Co-combustion Of Sludge Research Articles

Simultaneous thermogravimetric-mass spectrometric study on the co-combustion of coal and sewage sludges

Abstract To combust coal together with a small percentage (<10%) of sewage sludge may be an option for the management of these wastes. Combustion of two different sewage sludge, one semianthracite coal and several sludges-coal blends (containing different dried mass% of each of the two sewage sludges) were studied by simultaneous TG/MS dynamic runs carried out at 5C min–1 in the temperature range 100–800C. No interactions have been observed between coal and sludge during the blends combustion. Neither the combustion process, neither the studied emissions have changed appreciably for the mass% of sludge in the blends considered in this work.

Comparison of the Catalytic Activity of Bed Materials from the Combustion of Biomass and Waste Fuels in a Circulating Fluidized Bed Boiler toward NO Reduction by CO

This paper reports the kinetic expressions for the catalytic activities toward NO reduction by CO of three bed materials from a 12 MWth circulating fluidized bed (CFB) boiler sampled during combustion of wood pellets and mixtures of wood pellets and two types of municipal sludge. The catalytic activity of the bed materials was determined by measuring the conversion of NO in a laboratory fixed bed quartz reactor in the temperature range from 870 to 1180 K. It was found that the activity of bed material increases upon addition of sludge to wood pellets. In the case of the bed material from the combustion of wood pellets, the catalytic activity was not significantly effected by the change of sample particle size, location in the boiler, or presence of char. Contrary, for the bed materials from the co-combustion of wood pellets and sludge, the particle size of 125−297 μm, which was enriched in ash particles originating from sludge, showed higher catalytic activities as compared to fractions 250−355 or 355−500...

04/01462 Co-combustion of sludge with coal: Nadziakiewicz, J. and Koziol, M. Applied Energy, 2003, 75, (3–4), 239–248

04/01462 Co-combustion of sludge with coal: Nadziakiewicz, J. and Koziol, M. Applied Energy, 2003, 75, (3–4), 239–248

Effects of sewage sludge and meat and bone meal Co-combustion on SCR catalysts

DeNOx catalysts for the selective catalytic reaction (SCR) in coal fired power plants are deactivated by catalyst poisons such as As, Na, K, P, etc. The deactivation rate depends on the fuel quality and the concentration of catalyst poisons in the fuel. However, operational parameters such as O2 content, residence time, combustion and flue gas temperature also have an influence on decreasing catalyst activity.Equilibrium calculations were carried out to identify possible catalyst deactivation reactions. The calculations concentrated on the elements phosphorus and sodium as primary catalyst poisons in animal residues or sewage sludge. A set of deactivated catalyst samples from different power plants were analysed with respect to surface area, chemical composition and permeability. From the results obtained, deactivation mechanisms were derived which seem to cause increased catalyst deactivation due to P-rich secondary fuels. The samples showed a high P and alkali concentration on the surface. The surface area and the pore volume decreased. Compared to pure coal combustion this decrease was significant for meat and bone meal co-combustion and was also noticed for samples exposed to sewage sludge co-combustion. A correlation between relative activity and Na and P concentration is established. The results of the surface analyses indicate pore condensation as a major deactivation mechanism.

Co-Combustion of Sludge with Coal or Wood

There are several options for co-combustion of biomass or waste with coal. In all cases the fuel properties are decisive for the success of the arrangement: contents of volatile matter and of potential emission precursors, such as sulphur, nitrogen, chlorine, and heavy metals. The content of alkali in the mineral substance of the fuel is important because of the danger of fouling and corrosion. Research activities at Chalmers University of Technology include several aspects of the related problem areas. An example is given concerning emissions from co-combustion in circulating fluidized bed with coal or wood as base fuels, and with sewage sludge as additional fuel. Two aspects of the properties of sludge are studied: emissions of nitrogen and sulphur oxides as well as of chlorine, because the contents of the precursors to these emissions are high. The possibility of utilizing the phosphorous in sludge as a fertilizer is also discussed. The results show that emissions can be kept below existing emission limits if the fraction of sludge is sufficiently small (<25%), but the concentration of trace elements in the sludge ash prevents the sludge from being used as a fertilizer.

