incinerators and Coal-fired Power Plant

The emission and distribution of polychlorinated debenzo-p-dioxins/dibenzofurans (PCDD/Fs) was investigated in two municipal solid waste incinerators (MSWIs) and one coal-fired power plant (PP) in southern Taiwan. Samples were collected from stack flue gases (SFG), bottom residues (BR), super heater (SH), economizer (EC), semi-dry absorber (SDA), bag filter (BF), and fly ash pit (FAP) in MSWIs. Stack flue gases, bottom residues and electrostatic dust collectors (ESD) in PP were also collected. In order to compare the difference between the results of MSWIs and PP, samples from SFG, BS, and FAP in a PP were also determined. Seventeen congeners of PCDD/Fs were analyzed by utilizing a high-resolution gas chromatograph/high-resolution mass spectrometer (HRGC/HRMS). Distributions of total PCDD/F-I-TEQ in each unit of MSWI-A and MSWI-B were SFG (0.3%, 0.07%), BR (3.9%, 0.62%), SH (0.17%, 0.24%), EC (4.2%, 0.05%), SDA (1.29%, 7.06%), and BF (90.14%, 91.97%), respectively. However, those in SFG, BS, and FAP of PP were 99.58%, 0.17%, and 0.25%, respectively. The above results indicated 99.5% PCDD/Fs were trapped in the fly ash of MWSI. On the other hand, 99.7% PCDD/Fs was emitted to the atmosphere from PP. The results of this study provide useful information for controlling PCDD/Fs in MSWIs and PP.

Distribution of polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins/dibenzofurans in ash from different units in a municipal solid waste incinerator

Polycyclic aromatic hydrocarbons (PAHs), polychlorinated-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are some of the major organic contaminants emitted in municipal solid waste incinerators (MSWIs). The distribution of PAHs and PCDD/Fs in different MSWI unit ashes, including bottom residue (BR), fly ash pit (FAP), fabric filter (FF), semi-dryer absorber (SDA), economizer (EC) and super heater (SH), has seldom been discussed. Average PAHs content in ash samples from BR, FAP, FF, SDA, EC and SH were found to be 0.020, 0.237, 0.234, 0.125, 0.037 and 0.034 µg TEQ g(-1), respectively. In addition, the range of total emission factor from different unit ashes varied between 0.30-13.85 mg TEQ tonne(-1) of waste, low molecular weight compounds (2~3-ring) being the dominant species. Furthermore, PAHs in ashes were mainly found in BR (41%) and FAP (31%). The FAP ash included 18% of PAHs coming from FF ash. On the other hand, PCDD/Fs content in BR, FAP, FF, SDA, EC and SH was found to be 0.0329, 1.1589, 1.2807, 0.1476, 0.6868 and 0.0921 ng I-TEQ g(-1), respectively. PCDD/ Fs emission factors in this study ranged between 1.029-67.740 µg I-TEQ tonne(-1) of waste, most PCDD/Fs being present in FAP (55%). The FAP ash included 33% of PCDD/Fs coming from FF ash. Therefore, PCDD/Fs content in FAP and FF exceeded the legal limit of 1 ng I-TEQ g( -1); therefore, a solidification process is necessary before landfilling in Taiwan.

排ガスエコノマイザのすす燃焼を模擬した並列沸騰流路の限界熱流束と流動特性

排ガスエコノマイザのすす燃焼を模擬した並列沸騰流路の限界熱流束と流動特性

Polychlorinated dibenzo- p-dioxins/dibenzofuran mass distribution in both start-up and normal condition in the whole municipal solid waste incinerator

Although many researches focused on the polychlorinated dibenzo- p-dioxins/dibenzofuran (PCDD/F) emissions from stack, in the bottom ash and in the surrounding environment, researches focused on PCDD/F mass distributions in the whole incineration plant have seldom been addressed. This study determined PCDD/F emissions in the whole plant. A high-resolution gas chromatograph/high-resolution mass spectrometer was utilized for analyzing 17 PCDD/F species. Experimental results displayed that PCDD/Fs were formed during fly ash from super heater (SH), economizer (EC), semi-dryer absorber (SDA) and fabric filter (FF) was transferred to fly ash pit. Mass distribution ratios of PCDD/Fs in g I-TEQ (Toxicity Equivalency Quantity) per week from stack, SH, EC, SDA, FF, generation and bottom residue (BR) in start-up operations were 14.6%, 0.1%, 8.3%, 1.0%, 41.7%, 33.4% and 0.9%, respectively. Above results indicated that main PCDD/F source in the MSWI was from fly ash. However, the fly ash is easily controlled and PCDD/F emitted from stack flue gases will be difficult to be handled. Therefore, we should pay more attention on PCDD/F emission from flue gases especially from start-up procedure. Besides, fly ash should be controlled by sodium hypophosphite before being landfilled. MSWI did require further detoxification treatments for the solid residues and flue gases.

