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Title: Sludge incineration in a spinning fluidized bed incinerator

Abstract

At the present time, the sewage treatment plants in the UK produce about 25 million tonnes of sewage sludge each year at a concentration of 4% solids. New regulations forbid sea dumping and in the near future new incinerators will be required to dispose of about five million tonnes per year. Bubbling fluidized bed incinerators are widely used to burn sewage sludge at a typical consumption rate of about 0.02 kg(dry)/s/m{sup 2}, and it follows that over 300 conventional fluidized bed incinerators of 3 meters bed diameter could be required to cope with the increased demand. At Sheffield University Waste Incineration Centre (SUWIC) research work is being carried out to develop a novel spinning fluidized bed incinerator. The key factor to note is that when air flows up through a bed of near mono-sized particles, it fluidizes when the pressure drop across the bed is equal to the weight of the bed. Normally, the weight of the bed is determined by gravity. However, if the bed is contained by a cylindrical air distributor plate that is rotating rapidly about its axis, then the effective weight of the bed can be increased dramatically. The airflow passing through the bed can bemore » increased proportionally to the g level produced by the rotation and it follows that the process has been intensified. In exploratory tests with a spinning fluidized bed the authors have achieved combustion intensities with coal combustion as high as 100 MW/m{sup 3}. A problem with burning coal is that it was difficult to remove the heat and rotating water seals had to be used to transfer cooling water into the bed. In the case of sewage and other sludges, this problem does not exist since the flue gases can remove the small amount of heat released. The rotating fluidized bed sludge incinerator is a novel device, which is very compact. It is able to solve the turndown problem encountered with conventional fluidized beds by simply changing the rotation speed. Bearing in mind that a centrifugal sludge de-watering unit is already used on sludge incineration plants, it is likely that the rotating fluidized bed can be combined with the de-watering unit, resulting in further process integration and intensification. Furthermore, the ash sintering system can be added to render the ash non-toxic and unleachable thus reducing the costs of its disposal.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Univ. of Sheffield (GB)
OSTI Identifier:
20006700
Report Number(s):
CONF-990534-
TRN: IM200008%%307
Resource Type:
Conference
Resource Relation:
Conference: 15th International Conference on Fluidized Bed Combustion, Savannah, GA (US), 05/16/1999--05/19/1999; Other Information: 1 CD-ROM. Operating system required: Windows 3.x; Windows 95/98/NT; Macintosh, Power Macintosh; UNIX. All systems need 2X CD-ROM drive.; PBD: 1999; Related Information: In: Proceedings of the 15th national conference on fluidized bed combustion, by Reuther, R.B. [ed.], [1800] pages.
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; INCINERATORS; SEWAGE SLUDGE; FLUIDIZED-BED COMBUSTION; DESIGN; DEWATERING EQUIPMENT; OPERATION

Citation Formats

Swithenbank, J., Basire, S., Wong, W.Y., Lu, Y., and Nasserzadeh, V.. Sludge incineration in a spinning fluidized bed incinerator. United States: N. p., 1999. Web.
Swithenbank, J., Basire, S., Wong, W.Y., Lu, Y., & Nasserzadeh, V.. Sludge incineration in a spinning fluidized bed incinerator. United States.
Swithenbank, J., Basire, S., Wong, W.Y., Lu, Y., and Nasserzadeh, V.. Thu . "Sludge incineration in a spinning fluidized bed incinerator". United States. doi:.
@article{osti_20006700,
title = {Sludge incineration in a spinning fluidized bed incinerator},
author = {Swithenbank, J. and Basire, S. and Wong, W.Y. and Lu, Y. and Nasserzadeh, V.},
abstractNote = {At the present time, the sewage treatment plants in the UK produce about 25 million tonnes of sewage sludge each year at a concentration of 4% solids. New regulations forbid sea dumping and in the near future new incinerators will be required to dispose of about five million tonnes per year. Bubbling fluidized bed incinerators are widely used to burn sewage sludge at a typical consumption rate of about 0.02 kg(dry)/s/m{sup 2}, and it follows that over 300 conventional fluidized bed incinerators of 3 meters bed diameter could be required to cope with the increased demand. At Sheffield University Waste Incineration Centre (SUWIC) research work is being carried out to develop a novel spinning fluidized bed incinerator. The key factor to note is that when air flows up through a bed of near mono-sized particles, it fluidizes when the pressure drop across the bed is equal to the weight of the bed. Normally, the weight of the bed is determined by gravity. However, if the bed is contained by a cylindrical air distributor plate that is rotating rapidly about its axis, then the effective weight of the bed can be increased dramatically. The airflow passing through the bed can be increased proportionally to the g level produced by the rotation and it follows that the process has been intensified. In exploratory tests with a spinning fluidized bed the authors have achieved combustion intensities with coal combustion as high as 100 MW/m{sup 3}. A problem with burning coal is that it was difficult to remove the heat and rotating water seals had to be used to transfer cooling water into the bed. In the case of sewage and other sludges, this problem does not exist since the flue gases can remove the small amount of heat released. The rotating fluidized bed sludge incinerator is a novel device, which is very compact. It is able to solve the turndown problem encountered with conventional fluidized beds by simply changing the rotation speed. Bearing in mind that a centrifugal sludge de-watering unit is already used on sludge incineration plants, it is likely that the rotating fluidized bed can be combined with the de-watering unit, resulting in further process integration and intensification. Furthermore, the ash sintering system can be added to render the ash non-toxic and unleachable thus reducing the costs of its disposal.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jul 01 00:00:00 EDT 1999},
month = {Thu Jul 01 00:00:00 EDT 1999}
}