Co-combustion of sludge with coal

Utilisation of waste-water sludge is one of the most difficult processes of environment protection because of the high moisture and contents of harmful substances. The waste-water treatment systems in Poland, especially in small towns, are often not separate from industrial sewage systems and this causes relatively large contents of heavy metals and other toxic substances in the sludge. Incineration is the only effective method of utilisation of such waste material. From the other side, coal is still the most popular fuel in Poland, and it is often used in many boilers producing hot water for the central heating of buildings or parts of the towns. Mostly they are stoker fired boilers of old construction, and they need urgent modernisation. The use of stoker-fired boilers for incineration of the sludge in small towns is the object of the analysis presented in this paper. There are two important points in the co-combustion of sludge with coal in a stoker-fired boilers: ecological and exploitation requirements. The important restriction of the sludge/coal ratio is the emission of harmful substances with the flue gas. There are substances originating from the components of the sludge: SO 2, NO x , HCl, heavy metals and dust. Their concentrations in the flue gas should meet the environmental regulations. The other factor influencing the co-combustion process is the change of physical and thermal properties of the fuel: heating value, moisture content and ash composition. These influence the thermal output of the boiler, the amount of air required for combustion, the volume of flue gases and dust concentration and particle distribution. In this paper, the results of experiments performed with an experimental boiler are presented. The effects of the following parameters are considered: composition and thermal parameters of the sludge and their change during the year, emissions of SO 2, NO x , CO and dust from the experimental boiler for various compositions of the fuel (sludge/coal ratio, moisture content). As a result of the analysis, the parameters limiting the amount of sludge in a mixture with coal are identified.

The behaviour of ashes and heavy metals during the co-combustion of sewage sludges in a fluidised bed

Co-combustion tests of dry sewage sludges with coal were performed in a pilot bubbling FBC aiming at the characterization of ashes and determining the behaviour of heavy metals in the process. The tests showed compliance with the regulatory levels as far as heavy metal emissions were concerned. The bottom ashes, which accounted for about 70% of the total ash production, were obtained in a granular form, with diameters ranging from 0.5 to 4 mm. The heavy metals were distributed in ashes obtained from different locations of the installation and their concentrations were found to vary depending on the location of capture. The increase in heavy metals content in bottom ashes was not found to lead to higher leachability and ecotoxicity compared to sewage sludges, suggesting that there could be opportunities for their further use. Mercury suffered vaporisation inside the reactor, thus leaving bottom ashes free of contamination by it. However, there was observed a strong retention of mercury in cyclone ashes due to the presence of unburned carbon which probably acted as an adsorbent. The effluent mercury was also found to be mostly associated with the particulate fraction, being less than 20% emitted in gaseous forms. The results suggested that the combustion of the sewage sludge could successfully be carried out and the amount of unburned carbon leaving the combustor but captured in cyclone was large enough to ensure substantial retention of mercury at low temperatures, hence could contribute to an improvement of the mercury release which still remains an issue of great concern to resolve during combustion of waste materials.

Potential for Sewage Sludge Co‐Combustion in the UK Based on German Experience

AbstractIncreasingly strict legislation, escalating costs and external pressures are causing the water industry to look for alternative strategies to agricultural recycling for the disposal of biosolids. Although the development of the ‘safe sludge matrix’has encouraged agricultural recycling, negative press has hampered this outlet and public perception is seen as a major threat. Accordingly, many water companies are looking towards thermal‐reduction technologies and have invested in thermal dryers and sludge incinerators; however, such technology has high capital costs and complex maintenance and operator requirements. An alternative method, i.e. co‐combustion, is becoming more popular in mainland Europe. Unlike incineration/drying, the capital expenditure is low and operator/maintenance risks are minimised.This paper (i) discusses a case study in which 40 000 dry tonnes of sludge per annum have been successfully combusted since 1996, and (ii) explores how this experience could be applied in a UK situation.

Characterisation of FBC ashes from co-combustion of coal with oily residues

In order to evaluate the environmental impact resulting from co-combustion of oily sludges, a detailed characterisation of the ashes produced was carried out. The main bulk composition and the trace elements were determined, thus allowing a comparison of the ashes produced from coal to those from co-combustion of the residue with and without limestone. The leachability was evaluated with two different standards, a European Norm and the US TCLP. The results differed according to the leaching pH dependence. Of the trace metals analysed, only Cr failed to meet the limits of natural groundwater by the EN procedures. The utilisation of limestone, thus capturing sulphates and part of Cl, had an adverse effect over the leachability. Cr was especially sensible, as the toxic hexavalent form was favoured in this case. The LOI of the ashes was found to be very high. As several mechanisms are believed to contribute to the overall result, low ashing temperatures are required for ashes from residues containing Cl, alkaline salts and carbonates. TGA was found to be a highly valuable technique to evaluate the unburned material.