Polychlorinated dibenzo- p-dioxins/dibenzofurans distributions in ash from different units in a municipal solid waste incinerator

This study determined the polychlorinated dibenzo- p-dioxins/dibenzofurans (PCDD/Fs) contents in ash in the super heater (SH), economizer (EC), semi-dryer absorber (SDA), fabric filter (FF), fly ash pit (FAP) and bottom residue (BR) in a municipal solid waste incinerator (MSWI). A high-resolution gas chromatograph/high-resolution mass spectrometer (HRGC/HRMS) was utilized for analyzing 17 PCDD/F species. Experimental results showed that average PCDD/F contents in ash samples from the SH, EC, SDA, FF, FAP and BR were 0.102, 0.788, 0.210, 1.95, 2.04 and 0.0218 ng I-TEQ g −1, respectively. PCDD/F content was very low in the SH and BR due to high temperatures (around 461 °C in the SH and 914 °C in combustion chamber). Conversely, total PCDD/F content was significantly high in ash samples from the EC (around 340 °C), mainly because the temperature is within the favorable range of 250–400 °C for PCDD/F formation due to de nova reformation mechanisms. Although the SDA operated at 245 °C, the PCDD/F content decreased very significantly, mainly because the temperature was relatively low and because calcium carbonate was introduced into flue gases to dechlorinate and dilute chlorine-containing species. PCDD/Fs were captured by the active carbon in the FF. Furthermore, the duration that fly ash remained in the FF was longer than that for other incinerator units, and thus causing an increasing trend of PCDD/Fs level downstream (except the SDA). Total PCDD/Fs emission factors (μg tonnes-waste −1; μg I-TEQ tonnes-waste −1) in ash samples from different units were: SH (42.3; 0.846), EC (326; 6.12), SDA (58.1; 1.10), FF (1540; 61.3), FAP (2950; 107) and BR (537; 4.31). Most PCDD/Fs in ash were contributed by the FF (about 56%), and the generation of PCDD/Fs in ash was significant (about 35%) during the transfer process from different units to the FAP. A strong and positive correlation in a logarithmic form existed between PCDD/Fs and chlorine (Cl −1) contents in ash. In Taiwan, the government policy for incineration residues advocates their reuse as road sub-bases or secondary building materials provided that total PCDD/Fs content is below the legal limit (1 ng I-TEQ g −1). Thus, ash with total PCDD/Fs content below the legal limit, such as that from the SH, EC, SDA and BR, can be collected and transferred to the FAP and reused. Ash with total PCDD/Fs content exceeding the legal limit, such as that from the FF, should be collected separately and be treated properly before being disposal in a landfill.

Acoustical Resonance Behind Tube Arrays in Exhaust Gas Economizer.

The tube-bank exhaust gas economizer is usually composed of a series of tubes arranged in a rectangular duct. The tube arrays in cross flow sometimes excite the acoustical vibrations of sound fields in the duct of the exhaust gas economizer. It is very important, for practical applications, to understand the conditions of the acoustical resonances in the duct with the tube bundles. The resonances occur when the frequencies of the flow periodicities inside the array coincide with those of the acoustical modes. At resonances, the intense pure tone noises, which may reach 120 dB, are produced. The acoustic modes typically excited are those related to the dimension perpendicular to both the fluid flow direction and the tube axes. Acoustical resonance in the economizer tube arrays has been suppressed by detuning the resonance with baffles that shift the acoustic natural frequency upwards. We have successfully employed a single baffle to suppress resonance.

A Study on Fuzzy Control Simulator of Naturally Circulated Boiler

The engineering equations, which have been used in many engineering companies, were employed for the dynamic modelling part in order to develop the naturally circulated boiler simulator. The fuzzy algorithm, which is similar to the algorithm of making decision by the human being, was developed for the boiler simulator controller and its simulated variables were compared with those of classical PID simulations to verify the stability and the effectiveness of fuzzy controller. The simulator is for the naturally circulated boiler and the main components are the furnace, the drum, the super heater, and the economizer. The combustion and thermal radiation dominant equations were used within the furnace and the mass conservation and the energy rate balance equations were employed for the drum part. The heat transfer rates were calculated using the logarithmic mean temperature differences both for the super heater and for the economizer. The simulations are very useful to understand the boiler operations and the engineering design of the main components. The main program was developed under the PC window condition by linking the fuzzy controller to the main boiler program using the Visual C++ language. The various operational conditions such as the abrupt changes of load, the changes of water supply pipes and the diameter of drum were simulated.