Conference:
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  • The concept of incinerating a sludge for destruction began a few decades ago with the advent of the multiple hearth incinerator. In the 1960's, the fluidized bed incinerator began to make inroads into the sludge incineration market, especially in smaller units that operated less than 24 hours/day. The fluidized bed incinerator gained further recognition when documentation appeared on the presence of hydrocarbons in the gaseous emissions from the multiple hearth, which ultimately led to legislation requiring after-burning of the multiple hearth's emissions. The posture of fluidized bed incineration was further enhanced by the development of heat exchange of the incineratormore » exhaust gas with the combustion air required for fluidization. Preheating this combustion air to 811/sup 0/K represented a considerable heat conservation. Today's heat exchange equipment can preheat the air to 922/sup 0/K.« less
  • Thermal Limited, a major player in the field of Fluidized Bed Boilers in India, has supplied on a turnkey basis, three boilers each of 22.5 tons per hour capacity as a part of Cogeneration system for PT. South Pacific Viscose, Indonesia. The plant generates huge volumes of sludge from its effluent Treatment Plant (ETP). The sludge produced from the ETP has a moisture content of about 98%, which is subsequently reduced to about 78% using a decanter before feeding the sludge into the boiler. The waste sludge has a negative heating value ({minus}150 kcal/kg on NCV basis) and required coalmore » as support fuel for burning. The plant`s requirement was to incinerate the entire sludge generated in the plant, which meant that nearly 50% of the fuel fed to the boiler consisted of the waste sludge. Additional requirements were to burn coal and oil as back-up fuels. This paper deals with the challenges encountered and various design features provided in the configuration of the incinerator-cum-boiler including conveying, feeding and spreading arrangement of the waste sludge for effective incineration in addition to burning coal and oil. Also included in the paper is a brief description of the automatic control logics for combustion control and bed temperature control.« less
  • The fluidized bed sewage sludge incineration plant of the city of Hamburg started its operation in May 1997. In cooperation with Hamburger Stadtentwaesserung the Technical University Hamburg-Harburg undertook an experimental program to measure the mass balance of mercury across this plant. During the first months of full operation the mercury concentrations in the flue gas and in the solid residues were measured. The measurements show that the concentration in the raw flue gas is between 500 to 950 {micro}g/m{sup 3} and part of the elemental mercury depends on the chlorine content of the fuel. The concentration of the mercury inmore » the flue gas is reduced over the first scrubber to 35--460 {micro}m/m{sup 3}. Some 77% of the mercury input are found in the sediment separated from the liquid of the acid scrubber. It is remarkable that the concentration of the elemental mercury increases while the gas passes through the scrubber. The concentration of mercury in the cleaned stack gas is less than 40 {micro}g/m{sup 3}. Since it is generally known that it is not easy to meet the limit of 50 {micro}g mercury per m{sup 3} (standard conditions, dry basis) of flue gas which is set by the German regulations for waste incineration, the measurements provide a comprehensive picture of the fate of mercury in a fluidized bed sludge incineration plant.« less
  • The results of an inquiry in 1997 show that the percentage of sewage sludge disposed of by incineration in Germany is 19%. Legal developments in Germany clearly show that this percentage amount is expected to increase in the next few years. According to legislation, the treatment of the sewage sludge will have to achieve a result of {le}5% combustible (according to TA-Siedlungsabfall, i.e., Technical guideline for handling and disposal of urban waste). Sewage sludge incineration will therefore become a preferred treatment process. Fluidized bed combustion is especially suitable in relation to the burn-up results. Around 19 sewage sludge incineration plantsmore » are operating in Germany, 17 of which have stationary fluidized bed furnaces, the others are multiple hearth roasters. The German statutory law affecting emissions from sewage sludge incineration plants is 17.BlmSchV (i.e., Paragraph 17 of the Federal Emissions Control Regulations). These regulations stipulate mandatory compliance with limit values as a daily average value figured in standard conditions. The intention is to build up an overview of the various possibilities to reduce the NO{sub x} emissions from one problematic industrial sludge by using primary measures, and if possible, to avoid expensive secondary measures, like the SNCR (selective non catalytic reduction) or SCR (selective catalytic reduction) processes.« less
  • At the present time, the sewage treatment plants in the United Kingdom produce about 25,000,000 t of sewage sludge each year at a concentration of 4% solids. New regulations in the United Kingdom forbid sea dumping, and in the near future new incinerators will be required to dispose of about 5,000,000 t per year. The research program at the Sheffield University consisted of design and construction of a small-scale cylindrical rotating fluidized bed incinerator with an inside diameter of 200 mm and an axial length of up to 200 mm. The fluidizing medium was silica sand and the bed depthmore » 30--50 mm. The rotational speed of the bed varied between 100 and 1,000 rpm. Coal, oil, sewage sludge, and chicken manure were burnt in the bed at temperatures between 700 and 900 C. Measurements of heat transfer rate, bed temperature, and exhaust gas composition were carried out over a range of operating conditions. The influence of rotational forces on basic fluidization characteristics were also investigated on a perspex model. The results obtained from the research work demonstrated that the rotating fluidized bed incinerator can produce considerably higher combustion intensities, has a wide turn-down range, has low toxic emissions, and has a more easy and rapid start-up than conventional stationary fluidized bed incinerators. Other advantages of the system include: good mixing, simpler fuel injection, low thermal inertia, and good heat transfer rates. Other potential applications for this system include boilers, open cycle gas turbines, and combined gas/steam cycles.« less