Ash formation during fluidized-bed incineration of paper mill waste sludge

Ash formation during industrial-scale bubbling fluidized bed (BFB) and circulating fluidized-bed (CFB) combustion of bark, waste wood and paper mill sludges has been studied. The principal ash formation mechanism was the sintering of 0.2–4 μm paper filler mineral particles into larger, porous ash agglomerates from 10 to 200 μm in size which dominated the fly ash total mass and specific surface area. Fly ash total mass concentration at the electrostatic precipitator inlet conditions varied from 4.5 g N -1 m -3 at BFB to 8.3 g N -1 m -3 at CFB while the respective total surface area concentrations as determined with nitrogen absorption were 32 and 83 m 2 N -1 m -3. During bark combustion in the BFB, we observed an ultrafine mode at 0.05 μm consisting of spherical particles and their chain-type agglomerates. Ultrafine mode mass and surface area concentrations were 3 and 0.1 m 2 N -1 m -3, respectively, as determined with the electrical low-pressure impactor and with the differential mobility analyzer. Ultrafine particles were formed via nucleation of volatilized ash species followed by particle growth via collision and coalescence and via vapor condensation. During waste wood combustion in the CFB, ultrafine particle concentration was significantly lower than during bark combustion in BFB, indicating reduced ash volatilization during CFB combustion. When co-firing sludge with bark in the BFB and with waste wood in the CFB ultrafine particle concentration was further reduced. Results from continuous aerosol measurements by the electrical low-pressure impactor (ELPI), by the scanning differential mobility analyzer (SMPS) and by the tapered element oscillating microbalance (TEOM) as the function of BFB process conditions suggest that co-combustion of sludge reduces significantly the ultrafine particle formation rate. No significant enrichment of alkali and trace metals in the ultrafine particles was observed.

The ash formation during co-combustion of wood and sludge in industrial fluidized bed boilers

Ashes from an industrial bubbling fluidized bed (BFB) and a circulating fluidized bed (CFB) boilers burning biomass and paper mill sludges are characterized. Bulk sampling was carried out with a simultaneous low pressure impactor sampling (BLPI) and with on-line monitoring of submicron ash gas phase size distribution. The principal ash forming mechanism was sintering of 1–10 μm inorganic paper filler particles, into 5–200 μm ash agglomerates. Despite few spherical particles no ash melting was detected. The fraction of vaporized and condensed ash was below 0.1 mass% in both units as determined with BLPI and with on-line monitoring. According to elemental mass size distributions no significant vaporization of any main element occurred including sodium and potassium. Wall deposit observed on refractory lining in BFB furnace was composed of sintered ash binding large ash and sand particles in the structure. No molten phases were detected to participate in the layer growth. Most quartz sand grains in the bed were covered by a thin layer of small ash particles, below 5 μm in size.

97/05070 Determination of the emissions of pollutants formed during the co-combustion of sludges with coals in a fluidized bed combustor: Gulyurtlu, I. et al. Solid Waste Manage.: Therm. Treat. Waste-to-Energy Technol., Proc. Int. Spec. Conf., 1995, (Pub. 1996), 451–458

Co-combustion studies were carried out with mixtures of sludges with South African coal using a bubbling fluidized bed combustor of 90 kW. The combustion gases leaving the combustor was analyzed for CO{sub 2}, CO, O{sub 2}, NO{sub x}, N{sub 2}O, and SO{sub 2}. Sorbents were used to reduce the levels of SO{sub 2} and the influence of sorbent in capturing heavy metals during the combustion. Particles were collected from the combustion gases using an isokinetic sampling probe and the solids recovered were then analyzed to determine the particle size range and the composition.

PAH emission from the incineration of waste oily sludge and PE plastic mixtures

A batch-type, controlled-air incinerator was used for the treatment of oily sludge and polyethylene (PE) plastic mixtures. The concentration and composition of 21 individual PAHs (polycyclic aromatic hydrocarbons) in the raw wastes, flue gas (gas and particle phases) and ash were determined. Stack flue-gas samples were collected by a PAH stack-sampling system. Twenty one individual PAHs were analyzed primarily by a gas chromatograph and a gas chromatography/mass spectrometer. Due to incomplete combustion, PAH content in the feeding wastes have a strong influence on PAH emission in both stack flue gas and ash residue. With the oily sludge in the feeding waste mixtures, the input mass of lower molecular weight PAHs — Nap, AcPy, Acp, Flu, PA, Ant and FL — was contributed mainly by liquid diesel, while the input mass of higher molecular weight PAHs — Pyr, CYC, CHR, BbF, BkF, BeP, BaP, PER, IND, DBA, BbC, BghiP and COR — was primarily contributed by the oily sludge. For the distribution of individual PAH mean output mass, lower molecular weight PAHs — Nap, AcPy, Acp and Flu — have > 87% of their mass discharged by the stack flue gas. However, the higher molecular weight PAHs — Ant, FL, CHR, BbF, BeP, BaP, PER, IND, DBA, BbC, BghiP and COR — have significant mass fractions (>18%) discharged by the ash residue. The total-PAH output/input mass ratios were between 0.00103 and 0.00360 and averaged 0.00203. This result indicated that the depletion of PAH mass in the combustion process was very significant. The PAH content in the fuel during the combustion process is the control factor of PAH emission. The co-combustion of oily sludge with plastic is a potential method of reducing the PAH emission and of saving the consumption of auxiliary fuel.