舶用排ガスエコノマイザの発生騒音と防止に関する研究

舶用排ガスエコノマイザの発生騒音と防止に関する研究

ディーゼル船排ガスエコノマイザのスート燃焼

The so-called“soot fire”, whichi is a heating surface melt-down failure of the exhaust gas economizer (EGE) of diesel ship, is so serious that it has been urgently waiting for effective countermeasures. This report developes a simulation model in order to investigate the sootburning and heat transfer process in the EGE, of which heating surface consists of finned tubes with parallel arrangement. The heat transfer equation of the model takes into consideration 4 factors, that is, the heat transported by the gas flow, the heat transmitted from gasside to waterside, the heat being accumulated in the finned tube materials, and the heat released by the soot burning. The soot burning was modelled by a surface combustion of a soot layer deposited on heating surface. The simulation model can explain successfully various empilical facts reported so far regarding actual ship's soot fire failures. The calculation results give valuable informations regarding the influences of gasside and waterside heat transfer coefficients, gas flow rate, soot carolific value, soot deposition thickness etc. Among them, the waterside heat transfer coefficient, that is, the condition of water circulation shows the most definite influence on the soot burning, and it is made clear that the soot burning cannot occur the melt-down failure when the water circulation is sufficient to prevent the dryout.

付着堆積したすすの燃焼特性

The flame-spreading phenomenon of combustible soot deposited on the flat plate is one of the basic problems in fire research. The study of the mechanism of burning of the soot deposited on the flat plate and glass wool was done. Therefore, in order to elucidate the soot fire mechanism, it is very important to measure the dissipation rate and luminous intensities profiles of soots. The experimental samples were taken out of the soot formed from various fuel oils and the soot emitted from various combustors. The value of chemical analysis of all the samples was checked quantitively, in advance of the experiments.The main results obtained are as follows:(1) The values of C/H and C/O in the soot formed decrease as the quality of fuel oil deteriorates.(2) The C/H value of soots after washing by water (Exhaust gas economizer) is relatively smaller compared with that before washing in water. The chemical reaction rate increases in accordance with the decrease of C/H value.(3) The cumbustion rate and Surface 1st damköhler number of the soot deposited increase as C/H value decreases.(4) The burning period of the soot becomes shorter as the thickness of attaching plate for soot becomes smaller.(5) The combustion rate rises the more acceleratedly because of the catalyzing reaction as the content of alkali or alkaline earth metals is higher.

スートファイア (排ガスエコノマイザメルトダウン事故) の発生機構

The mechanism of soot-fire accident of exhaust gas economizer in diesel ship is investigated in this report. This is the second report following the first one, in which the process of soot-burning of exhaust gas economizer was studied by a simulation model. According to the soot-burning simulation, temperature of heat transfer surface seldom reaches its melting point only by soot-burning. So it is difficult to consider that soot-fire is occurred only by heat released by the soot-burning. It has been reported the oxidative heat of tube materials might be another heat source. The experiments, therefore, are carried out in order to measure the rate of oxidation of tube materials, and reveal that there is a possibility that the oxidative heat might be another heat source when the oxidation rate is accelerated by the high temperature steam atmosphere and the“break-away”oxidation. Accordingly it is made clear the soot-fire is occurred by a series of events, that is, burning of soots deposited on finned tubes, waterside dry-out of the finned tubes induced by the soot-burning, sudden degradation of waterside heat removal due to the dry-out, rapid increase of fin temperature, and further increase of the fin temperature due to oxidation of iron, and finally melt-down of the heat transfer surfaces.

大形排ガスエコノマイザスートファイアの研究と防止対策実施例

On a diesel ship provided with an exhaust gas economizer, there are problems with soot fire which occurs in the economizer itself and safety against fired soot exhausted from the funnel.Not only ship owners and ship builders but also persons concerned have placed great importance on the soot fire and taken preventive measures. It, however, remains an unsolved problem.This report covers;1) investigation of the process of occurrence of soot fire2) preventive measures against soot fire3) the effect achieved by the preventive measuresOn a container ship which has a steam turbo generator plant by a large exhaust gas economizer.The preventive measures against soot fire given in this report is not effective on all kind of exhaust gas economizer plants, but shows a guideline for preventing soot fire.

低周波音波によるボイラおよび排ガスエコノマイザ用クリーニング装置

At the present time, the major method for cleaning boiler and exhaust gas economizer on board is to blow the soot by steam or air. But this soot blowing cleaning device requires the high pressure and much quantity of steam or air consumption to have satisfactory cleaning effect.On the other hand, for the reason to equip the tubo generator utilized low steam pressure and the economizer of high heat recovery ratio for modernized ship, available steam pressure is decrease and adhesion of soot is intensified, therefore soot trouble is easy to happen. INFRAFONE is new method of cleaning device by using infrasound, and can offer the economical and effective way to solve the soot problem.

スートファイアによる焼損の調査と基礎的研究

The exhausted quantity of soots and hydrocarbons from diesel engine have a tendency to increase as the quality of marine fuel oil deteriorates. Their soots are composed by formed soots from gas phase and cenosphere (such as residual carbon), stick to the surface of exhaust gas economizer, and prevent the heat transfer rate for soot diposits. The heat transfer pipe may occur the heavy damage for oxidation of soot deposits (soot fire), and melt for high temperature.It is important to be the basic researches on soot oxidation of fin surface.This studies become the principal experiments on the combustion state of soot pellicle on the fin surface, and on the changes in quality of fin surface with combustion.

An optimal planning method for a marine heat and power generation plant by considering its operational problem

The objective of this paper is to develop a computer-aided optimal planning method for designing a marine heat and power generation plant which is composed of combining Diesel and turbogenerators, an exhaust gas economizer, auxiliary boilers and so forth. As there exist many alternative combinations concerning generators and boilers in constructing the abovementioned plant, it is important to determine the plant construction properly by selecting total numbers and scales of respective generators and boilers so as to optimize the long-term economy of the plant. In this planning method, several design conditions are first set which are necessary for the planning of the objective plant, i.e. several patterns of ship's operational condition are set first, and both energy demands and steam output from an exhaust gas economizer are estimated for each pattern. Next, setting an alternative plant composed of combining generators and boilers adequately, the optimal operational policy for each pattern is determined by minimizing the fuel cost under several physical constraints based on linear and quadratic programming methods. Considering the results obtained above hierarchically, annual capital and operational costs of each plant are calculated, and the best plant construction is lastly determined by comparing the economy of all alternative plants. A numerical study has been carried out on a plant of a high speed container ship actually planned, and it is ascertained that to find the best construction of the plant the optimal planning method proposed here is advantageous compared with the conventional trial and error method.

最近の性能向上型排ガスエコノマイザプラント

The exhaust gas economizer is one of the most efficient measures for the exhaust heat recovery of the Diesel ship. In responding the strong demand of the fuel conservation, various advanced plants with turbo-generating system have been developed and have been successfully installed onto the Diesel ships in service. In spite of the difficulties of the decreasing gas temperature, the decreasing gas flow rate, the severe deterioration of fuel grade, etc., those newly developed plants have achieved the remarkable improvement of the exhaust heat recovery rate in comparison with the plants in the age of 1969. The main technological features of the advanced plants are the followings, that is, the first is the introduction of two-or three-stage pressure system, the second is the use of extended heating surface, and the third is the designs of various countermeasures against the low temperature fouling and corrosion. These features, however, have brought not only desirable improvements but also undesirable impacts such as the damage of generating tubes, the soot fire etc. Although most of impacts have already been overcomed, the soot fire, which is the most impressive and serious fault, is still troubling the people concerned and is demanding the reliable solution.

船内廃熱回収システムによる省エネルギ

As waste heat recovery system of main engines in motor ships, various turbogenerating systems have recently been proposed by shipbuilders and engine builders with practical applications on board. The Mitsui-ATG system, or Mitsui Advanced Turbo-Generating System, has been developed through the introduction of a new concept of “Parallel temperature difference” in an exhaust gas economizer by putting a low pressure steam generator (LPSG) in the system.In this paper, the Mitsui-ATG system is presented with its concept, flow diagram, distinctive features, performance, the results of the sea trials and the measurements on the running services on board.

Exergy Recovery with an Exhaust Gas Economizer System

The power conversion system from the exhaust waste heat with the Rankine system is regarded as one of the promising energy saving technologies. However, the heat exchange for the recovery of the waste heat are usually too large. The size and the exergy recovering efficiency of the heat exchange have been studied and compared with the exhaust gas economizers of practical use which are generally installed in the motor ships. It has been made clear that for the practical use, the exergy recovering efficiency per unit size of the heat exchanger is one of the important factors. To improve the heat exchanger efficiency from this aspect, a new system of exhaust gas economizer of heating under the constant specific volume is proposed and tested. Fairly favourable results have been obtained.